Optimization of two-phased anaerobic sludge digestion using the pressurized ultra filtration membrane with a mesh screen (MS-PUFM)

•The optimization with an innovative MS-PUFM system was evaluated.•The two-phased anaerobic bioreactors coupling with the MS-PUFM system was tested.•Anaerobic mesophilic bioreactors were used.•Mesh screen contributed 20% decrease of operating cost and 33% increase of permeate flux.

To alleviate problems of membrane bioreactors with membrane fouling control, the optimization of the two-phased anaerobic mesophilic bioreactors coupling with the MS-PUFM system was evaluated. The chemical oxygen demand (COD) removal efficiency of anaerobic sludge digestion with the MS-PUFM system was raised from 40% to 97%. VFA concentration was sustained to be in the range 110–138 mg L−1, which was within the optimum range. In the methanogenic bioreactor, methane generation was improved due to the effective reduction of methanogene washout with the MS-PUFM system, and the optimum operating pressure of the MS-PUFM system resulted less than 3 kgf cm−2. Mesh screen contributed 20% decrease of operating cost and 33% increase of permeate flux from 10 to 15 L m−2 h−1 with preliminary solids reduction. As a result, the MS-PUFM system showed practical feasibilities for the digestion of sewage sludge, where current commercial system processes utilizing higher biomass density are not appropriate.