S. Sakai

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.

Leaching behavior of PCBs and PCDDs/DFs from some waste materials

Although it is well known that some waste materials and their incinerator residues contain persistent organic pollutants (POPs) such as PCBs and PCDDs/DFs, little attention has been paid to the leaching behavior of these chemicals because of their low solubility. Due to the coexistence of surfactants in wastes, however, leaching concentration of POPs may increase. Therefore, leaching tests with and without those substances were conducted in order to understand the influence of surfactant-like substances on POPs leaching. In those tests, linear alkylbenzene sulfonate (LAS) and humic acid were used as surfactant-like substances. Shredder residues from car/electrical goods recycling and fly ash from a municipal solid waste (MSW) incinerator were used in these leaching tests. Furthermore, an experiment was carried out to understand the influence of fine particles on the leaching concentration of POPs. The results indicate that surfactant-like substances increase the leaching concentration of POPs, and fine particles related closely to the transporting behavior of POPs.

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.

Leaching behavior of persistent organic pollutants (POPs) in shredder residues.

It is well known that some kinds of waste contain persistent organic pollutants (POPs) such as PCDD/DFs and PCBs. Leaching behaviors of these chemicals, however, have not been focused so much because of their low leachability. On the other hand, shredder residues originated from automobiles and electric appliances consist mainly of plastics, such as PVC, which contain additives including DEHP. In this study, contents analyses and leaching tests with and without surfactant-like substances for shredder residues were conducted. As a result, shredder residues from automobile and electric appliance contained PCBs in ppm level and a quantity of PCDD/DFs. Surfactant-like substances increase the leaching concentration of POPs. DEHP also leached out considerably even though using distilled water.

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.

System Design and Full-Scale Plant Study on a Drying-Incineration System for Sewage Sludge

The system design of a drying-incineration process for sewage sludge is discussed using an energy-balance model of the system. In particular, the profitability of this system is considered from the energy and cost points of view. An energy-balance model including drying, incineration, waste heat recovery, and exhaust gas treatment processes was formulated. This showed that autothermic conditions could be established at a lower dewatered cake calorific value, i.e., 350 to 400 kcal/kg wet solids (WS), in the drying-incineration system, in contrast to the higher dewatered cake calorific value of 700 to 750 kcal/kg WS necessary to produce autothermic conditions in direct incineration systems. The drying-incineration system had reduced energy costs but involved an increase in investment costs due to construction of the dryer. The authors designed a full-scale plant at the East Area Sludge Center in Kobe City, Japan. The capacity of one line in this plant is 200 tons of cake per day. From the results of full-scale operation, fuel oil consumption was 23 l/t cake (at a cake moisture content of 81.2% and a low calorific value of 180 kcal/kg), which is a lower value compared to conventional incineration systems.

Design of a small-scale incinerator with low PCDD/PCDF emissions

Attempts were made to achieve complete combustion by improving secondary combustion for the purpose of reducing PCDDs/PCDFs in a small-scale incinerator. Particular emphasis was placed on improving gas turbulence in the chamber. First, the gas flow in the chamber was analyzed by the flow visualization technique, using laboratory scale equipment. Then, the combustibility was evaluated using a model gas containing standard carbon monoxide. Finally, the reduction of PCDDs/PCDFs was confirmed with an actual plant. A resultant finding was that PCDDs/PCDFs emissions at the incinerator outlet can be significantly reduced by changing the gas flow pattern in the secondary combustion chamber.

PCDD/Fs reduction in batch type refuse incinerators

Abstract Emission of dioxins in the exhaust gas during start-up and shut-down of batch type refuse incineration plants was studied. The result of our research are as follows: (1) At the time of starting up the plant, using a burner to raise furnace temperature fast reduces dioxin emission. (2) At the time of shut-down, dioxin emission can be better reduced by burn-out operation than by ember-saving method. The effect of using a burner was not evident. (3) To prevent synthesis of dioxins in air heater, it is necessary to lower the air heater inlet gas temperature. (4) To reduce the total emission, it is essential to control the emission rate of dioxins at steady running as it constitutes approximately 70% of the total emission.