Biomethanation of Sewage Sludge with Food Waste Leachate Via Co-Digestion

Impact of dewatering inorganic coagulants on anaerobic digestion treating food waste leachate

Anaerobic digestion of food waste leachate (FWL) provides a viable solution for waste treatment and energy production. Returning solids from digested sludge to the reactor maintains a high microbial concentration and enhances digestion efficiency. However, this requires coagulants because the digestate has low dewaterability. This study analyzed methane production and microbial communities using biochemical methane potential tests for inorganic coagulants (AlCl3, Al2(SO4)3, FeCl3, and Fe2(SO4)3) in FWL treatment. Cumulative methane production was the highest in the control and decreased in the order of Fe2(SO4)3, AlCl3, FeCl3, and Al2(SO4)3. Iron ions inhibited H2S production while aluminum ions increased it compared to the control group. Despite the absence of significant changes in microbial communities following coagulant injection, a substantial increase in damaged cells was observed. These findings highlight the intricate repercussions of coagulant introduction in anaerobic digestion, emphasizing notable alterations in methane production dynamics and the integrity of microbial cells.

Anaerobic co-digestion of sewage sludge pretreated by thermal hydrolysis and food waste: gas production, dewatering performance, and community structure

Anaerobic co-digestion can effectively break the limitations of mono-digestion. However, there are still some problems such as long residence time, unsatisfactory methane yield, and unstable performance for co-digestion of sewage sludge (SS) and food waste (FW). Therefore, the SS in the reactor treating co-digestion of SS and FW is considered to be pretreated by thermal hydrolysis. In this work, the anaerobic co-digestion of SS of thermal hydrolysis pretreatment (THP) and FW significantly improved the stability, methane production of the digestive reactor, and dewaterability of the digested sludge. The R6 obtained the most cumulative methane production (315.76 mL/g VS). In addition, compared to R3, the cumulative methane production and maximum methane production rate of R5 increased by 9.93% and 14.56%, respectively. The dewaterability of R4, R5, and R6 was improved, while the dewatering performance of the R3 decreased to a greater extent. The results of the kinetic model fitting were consistent with the experimental results. Among them, the hydrolysis constants (Kh) of anaerobic co-digestion of THP-SS and FW were 0.121, 0.130, and 0.114 d-1, respectively, which were higher than those of other groups. And the estimated lag time (λ) of co-digestion was also lower than that of mono-digestion groups. Microbial community analysis indicated that the bacterial diversity and richness of anaerobic co-digested groups of THP-SS and FW were enhanced, while the methanogens with acetoclastic pathway became the main methanogenic microorganisms. This work provides essential information on anaerobic co-digestion containing different THP-SS contents.

Biogas recovery from fresh landfill leachates by using a coupled air stripping-up follow anaerobic sludge blanket (UASB) process

The present study focuses on fresh leachates treatment using anaerobic digestion. To overcome the unsuitable raw characteristics, appropriate pretreatment conditions were identified based on Batch tests. A subsequently optimized pretreatment-anaerobic two stages UASB coupled treatment was studied. The performance of the overall coupled treatment was assessed by monitoring volatile fatty acids (VFA), COD and ammonium removal, and biogas performance. Results showed that combining acidity correction to short aeration gives a synergetic effect and allowed appropriate anaerobic start-up conditions. Under continuous aerobic pretreatment-UASB digestion, significant removal of NH+4 (75.87%), COD (19.14%), and VFA (20.3%) were achieved during the aeration step resulting in the total abatement of 88.66%, 83.6% and 70.39% for NH+4, COD, and VFA, respectively. The process allowed good biogas performance up to 2,470 mL biogas/L and 123 mL CH4/gCOD removed, with gradual improvement from the first to the second UASB reactor. Inlet COD and VFA feeding rate seemed to be the main key parameters with 45.37 g COD/L.d and 18.43 g VFA/L.d as a critical threshold. Therefore, the anaerobic digestion of high COD leachates is highly feasible and the aerobic–anaerobic coupled treatment is a promising technical scenario that deserves further studies.