Treatment of domestic sewage by a metal membrane bioreactor

A submerged flat metal MBR (membrane bioreactor) was used to treat synthetic domestic sewage in this study. The experiment was continued for 270 days and ran under two modes as AMBR (aerobic membrane bioreactor) and A/O-MBR (anoxic/aerobic membrane bioreactor) at a permeate flux of 0.4-1 m3/(m2 d). PVA (polyvinyl alcohol) gel beads were added to the aeration tank with a volume ratio of 10% at the end of the A/O-MBR mode. The mean COD and TN removal efficiencies achieved 96.69 and 32.12% under the AMBR mode, and those were 92.17 and 72.44% under the A/O-MBR mode, respectively. SND (simultaneous nitrification and denitrification) occurred at high MLSS (mixed liquor suspended solids) concentration. The metal membranes reduced effluent COD during filtration. The system ran stably for 115 days at a permeate flux of 0.8-1 m3/(m2 d) without changing membranes under the AMBR mode, but the membrane filterability decreased gradually under high MLSS or A/O-MBR mode, and the addition of PVA worsened the membrane filterability on the contrary. PSD (particle size distribution) and sludge fractions had evident influence on membrane fouling. The main fouling mechanism was cake formation under the AMBR mode, and that was pore blocking under the A/O-MBR mode.     

Denitrification with corncob as carbon source and biofilm carriers

In this research the agricultural by-product corncob was investigated as a carbon source as well as a biofilm carrier to remove organic matter, expressed as chemical oxygen demand (COD) and nitrate nitrogen (nitrate-N), from wastewater in a batch laboratory reactor. The performance of a reactor with corncob as the carbon source and the biofilm carrier was compared with a control batch reactor with suspended plastic carriers and glucose as the sole carbon source. With 60 vol% of corncob carriers inside the reactor, a soluble COD/N ratio of 4.2 g COD g N(-1) was enough for total denitrification, nearly half of the control reactor (9.5 g COD g N(-1)), at 23 h reaction time. The specific denitrification rate decreased with increasing soluble COD consumption for both reactors. Nitrate and COD removal efficiencies decreased with shorter retention times, with accentuated effects in the reactor. This study suggested corncob as a feasible carbon source and that reaction time was a limiting factor with corncob used as the carbon source for denitrification.     

Confectionery industry: a case study on treatability-based effluent characterization and treatment system performance

Source-based wastewater characterization and stream segregation provide effective management of industrial wastewaters. The characterization of wastewater sources from a confectionery factory was presented and performance of the wastewater treatment plant was evaluated in this study. All of the wastewater sources in the factory, except the vacuum water line, can be characterized by high concentrations of soluble pollutants and low pH. High organic content of the wastewater generated from the confectionery industry promoted the application of anaerobic technology as a pre-treatment before the conventional aerobic treatment. The average chemical oxygen demand (COD) removal and biogas production for expanded granular sludge bed reactor were 88% and 1,730 Nm(3)/day, respectively. The effluent from the investigated facility can be used for irrigation provided that conductivity values are within acceptable limits.     

Nitrogen and phosphorus effluent loads from a paddy-field district adopting collective crop rotation

Japanese paddy rice systems commonly adopt the rotation of vegetables, wheat and soybeans with paddy rice. Crop rotation may, however, increase the nutrient load in effluent discharged from the district because more fertilizer is applied to the rotation crops than is applied to paddy crops. We investigated a paddy-field district subject to collective crop rotation and quantified the annual nutrient load of effluent from the district in three consecutive years. The total annual exports of nitrogen and phosphorus over the investigation period ranged from 30.3 to 40.6 kg N ha(-1) and 2.62 to 3.13 kg P ha(-1). The results suggest that rotation cropping increases the effluent nutrient load because applied fertilizer is converted to nitrate, and surface runoff is increased due to the absence of shuttering boards at the field outlets.     

Diel vertical migration and nutrient transport of the dinoflagellate Peridinium bipes f. occultatum in a thermally stratified reservoir

Field observations were conducted with respect to the vertical migration of the dinoflagellate Peridinium bipes and its influence on vertical nutrient transport in a stratified reservoir. P. bipes migrated vertically with circadian rhythms; that is, P. bipes migrated downward and accumulated in the top layer of the hypolimnion from evening to night and then migrated upward and accumulated in the epilimnion in the early morning. In the top layer of the hypolimnion, a rapid decrease in nutrient concentration was observed in the evening, presumably due to uptake by P. bipes. Active migration from the epilimnion to the top of the hypolimnion was also suggested by estimation of the descent velocity of P. bipes, which was advantageous for the uptake of nutrients. Moreover, based on the equilibrium of forces during migration, the energy cost of vertical migration could be inferred to be negligible. The results suggest that active vertical migration of P. bipes played an important role in nutrient transport between the hypolimnion and the epilimnion in a stratified reservoir.     

Performance evaluation and effect of biogas circulation rate of a bubble column for biological desulfurization

Biological desulfurization using a bubble column reactor was investigated in a continuous biogas treatment. Rapid biogas circulation between the digester and the bubble column for biological desulfurization was used to stimulate the gas-liquid mass transfer of H(2)S. A positive correlation between the biogas circulation rate and H(2)S removal rate was observed. Moreover, the increase in the circulation rate stimulated the O(2) mass transfer, eventually translating into an increase in sulfate production from the oxidation of H(2)S. Throughout the continuous experiment, the reactor retained sufficient levels of sulfide-oxidizing bacteria. A comparison of the results of the continuous biogas treatment and batch tests suggests that the gas-liquid mass transfer rate of H(2)S was the rate-limiting step in the biological desulfurization in the reactor, indicating that the mass transfer efficiency of H(2)S needs to be improved to enhance the desulfurization performance.     

Removal of micropollutants in municipal wastewater treatment plants by powder-activated carbon

Micropollutants (MP) are only partly removed from municipal wastewater by nutrient removal plants and are seen increasingly as a threat to aquatic ecosystems and to the safety of drinking water resources. The addition of powder activated carbon (PAC) is a promising technology to complement municipal nutrient removal plants in order to achieve a significant reduction of MPs and ecotoxicity in receiving waters. This paper presents the salient outcomes of pilot- and full-scale applications of PAC addition in different flow schemes for micropollutant removal in municipal wastewater treatment plants (WWTPs). The sorption efficiency of PAC is reduced with increasing dissolved organic carbon (DOC). Adequate treatment of secondary effluent with 5-10 g DOC m(-3) requires 10-20 g PAC m(-3) of effluent. Counter-current use of PAC by recycling waste PAC from post-treatment in a contact tank with an additional clarifier to the biology tank improved the overall MP removal by 10 to 50% compared with effluent PAC application alone. A dosage of 15 g PAC m(-3) to a full-scale flocculation sand filtration system and recycling the backwash water to the biology tank showed similar MP elimination. Due to an adequate mixing regime and the addition of adapted flocculants, a good retention of the fine fraction of the PAC in the deep-bed filter were observed (1-3 g TSS m(-3); TSS: total suspended solids). With double use of PAC, only half of the PAC was required to reach MP removal efficiencies similar to the direct single dosage of PAC to the biology tank. Overall, the application of PAC in WWTPs seems to be an adequate and feasible technology for efficient MP elimination (>80%) from wastewater comparable with post ozonation.     

Revealing microbial community structures in large- and small-scale activated sludge systems by barcoded pyrosequencing of 16S rRNA gene

The diversity of bacterial groups in activated sludge from large- and small-scale wastewater treatment plants was explored by barcoded pyrosequencing of 16S rRNA gene. Activated sludge samples (three small and 17 large scale) were collected from 12 wastewater treatment plants to clarify precise taxonomy and relative abundances. DNA was extracted, and amplified by 4 base barcoded 27f/519r primer set. The 454 Titanium (Roche) pyrosequences were obtained and analyses performed by Quantitative Insight Into Microbial Ecology (QIIME) with around 100,000 reads. Sequence statistics were computed, while constructing a phylogenetic tree and heatmap. Computed results explained total microbial diversity at phylum and class level and resolution was further extended to Operational Taxonomic Unit (OTU) based taxonomic assignment for investigating community distribution based on individual sample. Composition of sequence reads were compared and microbial community structures for large- and small-scale treatment plants were identified as major phyla (Proteobacteria and Bacteroidetes) and classes (Betaproteobacteria and Bacteroidetes). Also, family level breakdowns were explained and differences in family Nitrospiraceae and phylum Actinobacteria found at their species level were also illustrated. Thus, the pyrosequencing method provides high resolution insight into microbial community structures in activated sludge that might have been unnoticed with conventional approaches.     

A groundwater perspective on the river basin management plan for central Portugal - developing a methodology to assess the potential impact of N fertilizers on groundwater bodies

The Water Framework Directive establishes that the river basin management plans must have a summary of the pressures and impacts of human activities, such as agriculture, on the chemical and quantitative status of groundwater bodies. In order to identify those areas where a potential impact from agricultural activities on groundwater bodies exists, but currently lacking groundwater monitoring data, a methodology was developed that combines the use of gross nitrogen balance values with the results of a specific vulnerability assessment index. A farm management efficiency parameter is added, to identify the factors that contribute to nitrogen use efficiency and to assess the near-future scenarios. This methodology allows the identification of significant pressures that may be responsible for a groundwater body failing good status where there is no representative monitoring network.     

Restoration of stormwater retention capacity at the allotment-scale through a novel economic instrument

Urbanisation results in changes to runoff behaviour which, if not addressed, inevitably degrade receiving waters. To date, most stormwater management has focussed on the streetscape and public open space. Given that much of the catchment imperviousness is located on private land, we developed and tested a novel economic instrument (a uniform price auction) for encouraging allotment-scale stormwater retention. We evaluated bids using an integrated environmental benefit index (EBI), based on the ability of the proposed works to reduce runoff frequency, pollutant loads and to reduce potable water demand. The uniform price auction resulted in 1.4 ha of impervious areas being effectively 'disconnected' from the stormwater system. The EBI provided an objective and transparent method of comparing bids, which varied in the type of works proposed (e.g. rainwater tank, rain-garden), the cost and the resulting environmental benefit. Whilst the pilot auction was a success, the public subsidy of works undertaken was around 85%, meaning that property owners a relatively small private benefit in the works. Future auction rounds will be revised to (i) test an EBI which is more focussed on the protection of streams (assessing changes to runoff frequency, baseflow volumes and water quality) and (ii) provide an auction process which is simpler to understand, and provides greater practical support for landholders who wish to undertake works.