swimming pool binded.pdf

1-1 CHAPTER 1 CODE OF PRACTICE ON ENVIRONMENTAL HEALTH FOR AQUATIC FACILITY Note: extract from NEA’s COPEH September 2021 1-2 1-3...

1-1 CHAPTER 1 CODE OF PRACTICE ON ENVIRONMENTAL HEALTH FOR AQUATIC FACILITY Note: extract from NEA’s COPEH September 2021 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9  1-10   2-1 CHAPTER 2 WATER CONSERVATION 1 Overview of Water Conservation 1.1 Water Scarcity Only 1% of the total water resources on earth are available for human use. While 70% of the world’s surface is covered by water, 97.5% of that is salt water. Of the remaining 2.5% that is freshwater, almost 68.7% is frozen in ice caps and glaciers. In developing countries, about 80% of illnesses are linked to poor water and sanitation conditions. 1 out of every 4 deaths under the age of 5 worldwide is due to a water-related disease. In developing countries, it is common for water collectors, usually women and girls, to have to walk several kilometers every day to fetch water. Once filled, pots and jerry cans weigh as much as 20kg (44lbs). 1.2 Responsibility We could explain water conservation as referring to reduce the usage of water and to recycle waste water for different purposes like cleaning, manufacturing, agriculture etc. Water is scarce. Every drop of it is precious. Everyone should act responsibly and be mindful of how it is used and there are hundreds of ways to save water. To prevent excessive flow rates at water fittings, PUB limits the maximum allowable flow rates at water fittings. In July 2009, the Mandatory Water Efficiency Labelling Scheme (WELS) was implemented to further reduce water consumption and save water. The requirements for water fittings in the table below: Area of Usage Maximum Allowable Flowrates i) Basin taps & mixers 4 L/min ii) Sink/bib taps and mixers 6 L/min iii) Shower taps & mixers 7 L/min Starting from January 2022, PUB will extend the MWELS to water-closet (WC) flush valves and only those with at least a 2-tick water efficiency rating are allowed in new and existing non-residential premises undergoing renovation. For more details, please refer to PUB website. Link: https://www.pub.gov.sg/wels/about A review was conducted in 2003 and the maximum allowable flow rates at various water fittings were reduced by between 25 and 33 percent to prevent water wastage. Commented [HTG(1]: The mandatory requirement on limiting maximum allowable flow rates at water fittings was applicable not only to public and commercial premises, it was also extended to all domestic premises.  2-2 The requirements can be found in the Singapore Standard 636:2018 – Code of Practice for Water Services. Commented [HTG(2]: CP48 has been replaced with SS636 : 2018, the Code of Practice for Water Services 2 Water Efficient Strategies - The 3 ‘Rs’ To be truly water-efficient, the Reduce, Replace and Reuse (3Rs) approach should be adopted in the initial stage of planning and designing of a building. Effectively implementing the 3Rs can result in substantial savings in water, as well as energy, therefore reducing the environmental impact of both water discharge and the need to pump water over long distances. Under the Reduce approach, building owners should plan and install a monitoring system so that water consumption can be tracked and reviewed adopt low pressure water system and choose water efficient systems for cooling, irrigation, etc, employ high water efficient labelled products and design a leak-free system. Besides reducing water usage, building owners should plan and design the building to Replace the use of potable water by substituting potable water with NEWater, sea water and rainwater wherever feasible for their non-potable usage such as irrigation, general washing, cooling tower, etc. Water Efficient Building Strategy Reduce Replace Reuse The 3Rs Under the Reuse approach, building owners should plan and design water- recycling in processes such as laundry and manufacturing, etc. Recycling rates of up to 75% have been achieved, especially for wafer fabrication plants. Many wafer fabrication and semiconductor plants incorporate some form of water reuse and recycling into their operations. Some of the best practices include: a) Improving cooling tower Cycles of Concentration (COC) to a minimum of 7 and 10 for potable water and NEWater cooling towers, respectively. b) Replace wet processes with dry processes where possible e.g. anisotropic etching with dry plasma etches instead of wet isotropic etches.  2-3 c) Improve in the efficiency of present processes used to produce UPW from NEWater or other sources of raw water. d) Optimize the tools and procedures for utilizing Ultrapure water (UPW) in production processes. e) Reuse spent rinse waters and other wastewater streams from existing production processes. For more details, please refer to the best practice guides available on PUB website. Link: https://www.pub.gov.sg/savewater/atwork/WaterEfficiencyBenchmarks With advances in water treatment technology, more industries can now tap on recycling to reduce their water consumption. Commented [HTG(3]: 3 Design a Water Efficient Swimming Pool The components for a water efficient swimming pool design comprise the following items: Design of balancing tank Reduction of water evaporation rate Reduce filter backwash cycle and minimize water discharge 3.1 Design of Balancing Tank The balancing tank should be designed with the following water efficiency features: Set the operating water level in the balancing tank at the appropriate level to minimize overflow. Install a pilot float operated valve system to ensure sufficient buffer between the maximum allowable level and overflow pipe. Install automatic water level sensors and solenoid valves to control incoming water supply. Allow a larger buffer to capture bather displacement and rain water, which can be used for backwash, make up for evaporation loss. Install private meter at make-up water inlet of swimming pool balancing tank to monitor and track water consumption for leak control management. Commented [HTG(4]: 3.1 To add-on: Allow a larger buffer to capture bather displacement and rain water, which can be used for backwash, make up for evaporation loss. Install private meter at make-up water inlet of swimming pool balancing tank to monitor and track water consumption for leak control management. Please refer our circular to swimming pool licensees in Dec 2018  2-4 PUB water Buffer Swimming Maximum operating level pool Normal operating level Minimum operating level Balancing Tank With Buffer Water level 24 hours later Water level dropped Check Evaporation Rate  2-5 Location Where Pool Evaporation could be Reduced 3.2 Reduction of Water Evaporation Rate The rate of evaporation is increased by high pool water temperature, high air temperature, low relative humidity and high wind speed at the pool surface. To reduce the evaporation rate, consider the following design features: Commented [HTG(5]: Build the swimming pool at a suitable location to avoid or minimize direct sunlight. Use plants around the pool to protect the pool from wind which increases the amount of water lost by evaporation. However, ensure that no excess water from the plants is overflowing into the pool. Use a pool cover where applicable. Stop operation of water features to minimise drift losses and wastage during gusty condition. Reduce the operating hours of water playgrounds during off peak hours. 3.3 Operation of water features and water playground Stop operation of water features to minimise drift losses and wastage during gusty condition Reduce the operating hours of water playgrounds during off peak hours. 3.4 Reduce Filter Backwash Cycle and Minimise Water Discharge Pool water is continually circulated to achieve the required levels of water quality specified by the National Environment Agency. Backwash frequency should be determined by pressure differential (head loss) with reference to the manufacturer’s guidelines. Commented [HTG(6]: To reduce the backwash frequency and time, consider the following methods: s  2-6 Use more effective filter media such as zeolite which reduces the frequency and duration of backwash. Manual cleaning or skimmer to reduce filter load. Optimise backwash cycles by monitoring the pressure drop between the inlet and outlet of the filter. Set backwash duration to about 3 minutes, however the backwash duration should not be longer than manufacturer’s guidelines and operators should further reduce the duration of the backwash via observation of the clarity of the backwash discharge using the sight glass Use rainwater for backwash. Reuse backwash water for irrigation and area cleaning.   3-1 CHAPTER 3 THE PRINCIPLES OF AN AQUATIC FACILITY (AF) 1 Sources of Water Pollution 1.1 Bathers (Swimmers) Bathers are the chief source of nitrogenous compounds in aquatic facility water. Ammonia nitrogen and organic nitrogen are discharged into the water by way of perspiration and urine. The amounts of each may vary. However, generally children are responsible for the greatest proportion of urine in the AF. High water temperature and air temperature increase the rate of perspiration. Other pollutants from bathers include: (a) Mucus liquids such as saliva and nasal discharges. (b) Hair, attaching to it are dirt, oil and grease and scales. Hair also damage equipment, such as pumps. (c) Dirt and bacteria carried on the body. 1.2 Airborne Pollutant Micro-organisms, dust, tree leaves, lawn clippings, sand particles, insects and worms also contribute to the pollution of aquatic facility water. 1.3 Rain Gases, e.g. sulphur dioxide (SO2), carbon dioxide (CO2), react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds. Sunlight increases the rate of most of these reactions. The result is a mild solution of sulfurous acid, nitric acid (a component of acid rain) and typically carbonic acid when they fall as rain. Generally, rain has a pH slightly under 6. This is because atmospheric carbon dioxide dissolves in the droplet to form minute quantities of carbonic acid, which then partially dissociates, lowering the pH. If airborne dust contains enough calcium carbonate to counter the natural acidity of precipitation, like in some desert areas, the rain that falls can be neutral or even alkaline. Rain below pH 5.6 is considered acid rain. 2 Types Of Aquatic Facility (a) Surflo (Perimeter Overflow) System (b) Side Surflo System (c) Biflo System (d) Ribbon Flow System  3-2 (e) Perimeter Flow System (f) Skimmer System 2.1 Surflo (Perimeter Overflow) System Balancing tank To filtration plant From filtration plant Figure 3-1 Surflo System Strainer AF AF Deck Scum channel Deck Swimming pool Floor inlet Treatment unit Inlet pipe Drain To Sewerage Balancing tank Filtration unit Holding tank Separation tank Pump Strainer Figure 3-2 Surflo (Perimeter Overflow) System Re-circulating Aquatic Facility Figure 3-1 shows the schematic of a typical aquatic facility. The main components generally used in an aquatic facility are also shown. Water is drawn from the balancing tank and pumped to the filter where it is filtered and then delivered to the heater if required. Chlorination and other treatments are next along the line. Finally, water is returned to the AF by inlet nozzles located along the length of the bed. Water entering the AF displaces an equal amount of water that overflows into a scum channel along the entire perimeter. The scum channel is continuous, free flowing and slopes towards the balancing tank. This directs the overflowed soiled water to flow into the balancing tanks to be drawn into the filter and treatment process. When it is necessary to empty the AF, water is also drawn from the drain at the deep end of the AF to speed up the disposal. A popular design, introduced in Singapore in 1970, it is proven to be able to remove surface pollutants rapidly. However the drawbacks of this system are:-  3-3 (a) Hydraulic studies indicated that the mixing confined to the path of circulation created by the nozzle direction. (b) There was difficulty encountered in mixing the large volume of water with chemicals uniformly. Surflo system was modified to overcome the drawbacks listed above and was renamed as Biflo system. 2.2 Side Surflo System Free flowing scum channel return to balancing tank Soiled water to Free flowing scum balancing tank channel return to balancing tank Filtered water from Flow from side surflo treatment plant inlet jets Flow from side surflo inlet jets Pool drain Filtered water from treatment plant Figure 3-3 Side Surflo System A variation of the surflo system is the side surflo system which has inlet nozzles located at the side of the AF improving chemical mixing. See Figure 3-3. 2.3 Biflo System Scum channel Balancing tank To filtration plant From filtration plant Drain system inlet To filtration plant Figure 3-4 Biflo System The Biflo System is an improvement over the Surflo System. This system draws 25 to 35% of the water through specially designed under drain system at the bottom of the AF. This arrangement was found to be more effective in uniform mixing of the chemicals with the AF water.  3-4 2.4 Ribbon Flow System From filtration plant To filtration plant Figure 3-5 Ribbon Flow System From the flow of the water, there are some shortcomings of this system:- (a) Inadequate mixing effectiveness of the water to achieve quality standard. (b) Not designed to remove surface pollutants. (c) Not suitable for long and deep AF. 2.5 Perimeter Flow System Surface water draw-off main From filtration plant To filtration plant Figure 3-6 Perimeter Flow System This system has the advantage of having more water inlets at the shallow end of the AF, where the accumulation of surface pollutants are more. However, the drawbacks are:- (a) The removal of surface pollutants is not effective. (b) It does not offer uniform mixing of the chemicals particularly the lower part of the AF. (c) It is not suitable for deep AF.  3-5 2.6 Skimmer System Skimmer Side wall return inlet Side wall return inlet Vacuum port Treatment unit Heater Multi-port valve Filter Skimmer Pump and motor Drain pipe Figure 3-7 Skimmer System Re-circulating Aquatic Facility Water is pumped continuously from the skimmer to the water filtration and treatment units and then returned to the AF via side-wall inlets. This system is mainly used in small (private or user) AF. The turn over period of every 6 hours is also applicable. Figure 3-7 shows the schematic of re-circulation and backwash. The usual filtration and treatment units for such type of aquatic facility are similar with that of big and public AF. Some drawbacks of Skimmer System includes:- (a) Return inlets cannot be located all over the AF. Therefore dead sections are created, consequently, creating also more maintenance work. (b) There is no provision for pumping requirements. This could cause the pump to run dry. (c) There is no provision for replenishment. Consequently, making up any water losses due to evaporation and operation will have to be done manually, maybe with a garden hose connected to a stand pipe. (d) Water level in the AF fluctuates with the number of bather. This could give rise to problems for the operation of the skimmer. 3 Overflow Channel (Scum Channel) of Aquatic Facility The purpose of the overflow channel, shown in Figure 3-8, is to carry away the soiled water to the balancing tank. Thus, it should be sized large enough to prevent flooding. It should be able to cater for at least 150%of the circulation rate. For the Level Deck System, the width of the overflow channel is taken as 225mm, the slope as 1:100, the starting point or the ‘peak’ as 150mm below the deck level.  3-6 Non-skid tiling, and grooved to provide finger grip for the 225m benefit of users Non-skid grating Overflow or Scum channel AF Flow towards balancing tank, and slope downwards at a gradient of 1:100 from the ‘Peak’ Figure 3-8 Details of Overflow Channel 4 Main Components and Equipment Used In Aquatic Facility 4.1 Balancing Tank Treated water pumped into the AF via the AF floor inlet nozzles will displace an equivalent amount of AF water. These displaced AF water overflows into a scum channel which slopes towards the balancing tank. There are strainers to remove hair and other debris before the displaced water is allowed to flow into the balancing tank. The functions of a balancing tank are:- (a) To ensure that requirements for pumping are met, especially preventing dry pumping by providing make-up water. (b) To provide make-up for any water loss. This could be achieved by float operated valve connected to a break cistern. Never connect directly to PUB mains, such way of connecting water supply for a aquatic facility could cause contamination. (c) To provide water for backwashing. Like all water storage tanks, there must be easy access and drain-off to facilitate inspection and maintenance. Water level sensor Vent pipe for pumped inflow Strainer Access cover From overflow Cat ladder channel Pumped inflow pipe Float operated inflow pipe From pool drain To circulation pump To drain or approved outfall. Figure 3-9 Typical Balancing Tank  3-7 4.2 Strainer Water from pool overflow channel Water from pool drain Straining: Water balancing: Pumping: Straining After straining, Recirculation pump protects pump by water is collected draws water from removing debris in a balancing balancing tank then Pool such as bugs, tank, which also delivers it to the hair, lint, leaves provides make- equipment stations. and stones. up water. pH balancing: Chlorination: Filtration: Strained, Acid or alkali is Chlorine (Cl2) is Filter removes filtered and added to adjust added to the water fine soil and chemically pH. pH is to provide a impurities not treated maintained at residual for previously water 7.2 to 7.8 to disinfection and destroyed by returns to insure chlorine oxidation. Chlorine chlorine pool reactions kills bacteria and reaction. needed for destroys impurities disinfection and which cause oxidation. turbidity, colour and odour. Figure 3-10 Overview of Re-circulation in a Aquatic Facility Lint basket Strainer coupled Outlet port of pump to or located Pool pump before a pump and motor Inlet port of pump Figure 3-11 Typical Strainer and Lint Basket Along the flow, water is strained by strainers and lint baskets to remove hair and other large debris such a leaves, before entering a filter. 4.3 Filtering Units (a) Sand filters Figure 3-12 shows a typical sand filter. Sand filters come in many sizes and it can be as large as the ones shown in figure 3-13.  3-8 Spreader for soiled Relief air tube water distribution Inlet Medium (Sand) region Outlet Socket for lateral Lateral Figure 3-12 A Typical Sand Filter Figure 3-13 Large Sand Filters (b) Diatomaceous Earth (DE) filter DE (diatomaceous Earth) filter is a very efficient type of AF filter. It can trap particles down to 3-5 microns; well below what the naked eye can see. Pressure gauge and Manifold relief valve assembly distributing fixed here soiled water to various elements Pressure gauge and relief valve assembly Filter element [or grid (fabric) Inlet Inlet or septum] Filter element carriage Outlet Figure 3-14 DE Filter  3-9 (c) Cartridge filter Cartridge filters are also used in AF, it traps particles 5 to 10 micron in size. They are used in small private AF and fountains, but not commonly used for large public AF. They may be used where a backwash line is not practical. Pleated cartridge filter element Inlet Outlet Figure 3-15 Cartridge Filter 4.4 Treatment Unit (a) Metering Pump and Chemical Tank Aquatic facility must be safe for bathers as well as the operators themselves, meaning that the water will have to be treated to achieve the following qualities:- (i) Correct amount of residual disinfectant and its by products. (ii) Correct water balance i.e. its pH value, total alkalinity, and hardness. (iii) Non-excessive undesirable residual chemicals i.e. sulphates, chlorides and cynaurates (if used). Chemical tank Metering pump Figure 3-16 Typical Metering Pump Figure 3-17 Typical Metering Pump and Chemical Tanks The treatment unit consists of dosing pumps (Metering pump) that feed the required dosage of chemicals for sanitizing the water.  3-10 Centrifugal pumps are used for pumping large amounts of water, of particular importance in water recirculation. Positive displacement pumps or more specifically, reciprocating diaphragm and peristaltic pumps are common ways to pump chemicals, often known as automatic chlorinators, chemical feeders, injectors, metering pumps; and the rotary peristaltic is often referred to as a tube, or squeeze tube pump. A good treatment unit not only disinfects, it should also feed the right dosage to maintain total alkalinity of the water. A control unit, together with an analyzer enables dosing to be done automatically. Handling liquefied chlorine is hazardous. A safer approach is using solutions of sodium hypochlorite or granular calcium hypochlorite for chlorinating the water. They are fed in regular dosages using the metering pumps. (b) Analyser A complete set of treatment unit would include an analyzer to monitor the chlorine and pH levels of the AF water, so that the metering pumps could feed the correct dosage of chlorine and pH adjuster. Some system provides direct readings of Free Chlorine in water at concentrations ranging from 0.1 to 10 ppm (parts per million) or mg/l (milligrams per litter). These are true readings of Free Chlorine. In addition some sensor is not affected by cyanuric acid (CYA) stabilizer and/or oxidizers, thereby assuring constant Free Chlorine levels at all times..  3-11 Figure 3-18 Typical Analyser  3-12 Figure 3-19 Example of an Analyser with Pump (c) Air-compressor and Air Blower When air and water backwashing method is employed, air compressor or an air blower is used to provide the required air for scouring the sand filter. Most filter manufacturer will specify the quantity of air required to effectively air scour the filter beds. Commonly used air scouring rate is 460 l/min/m2 of filter air. (d) Separation Tank and Holding Tank The function of a separation tank is to separate the dirt and flocculent in the waste water before it is discharged into the sewerage. If separation tank is installed, it should be cleaned after each filter cleaning. The separation tank is simply a cylindrical container that holds a bag that traps dirt and flocculent in the backwash water. It may be incorporated into the holding tank. The holding tank (an NEA requirement), which is actually a large concrete tank, intercepts and holds any waste or sullage water before discharging into the Authority’s sewer. Filter Inlet bag Outlet Figure 3-20 Typical Separation Tank  3-13 Figure 3-21 DE Separation Tank Designed to work with vertical grid diatomaceous earth (DE) filters, with 80 square feet of filtration area, the DE Separation tank is ideal for water conservation and savings during backwashing by returning chemically treated backwash water to the AF.   4-1 CHAPTER 4 THE SYSTEMATIC OPERATION AND FLOW OF A TYPICAL FILTRATION PROCESS 1 Types of Filtration Unit There are three common types of filter for use in AF, namely:- (a) Sand filters. (b) Diatomaceous Earth (DE) filters. (c) Cartridge filters. Air relief tube 1.1 Sand Filters Spreader (diffuser) Flow of soiled AF water Soiled AF Freeboard water in (Approx. 50%) Flow of soiled AF water percolating Medium (sand) the filter medium region (Approx. 50%) Filtered water Flow of filtered returning to water returning to the AF the AF Lateral Figure 4-1Filtration of AF Water in a Sand Filter Spreader Inlet Silica sand Lateral Gravel support Front Side Figure 4-2 Sand Filter Media Figure 4-1 and 4-2 show typically the workings of a sand filter during filtration mode.  4-2 All sand filters have the same mode of operation. When in the filtration mode, water flows from top to bottom. Soiled water from the AF flows in via the filter's inlet pipe, which leads to the water distribution head (Spreader) inside the tank. As water percolates through the sand by gravity plus pressure built-up in filter, the sharp edges of the sand trap the dirt from the AF water. All filters have some sort of lateral or under- drain with slots to hold back sand while allowing clean, filtered water to pass through. The silica sand (Commonly called AF grade sand) in the filter could be uniform in size of approximately 0.35 to 0.6 mm in diameter, or graded in different sizes for large capacity sand filters. The filters operate on the basis of "depth" filtration; dirt is driven through the sand bed and trapped in the minute spaces between the particles of sand. Initially, a clean sand bed will remove larger particles, and then, as the bed starts to load up with dirt, it will remove finer particles. Examples of other filter medium are anthracite coal and garnet. The two main types of sand filter are:- (a) Rapid sand filter, pressurised, having filtration rate of 80 to 120 liters/min/m2. (b) High rate sand filter, pressurised, having filtration rate of 400 to 600 liters/min/m2. AFs can install more than one unit and up to any number of units of the sand filter to meet required filtration rate. Valves and pressure gauges are used to operate the filtration and backwash modes. 1.2 DE Filters Flow of soiled AF water Flow of filtered water returning to the AF Filtered water returning to the AF Soiled AF water in Figure 4-3 Filtration of AF Water in a DE Filter  4-3 Figure 4-3 shows typically the workings of a DE filter during filtration mode. Soiled AF water flows into the cylinder, then into the filter elements (Also known as grids or septums), and then outwards via the manifold. DE filters, which operate under pressure, come in standard units of various filter media area with a filtration rate of 1 to 2 GPM/ft2. Shaped in the form of cylindrical tanks, it is easy to remove and maintain filter elements that must be pre-coated on the outer surface with DE in order to work. Do not operate the pump without having the DE coating the elements. Doing so will cause the pressure to rise very quickly and if left in this manner the pressure may tear the elements. Besides regular backwash, the filter elements must be taken out of the container and cleaned at least once a year. Chemicals and brushing may be required to remove scale, rust, suntan oils, cosmetics and other deposits that are clogging the filter element fabric. AFs can install more than one unit and up to any number of units of the DE filter with valves to control the AF’s filtration and backwash modes plus other requirements. 1.3 Cartridge Filter Flow of soiled AF water Flow of filtered water returning to the AF Soiled AF water in Filtered water returning to the AF  4-4 Figure 4-4 Filtration of AF Water in a Cartridge Filter Figure 4-4 shows typically the workings of a cartridge filter during filtration mode. Soiled AF water flows into the filter unit and then forced through the pleated elements of the filter from ‘out’ to ‘in’ and returned to the AF. Cartridge filters can come in cylindrical shape and in various sizes. Some cartridge filters come in more than one element. They all work in the same way with a filtration rate of 0.5 to 1 GPM/ft2. Most cartridges are discarded when they are clogged, though they can be removed and backwashed with a hose. 2 Backwash Holding Tank Access cover Floor Overflow pipe Backwash Outlet water in directing Baffling backwash water to sewerage Settled sludge Overflow and de-sludging Submersible pump for overflowed pipe water and desludging Sump Figure 4-5 Concrete Holding Tank A backwash water holding tank is for holding filter backwash water before it is discharged into the sewer. Its capacity must be able to contain the volume of at least one backwash. The function of a backwash water holding tank is to settle suspended solid in the backwash water. The tank is dewatered after settling and prior to subsequent backwashes.  4-5 Settled sludge is periodically removed to prevent flushing of the solids into the sewerage during subsequent backwashing. For a very small user AF, a separation tank can be used, instead of a holding tank. Similarly, the sludge in the filter bag must be removed periodically manually, not discharged into the sewerage. 3 Basic Constructional Requirements for an AF 3.1 Soundness Of The Structure Most commonly used material is reinforced concrete which is structurally strong and flexible in material handling on site. The AF must be structurally sound, being:- (a) Able to withstand load, consisting of pressure from the ground and ground water when the AF is empty. (b) Able to withstand load, consisting of water pressure on the inside when the AF is full. (c) Able to withstand settlement of the AF shell due to ground movement, which may result in cracking of the floor or walls or both. (d) Able to withstand thermal and/or drying shrinkage stresses in the concrete. Otherwise, walls would crack when the stresses exceed the tensile strength of the concrete. (e) Not porous, e.g. honeycombing in concrete. For smaller AFs, other materials used include:- (a) Aluminium sheet lining. (b) Lightweight glass reinforced concrete sprayed on steel skeleton. (c) Premoulded glass reinforced fibre. 3.2 Waterproofing Of The Structure The AF must be watertight against loss of water when it is full and if constructed below ground level, against infiltration of water from the subsoil when it is empty.  4-6 3.3 Finishing Of The Structure The AF must be finished in attractive, smooth and impermeable surface finishing. In addition, materials used must also be:- (a) Slip resistant. (b) Non toxic to human and environment. (c) Easily cleaned and maintained. (d) Able to withstand design stresses. (e) Colours, patterns or finishes of the AF interior shall not obscure the existence or presence of objects, steps or surfaces within the AF. (f) Such that all the material surfaces must not be a cutting, pinching, puncturing or abrasion hazard under casual contact and intended use by bathers. Min 5.0m of unobstructed Diving board entirely headroom of non-slip material Deck Max 1.0m of for 2.5m (min) depth of water, increased by a max of 1.0m AF for every 0.3m increase in depth beyond 2.5m Figure 4-6 Elevation of Section of AF Min 3.0m between side wall and diving board Deck AF Min 3.0m between adjacent and between two diving boards Figure 4-7 Plan of Section of AF  4-7 3.4 Provision Of Diving Board Diving board should only be provided when the minimum depth of the water and the dimensions of the area comply with recommendations and regulations, some of them as shown in Figure 4-6 and 3-7. 3.5 Provision Of Walkway A walkway of adequate width and with a sloped, non-skid paved deck should be provided around the AF as shown in Figure 4-8. Another point to note is that inspection chambers are not allowed to be located within this non-skid paved deck. Non-skid paved deck surrounding AF 1:40 gradient Overflow or Scum channel AF Flow towards balancing tank Figure 4-8 Details of Non-skid Paved Deck Around AF 3.6 Provision Of Safety Step At least one ladder or steps must be provided for every 30.0m of the AF perimeter. The ladder or steps must have a minimum width of 350mm with handrails where feasible. Ladder or steps 350mm min with handrails 30.0m max 30.0m max Figure 4-9 Distance Between Ladders/Steps Around The AF  4-8 3.7 Provision Of Safety Step On Wall For the benefit of children using the deep section of the AF, a 100mm width safety step, see Figure 4-10, should be built along the entire wall at 900mm below AF surface. Safety step Figure 4-10 Safety Step On Wall Around The AF 3.8 Recommended Minimum Size Of AF AF can be rectangular or free form in shape. Its shape and size will depend on the use. For swimming use, a rectangular shape is preferred and its minimum size would be 5.0m long, 2.5m wide and 1.0m deep. 3.9 Recommended Loading For AF One recommendation on AF loading for pubic AF is a minimum of 2m2 of AF surface area per person in the AF. For comfort, an allowance should be made of about 3.5m2 of AF surface area per swimmer. Of course, it is difficult to control the number of people entering an AF. At peak periods, very little if any swimming can be accomplished. For proper swimming, a lane of at least 2.0m wide is required. 3.10 Provision Of Shower And Footbath The right way to use an AF is to shower oneself before entering the AF. This way, the filtration and treatment unit would not be ‘overloaded’. Pre-cleansing facilities includes shower and footbath, and their waste water is directed to the premise’s sanitary drainage system. 3.11Provision Of Changing And Sanitary Facilities Changing and sanitary facilities must be provided for in an AF. Plumbing and sanitary systems for these facilities will be, like all domestic system, in accordance with the Code of Practice on Environmental Health.  4-9 The changing facilities can be arranged in many ways. One preferred layout is that the bathers returning to the cubicles from the AF enter them (Changing facilities) by the same route as they left them; then they change into their street clothes and leave the cubicle by the door through which they entered originally. This arrangement would minimize polluting the AF environment. 4 Terminologies 4.1 Turnover Rate Turnover rate is defined as the number of hours of plant operation to treat the entire contents of the AF, i.e. the time taken to move the AF’s water through the circulation system once. The objective is to move the water from all parts of the AF and to return properly treated water, evenly distributed throughout the AF. The Code of Practice on Environment Health stipulates the turnover rates that is required to be provided by the circulation pumps. Example: What is the circulation rate for an Olympic size AF that has a volume of 1680m3 of water and requires a turnover rate of 6 hours? Solution: Circulation rate = Volume of AF Water / Turnover Rate = 1680m3 / 6 hours = 280 m3 / hour 4.2 Pressure Head ‘H’ = Height of water raised Discharge Inlet or eye Figure 4-11 The Pump Head  4-10 Pressure head or pump head (Symbol: H) represents the net work done on a unit weight of liquid in passing from the inlet or eye to the discharge at the pump exit. It is measured in metres of liquid pumped (i.e. able to raise). 4.3 Positive Suction Head Water level of source Positive suction head Figure 4-12 Positive Suction Head Positive suction head is the height of the water level of the water source above the suction port (inlet or eye) of the pump. 4.4 Negative Suction Head Negative suction Water level head of source Figure 4-13 Negative Suction Head Negative suction head is the height of the water level of the water source below the suction port (Inlet or eye) of the pump. 4.5 Rate Of Evaporation Evaporation is the changing of water from a liquid state to a gas. It is usually used to indicate a change of state below the boiling point of water. The evaporation rate can be measured by noting the change in the depth of water in a glass, a pail, a puddle or an AF over a given time period (Usually a day). Placing a ruler in any of these gives a scale that one can use to read the drop in the surface elevation in a day or more. Normal rate of evaporation is 3 to 5mm per week. However, in an AF, the rate depends on the outdoor temperature and humidity.   5-1 CHAPTER 5 MAINTENANCE AND TROUBLESHOOTING PROCEDURES FOR THE CIRCULATION PUMPS 1 Operation of Circulation Pump 1.1 Parts of A Centrifugal Pump Impeller Rotation direction Impeller eye Impeller vane Top casing Bottom casing Discharge port Inlet port leading to the impeller eye Figure 5-1 Centrifugal Pump Top casing Air-cock Impeller Suction port Bottom casing Discharge port Figure 5-2 Split Case Centrifugal Pump with Air-Cock Air cock is usually located 600 mm min. here, on the discharge pipe, Pump near the pump, discharging (Recommended discharge pipe height) upwards for air release purpose. Figure 5-3 Other Location Of Air-Cock  5-2 Gland packing Packing material Gland nut Gland box Figure 5-4 Gland Section Of Pumps Impeller Impeller vane Bearing Impeller key Shaft Bearing housing Gland section using mechanical seal Mechanical seal Figure 5-5 Parts Of A Split Case Centrifugal Pump 1.2 Operation of the Re-circulation Pump Discharge Coupling Figure 5-6 End Suction Centrifugal Pump A pump circulates liquids through piping systems. It provides the pressure necessary to overcome the resistance to liquid flow in a piping system. The common type of pumps used for circulation is the centrifugal pump.  5-3 The centrifugal pump employs one or more impellers with fixed blades housed in a suitably shaped casing. The impeller(s) are mounted on a rotating shaft while the casing is fixed. The centrifugal pump increases the pressure of a liquid by first increasing its velocity, and then converting the velocity energy to pressure energy. As the impeller rotates, the liquid in the impeller will be thrown outwards towards its periphery by centrifugal force. This movement of liquid from the centre of the impeller (Eye of the impeller) to the periphery causes a low pressure at the eye of the impeller which will result in new liquid from the suction line to be drawn in. The liquid leaving the periphery of the impeller has to be contained to increase its pressure. The casing cum volute contains and guides the liquid toward the discharge opening. The action of the impeller increases the velocity of the liquid, but not its pressure. To increase the pressure available at the pump discharge, the velocity energy is converted into pressure energy by decreasing its velocity. This is accomplished by increasing the flow area of the volute section of the pump casing. The volute which converts velocity energy into pressure energy, is designed as a progressively expanding collection chamber that receives the liquid from the impeller and serves as the passage way to the discharge pipe. 1.3 Performance Characteristics of Re-circulation Pump The pump performance characteristics can be expressed by using five parameters:- (a) Capacity, Q. (b) Pressure head, H. (c) Hydraulic or liquid or water power, WP. (d) Brake power, BP. (e) Pump efficiency, µ. These parameters are influenced by the pump speed, N and the impeller diameter, D. 1.4 Function of the Re-circulation Pump The re-circulation pumps should have the ability to ensure a turnover rate of not more than 6 hours. Meters should be installed on all re-circulation systems and shall be capable of measuring flows of 1.5 times the designed flow rate. There should be at least 1 standby pump unit to supplement the duty pump(s) provided in the filtration system.  5-4 2 Common Faults and Remedies of Circulation Pump 2.1 Common Faults The most common faults are leaks, noise and vibration. Sensory detection methods are very accurate in detecting these faults, namely, visual for leaks; hearing for noise; touch for vibration and touch together with smell could be employed to detect excessively hot equipment. 2.2 Other Common Faults Common Fault Causes Remedies 1 Motor not running Motor thermal protector tripped Allow motor to cool. Restart the pump, then call a qualified electrician. Open circuit breaker or blown Determine the cause, then fuse call a qualified electrician. Pump impeller binding or Check all rotating parts, and jammed correct as required. 2 Pump will not turn Air lock in the pump Shut off pump for off approximately one minute, then restart. Repeat until air lock clears, operating the air- cock as well. Influent flow is matching pump’s Larger pump may be discharge capacity required. a small tap 3 Little or no liquid Check valve installed Check flow arrow on valve, or valve for delivered by pump backwards, plugged or stuck in and check valve operation as controlling closed position well. the Pipe may Excessive system head Call the system installer. entrance or escape of burst! Plugged or blocked pump inlet Inspect and clear as required. air from a Low voltage, phase loss or Check voltage, then call a pipe caused by a pump wired incorrectly qualified electrician. blown fuse, Incorrect rotation Check rotation, then call a thermal qualified electrician to overload, broken interchange the polarity, and wire, worn any two phases for a 3 phase contact or motor. mechanical failure Air lock in the pump Shut off pump for approximately one minute, then restart. Repeat until air lock clears, operating the air- cock as well. Worn or damaged Impeller Inspect impeller, replace as required.  5-5 Common Fault Causes Remedies Defective or improperly Inspect, re-adjust or replace positioned liquid level controls water level sensor and controller as required. 4 Pump cycles Inoperative discharge check Inspect, repair or replace as constantly valve required. Defective or improperly Inspect, re-adjust or replace positioned liquid level controls water level sensor and controller as required. Excessive influent for this size Call the system installer. of pump 5 Power Binding rotating parts Check all rotating parts, and consumption too correct as required. high Incorrect impeller diameter Check and replace correct diameter. Head too low causing Call the system installer. excessive flow rate Mis-aligned pump and motor Check alignment between the motor and pump, realign as required. 6 Excessive noise Binding rotating parts Check all rotating parts, and and vibration correct as required. Defective motor Call the system installer to replace the motor. Incorrect rotation Check rotation, then call a qualified electrician to interchange the polarity, and any two phases for a 3 phase motor. Cavitation Ensure foot valve strainer is not blocked. Suction lift too high or suction Check with vacuum gauge, losses excessive then call system installer. Worn or plugged Impeller Inspect impeller, replace or correct as required. Head too low, causing Call the system installer. excessive flow rate Worn bearings Replace the bearings. Loose pump or piping Secure the pump or piping, replace the fasteners, supports and dampers if necessary. Mis-aligned pump and motor Check alignment between the motor and pump, re-align as required.  5-6 2.3 Checking Mis-alignment A simple method would be using straight edge and a set of feeler gauge to check and set alignment. Coupling Shaft (motor) Shaft (pump) Feeler gauge Figure 5-7 Angular Mis-Alignment Straight edge Figure 5-8 Parallel Mis-Alignment Figure 5-9 Correct alignment A dial indicator can be used to attain more accurate alignment. The dial readings will indicate whether the driver has to be raised, lowered or moved to either side. Accurate alignment of shaft centers can be obtained with his method even where faces or outside diameters of the coupling are not square or concentric with the bores. After each adjustment, re-check both parallel and angular alignments.  5-7 Dial indicator Dial indicator reading Reference mark Spacer to take up bearing slack Figure 5-10 Using Dial Indicator To Check Parallel (Left) And Angular (Right) Alignment 2.4 Cavitation in Centrifugal Pumps If a liquid falls below the vapour pressure at the temperature concerned, the liquid boils and vapour bubbles form. These bubbles are carried along by the flow, and on reaching the eye of the pump where the pressure is higher they suddenly collapse as the vapour condenses to liquid again. This phenomenon is called cavitation. A cavity results and the surrounding liquid rushes in to fill it. The liquid moving from all directions collides at the centre of the cavity giving rise to very high local pressures of up to 1 GN/m. This process is called an implosion. Any solid surface in the vicinity is also subjected to these intense pressures, because even if the cavities are not actually at the solid surface, the pressures are propagated from the cavities by pressure waves. This alternate formation and collapse of vapour bubbles may be repeated with a frequency of many thousand times a second. The intense pressures, even though acting for only a very brief time over a tiny area, can cause severe damage to the surface. The two serious undesirable effects of cavitation are:- (a) Besides being destructive, cavitation also disturbs the flow reducing pump efficiency. (b) A dangerous erosion or pitting of the metal parts. This is accompanied by considerable vibration and noise.   1-1 CHAPTER 6 CHEMICAL FOR THE DOSING PROCESS AND METHODS TO ACHIEVE DESIRED WATER QUALITY 1 Main Chemicals Used In A Re-circulating AF System Chemical Usage pH Chlorine gas Disinfectant Acidic Calcium hypochlorite Disinfectant Alkaline Sodium hypochlorite (bleach) Disinfectant Alkaline Lithium Hypochlorite Disinfectant Alkaline Sodium di-chloro isocyanurate (Dichlor) Disinfectant Acidic Sodium trichloro-iso-cyanurate (Trichlor) Disinfectant Acidic Cyanuric acid Stabiliser Acidic Sodium bi-sulphate (dry acid) pH adjuster Acidic Hydrochloric acid (Muriatic acid) pH adjuster Acidic Carbon dioxide (CO2) pH adjuster Acidic Sodium carbonate (Soda ash) pH adjuster Alkaline Sodium bi-carbonate pH adjuster Alkaline Aluminium sulphate (Alum) Flocculate Acidic Copper sulphate Algaecide NA (inorganic salt) 2 Disinfectant 2.1 Chlorine Gas If cost were the only consideration, gas chlorine (Liquefied chlorine gas, chemical formula Cl2) would be the hands-down winner. However, most people or even service technicians would rather not be anywhere near gas chlorine, whether it is cheap or not. There must be factors other than cost to consider in making buying decision: (a) Desired water quality. (b) Understanding the product. (c) How the product fits with the water-treatment program. (d) Ease of use. (e) Safety. (f) Availability. (g) Storage and handling. (h) Previous experience. (i) Authority’s approval.  1-2 Gas chlorine is the purest form of chlorine one can buy. There are no fillers or carriers. So all the chlorine added to the AF water is used for disinfecting, sanitizing and oxidizing. Gas chlorine is the least expensive type of chlorine to buy. But it is the most dangerous to use and store. It is subjected to the largest amount of government regulation. Using chlorine gas for AF disinfecting is not permitted in Singapore as it is a ‘Green House’ gas. However, chlorine can also be obtained from various chemical compounds, notably from hypochlorites. 2.2 Hypochlorites Due to their low stability, hypochlorites are very strong oxidizing agents. They react with many organic and inorganic compounds. Reaction with organic compounds is very exothermic and may cause ignition. So, hypochlorites should be handled with care. They can oxidize manganese compounds, converting them to permanganates. Hypochlorites decompose in sunlight, giving off chlorides and oxygen. The various types are: (a) Calcium Hypochlorite Powder Chlorine or 65% available chlorine, sold under many labels and also in tablet form, it reacts instantly on contact with the water to form Hypochlorous Acid. Calcium Hypochlorite has a high pH and will therefore raise the pH of the water into which it is added. It will also increase the calcium hardness level of the water over a period of time. (b) Sodium Hypochlorite Liquid chlorine and is a very common form of chlorine addition for AF. It normally has a strength of 12.5% available chlorine, the rest being a carrier. It will instantly react with the water to form Hypochlorous Acid. Sodium Hypochlorite has a high pH and will increase the pH of the water in to which it is added. (c) Lithium Hypochlorite It is a white granular substance with a chlorine-like odour. It can provide 35 percent available chlorine. It is calcium free, dust free and non-flammable. It has a long shelf life (It will lose only 0.1 % of its available chlorine level per month), and because it contains no calcium, it dissolves rapidly without clouding. Among all the chlorine-lithium-hypo, it is the most expensive to use. When broadcast over the surface of the AF it will dissolve before reaching the bottom, very appropriate for regular and super-chlorination. The pH of lithium hypochlorite is 10.7, so it causes an alkaline condition to occur in the AF. 3 Stabiliser and Disinfectant 3.1 Cyanuric Acid (Stabiliser) A weak acid, also known as CYA, which can be added directly to the AF water or in conjunction with some chlorines to act as a barrier to the effect that sunlight has on breaking down the chlorine in the AF water. Without cyanuric acid, 95 percent of the chlorine in the AF could be destroyed in just two hours.  1-3 The Cyanuric Acid will lower the pH level slightly and it will also reduce the speed at which chlorine can react to kill bacteria, virus and algae spore. It is therefore normal to operate with a higher chlorine level when using Cyanuric Acid in an AF. A Cyanuric Acid (Or Stabiliser) level of 30 to 50ppm or mg/l is normal for most AF. 3.2 Sodium Di-chloroisocyanurate (Stabilised Disinfectant) Also known as dichlor is a complex powder chlorine compound. Dichlor is produced by adding soda ash and cyanuric acid to a solution of trichlor. When dried the result is a granule that may provide 56 percent or 62 percent available chlorine, depending on the method of manufacture. The 56-percent formulation is by far the most readily available of the two. Containing cyanuric acid, dichlor is a stabilised chlorine donor and is incompatible with and should not be confused with any other chlorine donor in granular form. Di-chlor lowers the pH of the AF water. 3.3 Sodium Tri-chloroisocyanurate (Stabilised disinfectant) Also known as trichlor, is a member of the stabilised isocyanurate chlorine family. It provides chlorine to disinfect the AF and spa and, at the same time, provide cyanuric acid stabiliser to shield chlorine from decomposition by the ultraviolet rays of the sun. Trichlor is produced as a tablet or stick and has a pH of 2.8 to 3.0. Trichlor has an available chlorine content of 89 to 90%. Tablets or sticks may be placed in "Chlorinators" installed on the return lines of the AF or spa plumbing downstream of the filter and heater. Trichlor does not dissolve quickly and is designed to be slow dissolving for use specifically in chlorinators. Do not place tablets or sticks directly on the AF surface because if done it will damage or bleach the AF surface and can cause damage to the AF or spa pumping equipment. There is no way to regulate the feed of chlorine into the water using this method. Because of the naturally low pH of trichlor it is very important to maintain the pH and total alkalinity levels of the water or damage to the AF or spa will occur. 4 pH Adjuster When chlorine is added to AF water, it produces two types of free chlorine, one fast acting and effective (Hypochlorus acid) and another which is slow acting and ineffective (Hypochlorite ion). These two chlorine variations are produced in a ratio determined by the level of pH. As the pH rises in value, less of the effective free chlorine is produced and at a pH of 8.0 only 20% of the free chlorine produced is effective. 4.1 Sodium Bi-sulphate Known also as dry acid, it is a dry white crystal that produces an acid when added to water. It is used for lowering the pH and total alkalinity of the AF water. It is safer to handle than hydrochloric acid (Muriatic acid).  1-4 4.2 Hydrochloric Acid Hydrochloric acid or Muriatic acid by its historical but still occasionally used name, is the aqueous (Water-based) solution of hydrogen chloride (HCl) gas. It is a strong acid. It is used for lowering the pH of AF water and should only be handled with appropriate safety precautions because it is a highly corrosive liquid. 4.3 Carbon Dioxide Carbon Dioxide (CO2) is a non-flammable gas. When mixed in water, it forms a mild acid (Carbonic Acid), which is strong enough to lower AF water pH without damaging the equipment. Carbon Dioxide (CO2) would eliminate the hazards and the hassles of handling acid- based products. Hydrochloric acid is dangerously corrosive; handling this chemical is very dangerous to the untrained. Dry acid (Sodium Bisulfate) is unfriendly to heating systems, in that this chemical precipitates in hot water, causing a corrosive form of scale. 4.4 Sodium carbonate Also known as soda ash, it is a chemical, a base that is used to raise the pH of acidic (Below pH 7.0) water. 4.5 Sodium bi-carbonate (Soda ash) Also called baking soda or bi-carbo it is a base that is used to raise Total Alkalinity in AF water with only a slight effect on the pH. Sodium bicarbonate can only raise the pH of the water to 8.5, regardless of the amount used. Care should be taken, however, to avoid adding large quantities at one time. 5 Flocculant 5.1 Alum (Aluminum Sulphate) Adding alum to AF water causes small particles and colloids to stick together to form heavier particles (floc) which could be easier filtered or sink to the AF bottom to be vacuumed clean. This process is called coagulation or flocculation. Alum is added only after backwashing. The amount to use to obtain efficient filtering will depend on the design of the filters and experience. As a general guide, 2 to 4 ozs of alum per square feet of filter area should be added. It should be added as a solution, 10% or less over a period of 1 to 2 hours by drip feed to the inlet side of the filters, preferably at the strainer boxes. If the alum is added too quickly, the pH of the water may be depressed below 5.5 at which level it will not form a floc but will pass through the filters. However, when this water mixes with the AF water, the pH will rise causing the alum to floc in the AF, hence causing cloudiness. Do not put the alum tablets in the circulation pump strainer basket because the water inside the flow is too fast. The filter is kept running full time. The alum dissolves and forms a coating on top of the filter sand. Then, as the little particles come by, it grabs them and keeps them. In doing so it blocks up the top of the filter and can increase the filter pressure. If the pressure gets too high, the coating breaks up and gets washed  1-5 through the filter and back into the AF taking all the little bits with it. Then it will be back to square one. So, always thoroughly backwash the filter before putting the alum in and keep an eye on the pressure while it is in there. If it gets too high, after backwash add more tablets. In any case backwash after 48hrs of filtration and if the AF isn't clear enough, do it again. It may take three or four goes before water could get perfectly clear. 5.2 Clarifier Clear water is free of particulate matter. When particles of dust and other matter become suspended in clear water, the AF takes on a cloudy appearance. The degree of cloudiness is determined by the amount of suspended matter. Ineffective filtration systems, high bather loads and the AF water supply are common factors that lead to cloudy AF. Small, microscopic particles that cannot be seen simply pass through the AF filter systems. Clarifier is a class of polymer based products that act on suspended, insoluble particles and organic debris to coagulate or clump them together, for easier and more efficient filtration. Some particles, especially dead algae, might otherwise pass right through some filters. There are many commercially produced clarifiers which are simply dropped into pump baskets. They dissolve within a 24 hours pump run time and boast of benefits such as being: (a) Non-toxic and bio-degradable. (b) Able to remove stain-causing metals and undissolved particles (c) Neutral and does not effect water chemistry If there are no successes with a clarifier, check the total dissolved solids (TDS) level, probably it is at a higher than normal level. If the TDS reading is 1500 parts greater than tap water, dilute the AF with fresh water. The difference between a clarifier and a flocculent is that a clarifier is designed to be used with a filter system, so particles coagulate in the filter. A flocculent is NOT to be used with the filtration system as the filter may clog. A flocculent is formulated to drop particles to the bottom of the AF, so they can be vacuumed away. Take note that most AF clarifier chemicals cannot be used in an AF with a D.E. (diatomaceous earth) filter. 6 Algae control Algae find their way into the AF by rain or wind and grow in colonies, resulting in algae blooms. Algae do not cause disease, but provide an ideal substrate for bacteria to thrive in. Algaecides can help to kill airborne spores blown into the AF. Algaecides are often formulated for a specific type of algae (Green algae, mustard algae, black algae) with black algae being the hardest to treat. Copper based algaecide is a chemical compound that contains the element copper. Copper Sulphate was one of the original copper algaecides. Too much copper in the water can cause green-coloured stains. Maximum level is about 0.2 ppm. Newer copper algaecides contain an ingredient that prevents the copper from staining but does not affect copper's ability to kill algae. These special copper algaecides are called chelated copper algaecides.  1-6 Once algae has grown in your AF, the best way to treat it is to shock the AF. Algaecide is only a preventative measure, and might do nothing to treat an existing problem. Copper is also used for various parts of equipment and plumbing in an AF. Corrosive water caused by misuse of chemicals, improper water balance, or placing trichlor tablets in the strainer box can cause copper to be dissolved from the equipment or plumbing and deposit the precipitates on hair, finger- nails or AF walls, not forgetting that high levels of copper also cause green water. Copper algaecides will not produce foam in an AF. Foaming can be a problem when using ‘quat’ algaecides although they are effective against many forms of algae. The ‘quat’ or ‘polyquat’ algaecides are quaternary ammonium compounds, which treat and prevent algae growth in a different way. These algaecides are safer to use than a copper based algaecide because they will not stain an AF. Although quats cannot cause staining, these algaecides may cause foaming if not used properly. Polyquat AF algaecides that cannot cause staining or foaming are typically more expensive than the other forms of algaecides. Creating conditions unsuitable for algae: (a) Keep the AF cover on - obviously not always practical (b) Do not have too many windows for an indoor AF (c) Keep the sanitiser level up at all times. Regular testing and maintenance of the chlorine level is essential (d) Do not use potassium salt in the water treatment process as it is a nutrient for algae. Not many AF use chemicals for algae control. If used, commonly, copper sulphate is chosen. But copper deposits on hair. Algae growth is common when the AF has poor circulation and when the disinfectant level or algaecide content in the water is low or neglected. Proper filtration and regular use of algaecide will keep the AF free of algae. Maintaining proper sanitiser levels, shock treatments and super-chlorination will help to prevent or destroy algae. Wire brushing and washing is still the best for algae control. 7 Treating Liquid Impurities Chloramines and other liquid impurities can be treated using the following methods: (a) Super chlorination. (b) Dilution. (c) Combination of super chlorination and dilution.  1-7 7.1 Super-chlorination Super-chlorination is the addition of an extra dose of chlorine to bring the free available chlorine level to 5ppm. This will restore its ability to control algae, bacteria and to destroy ammonia, nitrogen, chloramines and other contaminants. Some algae spores can become immune to small regular doses. Super chlorination is recommended weekly when: (a) Temperature is over 32oC (90oF) most of the time (b) AF has high bather load (c) Long periods of rain or high winds carrying debris and dirt (d) Anytime, chloramines concentration exceeds 0.4 mg/litre During super-chlorinating: (a) Stop the public from using the AF and do not resume swimming until chlorine residual drops below 3.0 ppm. A good way would be to allow the sun to dissipate the excess chlorine. (b) Stop introducing cyanuric acid and sodium bi-carbonate. (c) Increase the recirculation rate by operating all the pumps. Super chlorination is not a preferred choice for most AF operators because of the: (a) High concentration of chlorine required. (b) The need to close the AF for three days or more, causing inconvenience to users. (c) The need to ensure water is back to normal of 1.0 to 3.0ppm. 7.2 Dilution Users are not allowed to use the AF during the process. To dilute the chloramines and contaminants, these steps are taken: (a) Backwash all the filters, drawing water from the balancing tank to do so. (b) Discharge all the backwash water into the holding tank. (c) Replenish the depleted water in the balancing tank with fresh water from PUB supply. This method has the following advantages: (a) Minimum interruption to the public. (b) Water quality will improve. (c) Filters are cleaned concurrently. (d) No need to use high concentration of chlorine. However, this method also has its disadvantages, namely: (a) No sterilization of pump piping and tanks. (b) Wasting of water, resulting in high PUB bill. 7.3 Combination of Super Chlorination and Dilution Users are not allowed to use the AF during the process. To use combination of chlorination and dilution method to dilute the chloramines and contaminants, follow the following steps which would take one day to complete:  1-8 Valve ‘A’ Water level sensor Strainer for pumped inflow From Balancing tank overflow channel From AF drain To circulation pump To drain or approved outfall. Figure 6 -1 Balancing Tank (a) Backwash all the filters, drawing water from the balancing tank to do so. (b) Discharge all the backwash water to the holding tank and do not replenish the depleted water in the balancing tank. (c) Open the valve (Valve A in Figure 6 -1) from the AF to the balancing tank. (d) Increase chlorine concentration of AF water, i.e. perform super chlorination but do not add cyanuric acid. (e) Increase the re-circulation rate by running all the pumps and keep the recirculation for 6 to eight hours. (f) After super chlorination, water will have high chlorine concentration. (g) At this point, replenish the balancing tank with PUB water to dilute the chlorine concentration to normal level, safe for bathers to use. This is the preferred method for most AF operators as it offers the following advantages: Minimum interruption to the public. Water quality will improve. Pumps, pipes and tanks are sterilized at the same time. Safe chlorine level in the AF water could be restored quickly. 8 Other Methods of Disinfecting AF Water 8.1 Ozone Ozone generator Ozone supply check valve Return Filter to AF Flow from Adjustable injector AF manifold Recirculation pump Figure 6-2 Ozone (O3) System  1-9 Ozone (O3) can be considered as the most powerful oxidizing and disinfecting agent that is available for AF and spa water treatment. However, it is unsuitable for use as a residual disinfectant. This is because it readily vapourises, leading to discomfort. Therefore, Ozone is most frequently used as a treatment step followed by de-ozonation and addition of a residual disinfectant, such as chlorine or bromine. The use of an ozonation system that is properly sized and integrated into the AF treatment system will allow ozone to act as the primary oxidizer and disinfectant. Ozone: (a) Destroys bacteria, viruses, mold, and mildew. (b) Eliminates spores, cysts, yeast, and fungus. (c) Oxidizes iron, sulphur, manganese and hydrogen sulphate. (d) Eliminates oils and other contaminants in water. (e) Oxidizes chloramines into chloride and nitrate (f) Keeps water clean and sparkling clear. (g) Keeps water fresh. Excess ozone must be destroyed using an activated carbon filter to form oxygen and carbon dioxide. Residual disinfectants would also be removed by the activated carbon filter and are, therefore, added after this. Excess ozone is toxic. It is heavier than air that could settle and be breathed in by AF or spa users and staff. It has been recommended that the ozone level in AF water should not exceed 0.05 mg/litre (DIN). 8.2 Ultraviolet radiation Quartz glass sleeve Treated water from outlet to AF Ballast UV Bulb Filtered water from filter to inlet Figure 6-3 Ultra Violet (UV) unit Like ozone, UV radiation is a plant-room treatment that purifies the re-circulating water, inactivating microorganisms and to a certain extent breaking down some pollutants (e.g. chloramines) by photo-oxidation. This decreases the chlorine demand of the purified water but does not leave a disinfectant residual in the AF water. Micro-organisms possess a repair mechanism, meaning that even after destruction of their DNA (Desoxyribonucleic acid) they are capable of reactivation. This process can be influenced by light and time expressed in terms of photo-reactivation. Medium pressure lamps, which not only destroy the DNA with their range of wave length but  1-10 also the cell components such as proteins and enzymes, are preferable in these cases. Reactivation is prevented. The following criteria dictate the selection of the appropriate UV system: (a) Type of micro-organisms to be destroyed. (b) Water flow rate to be treated. (c) Type of lamps (Low pressure or medium pressure). (d) UV dose (= UV-fluence; energy absorbed by micro-organisms). (e) Water temperature. (f) Requested radiation intensity. For UV to be most effective, the water must be pretreated to remove turbidity that will cause particulate matter that prevents the penetration of the UV radiation or absorbs the UV energy. Water hardness, the level of suspended solids such as iron, manganese as well as humic acid are also important. The different substances in the water reduce the transmission value and may foul the UV system or even lead to deposits on the quartz glass sleeves. Disadvantages of UV are the lack of a field test that readily establishes the efficiency of the process desirable for adequate water quality management and its inability to provide any residual disinfecting capacity to protect against recontamination.   7-1 CHAPTER 7 TYPICAL CHEMICAL DOSING PROCESS AND WATER QUALITY 1 Regulations and Requirements In Chapter 1, the COPEH September 2021 sets the minimum requirements for an AF. Some of the areas included are as follows: (a) Objectives of the Code of Practice. (b) Minimum design criteria. This Chapter deals with maintenance of water quality, which is very important in terms of health safety concerns for bathers or swimmers using the AF. 2 Liquid Impurities and Contaminants The main contributor of liquid impurities is the bather or user, contributing contaminants such as:- (a) Mucus liquids. (b) Perspiration. (c) Urine. (d) Cosmetics. (e) Hair oils and lotions. Soil impurities, mainly ammonia, are other contributors. The free chlorine combines with nitrogen or ammonia compound in these contaminants to become chloramines. 3 Chemical Dosing Process and the Chemicals used The chemical dosing process involves:- (a) Disinfecting. (b) pH correction. (c) Stabilisation of disinfectant. (d) Algae control.  7-2 Scum channel Re-circulation pump AF Return pipe Balancing tank Filtration unit Disinfecting pH correction Stabilisation of disinfectant Note: 4 sets of Algae control injector valve in this instance Figure 7-1 Chemical Dosing Process 3.1 Disinfecting How is Chlorine made? Chlorine is produced by the electrolysis of salt water. When electricity is passed through 2NaCl (Salt) and 2H20 (Water), the atoms dissociate into Cl2 (Chlorine) + 2NaOH (Sodium Hydroxide) + H2 (Hydrogen). Cl2 is isolated in its gaseous form, and used to create other chlorine compounds used for sanitizing, bleaching and production of plastics and related products. How does Chlorine cleanse? When chlorine is added to water, another dissociation occurs, i.e. Cl2 (Chlorine) + H2O (Water). We get a reaction which leaves us with HOCl (hypochlorous acid) + HCl (Hydrochloric acid). Cl2 + H2O → HOCl (Hydrochlorous acid)