Kazuei Ishii

Influence of moisture content, particle size and forming temperature on productivity and quality of rice straw pellets.

A large amount of rice straw is generated and left as much in paddy fields, which causes greenhouse gas emissions as methane. Rice straw can be used as bioenergy. Rice straw pellets are a promising technology because pelletization of rice straw is a form of mass and energy densification, which leads to a product that is easy to handle, transport, store and utilize because of the increase in the bulk density. The operational conditions required to produce high quality rice straw pellets have not been determined. This study determined the optimal moisture content range required to produce rice straw pellets with high yield ratio and high heating value, and also determined the influence of particle size and the forming temperature on the yield ratio and durability of rice straw pellets. The optimal moisture content range was between 13% and 20% under a forming temperature of 60 or 80 °C. The optimal particle size was between 10 and 20mm, considering the time and energy required for shredding, although the particle size did not significantly affect the yield ratio and durability of the pellets. The optimized conditions provided high quality rice straw pellets with nearly 90% yield ratio, ⩾ 12 MJ/kg for the lower heating value, and >95% durability.

Estimation of methane emission rate changes using age-defined waste in a landfill site

Long term methane emissions from landfill sites are often predicted by first-order decay (FOD) models, in which the default coefficients of the methane generation potential and the methane generation rate given by the Intergovernmental Panel on Climate Change (IPCC) are usually used. However, previous studies have demonstrated the large uncertainty in these coefficients because they are derived from a calibration procedure under ideal steady-state conditions, not actual landfill site conditions. In this study, the coefficients in the FOD model were estimated by a new approach to predict more precise long term methane generation by considering region-specific conditions. In the new approach, age-defined waste samples, which had been under the actual landfill site conditions, were collected in Hokkaido, Japan (in cold region), and the time series data on the age-defined waste samples methane generation potential was used to estimate the coefficients in the FOD model. The degradation coefficients were 0.0501/y and 0.0621/y for paper and food waste, and the methane generation potentials were 214.4 mL/g-wet waste and 126.7 mL/g-wet waste for paper and food waste, respectively. These coefficients were compared with the default coefficients given by the IPCC. Although the degradation coefficient for food waste was smaller than the default value, the other coefficients were within the range of the default coefficients. With these new coefficients to calculate methane generation, the long term methane emissions from the landfill site was estimated at 1.35×10(4)m(3)-CH(4), which corresponds to approximately 2.53% of the total carbon dioxide emissions in the city (5.34×10(5)t-CO(2)/y).

Estimation of the biodegradation rate of 2,3,7,8-tetrachlorodibenzo-p-dioxin by using dioxin-degrading fungus, Pseudallescheria boydii.

We are developing a bioreactor system for treating dioxin-contaminated soil or water using the dioxin-degrading fungus, Pseudallescheria boydii (P. boydii). In order to design the bioreactor system, this study estimated the rate at which P. boydii degraded 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), which is the most toxic of the dioxins. The experimental results showed that P. boydii degraded 2,3,7,8-TCDD during its logarithmic growth phase, using glucose as a carbon source for growth, and that the growth of P. boydii was not affected by 2,3,7,8-TCDD concentrations usually found at contaminated sites. These results were then used to apply successfully an existing mathematical model to the degradation of 2,3,7,8-TCDD by P. boydii. This allowed an estimation of the rate of degradation of 2,3,7,8-TCDD by P. boydii that can be used in the design of the bioreactor system.

A needs analysis method for land-use planning of illegal dumping sites: A case study in Aomori-Iwate, Japan

Land use at contaminated sites, following remediation, is often needed for regional redevelopment. However, there exist few methods of developing economically and socially feasible land-use plans based on regional needs because of the wide variety of land-use requirements. This study proposes a new needs analysis method for the conceptual land-use planning of contaminated sites and illustrates this method with a case study of an illegal dumping site for hazardous waste. In this method, planning factors consisting of the land-use attributes and related facilities are extracted from the potential needs of the residents through a preliminary questionnaire. Using the extracted attributes of land use and the related facilities, land-use cases are designed for selection-based conjoint analysis. A second questionnaire for respondents to the first one who indicated an interest in participating in the second questionnaire is conducted for the conjoint analysis to determine the utility function and marginal cost of each attribute in order to prioritize the planning factors to develop a quantitative and economically and socially feasible land-use plan. Based on the results, site-specific land-use alternatives are developed and evaluated by the utility function obtained from the conjoint analysis. In this case study of an illegal dumping site for hazardous waste, the uses preferred as part of a conceptual land-use plan following remediation of the site were (1) agricultural land and a biogas plant designed to recover energy from biomass or (2) a park with a welfare facility and an athletic field. Our needs analysis method with conjoint analysis is applicable to the development of conceptual land-use planning for similar sites following remediation, particularly when added value is considered.

Numerical model for a watering plan to wash out organic matter from the municipal solid waste incinerator bottom ash layer in closed system disposal facilities.

Bottom ash from municipal solid waste incineration (MSWI) is a main type of waste that is landfilled in Japan. The long-term elution of organic matter from the MSWI bottom ash layers is a concern because maintenance and operational costs of leachate treatment facilities are high. In closed system disposal facilities (CSDFs), which have a roof to prevent rainfall from infiltrating into the waste layers, water must be supplied artificially and its quantity can be controlled. However, the quantity of water needed and how to apply it (the intensity, period and frequency) have not been clearly defined. In order to discuss an effective watering plan, this study proposes a new washout model to clarify a fundamental mechanism of total organic carbon (TOC) elution behavior from MSWI bottom ash layers. The washout model considers three phases: solid, immobile water and mobile water. The parameters, including two mass transfer coefficients of the solid-immobile water phases and immobile-mobile water phases, were determined by one-dimensional column experiments for about 2 years. The intensity, period and frequency of watering and other factors were discussed based on a numerical analysis using the above parameters. As a result, our washout model explained adequately the elution behavior of TOC from the MSWI bottom ash layer before carbonation occurred (pH approximately 8.3). The determined parameters and numerical analysis suggested that there is a possibility that the minimum amount of water needed for washing out TOC per unit weight of MSWI bottom ash layer could be determined, which depends on the two mass transfer coefficients and the depth of the MSWI bottom ash layer. Knowledge about the fundamental mechanism of the elution behavior of TOC from the MSWI bottom ash layer before carbonation occurs, clarified by this study, will help an effective watering plan in CSDFs.

Appropriate conditions for applying NaOH-pretreated two-phase olive milling waste for codigestion with food waste to enhance biogas production.

The high methane gas production potential of two phase olive milling waste (2POMW) makes its application to biogas plants in business an economical process to increase the productivity of the plants. The objective of this study was to investigate the appropriate conditions for the codigestion of NaOH-pretreated 2POMW with food waste. NaOH pretreatment can increase the methane production by increasing the soluble chemical oxygen demand (sCOD), but it may cause inhibition because of higher levels of alkalinity, sodium ion, volatile fatty acids and long chain fatty acids (LCFAs). Therefore, the first experimental phase of this study aimed to investigate the effect of different mixing ratios of 2POMW to food waste. A continuous stirred tank reactor experiment with different mixing ratios of 3%, 4.3%, 5.7% and 8.3% (2POMW: food waste) was conducted. NaOH pretreatment in the range of 6-20% was used. A mixing ratio up to 4.3%, when 10% NaOH pretreatment was used, caused no inhibition and increased methane production by 445.9mL/g-VS(2POMW). For this mixing ratio an additional experimental phase was conducted with the 20% NaOH pretreatment as the 20% NaOH pretreatment had the highest sCOD. The methane gas production was increased by 503.6mL/g-VS(2POMW). However, pH adjustment was required for applying this concentration of the high alkalinity 20% NaOH-pretreated 2POMW. Therefore, we consider using 10% NaOH pretreatment in a mixing ratio of 4.3% to be more applicable. The increase in methane gas production was correlated to the oleic acid concentration inside the reactors. The high oleic acid concentration of 61.8mg/L for the 8.3% mixing ratio was responsible for the strong inhibition. This study showed that adjusting the appropriate mixing ratio of the NaOH-pretreated 2POMW could increase the electricity production of a reactor that regularly receives food waste.

Centralization of dairy farming facilities for improved economics and environmental quality.

In Japan, most farm animal excreta has been stored directly on farmland. Runoff from this storage has often caused water pollution. Biogasification is anticipated as an important technology to manage excreta properly, but complex problems hinder its introduction. Economic aspects of management have been especially difficult for dairy farmers. For this study, structural problems regarding introduction of biogasification into dairy farming were identified. Subsequently, a desirable system of dairy farming including biogasification was suggested, and an evaluation model of the financial balance was constructed. A case study using current financial balances of several systems of dairy farming was evaluated using the constructed model and actual data. The systems were based on several policy alternatives including the suggested system mentioned above. Results show that a farmer can obtain sufficient income from a system featuring centralization of dairy housing and biogasification facilities and coordinated management by over six farmers.

Numerical Simulation Of Nitrogen GroundwaterPollution For Proper Management OfCow Manure

About 20 million tons of cow manure is generated in Hokkaido, Japan, each year. Approximately 94% of this manure is reported to be recycled. However, the actual amounts of cow manure generated and of manure applied to pastures as compost or soil improver are not entirely clear, and so the reported rates of cow manure recycling are unlikely to represent the realities of current cow manure management. It is possible that excessive amounts of manure are being applied to pastures, leading to nitrate-nitrogen leaching and groundwater pollution. Therefore, it is necessary to assess the mass balance of nitrogen in the system to determine appropriate management strategies for cow manure. In this study, the nitrogen mass balance was calculated for cow manure during all stages of the process, from its generation to its application as a compost or soil improver. The nitrogen mass balance was determined through site investigations. Assuming a typical model of dairy farming, the actual amount of nitrogen applied in pastures was calculated in terms of nitrogen use efficiency, depending on vegetation type. The potential for groundwater pollution was evaluated by numerical simulations based on the nitrogen mass balance. The results showed that when large amounts of manure are applied to pastures, excess nitrogen will be present in the system, which may be susceptible to leaching and lead to groundwater pollution. Methods for cow manure management are discussed based on the results of the numerical simulations.

Study on the Economic Size of Pellet Plant for Developing Heat Recovery Systems of Forest Residue Based on Survey of Wood Fuel Demand in Ashoro town and its neighboring area

本研究は，林地残材をペレットとして利用している足寄町を対象に，さらなる林地残材の拡大利用を目指した林地残材拡大熱利用システムの事業規模決定のための方法論を検討した。特に足寄町周辺の熱利用施設へのアンケート調査により，代替燃料としてのペレット購入希望価格，配送距離及び平均1日ペレット使用量からなる熱需要構造を明らかにした上で実行可能な事業規模の算出を試みた．その結果，119 kmの配送距離の範囲内で，合計12施設，ペレット量2,627 t/年の熱需要を明らかにした．そして灯油価格が105円/L、A重油価格が97円/Ｌにまで値上がりしたと仮定すると，1,800 t/年の事業規模であれば，ペレットは配送費を加えた販売価格で全て売却されるので事業として成立する可能性があることを明らかにした．

Study of reduction of odor from cow excreta by composting and biogasification

固形物などの臭気試料を簡便に調製する方法を提案するとともに，その方法を用いて牛ふん尿および牛ふん尿の堆肥化物とバイオガス化液状残渣（液肥）の臭気指数を測定した．牛ふん尿の臭気ポテンシャル*は24～35と幅広い値であった．牛ふん尿の堆肥化物と液肥の臭気ポテンシャル（Y）は，牛ふん尿の臭気ポテンシャル（X）より3～11低い20～25の値であり，堆肥化とバイオガス化による牛ふん尿の臭気低減効果を定量的に示すことができた．