Yuan TZhang ZLei ZShimizu KLee D.-J.DUU-JONG LEE2022-03-222022-03-22202209608524https://www.scopus.com/inward/record.uri?eid=2-s2.0-85120462078&doi=10.1016%2fj.biortech.2021.126412&partnerID=40&md5=8fc6cb0cb998cae8296133eeb2af2d4fhttps://scholars.lib.ntu.edu.tw/handle/123456789/598196Biogas upgrading is an essential process for efficient and safe utilization of biogas produced from anaerobic digestion (AD), a cost-effective and environmentally friendly technology for bioenergy recovery from organic wastes. Biogas recirculation in AD reactors has been recently reported as a cost-effective and promising method to enhance methane content in biogas. This review aimed to summarize the state-of-the-art of biogas recirculation-based AD systems to better understand the possible mechanisms and main factors relating to in-situ biogas upgrading. It shows that biogas recirculation in the AD reactor can not only enhance methane content via both physicochemical and biological effects, but also help establish a robust AD system with high buffering capacity for highly efficient treatment of various organic wastes. More research works are demanding for a better understanding of the mechanisms and the optimization of the whole AD system, targeting its further development for high-calorie bioenergy production. ? 2021 Elsevier LtdBiogas recirculationHigh buffering capacityIn-situ biogas upgradingMethane enhancementMicrobial activityBiogasCost effectivenessMethaneWastesWastewater treatmentBiogas upgradingBuffering capacitiesCost effectiveMethane contentMicrobial activitiesOrganic wastesAnaerobic digestionbiofuelmethaneanaerobic growthbioreactorwastewaterAnaerobiosisBiofuelsBioreactorsWaste Water[SDGs]SDG11review10.1016/j.biortech.2021.126412348386262-s2.0-85120462078