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The multi-criteria analysis gives the opportunity to researchers, designers and decision-makers to examine decision options in a multi-dimensional fashion. On this basis, four tertiary wastewater treatment (WWT) technologies were assessed regarding their sustainability performance in producing recycled wastewater, considering a 'triple bottom line' approach (i.e. economic, environmental, and social). These are powdered activated carbon adsorption coupled with ultrafiltration membrane separation (PAC-UF), reverse osmosis, ozone/ultraviolet-light oxidation and heterogeneous photo-catalysis coupled with low-pressure membrane separation (photocatalytic membrane reactor, PMR). The participatory method called simple multi-attribute rating technique exploiting ranks was employed for assigning weights to selected sustainability indicators. This sustainability assessment approach resulted in the development of a composite index as a final metric, for each WWT technology evaluated. The PAC-UF technology appears to be the most appropriate technology, attaining the highest composite value regarding the sustainability performance. A scenario analysis confirmed the results of the original scenario in five out of seven cases. In parallel, the PMR was highlighted as the technology with the least variability in its performance. Nevertheless, additional actions and approaches are proposed to strengthen the objectivity of the final results. [ABSTRACT FROM AUTHOR]

An anaerobic phosphorus release tank was introduced to an anaerobic-anoxic-aerobic (A2/O) process treating domestic sewage to enhance the phosphorus removal at low temperature. Phosphorus release of the activated sludge from the second sedimentation tank was evaluated at 14 WC by batch cultures, and the nutrient removal in the modified low temperature A2/O process was further investigated at the same temperature. The results showed that the feasible sludge retention time was 14 h for sequencing batch reaction and 12 h for continuous flow operation. The ratio of raw sewage to activated sludge from the second sedimentation tank was 1:1 in volume to meet the demand of carbon resource for the growth of phosphorus release microbes. The feasible chemical oxygen demand (COD) loading rate of the activated sludge in the phosphorus release tank was 0.015-0.02 g COD/g MLSS (mixed liquor suspended solids) and the nitrate concentration should be less than 5 mg/L. The phosphorus release was doubled when the sludge was blended intermittently and gently. The anaerobic phosphorus release of the activated sludge improved the phosphate removal remarkably, as well as the removal of NH4+-N and total nitrogen (TN) in the modified low temperature A2/O process. The effluent COD, NH4+-N, TN and total phosphorus could meet a stricter discharge standard. [ABSTRACT FROM AUTHOR]

Photocatalytic activities were found to be enhanced when noble metals were deposited on the semiconductors because the metal nanoparticles store electrons within them and in turn are recognized to act as a sink for photoinduced charge carriers, promoting interfacial charge transfer processes. This motivates us to modify the bare ZnO powder by doping with nano sized silver to yield metal-semiconductor nanocomposites by simple material syntheses route to suppress detrimental recombination of the photogenerated charge carriers. The materials were characterized by different analytical techniques and it is potentially utilized for the photocatalytic degradation of an azo dye (Acid Red 88; AR88) in the visible region (λ > 400 nm). A possible mechanism for the photocatalytic degradation of AR88 by Ag-ZnO in the absence and presence of other oxidizing agents (peroxomonosulfate (PMS), peroxodisulfate (PDS) & hydrogen peroxide (H2O2)) has been proposed. The extent of mineralization of the target pollutant was also evaluated using Total Organic Carbon (TOC) analysis. [ABSTRACT FROM AUTHOR]

During the last two decades there has been growing interest in the capacity of riparian buffer zones to remove nitrate from ground waters moving through them. Riparian zone sediments often contain organic carbon, which favors formation of reducing conditions that can lead to removal of nitrate through denitrification. Over the past decade the National Water Quality Assessment (NAWQA) Program has investigated the transport and fate of nitrate in ground and surface waters in study areas across the United States. In these studies riparian zone efficiency in removing nitrate varied widely as a result of variations in hydrogeologic factors. These factors include (1) denitrification in the up-gradient aquifer due to the presence of organic carbon or other electron donors, (2) long residence times (>50 years) along ground-water flow paths allowing even slow reactions to completely remove nitrate, (3) dilution of nitrate enriched waters with older water having little nitrate, (4) bypassing of riparian zones due to extensive use of drains and ditches, and (5) movement of ground water along deep flow paths below reducing zones. By developing a better understanding of the hydrogeologic settings in which riparian buffer zones are likely to be inefficient we can develop improved nutrient management plans. [ABSTRACT FROM AUTHOR]

The amount of assimilable organic carbon (AOC) and bacterial regrowth was studied in drinking waters from seven Finnish surface and groundwater works. Bacterial regrowth in drinking waters was studied by in vitro laboratory incubation tests and by enumerating the microbes in distribution networks. Bacterial numbers were counted as heterotrophic viable counts and as total direct counts (AODC). The bacterial production activity was studied as ³H-thymidine uptake. AOC, measured with a bioassay was 390±130mg/l and 170±60mg/l in drinking waters produced from surface waters and from groundwaters respectively. The content of AOC was slightly reduced in distribution pipelines of groundwater works whereas in the distribution pipelines of surface water works it was reduced by 40%. Bacterial regrowth occurred in all drinking waters. Surprisingly, the heterotrophic regrowth was greater in drinking waters produced from groundwaters than in those produced from surface waters. AOC levels correlated poorly with the in vitro bacterial growth tests and with occurrence of bacteria in distribution networks. [ABSTRACT FROM AUTHOR]