Effect of Loading Rate and HRT on the Removal of Cephalexin and 7- ACA Antibiotic Intermediates During the Operation of Submerged Flat Sheet Membrane System for Pharmaceutical Wastewater Treatment

The viability of treating high-concentration antibiotic wastewater by an anaerobic membrane bioreactor (AMBR) was studied using submerged flat sheet membrane. The major problems for these modules are concentration polarization and subsequent fouling. By using gas-liquid twophase flow, these problems can be ameliorated. The objective of the study was to determine the effect of organic loading rate and hydraulic retention time on the removal of cephalosporin derivative, viz., cephalexin (C16H17N3O4S.H2O) and the intermediates [7-amino-3-deacetoxycephalosporanic acid (7-ADCA) and acyl group (Phenyl acetic acid)] in the AMBR with enhanced biodegradation using bioaugmentation technique. The effect of various hydrodynamic factors such as airflow rate, nozzle size, intermittent filtration, channel gap width, feed concentration, imposed flux, and the use of membrane baffles were investigated. Experiments conducted on model feeds showed that fouling reduction increased with air flow rate up to a given value and beyond this flow rate no further enhancement was achieved. Based on the critical examination of results, the industry is looking for the alternatives of either direct disposal of 7-amino-3-deacetoxycephalosporanic acid (7-ADCA) and Phenyl acetic acid or for further degradation and disposal, which will essentially require additional cost and maintenance. The present regulatory standard implemented in developing countries does not envisage such disposal alternatives and hence the present study was aimed at the complete removal of intermediates [(7-ADCA) and Phenyl acetic acid] prior to discharge. The study showed the importance of the size of the gap between the submerged flat sheet membranes and observed that as the gap was increased from 5 mm to 12 mm, the fouling became worse and the degree of fouling reduction by two-phase flow decreased by at least 37% based on suction pressure rise. The study also reported the effects of baffles in improving air distribution across a flat sheet submerged membrane. It was found that baffles could decrease the rate of fouling by at least a factor of 1.7, and significantly increase critical flux.