Bisphenol A retention in the direct ultrafiltration of greywater

Decentralised treatment is an increasing trend in the attempts to manage water more wisely in light of water restrictions, overconsumption and drought. Greywater is a fraction of household wastewater that offers the potential to be treated locally and then reused for garden irrigation, car washing and toilet flushing. In this paper the performance of submerged and direct ultrafiltration (UF) of synthetic greywater was investigated with regards to organic trace contaminant, namely bisphenol A (BPA), and fouling. The synthetic greywater solution consisted of inorganic particulates (kaolin), organic fibres (cellulose), protein (casein), surfactant (sodium dodecyl sulphate, SDS), humic acid (HA), calcium, sodium chloride electrolyte and sodium bicarbonate buffer. Results indicate that UF can remove 30–45% of BPA. This removal is attributed to partitioning of the compound to the membrane material, suspended and dissolved solids as well as the fouling layer. Humic acid and calcium were the main contributors to fouling, which also affected BPA retention. Fouling increased with an increase in HA concentration, which calcium contributed most to fouling at a concentration of about 0.5 mM. At higher concentration of calcium aggregation appeared to reduce fouling significantly. The implications of this study are that trace contaminant–solute interactions play an important role for retention potential and this relationship offers room for optimization by selecting particulate additives with a high affinity for target compounds. This is of particular importance if such contaminants are a concern (which is dependent on the product water application) and in the absence of biological treatment which is in this case not desired. The separation of greywater into fractions of low and high strength is of advantage if this can eliminate the presence of humic substances.