1. by, Vikas Kumar VermaEnrol.No.-11519016. M.Tech. (1stSem.)Environmental Engg.

2. What is a Septic Tank? A Septic Tank is a below ground watertight box (concrete, plastic or fiberglass), often about 9 x 5 x 6 feet. It separates the liquids and solids, provides digestion of some organics (mainly by bacteria which live without oxygen) and storage. It discharges partially filtered and clarified effluent to the drainfield for final treatment. 3. Who has a Septic Tank System? If a building (with plumbing facilities) is not on a city sewer system, then in most cases it has a septic tank system (also known as an On-site Wastewater Disposal System, or Subsurface Wastewater Disposal System) to dispose of the wastewater. 4. What is an On-site WastewaterSystem? An On-site Wastewater Disposal System collects, treats and disposes of all the wastewater produced in a building. A conventional system includes a Septic Tank, a Distribution Device and a Drainfield 5. What is a Drainfield? The Drainfield (also known as thenitrification field) is the area which containsthe pipes (and/or other approved materials).It receives the effluent (partially treatedcloudy liquid) from the septic tank fordistribution, treatment ( mainly by bacteriathat need oxygen) and absorption into thesoil. Approved Drainfields are made from manymaterials including pipe and gravel, plasticchambers, concrete blocks, polystyreneaggregate and other piping systems. 6. What does an On-siteWastewater Disposal System do?Avoids the spread of disease by preventinghuman sewage from contaminating theground surface, well water supplies andstreams. 7. Typical Septic System Houseevapotranspiration well septic tankba sem ent tre nche s effluentba ffle soil ab so rptio n tre atme ntgro und wa terstrea ms, lake s 8. Diagram of septic tank 9. Schematic of conventional septic tank Inspection opening Access opening near side wall at Inspection opening 150150 mm diameter least 600 mm diametermm diameter InletAt least 25 mm 20% of Outlet Liquid levelLiquid depthWater lineAt least 75 mmScum20% of Liquid depth(150 mm, minimum)40% of40% ofScum clear space Liquid depthLiquid depthLiquid depth (75 mm, minimum)Clear space Scum clear space(300 mm, minimum)Sludge Sludge First compartment 2/3 lengthsecond compartment 1/3 length Total length equals two to three times width 10. View Cross Section of Tank 11. Element of Septic Tank 12. SEPTIC TANK It is a primary horizontal continuous flowtype of sedimentation tank having extraprovision to digestion of settled sludge Properties. Detention time- 12 to 36 hr It removes 60% to 70% of dissolve matters. Cleaning period-6 month to 3 years 13. Tank Sizing Generally prescribed for individual homesbased on home size Criteria: Hydraulic detention time plussolids storage 1 to 2 days detention of design flow Add solids storage volume equal to 1/3 1/2 of the above hydraulic detention 14. Tank MaterialsReinforced concrete Fiberglass-reinforced plastic(FRP)Polyethylene/Poly-propylene 15. Tank Functions Solids removal by settling & floatation 60-80% solids removal Anaerobic digestion Storage of solids 16. Factors that Influence AnaerobicDigestion pH Teperature Chemicals Highly variable flow patterns Pharmaceuticals and personal care products(PPCPs) Process wastewaters Lack of tank maintenance 17. What Happens in the TankINOUTSCUMSLUDGE 18. Anaerobic DigestionORGANIC GASES + HUMUSMATTERCO2CH4H2SNH3 19. Biological Activity in the SepticTank Anaerobic (without Oxygen) Incomplete Cheap and easy Reliable Gases produced are odoriferous Not all solids in tank are biodegradable Need to be stored until removed during pumpout 20. Average Removal of BOD,TSS, and Grease in Septic TankAverage Raw Average % Removal ParameterSewage SepticInfluentTank Effluent BOD (mg/L) 308 12260TSS (mg/L)316 72 77 Grease 102 21 79(mg/L) 21. Computer program for septic tank#include#include#includeVoid main (){Clrscr ();Double population, per capita rate, detention time, quantityof sewage, rate of deposition, period of cleaning, volume ofsludge, capacity, depth, surface area, width, lengthPrint f (enter population);Scan f (%f, & population);Print f (enter per capita rate,);Scan f (%f, & per capita rate);Quantity of sewage=0.8*per capita rate*population 22. Print f (enter rate of deposition);Scan f (%f, & rate of deposition);Print f (enter period of cleaning);Scan f (%f, & period of cleaning);Volume of sludge= (rate of deposition*period ofcleaning)/1000Capacity=quantity of sewage+ volume of sludgePrint f (enter depth);Scan f (%f, & depth);Surface area= volume of sludge/depthWidth=power (surface area/3), 0.5);Print f (width=%d, b);Length=3*widthPrint f (length=%d, l);getch (); 23. OUTPUT Enter population= 120 Enter per capita rate= 150 Enter rate of deposition= 30 Enter depth of tank= 1.5m Width= 2.1m Length= 6m 24. Role of the septic tankAnaerobic fermentation of solidsReduce the load of pathogens in the effluentHold the effluent for 2-3 days for improved safetyRetain solid material to prevent blockage of further disposal system 25. Advantage1. It can be easilyDisadvantage constructed. 1. Its size should be2. No maintenancevery large to serve problem.many people.3. It excellently 2. Smell problem remove BOD.3. It needs periodic4.Very less amount cleaning. of solids are produced.5. Low cost 26. Some things which can be done to prolongthe life of a Septic System: Pump out the accumulated solids from theSeptic Tank regularly (check it every 3 years,and typically pump it every 5-7 years). Dont overload it (minimize water usage). Dont put things which dont readilydecompose into a Septic System (grease,cooking oils, sanitary napkins, chemicals,etc). Dont drive on it, or build over it. 27. Failures of a Septic System1.Failure by surfacing Failing Septic Systems often show up as a wet or mushy area above the drainfield (often because the drainfield can no longer absorb the effluent). 28. Ways to spot a failing septicsystem Failing septicsystems can oftenbe spotted fromthe road. Nutrients fromeffluent oftencause the grassto grow greener. 29. Anaerobic digestion process is widely used for the treatmentof biodegradable organic waste.Anaerobic digester depends upon different empirical rules.Mathematical models are very helpful in the betterunderstanding anaerobic digester . By analyzing thesesmodels we can also apply computer technique on anaerobicdigesters. 30. The anaerobic digester is conceived as an input-outputmodel with organic waste as input and carbon dioxide andmethane production per unit weight of substrate as output.The output is a function of the following state variables-s. No. Name Symbol1. pH pH2. Alkalinity Ca3. Volatile acid conc.Cva4. Total nitrogen conc. CN5. TemperatureT 31. For the purpose of analysis these state variables are denoted asX1, X2, X3,X4 and X5 and the state vector by X.The input u is in the form of volatile solid (vs) loading doneonce everyday and expressed as gm per litre of digester isdenoted by C.The output vector consists of the following variables-s. No.NameSymbol1.Unit carbon qCO2dioxide discharge2.Unit methaneqCH4dischargeAnd for the purpose of analysis they will be denoted by Y1and Y2; and output vector by Y. 32. The system is described by the following differential equations:dx/dt = f1(x,u).(1)in which X is (x1,x2,x3,x4,x5 )T. knowing the initial conditions andthe input u(t), equation (1) can be solved by using an appropriatenumerical method. Thus the state variables are expressed as afunction of time and input.The output is a function of state variables and the input variables,which can be written as-Y=f2(X,u)..(2)In which Y is (y1, y2)TIn digester input is known & parameters are also known then atany stage we can know what would be the output. 33. In the present investigation two types of equations, linear andexponential, are fitted to the data. For mathematical convenience uis denoted as x6. 1. Linear equation A typical output y is related to the input and state variables by the following linear equation- Y=a1x1+a2x2+a3x3+a4x4+a5x5+a6x6 .(3) In which a1s are unknown constants to be determined in such manner that there is a good agreement with the data. The error i in the ith data van be written as- i= yi-( a1x1+a2x2+a3x3+a4x4+a5x5+a6x6) .. (4)in which yi is the ith observed output. 34. Squaring i (all the errors become positive) and summing onegets:E=(yi- aj xji)2 (5)For minimizing E, we have dE/daj=0; for j= 1, 2,3.6using equation (5) and (6) one gets2 (yi- aj xji) xk =0.(7)Simplifying equation (7); one getsaj xji xki= yi xki ; for k= 1, 2, 3.6 . (8)Equation (8) is a system of linear simultaneous equation in ajwhich can be solved using standard procedure. 35. 2. Non linear EquationThe following state output equation is proposedY=k.x1a1. x2a2. x3a3. x4a4. x5a5.In which k is constant. x6a6 (9)Taking logarithms one getsLog y= log k+ a1 log x1+ a2 log x2 + a3 log x3 + a4 log x4 + a5log x5 + a6 log x6 (10)It is a linear formulation in log x and log y . by changing thevariables and using an equation similar to eq. (8) the constant ajcould be evaluated. 36. ConclusionSeptic tank is widely used in waste water treatment. This method hasseveral significant advantages like very less by-products low energy,low space requirement and highly efficient.In septic tank, the treatment process is anaerobic present and due tomodeling of anaerobic system and the analysis of anaerobictreatment has become simple.By model analysis we can also write the several computer programsfor given input and parameter at different time.