BACKGROUND This study used particle size distribution (PSD) to reveal how chemical conditioning inflicted changes on different chemical oxygen demand (COD) size fractions to improve the potential of two‐phase membrane separation as an effective preliminary step for the sustainable management of olive processing wastewaters. RESULTS Experiments were designed to explore: (i) the potential of membrane separation as a pretreatment step; and (ii) the way in which chemical conditioning improved the removal potential of membrane treatment. Particle size distribution analysis was conducted to observe changes inflicted on different COD size fractions by chemical conditioning. The chemically enhanced membrane process achieved 95% COD removal, reducing the effluent COD to 6000–8000 mg L−1 range and the total phenol down to 100 mg L−1. Chemical conditioning also removed a significant portion of soluble COD, so that the resulting PSD fingerprint in the effluent was properly reshaped to allow effective removal by membrane treatment. CONCLUSION The investigated treatment schemes involving pretreatment of oil wastewater by chemical conditioning together with membrane filtration offered high COD reduction in the effluent and biodegradable permeate when properly diluted for co‐treatment with a compatible wastewater stream. The use of chemical conditioning prior to membrane filtration improved final permeate quality and ultrafiltration membrane flux. © 2016 Society of Chemical Industry

BACKGROUND The study focused on the biodegradation of pretreated olive mill wastewater (OMW) properly diluted in and mixed with a biodegradable substrate and/or domestic sewage stream. It utilized the permeate of a chemically conditioned two‐stage ultrafiltration/nanofiltration system with COD of 5700 mg L−1 and a total phenol content of 100 mg L−1. Peptone mixture with similar characteristics to domestic sewage was adopted as the biodegradable synthetic substrate. The study relied on two sets of microbial culture; one acclimated to peptone and the other to a mixture of peptone and domestic sewage. Respirometric analyses were conducted on pretreated OMW diluted in the selected substrate using corresponding biomass seeding. RESULTS Model evaluation of the oxygen uptake rate profiles indicated that the pretreated OMW was fully consumed in the respirometric tests. There were no inhibitory/toxic impacts of OMW dosing on the biomass. The entire biomass participated in the utilization of OMW/substrate with no metabolic adjustment problems. CONCLUSION Experimental results provided conclusive evidence that co‐treatment with a domestic sewage stream is a viable option for OMW management, after a chemically conditioned two‐stage filtration used as the pretreatment step. Pretreatment removes the recalcitrant nature of the wastewater, which becomes fully biodegradable under appropriate dilution and mixing conditions. © 2016 Society of Chemical Industry