Tradeoff between micropollutant abatement and bromate formation during ozonation of concentrates from nanofiltration and reverse osmosis processes.

Water treatment with nanofiltration (NF) or reverse osmosis (RO) membranes results in a purified permeate and a retentate, where solutes are concentrated and have to be properly managed and discharged. To date, little is known on how the selection of a semi-permeable dense membrane impacts the dissolved organic matter in the concentrate and what the consequences are for micropollutant (MP) abatement and bromate formation during concentrate treatment with ozone. Laboratory ozonation experiments were performed with standardized concentrates produced by three membranes (two NFs and one low-pressure reverse osmosis (LPRO) membrane) from three water sources (two river waters and one lake water). The concentrates were standardized by adjustment of pH and concentrations of dissolved organic carbon, total inorganic carbon, selected micropollutants (MP) with a low to high ozone reactivity and bromide to exclude factors which are known to impact ozonation. NF membranes had a lower retention of bromide and MPs than the LPRO membrane, and if the permeate quality of the NF membrane meets the requirements, the selection of this membrane type is beneficial due to the lower bromate formation risks upon concentrate ozonation. The bromate formation was typically higher in standardized concentrates of LPRO than of NF membranes, but the tradeoff between MP abatement and bromate formation upon ozonation of the standardized concentrates was not affected by the membrane type. Furthermore, there was no difference for the different source waters. Overall, ozonation of concentrates is only feasible for abatement of MPs with a high to moderate ozone reactivity with limited bromate formation. Differences in the DOM composition between NF and LPRO membrane concentrates are less relevant than retention of MPs and bromide by the membrane and the required ozone dose to meet a treatment target.

Forward osmosis for the treatment of reverse osmosis concentrate from water reclamation: process performance and fouling control.

While high quality water reuse based on dual membrane filtration (membrane filtration or ultrafiltration, followed by reverse osmosis) is expected to be progressively applied, treatment and sustainable management of the produced reverse osmosis concentrate (ROC) are still important issues. Forward osmosis (FO) is a promising technology for maximising water recovery and further dewatering ROC so that zero liquid discharge is produced. Elevated concentrations of organic and inorganic compounds may act as potential foulants of the concentrate desalting system, in that they consist of, for example, FO and a subsequent crystallizer. The present study investigated conditions under which the FO system can serve as concentration phase with the focus on its fouling propensity using model foulants and real ROC. Bulk organics from ROC consisted mainly of humic acids (HA) and building blocks since wastewater-derived biopolymers were retained by membrane filtration or ultrafiltration. Organic fouling of the FO system by ROC-derived bulk organics was low. HA was only adsorbed moderately at about 7% of the initial concentration, causing a minor flux decline of about 2-4%. However, scaling was a major impediment to this process if not properly controlled, for instance by pH adjustment or softening.

The fate of 14C-radiolabelled diclofenac and 4'-hydroxydiclofenac in membrane bioreactor treatment of wastewater.

This study aimed at enhancing knowledge on the fate of diclofenac (DF), together with its main human metabolite 4'-hydroxydiclofenac (4'OHDF), during wastewater treatment by using a laboratory-scale membrane bioreactor (MBR). The reactor was fed continuously with non-radiolabelled diclofenac for a one month period prior to a single pulse of a 14C-radiolabelled solution of DF and 4'OHDF. The solution spike contained approximately 25% 4'OHDF and 65% DF, which corresponds to the ratio observed in municipal sewage, as well as traces of two other metabolites. The radioactivity was monitored for a total of twelve days in the various output streams. The calculation of the complete mass balance in the system demonstrated that the major part of the radioactivity left the reactor with the permeate (88.7%), while 2.1% was recovered in the excess sludge. Negligible amounts were recovered in the off-gas traps and on the membranes. Chromatographic analyses of effluent samples, by means of HPLC-MS coupled in parallel to a radiodetector, displayed a different pattern than the one of the spiked solution. It showed the occurrence of three additional metabolites.

Managed aquifer recharge with reclaimed water: approaches to a European guidance framework.

Managed Aquifer Recharge (MAR) with reclaimed water plays a particular role in water stress mitigation, due to both the large potential benefits achieved in terms of sustainable water resources management as well as the complexity of the planning and implementation. This paper focuses on the role of policy in establishing water quality related legal frameworks that are crucial for MAR development. It analyses and compares the current practice of shaping boundary conditions, particularly in a European context but with some international comparison. The work reports on the legal aspects considered most relevant for MAR in the European Union and summarises issues addressed in aquifer recharge regulations and guidelines. Some potential actions are proposed to develop a suitable guidance framework for further exploitation of MAR benefits.

The ecological impact of membrane-based extraction of phenolic compounds--a life cycle assessment study.

Many phenolic compounds show high boiling points, low molecular weights, moderate polarities or high toxicities. Therefore, conventional wastewater treatment is limited or expensive. Recycling of the separated compounds is often not possible. But, if liquid-liquid reactive extraction is linked to a non-porous membrane, some or all of the above mentioned limitations may be overcome. The key element is a composite membrane with a dense, hydrophobic top layer which avoids the mixing of the two aqueous fluid streams. The dilute phenol stream is one of them, the other is caustic soda as stripping solvent. Since the basics of this technology have been discussed before, the scope of this study is to facilitate process implementation and integration. To this end, a life cycle assessment framework is used to identify the optimal equipment size for the treatment of wastewater that may, for example, originate from the production of polycarbonate. Limiting for this application is not the environmental performance though, but most likely process economics.

Capillary nanofiltration coupled with powdered activated carbon adsorption for high quality water reuse.

Direct capillary nanofiltration was tested for reclamation of tertiary effluent from a municipal wastewater treatment plant. This process can be regarded as a promising treatment alternative for high quality water reuse applications when combined with powdered activated carbon for enhanced removal of organic compounds. The nanofiltration was operated at flux levels between 20 and 25 L/(m2 h) at a transmembrane pressure difference of 2-3 bar for approximately 4,000 operating hours. The study was conducted with PAC doses in the range from 0 to 50 mg/L. The plant removal for DOC ranged from 88-98%. The sulfate retention of the membrane filtration process was between 87 and 96%. The process provided a consistently high permeate quality with respect to organic and inorganic key parameters.

Comparative investigation on the impact of polymeric substances on membrane fouling during sub-critical and critical flux operation of a municipal membrane bioreactor.

Soluble organic macromolecules are ubiquitous in activated sludge supernatant. For the operation of membrane bioreactors (MBR) this group of substances is considered as the dominant factor causing severe membrane fouling due to the concentration polarisation phenomenon. The well established critical flux concept for the characterisation of membrane bioreactor's operation limits is based on filtration data only. As there is an cause-and-effect relation between the partial retention of organic compounds and the limited flux according the critical flux concept the aim of this study was to draw a comparison between different permeate fluxes on the retention of organic macromolecules. Thus, a municipal pilot-scale MBR with three capillary hollow fibre membrane modules was operated in sub critical, critical and supercritical flux mode, respectively and the retention of macromolecules was quantified by size exclusion chromatography. Three permeate extraction pumps allow a simultaneous operation with different operational conditions for each membrane module and proved the crucial impact of permeate flux on the fouling rate. The interchange of these conditions gave evidence of an optimised start-up procedure for MBRs characterised by higher permeate fluxes. An increased flux causes both a higher retention of soluble macromolecules and subsequent a higher fouling rate.

Removal of endocrine disruptors and cytostatics from effluent by nanofiltration in combination with adsorption on powdered activated carbon.

Direct capillary nanofiltration also in combination with an upstream powdered activated carbon treatment was tested for high quality water reuse of tertiary effluent from a municipal wastewater treatment plant. Two endocrine disruptors (BPA and EE2) and two cytostatics (CytR and 5-FU) were spiked in concentrations of 1 to 2 microg/L to evaluate the process performance. In direct NF the real total removal of the micropollutants was between 5 and 40%. Adsorption to the membrane played a major role leading to a seemingly total removal between 35 and 70%. Addition of powdered activated carbon and lignite coke dust largely reduced the influence from adsorption to the membrane and increased the total removal to >95 to 99.9% depending on the PAC type and dose. The cytostatics showed already in direct NF a very high removal due to unspecified losses. Further investigations are ongoing to understand the underlying mechanism. The PAC/NF process provided a consistently high permeate quality with respect to bulk and trace organics.

Potentials of using nanofiltration to recover phosphorus from sewage sludge.

Due to the depletion of mineral phosphorus resources there is an increasing demand for efficient phosphorus recovery technologies. In this study the potential of nanofiltration to recover phosphorus from pre-treated sewage sludge is investigated. The efficiency of three commercial nanofiltration membranes (Desal 5DK, NP030; MPF34) was tested using model solutions. Desal 5DK showed the best selectivity for phosphorus. A pH of lower than 1.5 was found to be most suitable. Desal 5DK was used on four different sewage sludge ash eluates and on one sewage sludge. In these experiments it was shown that a separation of phosphorus from undesired components such as heavy metals was possible with significant variations in the efficiency for the different ash and sludge types. Additionally the achievable product recovery was investigated with model solutions. A product recovery of 57.1% was attained for pH 1 and 41.4% for pH 1.5.

A critical evaluation of combined engineered and aquifer treatment systems in water recycling.

Australian experience at five research sites where stormwater and reclaimed water have been stored in aquifers prior to reuse, have yielded valuable information about water treatment processes in anaerobic and aerobic aquifers. One of these sites is the stormwater to potable water ASTR project at the City of Salisbury, a demonstration project within the broader EC project 'RECLAIM WATER'. A framework for characterising the effectiveness of such treatment for selected organic chemicals, natural organic matter, and pathogens is being developed for inclusion in new Australian Guidelines for Management of Aquifer Recharge. The combination of pre-treatments (including passive systems such as reed beds) and aquifer treatment effectiveness in relation to source waters and intended uses of recovered water will be described. Advantages and disadvantages of various types of pre-treatments in relation to effectiveness and sustainability of managed aquifer recharge will be discussed taking account of aquifer characteristics. These observations will be consolidated into a draft set of principles to assist in selection of engineered treatments compatible with passive treatment in aquifers.

Comparing the effluent organic matter removal of direct NF and powdered activated carbon/NF as high quality pretreatment options for artificial groundwater recharge.

Direct nanofiltration and nanofiltration combined with powdered activated carbon known as the PAC/NF process were tested regarding the removal of effluent organic matter for reclamation of tertiary effluent from a municipal wastewater treatment plant. They can be regarded as a promising treatment alternative for high quality water reuse applications, especially for direct injection. The total removal for DOC was above 90% with permeate concentrations below 0.5 mg/l. Size exclusion chromatography and fluorescence EEM proved to trace origin of the organic matter even in low concentration ranges. The type and dosage of adsorbent influences the process performance significantly and allows process optimization.

Emerging contaminants and treatment options in water recycling for indirect potable use.

Solutions to global water stress problems are urgently needed yet must be sustainable, economical and safe. The utilisation of alternative water sources like reclaimed municipal wastewater is one of the most obvious and promising options in integrated water resources management. Among the various beneficial uses of reclaimed wastewater Aquifer Recharge (AR) receives growing attention because it features advantages such as additional natural treatment, storage capacity to buffer seasonal variations of supply and demand as well as mixing with natural water bodies which promotes the acceptance of further uses, particularly indirect potable use. Major concerns about the safety of this exploitation route of an alternative water source are connected to microbial and chemical contaminants occurring in wastewater, among which are emerging trace organics like endocrine disrupters and pharmaceuticals. This paper reviews the current international debate about the relevance of emerging contaminants and technical mitigation options in water recycling for indirect potable use.

Monitoring reverse osmosis treated wastewater recharge into a coastal aquifer by environmental isotopes (B, Li, O, H).

Artificial recharge (AR) is gaining importance as a management tool in water stressed regions. The need to prove recovery performance requires new monitoring tools for AR systems. A novel combination of environmental isotope tracers (B, Li, O, H stable isotopes) was tested for the monitoring of AR of tertiary treated, desalinated domestic wastewater into a coastal dune aquifer in Flanders, Belgium. No significant isotope fractionation was observed for the treatment process, which includes low pH RO desalination. The wastewater, after infiltration through ponds and before recovery through pumping wells is characterized by low molar Cl/B ratios (3.3 to 5.2), compared to 130 to 1020 in the wider study area, delta(11)B values close to 0% per hundred, rather homogeneous delta(7)Li values (10.3 +/- 1.7% per hundred), and a 18O and 2H enrichment with respect to ambient groundwater due to evaporation in the infiltration ponds. This confers to the AR component a unique isotopic and geochemical fingerprint. Immediately downstream of the pumping wells and in the deeper part of the aquifer no evidence of AR wastewater could be found, indicating a high recovery efficiency. In the wider area and in the deeper part of the aquifer, isotopes evidence mixing of coastal rain and a fresh paleo-groundwater component with residual seawater as well as interaction with the aquifer material. Combining several isotope tracers provides independent constraints on groundwater flow and mixing proportions as a complement to hydrodynamic modeling and geochemical studies.

Economic considerations and decision support tool for wastewater reuse scheme planning.

The reuse of upgraded wastewater for beneficial uses is increasingly adopted and accepted as a tool in water management. However, funding of schemes is still a critical issue. The focus of this paper is on economic considerations of water reuse planning. A survey of pricing mechanisms for reclaimed water revealed that most schemes are subsidised to a great extent. In order to minimise these state contributions to the implementation and operation of reuse projects, their planning should identify a least cost design option. This also has to take into account the established pricing structure for conventional water resources and the possibility of gaining revenues from reclaimed water pricing. The paper presents a case study which takes into account these aspects. It evaluates different scheme designs with regard to their Net Present Value (NPV). It could be demonstrated that for the same charging level, quite different amounts of reclaimed water can be delivered while still producing an overall positive NPV. Moreover, the economic feasibility and competitiveness of a reuse scheme is highly determined by the cost structure of the conventional water market.

Removal of endocrine disrupting compounds with membrane processes in wastewater treatment and reuse.

Endocrine disrupting compounds can affect the hormone system in organisms and are the subject of environmental and human health concerns. The effluents of wastewater treatment plants contribute to the emission of estrogenically active substances into the environment. Membrane technology, which is an advanced wastewater treatment option, is the subject of this research. The removal techniques under investigation are membrane bioreactors, reverse osmosis, and nanofiltration. Eleven different nanofiltration membranes were tested in the laboratory set-up. The observed retention of NP and BPA ranged between 70% and 100%. The contact angle is an indicator for the hydrophobicity of a membrane, whose influence on the permeability and retention of NP was evident. Regarding the retention of BPA no dependency on the contact angle was observed. Results of the investigation of a full-scale landfill leachate treatment plant indicate a bisphenol A (BPA) removal of more than 98% with membrane bioreactors and reverse osmosis. The mass balance indicates that biological degradation is the most important removal process in the membrane bioreactor configuration.

Removal of hormones and pharmaceuticals in the Advanced Water Recycling Demonstration Plant in Queensland, Australia.

An advanced water recycling demonstration plant was employed to investigate the effectiveness of a number of treatment technologies in the removal of some residuals of commonly prescribed pharmaceuticals as well as natural and synthetic hormones found in sewage. Analysis of targeted compounds was carried out by solid-phase extraction (SPE) and gas chromatography-mass spectrometry (GC-MS). Initial tests were undertaken to determine the background concentrations of the analytes during various stages of treatment. Subsequent tests, undertaken by spiking with standard solutions of the target compounds provided further information on the removal efficiencies of some selected treatment modules. The results of the study indicate that while ozonation, microfiltration and nanofiltration were partially effective, treatment by reverse osmosis was the most universally successful in the removal of the target residuals. While significantly more data is required for a full evaluation, this initial investigation suggests that reverse osmosis may be an effective means of removing a wider range of pharmaceutically active residuals and hormones from treated sewage.

Occurrence and removal of endocrine disrupters in landfill leachate treatment plants.

Endocrine disrupting compounds can affect the hormone system in organisms. Industrial chemicals with estrogenic effects were detected in large quantities in landfill leachates. Membrane technology has proven to be an effective barrier to these substances and thus widely applied in the treatment of landfill leachate. The removal techniques under investigation are membrane bioreactors, nanofiltration, activated carbon adsorption, ozonation as well as reverse osmosis. Investigations were conducted at two different landfill leachate treatment plants with a variety of process configurations. The xenoestrogenic substances nonylphenol and bisphenol A were detected in high microg/L-ranges in raw landfill leachate. Membrane bioreactors (MBRs) were capable of removing more than 80% of the nonylphenol load. Final effluent concentrations range between 1-12 microg/L nonylphenol and 3-30 microg/L bisphenol A respectively. Reverse osmosis treatment proved to be less effective in nonylphenol and bisphenol A removal than MBR with further polishing stages like nanofiltration and activated carbon adsorption.