How high salt shock affects performance and membrane fouling characteristics of a halophilic membrane bioreactor used for treating hypersaline wastewater.

In the present study, the effect of short-term salt shocks (13% and 20%) on the performance of a halophilic MBR bioreactor used to treat a hypersaline (5% salt) synthetic wastewater was considered. 13% and 20% salt shocks resulted in a transient and permanent decrease in chemical oxygen demand removal efficiency, respectively which could be correlated with soluble microbial products (SMP) concentration and specific oxygen uptake rate values of the halophilic population. DNA leakage tests suggested that both 13% and 20% short-term salt shocks resulted in some cell structural damage. During both 13% and 20% salt shocks mixed liquor SMP, extracellular polymeric substances (EPS), zeta potential and endogenous respiration increased while relative hydrophobicity, EPSp/EPSc and exogenous respiration decreased; in both cases, however, the pre-shock values for these parameters were restored after the removal of the salt shock. 13% salt shock resulted in a transient increase in the membrane fouling rate and a permanent rise in total membrane resistance (Rt). On the other hand, both membrane fouling rate and Rt increased during 20% salt shock. Membrane fouling rate initially reduced after the 20% salt shock removal but after 5 days a "TMP jump" occurred. The latter was caused by the higher steady state SMPc and SMPp concentrations after removal of 20% salt shock compared to pre-shock values. This might have either resulted in a decrease in critical flux or an increase in local flux above critical flux in some parts of the membrane. The contribution of cake layer resistance to overall membrane resistance increased after the 13% and 20% salt shocks. The findings of the present study reveal the robustness of halophilic MBRs against salt shocks in the treatment of hypersaline wastewater. However, in cases of very high salt shocks, appropriate membrane fouling reduction strategies should be carried out during its operation.

Integrating electrocoagulation process with up-flow anaerobic sludge blanket for in-situ biomethanation and performance improvement.

In this study, the integration of the electrocoagulation (EC) process with anaerobic digestion as a novel in-situ biomethanation approach was considered for the first time. As a result of this integration (iron electrodes, current density of 1.5 mA/cm2 and an exposure mode of 10-min-ON/ 30-min-OFF), the carbon dioxide content of biogas reached below 2%. Also, the methane production rate improved by 18.0 ± 0.4%, whereas the removal efficiencies of chemical oxygen demand, turbidity, phosphate, and sulfate increased by 12.0 ± 1.5%, 30.7 ± 1.7%, > 99%, and 75.7%, respectively. Anaerobic granular sludge characteristics were also improved. Moreover, the EC process stimulated growth and quantity of functional microorganisms, especially Acinetobacter in bacterial and Methanobacterium in archaeal community. Methane concentration, however decreased due to possible excess hydrogen production. The application of the biogas as bio-hythane, and the optimization of the hybrid bioreactor to decrease hydrogen production, are possible avenues for further research.

Considering a membrane bioreactor for the treatment of vegetable oil refinery wastewaters at industrially relevant organic loading rates.

The present study aims to shed more light on the use of membrane bioreactors (MBRs) for the treatment of vegetable oil refinery wastewaters (VORWs). A MBR was operated for 157 days in which it was fed with real VORW of varying composition at a range of organic loading rates (0.20 ± 0.05-3.79 ± 0.29 kg COD m-3 day-1). The hitherto unconsidered fate of VORW constituents through the biological process was followed using gas chromatography/mass spectrometry analysis. This analysis revealed that only 19% of the identified feed constituents remained in the MBR effluent whereas ten new compounds were formed. Linear correlation analysis attributed the effluent residual COD to soluble microbial products (SMP) and non-readily biodegradable recalcitrant oily compounds. Trend of change of MLSS, mixed liquor viscosity and SMP with increasing OLR suggested that when MBR is operated under industrial conditions for the VORW treatment, the mixed liquor fouling propensity potentially increases with increasing OLR in the range studied.

Treatment of hypersaline produced water employing a moderately halophilic bacterial consortium in a membrane bioreactor: effect of salt concentration on organic removal performance, mixed liquor characteristics and membrane fouling.

In this study the organic pollutant removal performance and the mixed liquor characteristics of a membrane bioreactor (MBR), employing a moderately halophilic bacterial consortium, for the treatment of hypersaline synthetic produced water containing 100-250 g L(-1) NaCl were considered. The COD and oil and grease (O&G) removal efficiencies in the range 81.6-94.6% and 84.8-94.0% respectively and MBR effluent turbidity lower than 2NTU were achieved. There was no pronounced membrane fouling at any salt concentration. O&G accumulation (less than 11% of the influent O&G) occurred in the mixed liquor at all salt concentrations, but biodegradation was identified as the major organic removal mechanism. With increasing salt concentration, initially increase in SVI and later formation of oil/biomass bodies took place but due to the presence of the membrane biomass washout did not occur. The mixed liquor was pseudoplastic and the apparent viscosity and flow behavior index generally increased with salt concentration.