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Septic Tank

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Septic Tank

  1. 1. by, Vikas Kumar Verma Enrol.No.-11519016. M.Tech. (1stSem.)Environmental Engg.
  2. 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. 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. 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. 5. What is a Drainfield? The Drainfield (also known as the nitrification field) is the area which contains the pipes (and/or other approved materials). It receives the effluent (partially treated cloudy liquid) from the septic tank for distribution, treatment ( mainly by bacteria that need oxygen) and absorption into the soil. Approved Drainfields are made from many materials including pipe and gravel, plastic chambers, concrete blocks, polystyrene aggregate and other piping systems.
  6. 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. 7. Typical Septic System House evapotranspiration well septic tank ba sem ent tre nche s effluent ba ffle soil ab so rptio n tre atme nt gro und wa ter strea ms, lake s
  8. 8. Diagram of septic tank
  9. 9. Schematic of conventional septic tank Inspection opening Access opening near side wall at Inspection opening 150 150 mm diameter least 600 mm diameter mm diameter Inlet At least 25 mm 20% of Outlet Liquid level Liquid depth Water lineAt least 75 mm Scum 20% of Liquid depth (150 mm, minimum) 40% of 40% of Scum clear space Liquid depth Liquid depth Liquid depth (75 mm, minimum) Clear space Scum clear space (300 mm, minimum) Sludge Sludge First compartment 2/3 length second compartment 1/3 length Total length equals two to three times width
  10. 10. View Cross Section of Tank
  11. 11. Element of Septic Tank
  12. 12. SEPTIC TANK It is a primary horizontal continuous flow type of sedimentation tank having extra provision 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. 13. Tank Sizing Generally prescribed for individual homes based on home size Criteria: Hydraulic detention time plus solids 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. 14. Tank MaterialsReinforced concrete Fiberglass-reinforced plastic (FRP) Polyethylene/Poly-propylene
  15. 15. Tank Functions Solids removal by settling & floatation 60-80% solids removal Anaerobic digestion Storage of solids
  16. 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. 17. What Happens in the TankIN OUT SCUM SLUDGE
  18. 18. Anaerobic DigestionORGANIC GASES + HUMUSMATTER CO2 CH4 H2S NH3
  19. 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. 20. Average Removal of BOD,TSS, and Grease in Septic Tank Average Raw Average % Removal Parameter Sewage Septic Influent Tank Effluent BOD (mg/L) 308 122 60TSS (mg/L) 316 72 77 Grease 102 21 79(mg/L)
  21. 21. Computer program for septic tank#include<stdio.h>#include<conio.h>#include<math.h>Void main (){Clrscr ();Double population, per capita rate, detention time, quantity of sewage, rate of deposition, period of cleaning, volume of sludge, 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. 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 of cleaning)/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. 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. 24. Role of the septic tankAnaerobic fermentation of solidsReduce the load of pathogens in the effluentHold the effluent for 2-3 days for improved safetyRetain solid material to prevent blockage of further disposal system
  25. 25.  Advantage1. It can be easily Disadvantage constructed. 1. Its size should be2. No maintenance very 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. 26. Some things which can be done to prolongthe life of a Septic System: Pump out the accumulated solids from the Septic Tank regularly (check it every 3 years, and typically pump it every 5-7 years). Don’t overload it (minimize water usage). Don’t put things which don’t readily decompose into a Septic System (grease, cooking oils, sanitary napkins, chemicals, etc). Don’t drive on it, or build over it.
  27. 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. 28. Ways to spot a failing septicsystem Failing septic systems can often be spotted from the road. Nutrients from effluent often cause the “grass to grow greener”.
  29. 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. 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 Symbol 1. pH pH 2. Alkalinity Ca 3. Volatile acid conc. Cva 4. Total nitrogen conc. CN 5. Temperature T
  31. 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. Name Symbol 1. Unit carbon qCO2 dioxide discharge 2. Unit methane qCH4 dischargeAnd for the purpose of analysis they will be denoted by Y1and Y2; and output vector by Y.
  32. 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. 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 a1’s are unknown constants to be determined in such manner that there is a good agreement with the data. The error ϵi in the ith data van be written as- ϵi= yi-( a1x1+a2x2+a3x3+a4x4+a5x5+a6x6) ….. (4) in which yi is the ith observed output.
  34. 34. Squaring ϵi (all the errors become positive) and summing onegets:E=Σ(yi- Σaj xji)2 (5)For minimizing E, we have dE/daj=0; for j= 1, 2,3…….6using equation (5) and (6) one gets2 (Σyi- Σaj xji) xk =0…. (7)Simplifying equation (7); one getsΣaj Σxji xki= Σyi 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. 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. 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.

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