Respirometric tests in a combined UASB-MBR system treating wastewater containing emerging contaminants at different OLRs and temperatures: Biokinetic analysis.

This research focuses on the application of respirometric techniques to provide new insights into the biokinetic behaviour of bacterial species developed in an Upflow Anaerobic Sludge Blanked -UASB reactor combined with a membrane bioreactor -MBR, treating urban wastewater with emerging contaminants frequently found in this kind of effluents. The lab-scale pilot plant was operated at different metabolic and operational conditions by limiting the organic loading rate- OLR of the influent. In a first stage, the MBR was performed with suspended biomass, while in a second stage bio-supports were introduced to operate coexisting suspended and fixed biomass. From the results of the microscopic monitoring of sludge, it was concluded that the decrease in OLR resulted in a greater disintegration of the floc structure, more dispersed growth, and a low presence of inter-floccular bonds. However, no effect of toxicity or inhibition of microorganisms caused by the presence of emerging contaminants -ECs was determined. Kinetic modelling was carried out to study the behaviour of the system. The results showed a slowing down of biomass degradative capacity at low OLR stages and operating at low temperatures of mixed liquor. In addition, a decrease in oxygen consumption was observed with decreasing biodegradable substrate, resulting in lower degradation of organic matter. Mean values of specific oxygen uptake rate and heterotrophic biomass yield at low OLR were SOUR end = 1.49 and 1.15 mg O2· g MLVSS-1 h-1 and YH,MLSSV end = 0.48 and 0.28 mg MLVSS· mg COD-1substrate at stage 1 (suspended biomass) and stage 2 (suspended and supported biomass), respectively. From the analysis of the endogenous decomposition constant (kd), a higher cell lysis was determined operating with suspended biomass (kd = 0.03 d-1) in comparison to the operation coexisting suspended and supported biomass (kd = 0.01 d-1). Heterotrophic biomass yield values (YH, MLVSS = 0.48 ± 0.06, 0.40 ± 0.01 and 0.29 ± 0.01 mg MLVSS· mg COD-1substrate at high, medium and low OLR) showed lower sludge production at low OLR due to the influence of substrate limitation on cell growth.

Carbamazepine removal from low-strength municipal wastewater using a combined UASB-MBR treatment system.

An Upflow Anaerobic Sludge Blanket reactor combined with a two-stage membrane bioreactor were operated for 193 days in order to evaluate the biological removal of carbamazepine (CBZ) from low-strength municipal wastewater. The system worked in three different organic load stages (0.7 ± 0.1 kg COD·m-3·d-1, 0.4 ± 0.1 kg COD·m-3·d-1 and 0.1 ± 0.0 kg COD·m-3·d-1) to assess the impact of the influent OLR on operational parameters such as anaerobic and aerobic sludge retention time (SRT), acidity, volatile fatty acids (VFAs), biomass activity or biogas production. The highest carbamazepine removals were achieved during the anaerobic stage (UASB reactor), reaching averages of 48.9%, 48.0% and 38.2% operating at high, medium and low OLR, respectively. The aerobic treatment (MBR) served as post-treatment, improving the removals, and the global UASB-MBR system reached averages of 70.0%, 59.6% and 49.8% when the influent was at medium and low OLR, respectively. The results demonstrate the potential of combined biological systems on the removal of recalcitrant pharmaceuticals.