A. F. van Nieuwenhuijzen

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.

Direct Wastewater Membrane Filtration for Advanced Particle Removal from Raw Wastewater

Direct filtration techniques were applied for fast and advanced particle removal in the pre-treatment of municipal wastewater, in order to optimise the total wastewater treatment system. Pilot-scale research into direct membrane ultrafiltration of raw wastewater indicated that this technique might be feasible. There was an average normalised production flux of 300 l/m2·h·bar at a TMP of 0.2 to 0.4 bar and a cross flow rate of 2.4 m/s. Removal performances were excellent with all suspended and colloidal substances being removed by the membranes with pore size of 30 nm. Furthermore the influence of the cross flow rate, the applied TMP and the cleaning procedure on the filtration performance was investigated. It was concluded that direct membrane filtration shows potential for wastewater treatment.

Cationic organic polymers for flocculation of municipal wastewater - Experiments and scenario study

Organic polymers can be favourable flocculants in comparison with inorganic (metal-)flocculants because chemical sludge production is absent and the increase in salt concentration of the effluent is low. Jar test experiments showed that a higher weight (8.106 g/mol; (+) 24%) cationic polyacrylamide gave good flocculation results, with turbidity- and CODparticulate removal efficiencies of 65-90% and a TSS removal of > 90% at relatively low dosing concentrations. Rapid coagulation mixing conditions were optimal with a mixing time of 30 s (G = 800 s-1). A decrease in low flocculation mixing time from 180 s to 30 s (G = 50 s-1) resulted in a decrease in particle removal of 25%. A scenario study was conducted to estimate the costs involved and to quantify the environmental impacts. The scenario study showed that the total costs of a complete wastewater treatment system based on coagulation-flocculation with organic polymers are in the same range (-5%) as those of a system with FeClv Total sludge production is 15% lower. Salinisation is of the order of +0.2 mg Cl per litre effluent for dosing polymer and +29 mg Cl per litre effluent for dosing FeCl3.