Performance of a three-stage membrane bioprocess treating the organic fraction of municipal solid waste and evolution of its archaeal and bacterial ecology.

A novel three-stage bioprocess achieved 75% volatile solids (VS) removal at an organic loading rate (OLR) of 4g VSL(-1)day, a solids retention time (SRT) of 66days, a hydraulic retention time (HRT) of 20days, at a temperature of 35 degrees C. The bioprocess consisted of an anaerobic hydrolytic reactor (HR) where the solids and liquid fractions of the Organic Fraction of the Municipal Solid Waste (OFMSW) were separated with a mesh. The leachate was pumped to a Submerged Anaerobic Membrane Bioreactor (SAMBR) and the treated permeate was polished in an Aerobic Membrane Bioreactor (AMBR). Denaturing Gradient Gel Electrophoresis (DGGE) and DNA sequencing analyses indicated that the increase in methane content in the HR caused by the excess sludge recycle from the SAMBR was associated with an increase in the number of hydrogenotrophic species, mainly Methanobrevibacter sp., Methanobacterium formicicum and Methanosarcina sp. At 20 degrees C VS removal dropped to 50% in the HR and some DGGE bands disappeared when compared to 35 degrees C samples, while some bands such as the one corresponding to Ruminococcus flavefaciens were reduced in intensity. The species associated with the COD-polishing properties of the AMBR correspond to the genera Pseudomonas, Hyphomonas and Hyphomicrobiaceae. These results highlight the positive effect of recycling the excess sludge from the SAMBR to re-inoculate the HR with hydrogenotrophic species.