Treatment of secondary effluent with biological activated carbon to reduce fouling of microfiltration membranes caused by algal organic matter from Microcystis aeruginosa

Abstract

Wastewater stabilisation lagoons frequently suffer from cyanobacterial blooms which can negatively impact subsequent water reclamation due to fouling of membranes by the resultant algal organic matter (AOM). Biological activated carbon (BAC) was investigated as a pre-treatment for reducing the fouling in the microfiltration (0.1µm PVDF) of biologically treated secondary effluent (BTSE) to which AOM had been added. The AOM was extracted from Microcystis aeruginosa in stationary phase which had been grown in either MLA growth medium or BTSE and so had different organic composition. Although the DOC concentration was the same, the feedwater containing AOM from the MLA culture led to a greater flux decline than the AOM from the BTSE culture due to its higher biopolymer content (MW≥20,000Da). BAC treatment substantially reduced the fouling potential of the BTSE (with and without the added AOM) due to biodegradation of biopolymers by the microorganisms and adsorption of humic substances by the activated carbon. When the BTSE was spiked with the cyanotoxin microcystin-LR, the BAC treatment gave a microcystin reduction of more than 90%. This study demonstrated the potential of BAC for mitigating the impact of AOM and removing cyanotoxin when treating cyanobacterially impacted secondary effluent using low pressure membranes.