Supercritical water gasification of sewage sludge using bench-scale batch reactor: advantages and drawbacks

Sewage sludge, a byproduct of municipal wastewater treatment, was gasified by supercritical water using a bench-scale batch reactor. Configuration of bench-scale batch reactor and operation procedures are discussed in detail. Experience and challenges that arose during the experiment are also shared. Using the bench-scale reactor under the condition of 600 °C, 23 MPa, and a reaction time of 60 min without catalyst presence, a total gas yield of 9.8 mol/(kg-sewage sludge) was obtained. Furthermore, investigations on operational parameters were conducted. Extension of reaction time up to 60 min increased the gasification, reaching a plateau thereafter. Investigation on pressure indicated the superiority of supercritical pressure. The addition of Ni as a catalyst also promoted gasification, although inorganic salts and char seemed to cover the catalyst surface. With regard to the prospect of future operation at a municipal waste water treatment plant, the effect of operational parameters on heavy metal concentration in the liquid phase is also discussed.     

Quantitative analysis of microbial biomass yield in aerobic bioreactor

We have studied the integrated model of reaction rate equations with thermal energy balance in aerobic bioreactor for food waste decomposition and showed that the integrated model has the capability both of monitoring microbial activity in real time and of analyzing biodegradation kinetics and thermal-hydrodynamic properties. On the other hand, concerning microbial metabolism, it was known that balancing catabolic reactions with anabolic reactions in terms of energy and electron flow provides stoichiometric metabolic reactions and enables the estimation of microbial biomass yield (stoichiometric reaction model). We have studied a method for estimating real-time microbial biomass yield in the bioreactor during food waste decomposition by combining the integrated model with the stoichiometric reaction model. As a result, it was found that the time course of microbial biomass yield in the bioreactor during decomposition can be evaluated using the operational data of the bioreactor (weight of input food waste and bed temperature) by the combined model. The combined model can be applied to manage a food waste decomposition not only for controlling system operation to keep microbial activity stable, but also for producing value–added products such as compost on optimum condition.     

Polychlorinated dibenzo-p-dioxins and dibenzofurans in paddy soils and river sediments in Akita, Japan

Paddy soils and sediments from the Yoneshirogawa, Omonogawa, and Koyoshigawa River Basins in Akita were analyzed for polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). The levels and compositions in those samples including soils from non-agricultural areas (non-agricultural soils) were investigated using isomer-specific analysis to determine characteristic sources. The PCDD/PCDF compositions in the samples were compared with respect to possible sources. The PCDD/PCDF concentrations in paddy soils were much higher than those in the non-agricultural soils and much higher than those found in other parts of Japan. Although PCDD/PCDFs were ubiquitous in sediments from river sources to mouths of the respective river basins, those concentrations were much lower than those from paddy soils and non-agricultural soils, and from other parts of Japan. Comparison of PCDD/PCDF homologues and isomer compositions for samples indicated that compositions of paddy soils and sediments, except for those from river sources, had similar characteristics to PCDD/PCDFs originating from impurities in herbicides, 2,4,6-trichlorophenyl 4-nitrophenyl ether (CNP) and pentachlorophenol (PCP), and that compositions of river-source sediments and non-agricultural soils resembled those of atmospheric depositions. Results of statistical analyses suggest that PCDD/PCDF contamination of paddy soils and sediments is attributable mainly to three sources: CNP, PCP, and atmospheric deposition. Results of this study also demonstrate that CNP and PCP are not only important contaminants of local areas of Japan, but that they exist throughout Akita, in northern Japan. We therefore conclude that PCDD/PCDF pollution caused by those compounds has a widespread influence on paddy soils and river sediments in Japan.     

Nylon recovery from carpet waste through pyrolysis under the presence of zinc oxide and the roll-milling treatment

Recycling of carpet waste is not extensively carried out because of its complex combination of materials. A representative type of carpet consists of three layers: nylon fibers, adhesives, and backing materials made of poly(vinyl chloride), PVC. Thermal treatment of carpet waste, thus, leads to the emission of hazardous chlorinated compounds. In the present work, we have employed the one-directional thermal treatment of the backing materials under the presence of zinc oxide, which promotes the thermal degradation of PVC. Nylon fibers could be effectively recovered by the consequent milling treatment from the brittle backing materials. The influence of process parameters, such as pyrolysis temperature and reaction time, on the separation efficiency is discussed.     

Wayfinding with a GPS-based mobile navigation system: A comparison with maps and direct experience

This study examined the effectiveness of a Global Positioning System (GPS)-based mobile navigation system in comparison to paper maps and direct experience of routes, by focusing on the user's wayfinding behavior and acquired spatial knowledge. Based on information received from one of these three media, participants walked six routes finding the way to goals. Results showed that GPS users traveled longer distances and made more stops during the walk than map users and direct-experience participants. Also, GPS users traveled more slowly, made larger direction errors, drew sketch maps with poorer topological accuracy, and rated wayfinding tasks as more difficult than direct-experience participants. Characteristics of navigation with these three learning media and possible reasons for the ineffectiveness of the GPS-based navigation system are discussed.     

Investigation of 1,4-dioxane originating from incineration residues produced by incineration of municipal solid waste

As a groundwater contaminant, 1,4-dioxane is of considerable concern because of its toxicity, refractory nature to degradation, and rapid migration within an aquifer. Although landfill leachate has been reported to contain significant levels of 1,4-dioxane, the origin of 1,4-dioxane in leachate has not been clarified until now. In this study, the origins of 1,4-dioxane in landfill leachate were investigated at 38 landfill sites and three incineration plants in Japan. Extremely high levels of 1,4-dioxane 89 and 340 microg l(-1), were detected in leachate from two of the landfill sites sampled. Assessments of leachate and measurement of 1,4-dioxane in incineration residues revealed the most likely source of 1,4-dioxane in the leachate to be the fly ash produced by municipal solid waste incinerators. Effective removal of 1,4-dioxane in leachate from fly ash was achieved using heating dechlorination systems. Rapid leaching of 1,4-dioxane observed from fly ash in a sequential batch extraction indicated that the incorporation of a waste washing process could also be effective for the removal of 1,4-dioxane in fly ash.     

Initial design process of the sustainability science ontology for knowledge-sharing to support co-deliberation

Implementation of the sustainability science (SS) approach is often difficult because of poor communication between experts from different academic fields. We focused on ontology engineering as a method of knowledge structuring that supports the co-deliberation process. However, SS is too broad for a few experts to construct an ontology because SS targets and covers almost all existing research fields from the viewpoint of problem-solving. The N-iteration process is required for completing an SS ontology. In the present paper, we discuss the initial design process for constructing an ontology on SS from the aspect of a knowledge-sharing tool to support co-deliberation. First, we identified the SS ontology by referring to the existing literature. Second, we traced the structuring process of the SS ontology, which is independent of the existing research domain. Third, we compared the SS ontology with existing ontologies or concept structures on SS. Fourth, we assessed the SS ontology produced in the initial process in terms of relevance and coverage and addressed areas for improvement in order to facilitate co-deliberation among researchers from different domains. As a result of developing the SS ontology and applying it to the mapping tool that we developed based on the ontology, we found the following three points: the SS ontology enables us to define concepts relevant to SS without overlapping by distinguishing part-of and attribute-of relationships at the upper level of the ontology; the SS-based mapping tool successfully represents the potential countermeasures required by the targeted problem for all scientific fields except experimental engineering; however, the SS ontology requires further improvement in order to represent the conceptual linkage arising from compound and secondary problems and the fulfillment of classes at the lower hierarchy of Shortage problem, and requires slots for the entire hierarchy. In addition, based on the discussion of the areas for improvement, we found that missing slots and classes should be added in the process in which we use or improve tools corresponding to a variety of requirements for supporting co-deliberation. In this way, we are able to propose an incremental process for constructing the SS ontology from the aspect of a knowledge-sharing tool to support co-deliberation.     

Accumulation and mobility of zinc in soil amended with different levels of pig-manure compost

Applying manure compost not only results in zinc accumulation in the soil but also causes an increase in zinc mobility and enhances zinc leaching. In this study, the physical and chemical characteristics of zinc, zinc profiles, and zinc balance were investigated to characterise the fate of zinc in fields where the quality and amount of pig manure compost applied have been known for 13 years. Moreover, we determined zinc fractionation in both 0.1 mol L^?1HCl-soluble (mobile) and -insoluble (immobile) fractions. Adsorption of zinc in the soil was enhanced with increasing total carbon content following the application of pig manure compost. The 159.6 mg ha^?1 year^?1manure applied plot (triplicate) exceeded the Japanese regulatory level after only 6 years of applying pig manure compost, whereas the 53.2 mg ha^?1 year^?1 manure applied plot (standard) reached the regulatory level after 13 years. The zinc loads in the plots were 17.0 and 5.6 kg ha^?1 year^?1, respectively. However, 5.9 % and 17.2 % of the zinc loaded in the standard and the triplicate pig manure compost applied plots, respectively, were estimated to be lost from the plough layer. Based on the vertical distribution of mobile and immobile zinc content, a higher rate of applied manure compost caused an increase in the mobile zinc fraction to a depth of 40 cm. Although the adsorption capacity of zinc was enhanced following the application of pig manure compost, a greater amount of mobile zinc could move downward through the manure amended soil than through non manure-amended soil.