Tutorial 7

The objective of this tutorial is to calculate the quantity and characteristics of the wastewater generated in the IIT campus.   For the purposes of this calculation, it is assumed that the water used for domestic and commercial establishments only will constitute the wastewater.  Since the IIT Kanpur campus is a fully sewered community, it is expected that 80 % of the water supply to the domestic and commercial establishments will become wastewater.   To determine the characteristics of the wastewater use the following unit loading factors, which are valid for domestic wastewater:

Soluble BOD5 :                         50 g/capita/d

Total Solids:                             200 g/capita/d

Organic Suspended Solids:       100 g/capita/d

Grit:                                          10 g/capita/d

Total Nitrogen:             8 g/capita/d

Free Ammonia:             0.6 x Total Nitrogen

Total Phosphorus:                     2 g/capita/d

The contributions from commercial establishments can be taken as half the above values.  Based on the information given above, calculate the wastewater flow and characteristics.

Wastewater generated will be conveyed to the wastewater treatment plant by three trunk sewers shown in Figure 1.  Several branch sewers and minor sewers will also be required.

Based on the sewer network shown in Figure 1, calculate the flow at each junction of the three trunk sewers.  Also calculate the flow at each junction of the branch sewers.

The wastewater flow will not be the same at all times of the day.  The wastewater flow at various times of the day are given as fraction of the design flow in Table 1.

Table 1.           Flow Fractions at various times of the day

 Time M-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-N Fraction 0.89 0.72 0.53 0.42 0.34 0.32 0.39 0.66 1.15 1.34 1.38 1.40

 Time N-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-M Fraction 1.38 1.32 1.25 1.14 1.06 1.06 1.07 1.19 1.30 1.30 1.24 1.12

Based on the information given above, calculate the dimensions of an equilization tank to be constructed for dampening the variations of flow, thus ensuring that the wastewater input to the wastewater treatment plant remains constant all through the day.