Effect of Oxic-Settling Anoxic Process on Operation Parameters and Biological Excess Sludge Reduction in Sequencing Batch Reactor Activated Sludge

Background and One of the solutions for sludge production is to reduce that via decreasing the yield coefficient by oxic-settling anoxic process with different oxidation reduction potential (ORP) in sequencing batch reactor (SBR) activated sludge.
We used 2 SBR reactors (20 L volume) that were controlled online. At a steady state in reactors, some parameters such as COD, DO, SVI, ORO, dry solids and moisture of sludge were tested during 12 months. Finally, yield coefficient and reduction rate of biological excess sludge were studied.
At 10-day sludge age, the best removal efficiency of COD (95%) was seen without any sludge bulking problems and the kinetic coefficient Y and Kd were 0.58 and 0.058, respectively. The anoxic and anaerobic phase of the sludge holding tank showed that sludge storage after 7 hours in the reactor with ORP=-238 decreased the yield coefficient from 0.58 in the control reactor to 0.25g of biomass in g of COD. Consequently, the excess sludge decreased by almost 60%. On the other hand, compared to the control reactor (92 ml/g), the SVI reduced to less than 40 ml/g.
Using holding tanks in aerobic conditions with ORP greater than 230mv could cause appropriate settling and lead to a high efficiency of COD removal from wastewater.