Lecture 11 Grit Removal - CVLE 453 Sanitary Engineering PDF

Lecture 11 Grit Removal CVLE 453: Sanitary Engineering Dr. Maher Kahil Dr. Rouba Joumblat  Wastewater Or Sewage Treatment STP Purpose of Sewage Treatment: To manage wastewater discharged f...

Lecture 11 Grit Removal CVLE 453: Sanitary Engineering Dr. Maher Kahil Dr. Rouba Joumblat  Wastewater Or Sewage Treatment STP Purpose of Sewage Treatment: To manage wastewater discharged from homes, businesses, and industries to reduce the threat of water pollution. To remove pollutants from wastewater for its recycling. TO AVOID POLLUTION AND HAVE AS PER HIM full SUSTAINABLE SYSTEM TO REUSE THE WATER AND USE TREATED SLUDGE To promote health concern and public hygiene. More than 50% diseases are spread by untreated sewage due to presence of various pathogens microorganisms ,etc... To preserve aquatic life and wildlife habitat. If sewage is disposed untreated in water bodies, it can result in following problems: TREAT IT BASED ON CHARACTERISTIC OF WATER W 3A HASAB BI SHUB BADON YST3MLO L MAY - Depletion of O2 resources of streams - Cause turbidity, colour in water bodies e said treated sludge and treated waste water to be used - Can be toxic to aquatic life Sewage is treated to be reused for Irrigation purposes and Ground water recharge  Wastewater Characteristics Sewage is 99.94% water, with only 0.06% of the wastewater dissolved and suspended solid material. bsawu=i treatment lal water hasab usage te3a Wastewater strength is expressed as oxygen demand i.e. the amount of oxygen required per unit volume of wastewater to break down all the organic compounds present. Oxygen demand is usually measured as BOD or COD. BOD : watse water include bacteria and they need to treat water by bacteria so BOD is amount od O2 required to oxidize organic matters in waste water biochemical oxygen COD depend on BOD The BOD is an important measure of water quality. It is a measure of the amount of oxygen needed (in mg/l or ppm) by bacteria and other microorganisms to oxidize the organic matter present in a water sample over a period of 5 days at 20 0C incubation. It is also called the "biological" oxygen demand. bod 5 since it take 5 days in lab to determine value of BOD Untreated domestic sewage has a BOD5 ranging from 100 mg/l to 300 mg/l. BOD sdepend on charectaristic on waste water iza domestic 2w industrial industry kd towsal 1500 Sewage also contains nutrients (such as ammonia and phosphorus), minerals, etc…. Ammonia can range from 12 to 50 mg/l and phosphorus can range from 6 to 20 mg/l in untreated sewage. IZA 3M Y3MLO TREATMENT W BADON YEST3MLO LA ZIRA3A MA BI SHILO PHOSPHOROUS  Wastewater Characteristics important to asses quality of waste water BOD, COD, TP, TN & SS are the five most common concepts in the wastewater treatment. BS YKONO 3ALYIN YE3NI WATER IS MORE POLLUTED BOD & COD represent the content of organic matter in the wastewater. Organic matter is composed of hydro & carbons which can be oxidized by strong oxidants or by microorganisms. The more oxygen consumed in the oxidation process, the more organic matters exist in the wastewater. The higher the BOD and COD values, the more serious the water was polluted. The organic matter in the wastewater is divided into degradable organic matter and non-degradable organic matter. Only the degradable organic matter can be utilized by the microorganism. So BOD means degradable organic matter. COD means all organic matter. The difference between these two data represents a non-degradable organic matter.  Typical characteristics of domestic wastewater (Polprasert, 1996) Parameter Concentration (mg/l) Strong Medium weak BOD 400 220 110 COD 1000 500 250 Org-N 35 15 8 NH3-N 50 25 12 Total N 85 40 20 Total P 15 8 4 Total Solids 1200 720 350 Suspended 350 220 100 solids  Municipal and Industrial Wastewater Treatment Municipal Wastewater treatment consists of four major categories. (i) Preliminarily treatment (ii) Primary treatment (iii) Secondary treatment and (iv) Tertiary treatment. The purpose of pretreatment is to protect the wastewater treatment plant (WWTP) equipment. Primary treatment removes those pollutants that are either settle or float. It removes 50% of suspended solids (SS) and 35% BOD. Secondary treatment removes up to 85% suspended solids and BOD. It does not remove nitrogen, phosphorus, or heavy metals significantly, nor completely remove pathogenic bacteria and viruses. When secondary process is not sufficient to fulfill the treatment cant rEmove P&N requirements then tertiary treatment has to be done. Tertiary treatment removes 99% BOD, Phosphorus, suspended solids, and bacteria, 95% of nitrogen. Most of the impurities are removed from wastewater as a solid, that is sludge. Sludge handling and disposal must also be carried out to achieve satisfactory pollution control. Components of waste water treatment plant SECONADRY( BIOLOGICLY BY COMPRESSING AIR) MN3TI HAWA LAL BACTERIA SO IT DEGRADATE WASTE WATER THEN FINE SCREEN SLUDGE RETURN ACTIVATED SLUDGE BRAJE3 JOZO2 MN BACTERIA' 3AL AERATION 7ATA YDAL 3M YSHT8IL W JOZO2 LAL PROCCESSING AEROBIC BACTERIA USES OXYGEN TO TREAT WASTE WATER LAMA YE5LAS L OXYGEN BI TSIR ANEAOBIC FA BI BATTEL 3NDA OXYGEN FA BI TSIR TOKOL Wastewater Treatment L BACTERIA TENYI 7ATTA TROU7 L BACTERIA AND SEDEMENTS IN TANK BI SIRO L BACTERIA YEKLO B3D LA HATA YET2ALO W YNAZALO 3AL BOTTOM OF SEDIMENTATION TANK GRITAND GREECE REMMOVAL 7ATA YSHILO ZYOUT W SH7OUM  Municipal and Industrial Wastewater Treatment Industrial Wastewater: The municipal WWTP are usually not designed to remove the impurities of industrial waste. The industrial waste can damage the sewer system and /or treatment units. Therefore, a pretreatment process for industrial waste is essential before disposing it in to sanitary sewer and treatment units. The objectives of pretreatment are: (i) Prevention of pollutants that interfere the operation of WWTP. (ii) To prevent WWTP of pollutants that will pass without treatment. (iii) To improve opportunities to recycle and reclaim municipal and industrial wastewater and sludge. Such type of industrial waste must not be allowed to sanitary sewer and treatment units. Like Toxic materials, waste that obstruct to flow of sanitary waste; oxygen demanding materials; heated waste of temperature more than 400C, petroleum oil; or products of mineral oils; toxic gases, vapors etc.  Oil and Grease HEK INDUSTRY BADON YKON 3NDON THEIR OWN TREATMENT Animal / Vegetable Meat Packing Food Processing Restaurants Biodegradable Usually Free Floating Petrochemical Cutting / Grinding Parts Degreasing Automotive Toxic Often Emulsified  So What’s The Problem With Oil and Grease ?? Environmental Problems Collection System Probs WWTP Problems Collection System Oil and Grease (FOG) At the Source NEED TO CONTROL  Factors Affecting Separation of Free Oil From Water Stoke’s Law 2(p - po)g VR = (d/2)2 gn VR Rise Velocity (p - po) Density difference between oil droplet and water n viscosity of water and oil g gravitational acceleration constant d diameter of the oil droplet  Factors Affecting Separation of Free Oil From Water Density (Specific Gravity) Viscosity Droplet Size KHAZAN 3M YFOT 3ALE WASTE WATER FI WASTES BI TOUSHO IZA kan 3ena oil  Factors Affecting Separation of Free Oil From Water A) Fuel Oil SG = 0.95 B) Fuel Oil SG = 0.85 Water SG = 1.00 Which Will Rise Faster? How Much Faster?  Factors Affecting Separation of Free Oil From Water A) Fuel Oil SG = 0.95 B) Fuel Oil SG = 0.85 Water SG = 1.00 A) Fuel Oil B) Fuel Oil 1.00 1.00 0.15 =3 -.95 -.85 0.05 0.05 0.15 B Fuel Oil Will Rise 3 Times Faster in Water Than A Fuel Oil  Effect of Temperature on Separation of Oil From Water Viscosity is Related to Friction - High Viscosity Opposes Flow The Lower the Viscosity of the Oil, the Faster it will Rise in Water  l Grit Chamber Grit are small inorganic solids like pebbles, sand, silt, eggshells, glass and metal fragment. As Grits are abrasive in nature and will cause wear on pumps. Grit deposits in pipes, sumps and clarifiers can absorb grease and solidify. They are non biodegradable and occupy valuable space in the digest. The physical operation to remove is termed as Grit Chamber.  PHYSICAL Grit Chamber may be rectangular or circular Grit chamber are provided to aerated ye3ni bhot fiha air (i) protect moving mechanical equipment from abrasion and abnormal wear (ii) Reduce formation of heavy deposits in pipelines (iii) Reduce the frequency of digester cleaning caused by excessive accumulation of grit and (iv) To separate inorganic particles from organic and disposed off of these particles just to wash without passing any further treatment process. Grit Chambers are usually located after bar racks and before sedimentation tanks. Many types of grit removal systems exist including (i) Horizontal flow Rectangular (ii) Aerated Grit Chamber (iii) vortex type (iv) detritus tank and hydro-cyclones.  Types of Grit Chambers Rectangular Horizontal-flow grit chamber: It is the oldest type of grit removal systems. The unit is designed to maintain a velocity of 0.3 m/s and to provide sufficient time for grit particles to settle at channel while organic particles are kept in suspension. The design of horizontal flow grit chamber be such that, the lightest particles of grit will reach the bed of the channel. Usually grit chambers must be designed to remove particles of diameter of 0.20 mm. The length of channel will be based on the settling velocity and control section, while cross section area will be based on the rate of flow and the number of channels.  Types of Grit Chambers Aerated Grit Chamber: Wastewater will move through the tank in a spiral path and will make two to three passes across the bottom of the tank. bhot hawa Aerated Grit chambers are normally designed to remove particles of size 0.20 mm or larger with 2 to 5 minute detention time at peak hour flow. This type of chamber may serve another useful purpose, if the sewage is anaerobic when it arrives at the plant, aeration serves to strip noxious gases from the liquid and to restore it immediately to an aerobic condition, which allows for better treatment. The diffusers are located about 0.45 to 0.60 meters above the normal plane of the bottom. bs badi do55 hawa bi haydi 2w bil aeration tank mnn khilal diffusers  Types of Grit Chambers MTL BANYO Vortex Type: v=0.3 m/s The vortex-type grit chamber consists of a cylindrical or conical tank in which the flow enters tangentially, creating a vortex flow pattern. Grit settles by gravity into the bottom of the tank (in a grit hopper) while effluent exits at the top of the tank. mtl banyuo  Design Criteria of Grit Chambers Water velocity not less than 30 cm/sec OFR (Over Flow Rate)= 1200 m3 /m2 /d Detention Time (DT) = 60sec Total depth =Y+0.50m water depth +0.5 m Example1: For flow rate = 200 L/sec, design the grit chamber. Solution: Velocity = 0.3 m/sec STANDARD DT = 60 sec Length = Velocity × D.T = 18 m OFR = 1200 m3/m2/d Volume = Q ×T , Area = Q /OFR , depth = Vol. / Area No of units = 2 B = Area / Length ×2 =……. m. Q = (200 / 1000) × 24 ×60 × 60 = 18000 m3/d Area = 18000 / 1200 = 15 m2 VOL = Q × DT = 0.2 × 60 = 12 m3 Depth = Vol. / Area = 12 / 15 = 0.8 m Total depth = Y + 0.5 m = 0.8 + 0.5 = 1.3 m Rectangular shape L = 18 m = 30 × 60 = 1800 cm B = 15 /2 ×18 = 0.42 m and Depth =0.8m Total depth = Y + 0.5 m = 0.8 + 0.5 = 1.3 m Circular shape Area of one unit= 15.00/2= π D2/4 D=3m Example2: aerated grit chamber Given Information: Qaverage = 0.5 m3/sec; Peak flow Factor = 2.7; no of tanks = 2; Volume of grit materials = 0.05 m3/(103 m3); DT= 180 sec; kel 1000 m^3 fiyo 0.05 m^3 grit Qair = 0.3 m3/(minute- m) W:D = 1.2 and D =3m Required: Dimensions; Air Supply and Grit materials Peak flow = 0.5 *2.70 = 1.35 m3/sec Volume of tanks required = Q * t = 1.35 m3/sec * 180 sec = 243 m3 Since two tanks are proposed then Volume of one tank = 121.5 m3 Volume = L * W * D where W : D = 1.2 and D = 3.0 m so W = 3.6 m V = 121.5 = L * 3.0 * 3.6 or L = 121.5/(3*3.6) = 11.25 m The dimensions are L = 11.25 m ; W = 3.6 m and D = 3.0 m Air Supply = 0.3 m3/ (minute-m) * 11.25 * 180/60 = 10.125 m3 Grit materials = 0.05m3/103m3 of flow = (0.05m3/103m3 )(1.35 * 3600 *24) = 5.832 m3/day Some Useful Definitions: Aerobic processes: are biological treatment processes that occur in the presence of oxygen. Anaerobic processes: are biological treatment processes that occur in the absence of oxygen. Anoxic denitrification: is the process by which nitrate nitrogen is converted biologically to nitrogen gas in the absence of oxygen. This process is also known as anaerobic denitrification. Facultative processes: are biological treatment processes in which the organisms can function in the presence or absence of molecular oxygen. Carbonaceous BOD removal: is the biological conversion of the carbonaceous organic matter in wastewater to cell tissue and various gaseous end products. In the conversion, it is assumed that the nitrogen present in the various compounds is converted to ammonia. Some Useful Definitions: BOD (Biochemical Oxygen Demand). A measure of the amount of oxygen consumed in the biological processes that break down organic matter in water. COD (Chemical Oxygen Demand). A measure of the oxygen required to oxidize all compounds in water, both organic and inorganic. DO (Dissolved Oxygen). The oxygen freely available in water. Dissolved oxygen is vital to fish and other aquatic life and for the prevention of odors. Dissolved Solids. Disintegrated organic and inorganic material contained in water. Organic Matter. Carbonaceous waste contained in plant or animal matter and originating from industrial sources. Pathogens. Microorganism that can cause disease for humans, animals and plants. They may be bacteria, viruses, or parasites and are found in sewage. TDS (Total Dissolved Solids). The total amount of dissolved solid materials present in an aqueous solution. TOC (Total Organic Carbon). TOC is a measure of the amount of carbon in a sample originating from organic matter only. TSS (Total Suspended Solids). A measure of the suspended solids. design of vortex grit chamber