Influence of Ethylene Dichloride Concentration on the Methanogenic Activity of Anaerobic Biomass

In this study, the inhibitory effect of ethylene dichloride (EDC) on biodegradation was investigated using the specific methanogenic activity (SMA) Test of anaerobic biomass.
In the present study, 40 SMA tests were performed using 120-ml vials in batch mode. Substrate, biomass, and biogas occupied 66%, 17%, and 17% (v/v) of the volume of each vial, respectively. The duration of each batch was 10 days. Produced methane was measured through gas replacement with 2N KOH solution as CO2 absorbent. The chemical oxygen demand (COD) test was performed on samples before and after each test. The variation in temperature and pH were retained at 35 ± 2ºC and 7, respectively. The input COD was measured for each vial at the beginning and end of the experiment. EDC was analyzed through gas chromatography-mass spectrometry (GC-MS) at the beginning and end of the experiment.
Findings: In this study, at the concentrations of 500, 1000, 5000, and 20000 mg/l of EDC, 12.6, 9.9, 2.98, and 0.86 ml CH4/g VSS decrease in the production in methane was observed, respectively. A decline in the efficiency of COD removal was also observed in the mentioned concentrations. The efficiency of COD removal at the mentioned concentrations was 68.9, 70.5, 54.4, and 33.8%, respectively. The inhibitory effects of EDC on methanogenic activity of anaerobic biomass started at EDC concentrations of higher than 750 mg/l. The amount of cumulative methane at EDC concentrations of 750, 5000, and 20000 mg/l was 30.7, 9.86, and 1.9 ml, respectively. EDC removal efficacy at concentrations of 500, 2000, and 3000 mg/l was obtained using GC-MS and was equal to 95.2%, 94.7%, and 93.8%, respectively.
The results of this study indicated that EDC concentrations of higher than 750 mg/l caused a reduction in methane production and bacterial activity.