Calcium effect on anaerobic biological treatment of fresh leachate with extreme high calcium concentration

• Treatment of leachate with extreme high calcium from MSW incineration plant.
• Determine calcium suppression threshold on anaerobic granules treating leachate.
• Mechanism study on calcium precipitation in granules.
• Impact comparison between calcium concentration and calcium precipitation.
• Microbial community analysis for granules under leachate with high calcium condition.

Fresh leachate from municipal solid waste (MSW) incineration plant in China always contains extremely high concentration of calcium which would reduce the bioactivity of microorganisms and lead to calcium precipitation in granules. This paper investigated the effect of high concentration of calcium on anaerobic granular sludge without calcium precipitation by static tests for 72 h, and on anaerobic bio-treatment process for treating fresh leachate in a laboratory-scale expanded granular sludge bed (EGSB) reactor with calcium precipitation for 132 d. The results showed that, suppression thresholds of calcium concentration for anaerobic granular sludge were 5000 mg/L from both static tests and EGSB reactor operation. Calcium precipitation in anaerobic granules was a gradual formation process, mainly in the form of calcium carbonate calcite. Compared with calcium precipitation, high calcium concentration was mainly responsible for the decrease of COD removal efficiency in treatment process. Only a few microorganisms survived when calcium concentration increased over 5000 mg/L, which was mainly concentrated in Clostridium of bacteria and Methanosaeta of archaea.