Long-term operation of a pilot-scale anaerobic membrane bioreactor (AnMBR) treating high salinity low loaded municipal wastewater in real environment

•Elevated OLR by fermentation liquid only increased biogas production not CH4 content.•Membrane fouling occurred following the addition of fermentation liquid.•High salinity did not affect the overall TMP value adversely.•Chloride concentration above 1500 mgCl− L−1 affected the biogas production adversely.•The final permeate of the AnMBR appears of high quality. Long term operation of an anaerobic membrane bioreactor (AnMBR) treating municipal wastewater was investigated in a real seawater intrusion spot in Falconara Marittima (Central Italy) on the Adriatic coastline. Changes in biological conversion and system stability were determined with respect to varying organic loading rate (OLR) and high salinity conditions. At an OLR of 1 kg COD m3−1 d−1, biogas production was around 0.39 ± 0.2 L d−1. The increase of the OLR to 2 kg COD m3−1 d−1 resulted in increase of biogas production to 2.8 ± 1.5 L d−1 (with 33.6% ± 10.5% of CH4) with methanol addition and to 4.11 ± 3.1 L d−1 (with 29.7% ± 11.8% of CH4) with fermented cellulosic sludge addition. COD removal by the AnMBR was 83% ± 1% when the effluent COD concentration was below 100 mg O2 L−1. The addition of the fermented sludge affected the membrane operation and significant fouling occurred after long-term filtration, where the trans-membrane pressure (TMP) reached up to 500 mbar. Citric acid solution was applied to remove scalants and the TMP reached the initial value. High saline conditions of 1500 mgCl− L−1 adversely affected the biogas production without deteriorating the membrane operation. The treated effluent met the EU quality standards of the D.M. 185/2003 and the new European Commission Resolution for reuse in agriculture.