Reduction of nitrates in a photocatalytic membrane reactor in the presence of organic acids

The present study explores the capability of the Photocatalytic Membrane Reactor (PMR) technology to remove nitrates from drinking water sources in the presence of organic electron donors. A systematic investigation was performed in a laboratory-pilot PMR, employing a hybrid TiO2/UV-A catalysis-ultrafiltration process, using formic acid as the most favorable hole scavenger for nitrate reduction. The naturally occurring humic acid as well as the cheaper and harmless acetic acid were also tested as sacrificial electron donors. The performance of the PMR system was evaluated in respect of nitrate and Total Organic Carbon (TOC) percentage removal. The results demonstrate the superiority of formic acid regarding nitrate reduction, followed by acetic acid and humic acid, as well as the negligible effect of nitrates on organic mineralization. Formic acid was further used to assess the effects of molar organic/nitrate ratio, catalyst dosage and power of irradiation per unit volume (PR) on nitrate reduction. With the present laboratory-pilot, the near optimum nitrate removal was-60 % and the TOC reduction-85 %; selectivity to dinitrogen was in the range 65-90 %. Key issues for improving this synergistic process and related R&D directions are discussed.

Automated summary

The study examined the potential of Photocatalytic Membrane Reactor (PMR) technology for nitrate removal from drinking water with organic electron donors. Formic acid was found to be the most effective hole scavenger, followed by acetic acid and humic acid. The PMR system showed superior performance in nitrate reduction and total organic carbon percentage removal. Further research is needed to optimize the process for improved efficiency.