The performance of an aerobic membrane-coupled bioreactor (MBR) operating at mesophilic- thermophilic transitional temperatures (40°C) treating oily rendering wastewater has been evaluated in terms of COD, BOD5, oil and grease, solids and ammonia removal at 5 and 10-day HRT. The COD removal efficiency increased from 78% to 96%, BOD5 removal from 87 to 99% and oil and grease removal from 92 to 95% with the increase in hydraulic retention time (HRT) from 5 to 10 days. The operation at atypically high temperatures showed promise as a treatment solution due to the low sludge yields of 0.03 g VSS/g COD.
The growth of industries producing high-strength and complex wastewaters makes it imperative to develop suitable treatment systems for these wastewaters. Aerobic biological processes operated at high temperatures are highly advantageous in treating high temperature, high strength industrial wastewaters due to its ability to combine the advantages of conventional aerobic and anaerobic processes that include rapid biodegradation kinetics and low biological solids production respectively (Rozich and Bordacs, 2002).
High treatment temperatures are considered to be advantageous for wastewaters with high oil and grease content, owing to the enhanced solubility of this contaminant at higher temperatures. Despite this advantage in thermophilic treatment, Çetin & Sürücü (1990), Barr et al. (1996), Tripathi & Allen (1999), Lapara and Alleman (1999) have documented the deterioration of sludge settleability with increasing temperature. The inability to separate sludge from effluent liquid combined with low sludge yields will result in washout of biomass and low quality effluent. Membrane technology was successfully employed in this experiment to overcome this problem. Though thermophilic reactor coupled with membrane is not a new concept and has been experimented by Lopetegui and Sancho (2003) and Klatt and Lapara (2003), the use of an immersed membrane at high temperatures is quite uncommon.