Effective treatment of reverse osmosis concentrate from incineration leachate using direct contact membrane distillation coupled with a NaOH/PAM pre-treatment process

Reverse osmosis is frequently used to process biologically treated leachate from municipal solid waste incineration plants. Reverse osmosis concentrate from incineration leachate (ROCIL) contains extremely high concentrations of monovalent and divalent ions (e.g. Na+, K+, Mg2+, and Ca2+) and some refractory organic pollutants (e.g. humic substances). In this study, lab-scale direct contact membrane distillation (DCMD) coupled with pre-treatment was applied to treat ROCIL NaOH and polyacrylamide (PAM) chemical precipitation and coagulation pretreatment effectively removed Ca2+ and Mg2+ (>99%) from the ROCIL, which also significantly improved the treatment efficiency of DCMD and slowed down membrane fouling caused by Mg-5(CO3)(4)(OH)(2)center dot 4H(2)O and CaCO3 scaling on the membrane surface. During the long-term operation of DCMD, ROCIL was concentrated 21 times and nearly all of the inorganic ions (>99.9%) and organic matter (>99%) were removed from the pre-treated ROCIL A strong interaction occurred due to the accumulation of humic substances and metal ions in the feed solution, which lead to inorganic and organic scaling deposited on the membrane surface and pores, but the wetting phenomenon was not serious. These results demonstrated that DCMD coupled with NaOH/PAM pretreatment can be a potential alternative for further treatment and concentration of ROCIL to obtain high quality water. (C) 2018 Elsevier Ltd. All rights reserved.