Regulation Of Selective Acidogenic Fermentation Of Organic Wastewater And The Products Recovery

Organic wastewaters are produced in many industrial and agricultural industries.The need for sustainable development has inspired a growing interest in valorizing organic wastewater through recovering energy and resources,for which two-step anaerobic bioconversion offers an attractive route.In this process,complicated organic matters in wastewater are converted to relatively simple volatile fatty acids(VFAs),which can either be directly recovered or in-situ utilized for further production of higher-value products.However,conversion selectivity of acidogenic process and conversion rate of targeted products still need considerable improvement to be economically practical.Here,we report an acid-stimulated organic wastewater treatment process for continuous,selective production of acetate,with concomitant generation of CH4 as the gaseous product.At acidic pH(5.0),the system produced a stable liquid stream rich in acetate(accounting for 66%of the liquid-phase products)and a CH4-rich gas stream.No hydrogen(H2)was detected in the gaseous phase.The microbial community analysis showed that,Bacteroides acidogens and hydrogenotrophic methanogens were enriched under the low pH condition.The enhanced hydrogen consumption created a low H2 partial pressure environment that was favorable for selective production of acetate.This work demonstrates the feasibility of diverting the anaerobic fermentation pathway towards selective co-production of acetate and CH4 by simply controlling the wastewater pH.After improving the selectivity of VFAs production,the next issue to be addressed is how to efficiently recover the produced VFAs from wastewater.Here,we designed an electrodialysis(ED)to concentrate and recover the VFAs in-situ.By using an acidogenesis-ED integrated system with 20.0 V applied voltage,the acetate was concentrated by 4-fold and the propionate and butyrate were concentrated by over 3-fold in the integrated system after 528-hours operation.This work demonstrated the feasibility of the acidogenesis-ED integrated reactor for wastewater valorization and discussed the remaining challenges and opportunities.Although short-chain VFAs are useful raw materials for many industries,it is more economically-attractive if higher-value products can be obtained from wastewater.Here,we attempted to recover medium-chain fatty acids(MCFAs)from organic wastewater by in-situ utilizing the produced acetate and ethanol for producing caproate through chain elongation.An anaerobic membrane bioreactor(AnMBR),which allowed a complete biomass retention to improve activity of MCFAs-related bacteria,was adopted to enhance the process.Clostridium kluyveri was identified as a major player in the production of caproate.The caproate production with wastewater fermentation effluent as substrate may be affected by the dissolved biogas.We examined the impacts of different biogas components,and found that the caproate production was not affected by CH4,promoted by CO2 and suppressed by H2.Regulation of H2 and CO2 can relieve the inhibition effect and avoid the excessive ethanol oxidation.The findings in this work may lay a basis for development of more sustainable anaerobic wastewater treatment technologies.