jesc.ac.cn Journal of Environmental Sciences 20(2008) 1281–1287 Occurrence and removal of organic micropollutants in the treatment of landfill leachate by combined anaerobic-membrane bioreactor technology XU Yiping, ZHOU Yiqi, WANG Donghong, CHEN Shaohua, LIU Junxin, WANG Zijian ∗ State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. E-mail: ypxu@rcees.ac.cn Received 3 January 2008, revised 18 February 2008; accepted 6 March 2008 Abstract Organic micropollutants, with high toxicity and environmental concern, are present in the landfill leachate at much lower levels than total organic constituents (chemical oxygen demand (COD), biochemical oxygen demand (BOD), or total organic carbon (TOC)), and few has been known for their behaviors in different treatment processes. In this study, occurrence and removal of 17 organochlorine pesticides (OCPs), 16 polycyclic aromatic hydrocarbons (PAHs), and technical 4-nonylphenol (4-NP) in landfill leachate in a combined anaerobic-membrane bioreactor (MBR) were investigated. Chemical analyses were performed in leachates sampled from different treatment processes, using solid-phase extraction and gas chromatography with electron capture detector and mass spectrometry. Concentrations of OCPs, PAHs, and 4-NP in the raw leachate were detected within the range from ND (not detected) to 595.2 ng/L, which were as low as only 10 −7 –10 −5 percentage of TOC (at the concentration of 2,962 mg/L). The removal of 4-NP was mainly established in the MBR process, in agreement with removals of COD, BOD, and TOC. However, the removals of OCPs and PAHs were different, mainly achieved in the anaerobic process. High removal efficiencies of both total organic constituents and organic micropollutants could be achieved by the combined anaerobic-MBR technology. The removal efficiencies of total organic constituents were in the order of BOD (99%) > COD (89%) > TOC (87%), whereas the removal efficiencies of investigated organic micropollutants were as follows: OCPs (94%) > 4-NP (77%) > PAHs (59%). Key words: anaerobic; landfill leachate; membrane bioreactor; organic micropollutant Introduction Landfill leachate constitutes a very complex mixture, which may contain a large number of xenobiotic organ- ic compounds encountered in the solid waste disposal site or formed as a result of chemical and biological processes within the landfill (Banar et al., 2006; Urase and Miyashita, 2003). Among them, some organic mi- cropollutants identified are highly toxic, carcinogenic, or even mutagenic, such as polycyclic aromatic hydrocarbons (PAHs), halogenated pesticides, phenols, and so on, al- though they are often found in trace levels (μg/L, ng/L or even lower) (Banar et al., 2006; Ozkaya, 2005). These organic micropollutants may create a potential risk to the quality of receiving water bodies and become a new pollution source of groundwater or surface waters (Alkalay et al., 1998; Baun et al., 2004). Hence, several studies have reported growing concern on identification, occurrence, and toxicity of these organic micropollutants in landfill leachates (Banar et al., 2006; Baun et al., 2003, 2004; Bras * Corresponding author. E-mail: wangzj@rcees.ac.cn. et al., 2000; Castillo and Barcelo, 2001; Grøn et al., 2000; Herbert et al., 2006; Nascimento Filho et al., 2003; Noma et al., 2001; Ozkaya, 2005; Urase and Miyashita, 2003), which are summarized in Table 1. Organic micropollutants contribute little to the level of total organic constituents, such as chemical oxygen demand (COD) and total organic carbon (TOC). Therefore, the main removal of COD and TOC may not indicate the significant decrease of trace organic contaminants, which has been seldom reported. The treatment of leachate is very complicated, expen- sive, and generally requires various and combined process applications (Ozturk et al., 2003). Biological techniques, anaerobic and aerobic treatment systems, have been stud- ied in landfill leachate during the last few decades, which have shown high performance. However, there are still some problems and challenges depending on characteris- tics of leachate (such as age) for application of biological techniques, which are hardly efficient for removal of biorefractory organics (Wiszniowski et al., 2006). Hence, physicochemical processes, such as membrane processes, advanced oxidation processes, and so on, have been widely used as posttreatment of biologically pretreated landfill