Building Water Supply Systems PDF

Chapter 13 BUILDING WATER SUPPLY SYSTEMS 13.1 THE BUILDING WATER SUPPLY SYSTEMS typically located in the hot and cold water Main Parts of Water Supply System supply at the fix- ture conne...

Chapter 13 BUILDING WATER SUPPLY SYSTEMS 13.1 THE BUILDING WATER SUPPLY SYSTEMS typically located in the hot and cold water Main Parts of Water Supply System supply at the fix- ture connection. Readily accessible valves used to close off the PLUMBING CODES water supply to a fixture, appliance, or - require that a potable water supply be ade- system. quately furnished to all plumbing fixtures. The water supply system in a building carries cold General Water Distribution System Layout and hot water through distribution pipes and delivers it to the plumbing fixtures. The water WATER SERVICE PIPE service line carries water from a district supply - is an underground pipe that is typically called pipe to the building. a lateral. It extends from the underground The main parts of a typical water supply system street main that is part of a district or city include the following. water system, and delivers pressurized potable water to a building plumbing system. The BUILDING SUPPLY OR WATER SERVICE water service lateral is connected to a water - is a large water supply pipe that carries meter that measures consumption. The water potable water from the district or city meter is typically located in an underground water system or other water source to the curb box located in the building’s front yard or building. islocated in the building interior, in which case WATER METER it is connected toa remote readout on the - is required by most district water supply exterior of the building, which allowseasy systems to measure and record the access for meter readings. If the building amount of water used. plumbing system is served by a well, a water meter is not needed unlessmonitoring of BUILDING MAIN consumption is required. - is a large pipe that serves as the principal artery of the water supply system. It WATER SOFTENING OR TREATMENT carries water through the building to the - is done after irrigation water and/or water for furthest riser. process equipment is removed. Once the RISER water supply main passes through the - is a water supply pipe that extends softening or treatment device (if used), the vertically in the building at least one story main pipe splits to provide water to a water and carries water to fixture branches. It is heater or water heating system that generates typically connected to the building main hot water before it is distributed. and runs vertically in the walls or pipe CONVENTIONAL RIGID-PIPE WATER chases. DISTRIBUTION METHOD FIXTURE BRANCH - fixture branches extend from a riser or main - is a water supply pipe that runs from the to the individualfixture being connected. A riser or main to the fixture being fixture branch is usually run inthe floor or in connected. Fixture branch pipes supply the wall behind the fixtures. the individual plumbing fixtures. A fixture INNOVATIVE HOMERUN WATER branch is usually run in the floor or in the DISTRIBUTION METHOD wall behind the fixtures. - individual branches begin at a main manifold FIXTURE CONNECTION located in a utility room or base-ment, usually - runs from the fixture branch to the near the water service. fixture, the terminal point of use in a The distribution configuration methods are plumbing system. A shut-off valve is described in the following:  chambers: the cold water chamber is o Rigid-Pipe Distribution Configuration supplied from the main water supply line - the hot and cold water distribution pipes and the hot water chamber is fed from the are installed parallel to one another as water heater. they convey hot and cold water to risers - Homerun configurations typically use and branch pipes. Running pipes parallel cross-linked poly-ethylene (PEX) or with building walls and floors arrange composite PEX-AL-PEX piping, which is pipes in an organized manner. suitable for cold and hot water use. - A branch supplying water to two or more fixtures is called a zone. A zone can supply Upfeed and Downfeed Distribution one or many fixtures on one floor or on a Two basic types of water supply few floors. Fixtures are typically located in distribution systems are used in buildings: the clusters called groups. upfeed (or upflow) system and the downfeed - There are times when the width of a wall (or downflow) systems. needs to be increased to allow for pipes running horizontally to pass by drainage UPFEED SYSTEM pipes (or other pipes) running vertically. - water pressure from the water supply These walls of increased thickness are main is relied on to drive water flow called plumbing walls. through the system. - In multistory buildings, risers are pipes that - In tall buildings, water must be supplied carry water vertically through walls or through a pumped upfeed distribution through enclosures called chases. A chase system. A pumped upfeed system is one in is a vertical opening through a floor or which water entering the building flows several floors that is enclosed with walls through pumps that maintain adequate between floors. A chase can enclose piping water pressure throughout the structure only or it can enclose electrical wiring sufficient to operate any plumbing fixture. and/or mechanical system ducting and/or - A vertical riser carries this high- pressure pipes that run vertically from floor to floor water to fixtures at the top of the building. through the building. Such a pressure in the distribution system - Pipe tunnels may be used on large projects is too great to use in plumbing fixtures to provide concealed space for the passage (e.g., lavatories and water closets). For this of mechanicals at ground level and from reason, at several zones water is removed building to building. Hangers from the top from the vertical riser, reduced in pressure or side of the tunnel are used to support at pressure-reducing stations and the pipes. distributed to the fixtures in that zone. - Readily accessible valves used to close off the water supply to a fixture, appliance, or DOWNFEED SYSTEM system are called shut-off valves. A shut- - In buildings that cannot be adequately off valve is required on the discharge side serviced to the top floor by an upfeed of the water meter. system, water is pumped to elevated storage tanks in, or on, the building, and o Homerun (Manifold) Distribution the water is fed down into the building by Configuration gravity. This gravity system, fed from the - consists of a plastic or metal plumbing upper stories to the lower, is called a manifold and flexible plastic piping. The downfeed distribution system. manifold serves as a common location from which all the plumbing fixtures are 13.2 WATER PRESSURE CONSIDERATIONS supplied. Manifolds have two separate  Hydrostatic Pressure Pressure Difference from Elevation HYDROSTATIC FORCE Change (Static Head) - is a force exerted by the weight of the fluid - In a plumbing supply system, pressure against the walls of a vessel containing the difference from elevation change or simply fluid. static head (ΔPstatic) is found by multiplying the vertical height (Z), in feet, by the factor HYDROSTATIC PRESSURE - the hydrostatic force per unit area, is per- of 0.433 psi/ft. pendicular to the interior walls at every point. If the pressure were not perpendicular, an Pressure Difference from Friction unbalanced force component would exist and - Pressure losses from friction, friction head the fluid would flow. (ΔPfriction), are more difficult to compute, as - If gravity is the only force acting on a fluid they are related to flow rate (gpm, L/min (e.g., the water in a gravity plumbing system), or L/s), fluid velocity (ft/s or m/s), pipe the hydrostatic pressure at any point in the diameter, pipe material and surface system is directly proportional to the weight of roughness, pipe length, and number of a vertical column of that water. fittings and valves. Water Pressure PRESSURE DROP CHARTS - Water pressure difference is the driving - have many lines and numbers; use them force behind fluid flow. Water pressure with care and review the information on available at the water service is lost as the chart before using it. Along the left and water flows through the piping of a right is the volumetric flow rate, and along plumbing system. This pressure loss or the bottom and top is the friction loss in pressure drop in a plumbing system is from the pipe. friction loss as the water moves through the system and pressure loss as water is 13.3 WATER SUPPLY DESIGN CONCERNS forced to a higher elevation (e.g., from the basement to an upper story). o Water Velocity - Noise, erosion of inner pipe walls and RESIDUAL WATER PRESSURE valves, and economy of installation, - is the pressure available at the outlet, just operation, and maintenance dictate the before a fixture. It affects water output of minimum and maximum water velocity in a fixture. a plumbing system. If pipe diameters are small, cost is low but noise, erosion (from Pressure Difference high velocities), and pumping costs (from - When forces acting on a fluid are unequal, high-pressure losses) are high. In contrast, molecules in the fluid move in the direction large diameter pipes reduce noise erosion of the least pressure. Fluid flow is caused and pumping costs, but result in high by a pressure difference in the fluid. A fluid installation costs. An intermediate pipe will always flow from a higher pressure diameter is desirable. region to a lower pres- sure region. o Cavitation Pressure difference (ΔP) is the driving - is a physical phenomenon that occurs in a force of fluid flow. liquid when it experiences a drastic drop in pressure that causes the liquid to vaporize into small vapor bubbles. Vaporization is a contaminated) water from entering the problem because the liquid being water supply. A PVB is similar to an vaporized expands greatly. AVB, except that the PVB contains a spring- loaded poppet. o Cross-connection - is an unsatisfactory connection or DOUBLE CHECK ASSEMBLY (DCA) OR arrangement of piping that can cause DOUBLE CHECK VALVE nonpotable water to enter the potable - is a backflow prevention device water system. A cross-connection can assembly that consists of two check cause used or contaminated water to mix valves assembled in series usually with with the water supply. It is an un- sanitary a ball valve or gate valve installed at and potentially hazardous condition. each end for isolation and testing. o Backflow o Water Hammer - is a type of cross-connection that occurs - the sudden closing of a valve will cause when con- taminated water or some other fast-flowing water to stop quickly, liquid or substance unintentionally flows resulting in a large increase in pressure. backwards into distribution pipes - To avert water hammer damage to a containing potable water. Simply, it is buildings plumbing system, air water flowing in the opposite direction chambers or water hammer arrestors from normal flow. Backflow can allow are used in the supply branches serving contaminants to enter the potable drinking each fixture. These devices use trapped water system through cross-connections. air to cushion the hydraulic shock. BACKPRESSURE OR BACK SIPHONING AIR CHAMBERS - is backflow caused by a negative - are 15 in to 5 ft long pipes or pipe-like pressure (vacuum) in a potable water devices. They are installed vertically system. A downstream pressure that is above the fixture water connection and greater than the supply pressure are concealed in the wall. Air is trapped causes backpressure backflow. within the air chamber. BACKFLOW PREVENTION DEVICE WATER HAMMER ARRESTORS - often called a vacuum breaker, is a - are patented devices that absorb device or plumbing assembly that hydraulic shock. Such devices, when when properly installed in a plumb- ing installed, must be accessible for system prevents backflow. maintenance. ATMOSPHERIC VACUUM BREAKER (AVB) o Thermal Expansion - the most common type, consists of a - No matter what type of piping material is body, a check valve like member (to used in the water sys- tem, some prevent backflow), and an atmospheric expansion in the pipe will occur. This opening. The AVB is not a testable expansion must be considered in the device. design of the system. The amount of PRESSURE VACUUM BREAKER (PVB) expansion will depend on the type of - is a type of backflow prevention device piping material and the range of used to keep nonpotable (or temperatures that the pipe will be o Volume Change With Temperature subjected. - Water is the only substance that can exist - Thermal expansion in the pipes of a as a solid, liquid, and gas at ordinary plumbing system must be accommodated temperatures. Like most substances, water to minimize damage from thermal ex- pands when it is heated. Unlike most movement. Expansion from temperature substances, the volume of water increases increases can push a pipe through a wall or when it freezes. cause it to burst. FREEZING - A phase change from liquid (water) to There are two methods in common use for solid (ice) results in about a 10% providing for expansion in pipelines: increase in volume. EXPANSION BENDS AND EXPANSION EXPANDING WATER LIQUID LOOPS - water expands above 39°F (4°C). - make use of pipe fabricated with U- Expansion is about 4.37% from 40°F shaped or circular bends. The increase (4.4°C) to 212°F (100°C). This in the length of pipe from thermal volumetric change from expansion (ΔV) expansion is accommodated by flexing equates to about 0.0254% per °F or springing of the bends or loops. (0.0457% per °C). EXPANSION JOINTS OPEN PLUMBING SYSTEM - in common use include the slip - such as a building water supply system, expansion joint and the corrugated pressurebuildup from thermal expansion joint. The slip expansion expansion of water is released each joint consists of a slip pipe and a flange, timea faucet or valve opens. Excess which is bolted to an adjoining pipe. pressure is released into the The slip pipe fits into the main body of surrounding air. the joint, which is fastened to the end of the other adjoining pipe. CLOSED PLUMBING SYSTEM - corrugated expansion joint consists of - where water is contained fully within a flexible corrugated section. The the system (e.g., a hydronic heating corrugated, accordion-like section is system), provisions arenecessary. A able to ab- sorb a certain amount of temperature-pressure relief (T/P) end movement of the pipe. valve is a safety valve installed in a system that remains closed at normal o Viscosity operatingpressures yet is permitted to - As water flows through a pipe, its viscosity open to release excessive pressure. (thickness) decreases with temperature They are commonly found as a safety decrease. Water at 40°F (4°C) is twice as feature on water heaters andboilers. viscous as water at 90°F (32°C) and four Expansion tanks, installed in a closed times as much at 170°F (77°C). As a result, system, provide additional volume in pumping energy and cost are higher when the closed system for expansion of water temperatures are lower. water from temperature increase. STEAM electrical systems. Leaking pipes also - Under standard atmospheric pressure create an environment for mold and (14.696 psi, 101.04 kPa), the boiling mildew to thrive. Pinhole leaks in copper point temperature of water is 212°F plumbing affects property owners (100°C). The boiling point temperature throughout the United States and varies with atmospheric or system elsewhere in the world. pressure. Water boils and is con verted to steam at its boiling point 13.4 WATER SUPPLY PIPES DESIGN METHODS temperature. ❖ Flow Rates o Aging - will vary by type of fixture and water - As pipes in a plumbing system are used, pressure at the fixture. A higher residual their inner walls become increasingly pressure results in a greater flow rate and rough. The effects of aging in a plumbing thus more water consumption. system are related to piping material, quality of water (e.g., hard versus soft), and ❖ Water Consumption water temperature. - Water use in many homes is lowest from about midnight to 5 AM , averaging less o Pipe Insulation than one gallon per person per hour. Use - Pipe insulation is applied to the outer climbs sharply in the morning around 6 AM walls of piping to reduce heat loss from the , to about 3 gallons per person per hour. pipe or prevent condensation on the outside pipe walls. Foam and covered ❖ Water Demand fiberglass insulation are common pipe - The instantaneous peak demand for insulation materials. water in a pipe serving a number of plumbing fixtures or serving an entire o Testing building is referred to as the design load. - The water supply system should be tested The design load is the maximum probable for leaks before it is covered with finish or peak instantaneous demand for materials to determine if it is watertight. domestic water by a group of fixtures. The Any leaks that occur should be repaired design load is typically expressed in gpm, with the joint compound originally used. L/min or L/s. - So, simply totaling fixture flow rates for all o Leaks fixtures in an entire building distribution - Surprisingly, plumbing leaks contribute system would give the total demand for significantly to water consumption in water usage only if all fixtures were used at operating plumbing systems. Leaks one time. In most instances, totaling account forabout 12.7% of household per fixture requirements provides a very high capita water use in a typical U.S.home estimate that results in overdesign of the (AWWA). A leak of just one drop per piping. second will wasteabout 2700 gal (10 200 L) of water a year. Leaks not only waste Method 1: Simple Empirical Design money and water, they can cause damage Method to walls, flooring, ceilings, furniture, and - Pipe sizes for the water supply system distribution pipe size based on the total of a single-family house and similar demand in WSFUs and the supply simple structures can be determined pressure (the available static pressure on the basis of experience and after static head loss). pertinent code requirements. Detailed Meter and distribution pipe can be sized analysis is not necessary in the design using the following methods: of simple systems. The fixture fed by the branch will influence branch pipe static head, in psi, ΔPstatic = -0.433Z diameter. Pipe diameter is determined static head, in kPa, ΔPstatic = -9.8Z by the pipe size serving the fixture. In the empirical design method, piping is Method 3: Velocity Design Method sized with rules of thumb based on - entails selecting the smallest pipe observation and experience. diameter without exceeding a preestablished maximum velocity for ❖ Fixture Units the design load in the pipe. It is typically - A method of estimating the design load used accurately in a downfeed system for a group of plumbing fixtures is typically and works well in preliminary design of based on a quantity called the fixture unit. a plumbing system provided the The fixture unit is an arbitrarily chosen system layout is reasonably measure that allows all types of plumbing symmetrical. This method does require fixtures to be expressed in common terms; an investigation of pressure loss to that is, a fixture having twice the ensure that residual pressure at the instantaneous flow rate of a second fixture most remote fixture is adequate. would have a fixture unit value twice as large. Method 4: Equal Friction Design Method - Dr. Roy Hunter of the National Bureau of - A more accurate approach to sizing the Stan- dards (now the National Institute of pipe diameter in a complex network of Standards and TecHnology, NIST) pipes is the equal friction design developed this method over a half century method. It is necessary to determine ago and it still serves as the basis for the total pressure drop required estimating the design load of a plumbing between the water service and the system. fixtureand equate this to a pressure - The Hunter method assigns a water drop per 100 ft over the equivalent supply fixture unit to each fixture. The length of pipe. water supply fixture unit (WSFU) is a probability factor that represents each 13.5 WATER TEMPERATURES fixture connected to the water supply ✓ Cold Water system and used to determine the total use - The temperature of water available in the of water within a given system. water supply system will vary. Water from shallow (just below frost line) underground water service lines enters the building at a Method 2: WSFU Design Table Method temperature that fluctuates with climate, - In residential and small commercial season, and location of the water service line. buildings, WSFU design tables can be In a moderate climate, it may range from 35°F used to establish meter and (2°C) in midwinter to 70°F (21°C) or more in midsummer. In hot climate regions, water and 49°C) with flow rates between 0.5 gpm and service temperature can reach temperatures 10 gpm. above 90°F (32°C) or more in the summer. In harsh desert climates, water must actually be 13.6 DOMESTIC WATER HEATING chilled for drinking. Consumption - Energy consumption for heating domestic ✓ Chilled Water water is the second largest energy user (after - The varying temperature of water extracted space heating) in the residential sector in from cold water supply lines is normally industrialized countries, accounting for about acceptable. In some instances chilled water is 14% of the energy used in a typical household. desired, such as from a drinking fountain. In this case, a chiller is used to cool water to a Types of Water Heaters temperature of about 50°F (10°C) before it is - A water heater is an appliance or system used. A chiller is a vapor compression that heats water for domestic or building refrigeration system that cools water much like service hot water use. a refrigerator. There are three types of water heaters: ✓ Heated Water STORAGE TANK WATER HEATERS - By definition, hot water is potable water that - consists of a storage tank and a heating is heated to at least 120°F. Heated water below medium. Typically, storage tank sizes 120°F (49°C) is typically called tempered include 30, 40, 50, 60, 65, 75, 80, 100, and water. Hot water used for household functions 120-gal (120- to 400-L) capacity. such as bathing, dishwashing, and clothes - remain the most popular type for washing is referred to as domestic hot water residential heating needs in the United (DHW). In commercial installations, hot water States. used in nondomestic applications is referred to Types of storage tank water heaters include as building service hot water (BSHW). The the following: temperature of heated water available in the o Residential storage tank water heaters water supply system will vary depending upon are designed for the residential market, need. but can be appropriate for many small - The hot water distribution temperature must commercial facilities. be higher than 120°F (49°C) because of the o Commercial storage tank water heaters concern over Legionella pneumophila are similar to residential models except (Legionnaires’ disease). This bacterium, which that they are available with much higher can cause serious illness when inhaled, can gas input ratings (1 000 000 Btu/hr or grow in domestic hot water systems at more) and larger storage tanks (up to 250 temperatures of 115°F (46°C) or less. gal). o Ultraefficient water heaters use power ✓ Tempered Water burners and enhanced heat exchangers to - is a blend of hot and cold water that is mixed force hot combustion gasses into at a thermostatic (mixing) valve. It is used in chambers and tubes that are submerged in applications requiring low-temperature hot the stored water. Ultraefficient water water. heaters are vented with plastic pipes that - An antiscald shower valve is a type of go directly through an outside wall. thermostatic valve required in residential Storage tank water heaters can also be showers. This valve can be preset to any classified on their method of venting: temperature between 60° and 120°F (15.5° o Nonventing (electric) o Naturally aspirated water heaters have a is heated directly inside the boiler in a flue that runs vertically through the center hydronic (hot water) heating system. of the tank. - A separate storage tank is required with an o Power-vented water heaters use a fan to indirect water heater. Like the tankless exhaust flue gases. coil, the indirect water heater circulates o Sealed-combustion water heaters have water through a heat exchanger in the supply air and exhaust air connections to boiler. But this heated water then flows to the outdoors. an insulated storage tank. These units do not require any indoor air to operate. There are two types of sealed- HEAT PUMP WATER HEATERS combustion water heaters. Some units have a - extract energy from outdoor air and use it flue up the center of the tank (similar to the to produce hot water very efficiently. Heat power-vented water heaters). The second type pump water heaters use an electric motor of unit has a heat exchanger that wraps around to run a compressor. the tank. SOLAR WATER HEATERS INSTANTANEOUS (TANKLESS) WATER - typically includes collectors mounted on HEATERS the roof or in a clear area of the yard, a - sometimes called tankless water heaters separate storage tank near the or demand water heaters, supply hot conventional heater in the home, water on demand. They do not rely on a connecting pipes, and an electronic standby storage in a tank to artificially controller. Throughout the year, the solar boost their capacity. Instead, they have a system preheats the water before it heating device that is activated by the flow reaches the conventional water heater. of water when a hot water valve is opened. Solar water heating systems can reduce - Instantaneous point-of-use water heaters the annual fuel cost of supplying hot water fit compactly under a fixture (e.g., sink or to a residence by more than half. lavatory) and heat water at the location where it is used. This device ensures that DESUPERHEATERS hot water is available without delay - is an attachment to an air conditioner or heat pump that allows waste heat from CIRCULATING WATER HEATERS that device to assist in heating domestic - consist of a separate storage tank that water. In hot climates, a desuperheater stores water heated by a heat exchanger. can provide most of a home’s hot water The heat exchanger may be a separate unit needs. that is heated by stream or hot water from a boiler or may be contained in a boiler. Energy Efficiency - The energy factor (EF) is a standardized TANKLESS COIL AND INDIRECT WATER measure used to express the efficiency of HEATERS residential heaters. It was developed by - A building’s space heating boiler can also the U.S. Department of Energy. It be used to heat water. Two types of water represents the amount of heat required to heaters that use this system are tankless warm up hot water for a typical home in a coil and indirect. year, divided by the amount of energy - No separate storage tank is needed in the input into the heater to warm that water. tankless coil water heater because water - As a result, the heat pump water heater industry relies on two indexes of energy  efficiency: coefficient of performance capacity to provide hot water during (COP), which is favored by manufacturers periods of peak use. of larger heat pump water heater systems. The EF of a typical heat pump water heater Sizing Storage Tank Water Heaters will be about 2.2. The COP is a measure of - Residential water heaters are typically the instantaneous energy output of a sized based on their first hour rating (FHR). system in comparison with its This rating is contained on the U.S. instantaneous energy input. Department of Energy Guide label found on all water heaters. The FHR relates to the Hot Water Recirculating Systems gallons of hot water available for one hour - In many medium and large commercial of peak demand. It is the maximum output buildings and even some residences, a hot of the water heater over an hour, in gallons water recirculating system continuously of hot water in a 100°F temperature rise. circulates hot water from the water- - Recovery rate is the quantity of water that heating unit through the hot water supply the burner or element can heat to a 100°F piping and back to the water heater (38°C) increase in one hour. through hot water recirculating piping. Sizing Instantaneous Water Heaters There are three types of hot water - Instantaneous water heaters are selected recirculating strategies as follows: based on the amount of hot water needed CONTINUOUS RECIRCULATING to meet the design load (peak - water is constantly recirculated from the instantaneous demand), in gpm or L/min, water heater through the piping. This type at a specific water temperature rise and of system is best suited for buildings other criteria. having round-the-clock occupancy. - Faster flow rates or cooler inlet (water TIMED RECIRCULATING supply) temperatures will reduce the - involves use of an electronic or water temperature available. Using electromechanical timer to shut off lowflow showerheads and water- circulation of hot water when the building conserving faucets are a good idea with is not occupied. instantaneous water heaters. THERMOSTATICALLY CONTROLLED RECIRCULATING Sizing a Large Multifamily Water Heating - relies on a sensor located at a remote System location in the recirculating line, which - As with one- and two-family water heaters, senses water temperature and activates a hot water system must be designed to the recirculating pump when water provide a sufficient supply of hot water for temperature drops below a use by building occupants during peak predetermined setting. periods of use. 13.7 DETERMINING WATER HEATING SIZE 13.8 WATER SUPPLY SYSTEM DESIGN Design Load EXAMPLE - Hot water use is not spread out over the ❖ Demand Load Example entire day. Instead, domestic use of hot - The first step in determining the demand water tends to peak in the morning hours load is to list the plumbing fixtures and again in the early evening (supper required on the project. time). As a result, a water heating system ❖ Upfeed System Design Example must be designed to have sufficient - Water supply pipes must be of sufficient impeller; that is, the drive and pump are size to provide adequate pressure to all directly connected. fixtures in the system at a reasonable cost. - Flexible coupled pumpdrive configurations ❖ Downfeed System Design Example minimize vibration and wear between the - The upfeed zone is limited to a practical pump and pump drive, especially for large maximum height of approximately 60 ft pumps. (20 m). - Constant speed drives are drives designed to operate at a specific speed (e.g., 1750, 13.9 PUMPS 3500 rpm). These drives are usually sized A pump is a mechanical device used to to handle the largest loads so they are move a fluid by converting mechanical energy typically oversized for normal operating to pressure energy called head. loads. - There are two types of speed control in Types of Pumps pumps: Multispeed drives have separate ✓ POSITIVE DISPLACEMENT PUMPS speed settings (e.g., high, medium, and - has an expanding cavity on the suction side low) so they can be adjusted to control of the pump and a decreasing cavity on the speed and, thus, pump flow rate. Variable- discharge side. An example of a positive speed drives provide speed control over a displacement pump is the human heart. continuous range. Variable speed drives Liquid is allowed to flow into the pump as control pump speed by changing the speed the cavity on the suction side expands. of the driver and thus flow rate. ✓ CENTRIFUGAL PUMPS - is made up of an outer casing that has a Pumping Configurations rotating wheel-like component called an - For some pumping installations it may be impeller inside a stationary cavity created necessary to use multiple pumps to meet by the casing and called the volute. Fluid is design requirements. drawn into the inlet port at the center of PUMPING IN PARALLEL the rotating impeller. - Parallel pumping entails installing two - The number of impellers determines the pumps side by side in a piping system. number of stages of a centrifugal pump. A When installing two identical pumps in single-stage pump has just one impeller parallel, the combined flow rate will be less and is better for low head service. A two- than double. stage pump has two impellers mounted in PUMPING IN SERIES series for medium head service. A - Series pumping involves installing two multistage pump has three or more pumps one in line with the other in a single impellers mounted in series for high head pipe in a piping system. Pumps in series service such as in deep well pumps. double the head at the same flow condition point. Pump Drives - Pumps are driven by a drive, usually an Pumping Configurations electric motor in building plumbing - The fundamental performance systems. A fuel-powered engine can also considerations of centrifugal pumps are drive a pump, but this type of drive is capacity, total dynamic head, brake TYPICALLY RESERVED FOR TEMPORARY OR horsepower, pump efficiency, and pump emergency applications. speed. - The pump drive may be close coupled such that it is on the same shaft as the pump  PUMP CAPACITY - In a pumping installation, the difference - Pump capacity (Qpump) is the flow rate at between the actual head of the liquid which liquid is moved or pushed by a pump available (as measured at the pump’s to the desired point in the system. suction inlet) and the vapor pressure of TOTAL DYNAMIC HEAD that liquid is called the net positive suction - Total dynamic head (ΔPTDH) is a pressure head available (NPSHa). This is the difference, expressed in feet (meters), that amount of NPSH available to the pump represents the measurement of the height from the suction line. of a liquid column that the pump can - NPSHa is directly related to system design, generate from the kinetic energy imparted while NPSHr is directly related to pump to the liquid. design. - Head is a term that can have units of a PUMP SPEED length (feet or meters) and pressure (e.g., - Pump speed (N) is tied to the rotational psi, Pa). speed of the drive (motor). It is expressed POWER AND HYDRAULIC EFFICIENCY in revolutions per minute (rpm). - The work performed by a pump is related to the total dynamic head and weight of Pump Affinity Laws the liquid pumped in a specific time period. - Pump affinity laws are scientific Brake horsepower (BHP) is the actual relationships that describe changes in horsepower delivered to the pump shaft pump capacity, total dynamic head, and under stated operating conditions of the BHP when a change is made to pump pump where horsepower is 550 speed, impeller diameter, or both. foot/pounds per second. Pump output is the water horsepower (WHP) delivered by Pump Performance Curves the pump. - A pump performance curve is a graph that - The water efficiency (ηwater) of a pump shows the flow rate that a specific pump (sometimes called the hydraulic efficiency) model and impeller size is capable of is expressed as a percentage of hydraulic pumping over a range of pressure horsepower to BHP over the differences. recommended operating range of the indicated impeller size(s). It describes the Using Pump Performance Curves change of centrifugal force (expressed as - Two variables affect pump performance, the velocity of the fluid) into pressure drive horsepower, and impeller size: total energy. dynamic head and pump capacity. These - The best efficiency point (BEP) is the hydraulic design conditions are specific to a operating condition at which a pump most particular piping installation and are used to efficiently converts shaft power to flow determine the required size of a pump. NET POSITIVE SUCTION HEAD - The intersecting point on a pump - The inlet of a pump sucks liquid into the performance curve where the desired pump pump. The term used to describe this capacity and total dynamic head match the suction pressure of a pump is net positive installation’s requirement is known as the suction head (NPSH). It is expressed in operating point (sometimes called the duty height, as feet or meters. The minimum point). head required to prevent cavitation with a specific liquid at a specific flow rate is 13.10 WATER SOFTENING called net positive suction head required Hard Water (NPSHr). - The presence of excess calcium (Ca) and/or magnesium (Mg) mineral ions in water  results in the water being referred to as hard water. - Soft water has a hardness of 3.5 GPG (60 ppm/60 mg/L) or less. Hard water has a hardness of 7 GPG (121 ppm/121 mg/L) or more. Softened water is any water that is treated to reduce hardness. - scale, a hard, crusty deposit visible on taps, shower fittings, toilets, and water-using appliances (e.g., boilers, water heaters), which clogs pipes, fixtures, and appliances, reducing equipment efficiency and increasing energy costs; and, scum, which reduces the cleaning effectiveness of detergents used for laundry, dish washing, and bathing. Water Softeners - Water softening is a process that reduces or removes calcium and magnesium ions from hard water. The most used softening methods in residential installations are ion exchange and reverse osmosis. ION- EXCHANGE WATER SOFTENER - An ion-exchange water softener operates by passing hard water through porous resin beads that have soft sodium/potassium ions attached to them. REVERSE OSMOSIS WATER SOFTENER - A reverse osmosis water softener works by forcing water under pressure against a semipermeable membrane, where water molecules form a barrier that allows other water molecules to pass through while excluding most suspended and dissolved materials, including ions contributing to hardness. It is called “reverse osmosis” because mechanical pressure is used to force water flow in a direction that is the reverse of natural osmosis (e.g., from a dilute to a concentrated solution).  Chapter 14 SANITARY DRAINAGE SYSTEM WASTEWATER TRAPS - sometimes referred to as sewage, is used - a U-shaped pipe that catches and holds a water. It comes from almost all sections of the small quantity of wastewater that is poured building, including bathrooms, kitchens, and down a fixture drain. The trapped water laundry areas, and in commercial projects, prevents gases resulting from wastewater equipment being serviced. Because organic decomposition from entering the building waste in wastewater tends to decompose through the drain pipes and the fixture. quickly, one of the primary objectives of the - The most acceptable type of trap is called a P- sanitary drainage system is to dispose of trap. S-traps and U-traps can easily be decaying wastes rapidly, before they cause siphoned, so they are prohibited by the objectionable odors or become hazardous to building code. An integral trap is built in as health. part of the fixture. The integral trap in a vitreous china water closet is cast as part of the 14.1 SANITARY DRAINAGE SYSTEM fixture. Conventional Sanitary Drainage and Vent - Historically, a building trap was located at the System end of the building drain (inside the building SANITARY DRAINAGE AND VENT SYSTEM and just before it connected to the sewer line). - sometimes referred to as the drain, waste, It was theorized that this trap would act as a and vent (DWV) system, is a network of pipes seal to keep gases from entering the building’s that remove wastewater from a building. In sanitary drainage system from the sewer line. this section the terminology and function of each of the parts are explained, but first a INTERCEPTORS discussion of system operation is needed. - are passive devices designed into a plumbing - In typical plumbing system operation, it system that trap, separate, and retain these consists of traps at each fixture, and fixture toxic or undesirable substances from branch, stack, and drain pipes that carry wastewater before it is discharged into the wastewater away from the plumbing fixtures sewer line. and out of the building. - Grease can solidify and coat the inner walls of pipes, creating a stoppage. Restaurants, GRAVITY SYSTEM cafeterias, and other commercial food - Gravity is the driving force behind establishments with cooking facilities must wastewater flow, so the sanitary drainage have a grease interceptor or grease trap that system is known as a gravity system. receives wastewater from sources such as sinks, dishwashers, floor drains, and washing VENT SYSTEM area drains before draining to the municipal - side of the system introduces and circulates sewer system. Manufacturing plants, vehicle air in the system to maintain atmospheric service facilities, car washes, and other similar pressure in the drain lines and ensure establishments must have an oil-sand adequate gravity flow of wastewater. Venting interceptor to separate and remove floatable prevents a negative pressure (suction) in the material (oils) and settleable materials (sands system that could suck water from fixture traps and metals) from wastewater before it is and allow sewer gases to infiltrate the building. discharged to the municipal sewer system. The vent system also exhausts sewer gases to Barber shops, beauty salons, pet grooming the outdoors. facilities, and any other establishments that Chief components of a sanitary drainage and discharge hair and/or other fibrous materials vent system: in wastewater must have a hair interceptor. FIXTURE BRANCHES SANITARY SEWER MAIN - Each plumbing fixture is connected - is a pipe through which the wastewater flows horizontally to the sanitary drainage system by as it is conveyed from a building to the a drain line called a fixture branch. Branch wastewater treatment plant. Typically, the piping, which serves urinals, water closets, minimum size of a community sanitary sewer showers, or tubs, is usually run under the floor. main for a gravity-based system should be 8 in When these fixtures are not on the branch, the (200) mm in diameter. piping may be run in the floor or in the wall behind the fixtures. CLEANOUTS - Provisions must be made to allow cleaning of STACKS the sanitary drainage system. Cleanouts are - The fixture branches feed into a vertical pipe screw-type fittings with a cap that can unscrew referred to as a stack. When the wastewater to allow access to the inside of the sanitary that the stack will carry includes human waste drain pipes. A cleanout should not have a from water closets (or from fixtures that have plumbing fixture installed in it or be used as a similar functions), the stack is referred to as a floor drain. Floor cleanouts (FCO) are found in soil stack. When the stack will carry all wastes horizontally positioned building drain or sewer except human waste, it is referred to as a lines that are installed in the floor or in the waste stack. Soil and waste stacks may be ground. Wall cleanouts (WCO) are placed in copper, plastic, galvanized steel, or cast iron. vertically positioned stacks. All cleanouts in These stacks service the fixture branches vertical stacks should be located no higher beginning at the top branch and go vertically than 48 in (1.2 m) above the floor. downward to the building drain. VENTING BUILDING DRAINS - are pipes that introduce sufficient air into the - The soil or waste stacks feed into a main drainage system to reduce air turbulence (from horizontal pipe referred to as the building siphoning or back pressure) and to release drain. By definition, the building drain extends sewer gases to the outside. The prime purpose to a point 2 to 5 ft (0.6 to 1.5 m) outside the of venting is to protect the trap seal. If traps did foundation wall of the building. Location of the not exist in a drainage system, a venting could building drain in the building depends primarily be eliminated. on the elevation of the community sewer line. Ideally, all of the plumbing wastes of the Types of venting methods are as follows: building will flow into the sewer (whether it is Individual Vents a community or a private sanitary system) by - The individual venting technique is defined as gravity. The drain is typically placed below the the installation of a vent pipe for every trap or first floor or below the basement floor. trapped fixture. It is the easiest method of ensuring the preservation of a trap seal but the BUILDING SEWER most costly because of the number of vent - is an extension of the building drain that pipes required in the venting system. An carries wastewater from the building drain to a individual vent must be located in close community sanitary sewer main or an proximity to the trap to properly vent it. individual on-site sewage treatment (OSST) system. In community sanitary wastewater Common Vents systems, the building sewer may also be known - The common venting method serves two as a house or building connection, or sanitary fixtures located on the same floor; it is sewer lateral. essentially an individual vent that serves no more than two traps or trapped fixtures. This type of vent must be located close to the traps group of fixtures ties in with the main vent it vents to properly vent it. stack, which extends to the exterior. AIR ADMITTANCE VALVES Wet Vents - An air admittance valve (AAV) is a pressure- - The wet venting method uses a single vent activated, one-way mechanical venting port pipe to provide venting for all of the fixtures of used to eliminate the need for expensive one or two bathroom groups (e.g., a water venting and roof penetrations. Wastewater closet, lavatory, shower, bathtub, and bidet) discharges cause the AAV to open, allowing air that are located on the same floor. The vent to circulate in the vent system. pipe for the lavatory typically serves as the - AAVs are typically made from polyvinyl vent for the other fixtures in the bathroom. chloride (PVC) plastic materials with ethylene propylene diene monomer (EPDM) rubber Circuit Vents valve diaphragms. - A circuit venting system is a horizontal venting pipe serving up to eight fixtures. Each POSITIVE AIR PRESSURE ATTENUATOR fixture must be connected to a single - A positive air pressure attenuator (PAPA) is a horizontal drain in this technique. The vent product developed to protect buildings of 10 or connection is made between the two more stories against the unwanted positive upstream fixtures—that is, those fixtures pressures (i.e., back pressure/positive connected to the horizontal drain pipe that are transients) generated in the DWV system. the farthest away from the vent stack. In this PAPAs are installed at the base of the soil and system, all of connections and the main piping waste stack and at various floor intervals, must remain in the horizontal orientation. depending on the height of the building. Vertical drops are generally not permitted. SOVENT® DRAIN AND VENT SYSTEM Combination Drain and Vent - The Sovent system is a system that combines - A combination drain and vent system allows the drain stack, branches, and vents into one the distance from trap to vent to be extended pipe system by using patented Sovent fittings. infinitely, provided the drain stays in the Fritz Sommer of Switzerland, whose work was horizontal orientation and there is a vent mainly driven by a need for resource- somewhere within the horizontal branch. It is conserving construction techniques, based on oversizing the horizontal drain, so developed and patented the Sovent® fittings in there is an increased likelihood of stoppage in the 1950s. the drain line. This is the most popular method - The system consists of four components: of venting a floor drain or venting island vertical stack piping, horizontal branches to fixtures. the fixtures, aerator fitting, and de-aerator fittings. These components work together to Relief Vent collect wastes from the plumbing fixtures and - A relief vent is a continuous pipe of lesser or transport them down a stack to the building equal diameter running parallel and alongside drain. the soil and waste stack in a multistory - The Sovent® stack is a vertical pipe that plumbing system. It is used to equalize air conveys wastes from the upper levels of a pressure within the stack. building to the base of the stack. The stack begins just above the bottom-most de-aerator A vent stack extends vertically through fitting (to be described later) and continues to the building and up through the roof to the just above the highest fixture connection. The exterior of the building. Vents from a fixture or main difference between the specially designed stack and the traditional waste and vent stack is the Sovent® stack will remain one DRAINAGE FIXTURE UNITS size throughout its entire length. - The draining rate for plumbing fixtures is - The Sovent® aerator fitting is made of two based upon the drainage fixture unit (DFU). separate chambers. The first chamber, called Similar to the water supply fixture unit (WSFU) an offset chamber, allows falling waste from introduced in Chapter 13, the DFU is an the upper floors to enter the chamber and pass arbitrarily chosen measure that allows all of around the horizontal branch inlets. This offset types of plumbing fixtures to be expressed in reduces the falling waste’s velocity, eliminating common terms; that is, a fixture having twice blockage before it is allowed to form. The the instantaneous drainage flow rate of a second chamber, named the mixing chamber, second fixture would have a fixture unit value is fully separated from vertical stack flow with twice as large. an internal separation baffle. - A Sovent® de-aerator fitting must be located DESIGN APPROACH at the base of each Sovent® stack and at any - The approach used to size drain and vent lines horizontal stack offset. This fitting is designed relies on tabular information found in code. to effectively deal with pressure fluctuations Table 14.2 indicates the maximum load in DFU that occur when vertical falling wastes and maximum pipe length for a given pipe suddenly turn horizontal. diameter. The minimum pipe diameter is based on the total connected DFU. In the case SEWAGE EJECTION of vent lines, maximum developed length for a - For the most part, sanitary drainage systems given pipe is also a criterion. Developed length rely on the force of gravity to create flow to is the “centerline” length of the lines, excluding discharge wastewater. In some building traps and trap arms. It is important to ensure installations, however, a fixture or group of that a larger pipe diameter does not flow into fixtures must to be installed below the level of a pipr having a smaller diameter. the nearest available sewer line. In these cases, - Traps and trap arms are sized based on a wastewater must be lifted to the level of the specific type of fixture. Some fixtures such as main drain or sewer by a pumping system urinals and water closets have integral traps called a sewage ejector. Typically, a sewage built into the fixture so trap size does not need ejector can pump solids from 2 to 4 in (50 to to be specified. 100 mm) in size or grinds solid wastes before For the horizontal fixture branch, from passing them through the ejector. Table 14.2, a 3-in diameter pipe is - A sewage ejector system consists of the sump selected. A 3-in diameter pipe used as basin, a motor-pump assembly, and a system a horizontal fixture branch can serve of automatic electrical controls. Wastewater up to 20 DFU. from the sanitary pipes flow by gravity into the For the waste stack, from Table 14.2, a sump basin, a pit that collects wastewater. 21 ⁄2 in diameter pipe can be selected - Typically, residential ejector systems must but the 3 in diameter horizontal fixture have the capacity of ejecting solids up to 2 in branch would then flow into a smaller (50 mm) in size. Depending on pump impeller pipe. A 3 in diameter waste stack is a design, a 4-in pump will normally handle prudent choice. spherical solids from 2 to 3 in and typically For the vent stack, from Table 14.4a, a range in motor size from 1 ⁄3 to 2 horsepower. 11 ⁄2 in diameter pipe is selected, Additionally, these systems are generally rated based on a 3 in diameter soil and waste to a maximum temperature of 180°F (82°F). stack and a capacity of up to 30 DFU. 14.2 DRAIN AND VENT PIPE DESIGN 14.3 SYSTEM INSTALLATION 14.4 SANITARY DRAINAGE AND VENT SYSTEM - On a small project, the drainage piping DESIGN EXAMPLE typically varies in size from 11 ⁄2 to 4 in. It can The following example conveys a be much larger in large hotels, apart- ments, typical design approach for the four-story and office buildings. This larger size of pipe apartment building used in the water supply often re- quires special provisions in wall width de- sign example in Chapter 13. or furred-out areas. -On larger projects with concrete walls and ceilings, it isusually necessary to provide sleeves (holes) in the concrete forthe pipes to pass through to get from space to space. It will alsobe necessary to provide inserts and hangers to support the pipes. - The open spaces provided in truss-type constructionmake it easier to run piping through to the desired location. The only points of difficulty would be where it needs to pass byductwork or some other large pipe that is going in the oppositedirection. This will require coordination with the contractor in- stalling any heating, air conditioning, or ventilating ductwork. - In wood frame construction, the holes are sometimesdrilled to allow the passage of the pipes. These should be at themiddle of any load-bearing wood members so that a minimum ofstructural damage is done. There are times when the width of awall needs to be increased to allow for pipes running horizontallyto pass by drainage pipes (or other pipes) running vertically. - Pipe chases run from floor to floor to allow stacks andvents to pass vertically between floors. A view of the interior ofa plumbing (wall). Chases aretypically located alongside elevator hoist ways and commonplumbing walls. A drain stack is shown in Photo 14.18. Pipe tunnels may be used on large projects to provideconcealed space for the passage of mechanicals at ground leveland from building to building. Hangers from the top or side of the tunnel are used to support the pipes. Access may be from either end of the tunnel or access floors may be provided.  Chapter 15 WASTEWATER TREATMENT AND DISPOSAL SYSTEM 15.1 WASTEWATER TREATMET STANDARDS manufacturing, commercial, laboratory, History and mining operations, including the - Before about 1850, human and liquid runoff from areas that receive pollutants industrial wastes were typically dumped in associated with industrial or commercial the street or alley or conveyed to the storage, handling, or processing. nearest body of water without treatment. Wastewater Constituents - About 1854, the connection between - Wastewater is mostly water by weight. cholera and sewagecontaminated water Wastewater released by residences, was first discovered. businesses, and industries is - In the 1970s, the U.S. Congress passed the approximately 99.94% water. Clean Water Act. This legislation led to the ORGANISMS establishment of national water quality - Many different types of organisms live in standards and limits for the discharge of wastewater and some are essential pollutants. contributors to treatment. Wastewater PATHOGENS - As described in the previous chapter, - Many disease-causing viruses, parasites, wastewater (sewage) is “used” water. and bacteria are present in wastewater. - is a combination of the liquid and water- These pathogens often originate from carried wastes from residences, people and animals that are infected with commercial buildings, industrial plants, or are carriers of a disease. and institutions, together with any ORGANIC MATTER groundwater, surface water, and storm - Organic materials that originate from water that has infiltrated the public plants, animals, or synthetic organic sewage system. compounds are found everywhere in the - Wastewater from residences, apartments, environment. motels, office buildings, and other similar - Biodegradable waste is easily broken types of buildings is referred to as down by aerobic bacteria, which are domestic wastewater. natural organisms. Waste that cannot be There are two types of domestic wastewater: broken down by other living organisms is GRAY WATER nonbiodegradable. - is wastewater that typically contains the - Biochemical or biological oxygen demand residues of washing processes. (BOD) is a measurement procedure used to BLACK WATER assess how fast biological organisms are - is wastewater that contains fecal matter depleting dissolved oxygen in a body of and urine. It is produced in water closets water, as measured in milligrams per liter (toilets), urinals, and bidets. (mg/L) over a 5-day period. - Some areas in the United States permit the OIL AND GREASE use of innovative gray water reuse - Bacteria do not quickly break down fatty systems that safely recycle household gray organic materials from animals, water for reuse in toilets or for irrigation to vegetables, and petroleum. conserve water and reduce the flow to INORGANICS treatment systems. - Inorganic minerals, metals, and - Commercial wastewater is nontoxic, compounds, such as sodium, potassium, nonhazardous wastewater from calcium, magnesium, cadmium, copper, commercial and institutional food service lead, nickel, and zinc, are common in operations and beauty salons. wastewater from both residential and - Industrial wastewater is process and nonresidential sources. nonprocess wastewater from NUTRIENTS systems, the system carries both sanitary - Wastewater often contains large amounts water and storm water. of the nutrients nitrogen and phosphorus, - The building drain in a building sanitary which promote plant growth. drainage system is connected to a building SOLIDS sewer about 2 to 5 ft (0.6 to 1.5 m) outside - Solid materials in wastewater can consist of the building. of organic and/or inorganic materials and - Certain types of sewers, such as inverted organisms. siphons and pipes from pumping stations, GASES flow under pressure, and are thus called - Many gases in wastewater can cause odors force mains. Urban sewer mains generally or are dangerous. discharge into interceptor sewers that join Other Important Wastewater Characteristics to form a large trunk line, which discharges TEMPERATURE wastewater into the community sewage - The best temperatures for wastewater treatment plant where it is treated. treatment range from 77° to 95°F. In Sewage Treatment and Disposal general, biological treatment activity - Sewage treatment is a multistage process accelerates in warm temperatures and designed to restore the quality of slows in cool temperatures, but extreme wastewater before it reenters a body of hot or cold can stop treatment processes water such as a stream, river, or lake. altogether. Processes involved in large wastewater pH treatment plants are usually classified as: - The acidity or alkalinity of wastewater Preliminary Wastewater Treatment affects both treatment and the - Preliminary treatment to screen out, grind environment. Low pH indicates increasing up, or separate debris is the first step in acidity, while a high pH indicates wastewater treatment increasing alkalinity (a pH of 7 is neutral). FLOW Primary Wastewater Treatment - Whether a system serves a single - Primary treatment is the second step in residence or an entire community, it must wastewater treatment. It separates be able to handle fluctuations in the suspended solids and greases from quantity and quality of wastewater it wastewater. receives to ensure proper continuous Secondary Wastewater Treatment treatment. - Secondary treatment is a biological treatment process to remove dissolved 15.2 COMMUNITY WASTEWATER TREATMET organic matter from wastewater. Sewage AND DISPOSAL microorganisms are cultivated and added Wastewater Removal to the wastewater. - A community wastewater treatment and Three approaches are used to accomplish disposal system, a network of pipes that secondary treatment: transport wastewater to treatment plants FIXED FILM SYSTEMS where it is treated and released to the - grow microorganisms on substrates such environment, serves most buildings in the as rocks, sand, or plastic. United States. SUSPENDED FILM SYSTEMS - Sanitary sewage is typically separated from - stir and suspend microorganisms in storm water (from rain and snowmelt) by wastewater. Some of the sludge is pumped a separate piping arrangement. In less back into the incoming wastewater to modern systems, known as combined provide “seed” microorganisms.  LAGOON SYSTEMS process, anaerobic digestion and - are shallow basins that hold the settlement of solids in wastewater takes wastewater for several months to allow for place. the natural degradation of sewage. Types of primary treatment equipment: SEPTIC TANK Final Treatment (Disinfection) - is a watertight, covered container - Final treatment involves disinfection; the designed to settle out and hold solid removal of diseasecausing organisms from wastes and partially treat wastewater with wastewater. beneficial bacteria. - Chlorination has become the standard - The lighter particles form a layer known as method of disinfection because it remains the scum. The remaining solids accumulate in the water after the treatment. as sludge in the bottom of the tank. Other treatments include the following: AEROBIC TANK - aeration, the exposure of treated water to - are a substitute for a septic tank. They air, which removes odors and improves consist of a trash tank, an aeration taste; corrosion removal, to balance the chamber, and a settling chamber. pH (acidity) of the treated water to prevent - work more effectively than septic tanks corrosion damage to pipes, remove odors, and thus can be smaller in size. and improve taste; and to soften the water. The softening process removes PUMP TANK calcium and magnesium that have - is a watertight container used to dissolved in water, making the hard water temporarily store clarified effluent before soft. it flows into a drainage field. Wastewater is first treated in an aerobic or septic tank. 15.3 ON-SITE INDIVIDUAL SEWAGE SAND FILTERS TREATMENT - is a lined, impermeable container On-Site Sewage Treatment containing a bed of granular material that - On-site sewage treatment (OSST) systems, provides additional treatment of effluent traditionally called septic systems, usually as it flows from the primary treatment tank consist of the building sewer, which leads to the drainage field. from the building into a septic tank and - In an intermittent sand filter, the effluent then into a distribution box that feeds the is dispersed throughout the upper portion fluid (effluent) into a drainage field or of the granular bed through perforated disposal field. pipes. - An OSST system consists of a primary - A recirculating intermittent sand filter treatment component, such as a septic requires a recirculating pump tank. The tank, and a disposal component, which is pump is used to mix filtrate with incoming typically the drainage field. septic tank effluent. - Inside the septic tank, anaerobic and TRASH/GREASE TANK aerobic bacteria convert the wastes into - is occasionally used in conjunction with an minerals, gases, and a liquid waste called aerobic tank. The trash tank removes the effluent. Clarified effluent leaves the materials that treatment microorganisms septic tank and flows in a pipe to a are unable to degrade. drainage field. CESSPOOL - is a covered underground container that Preliminary Treatment Equipment receives untreated sewage directly from a - Wastewater from a building is first treated building and discharges it into soil. in primary treatment equipment such as High-Level Alarms tanks or filters. In the primary treatment - is used to alert the homeowner or building field network. These systems are also operator if liquid inside a tank reaches a called leaching chambers, galleys, and flow level that is higher than it would be if the diffusers. pump were operating normally or if the EVAPOTRANSPIRATION BED OR TRENCH liquid inflow is greater than the maximum DRAINAGE FIELD pumping capacity of the pump. - An evapotranspiration (ET) bed or evapotranspiration trench drainage field Secondary Treatment and Disposal treats wastewater by evaporating the Equipment water from the soil and by transpiring the - A drainage field provides secondary water into the air through plants and treatment and is the final disposal location grasses. for clarified effluent from wastewater. LOW-PRESSURE DOSING DRAINAGE FIELD Types of drainage fields: (LPD) ABSORPTION DRAINAGE FIELD - drainage fields typically consist of narrowly - consists of rows (called lines) of cut 6 to 12 in wide trenches, containing underground pipes through which the small-diameter PVC dispersion pipes. LPD clarified effluent passes. systems also include a pump tank and an - A distribution box receives the effluent electrical control system. from the septic tank and distributes it - Pumped effluent low-pressure dosing equally to each individual line of the drainage fields are a basic LPD trench drainage field system intended for single-family homes - Perforated pipe (pipe with holes), and cannot be used for commercial or frequently called drain tiles because they institutional facilities. used to be made of clay tile pipe, disperse ABSORPTION MOUNDS the clarified effluent throughout the - consist of septic tank(s), a pump tank, drainage field. effluent pump and controls, and an above- - An absorption drainage trench is an grade drainage system. absorption field that consists of one or SPRAY DISTRIBUTION more individual trenches containing the - systems spray the disinfected effluent drainage pipes. onto the ground surface in a manner - An absorption drainage bed is an open similar to a lawn irrigation system. drainage field without trenches containing LEACHING CHAMBER DRAINAGE FIELD the drainage pipes. - Leaching chambers are proprietary, GRAVEL-LESS DRAIN FIELDS commercially produced plastic chambers - distributes effluent into the soils through pre-molded into a dome shape. They can gravel-less drain pipe instead of gravel. As be easily assembled and placed in a result, these systems are also called no trenches. gravel or no rock drain field systems. SUBSURFACE DRIP DRAINAGE FIELD - Fabric-wrapped drain field systems use - Subsurface drip systems consist of a septic proprietary, largediameter, corrugated, tank, a pump tank, a filtering device, and a and perforated polyethylene tubing drip distribution system. An aerobic tank is covered with permeable nylon geotextile typically used for the primary treatment filter-like fabric to distribute water around process. the pipe. - A chamber-type drain field system SEEPAGE PIT consists of several arch-shaped, open- - is a deep underground container that bottomed plastic chamber segments receives clarified effluent from a septic connected to form the underground drain tank. General Regulations - Design is usually based on the maximum - Typically, an OSST system should not be daily wastewater flow rate and average installed, repaired, or rehabilitated where percolation rate. Maximum daily a community sanitary sewer system is wastewater flow rate (Q) is typically available or where a local ordinance expressed in gallons per day or liters per requires connection to a community day. system. - Minimum drainage area requirements for septic tank effluent are based on type of 15.4 TESTING OF SOIL AND WATER FOR system and average percolation rate DRAINAGE (tperc) of the soil in min/in (min/cm). Soil Evaluation - is an assessment of subsurface soil Design of a Seepage Pit conditions at a specific site that is - The size of the seepage pit is typically conducted under the supervision of a based on the outside area of the walls of professional engineer or professional the seepage pit. geologist. - A minimum depth of unsaturated soil Avoiding Potential Design Problems beneath the planned soil absorption - One of the most wasteful uses of a system is required to restore wastewater residential OSST system is the connection before it reaches a limiting layer. A limiting of a clothes washing machine. layer may be an impervious soil layer, bedrock, or a high water table. 15.6 OSST SYSTEM INSTALLATION Location Soil Percolation Test - Individual sewage disposal requires finding - is a subsurface soil test at a depth of a an appropriate location on the site to place proposed absorption system to determine all of the system components, especially the water absorption capability of the soil. the drain field, which takes a considerable - is required for any system dependent on amount of area. soil absorption for effluent disposal. Installation BOD Test - Typically, a backhoe will be needed to - measures the amount of dissolved oxygen excavate holes for the septic tank or organisms are likely to need to degrade seepage pits and any trenches for wastes in wastewater. This test is distribution piping and disposal fields. In a important for evaluating both how much community OSST system, a trench must be treatment wastewater is likely to require dug from the building to the community and the potential effect that it can have on line. receiving waters. Coliform Test 15.7 GRAY WATER REUSE SYSTEM - determines whether wastewater has been Gray Water and Black Water adequately treated and whether water - Gray water (also spelled grey water) is quality is suitable for drinking and untreated wash water from bathtubs, recreation. showers, lavatory fixtures, and clothes washing machines. 15.5 DESIGN EXAMPLE OF AN INDIVIDUAL - Black water contains toilet wastes (e.g., OSST SYSTEM feces, cellulose from toilet paper, and nitrogen compounds) from water closets Design of a Septic Tank/Absorption Field (toilets), urinals, and bidets. Black water may also carry hazardous chemicals from  activities such as cleaning car parts, 15.8 ALTERNATIVE WASTEWATER washing greasy/oily rags, or disposing of TREATMENT SYSTEM waste solutions from home photo labs or - Alternative wastewater treatment systems similar hobbyist activities. Compared to serve as an option for the sewage treatment gray water, black water has a large amount systems described previously. of organic and pathogenic pollutants. Privy/Latrine Gray Water Reuse - One of the oldest and most basic methods - Gray water needs to be filtered to remove of waste disposal is the pit privy or latrine, large waste particles before being used or a pit dug below an outhouse structure that treated. This primary treatment will collects human body wastes. reduce the solids in the wastewater. Composing Toilets Gray Water Diversion Devices - is a self-contained waste treatment system - Gray water diversion devices do not treat that uses natural biological decomposition gray water but use it directly as irrigation to convert toilet wastes into water vapor, water. Gray water is piped to outdoor carbon dioxide, and a stable compostlike vegetation through subsurface irrigation end product. lines. - It is essentially an “in-house” outhouse. GRAVITY DIVERSION DEVICE Bi-Level Composing Toilets - is a fitting configuration that diverts gray - are relatively large, two-story, watertight water from a plumbing fixture directly to containers equipped with a chute that an irrigation line. A Suldi Gray Water connects the toilet receptacle to the Diversion Valve is designed to fit under a composting unit located in the basement. laundry sink. PUMP DIVERSION DEVICE Selft-Contained Composing Toilets - has a similar irrigation piping arrangement - The second type of composting toilet is a to the gravity diversion device, but smaller unit in which the toilet receptacle includes a surge tank to temporarily store and composting tank comprise a single and limit the flow of gray water during self-contained unit located on the sudden surges. bathroom floor. Gray Water Treatment Systems Incinerating Toilets - Gray water treatment systems (GTS) are - are self-contained waterless systems that more complex systems that collect, store, do not require being hooked up to a sewer and treat gray water to a quality standard system or an inground septic system for irrigation and/or sewage processing (except to dispose of gray water). They rely (flushing toilets). on electric power or natural or propane