Influence of oxygen flow rate on reaction rate of organic matter in leachate from aerated waste layer containing mainly incineration ash.

It is known that aeration reduces rapidly the concentration of organic matter in leachate. However, the oxygen flow rate required to attain a certain reaction rate of organic matter should be carefully estimated. In this study, using the oxygen ratio (the ratio of oxygen flow rate by aeration to oxygen consumption rate of waste layer) as a parameter, the reaction rate of organic matter in leachate from landfilled incineration ash and incombustible waste upon aeration was evaluated. Total organic carbon (TOC) in the leachate was reduced rapidly when the oxygen ratio was high. The decomposition rate exceeded the elution rate of TOC in the leachate from the waste layer for several days when the oxygen ratio was above 10(2). The results indicate that the oxygen ratio can be used as a parameter for the aeration operation in actual landfill sites, to rapidly stabilize organic matter in leachate.

Adopted technologies and basis for selection at municipal solid waste landfill facilities constructed in recent years in Japan.

In Japan, as the construction of new landfill facilities has become extremely difficult and the number of sites procured for landfill construction has decreased due to the 'not in my back yard' (NIMBY) syndrome, it has been assumed that the adoption of new technologies has increased. As the performance of new technologies exceeds that of conventional technologies, it is also assumed that residents would prefer the use of these new technologies and therefore any construction plans should be devised to ensure their use to ensure residents' satisfaction. In the present study, the technologies adopted for municipal solid waste landfill facilities constructed in recent years (2000 to 2004) in Japan and the bases for their adoption were investigated by means of a questionnaire survey. One of the main bases for the adoption of new technologies was the request by residents for new technology for roofing, rather than the other for new technologies for barrier systems, leachate treatment, and monitoring. In addition, it is possible that the municipalities did not recognize the difference between conventional and new technologies as defined in this study. The roof-type landfill that isolates waste from the surrounding environment was one of the requirements for the construction of new landfill facilities identified in the present investigation, and in this regard waste isolation should be required in all circumstances.

Investigation on the components removed in loss on ignition test of sandy crushed construction and demolition waste.

Processed sandy residue generated from mixed construction and demolition waste (mixed C&D-W) was investigated for possible deposition in landfill. The basic properties and the components removed in the loss on ignition (LOI) test were examined. The target material for decreasing LOI was elucidated and the validity of LOI used as landfill standard for inert industrial solid waste was discussed. LOI of most of the samples was above 5% and therefore, in principle, processed sandy residue should not be deposited in inert-type landfill. As LOI of sandy residue was mainly due to bound water, the LOI could not be decreased to below 5% even if wood, which is the major organic matter in the sandy residue, was removed. However, decreasing the amount of wood could lead to a subsequent decrease in the amount of dissolved organic matter. Therefore, the LOI of processed mixed C&D-W used as landfill standard for inert industrial solid waste should be re-evaluated.

Characteristics of fine processed construction and demolition waste in Japan and method to obtain fines having low gypsum component and wood contents.

A method to obtain processed residue from mixed construction and demolition waste (mixed C&D-W) - free from environmental pollutants - for deposition in landfill is discussed. In particular, additional sieving, the presence of gypsum board in mixed C&D-W at the first stage of manual presorting, and the color of processed residue were studied for the basic characterization of the different fractions. Considerable precautions should be taken to prevent leaching of hazardous substances, such as T-Hg, Pb, Cr(6+), As, and fluoride and its compounds, when processed residue, particularly in crushed fraction at an intermediate treatment facility, is used as construction material. A relatively high content of gypsum was noted in processed residue generated at demolition work compared to that generated at construction work in processed residue from mixed C&D-W in which the presence of gypsum board was observed at the first stage of manual presorting, and in white processed residue. Additional sieving for removal was ineffective because gypsum and wood have wide particle size distributions. To obtain processed residue having low gypsum and wood contents, white processed residue should be removed to eliminate gypsum (content, 59% of initial sample), and brown or brown and yellow processed residue should be removed to eliminate wood (content, 32% of initial sample) without mixing with processed residue containing other colors at stockyards. The removed residue should be deposited in a controlled-type landfill site.

Improvement of permeability of waste sludge by mixing with slag or construction and demolition waste.

To determine the allowable ratio of waste sludge required to ensure an aerobic zone in the landfill, we investigated sludge permeability, which involved mixing sludge, the major landfill waste in Japan, at different mixing ratios with other wastes (slag and construction and demolition waste (C&D)). We measured parameters of sample permeability and analyzed parameters that exert a large influence on oxygen penetration depth with a simulation model accounting for both diffusion and convection driven by temperature gradients. We also determined the critical volumetric contents in which gas and/or water permeability change significantly when sludge is mixed with sand or gravel. From the results of the simulations, gas permeability of the layer, the difference between inside and outside temperatures and the oxygen consumption rate exert a large influence on the resulting oxygen penetration depth. The allowable ratio of sludge required to ensure an aerobic zone in the landfill was determined by considering the balance of the above three parameters. By keeping volumetric sludge content to below 25%, air convection and oxygen penetration depth of several meters were achieved in the modeling.

Evaluation of mutagenic activities of leachates in landfill sites by micronucleus test and comet assay using goldfish.

To develop a simple system for monitoring the presence of mutagens/carcinogens in the leachates from landfill sites, we used a micronucleus test and a single cell gel electrophoresis (comet) assay originally developed for mice and rats on goldfish (Carassius auratus). The goldfish were exposed for 9 days to the leachate with chemical and biological treatment (treated leachate) or without treatment (raw leachate). The goldfish exposed to several samples died because of the high concentrations of NaCl or ammonium ion (NH4+). In the comet assay using peripheral erythrocytes, the raw leachates showed higher mutagenic activity than the treated leachates. In the micronucleus test, it was difficult to detect the micronuclei in peripheral erythrocytes. On the other hand, the frequency of micronuclei was high in gill cells of goldfish exposed to the raw leachates compared to the treated leachates. A combination of the two bioassays was shown to be useful to evaluate the mutagenic activity of the leachates. We also propose a new scoring method for determination of water quality by using acute toxicity and mutagenic activity.

Impact of chemical components of organic wastes on L(+)-lactic acid production.

Lactic acid production from several organic wastes that had different chemical compositions was examined, and the factors strongly impacting yield were determined. The bioconversion of sugars to lactic acid was affected by the ratio of total sugars to total nitrogen content (the TS/N ratio), and was improved by nitrogen supplementation to adjust the TS/N ratio > or =10. Lactic acid yield was also affected by the fermentable sugars contents, i.e. various oligosaccharides constituted of mainly C6-sugars. The estimation of the fermentable sugars was determined by the total sugars content in starchy materials, such as kitchen wastes, but in lignocellulosic materials, the estimation was affected by the hemicellulose contents. The estimation model of the fermentable sugars was proposed by multivariate analysis using organic components as variables.

Effects of insufficient air injection on methanogenic Archaea in landfill bioreactor.

In this study, methanogenic Archaea diversity in an aerated landfill bioreactor filled with co-disposed incineration bottom ashes and shredded incombustible wastes was monitored and analyzed as a function of time using molecular techniques. Besides, the effects of insufficient air injection on the bioreactor performance and methanogenic diversity were evaluated thoroughly. Results indicated that rapid bio-stabilization of solid waste are possible with aerated landfill bioreactor at various oxygen and oxidation reduction potential levels. Slot-blot hybridization results of leachate samples collected from aerated landfill bioreactor showed that archaeal and bacterial activities increased as stabilization accelerated and bacterial populations constituted almost 95% of all microorganisms. The results of slot-blot hybridization and phylogenetic analysis based on 16S rRNA gene revealed that Methanobacteriales and Methanomicrobiales were dominant species at the beginning while substituted by Methanosarcina-related methanogens close to the end of the operation of bioreactor.

Heavy metal leaching from aerobic and anaerobic landfill bioreactors of co-disposed municipal solid waste incineration bottom ash and shredded low-organic residues.

In this study, heavy metal leaching from aerobic and anaerobic landfill bioreactor test cells for co-disposed municipal solid waste incineration (MSWI) bottom ash and shredded low-organic residues has been investigated. Test cells were operated for 1 year. Heavy metals which were comparatively higher in leachate of aerobic cell were copper (Cu), lead (Pb), boron (B), zinc (Zn), manganese (Mn) and iron (Fe), and those apparently lower were aluminum (Al), arsenic (As), molybdenum (Mo), and vanadium (V). However, no significant release of heavy metals under aerobic conditions was observed compared to anaerobic and control cells. Furthermore, there was no meaningful correlation between oxidation-reduction potential (ORP) and heavy metal concentrations in the leachates although some researchers speculate that aeration may result in excessive heavy metal leaching. No meaningful correlation between dissolved organic carbon (DOC) and leaching of Cu and Pb was another interesting observation. The only heavy metal that exceeded the state discharge limits (10mg/l, to be enforced after April 2005) in the aerobic cell leachate samples was boron and there was no correlation between boron leaching and ORP. Higher B levels in aerobic cell should be due to comparatively lower pH values in this cell. However, it is anticipated that this slightly increased concentrations of B (maximum 25mg/l) will not create a risk for bioreactor operation; rather it should be beneficial for long-term stability of the landfill through faster washout. It was concluded that aerobization of landfills of heavy metal rich MSWI bottom ash and shredded residues is possible with no dramatic increase in heavy metals in the leachate.

Development of a genotoxicity detection system using a biosensor.

The umu-lux test is a genotoxicity test using the two genetically modified S. typhmurium TA1535 strains (TL210 and TL210ctl) transformed with the luxCDABE (luciferase gene and fatty acid reductase genes) of Vibrio fischeri as a reporter gene. The TL210 strain detects genotoxicants and the TL210ctl strain detects cytotoxicants. In order to develop a highly sensitive, simple and rapid genotoxicity detection system, we constructed a biosensor using these immobilized strains. The biosensor consists of two immobilized microbial membranes, a sample vessel and photodetectors, and the genotoxicity detection system consists of the biosensor, an isothermal box, a photodetector and an air pump. The total measurement time for genotoxicants using this detection system is about 4 h. When 2% (v/v) DMSO was used as a control, the TL210 strain was not emitting light while the TL210ctl strain was. When 0.3 mg/l 4NQO was used as a genotoxicant, TL210 strain and TL210ctl strain were both emitting light. When HgCl2 was used as a cytotoxicant, neither the TL210 strain nor the TL210ctl strain were emitting light. Therefore, the false negative prevention function of a biosensor using the TL210ctl strain has been checked. These results show that our proposed system can correctly detect genotoxicants.