Bioelectrochemical Anaerobic Digestion Enhances Food Waste Leachate Treatment And Bioenergy Recovery

Food wastes（FWs）leachate is categorized as a complicated high-strength effluent that requires treatment to avoid eutrophication and other health risks.However,simultaneous bioenergy recovery and organic matter degradation are a promising way to treat food waste leachate.Thus,AD（AD）as an efficient biological process has been proposed to treat FWs.However,by incorporating a microbial electrolysis cell（MEC）into the AD process can enhance the entire process in terms of pollutant removal and energy recovery.In the study,for the treatment of FW leachate and the recovery of bioenergy,a continuous stirred microbial electrolysis cell（CSMEC）and a combined reactor of an extended granular sludge bed（EGSB）and MEC（EGSB-MEC）was developed.The organic loading rate（OLR）,influent chemical oxygen demand（COD）,and hydraulic retention time（HRT）,were used to evaluate the performance of both CSMEC and the EGSB-MEC processes.A BPANN mathematical model was also developed for control and optimization of the CSMEC and EGSB-MEC process.Microbial communities of the suspension sludge and electrode biofilm in the reactors under different operation conditions were also investigated based on 16S r RNA gene sequencing.Inocula（activated sludge）with 14212.47 mg/L mixed liquor suspended solids（MLSS）and 8156.13 mg/L mixed liquor volatile suspended solids（MLVSS）were used to start-up all reactors.Start-up period lasted for 100 days,the COD removal of the CSMEC reached a maximum of 88.2%,while that of the CSTR reached a maximum of76.25%.Biogas yield increased from 0.1 to 1.5 L/L/d in the CSMEC and 0.089 to 1.159L/L/d in the CSTR with the increase in OLR from 1.24 to 5.36 kg COD/m³.With increasing OLR,methane content in biogas increased from 56.81%to 79.86%in the CSMEC and from 49.85%to 64.59%in the CSTR,respectively.Both the performance of the CSMEC and CSTR was further investigated with the changes and influent COD and HRT.The highest COD removals in the CSMEC（94.38%）with an OLR of 4.26 kg _COD/m³and CSTR（79.8%）with an OLR of 8.13kg _COD/m³ were obtained,respectively,but they all subsequently declined slightly when OLR was increased.The mean p H in the CSMEC and CSTR over the course of the study was 7.91±0.4 and 7.76±0.1 respectively.NH₄⁺effluent in the CSMEC rose to an average of 153.62±18.47 mg/L and that of the CSTR averaged 174.05±29.7 mg/L.An increase in biogas and methane production was observed in both CSMEC and CSTR with a matching increase in OLR.Methane production increased from 0.72 to 4.79L/L/d,while biogas production increased from 1.09 to 6.27 L/L/d in the CSMEC,0.8 to5.22 L/L/d and of 0.46 to 3.88 L/L/d for biogas production and methane yield respectively in the CSTR.EGSB-MEC was operated to treat the effluent of CSMECs.The EGSB-MEC showed a maximum COD removal rate of 95.84%with an HRT of 24 h and an OLR of2.61 kg _COD/m³.d,while the EGSB had an OLR of 2.04 kg _COD/m³.d and the highest COD removal rate of 80.03%.The biogas production rate and methane yield of the EGSB-MEC increased by 0.14 to 1.67 L/L/d and 0.09 to 0.99 L/L/d,respectively.In the EGSB-MEC,methane and carbon dioxide content ranged from 52.65 to 747.61%and18.25 to 39.26%,respectivelyThe microbial populations in anaerobic sludges and electrodes biofilms were investigated by Illumina sequencing of bacterial 16S r RNA gene amplicons.Firmicutes,Synergistetes,Bacteroidetes,Thermotogae,Chloroflexi and Proteobacteria were observed to the dominant phyla in the sludge of the CSMEC.The dominant populations in the CSMEC biofilms were affiliated with Methanosaeta,Methanobacterium,Methanosarcina and Methanocorpusculum.Methanosaeta,Methanosarcina,Methanobacterium and Methanofollis were the dominant genera aligned with the CSTR sludge.The dominant bacterial phyla belonged to Bacteroidetes,Proteobacteria,Firmicutes,Chloroflexi,Synergistetes,and Actinobacteria in the EGSB-MECcm biofilm,while Bacteroidetes,Proteobacteria,Firmicutes,Synergistetes,and Chloroflexi dominated the EGSB sludge.The dominant phylum,Euryarchaeota,was found in all four（4）samples,with relative abundances of 82.46%in the EGSB sludge with complete mixing,91.68%in the anode biofilm of EGSB-MEC,92.94%in the cathode biofilm of EGSB-MEC and 91.00%in the EGSB-MEC sludge with complete mixing.A backpropagation-artificial neutral networks（BPANN）was used to estimate the biogas yield,in both the CSMEC and EGSB-MEC.The BPANN model demonstrated significant performance,indicating possible control and optimization of the AD-MEC process.For the exactitude of the optimal BPANN model,the determination coefficient（R²）,index of agreement（IA）,and fractional variance（FV）were 0.8902,0.925 and0.0715 in the CSMEC,0.9414,0.966 and 0.0484 in the CSTR,0.9743,0.9868 and0.0291 in the EGSB-MEC and 0.9538,0.9757 and 0.0309 in the EGSB respectively.The findings of this study revealed that BPANN is more accurate and reliable in predicting and optimizing process parameter interactions in connection to biogas production in both the CSMEC,CSTR,EGSB-MEC and EGSB.Most of all,the coupling of the CSMEC to the EGSB-MEC process was deemed a promising technique for the treatment of FWs leachate and bioenergy production.The microbial communities discovered contributed to the satisfactory performance in terms of pollutant removal and bioenergy generation.The developed BPANN model was capable of giving accurate AD-ME predictions and simulations,as well as controlling and optimizing the AD-MEC process for improved efficiency of biogas production.