Abstract:
ABSTRACT
Wastewater treatment by physico-chemical processes is highly cost effective, but it results in concentration of pollutant rather than removal only. Biological treatment, on other hand, converts pollutants into valuable biomass. A pilot scale waste water treatment plant was operated on site to treat wastewater of Paharang Drain using activated sludge process. The plant set up consisted of an aeration tank with working volume of 1000 gallons and a sedimentation tank or clarifier with working volume of 500 gallons. The pH of wastewater was maintained between 7 and 8.5 throughout the experimentation. The temperature of waste water in aeration tank remained between 22 to 28 oc throughout the operational period. The study was conducted for period of ten months.
The activated sludge process was used at three different hydraulic retention time (HRT) of 12 hr, 10 hr and 8 hr with an average MLSS concentration of 3500 mg/L. Under each HRT the pilot plant was operated for a period of 2-3 month. The maximum chemical oxygen demand (COD) removal efficiency of 81.4 % was found with 12 hr HRT as compared to 83.3 % and 92.4 % in 10 hr and 8 hr respectively. The average COD removal efficiency was 77 %, 79.8 % and 86.6 % under the HRT of 12 hr, 10 hr and 8 hr respectively. Similarly maximum biological oxygen demand (BOD5) removal efficiency of 81.9 was found atl() hr HRT as compared to 91.1 % at 8 hr HRT. The average BOD5 removal efficiency was 78.4%, and 87.1 % under the HRT of 10 hr and 8 hr respectively. The maximum total organic carbon (TOC) removal efficiency of
69.8% was found at 12 hr HRT as compared to 65.9 % and 81.2 % in 10 hr and 8 hr respectively. The average TOC removal efficiency was 64.2%, 64.6 % and 75.2% under the HRT of 12 hr, 10 hr and 8 hr respectively.
The maximum total suspended solids (TSS) removal efficiency of 89.1 % was found with 12 hr HRT as compared to 93.4 % and 97.8 % in 10 hr and 8 hr respectively. The average TSS removal efficiency was 86.8 %, 89.2 %, and 95.5% under the HRT of 12 hr, 10 hr and 8 hr respectively. Eight hour HRT was found optimum because at this HRT, the average values of BOD5 reduced from 274.6 to 35.5 (mg/L), COD from 459.7 to 63.9 (mg/L), TSS from 528.2 to 23.4 (mg/L) and TOC from 134.3 to 33.2 (mg/L). Values of all parameters are under the limits prescribed by National Environmental Quality Standards (NEQS). Thus, Activated Sludge Process
(ASP) brought the effluent into allowable discharge limits of NEQS.
