Effect of coagulant addition on membrane fouling and nutrient removal in a submerged membrane bioreactor

Abstract

This study was conducted to investigate the characteristics of membrane fouling and removal of phosphorous in a membrane bioreactor process by addition of inorganic coagulants directly into aerobic tank of a pre-anoxic nutrient removal system. In order to determine the specific cake resistance of activated sludge floc for different coagulants used, jar test and dead-end filtration experiments were performed. The permeate flow rate increased as well as phosphate removed effectively, as the dosage of alum increased, both in the jar test and dead-end filtration experiments. Considering the phosphorous removal capacity, flux variations, pH range and specific resistance, it seems that the use of alum was effective in concentration range from 200 to 500 mg/L. Ferric chloride was efficient in causing decline in specific resistance, on the other hand, it caused decrease in pH than that of alum. The bench scale MBR performance test was conducted to evaluate the effect of coagulant addition into a MBR process. It was found that addition of alum in the aeration tank had a positive effect on phosphorus removal along with minimization of membrane fouling. The MBR performance elucidated that addition of 30 mg/L of alum was effective to remove 3 mg/L phosphorous in feed for MBR process with reduction in membrane fouling factor without deterioration in nitrogen removal efficiency. The particle size analysis further confirmed that coagulation with alum could minimize membrane fouling because the relative small particles in the MBR reactor, which are considered as a cause of membrane fouling, could became bigger particles due to the addition of coagulant.