Ecological remediation began in the late twentieth century. It embodies a comprehensive technology that activates the self-cleaning functions of ecosystems utilizing ecological principles with the help of biological, physical, chemical and engineering methods. Remediation of contaminated soil, ecological reclamation of abandoned mining sites and the application of sewage water in land treatments are focal research areas in pollution ecology within our institute.
Phytoremediation is one of the biological methods for the remediation of soils contaminated with PAHs, and has now incorporated a set of integrative technologies including complexation-induced phyto-remediation, the use of intercropping systems for phyto-remediation, and treatment and disposal of plants after phyto-remediation. Microbial degradation of organic pollutants in soil is the primary method for remediation of contaminated soils, and integrative remediation techniques such as phyto-microbial, electrokinetic-microbial, and leaching-microbial remediation, have been established. Ecological reclamation of mining areas uses plant populations suitable for vulnerable ecosystems and establishes a healthy ecological system at these sites through soil quality improvement and nutrient adjustment. Land treatment systems for wastewater have certain advantages for small towns and can play an important role in improving regional environmental quality. These systems, including subsurface infiltration, slow infiltration and artificial wetlands, are widely applicable in different regions of China.
Screening of plants for bioremediation. We have systematically constructed a method for identifying weed species that may accumulate or hyperaccumulate heavy metals. Solanum nigrum L., Rorippa globosa (Turcz.) Thell., and Bidens pilosa L. have been found to be a Cd-hyperaccumulator. Four other species, including Taraxacum mongolicum L., have been identified as Cd-accumulators. Oenothera biennis L. is recognized as a Cd and Cu excluder. Rice cultivars such as Liaoxing 13 and Shendao 4, and the eggplant cultivar Liaoqie 3 have been identified as low accumulation crops for Cd, Hg and Pb.
We also studied microbial community structure in PAH-contaminated soils and isolated efficient microbial strains with high potential to biodegrade organic contaminants in the soil. A new product has been commercialized. We have utilized microbial immobilization and mycorrhizal techniques in the remediation of contaminated soils, developed a theoretical framework for phyto-microbial remediation, studied the effects of environmental factors on co-metabolism of microorganisms, and identified co-metabolic substrates for microorganisms, surfactants and electron acceptors as remediation agents.
Remediation of soils polluted with heavy metals and organic chemicals. Focusing on soils contaminated with Cd-PAHs, we established a rotational cropping system involving the Cd-hyperaccumulator Solanum nigrum L. that is planted and harvested in the first season, followed by growing Chinese cabbage in the second half of the year. This study was supported by the “863 Project”.
Phyto-microbial remediation of agricultural soils contaminated with organic compounds. For agricultural soils contaminated with organic compounds, we developed microbial immobilization and mycorrhizal techniques; and set up a theoretical framework and identified optimal conditions for integrative phyto-microbial remediation of PAH-contaminated soil, taking into account remediation cost, outcomes and environmental benefits. We established a demonstration project of in situ remediation of contaminated soils in the Shenfu waste water irrigation area, which consisted of eight demonstration zones, including different tillage treatments, microbial remediation, mycorrhizal-phytoremediation, and integrated phyto-microbial remediation. Long-term field studies have confirmed that phytoremediation facilitates biodegradation of PAHs in rhizospheric soils.
The construction of demonstration sites along with remediation practices have provided technical support for large-scale remediation of soils contaminated with organic pollutants. The project report "Ecological remediation techniques for contaminated soil in wastewater irrigation areas" was listed in the National Key Scientific and Technological Achievement Extension Program to facilitate its application in contaminated agricultural soils. The Institute of Applied Ecology, Chinese Academy of Sciences was named as "National Technology Support Institution for Remediation of Petroleum Contaminated Soils".
Electrokinetic remediation of contaminated soil. Utilizing electric field methodologies, we proposed a symmetrical electric field method for remediation of soils contaminated with PAHs through optimal placement of the electrode matrix. In the process we established a method of rotating the electrodes. This method overcame the shortcomings of anodic acidification and low electric field efficiency in existing technologies, effectively stimulated the microbial activity, as well as enhanced the rate of biodegradation in the electric field. We also quantitatively analyzed the contributions of electrokinetics and microorganisms to the degradation processes of pollutants; optimized the microbial community structure and its spatial distribution; revealed the terminal oxidation mechanisms of long-chain alkanes in the process of electrokinetic remediation; illustrated the process of degradation of PAHs in the electric field; and formulated a procedure for rapid degradation of refractory heavy PAHs. We believe that these represent significant achievements in electric field design, system control and equipment design.
Wastewater land treatment system (WLTS). WLTS is a water treatment system incorporating both water treatment and utilization. It places environmental quality as the highest priority in wastewater management and follows three basic principles ¾ optimization of ecological, social and economic benefits. Our research team has established a comprehensive system of land treatment technology, including a land classification system, suitability analysis, land treatment types, land treatment process parameters, engineering designs and an expert system. A safe protection system of WLTS was established to prevent secondary pollution of soil and groundwater, including influent and effluent water quality control, pretreatment regimes, restrictive hydraulic loading and retrieval of regenerated water. We built several demonstration projects as alternatives for wastewater secondary and tertiary treatments.
Ecological reclamation of mining sites. The pollution ecology team has developed technologies for remediation of contaminated soil in magnesite areas. These involve the breaking of surface soil crusts, improvement of deep soils and comprehensive restoration of soil quality. To break the cement-like crust of contaminated surface soil, we found that the soil infiltration rate can be used to determine soil crust condition, and can also be employed as an index for screening amendments that can facilitate crust breaking. To improve the quality of contaminated subsurface soil, we found that mixed application of 4-furaldehyde residue and phosphor-gypsum as soil amendments significantly increased microbial activity and plant growth. For ecological restoration of soil-plant systems in mining areas, we have found that Kochia scoparia, Cassia nomame, Hordeum jubatum, Ziziphus jujube, Robinia pseudoacacia, and Rhus typhina can absorb large quantities of magnesium from contaminated soil and increase TOC, TN, soil microbial biomass C and N, suggesting that it is feasible to use these plants in vegetation restoration on abandoned mining lands.
According to the degree of soil contamination and compaction, and the extent of the deterioration of vegetation in Haicheng County, we proposed a number of vegetation restoration techniques for areas polluted with magnesite. Foremost among these was the creation of an artificial plantation of multiple species and age classes at the contaminated site.