Effect of Wastewater Treatment on Bio-kinetics of Dissolved Oxygen in River Ravi

Waste management studies are usually done using calibrated and verified water quality models. Ravi River located in Lahore, Pakistan is receiving untreated wastewater from number of outfalls and surface drains and thus model calibration and verification are done using the data under the prevailing conditions. The water quality objectives can only be met with wastewater treatment wherein the model rate coefficients may change. The objective of this paper is to study the changes that may occur in these coefficients as a result of wastewater treatment. For this purpose, long-term BOD analyses have been carried out using river water and wastewater after different degrees of treatment. A laboratory scale biological reactor was used to study the effect of biological treatment on rate coefficients at 3, 6 and 10 days detention times. The study results show that CBOD biokinetic rate coefficient (K) reduces significantly from 0.25 day for raw wastewater to 0.1 day for the wastewater treatment for 3 days detention time in the biological reactor. Further reductions in the value of K to 0.07 day and 0.05 day occurred for a treatment level corresponding to 6 and 10 days detention times, respectively. The NBOD rate coefficient (Kn) was found to be 0.08 day for 3 days detention time and 0.06 day after treatment in the biological reactor at 6 and 10 days detention times.