Biofouling control in reverse osmosis membranes by concentrated free ammonia in hydrolysed urine

Abstract

Reusing source-separated urine as fertiliser enhances wastewater circularity, but further concentration is needed. Reverse osmosis (RO) is a promising option due to its low energy consumption but is susceptible to biofouling. Free ammonia in hydrolysed urine (HU) can be a biocidal agent at concentrations reached in RO concentrates. This study investigated the biocidal effects of concentrated free ammonia in concentrated HU and the feasibility of using it to reduce RO biofouling. Hydrolysed urine was pre-concentrated at different volume reduction factors (VRFs) (1.0, 1.7, 2.3 and 3.0) and was recirculated through a RO system for seven days. Using 3.0 VRF HU as feed, the RO permeate flux decline was 67 % lower than 1.0 VRF HU. The number of bacterial cells on the RO membrane exposed to 3.0 VRF HU was four orders of magnitude lower than 1.0 VRF HU. The dead bacteria fraction increased from 1 % with 1.0 VRF HU to 68 % with 3.0 VRF HU. The mass of organic foulants was reduced by 98 % with 3.0 VRF HU compared to 1.0 VRF HU. This study shows free ammonia in 3.0× concentrated HU is sufficient to reduce fouling in RO, which can potentially reduce the operational costs.