Septic Tank

1. COMPUTATIONAL TECHNIQUEs IN septic tank by, Vikas Kumar Verma Enrol.No.- 11519016. M.Tech. (1 st Sem.) 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 Wastewater System? 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 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. What does an On-site Wastewater Disposal System do? Avoids the spread of disease by preventing human sewage from contaminating the ground surface, well water supplies and streams.

7. Typical Septic System

8. Diagram of septic tank

9. Schematic of conventional septic tank Inspection opening 150 mm diameter Inlet At least 75 mm At least 25 mm Access opening near side wall at least 600 mm diameter Inspection opening 150 mm diameter Liquid level 20% of Liquid depth Water line 40% of Liquid depth Scum clear space (75 mm, minimum) Scum clear space (300 mm, minimum) 20% of Liquid depth (150 mm, minimum) Scum Clear space Sludge Sludge Outlet 40% of Liquid depth Liquid depth First compartment 2/3 length second 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 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. 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. Tank Materials Reinforced 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 Anaerobic Digestion pH Teperature Chemicals Highly variable flow patterns Pharmaceuticals and personal care products (PPCPs) Process wastewaters Lack of tank maintenance

17. What Happens in the Tank IN OUT SLUDGE SCUM

18. Anaerobic Digestion ORGANIC MATTER GASES + HUMUS CO 2 CH 4 H 2 S NH 3

19. Biological Activity in the Septic Tank 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 Tank Parameter Average Raw Sewage Influent Average Septic Tank Effluent % Removal BOD (mg/L) 308 122 60 TSS (mg/L) 316 72 77 Grease (mg/L) 102 21 79

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, length Print 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 of cleaning)/1000 Capacity=quantity of sewage+ volume of sludge Print f (“enter depth”); Scan f (“%f”, & “depth”); Surface area= volume of sludge/depth Width=power (surface area/3), 0.5); Print f (“width=%d”, b); Length=3*width Print 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. 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 Role of the septic tank

25. Advantage It can be easily constructed. No maintenance problem. It excellently remove BOD. Very less amount of solids are produced. Low cost Disadvantage Its size should be very large to serve many people. Smell problem It needs periodic cleaning.

26. Some things which can be done to prolong the 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. Failures of a Septic System 1.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 septic system Failing septic systems can often be spotted from the road. Nutrients from effluent often cause the “grass to grow greener”.

29. Mathematical modelling of anaerobic digestion process Anaerobic digestion process is widely used for the treatment of biodegradable organic waste. Anaerobic digester depends upon different empirical rules. Mathematical models are very helpful in the better understanding anaerobic digester . By analyzing theses models we can also apply computer technique on anaerobic digesters.

30. Analytical formulation The anaerobic digester is conceived as an input-output model with organic waste as input and carbon dioxide and methane 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 C a 3. Volatile acid conc. C va 4. Total nitrogen conc. C N 5. Temperature T

31. For the purpose of analysis these state variables are denoted as X 1, X 2 , X 3, X 4 and X 5 and the state vector by X. The input u is in the form of volatile solid ( vs ) loading done once everyday and expressed as gm per litre of digester is denoted by C. The output vector consists of the following variables- s. No. Name Symbol 1. Unit carbon dioxide discharge qCO2 2. Unit methane discharge qCH4 And for the purpose of analysis they will be denoted by Y 1 and Y 2 ; and output vector by Y.

32. The system is described by the following differential equations: dx/ dt = f 1 ( x,u )……. (1) in which X is (x 1 ,x 2 ,x 3 ,x 4 ,x 5 ) T . knowing the initial conditions and the input u(t), equation (1) can be solved by using an appropriate numerical method. Thus the state variables are expressed as a function of time and input. The output is a function of state variables and the input variables, which can be written as- Y=f 2 ( X,u )….. (2) In which Y is (y 1 , y 2 ) T In digester input is known & parameters are also known then at any stage we can know what would be the output.

33. In the present investigation two types of equations, linear and exponential, are fitted to the data. For mathematical convenience u is denoted as x 6 . 1. Linear equation A typical output y is related to the input and state variables by the following linear equation- Y=a 1 x 1 +a 2 x 2 +a 3 x 3 +a 4 x 4 +a 5 x 5 +a 6 x 6 ……. (3) In which a 1 ’s are unknown constants to be determined in such manner that there is a good agreement with the data. The error ϵ i in the i th data van be written as- ϵ i = y i -( a 1 x 1 +a 2 x 2 +a 3 x 3 +a 4 x 4 +a 5 x 5 +a 6 x 6 ) ….. (4) in which y i is the i th observed output.

34. Squaring ϵ i (all the errors become positive) and summing one gets: E= Σ ( y i - Σ a j xj i ) 2 (5) For minimizing E, we have dE / da j =0; for j= 1, 2,3…….6 using equation (5) and (6) one gets 2 ( Σ y i - Σ a j x ji ) x k =0…. (7) Simplifying equation (7); one gets Σ a j Σ x ji x ki = Σ y i x ki ; for k= 1, 2, 3…….6 …. (8) Equation (8) is a system of linear simultaneous equation in a j which can be solved using standard procedure.

35. The following state output equation is proposed Y=k.x 1 a1 . x 2 a2 . x 3 a3 . x 4 a4 . x 5 a5 . In which k is constant . x 6 a6 …(9) Taking logarithms one gets Log y= log k+ a 1 log x 1 + a 2 log x 2 + a 3 log x 3 + a 4 log x 4 + a 5 log x 5 + a 6 log x 6 … (10) It is a linear formulation in log x and log y . by changing the variables and using an equation similar to eq. (8) the constant a j could be evaluated. 2. Non linear Equation

36. Conclusion Septic tank is widely used in waste water treatment. This method has several 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 to modeling of anaerobic system and the analysis of anaerobic treatment has become simple. By model analysis we can also write the several computer programs for given input and parameter at different time.

37. THANK YOU!!!!!!!