Environmental life-cycle comparisons of two polychlorinated biphenyl remediation technologies: Incineration and base catalyzed decomposition

https://doi.org/10.1016/j.jhazmat.2011.04.073Get rights and content

Abstract

Remediation action is critical for the management of polychlorinated biphenyl (PCB) contaminated sites. Dozens of remediation technologies developed internationally could be divided in two general categories incineration and non-incineration. In this paper, life cycle assessment (LCA) was carried out to study the environmental impacts of these two kinds of remediation technologies in selected PCB contaminated sites, where Infrared High Temperature Incineration (IHTI) and Base Catalyzed Decomposition (BCD) were selected as representatives of incineration and non-incineration. A combined midpoint/damage approach was adopted by using SimaPro 7.2 and IMPACTA2002+ to assess the human toxicity, ecotoxicity, climate change impact, and resource consumption from the five subsystems of IHTI and BCD technologies, respectively. It was found that the major environmental impacts through the whole lifecycle arose from energy consumption in both IHTI and BCD processes. For IHTI, primary and secondary combustion subsystem contributes more than 50% of midpoint impacts concerning with carcinogens, respiratory inorganics, respiratory organics, terrestrial ecotoxity, terrestrial acidification/eutrophication and global warming. In BCD process, the rotary kiln reactor subsystem presents the highest contribution to almost all the midpoint impacts including global warming, non-renewable energy, non-carcinogens, terrestrial ecotoxity and respiratory inorganics. In the view of midpoint impacts, the characterization values for global warming from IHTI and BCD were about 432.35 and 38.5 kg CO2-eq per ton PCB-containing soils, respectively. LCA results showed that the single score of BCD environmental impact was 1468.97 Pt while IHTI's score is 2785.15 Pt, which indicates BCD potentially has a lower environmental impact than IHTI technology in the PCB contaminated soil remediation process.

Highlights

► We study the environmental impacts of two kinds of remediation technologies including Infrared High Temperature Incineration(IHTI) and Base Catalyzed Decomposition(BCD). ► Combined midpoint/damage approaches were calculated for two technologies. ► The results showed that major environmental impacts arose from energy consumption. ► BCD has a lower environmental impact than IHTI in the view of single score.

Introduction

Polychlorinated biphenyls (PCBs) are one of the first historically recognized persistent organic pollutants (POPs) and most widespread in the environment [1]. Owing to their desirable and excellent physical–chemical properties, a total of about 1.2 million tons of PCBs were produced and widely applied in industry as the coolants, lubricants in transformers, dielectric fluids in capacitors, pesticides and so on [2]. Although most countries stopped their PCB production by the late 1980s, PCBs still exist in old electric and transformer equipments. It was estimated that more than half of the PCBs was still in use or in storage, or deposited in landfills. Nearly one third was released to the general environment, and only few had been destroyed. PCBs released from evaporation, leakage, illegal recycling, improper disposal [3], [4] and accidents posed high potential harmful affects to man through the bioaccumulation in organisms and the biomagnification in the food chain. Because of their persistence in the environment, PCB concentrations could hardly decrease in most of contaminated sites without remediation actions [5], [6]. As a significant portion of PCBs ever produced remains in service, in storage or in landfills, the management of PCB contaminated sites and PCB-containing wastes will be a major concern in the future.

At present, high temperature incineration is widely used in developed countries to treat PCB wastes [7], [8], [9], which is well developed and generally a thermal oxidation and destruction technology. Most high temperature incineration plants have been built not only for the purpose of destroying PCBs, but also for the disposal of other hazardous wastes. Very high temperature, stringent operating conditions (maintenance at 1200 °C for 2-s residence time or 1600 °C for 1.5-s residence time) with limited feed rate of PCBs are required to achieve high destruction and removal efficiency (DRE) in a incineration process. When operating conditions do not meet the above requirements, PCBs could be evaporated out and highly toxic PCDDs/PCDFs (dioxins and furans) might be formed and released from the incinerators [5], [10]. Some industrialized countries are just limiting the PCB incineration and trying to find alternative destruction technologies for their PCB-containing wastes [11].

Non-incineration processes generally operate at a low temperature and in a depleted or ambient oxygen atmosphere [12]. Though such technologies may also produce dioxins or furans, they need less equipment to remove these chemicals than the oxidizing process, for example high temperature rotary kiln. Base on their advantages, non-incineration demonstration and application is just being promoted by Global Environment Facility (GEF) as a preferred treatment for persistent organic pollutants, especially PCBs, in Slovakia, the Philippines, China and South Africa. Base Catalyzed Decomposition (BCD) [13], developed by EPA's Risk Reduction Engineering Laboratory in cooperation with the National Facilities Engineering Services Center (NFESC) to dispose liquids, soils, sludge and sediments contaminated with chlorinated organic compounds [14], is one of such non-incineration technology. BCD is a catalytic hydrogenation process in which atoms of chlorine are removed from molecules and replaced by hydrogen atoms. In a BCD process, contaminated soil is excavated and screened to remove large particles, then crushed and mixed with sodium bicarbonate and carrier oil which acts both as suspension medium and hydrogen donor. Several different combinations of reagents can be used in the mixture process, all of which utilize a basic (caustic) reagent such as sodium hydroxide or sodium bicarbonate, usually in combination with liquid carriers/reagents as well as catalytic materials. The addition of alkali often enhances the stripping of chlorinated hydrocarbons from difficult matrices. Then, the mixture is heated to about 200–400 °C in a rotary reactor. Under these conditions, significant fractions of the POPs are destroyed in the desorption process, especially in the presence of alkali. And hydrogen splits off from the carrier/donor oil and hydrogenates the bonded chlorine during the operation. The soil left behind is removed from the reactor and can be returned to the site. The oil and salt containing sludge could be disposed as fuel in a cement kiln. The volatilized contaminants are captured, condensed and treated separately. The concentration of PCBs in the vaporized phase that has been treated by BCD process was reported to be as high as 45,000 ppm, and could be reduced to less than 2 ppm.

A major question regarding the choice of PCB treatment technologies remains. It is not clear which technology is the “best”, nor can it be said that one best technology exists for all cases. At most of the time, evaluation criteria for remediation technologies involve destruction and removal efficiency (DRE) and treatment cost. However, the environmental impact of the whole treatment process should be considered with high priority in the selection of a remediation technology. Several methods were developed for assessing the environmental impact, which reveals a wide diversity of approaches from the point of view of objectives, concepts and potential users. For example, environmental risk mapping (ERM) approach generally deals with a single environmental impact, such as the risk of nitrate leaching [15] or pesticide transportation [16]. Multi-agent system (MAS), multiple linear programming approaches (LP) and analytic hierarchy process (AHP) was used to evaluate the environmental impacts from groundwater quantity management, chemical production optimization and construction of a sustainable farming system, respectively [17], [18], [19].

As far as we are aware, there has until now been no systematic study that objectively correlate environmental impacts and benefits of various PCB treatment technologies. Life cycle assessment (LCA) is an internationally standardized methodology for systematic and quantitative evaluation of environmental impacts [20] of functionally equivalent products or services through all stages of their life cycles, which was widely used in soil and groundwater remediation to evaluate the negative and positive impacts concerned [21], [22]. Related studies showed that LCA was an effective tool to identify environmental impacts and improve remediation technology in the trichloroethene, heavy metal and polycyclic aromatic hydrocarbon contaminated sites [23], [24], [25].

This study presents LCAs for (i) an infrared incineration technology disposal plant, and (ii) a BCD technology treatment plant for PCB contaminated wastes. The LCA framework was prescribed by ISO 14040.

Section snippets

Process descriptions

The flow diagrams of two selected PCB remediation technologies are shown in Fig. 1. Infrared High Temperature Incineration (IHTI) is a mobile thermal processing system that using electrically powered silicon carbide rods to heat organic wastes up to 1010 °C to destroy organic pollutants. It was used for the treatment of 34,000 tons of PCB contaminated soil at the Rose Township Dump Superfund Site in 1992–1993 [26]. For BCD process, PCBs are firstly separated from the soil by thermal desorption,

Life cycle assessment

LCA (also known as life cycle analysis and cradle-to-grave analysis) is a technique to assess the impacts that a product or process making on the environment throughout its life span. The procedures of LCA are part of the ISO 14000 environmental management standards, which is carried out in four distinct phases [28], [29], [30], [31]: (1) goal and scope definition; (2) inventory analysis; (3) impact assessment; and (4) interpretation. In this study, we performed LCA of two PCB remediation

Acknowledgment

This work was financially supported, in part, by the National Natural Science Foundation of China (20977105 and 50708110).

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