M. Hiraoka

Coplanar PCBs and PCDDs/PCDFs in municipal waste incineration

Abstract With the objective of developing an efficient method of analyzing non-ortho substituted chlorobiphenyls (hereinafter referred to as Co-PCBs) produced in the municipal waste incineration, particularly a method of simultaneous analysis of Co-PCBs and PCDDs and PCDFs, the alumina column three-fraction method was studied. Recovery tests using standard substances, and analyses of actual samples (exhaust gas and flyash) were conducted. The percent contribution of Co-PCBs to the total PCB concentration in exhaust gas and flyash from municipal waste incineration was about 5 to 10%, higher than that in Yusho oil and PCB oil, which has about 1%. Also, the toxicity of Co-PCBs accounted for about several percents of the 2,3,7,8-TCDD toxic equivalent concentration (TEQ); Co-PCBs do not appear to be detected at concentrations as high as in fish and human tissue. However, further investigation should be continued, since the number of samples analyzed was too small to fully assess the status of Co-PCBs involved in the incineration of municipal waste.

Behavior of coplanar PCBs and PCNs in oxidative conditions of municipal waste incineration

Abstract Non-ortho PCBs and mono-ortho PCBs are formed during primary combustion of municipal solid waste under oxidative conditions. Concentrations of coplanar PCBs in starved-air condition (O2 content of about 3%) are much higher than at O2 of 9.6%. In the secondary combustion, much of coplanar PCBs are destroyed. PCDDs/PCDFs are also reduced in the secondary combustion. Coplanar PCBs formation is probably via dimerization of chlorobenzenes (CBs) in the starved atmosphere of primary combustion. De novo synthesis of coplanar PCBs is also observed. PCNs in the outlet of combustion chambers are detected at similar concentrations as the total PCDDs/PCDFs.

Formation and emission of non-ortho CBs and mono-ortho CBs in municipal waste incineration

Abstract Non-ortho CBs, Mono-ortho CBs and PCDDs/PCDFs in the exhaust gas and fly ash from municipal waste incineration were analyzed quantitatively. The results of this quantitative analysis show that the total concentrations of Non-ortho CBs and Mono-ortho CBs are at the same level, but the toxicity equivalent concentration of Mono-ortho CBs is smaller than that of Non-ortho CBs. The number of samples, however, is too few to generalize about PCB behavior in municipal waste incineration, and very little of the PCB formation mechanism is known. Two different behaviors were observed from the de novo synthesis experiments of PCBs. One is the same or lower level after the heat treatment of 300°C air conditions. The other is the remarkable increase of Non-ortho CBs and Mono-ortho CBs after the treatment.

Catalytic destruction of PCDDs in flue gas

Abstract Many kinds of hydrocarbons are known to be decomposed by catalytic reaction at comparatively low temperatures. The technology of catalytic destruction is applied in many fields, for example, for automobile engine exhaust gas, deodorization from stack gas. We are trying to apply the catalytic destruction technology to reduce PCDDs concentration levels in the flue gas from municipal solid waste incinerators. Because the temperature of flue gas from the incinerator is comparatively low after the waste heat boiler and air pollution control units, 250 to 300 degrees Celsius, the final clean-up of the flue gas should be conducted at a low temperature. First, we had conducted laboratory experiments to confirm the reduction of PCDDs by catalytic destruction. And, at the next stage, we had conducted test plant experiments. Moreover, we have a plan to proceed to the pilot plant experiments. We present here the preliminary results obtained from these experiments, and the availability of the catalytic destruction for PCDDs in flue gas is reviewed in this short report.

Sewage Sludge Melting Process by Coke-Bed Furnace: System Development and Application

A sewage sludge melting process by coke - bed furnace, which is an application of cupola melting technology, was developed. The outline of the course of the development from the bench - scale experiment to the construction of a commercial plant is described. The process is a more sophisticated one which enables high volume reduction, stabilization and utilization of sewage sludge. The slag produced by the process has a volume reduction ratio of 1/9 to 1/40 compared with dewatered sludge, and potential to be utilized as road subbase material and concrete aggregate. The operational cost of the process is estimated to be comparable to that of the conventional ones.

Japan's guidelines for controlling dioxins and dibenzofurans in municipal waste treatment

After waste reduction and recycling, municipal waste must be incinerated and/or buried in landfills. Incineration plays an important role as a waste treatment method in Japan because of Japans high population density and limited landfill area. Of the 46 million tons of municipal waste produced in 1987, 73% was incinerated. In December 1990 the Ministry of Health and Welfare promulgated guidelines for control of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in municipal waste treatment. This guideline is based on the stand point that PCDDs/PCDFs discharge should be prevented as low as technically and practically possible. The guidelines are outlined as follows. Under these conditions, PCDDs/PCDFs are expected to amount to less than nearly 0.5 ng-TEQ/m3N in new continuous type furnaces, which account for 70% of the total incineration capacity. Other types of furnaces are expected to result in much lower concentrations than at present.

Catalytic destruction of PCDDs/PCFFs in municipal solid waste flue gas

Abstract Catalytic destruction technology was applied to reduce PCDDs/PCDFs concentration levels in the flue gas from a municipal solid waste incinerator. Using common combustion techniques, high temperatures (> 1000 °C) are required to decompose PCDDs/PCDFs. However, from an energy saving perspective, it is more efficient to perform exhaust gas cleanup at low temperatures because the incinerator flue gas temperatures are comparatively low after leaving the waste heat boiler and air pollution control unit (250–300 °C). The ability to remove PCDDs/PCDFs by catalytic destruction was previously confirmed by the authors, with the presented study conducting pilot plant experiments using exhaust gas (max. 1900 N m3/hr) induced from the outlet of the electrostatic precipitator of a municipal solid waste incinerator. A PCDDs/PCDFs destruction ratio of at least 99% was obtained at temperatures less than 300 °C, being dependent on space velocity and the catalyst geometric properties.

The removal efficiency of dioxin in flue gas of MSW incinerator — Comparison of a fabric filter with an electrostatic precipitator —

Abstract This study was carried out at the pilot plant which was equipped a fabric filter in order to confirm the removal efficiency of Dioxin. PCDDs and PCDFs can be removed by the fabric filter. The removal efficiency of PCDDs and PCDFs was 96.9%.

Control of dioxins from municipal solid waste incinerator

Abstract The purpose of this study is to establish whether intermediate products, which are remained as unburned components and become the precursors to form the PCDD, can be reduced by improvement of the plant operation. The change of the PCDD levels was analyzed along the stream of the flue gas. Two test programs were conducted to reduce the emission levels of PCDD at municipal solid waste (MSW) incinerators. They were as follows; 1. (1) High temperature incineration to reduce unburned components. 2. (2) Investigation of the relationship between CO contents and PCDD levels at an incinerator which was operated by reductive two-step combustion mode to reduce NOx emission level.

Estimation of the environmental fate of PCDD emitted from municipal solid waste incinerators

Abstract Polychlorinated- p -dioxins (PCDD) have been detected within various media in Japan including air, sea water, river water, sediment and biota. Municipal solid waste incinerators are well-known as one of the major sources of these pollutants. In order to evaluate the effect of these pollutants, PCDD emission data published in Japan was collected and analyzed to estimate the release of PCDD from municipal solid waste incinerators into the environment. A compartmental model was used to calculate the environmental concentration of PCDD released from municipal solid waste incinerators and the predicted concentrations were then compared with the observed concentrations.