Method selection for sustainability assessments: The case of recovery of resources from waste water.

Sustainability assessments provide scientific support in decision procedures towards sustainable solutions. However, in order to contribute in identifying and choosing sustainable solutions, the sustainability assessment has to fit the decision context. Two complicating factors exist. First, different stakeholders tend to have different views on what a sustainability assessment should encompass. Second, a plethora of sustainability assessment methods exist, due to the multi-dimensional characteristic of the concept. Different methods provide other representations of sustainability. Based on a literature review, we present a protocol to facilitate method selection together with stakeholders. The protocol guides the exploration of i) the decision context, ii) the different views of stakeholders and iii) the selection of pertinent assessment methods. In addition, we present an online tool for method selection. This tool identifies assessment methods that meet the specifications obtained with the protocol, and currently contains characteristics of 30 sustainability assessment methods. The utility of the protocol and the tool are tested in a case study on the recovery of resources from domestic waste water. In several iterations, a combination of methods was selected, followed by execution of the selected sustainability assessment methods. The assessment results can be used in the first phase of the decision procedure that leads to a strategic choice for sustainable resource recovery from waste water in the Netherlands.

Bio-plastic (poly-hydroxy-alkanoate) production from municipal sewage sludge in the Netherlands: a technology push or a demand driven process?

Valorisation of components from municipal 'waste' water and sewage sludge gets more and more attention in order to come to a circular economy by developing an efficient 'waste' to value concept. On behalf of the transition team 'Grondstoffenfabriek' ('Resource factory') a preliminary research was performed for all the Dutch water boards to assess the technical and economical feasibility of poly-hydroxy-alkanoate (PHA)-production from sewage sludge, a valuable product to produce bio-plastics. This study reveals that the production of bio-plastics from sewage sludge is feasible based on technical aspects, but not yet economically interesting, even though the selling price is relatively close to the actual PHA market price. (Selling price is in this particular case the indicative cost effective selling price. The cost effective selling price covers only the total production costs of the product.) Future process optimization (maximizing the volatile fatty acids production, PHA storage capacity, etc.) and market developments are needed and will result in cost reductions of the various sub-processes. PHA-production from sewage sludge at this stage is just a technology; every further research is needed to incorporate the backward integration approach, taking into account the market demand including associated product quality aspects.

Investigating phosphorus limitation in a fixed bed filter with phosphorus and nitrogen profile measurements.

In 2000, the European Union adopted the European Water Framework Directive (WFD) (European Commission, 2000). The WFD focuses on increasingly stringent nutrient standards including ultra low nitrogen (< 2.2 mg N-total/L) and phosphorus concentrations (< 0.15 mg total phosphorus/L) in receiving surface waters and in relevant point sources like wastewater treatment plant (WWTP) effluent. Expansion of WWTPs with advanced post-treatment processes, like effluent filtration, is widely proposed to meet possible future effluent discharge standards. When combining biological nitrate-nitrogen and chemical phosphorus removal in one filter, phosphorus limitation in the denitrifying process may occur. This study investigated where in the filter bed and under which conditions phosphorus limitation occurs. Profile measurements for nitrate, nitrite, and orthophosphorus (PO4-P) combined with chemical oxygen demand (COD) and 02 were conducted. Results showed that the required PO4-P/NOx-N ratio is approximately 0.006 mg/mg after phosphorous precipitation and flocculation. Profile measurements have proven to be an applicable and useful tool. It showed how nitrate and orthophosphorus are removed through the filter bed based on the PO4-P/NOx-N ratio. When orthophosphorus is removed more rapidly and efficiently compared to nitrate, the PO4-P/NOx-N ratio decreases. When PO4-P/NOx-N ratio thresholds are approximately 0.006 mg/mg for a certain period of time and water temperatures varied significantly, orthophosphorus limitation may occur. Changing the filter-bed configuration or decreasing the coagulant dosage can prevent limitation of the denitrifying process because of a phosphorous shortage.

Advanced treatment of WWTP effluent with filtration leading to a pretreatment technique for membrane filtration.

In 2000 the European Union introduced the Water Framework Directive (WFD). The aim of the WFD is having an ecological and chemical balance for all surface waters in Europe in 2015. The European Commission identified 33 priority substances and their maximum allowable concentrations, FHI-values (Fraunhofer Institute), which are specified in the Annex of the WFD. The objective of this research is to achieve the removal of suspended solids, nitrogen and total phosphorus together with priority substances. All these substances will be removed in one filter called a "One Step Total Effluent Polishing filter" i.e. 1-STEP(®) filter. For this purpose a filter pilot plant was tested at the WWTP Horstermeer. The results show that the filter can fulfil the target values in the filtrate water for total nitrogen (2.2 mg Ntotal/L) and total phosphorus (0.15 mg Ptotal/L). The majority of the priority (hazardous) substances in the WWTP effluent are already below the detection limit. Due to the low concentration ranges, the results on the removal of medicine and pesticides are only indicative. A decreasing tendency in the removal efficiency is shown for all measured compounds. The average specific ultrafiltration resistance (SUR) value decrease of the filter is 55% and the final value is always below 5·10(12) m(-2). This indicates that the filtrate water of the filter is very well filterable and can be used as ultrafiltration feedwater.

Innovative phosphorus distribution method to achieve advanced chemical phosphorus removal.

Since November 2006 a large-scale research project has been carried out at Wastewater Treatment Plant (WWTP) Leiden Zuidwest (within the Rijnland District Water Control Board). This research focuses on advanced removal of nutrients (phosphorus and nitrogen), heavy metals and priority hazardous substances from WWTP-effluent with different treatment techniques to reach an effluent quality, which could be required in the future by the Water Framework Directive (WFD) 2000/60/EC. Within the WFD-approach to guarantee an ecological and a chemical "good status" of the receiving water bodies, the focus is more and more on ultra low phosphorus concentrations in effluent. To be able to reach these stringent goals more insight into phosphorus components in effluent is required. A new method of distribution of phosphorus is used to determine orthophosphate, metal bound phosphorus, dissolved "organic" phosphorus and particulate "organic" phosphorus. This knowledge about the distribution of phosphorus makes it possible to compare different filter concepts and different process parameters, for example flocculation time, initial mixing energy and filtration rates. When comparing (filter concept 1) continuous sand filtration with (filter concept 2) dual media filtration for phosphorus removal, it appears that, a higher percentage of the formed metal bound phosphorus will pass the continuous sand filter. The ortho-phosphorus which is not bound to trivalent metal after coagulation will remain dissolved ortho-phosphorus and will pass the filter bed. This is shown in both filter concepts. The dissolved 'organic' phosphorus decreases after flocculation and the particulate 'organic' phosphorus increases which suggests that it may be colloidal or associated with colloidal material. With continuous sand filtration 50% of the particulate phosphorus is removed. In the dual media filter even 86% of the particulate phosphorus is removed.

The limits and ultimate possibilities of technology of the activated sludge process.

The (low loaded) biological nutrient removing activated sludge process is the generally accepted and applied municipal wastewater treatment method in the Netherlands. The hydraulical and biological flexibility, robustness and cost efficiency of the process for advanced removal of nutrients like nitrogen and phosphorus without (too much) chemicals results in a wide application of the activated sludge process within Dutch waterboards. Presumably, wastewater treatment plants will have to contribute to the improvement of the quality of the receiving surface waters by producing cleaner effluent. In this perspective, the Dutch research organisation STOWA initiated a research project entitled "The Boundaries of the Activated Sludge Process" to investigate the possibilities and limitations of activated sludge processes to improve the effluent quality. It is concluded that the activated sludge process as applied and operated at WWTP's in the Netherlands has the potential to perform even better than the current effluent discharge standards (10 mg Ntotal/l and 1 mg Ptotal/l). Reaching the B-quality effluent (<5mg Ntotal/l and <0.3 mg Ptotal/l) will be possible at almost all WWTPs without major adjustments under the conditions that: the sludge load is below 0.06 kg BOD/kg TSS.d the internal recirculation is above 20 the BOD/N ratio of the influent is above 3. Complying with the A-quality effluent (<2.2 Ntotal/l and <0.15 mg Ptotal/l) seems to be difficult (but not impossible) and requires more attention and insight into the activated sludge process. Optimisation measures to reach the A-quality effluent are more thorough and are mostly only achievable by additional construction works (addition of activated sludge volume, increasing recirculation capacity, etc.). It is furthermore concluded that the static HSA-results are comparable to the dynamic ASM-results. So, for fast determinations of the limits of technology of different activated sludge processes static modelling seems to by sufficient.

Review on the state of science on membrane bioreactors for municipal wastewater treatment.

Over the past two decades the field of application for membrane bioreactors has broadened towards the municipal wastewater treatment sector. The Global Water Research Coalition (GWRC) determined MBR technology to be of priority for collaborative research and decided to conduct a project with the aim to determine the current state of the science in the field of MBR for municipal wastewater treatment and to develop a phased research strategy represented by priority research projects, like a State of the Science report with regard to MBR technology. This paper describes the state of the science with regard to MBR technology for municipal wastewater treatment by 2007, derived by literature review on recent publications, database analysis and international questionnaires. The research efforts from the past seven years can be characterised by the following prioritised list: (1) membrane fouling, (2) effluent quality, (3) energy consumption (aeration) and (4) cost considerations. The research needs for the near future as identified with the questionnaire are comparable to the main topics of research as identified in the literature review: membrane fouling is still the main problem requiring thorough attention from scientists; effluent quality is a main driver for the application of the technology. There remain some important questions however, with regard to the removal of EDC and micro pollutants. Much of the research activities on MBR are repeated more than once by research groups world-wide. This is only partially caused by a lack of knowledge exchange between researchers. However, lacking information exchange between Europe and the USA on MBR research is identified as a potential bottleneck. Another point of attention is the fast that research results can not easily be translated to other (more practical) situations, since much of the research is carried out at pilot scale.

Particle related fractionation and characterisation of municipal wastewater.

Several studies show that a more detailed characterisation of the particulate matter in municipal wastewater gives a better understanding and prediction of removal efficiencies of physical-chemical treatment techniques and the application of optimal chemical dosages. Such a characterisation should include the distribution of contaminants over various particle sizes. This article describes a method and results of experimental and full-scale investigations, conducted to determine how contaminants in wastewater are distributed over different particle sizes. For this purpose, particle size fractionations of wastewater influents originating from more than thirteen WWTP were carried out. One of these fractionations (WWTP Venray) is shown and interpreted in this article. First, the wastewaters were fractionated into 5 to 6 particle fractions (45, 5.0, 1.0/1.2, 0.45 and 0.1 microm) after which the fractions were analyzed for various water quality parameters like organic components, nutrients, salts, solids and turbidity. Based on the results the effects of removal of the different size fractions on design of the biological treatment and energy balance of a wastewater treatment plant can be assessed. The method also indicates whether a certain wastewater is efficiently treatable with physical-chemical pre-treatment methods. It is concluded wastewater fractionation on particle size is very useful, but that wastewater characteristics and particle size distributions should not be generalised, but have to be interpreted as indications for a certain average wastewater composition. To give more insight into the distribution of contaminants over particle size and the particle removal potential, a specific wastewater fractionation has to be carried out per WWTP.

Flotation with polyelectrolytes as a first step of a more sustainable wastewater treatment system.

Within the framework of a research programme into more sustainable wastewater treatment systems based on physical-chemical pretreatment the application of dissolved air flotation (DAF) with polyelectrolytes as a primary treatment was investigated. Experiments with municipal wastewater were carried out in 2.5 I flotation batches and in a 100 I DAF pilot reactor. Two cationic polyelectrolytes (PEs) with molecular weights of 4 x 10(6) g/mol and 8 x 10(6) g/mol, were tested. The higher weight PE was more effective in removing turbidity and was used in the pilot experiments for coagulation/flocculation. Within the pilot system experiments the dry solids concentration of the float layer as well as the removal efficiencies of turbidity, CODparticulate, CODdissolved and nutrients, were studied. Typical results were that the obtained dry solids concentration of the floated sludge was 10%, when the float layer was removed after several hours. By using polyelectrolytes it was possible to remove more than 80% of CODparticulate and turbidity at dosages of 7-8 mg/g influent COD (i.e. 5 mg PE/100 NTU). The removal efficiency of CODdissolved was low. There was a proportional relationship between CODparticulate and turbidity. This led to the conclusions that by introducing a dosing control strategy based on continuous turbidity measurements a constant CODparticulate removal efficiency can be obtained.

Direct influent filtration as a pretreatment step for more sustainable wastewater treatment systems.

Within the scope of a research programme into wastewater treatment scenarios based on physical-chemical pretreatment, the application of direct influent filtration (DIF) as a first treatment step in a wastewater treatment system was investigated. The aim of the experimental research was to investigate the feasibility of DIF as a pretreatment step for advanced particle removal. With a large scale pilot-plant filter at WWTP Leiden-Noord, The Netherlands the removal characteristics for suspended and colloidal material were investigated as well as operational conditions of eight different filter configurations. From the experimental research it was concluded that filtration of raw wastewater is possible, notwithstanding the relatively short run-times due to clogging. In general, the filters produced a filtrate with a constant quality with low concentrations of solids and low turbidity. Without addition of chemicals hardly any colloids and solubles were retained, but only suspended particulates were removed. After dosage of iron or polymer, it was possible to remove more suspended matter and a high proportion of colloidal material. Finally it was concluded that DIF could be applied as a compact treatment system to produce a high quality primary effluent with a constant composition, but for practical application further research has to be done.