Long-term performances and membrane lifespan of full-scale MBR treating filtrate from sludge ultra-dewatering.

ABSTRACT

An MBR treating filtrate from sludge ultra-dewatering (FSD) was studied to evaluate the real applicability to concentrated effluents. The MBR operation is comparable to conventional wastewater MBRs in terms of F/M and nitrogen to sludge ratios, SRT and MLSS in biological tanks. On the contrary, the volume treated is lower with a comparable pollution load, the effluent being concentrated in nitrogen and carbon. Very high and stable ammonium (97.7 ± 2.4%), total phosphorus (81.8 ± 11.9%), chemical (89.5 ± 2.3%) and biochemical oxygen demands (98.8 ± 0.7%) removals are observed despite a significant modification of the FSD composition. The MBR removal performances are whether comparable or greater than those reported at full-scale for Sharon or Anammox processes. The evolution of membranes properties, in particular, the decrease of permeability induced by the irreversible fouling, leads to a decrease of the daily permeate volume produced and an increase of the chemical cleaning need. The membrane lifespan was determined to be 5.5 years based on both the permeability loss and TSS in permeate. The permeability is directly correlated to the cumulated filtered flux of colloidal matter and a total of 350 kg O2/m2 of the membrane (COD in the supernatant) is needed to reach a permeability below 100 LMH/bar. The specific energy consumption is comparable to other wastewater MBRs in kWh/kgCOD removed but the intensive chemical cleanings need to be 2.5-4.5 times more frequent. Overall, it can be concluded that MBR is adapted to treat FSD efficiently.