A two-sludge system is one of the wastewater treatment systems to utilize denitrifying phosphate accumulating organisms (DPAOs) which can simultaneously remove nitrogen and phosphorus under an anoxic condition. In the two-sludge system, DPAOs for denitrification-dephosphatation are separated from a nitrification process. The denitrification-dephosphatation process consists of anaerobic, anoxic and reaeration treatments. In this study, 4 sets of operational conditions of the denitrification-dephosphatation process were investigated using sequencing batch reactor (SBR), in terms of removal efficiencies and accumulation of DPAOs. In the SBR experiment, treated water in the nitrification process was replaced by KNO3 solution. In runs with only a 10-min reaeration or a limited aeration, SVI increased to 300 mL/g and some activated sludge was washed out. The run with a 60-min reaeration following 90-min anaerobic and 120-min anoxic treatments showed a good sedimentation property and the best nitrogen and phosphorus removal, so they were selected as the improved system conditions. From the calculations based on pumping rates and oxygen demands, it was found that the electricity consumption of the two-sludge system was about 30% less than the A2/O system, because no circulation pump was necessary and aeration time was shortened.
During the monsoon season in 2011 (July to August), 33 rainwater samples were collected at Gongabu, Kathmandu Valley, Nepal. The major ions and stable isotopic compositions of nitrogen and oxygen of NO3- were measured to identify the NO3- sources in rainwater. Temporal variation in the major ions in rainfall shows that higher concentration corresponds to low rainfall, but a high volume of rainfall also shows the same pattern, indicating an atmosphere polluted with dust. Rainwater chemistry was analyzed using correlation and principal component analysis to identify the possible sources of the measured ions. Two components were identified, which accounted for 85.5% of total variance: (1) soil and secondary particles (73.6%) that were possibly from fertilizers and incomplete combustion of fuel (K+, Cl-, NH4+, NO3-, SO42- and Mg2+); and (2) soil (11.9%) of natural origin (Ca2+ and HCO3-). The concentration of NH4+ was generally high when compared to NO3-. However, NO3- concentration was high in some rainfall events, making it difficult to identify the origin as either agricultural or industrial activities. The δ15N value was within the range -5.9‰ to +3.3‰ for NO3-. Moreover, a relatively low and unique value of δ18O of NO3- (+12.2‰ to +44.5 ‰) was found, compared with most values reported from around the world (› +60 ‰). This suggests the deposition of soil containing nitrate fertilizers and its mixture of atmospheric nitrate that had low δ18O values.
This study examined the mechanisms of dominant species transition from Microcystis aeruginosa to mainly Cyclotella sp. and also Scenedesmus quadricauda as a consequence of phosphorus reduction caused by dilution in Lake Tega. The growth potentials and competitive abilities for each species were investigated through a series of culture experiments and the effect of phosphorus fluctuation on the species transition was discussed. The monoculture experiment for each species showed that S. quadricauda possessed the growth superiorities compared to other species under phosphorus-limited condition, representing the highest maximum growth rate (0.32 day-1) and the highest Chl.a division ability (5.6 times) in phosphorus-free condition. The competitive experiment culturing all species together in the same medium indicated that the condition at PO4-P = 0.5 mg/L led to the predominance of M. aeruginosa, reflecting the condition before dilution. On the other hand, at PO4-P = 0.1 mg/L, which represented the condition after dilution, S. quadricauda completely dominated and the predominance of Cyclotella sp. was never observed. Accordingly, it could be concluded that the predominance of Cyclotella sp. was affected by the dilution in Lake Tega and would be attributed not to phosphorus reduction but other factors such as nitrogen, light intensity, dilution rate and/or their interaction.
Rapid urbanization and population growth, coupled with climate change, have created major challenges on urban planners and water professionals in Hanoi City to find out effective measures to sustain the growing water demand of the city. This study investigates the recent trends in residential water use, as well as the principal factors and challenges that affect the water demand of the city. A series of micro-component surveys have been conducted for a better understanding of water usage, and potential of water saving and demand management at household levels. Consequently, a range of effective water demand management (WDM) interventions, including water metering, reduction of water loss, promotion of using water-wise appliances, reforming water tariff structure to promote responsible uses, and utilization of rainwater, have been proposed as strategic approaches towards a sustainable urban water use system for the city in the future. Prospects and constraints likely to be faced while implementing these WDM interventions are also discussed in this paper.
The reduction of selenate [Se(VI)] from a simulated wet flue gas desulfurization (FGD) wastewater was attempted using photocatalyst and microorganisms. The photocatalyst reduction method consisted of TiO2 and HCOOH as a photocatalyst and a hole scavenger, respectively. When a simple 0.5 mg/L Se(VI) solution was used, the photocatalytic reduction gave an efficient removal of Se(VI). In contrast, the photocatalytic reduction could not remove Se(VI) from the simulated FGD wastewater, due to the excess amount of co-existing SO42- anion. Also, a biological reduction which used Se(VI)-reducing bacteria was investigated. When three kinds of bacteria (E. cancerogenus, P. stutzeri, and P. denitrificans) were used, Se(VI) in the simple 0.5 mg/L Se(VI) solution was effectively removed. However, for E. cancerogenus, the removal of Se(VI) was inhibited by the co-existing NO3- anion in the wastewater.
In the present study, to evaluate the conversion of intracellular PHB to methane gas, excess activated sludge with and without the accumulation of polyhydroxybutyrate (PHB) was subjected to anaerobic digestion. Excess activated sludge was collected from a laboratory activated sludge reactor and a part was fed with acetate in aerobic condition to obtain excess activated sludge with PHB accumulation. Then, excess activated sludge with and without PHB accumulation were mixed with anaerobic digested sludge, and the degradation of PHB and formation of methane gas were monitored during anaerobic fermentation at 37°C. For excess sludge with PHB accumulation, more than 75% of PHB was degraded only within the initial 2 days of incubation. Besides, 25% more methane gas was produced from excess sludge with PHB than without PHB accumulation. High production of methane gas indicates that PHB accumulated inside the cells of heterotrophic bacteria can easily be digested in anaerobic digestion process.
Typhoon No. 14 that hit Japan on 30th October 2010 brought a huge water mass that increased the water volume and nutrient into the Atsumi Bay estuary, Japan. The aims of this research were to clarify the impact of a typhoon on the physical properties and nutrient concentrations of Atsumi Bay. This study summarizes the effects of a typhoon on nutrient fluxes from rivers to the estuary, which is revealed by the less-saline surface coastal water. The elevated surface chlorophyll a concentrations along the Toyo River transect were possibly caused by phytoplankton uptake on nutrient supply. The greatest increases of concentrations of nitrogen and phosphorus after typhoon generally appeared in the surface waters along the Umeda River transect caused by high nutrient concentrations from Umeda River; but decreased along the Toyo River transect due to dilution by seawater and possibly caused by phytoplankton uptake. The pre-typhoon predominant species of dissolved nitrogen (DN) is dissolved organic nitrogen (DON), it was changed to be 54% of dissolved inorganic nitrogen (DIN) along the Umeda River transect after typhoon in the surface layer. The lower post-typhoon bottom concentration of nutrient along both the Toyo and Umeda River transects was influenced by the disturbances of hypoxic condition in the bottom layer.
A microbial fuel cell (MFC) is defined as a system in which microorganisms function as catalysts to convert chemical energy into electrical energy. A typical MFC acts with a couple of reactions; anodic bioreactions by exoelectrogenic bacteria and a cathodic reaction of oxygen reduction. This research focused on the cathodic reaction of a single chamber MFC with a cathode exposed to the air (air-cathode), and the pH of water attached on air-cathode (air-cathode pH) was actively controlled for the enhancement of the cathodic reaction. The active control of the air-cathode pH successfully improved the coulombic efficiency of the MFC due to the enhancement of proton supply to the air-cathode, which accelerated the cathodic reaction. The enhancement effect at the acidic condition of the air-cathode pH was larger than that at neutral and alkaline conditions. However, the long-term operation revealed that the power generation almost stopped at the acidic condition due to the inactivation of exoelectrogenic bacteria on the anode. Consequently, pH 7.0 was the most effective condition in this study. In this condition, no bad influence was observed on the biofilm. The observed electric current and coulombic efficiency were 2.9 and 2.7 times higher than those without the air-cathode pH control, respectively.
Feasibility study of an up-flow staged sludge bed (USSB) for treatment of starch wastewater industry was investigated. The bioreactor was examined under both acidogenesis and methanogenesis conditions for hydrogen and methane production, respectively. The acidogenic reactor was operated at a hydraulic retention time (HRT) of 8 h and organic loading rate (OLR) of 60.0 ± 6.6 kg-COD/(m3•d). Hydrogen yield was 312.5 ± 26.2 L-H2/kg-COD-removed representing 22.5% of the theoretical value. At longer HRT of 24 h and OLR of 20.0 ± 2.2 kg-COD/(m3•d), 41.0 ± 3.6% of the total influent COD was converted to methane, and amounted to 240.0 ± 18.1 L-CH4/kg-COD-removed which represented 68% of the theoretical value. These results were used to estimate the cost and economic analysis of a full scale starch wastewater treatment plant treating 300 m3/d. Environmental benefits provided an additional profits to enhance the cash-flow analysis. The economic analysis revealed that, starch wastewater treatment plant would return its investment in a payback period of 1.9 ± 0.1 and 1.8 ± 0.1 years, with an energy profit of 22 and 11.23 US$/GJ in terms of hydrogen and methane production, respectively.