Bio-energy recovery from high-solid organic substrates by dry anaerobic bio-conversion processes: A review

Dry anaerobic bio-conversion (D-AnBioC) of high-solid organic substrates (OS) is considered as a sustainable option for waste management practices in different parts of the world. The basic technology is well implemented, but the improvements are still under way in terms of optimization and pre- and post-treatments of the feed and end-products, respectively. The purpose of this review is mainly to: (1) provide existing knowledge and research advances in D-AnBioC systems to treat high-solid OS; (2) identify major issues involved in bioreactor designing; (3) present factors influencing the bio-conversion efficiency; (4) discuss the microbiology of system operation; (5) provide examples of existing commercial-scale plants; (6) discuss energy and economics requirements. From the detailed literature review, it is clear that the characteristics of OS are the major factors governing the overall process and economics. It shows that not all OS are profitably recycled using D-AnBioC systems. Compared to single-stage continuous systems, batch systems under a multi-stage configuration appears to be economically feasible, however, it must be noted that the available data sets are still inconclusive. Also, limited information is available on green house gas mitigation and restoration of nutrients from the digested residue during post-treatment schemes. A summary at the end presents important research gaps of D-AnBioC system to direct future research.