A pilot oxidation pond plant was designed and constructed at the Karachi University of Campus for the treatment of domestic wastewater. Performance of this system was evaluated for three consecutive years (1991-1993) with respect to BOD5, COD, TKN, NH3-N, PO4-P, TCC, TFC and TFS count. The results reported are pertaining to two facultative ponds connected in series and designated as P-3 and P-4.
In the first year (1991) of study, the treatment efficiency of oxidation ponding system was evaluated at a BOD5 loading rate of 500 Kg/ha.d with a total retention time of 15 days (7.5 days in each pond) in relation to different climatological factors.
In the second year (1992) ponds performance efficiency was evaluated at a higher BOD5 load of 1168 Kg/ha.d with retention time of 5.8 days (2.9 days in each pond).
In the third year (1993) the performance efficiency was evaluated by recycling 50% oxygen-rich effluent with 50% influent with a total retention time of 2.9 days (1.45 days in each pond) and total BOD5 loading rate of 1340 Kg/ha.d.
1During the entire period of study, the BOD5 removal efficiency was greater than 70%. This is considered to be satisfactory especially wit respect to a very high organic loading and short retention time.
2During the entire period of study, the monthly average residual BOD5 remained within a range of 19-76 mg/L. Whenever soluble BOD5 (filtered) of the effluent was measured , it was found to be between 10-42 mg/L.
3A very high BOD5 loading reate (500 Kg/ha.d, 1168 Kg/ha.d and 1340 Kg/ha.d) could be sfely applied in the facultative ponding system without causing odour nuisance or undesirable physical changes in the ponds.
4with the recirculation of oxygen-rich pond’s effluent it was possible to increase BOD5 loading rate.
5It was observed that the algal bacterial symbiotic system performed well even at a high BOD5 load with no or little indication of undesirable odour
6The COD removal tends show trend similar to that of BOD5 removal though in general the BOD5 removal efficiency was better than COD removal efficiency.
7The removal of NH3-N, TKN and PO4-P was found to be in direct relationship with retention time. The maximum removal efficiency of these parameters was observed during summer months with high wind velocity and ambient temperature(April to August).
8The removal of coliforms and faecal coliforms was higher in the primary pond while in the secondary pond no further significant removal was observed. Unlike coliforms and faecal coliforms, the removal of faecal streptococci was more pronounced in the secondary pond. In general, the removal of these organisms followed seasonal fluctuations
9The physical performance of the ponds was also appreciably good with no mosquito breeding problem.
10The multiple regression models developed for BOD5 and faecal coliforms removal were statistically significant.
11The model for faecal coliform removal shows that none of the climatological factor plays a significant role in faecal coliform killing. It seems likely that oxygen plays an important role in the destruction of faecal coliforms.
12The cost comparison of biomechanical and biological systems( oxidation ponds) operating in Pakistan indicates that oxidation ponds are much more economical than the biomechanical systems of wastewater treatment.
13The ponds effluent successfully met the National Environmental Quality Standards (NEQS) criteria at all the three BOD5 application rates viz 500, 1168 and 1340 Kg/ha.d