Question 6 A wastewater sample was collected after screening

Question 6 A wastewater sample was collected after screening and grit removal step from Waterloo WWTP. The sample was analyzed in the lab. The sample was found to have the following properties: Total COD 350 mg/L Soluble COD 200 mg/L BOD, 220 mg/L VSS/TSS ratio is 0.7 Removal efficiency of the primary clarifier in the WWTP is 60% for both VSS (both nbVSS and bVSS) and FSS. Assume that biological activity is restricted in primary clarifier, and all soluble compounds pass through. The effluent from primary clarifier is further treated in active sludge

Solution

To calculate rb COD we use formula sCOD = rbCOD + nbsCOD

Where sCOD is soluble COD = 200mg/L, so rb COD

200 = rbCOD + 50; rbCOD = 150 mg/L

Now for calculating sb COD we use formula bCOD = rbCOD + sbCOD

However, we don’t have bCOD [Biodegradable COD], to calculate that we use

bCOD (1.7) of (BOD)

bCOD = 1.6 x 220 = 352 mg/L

Now bCOD = rbCOD + sbCOD

352 = 150 +sbCOD; sbCOD = 352-150 = 198 mg/L