Enhancement of Anaerobic Methane Production by Removal of Organic-bonding Metals from Sewage Sludge

Abstract

To improve anaerobic digestion biogas yield, the removal of organic-bonding metals by EDTA pretreatment was investigated to strengthen the anaerobic biogas effect. The results showed that after EDTA pretreatment (experimental group), the organic-bonding metals were reduced from (5.09±0.57)% to (1.37±0.20)% (calculated with TS) and dissolved organic matter increased significantly (SCOD improved 627%), suggesting that this method could remove a large amount of organic-bonding metals and enhance the dissolution of organic sludge. According to the results for the apparent activation energy (AAE) of sludge organic matter dissolution, the AAE of the experiment group was 36% lower than the control group, showing that pretreatment could effectively reduce the reaction energy barrier for organic matter dissolution. In a test of anaerobic acid production lasting 16 days, the VFAs of the experiment group were higher than the control group, with the largest upgrade of 42%. In the anaerobic methane production test (BMP) that lasted for 22 days, compared with control group, the accumulated biogas production of the experiment group increased by 48%. Through further research on the dynamics of methane production, the rate-limiting step in the experiment group was methanogenesis, while that of the control group was hydrolysis, indicating that removal of organic-bonding metals by EDTA pretreatment could effectively accelerate the hydrolysis rate.