Biological pre-treatment to enhance low pressure membrane filtration for wastewater reclamation
Creators: name: Pramanik, Biplob
Publisher: name: RMIT University
Year: 2024

description: Wastewater effluent is a good target for water reclamation for industrial and agricultural uses. However, biologically treated secondary effluent (BTSE) contains polysaccharides, proteins, amino-sugars, humic materials, inorganics, particulate matter, and cell components which require further treatment. Low pressure membrane processes (microfiltration and ultrafiltration) are frequently employed for tertiary treatment. However, the deposition of the foregoing organic components causes membrane fouling which limits the efficiency of the reclamation process, therefore these components need to be removed to enable the sustainability of these processes. In this work, pre-treatment of BTSE using lab-scale biological activated carbon (BAC) was investigated to control organic fouling of microfiltration membrane via single- and multi-cycle filtration approaches. A mass balance for the organic content in the system confirmed that the carbohydrate content contributed more to the hydraulically reversible fouling than the proteins. <br><br>The increase in the flux decline with successive filtration cycles was attributed largely to the protein content of the feedwater. BAC treatment of the BTSE resulted in a marked improvement in permeate flux. This was mainly due to the effective removal of high molecular weight (MW) substances such as biopolymers by biodegradation by the microorganisms and removal of humic substances by adsorption by the activated carbon. Moreover, longer empty bed contact time (60 min cf. 40 min cf. 20 min) gave greater organics removal and led to improved microfiltration performance. BAC was also investigated as a pre-treatment to reduce the organic fouling and biofouling potential of RO membranes for the desalination of a moderately saline BTSE. The BAC effectively reduced the organic content and biofouling potential component of the RO membrane. The impact of cyanobacterial blooms (exemplified by Microcystis aeruginosa) in wastewater stabilisation lagoons on the BAC treatment of the BTSE and the resultant performance of the microfiltration process was evaluated by the addition of algal organic matter (AOM). BAC treatment substantially reduced the fouling potential of the AOM-containing BTSE. <br><br>When the BTSE was spiked with microcystin, BAC effectively reduced the microcystin concentration (by more than 90%). Over long term operation of the BAC system, high MW biopolymers were consistently removed, whereas the removal of humic substances decreased from 52% to 25% after two years of BAC operation due to the reduction in adsorption capacity of the activated carbon; this led to decrease in unified membrane fouling index from 78% to 43% indicating that humics also played an important role in microfiltration membrane fouling. Therefore, coagulation (5 mg Al3+ or Fe3+/L) and magnetic ion exchange resin (MIEX) pre-treatment for BAC were compared for enhancement of microfiltration performance. It was found that MIEX (10 mL/L) followed by BAC led to markedly greater organics and fouling reduction (93%) than coagulation combined with BAC (65% for alum + BAC and 70% for ferric chloride + BAC). This was shown to be due to the greater removal of humic substances by the MIEX. This study demonstrated that BAC is potentially a promising pre-treatment system for enhancing the performance of microfiltration in the reclamation of BTSE.