Recent Progress on Dry Anaerobic Digestion of Organic Solid Wastes: Achievements and Challenges

Recent works on dry anaerobic digestion (AD) show that not only methane but also hydrogen, volatile fatty acids (VFAs), and ethanol can be produced from municipal solid waste (MSW), dewatered sewage sludge, animal manure or crop residue by dry AD processes. Up to now only methane production from household wastes has already been commercialized by using dry AD technology. Single-stage dry AD processes with semi-continuous or continuous operation mode dominates the commercialized dry AD plants. To get enhanced biogasification efficiency, naturally microbial pretreatment methods (like stack-pretreatment and aerobic or facultative composting) and co-digestion are practically useful for dry AD, especially for the treatment of carbon-and nitrogen- rich organic solid wastes, i.e. crop residue and animal manure. Dry AD could achieve comparable production efficiency to wet AD systems, yielding 121 - 340 L of CH4 from per gram volatile solids (VS) of organic fraction of MSW (OFMSW) and 51 -55 ml H-2/g-VSreduced from OFMSW, sewage sludge, and paper and food wastes. Still, future researches are necessary and demanding for dry AD to better challenge with other low-cost treatment and disposal methods, which are also proposed in this review mainly relating with its longer solids retention time, feedstocks collection, inhibitory substances, online process monitoring, and establishment of process assessment index system.