Intermediate Accumulation and Process Stability for Facultative and Obligate Anaerobic Treatment of Leachate from Waste Transfer Stations

The leachate from municipal solid waste transfer stations has a complex composition of pollutants, contains high concentrations of organic matter, and produces odors. The anaerobic digestion of leachate generates excessive volatile organic acids (VFAs), acidifying the digestate and destabilizing or even collapsing the anaerobic process. To solve these issues, we set up a facultative anaerobic system with air exposure and an obligate anaerobic system without air exposure to explore the impact of anaerobic degree on intermediate accumulation and anaerobic process stability. When the organic loading raised from 0.6 to 6.0 kg COD/(m(3)d), VFA accumulation in the facultative system peaked at 3.30 g COD/L, and the chemical oxygen demand (COD) removal rate dropped from 95% to 60%. By contrast, the obligate system remained stable, with VFA concentrations below 0.50 g COD/L and COD removal rates between 85% and 99%. Microbial sequencing shows that VFA-oxidizing bacteria enhanced VFA degradation, such as Syntrophomonas and Smithella, which increased from 4.62% and 0.76% in the facultative system to 17.64% and 0.88% in the obligate system, respectively. Coenzyme F420 concentration as an indicator of methanogenic activity was 50% higher in the obligate system. Therefore, an obligate anaerobic system is promising to alleviate acidification for stable anaerobic digestion of leachate.