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 interfloccular 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 O-2 center dot g MLVSS-1 h(-1) and Y-H,Y- MLSSV end = 0.48 and 0.28 mg MLVSS center dot mg CODsubstrate-1 at stage 1 (suspended biomass) and stage 2 (suspended and supported biomass), respectively. From the analysis of the endogenous decomposition constant (k(d)), a higher cell lysis was determined operating with suspended biomass (k(d) = 0.03 d(-1)) in comparison to the operation coexisting suspended and supported biomass (k(d) = 0.01 d(-1)). Heterotrophic biomass yield values (Y-H,Y- MLVSS = 0.48 +/- 0.06, 0.40 +/- 0.01 and 0.29 +/- 0.01 mg MLVSS center dot mg CODsubstrate-1 at high, medium and low OLR) showed lower sludge production at low OLR due to the influence of substrate limitation on cell growth.

Automated summary

This research investigates the biokinetic behavior of bacterial species in an UASB-MBR system treating urban wastewater with emerging contaminants using respirometric techniques. The results show that a decrease in organic loading rate leads to the disintegration of floc structure, dispersed growth, and weak interfloccular bonds. However, no toxicity or inhibition caused by the presence of emerging contaminants is observed.