Yusaku Ono

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.

Gypsum and organic matter distribution in a mixed construction and demolition waste sorting process and their possible removal from outputs

With insufficient source separation, construction and demolition (C&D) waste becomes a mixed material that is difficult to recycle. Treatment of mixed C&D waste generates residue that contains gypsum and organic matter and poses a risk of H(2)S formation in landfills. Therefore, removing gypsum and organic matter from the residue is vital. This study investigated the distribution of gypsum and organic matter in a sorting process. Heavy liquid separation was used to determine the density ranges in which gypsum and organic matter were most concentrated. The fine residue that was separated before shredding accounted for 27.9% of the waste mass and contained the greatest quantity of gypsum; therefore, most of the gypsum (52.4%) was distributed in this fraction. When this fine fraction was subjected to heavy liquid separation, 93% of the gypsum was concentrated in the density range of 1.59-2.28, which contained 24% of the total waste mass. Therefore, removing this density range after segregating fine particles should reduce the amount of gypsum sent to landfills. Organic matter tends to float as density increases; nevertheless, separation at 1.0 density could be more efficient.

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, Cr6+, 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.

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.

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.

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.

Influence of oxygen flow rate and compost addition on reduction of organic matter in aerated waste layer containing mainly incineration residue

Landfilling municipal solid waste incineration (MSWI) residue alkalizes the waste layer, causing a subsequent decrease in microbial activity and a delay in the decomposition of organic matter. In this study, efficiencies of neutralization of the leachate and organic matter decomposition in the waste layer in a column filled with MSWI residue using aeration and compost addition were evaluated. Total organic carbon (TOC) reduction in the waste layer is large at high oxygen flow rate (OFR). To effectively accelerate TOC reduction in the waste layer to which compost was added, a high OFR exceeding that by natural ventilation was required. At day 65, the pH of the leachate when OFR was above 10(2) mol-O2/(day x m3) was lower than that when OFR was below 10(1) mol-O2/(day x m3). At the same OFR, the pH of waste sample was lower than that of waste sample with compost. Although leachate neutralization could be affected by compost addition, TOC reduction in the waste layer became rather small. It is possible that humic substances in compost prevent the decomposition of TOC in MSWI residue.