Analysis of the Engineering Applications and Business Models of Soil Remediation Technologies for Polluted Sites in China

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This post was last edited by yinkuilin6868 on February 25, 2016, at 09:23. In recent years, with the adjustment of China’s industrial structure and the acceleration of urbanization, major cities across the country have implemented policies such as “shifting from secondary industries to tertiary industries” and “relocating industries out of urban areas to industrial parks”. As a result, a large number of polluting enterprises in industries like chemicals, metallurgy, petroleum, transportation, and light manufacturing have been relocated or shut down one after another. During the redevelopment of contaminated soils at sites left behind after the relocation of numerous industrial enterprises, the pollutants pose a direct threat to the health of people engaged in production and daily life on that land. As the area of soil pollution in China continues to expand, there has been an emergence of composite and mixed high-risk pollution zones, which show a trend of spreading from urban suburbs to rural areas and from localized areas to broader regions. From April 2005 to December 2013, the **Ministry of Environmental Protection and the Ministry of Land and Resources jointly conducted a survey on the soil pollution situation across the country; the survey sites covered all arable land, as well as some forest land, grassland, unused land, and construction land. The survey results indicate that the overall condition of the soil environment nationwide is concerning; soil pollution is relatively severe in some areas. The environmental quality of arable land soil is worrying, and soil environmental problems are prominent in industrial and mining waste sites. Human activities such as those related to industry, mining, and agriculture, along with high background levels of soil contaminants, are the main causes of soil pollution or excessive pollutant concentrations. Given the limited land resources and fragile environmental carrying capacity, actively carrying out soil pollution remediation and management can provide strong assurance for China’s achievement of green and sustainable development. Based on the situation of soil pollution in China and the characteristics of polluted sites, this article introduces the current status of the engineering application of several typical soil remediation techniques for polluted sites in China, including the applicable features of these engineering technologies, system composition, engineering equipment, case studies, and reference costs. Taking into account the current characteristics of China’s soil remediation industry, it systematically analyzes the business models of the domestic contaminated site soil remediation industry at present, as well as its future development trends. 1 Current status of the engineering application of soil remediation technologies in China 1.1 Desorption and adsorption removal technologies 1.1.1 Engineering applications Desorption and adsorption removal technologies can be divided into normal-temperature desorption and thermal desorption; thermal desorption is also known as heat desorption technology. It can be further classified into low-temperature heat desorption (where the soil is heated to below 315 °C) and high-temperature heat desorption (where the soil is heated to above 315 °C). In domestic engineering applications, the normal-temperature desorption technique typically involves piling up the contaminated soil into strips, and then using turning equipment to turn over these soil piles, thereby allowing the volatile pollutants in the soil to be removed through volatilization. The treatment systems and equipment utilized in thermal desorption technology are relatively complex; examples include drum-type thermal desorption systems, fluidized bed thermal desorption systems, microwave thermal desorption systems, and far-infrared thermal desorption systems. In domestic projects, the mainly used system is the drum-type thermal desorption system. This system primarily consists of a feeding system, a thermal desorption system, and a off-gas treatment system. The heating method can be either direct or indirect heating. Under normal conditions, the temperature of the soil during direct heating treatment is 150 to 650 °C, while it is 120 to 530 °C during indirect heating treatment. In domestic engineering applications, to ensure the efficiency and energy consumption of thermal desorption, the soil must be pretreated prior to feeding, so that its moisture content is below 25% and the maximum soil particle size does not exceed 50 mm. 1.1.2 Engineering case: After a chemical plant was decommissioned, site investigations and risk assessments revealed that the soil within the plant area was contaminated with composite organic substances primarily consisting of VOCs and SVOCs. The main pollutants included BTEX, organophosphorus pesticides, polycyclic aromatic hydrocarbons, etc. The scale of this project was approximately 200,000 m³. For slightly contaminated soil, ambient-temperature desorption technology is employed; for heavily contaminated soil, drum-type thermal desorption technology is used to uniformly heat the soil to 300–550 °C. The removal rate of pollutants in the oxidation incineration chamber exceeds 99.9%. After remediation, the concentration of pollutants in the soil meets the remediation targets. The actual construction cost of the project is approximately 1,000 yuan per cubic meter. 1.2 Chemical oxidation/reduction technologies
1.2.1 Engineering applications
Currently, in the application of chemical oxidation/reduction technologies in China, common oxidizing and reducing agents include Fenton’s reagent, manganates, persulfates, ozone, hydrogen sulfide, sodium bisulfite, ferrous sulfate, calcium polysulfide, and zero-valent iron. Among these, persulfates and zero-valent iron are currently regarded as preferred oxidizing and reducing agents both domestically and internationally. Engineering application technologies can be divided into in-situ treatment technologies and ex-situ treatment technologies. The ex situ treatment system mainly includes soil pretreatment, chemical mixing, and the impermeability system. The pretreatment system involves crushing, screening of contaminated soil, or adding amendments, etc. The main equipment includes crusher-screen buckets, excavators, etc. A chemical mixing system is used to mix and stir contaminated soil with chemicals; the main equipment includes soil remediation machines and shallow soil stirrers. An impermeable system is a reaction tank with impermeability properties that can prevent damage from mixing equipment; it is usually constructed using impermeable concrete or an impermeable membrane along with a protective layer. The in-situ treatment system mainly consists of a chemical preparation/storage system, an injection system, a monitoring system, etc. The chemical is injected into the contaminated area through injection wells; the number and depth of these wells are determined based on the size of the contaminated area and the extent of contamination. Monitoring wells are placed around the injection wells as well as at the periphery of the contaminated area, so as to monitor the pollutants in the contaminated area, as well as the distribution and movement of the chemical during and after the remediation process. For soils with low permeability, soil mixing techniques or hydraulic fracturing techniques can be used to help disperse chemical agents into the contaminated soil. 1. 2. 2 Engineering Case: At a pesticide manufacturing plant, site surveys and risk assessments revealed that the main pollutants were various organic compounds such as o-toluidine, p-chlorotoluene, and 1,2-dichloroethane. The area affected by groundwater contamination was approximately 6,000 m2, with a contamination depth of up to 18 m. Taking into account the characteristics of pollutants in the site, pollutant concentrations, soil properties, and the requirements of the project development, in-situ chemical oxidation technology was selected for the treatment of groundwater pollution in areas where excavation is not required. The operational and management costs for the entire remediation project range from 2,000 to 2,500 per m2. 1.3 Chemical washing technology
1.3.1 Engineering applications
In the application of chemical washing technology, surfactants and organic solvents are generally chosen as washing agents for organic pollutants; inorganic acids, organic acids, complexing agents, etc., are typically used as washing agents for heavy metal pollution. For cases involving combined contamination by both organic substances and heavy metals, a combination of both types of washing agents can be considered. Engineering application technologies can also be divided into in-situ treatment technologies and ex-situ treatment technologies. However, in domestic engineering applications, due to limitations such as site conditions, in-situ treatment technologies are rarely used; instead, ex-situ chemical leaching technologies are more commonly employed. The ex-situ treatment system mainly includes soil pretreatment, screening, washing, soil-water separation, wastewater treatment, and volatile gas control systems, etc. The main equipment includes soil pretreatment equipment (such as crushers, screens, etc.), conveying equipment (such as screw conveyors, belt conveyors, etc.), physical screening equipment (such as wet vibrating screens, drum screens, etc.), enhanced leaching equipment (such as leaching mixing tanks, horizontal oscillators, chemical dosing equipment, etc.), soil and water separation and dewatering equipment (such as dewatering screens, filter presses, centrifuges, etc.), sewage treatment systems (such as sedimentation tanks, physicochemical treatment systems, etc.), slurry conveying systems (such as slurry pumps, pipelines, etc.), and automatic control equipment. This technique is more effective for large-particle soils where pollutants are concentrated (such as gravel, sand, fine sand, and similar soils); it is more difficult to treat clay. The percentage of fine particles in the soil is a key factor determining the effectiveness and cost of this remediation method. If the soil contains more than 25% clay particles, the remediation costs will increase, and in such cases, chemical leaching techniques are generally not considered. 1. 3.2 Engineering case: Through site investigation and risk assessment, it was found that in certain areas of a chlorinated organic pesticide plant site, the soil was contaminated with organic substances. The main pollutants were BHC and DDT; their maximum concentrations reached 46.4 mg/kg and 33.2 mg/kg respectively. The scale of the project is approximately 1,000 m³. The contaminated soil mainly consists of miscellaneous fill; the content of coarse particles (2–10 mm) is approximately 58%, that of sand particles (0.3–2 mm) is nearly 25%, and that of fine particles (less than 0.3 mm) is around 17%. Based on the characteristics of pollutants, their concentrations, and the properties of the soil, the ex-situ chemical washing technique was selected for treating this miscellaneous fill. After remediation, the removal rate of pollutants from the soil exceeded 85%, meeting all the required remediation targets. The operating cost of the system equipment for this project is approximately 300 yuan per cubic meter, while the cost of washing agents and wastewater treatment chemicals is about 240 yuan per cubic meter. 1.4 Solidification/Stabilization technologies
1.4.1 Engineering applications
The remediation materials used in solidification/stabilization technologies can be broadly classified into three categories: inorganic binders (such as cement, pozzolanic materials, lime, apatite, and slag), organic binders (such as organic clays, asphalt, epoxies, polyesters, and waxes), and special additives (such as activated carbon, pH regulators, neutralizers, and surfactants). Engineering applications include both in-situ and ex-situ treatment techniques; in domestic engineering projects, the ex-situ curing/stabilization technique is more commonly used. The ectopic treatment system mainly includes soil pretreatment, chemical addition, and mixing systems. The main equipment includes soil excavation equipment (such as excavators), soil moisture regulation equipment (such as transfer pumps, sprayers, dehydrators, etc.), soil crushing and screening equipment (such as crushers, crushing hoppers, vibrating screens, screening and crushing hoppers, etc.), and equipment for mixing soil with chemicals (such as twin-shaft mixers, single-shaft spiral mixers, cutting-hammer mixing machines, etc.). During the repair process, the degree of mixing between the soil and the chemicals is a key indicator for the successful application of this technique; the more uniform the mixing, the better the curing/stabilization effect. Pre-treatment by crushing the soil facilitates better mixing and contact with the chemicals, and it is generally required that the particle size of the crushed soil not exceed 50 mm. 1. 4. 2 Project Example: In an electronic plating workshop, site surveys and risk assessments revealed that the soil in most areas of the site was contaminated with heavy metals; the main pollutants were copper, zinc, and silver, with maximum concentrations of 1,560, 385, and 3,306 mg/kg respectively. The scale of the project was approximately 2,000 m3. The contaminated soil is mainly clay and silty clay, with a contamination depth of 1 to 4 meters. Taking into account the characteristics of pollutants in the site, their concentrations, and soil properties, the ex-situ solidification/stabilization technique was selected for the remediation of contaminated soil. The soil obtained after remediation met all the required standards, and the overall cost of the project was approximately 600 yuan per m3. 1. 5 Combined remediation: Some soil pollution areas in China are characterized by complex pollution, and it is difficult to achieve satisfactory results using a single remediation method; therefore, there is a need to develop remediation techniques that combine multiple technologies [11]. For the remediation of contaminated soil with multiple pollutants, techniques such as desorption, chemical oxidation/reduction, chemical leaching, and solidification/stabilization can be used in combination. For example, chemical leaching technology is used in the pretreatment stage of solidification/stabilization remediation, and it can effectively remove some volatile and semi-volatile organic pollutants from the contaminants, thereby enhancing the solidification effect. Before chemical oxidation remediation, room-temperature desorption technology can effectively remove a portion of the volatile organic pollutants present in the contaminants, reducing the amount of oxidizing agents needed and thus lowering the costs of remediation. 2 Analysis of the business models in China’s polluted soil remediation industry: During the 12th Five-Year Plan period, approximately 30 billion yuan in central government funds were allocated for the remediation of polluted soil across the country. According to industry experts, driven by this amount of funding, local governments and private investors may be attracted to this field, and the soil remediation market is expected to reach a value of hundreds of billions or even trillions of yuan. However, despite the huge potential for the market size of China’s soil remediation industry, the lack of a sound business model has consistently posed a problem of funding shortages for its development. Currently, there are three main sources of funding for the soil remediation industry in our country: \"whoever pollutes must clean it up,\" \"whoever benefits must clean it up,\" and \"funding provided by external parties.\" 1) The “who pollutes, who cleans up” approach is applicable to polluted sites where the responsible party for the pollution is clear; this approach falls under the “polluter pays” principle. Regarding contaminated sites, it is necessary to identify the relevant responsible parties in a legal sense, with these parties providing the funds needed for the remediation of such sites. 2) \"Who benefits, who governs\" – this model falls under the \"payeur pays\" principle. It makes full use of market mechanisms, with the developers or users of the polluted site responsible for financing the restoration of that site; the expected increase in value resulting from the redevelopment and reuse of the polluted land serves as the commercial return for carrying out soil pollution remediation. 3) The **“funding”** model: For polluted sites where the responsible party for the pollution is unclear and where there is no effective mechanism for generating revenue, **or local authorities** are responsible for raising the funds needed to cover the costs of repairing such sites. Due to historical reasons, the main sources of soil pollution in our country are various state-owned factories. After multiple rounds of restructuring, the ownership patterns of many of these factories have become unclear, making it difficult to identify the entities responsible for the pollution. Relying solely on the \"capital contribution model\" to fund the restoration of polluted sites imposes a huge financial burden on these entities. How to address the issue of insufficient funding and improve the efficiency of pollution control has become a bottleneck hindering the development of the soil remediation industry. In response to this situation, the PPP model that has emerged in recent years has proven to be suitable for China’s national conditions, and it is expected to become a new business model for the soil remediation industry. PPP stands for Public-Private-Partnership, which refers to public-private collaboration. In a broad sense, any form of cooperation with private entities (such as the common BOT, BT, and EPC models) can be considered a PPP model. But in a narrow sense, the PPP model refers to **sharing risks with private entities through cooperation**, granting them the right to operate projects on a concession basis, with profits being shared among all parties involved. For example, in 2014, a domestic environmental remediation company entered into a partnership with Yuetang District in Xiangtan City. The government and the company jointly established a joint venture to carry out comprehensive treatment of the soil contaminated by heavy metals in the industrial park in that district. Once the remediation was completed, the entire industrial area was to be developed into an ecological new town, and the environmental remediation company would earn profits from the subsequent land transactions. “The \"Yuetang Model\" is an application of the PPP model; it involves obtaining value-added benefits through the development and transfer of soil remediation projects, thereby breaking through the funding constraints in this industry, bringing in third-party funds, and improving the mechanism from soil remediation to the realization of profits. 3 Conclusion: China faces a shortage of land resources and severe soil pollution problems. With the conduct of site surveys, assessments, and remediation efforts in major cities in recent years, and through the continuous introduction of advanced foreign technologies and equipment, soil remediation techniques in China have now been largely put into practical use. However, introducing complete sets of ready-made technical equipment is subject to foreign intellectual property protections, is costly, and also presents the issue of incompatibility with local conditions. It is necessary to conduct adaptive analyses based on the characteristics of soil pollution in China, absorb advanced foreign experiences, and strengthen research and development of domestic restoration materials and equipment, so as to establish engineering technologies, restoration materials, and engineering equipment with independent Chinese intellectual property rights at an early date. As China pays increasing attention to soil environmental pollution, the prospects for the soil remediation industry are very promising. However, most projects currently face the challenge of insufficient funding for environmental remediation. The business model of environmental remediation services based on the PPP approach offers a viable solution to this issue. In the future, with the introduction of environmental taxes in China and the implementation of the Action Plan for Soil Pollution Prevention and Control, there will be more diverse sources of financial support at the local level, enabling more soil remediation projects to adopt the PPP model. This will accelerate the progress of soil remediation efforts in China.