Keisuke Hanaki

Nitrous oxide production in high-loading biological nitrogen removal process under low COD/N ratio condition

Effects of influent COD/N ratio on N2O emission from a biological nitrogen removal process with intermittent aeration, supplied with high-strength wastewater, were investigated with laboratory-scale bioreactors. Furthermore, the mechanism of N2O production in the bioreactor supplied with low COD/N ratio wastewater was studied using 15N tracer method, measuring of reduction rates in denitrification pathway, and conducting batch experiments under denitrifying condition. In steady-state operation, 20-30% of influent nitrogen was emitted as N2O in the bioreactors with influent COD/N ratio less than 3.5. A 15N tracer study showed that this N2O originated from denitrification in anoxic phase. However, N2O reduction capacity of denitrifiers was always larger than NO3(-)-N or NO2(-)-N reduction capacity. It was suggested that a high N2O emission rate under low COD/N ratio operations was mainly due to endogenous denitrification with NO2(-)-N in the later part of anoxic phase. This NO2(-)-N build-up was attributed to the difference between NO3(-)-N and NO2(-)-N reduction capacities, which was the feature observed only in low COD/N ratio operations.

Nitrification at low levels of dissolved oxygen with and without organic loading in a suspended-growth reactor.

Abstract Laboratory-scale mixed flow reactors with DO (dissolved oxygen) control were operated at 25°C using substrate containing 80 mg l−1 of NH3-N. DO of 0.5 mg l−1 produced no effect on ammonia oxidation of the reactor. Determination of the biomass index based on the substrate utilization rate revealed that low levels of DO elevated the growth yield of ammonia oxidizers by double. This high growth yield compensated the reduced specific substrate utilization rate at low levels of DO. Kinetic analysis showed that the μm value was not significantly changed by low DO because of the elevated growth yield. Growth yield of nitrite oxidizers was not increased by low DO. Nitrite oxidation was strongly inhibited by 0.5 mg l−1 of DO, and accumulated nitrite reached almost 60 mg l−1. The saturation constant in terms of DO (Ko), estimated based on specific substrate utilization rate, was 0.32 mg l−1 for ammonia oxidation, while this value for nitrite oxidation could not be obtained. The interacting effect of low DO and organic loading was examined by adding glucose to the substrate. The inhibitory effect on ammonia oxidation by organic loading through heterotrophic activity was enhanced by low DO. The results suggest that the Ko value in a system with organic loading is larger than the above value which was estimated in a system without organic loading. Simultaneous nitrification and denitrification took place to some extent when glucose was fed at low DO.

Statistical downscaling of hydrometeorological variables using general circulation model output

Abstract Empirical relationships between daily hydrometeorological variables for a catchment in Nagano prefecture, Japan and three indices of regional atmospheric circulation are examined with a view to assessing their use in General Circulation Model (GCM) downscaling. The indices (vorticity, flow strength and angular direction of airflow) were calculated by using daily grid-point sea-level pressure data derived from: (a) the National Centers for Environmental Prediction, NCEP Re-analysis data set (1979–1995); and (b) the UK Meteorological Office, Hadley Centre coupled ocean-atmosphere model (HadCM2SUL) for two periods indicative of present (1980–1999) and future greenhouse gas plus sulfate aerosol forcing (2080–2099). Statistical models of the surface variables were then “forced” by using the three airflow indices obtained from HadCM2SUL. The differences between the NCEP and HadCM2SUL “present” downscaled variables were generally greater than those arising between the downscaling of the two GCM airflow scenarios. The lack of change in downscaled surface variables between the 1980–1999 and 2080–2099 data was attributed to the low sensitivity of atmospheric circulation patterns in HadCM2SUL to greenhouse gas forcing.

Effects of the activity of heterotrophs on nitrification in a suspended-growth reactor

Ammonia (80 mg l−1 as N), with various concentrations of glucose, was continuously fed to laboratory scale reactors at 25°C to examine the effect of the activity of heterotrophs on nitrification. The assimilation of ammonia by heterotrophs happened in preference to nitrification, and reduced the available ammonia for nitrification. Glucose addition of 160, 500 or 1000 mg l−1 (as COD) decreased ammonia removal and ammonia oxidation to nitrite, and elevated the effluent ammonia concentration. The results clearly indicate that the addition of organic matter, which provokes the growth of heterotrophs, inhibits ammonia oxidation. Determination of the biomass index with batch experiments enabled estimation of kinetic constants for ammonia oxidizers (μm = 0.66 d−1, K = 1.0 mg l−1) and for nitrite oxidizers (μm = 0.58 d−1, K = 0.35 mg l−1) when no glucose was added. The addition of glucose to the reactor resulted in a high K (7.2 mg l−1 when 1000 mg l−1 of COD was added) whereas μm was unchanged in the ammonia oxidation. It is suggested that inhibition takes place by decreasing the affinity between the ammonia oxidizers and ammonia. Experiments using acetate showed that toxic effect by organic matter is unlikely. One hypothesis is that transportation of ammonia from bulk water to the cell of the ammonia oxidizer is hindered by the presence of the crowded cells of the heterotrophs. Nitrite oxidation was not directly affected by organic loading.

Identification and quantification of sulfur and nitrogen containing odorous compounds in wastewater

Sulfur and nitrogen containing malodorous compounds were identified and quantified in the samples taken from each step of sewage treatment employing aerated biofilters for advanced treatment. The sulfur compounds hydrogen sulfide, carbon disulfide, methyl mercaptan, dimethyl sulfide and dimethyl disulfide were detected by using GC-FPD with a headspace method and a modified purge and cold trap method. With a purge and cold trap method and a FPD system, the minimum detectable concentration of dissolved sulfur containing volatiles reached the ng l−1 level. As nitrogen containing compounds, indole, 3-methylindole, trimethylamine, dimethylamine and n-propylamine were present in the same wastewater samples. To determine indole and 3-methylindole, n-hexane extraction method was used, and for identifying and quantifying primary and secondary phase aliphatic amines, derivatization with o-phtalaldehyde (OPA) and N-succinimdyl-p-nitrophenylacetate (SNPA) was applied with HPLC. Trimethylamine was identified by directly injecting the filtered samples into GC-FTD. Detectable concentration of dissolved low aliphatic amines and indoles was about 10 μg l−1. Large amounts of nitrogen containing compounds remained after secondary treatment compared with sulfur containing compounds.

Protection of methanogenic bacteria from low pH and toxic materials by immobilization using polyvinyl alcohol

Abstract The applicability of cell immobilization to the anaerobic treatment process using the polyvinyl alcohol (PVA)-boric acid method was investigated. The acetate-utilizing methanogens were cultivated, concentrated and immobilized. The beads formed were stable for one year maintaining methanogenic activity. The possible advantage of immobilized cells over non-immobilized cells for low pH shock and for the presence of toxic substances was examined. The immobilized cells recovered their methanogenic activity faster than the non-immobilized cells from the inhibition caused by transient low pH (5.0) for 12–48 h in a continuously fed reactor. Formation of a pH gradient within the bead due to the consumption of acetic acid inside the bead is a possible mechanism of relief of the inhibitory effect. Batch experiments showed that the inhibitory effect of phenol, oleic acid, nickel, sulfide and propionic acid on the methanogenic bacteria was also reduced by immobilizing the bacteria. Formation of a pH gradient or the adsorption of toxic materials by PVA are likely mechanisms of this relief of inhibition.

WILLINGNESS TO PAY FOR WASTE MANAGEMENT IMPROVEMENT IN DHAKA CITY, BANGLADESH

We employed the contingent valuation method to estimate the willingness to pay of the respondents to improve the waste collection system in Dhaka city, Bangladesh. Our objective was to estimate how WTP differs between respondents who received or did not receive door to door waste collection. The methodology consisted of asking people directly about their willingness to pay an additional waste collection service charge to cover the costs of a new waste management project. The mean value of WTP for areas that received waste collection service areas was higher than for residents of areas that did not but the difference was not statistically significant. The aggregate value of WTP of the respondents in Dhaka city was 7.6 million Taka (USD0.1 million).

Removal of odorous compounds in wastewater by using activated carbon, ozonation and aerated biofilter

Abstract Activated carbon, ozonation and aerated biofilters were applied to eliminate odor-causing compounds that occur in wastewater and effluents from the activated sludge process. Odorous organics used in this experiment were sulfur containing odorous compounds which include carbon disulfide, methyl mercaptan, dimethyl sulfide and dimethyl disulfide, and nitrogen containing compounds such as ammonia, trimethylamine, dimethylamine and n-propylamine. The removal of sulfur containing odorous compounds by activated carbon, was very effective compared to nitrogen containing compounds under the same experimental conditions. Sulfur containing substances were oxidized with ozone rapidly, while the reaction of low aliphatic amines with ozone occurred slowly. Methane sulfonic acid was converted from methyl mercaptan through dimethyl disulfide by ozonation. Ammonia and trimethylamine was converted to nitrate and nitromethane by ozonation, respectively. More than 80% of the sulfur and nitrogen containing malodorants were removed by acclimated microorganisms in an aerated biofilter at about 30 min of hydraulic retention time. Neither carbon disulfide nor dimethyl disulfide were removed at all in the biofilter without aeration. Conclusively, the aerated biofilter was the most acceptable process for eliminating sulfur and nitrogen containing odorous compounds in wastewater as it produced none of the oxidized organics noticed with ozonation, and it had an equally high removal efficiency for both sulfur and nitrogen containing odorous compounds.

Assessment of the environmental impact of management measures for the biodegradable fraction of municipal solid waste in Sao Paulo city

There is increasing concern about landfilling of biodegradable wastes. Therefore, biological treatment processes such as composting and biogasification have been considered as alternative strategies for managing those wastes. In this work, life cycle assessment was employed to compare the environmental impacts of landfilling, composting, and biological treatment of municipal solid waste in São Paulo City, Brazil. Energy consumption, recovered resources, and emissions to air and water were quantified and analyzed in terms of their potential contribution to global warming, acidification, and nutrient enrichment impact. The results demonstrated that processes that require high levels of energy consumption, such as wastewater treatment, play an important role in the outcome of environmental impact potentials. It was found that the landfilling of all waste is generally the worst strategy from an environmental point of view. However, significant reductions in the resulting impacts can be accomplished through biogasification and composting of the biodegradable fraction. Regarding composting, the application of a biofilter for gas treatment reduced significantly the gaseous emissions.

Improvement of urban thermal environment by managing heat discharge sources and surface modification in Tokyo

This paper analyzes the implications of anthropogenic heat discharges into the urban thermal environment of Tokyo. Heat discharges by the representative office, commercial and residential buildings were simulated with the help of the DOE-2 building energy simulation model. The approach used in this paper also takes into account the heat storage within building structures. The geographical information system based technique was used to estimate the heat discharge distribution all over Tokyo. The mesoscale analyses of the urban climate were carried out with a model that was based on the Colorado State University Mesoscale Model. The improvements in the urban thermal environment via the various measures were analyzed for two types of scenarios, namely, scenarios related to the management of heat discharge sources and urban surface modifications. The maximum improvement in average temperature for daytime was found to be 0.47°C (at noon) as a result of greening the areas around the buildings of Tokyo. Similarly, the maximum improvement in average temperature for the evening was found to be 0.11°C by discharging all heat to the ground.