A critical control point approach to the removal of chemicals of concern from water for reuse.

The reuse of water in a range of potable and non-potable applications is an important factor in the augmentation of water supply and in improving water security and productivity worldwide. A key hindrance to the reuse of water is the cost of compliance testing and process validation associated with ensuring that pathogen and chemicals in the feedwater are removed to a level that ensures no acute or chronic health and/or environmental effects. The critical control point (CCP) approach is well established and widely adopted by water utilities to provide an operational and risk management framework for the removal of pathogens in the treatment system. The application of a CCP approach to barriers in a treatment system for the removal of chemicals is presented. The application exemplar is to a small community wastewater treatment system that aims to produce potable quality water from a secondary treated wastewater effluent, however, the concepts presented are generic. The example used seven treatment barriers, five of which were designed and operated as CCP barriers for pathogens. The work demonstrates a method and risk management framework by which three of the seven barriers could also include a CCP approach for the removal of chemicals. Analogous to a CCP approach for pathogens, the potential is to reduce the use of chemical analysis as a routine determinant of performance criteria. The operational deployment of a CCP approach for chemicals was augmented with the development of a decision tree encompassing the classification of chemicals and the total removal credits across the treatment train in terms of the mechanistic removal of chemicals for each barrier. Validation of the approach is shown for an activated sludge, ozone and reverse osmosis barrier.

Development of a predictive framework to assess the removal of trace organic chemicals by anaerobic membrane bioreactor.

This study aims to develop a predictive framework to assess the removal and fate of trace organic chemicals (TrOCs) during wastewater treatment by anaerobic membrane bioreactor (AnMBR). The fate of 27 TrOCs in both the liquid and sludge phases during AnMBR treatment was systematically investigated. The results demonstrate a relationship between hydrophobicity and specific molecular features of TrOCs and their removal efficiency. These molecular features include the presence of electron withdrawing groups (EWGs) or donating groups (EDGs), especially those containing nitrogen and sulphur. All seven hydrophobic contaminants were well removed (>70%) by AnMBR treatment. Most hydrophilic TrOCs containing EDGs were also well removed (>70%). In contrast, hydrophilic TrOCs containing EWGs were mostly poorly removed and could accumulate in the sludge phase. The removal of several nitrogen/sulphur bearing TrOCs (e.g., linuron and caffeine) by AnMBR was higher than that by aerobic treatment, possibly due to nitrogen or sulphur reducing bacteria.

Removal of polycyclic musks by anaerobic membrane bioreactor: biodegradation, biosorption, and enantioselectivity.

This study aims to investigate the performance of anaerobic membrane bioreactor (AnMBR) for removing five polycyclic musks (PCMs), which are common active ingredients of personal care and household cleaning products. A laboratory scale AnMBR system was used in this investigation. Concentrations of the PCMs in both the liquid and biosolids phase were measured to conduct a mass balance analysis and elucidate their fate during AnMBR treatment. The AnMBR was effective for removing PCMs from the aqueous phase by a combination of biotransformation and sorption onto the biosolids. However, biotransformation was observed to be the dominant removal mechanism for all five PCMs. Enantioselective analysis of the PCMs in influent, effluent and biomass samples indicated that there was negligible enantioselectivity in the removal of these PCMs. Accordingly, all enantiomers of these PCMs can be expected to be removed by AnMBR with similar efficiency.

A novel membrane distillation-thermophilic bioreactor system: biological stability and trace organic compound removal.

The removal of trace organic compounds (TrOCs) by a novel membrane distillation-thermophilic bioreactor (MDBR) system was examined. Salinity build-up and the thermophilic conditions to some extent adversely impacted the performance of the bioreactor, particularly the removal of total nitrogen and recalcitrant TrOCs. While most TrOCs were well removed by the thermophilic bioreactor, compounds containing electron withdrawing functional groups in their molecular structure were recalcitrant to biological treatment and their removal efficiency by the thermophilic bioreactor was low (0-53%). However, the overall performance of the novel MDBR system with respect to the removal of total organic carbon, total nitrogen, and TrOCs was high and was not significantly affected by the conditions of the bioreactor. All TrOCs investigated here were highly removed (>95%) by the MDBR system. Biodegradation, sludge adsorption, and rejection by MD contribute to the removal of TrOCs by MDBR treatment.

The fate of pharmaceuticals, steroid hormones, phytoestrogens, UV-filters and pesticides during MBR treatment.

This study examined the relationship between molecular properties and the fate of trace organic contaminants (TrOCs) in the aqueous and solid phases during wastewater treatment by MBR. A set of 29 TrOCs was selected to represent pharmaceuticals, steroid hormones, phytoestrogens, UV-filters and pesticides that occur ubiquitously in municipal wastewater. Both adsorption and biodegradation/transformation were found responsible for the removal of TrOCs by MBR treatment. A connection between biodegradation and molecular structure could be observed while adsorption was the dominant removal mechanism for the hydrophobic (logD>3.2) compounds. Highly hydrophobic (logD>3.2) but readily biodegradable compounds did not accumulate in sludge. In contrast, recalcitrant compounds with a moderate hydrophobicity, such as carbamazepine, accumulated significantly in the solid phase. The results provide a framework to predict the removal and fate of TrOCs by MBR treatment.

Removal of N-nitrosamines by an aerobic membrane bioreactor.

This study investigated the fate of eight N-nitrosamines during membrane bioreactor (MBR) treatment. The results suggest that biodegradation is mainly responsible for the removal of N-nitrosamines during MBR treatment. Other removal mechanisms were insignificant (e.g. adsorption to sludge) or not expected (e.g. photolysis and volatilization) given the experimental conditions and physicochemical properties of the N-nitrosamines studied here. N-nitrosamine removal efficiencies were from 24% to 94%, depending on their molecular properties. High removal of N-nitrosamines such as N-nitrosodimethylamine and N-nitrosodiethylamine could be explained by the presence of strong electron donating functional groups (EDG) in their structure. In contrast, N-nitrosomorpholine possessing the weak EDG morpholine was persistent to biodegradation. The removal efficiency of N-nitrosomorpholine was 24% and was the lowest amongst all N-nitrosamines investigated in this study.

Effect of organic loading rate on VFA production, organic matter removal and microbial activity of a two-stage thermophilic anaerobic membrane bioreactor.

This study focused on the VFA (volatile fatty acid) profile variation with organic loading rate (OLR) of a two stage thermophilic anaerobic membrane bioreactor (TAnMBR). The two stage TAnMBR treating high strength molasses-based synthetic wastewater was operated under a side-stream partial sedimentation mode at 55°C. Reactor performances were studied at different OLR ranging from 5 to 12 kg COD m(-3) d(-1). Operational performance of TAnMBR was monitored by assessing biological activity, organic removal efficiency, and VFA. The major intermediate products of anaerobic digestion were identified as acetate, propionate, iso-butyrate, n-butyrate and valerate. Among them acetate and n-butyrate were identified as the most abundant components. Increase of OLR changes the predominant VFA type from acetic acid to n-butyric acid and the total VFA concentration was increased with increased OLR. Moreover, increased OLR increased organic removal efficiency up to second loading rate and dropped in third loading rate while biological activity was increased continuously.