Tutorials 9 and 10

Based on the discussions of tutorial numbers 7 and 8 following information is available regarding wastewater characteristics of IIT Kanpur campus:

·        Wastewater Quantity, i.e., average and minimum and maximum wastewater flow-rate per hour.

·        Wastewater Quality, i.e., BOD5, TSS, Grit, TKN, Phosphate etc.

Objective of wastewater treatment is to obtain effluent with BOD5 <10 mg/L, TKN< 1 mg/L, Nitrate< 1 mg/L, and Phosphorus < 0.5 mg/L.  Based on the above objectives, the following wastewater treatment chain was decided upon:

A.     Solid Waste from Bar-Rack

B.     Sludge From Grit Chamber

C.     Sludge from Primary Sedimentation Tank

D.     Sludge from Secondary Sedimentation Tank

The extended aeration process is designed for combined carbon oxidation and nitrification, and the tertiary treatment should result in removal of nitrogen and phosphorus to the desired levels.

Assume 100 % removal of Grit in the grit chamber, 80% removal of inorganic suspended solids, and 80% removal of volatile suspended solids in the primary sedimentation tank..  Total suspended solids concentration effluent from secondary treatment is 25 mg/L.

50 kW surface aerators should be used for aeration purposes.  Manufacturers of such aerators specify that the oxygen transfer capacity of these aerators is 2.0 Kg O2/kW-h under standard conditions.  Based on this information, calculate the total power requirement for satisfying oxygen requirements in the aeration tank.  The operating temperature of the aeration tank is expected to be 30oC.  The steady state dissolved oxygen concentration in the aeration tank should be 3 mg/L.  Saturation concentration of oxygen in water at 20oC is 9.1 mg/L and at 30oC is 7.5 mg/L.  Calculate the power requirement to keep the bio-mass in suspension in aeration tank.  Based on the above two values, decide on the aerator requirements.

·        Design and size the wastewater treatment units based on the above information.  Calculate chemical requirements.

Hydraulic Design:

Based on maps of IIT Kanpur campus given in tutorial 5, it was decided that the wastewater treatment plant would be sited in the empty land available in the western end of the campus, adjacent to the water treatment plant sited in this area earlier.

The plant should be designed such that wastewater through the plant flows without pumping.  This may be impossible in a place with flat terrain, as is the IIT Kanpur campus, unless the ground elevations at the plant site are changed significantly through earthwork.  Luckily, as per our design, significant amount of soil is available for this purpose from the excavation of the raw water tanks, as described in tutorial 2.  A part of this soil will be used to change the ground elevation at the wastewater treatment plant site.

For determining the hydraulic grade line, or the water surface level at various parts of the treatment plant, the head-loss through various treatment units must be known (see schematic in Figure 1).  Following information regarding water surface levels are given:

·        Bar Rack:                                       Headloss through bars, 0.2 m

·        Grit Chamber:                                 As per open Channel specifications

·        Primary Sedimentation Tank:           0.4m water level difference between inlet and outlet

·        Aeration Tank:                                0.6m water level difference between inlet and outlet

·        Secondary Settling Tank:                0.6m water level difference between inlet and outlet

·        Oxidation Pond:                              0.8m water level difference between inlet and outlet

·        Fish Pond:                                      0.8m water level difference between inlet and outlet

Water will be conveyed from one process unit to another through open channels of 1:100 slope.

Water from the tertiary settling tank should be available with a head of approximately 5 m above the ground level, i.e., at an elevation of 135 m.  This water will flow over a cascade of 3 m height for aeration and odour removal, and will be conveyed through an open channel to a small ‘nalla’ in the extreme western end of the campus flowing southwards towards Pandu River flowing in the Southern end of Kanpur City.

Figure 1.         Treatment Plant Hydraulics

·        Design the layout of the wastewater treatment plant, based on the plant sizing done earlier.

·        Clearly mention the ground level and corresponding water level at various points of the treatment plant.

·        Mention the quantity and degree of earthwork required for changing the ground level at the plant location.

·        Design the required pumps (for wastewater pumping and sludge recycling) and other water conveyance units such as open channels and pipes.