Multi-stage semi-dry anaerobic digestion of ofmsw and cattle manure improved by natural zeolites

This paper reports the improvement obtained by natural zeolites for anaerobic digestion of the organic fraction of municipal solid waste and cattle manure. A full scale multi-stage reactor was used for the tests. A first dry stage was used for hydrolysis and acidogenesis, equipped with a leachate accumulation and recirculation unit. Leachate is then continuously directed to a second wet stage, in which methanogenesis and biogas production occur. The obtained wastewater presents a low organic content and might be recirculated in the leachate collection tank: however, ammonia level must be preliminary reduced. For this purpose, natural zeolites were tested as a valid alternative to currently used approaches. The obtained water has a low nitrogen content and could be continuously be recirculated without leading to inhibition phenomena. When saturated, natural zeolites are added to the compost obtained from the solid residue of the first dry stage, improving its slow release of water and ammonia into the soil. The plant was monitored for 80 days: no ammonia inhibition was observed, the concentration of this compound being always below 320 mg/L.