Mechanism and favourable operating conditions of organic substrate removal in Microaerophilic Upflow Sludge Bed Reactor (MUSB)

The experimental investigation of mechanism and favourable operating conditions of organic substrate removal in Microaerophilic Upflow Sludge Bed Reactor (MUSB) was carried out. COD was degraded due to attached aerobic biomass in Aeration Vessels (AV). And in nonaerated Biological Vessels (BV) COD was found to be degraded either due to aerobic metabolism utilizing oxygen coming from AV or due to sulfur metabolism utilizing sulfate as an electron acceptor. Sulfate reducing bacteria outcompeted methane producing bacteria. Yield coefficient was evaluated using Phosphorus balance and was found to vary between 0.4 and 0.5. With increase in retention time COD removal efficiency was increased. At an organic loading of 1.4 kg COD m−3 d−1, 80% of COD removal efficiency was achieved in 4,5 h. The maximum loading which can be applied was found to be limited due to availability of sulfate ion in the influent. At an organic loading of 2.4 kg COD m−3 d−1, COD removal efficiency was reduced to 60%. At higher loading i.e. 2.4 kg COD m−3 d−1, at a retention time of 3.5 h, sulfide was found to be dissolved in the effluent and contributed as inorganic COD and reduced the COD removal efficiency. Upflow velocity in BV affected considerably the shape and characteristics of granules formed. At an upflow velocity of 110–140 m d−1, rigid granules with diameter varying from 4 to 6 mm were formed.