Simulation and optimization of up flow anaerobic sludge blanket reactors (UASBS) in a dairy waste water treatment plant

Abstract

Anaerobic digestion is commonly used in industrial waste water treatment applications and it is a combination of many biochemical and physicochemical processes. Modeling and simulation of an anaerobic digestion is very vital to identify the behavior of industrial waste water treatment plant to optimize its operations. In this research, anaerobic digestion model called ADM1(Anaerobic digestion model no 1) developed by IWA task group is applied to model and simulate UASB reactors. ADM1 model comprises with dynamic state variables which represent all biological and physic chemical reactions. This model was built in simulator called Aquasim 2.1f (Reichert, 1998).To model UASB reactors, simplified model is proposed based on different research compartments.UASB modeled by simulator taking as three CSTR compartments named sludge bed, blanket and settler. Influent for experimented waste water plant is waste water generated from dairy plant. Experiments were conducted at waste water treatment plant (WWTP) under three volumetric flow rates 10m3/d,15m3/d and 25m3/d. plant is actually operates at 25m3/d. Three parameters such as cumulative gas volume, pH and COD were measured. At the same volumetric flow rate WWTP was simulated with the new model and parameters such as VFA, gas composition ,inhibition and biomass growth rates were obtained. By varying recycle ratio from bed to blanket and settler to blanket, appropriate recycle ratio is replaced to get best fitted model. (bed to blanket-0.8 and settler to blanket 0.6). Optimization was performed under two scenarios.ie by varying volumetric flow rates and input COD level. it was found that above 30m3/d UASB become unstable producing 21% of CH4 and 75% of CO2 .Also it can be found that 7500mgCOD/l can be treated at the volumetric rate of 30m3/d without any instability