Submerged anaerobic membrane bioreactors for Kraft evaporator condensate treatment : feasibility and membrane fouling studies

Abstract

In this study, the primary goal was to develop better treatment technologies for energy recovery from Kraft evaporator condensate (EC) using thermophilic and mesophilic submerged anaerobic membrane bioreactors (SAnMBRs). Specific objectives were to study the feasibility of using submerged AnMBRs for Kraft evaporator condensate treatment, to quantify the chemical oxygen demand (COD) removal efficiency and biogas production (chemical composition and rate), to characterize sludge properties, including particle size and extracellular polymeric substances (EPS), and to understand and control membrane fouling. The feasibility of using a submerged anaerobic membrane bioreactor (AnMBR) for Kraft evaporator condensate treatment was studied at 3 7°C over a period of 7 months. Under the various tested organic loading rates, a high, stable chemical oxygen demand (COD) removal efficiency was achieved for three stages of influent CODs. The permeate was of high quality, and the resulting biogas, composed of 85% methane, was of excellent fuel quality. It was found that the bubbling of recycled biogas was effective for in-situ membrane cleaning, depending on the recycle flow rate of produced biogas. Toxic feed shocking, due to total reduced sulfur (TRS) compounds and a high pH (due to pH probe failure) resulted in deflocculation, which led to an increase in membrane filtration resistance caused by fine floes.