New insight into fate and fouling behavior of bulk Dissolved Organic Matter (DOM) in a full-scale membrane bioreactor for domestic wastewater treatment

Abstract

Dissolved Organic Matter (DOM) and active biomass concentrations from a full-scale membrane bioreactor (MBR) treating domestic wastewater were investigated during a period of 488 days. Bulk DOM is known to be a major membrane foulant in MBR. Active biomass activity, which depends on operating parameter variations, is a major source of DOM, due to soluble microbial product (SMP) secretion. To establish the link between DOM, active biomass concentration, operating conditions, and later membrane fouling, heterotrophic and autotrophic bacteria were first quantified using respirometric measurements. Comparing their evolution with operating conditions and parameters using Principal Component Analysis (PCA), SRT and temperature were identified as the parameters with the most impact on active biomass concentrations. Proteins from Biopolymers and humic substance (HS + BB) concentrations were quantified using a 3DEEM pseudo-quantitative method. Active biomass and DOM concentration fluctuations were similar, confirming that DOM was mainly constituted by SMP produced by the active biomass, and consequently dependent on SRT and temperature modifications. HS + BB were produced eight times faster than Proteins from BP and therefore accumulated faster on the membrane despite their low membrane rejection. Consequently, large amounts of HS + BB can accumulate, modifying the initial membrane properties. The membrane resistance evolution was dependent on Proteins from Biopolymers accumulation and these molecules showed no fouling propensity modifications despite seasonal variations. As a consequence, this study strongly emphasized the interest of using a 3DEEM pseudo-quantitative method for on-line application in order to follow the full-scale MBR process and membrane fouling.