Elimination of trace organics in an MBR/RO system for water reuse

An intensive programme for detection of trace organics was performed in a membrane bioreactor (MBR) plant in Almunecar (south of Spain) over 1 year. The compounds investigated included 15 pharmaceutically active compounds, 12 polycyclic aromatic hydrocarbons and eight other compounds (nonylphenols, linear alkylbenzene sulphonates and phthalates). The MBR operated with two lines in parallel using a hollow fibre and a flat sheet membrane respectively. Additionally, a reverse osmosis (RO) plant treated the MBR permeate over 1 month and the elimination of trace organics by the MBR/RO system was assessed. The elimination efficiency of trace organics by the MBR was similar to that found in a conventional activated sludge plant treating the same influent. The concentration of trace organics was reduced after the MBR to a great extent and no significant differences were found between the two lines operating in parallel. The elimination efficiency increased up to 80–100% after passing the RO system. The results indicated that the MBR effluent reached the standard required by the Spanish Royal Decree for Water Reuse and can therefore be reused for multiple purposes, but advanced treatment like RO is necessary when the highest effluent quality is required.