Anaerobic membrane bioreactors: enhancing performance of an external tubular nano filtration membrane module
University of New Brunswick
An anaerobic membrane bioreactor (AnMBR) integrated with an external nano filtration tubular membrane module was operated for approximately 577 days in a cross flow mode to treat a potato-starch based high-strength (highly concentrated in chemical oxygen demand (COD)) wastewater. Research objectives were to enhance the physical and chemical aspects of membrane fouling prevention, without hindering the reactor performance. First, the rate of membrane fouling was reduced through optimizing the physical cleaning processes applied to the membrane module. Secondly, different chemical cleaning methods were applied to two membrane modules with a goal of selecting an optimal cleaning methodology to apply to fouled membrane modules. Investigations conducted alongside the chemical and physical cleaning optimizations analyzed a decline in the methanogenic activity of the biomass, the foaming propensity of the reactor, and a micronutrient deficiency affecting the performance of the bioreactor. Conclusions found that incorporating a single chemically enhanced backwash (CEB) cycle offered a larger increase in sustainable membrane flux (therefore lower rate of membrane fouling) than varying the permeate backwash duration, frequency, or flow rate. Throughout this period of data collection the reactor was able to maintain a COD removal efficiency greater than 97%, a total suspended solids (TSS) removal efficiency greater than 99%, and methane yields within 71% – 89% of theoretical. A caustic clean without backwashing cycles and with a longer soak-time using a mixed 1% NaOH and 1% Sodium Hypochlorite solution was the best chemical cleaning methodology. Organic loading rate (OLR) had the largest influence on the foaming propensity of the reactor, and biomass activity declined by approximately 65% over the course of this research project.