Impact of solids retention time on the biological performance of an AnMBR treating lipid-rich synthetic dairy wastewater

In this study, the impact of applied solids retention time (SRT) on the biological performance of an anaerobic membrane bioreactor (AnMBR) treating synthetic dairy wastewater with high lipid content was assessed. Two side-stream AnMBR systems were operated at an SRT of 20 and 40 days (R20 and R40, respectively), equipped with an inside-out tubular membrane operated in cross-flow mode under full-scale operational conditions, i.e. crossflow velocity, transmembrane pressure, membrane flux. Successful operation was achieved and removal efficiencies of both reactors were up to 99% applying an organic loading rate (OLR) of 4.7 g COD L−1 d−1. No precipitation of lipids was observed throughout the operational period, keeping the lipids available for the anaerobic degradation. Long chain fatty acid (LCFA) accumulation was very modest and amounted 148 and 115 mg LCFA-COD per gram of volatile suspended solids (VSS) for R20 and R40, respectively. At an SRT of 40 days, a slightly better biological conversion was obtained. Periodically performed specific methanogenic activity (SMA) tests showed stabilization of the SMA for R40 sludge, whereas for R20 sludge the SMA continued to decrease. This study revealed a more stable reactor performance operating the AnMBR at an SRT of 40 days compared to 20 days.Accepted Author ManuscriptSanitary EngineeringBT/Environmental Biotechnolog

Influence of the Sludge Retention Time on Membrane Fouling in an Anaerobic Membrane Bioreactor (AnMBR) Treating Lipid-Rich Dairy Wastewater

This study evaluated the effects of sludge retention time (SRT) on the membrane filtration performance of an anaerobic membrane bioreactor (AnMBR) fed lipid-rich synthetic dairy wastewater. The membrane filtration performance was evaluated in two AnMBR systems operated at two different SRTs, i.e., 20 and 40 days. For the AnMBR operated at 40 days, SRT exhibited worse membrane filtration performance characterized by operational transmembrane pressures (TMP) exceeding the maximum allowed value and high total resistances to filtration (Rtotal). The sludge in the two reactors evaluated at the different SRTs showed similar sludge filterability properties. However, the sludge in the reactor operated at 40 days SRT was characterized by exhibiting the highest concentrations of: (i) total suspended solids (TSS), (ii) small-sized particles, (iii) extracellular polymeric substances (EPS), (iv) soluble microbial products (SMP), (v) fats, oils and grease (FOG), and (vi) long-chain fatty acids (LCFA). The cake layer resistance was the major contributor to the overall resistance to filtration. The high TSS concentration observed in the AnMBR systems apparently contributed to a less permeable cake layer introducing a negative effect on the membrane filtration performance.Sanitary EngineeringBT/Environmental Biotechnolog