International network for natural sciences – research journal
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Optimization of hydraulic retention time (HRT) employing statistical tools of a lab-scale sequencing batch rector (SBR) treating real wastewater of a University campus

By: Ghalib Hasnain, Sher Jamal Khan, Saud Ahmed Khan, Usama Awais, Muhammad Junaid, Ahmed Ali, Nelufar Raza, Saimar Pervez

Key Words: Activated sludge, Hydraulic retention time, Reclamation, Sequencing batch reactor (SBR), Wastewater.

J. Bio. Env. Sci. 9(2), 129-141, August 2016.


Two lab-scale sequencing batch reactors (SBR) with combined capacity of 45 L/day, each having holding volume of 6 L were installed and operated at Institute of Environmental Sciences and Engineering (IESE) lab. The SBR systems were automated for variable hydraulic retention time (HRT) to treat real university wastewater (average COD = 220 mg/L). The HRT optimized based upon activated sludge growth pattern, and COD & BOD removal rates from unsteady to steady state condition. The optimized results will be utilized for under construction bio-tanks at the full scale membrane bioreactor (MBR) plant for reclamation and reuse of university wastewater. Each treatment cycle was operated with 2 and 3hr HRT (aeration time), followed by 30 minutes settling and 15 minutes decant time. The sludge withdrawal was based upon solids retention time (SRT) of 15 days and approximately 4 g/L mix liquor suspended solids (MLSS). Nutrient removal, COD, BOD, Total suspended solids (TSS), Total dissolved solids (TDS), temperature & pH, extracellular polymeric substances (EPS), microbial counts and Total Organic Carbon (TOC) for influent & effluent and sludge volume index (SVI), EPS, capillary suction time and MLSS/MLVSS for sludge were analyzed through standard operating procedures.


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