Coal chemical industry membrane concentrates: characterisation and treatment by ozonation and catalytic ozonation processes

Abstract

Environmental context Reverse osmosis (RO) is widely used for the treatment of hazardous wastewaters produced from the coal chemical industry (CCI) to achieve zero liquid discharge however the use of RO inevitably results in accumulation of refractory organic matter in the RO membrane concentrate, the treatment of which is challenging. This work provides useful insights into the organic composition of RO concentrates obtained from a range of real CCI wastewaters. The efficacy of treatment of these concentrates by ozonation processes is assessed as is the cost effectiveness of such treatment. Rationale The enactment of increasingly stringent regulations has prompted the implementation of membrane technologies such as reverse osmosis (RO) in the management of coal chemical industry (CCI) wastewaters with the goal of achieving zero liquid discharge (ZLD). However, this practice inevitably results in the production of high salinity concentrates containing refractory organic matter. Methodology In this study, we characterised the organic composition of RO concentrates obtained from the CCI using a variety of methods including liquid chromatography–organic carbon/nitrogen detection (LC-OCND) and investigated the degradability of organic compounds present in these concentrates by ozonation and catalytic ozonation processes. Results and discussion Organic analysis using LC-OCND revealed that humic-like substances and low molecular weight neutral compounds were the dominant constituents in the CCI concentrates examined. Measurement of degradability of the CCI concentrate by a pure ozonation process showed low treatment efficiency (~20% dissolved organic carbon (DOC) removal) as a result of the refractory nature of the organic compounds present in the wastewater. The degradation of these organics by a catalytic ozonation process employing a commercially available Fe-oxide based catalyst was higher than that observed by pure ozonation although the extent of organics removal (DOC removal ~47%) is still low due to the refractory nature of the organics as well as the influence of salts on the catalyst performance. Techno-economic analysis of the pure ozonation and catalytic ozonation processes indicated that the total cost of implementation of the ozonation processes (homogeneous or heterogeneous) for CCI concentrate treatment is negligible compared with the overall cost of the complete ZLD process.