Ultrafiltration as an advanced tertiary treatment of anaerobically digested swine manure liquid fraction: A practical and theoretical study

The removal of the organic matter of the swine manure liquid fraction has been carried out by an integral process based on two stages: anaerobic digestion in an expanded granular sludge bed (EGSB) reactor followed by ultrafiltration (UF) as a tertiary treatment. The lab-scale EGSB reactor was operating for 39 weeks with a hydraulic retention time (HRT) of 3.8 days; leading to a 70% tCOD removal and a biogas production of 0.15 Nm3 CH4 kg−1 tCOD removed. The UF process was studied in two different geometry and configuration membrane modules: external tubular (E-T) and submerged hollow fiber (S-HF). Both lab-scale systems have been compared in terms of the filtration selectivity and productivity and the S-HF has been the most selective and productive configuration in the filtration of the EGSB effluent. The whole process (EGSB + S-HF) provides a permeate flow without solids and yields a tCOD removal around 90%. Finally this paper proposes a satisfactory model for the UF of the EGSB effluent in the S-HF module. Both the membrane intrinsic resistance (RM) and the specific cake resistance (α) have been calculated.

► Lab-scale EGSB reactor innovatively applied to treat swine manure liquid fraction. ► UF as tertiary treatment in external tubular (E-T) and submerged hollow fiber (S-HF). ► S-HF is most productive and selective. ► Filtration theory and Darcy's law valid at low permeate flow rate in the S-HF. ► Cake compressibility model necessary when flow rates higher than 5 L/h.