Environmental Water Treatment Knowledge: The Meaning and Role of Heavy Metal Pollution
Heavy metal pollution refers to environmental pollution caused by heavy metals or their compounds. For example, Minamata disease in Japan was caused by mercury pollution. The degree of harm depends on the concentration and chemical form of the heavy metals present in the environment, food and organisms.
In addition, many other factors must be taken into account in actual engineering applications.
The safe concentration of lead for aquatic organisms is 0.16 mg/L. When rice and wheat are irrigated with water containing 0.1-4.4 mg/L of lead, the lead content in the crops increases significantly.
In addition, many other factors must be taken into account in actual engineering applications.
Cadmium can replace calcium in bone, causing severe softening of the skeleton and brittle bones, and can lead to impaired stomach function, interference with the zinc enzyme system in humans and organisms, and a rise in hypertension. Those most vulnerable are mining workers and people with weakened immunity. At a cadmium concentration of 0.1 mg/L in water, the self-purification of surface water is mildly inhibited; the safe concentration of cadmium for silver carp is 0.014 mg/L; irrigation with water containing 0.04 mg/L of cadmium causes obvious contamination of soil and rice, and irrigation water containing as little as 0.007 mg/L of cadmium can already cause pollution.
In addition, many other factors must be taken into account in actual engineering applications.
Environmental pollution caused by nickel and its compounds. During the smelting of nickel ore and iron and steel, some ore dust enters the atmosphere with the airflow. During roasting, nickel and its compounds are also emitted, mainly as water-insoluble nickel sulfide (NiS), nickel oxide (NiO) and metallic nickel dust, becoming particulates in the air. Nickel dust produced by combustion, when it meets hot carbon monoxide, forms volatile, highly toxic and carcinogenic nickel carbonyl [Ni(CO)4]. Workers in nickel refining have higher incidences of nasal and lung cancers. Wastewater from the nickel-plating industry, machinery manufacturing and metalworking often contains nickel, and the alkaline method is commonly used to treat industrial wastewater, causing nickel to precipitate as nickel hydroxide [Ni(OH)2] and be removed. Nickel can accumulate in soil; the settling of nickel-containing atmospheric particulates, irrigation with nickel-containing wastewater, decay of animal and plant residues and rock weathering are all sources of soil nickel. Plant growth absorbs nickel from the soil. The plants with the highest nickel content are green vegetables and tobacco, reaching 1.5-3 ppm. The critical concentration at which nickel becomes toxic to rice is 20 ppm. China stipulates a maximum allowable concentration of 0.001 mg/m3 for nickel carbonyl in workshop air and 0.5 mg/L for nickel in surface water.
Moreover, from an industry-development perspective, market demand is also driving technological progress.
Experts point out that the relatively backward processes, equipment and R&D of China's plastics producers are the main cause of serious pollution, while poor management, local protectionism and weak public environmental awareness aggravate it, making strengthened control urgent. Producers should look to the future, promote environmental protection, and use eco-friendly additives so that the PVC industry can develop healthily and over the long term.
In addition, many other factors must be taken into account in actual engineering applications.
Promote closed-loop circulation and non-toxic processes vigorously to reduce or eliminate pollutant emissions. Recover and treat industrial 'three wastes' (waste gas, wastewater and residue), turning harm into benefit. Purify the discharged 'three wastes' and strictly control the amount and concentration of pollutant emissions so that they meet discharge standards.
Furthermore, this technology also sees broad application and practice in related fields.
Deep ploughing, i.e. deep tillage, turns over and mixes the upper and lower soil layers to reduce the pollutant content of the surface soil. This method disturbs a relatively small volume of soil, but is not suitable for severely contaminated areas.
At the same time, the supporting processes and equipment are being continuously optimized and upgraded.
In recent years, introducing treatment technologies from other industrial fields, especially for wastewater and air pollution, into soil remediation has opened new avenues for soil pollution control research, such as magnetic separation, anion-cation membrane exchange and bioreactors. Although most are still at the experimental exploration stage, actively absorbing and adapting new technologies and materials to reduce remediation costs and improve engineering practicality on the basis of guaranteed treatment effect is of great practical significance.
Moreover, from an industry-development perspective, market demand is also driving technological progress.
(I) Carry out in-depth soil environmental quality surveys. Building on existing relevant surveys, with agricultural land and land used by key-industry enterprises as the focus, conduct a detailed survey of soil pollution; by the end of 2018, ascertain the area and distribution of soil pollution in agricultural land and its impact on the quality of agricultural products; by the end of 2020, grasp the distribution of contaminated plots at key-industry enterprise sites and their environmental risks. Formulate an overall survey plan and technical regulations, provide technical guidance, supervision and inspection, and review of results. Establish a regular soil environmental quality survey system, conducted once every 10 years. (Led by the Ministry of Environmental Protection, with participation from the Ministry of Finance, the Ministry of Land and Resources, the Ministry of Agriculture and the National Health and Family Planning Commission, etc.; implemented by local governments at all levels, which are responsible for implementation hereinafter and are not repeated.)
(II) Build a soil environmental quality monitoring network. Plan and integrate soil environmental quality monitoring sites in a unified manner; by the end of 2017, complete the setup of national-controlled soil environmental quality monitoring sites and build a national soil environmental quality monitoring network, giving full play to industry monitoring networks and basically forming soil environmental monitoring capability. Each province (region, city) shall conduct at least one training session for soil environmental monitoring technical personnel every year. Localities may add monitoring sites and additional characteristic pollutant monitoring items as needed and increase monitoring frequency as appropriate. By the end of 2020, achieve full coverage of soil environmental quality monitoring sites in all counties (cities, districts). (Led by the Ministry of Environmental Protection, with participation from the NDRC, the Ministry of Industry and Information Technology, the Ministry of Land and Resources and the Ministry of Agriculture) [4]
At the same time, the supporting processes and equipment are being continuously optimized and upgraded.
(V) Build a standards system in a systematic way. Improve standards and technical specifications for soil pollution prevention. By the end of 2017, issue soil environmental quality standards for agricultural and construction land; complete the revision of technical specifications for soil environmental monitoring, investigation and assessment, risk control, and remediation, and the technical guidelines for environmental impact assessment; revise standards for toxic and hazardous substance limits in fertilizers, feeds and irrigation water and for pollutant control in agricultural sludge, further tightening pollutant control requirements; revise agricultural film standards to raise thickness requirements and study the formulation of degradable agricultural film standards; revise pesticide packaging standards to add requirements preventing pesticide packaging waste from contaminating soil. Revise pollutant discharge standards in a timely manner to clarify special discharge limit requirements. Improve analytical and testing methods for soil pollutants and develop soil environmental standard samples. Localities may formulate local soil environmental quality standards stricter than the national standards. (Led by the Ministry of Environmental Protection, with participation from the MIIT, the Ministry of Land and Resources, the Ministry of Housing and Urban-Rural Development, the Ministry of Water Resources and the Ministry of Agriculture, etc.)
Building on this, industry experts have also carried out extensive research and improvements.
(VIII) Effectively strengthen protection. [4] Control pollution from enterprises. Strictly control the establishment of new non-ferrous metal smelting, petroleum processing, chemical, coking, electroplating and tannery enterprises in areas concentrated with priority-protected cultivated land; existing enterprises in these industries shall adopt new technologies and processes and accelerate upgrades to meet higher standards. (Led by the Ministry of Environmental Protection and the NDRC, with participation from the MIIT)
(IX) Vigorously promote safe utilization. Based on soil pollution status and excessive agricultural product levels, counties (cities, districts) with concentrated safe-utilization cultivated land shall, in light of local main crop varieties and planting habits, formulate and implement safe-utilization plans for contaminated cultivated land, adopting agronomic regulation, substitute planting and other measures to reduce the risk of excessive agricultural products. Strengthen agricultural product quality testing. Strengthen technical guidance and training for farmers and farmer cooperatives. By the end of 2017, issue technical guidelines for the safe utilization of contaminated cultivated land. By 2020, achieve safe utilization of 40 million mu of mildly and moderately contaminated cultivated land. (Led by the Ministry of Agriculture, with participation from the Ministry of Land and Resources, etc.)
(X) Fully implement strict control. Strengthen the use management of strictly-controlled cultivated land, delimit prohibited areas for the production of specific agricultural products by law, and strictly prohibit the planting of edible agricultural products; for those that threaten groundwater and drinking-water source safety, the relevant counties (cities, districts) shall formulate environmental risk control plans and implement relevant measures. Study incorporating strictly-controlled cultivated land into the country's new round of returning farmland to forest and grassland, and formulate and implement plans for adjusting the planting structure of heavily contaminated cultivated land or returning it to forest and grassland. Continue pilots for the remediation of heavy-metal-contaminated cultivated land and the adjustment of crop planting structure in the Chang-Zhu-Tan region of Hunan. Implement a cultivated-land rotation and fallow system pilot. By 2020, strive to achieve 20 million mu of planting-structure adjustment or return of heavily contaminated cultivated land to forest and grassland. (Led by the Ministry of Agriculture, with participation from the NDRC, the Ministry of Finance, the Ministry of Land and Resources, the Ministry of Environmental Protection, the Ministry of Water Resources and the State Forestry Administration)
Building on this, industry experts have also carried out extensive research and improvements.
(XII) Clarify management requirements. Establish an investigation and assessment system. By the end of 2016, issue technical regulations for soil environmental investigation and assessment of construction land. Starting in 2017, for land of non-ferrous metal smelting, petroleum processing, chemical, coking, electroplating and tannery enterprises whose land-use rights are to be recovered, and for land of the above enterprises whose intended use is to be changed to residential, commercial, school, medical, elderly-care or other public facilities, the land-use right holder shall be responsible for conducting soil environmental investigation and assessment; where already recovered, the city or county people's government where it is located shall be responsible. Starting in 2018, for heavily contaminated agricultural land converted to urban construction land, the city or county people's government where it is located shall organize and conduct the investigation and assessment. The investigation and assessment results shall be filed with the local environmental protection, urban-rural planning and land resources departments. (Led by the Ministry of Environmental Protection, with participation from the Ministry of Land and Resources and the Ministry of Housing and Urban-Rural Development)
Furthermore, this technology also sees broad application and practice in related fields.
Strictly prevent mineral-resource development from polluting soil. Starting in 2017, regions with concentrated mineral-resource development activities in Inner Mongolia, Jiangxi, Henan, Hubei, Hunan, Guangdong, Guangxi, Sichuan, Guizhou, Yunnan, Shaanxi, Gansu, Xinjiang and other provinces (regions) shall implement special discharge limits for key pollutants. Comprehensively rectify historical tailings ponds, and improve measures for capping, soil covering, flood discharge, dam reinforcement and other hidden-danger treatment and pond closure. Enterprises with key regulated tailings ponds shall conduct environmental risk assessments, improve pollution-control facilities and stock emergency supplies. Strengthen radiation safety supervision of mineral-resource development and utilization activities; relevant enterprises shall monitor soil radiation in their mining areas every year. (Led by the Ministry of Environmental Protection and the State Administration of Work Safety, with participation from the MIIT and the Ministry of Land and Resources)
Strengthen pollution prevention and control in heavy-metal-related industries. Strictly implement heavy metal pollutant discharge standards and related total-amount control targets, intensify supervision and inspection, and for enterprises that still fail to meet standards after rectification, order them to suspend business or close by law, and publicly disclose the list of such enterprises. Continue to eliminate backward capacity in key heavy-metal-related industries, improve access conditions for such industries, and prohibit the construction of projects with backward capacity or severely overcapacity. Phase out ordinary incandescent lamps on schedule. Raise the elimination standards for backward capacity in industries such as lead-acid batteries, and gradually withdraw backward capacity. Formulate clean-production technology promotion plans for key heavy-metal-related industrial industries, and encourage enterprises to adopt advanced and applicable production processes and technologies. By 2020, the discharge of key heavy metals in key industries shall fall by 10% compared with 2013. (Led by the Ministry of Environmental Protection and the MIIT, with participation from the NDRC)
Strengthen the treatment and disposal of industrial waste. Comprehensively rectify the storage sites of tailings, coal gangue, industrial by-product gypsum, fly ash, red mud, smelting slag, calcium carbide slag, chromium slag, arsenic slag, and solid waste from desulfurization, denitrification and dust removal; improve facilities against blowing-away, loss and leakage, formulate remediation plans and implement them in an orderly manner. Strengthen comprehensive utilization of industrial solid waste. Clean up and rectify the recycling activities of electronic waste, waste tires and waste plastics, guiding relevant enterprises to adopt advanced and applicable processing technologies and cluster development, centrally build and operate pollution-control facilities, and prevent contamination of soil and groundwater. Starting in 2017, conduct pilot coordinated treatment of wastewater and sludge, and waste gas and slag, in some cities in the Beijing-Tianjin-Hebei, Yangtze River Delta and Pearl River Delta regions. (Led by the Ministry of Environmental Protection and the NDRC, with participation from the MIIT and the Ministry of Land and Resources)
(XIX) Control agricultural pollution. Use chemical fertilizers and pesticides rationally. Encourage farmers to apply more organic fertilizer and reduce fertilizer use. Apply pesticides scientifically, promote professional, unified pest prevention and control and green control of crops, and popularize highly effective, low-toxicity, low-residue pesticides and modern plant-protection machinery. Strengthen the recovery and treatment of pesticide packaging waste; starting in 2017, conduct pilots in some major grain (oil) counties and key vegetable-industry counties in Jiangsu, Shandong, Henan, Hainan and other provinces; by 2020, extend to 30% of major grain (oil) counties and all key vegetable-industry counties nationwide. Promote clean agricultural production, conduct pilots for the resource utilization of agricultural waste, and develop a batch of replicable and promotable technical models for the prevention and control of agricultural non-point-source pollution. Strictly prohibit the direct use of urban domestic waste, sludge and industrial waste as fertilizer. By 2020, achieve zero growth in the use of chemical fertilizers and pesticides for major crops nationwide, raise the utilization rate to above 40%, and raise the coverage of soil-testing-formula fertilization technology to above 90%. (Led by the Ministry of Agriculture, with participation from the NDRC, the Ministry of Environmental Protection, the Ministry of Housing and Urban-Rural Development and the Supply and Marketing Cooperatives, etc.)
Strengthen the recovery and utilization of waste agricultural film. Severely crack down on the illegal production and sale of substandard agricultural film. Establish and improve the recovery, storage, transport and comprehensive utilization network for waste agricultural film, and conduct recovery and utilization pilots; by 2020, provinces with high agricultural-film use such as Hebei, Liaoning, Shandong, Henan, Gansu and Xinjiang shall strive to achieve full recovery and utilization of waste agricultural film. (Led by the Ministry of Agriculture, with participation from the NDRC, the MIIT, the Ministry of Public Security, the State Administration for Industry and Commerce and the Supply and Marketing Cooperatives, etc.)
Strengthen pollution prevention and control in livestock and poultry breeding. Strictly regulate the production and use of veterinary drugs and feed additives to prevent overuse and promote source reduction. Strengthen the comprehensive utilization of livestock and poultry manure, and conduct pilots combining crop and livestock farming and cyclic development in some major pig-county areas. Encourage and support the construction of livestock and poultry manure treatment and utilization facilities; by 2020, the proportion of large-scale farms and farming communities equipped with waste-treatment facilities shall reach above 75%. (Led by the Ministry of Agriculture, with participation from the NDRC and the Ministry of Environmental Protection)
(XX) Reduce domestic pollution. Establish a coordination mechanism among government, communities, enterprises and residents; through classified collection and comprehensive recycling, promote waste reduction, resource utilization and harmlessness. Establish a village cleaning system, advance rural domestic waste treatment, and implement rural domestic sewage treatment projects. Rectify non-standard waste landfills. Deepen the 'reward-for-treatment' policy and expand the scope of joint rural environmental remediation. Advance pilots for co-processing domestic waste in cement kilns. Encourage the use of treated, standards-compliant sludge for landscaping. Conduct demonstrations of resource utilization such as producing building materials from construction waste. Strengthen the safe disposal of heavy-metal-containing waste such as spent mercury-oxide batteries, nickel-cadmium batteries, lead-acid batteries and mercury-containing fluorescent tubes and thermometers. Reduce excessive packaging and encourage the use of eco-labeled products. (Led by the Ministry of Housing and Urban-Rural Development, with participation from the NDRC, the MIIT, the Ministry of Finance and the Ministry of Environmental Protection) [4]
It is worth noting that the technologies and standards in this field continue to evolve and improve.
'Theoretically, heavy-metal-contaminated soil can be remediated, but fully restoring its ecological function is very difficult,' Chen Shibao told a reporter from the Economic Information Daily. At present, many remediation measures for heavy-metal-contaminated soil have been proposed around the world. Soil remediation mainly comprises two principles: containment (in-situ remediation) and removal (ex-situ); based on these two principles, remediation mainly includes isolation and encapsulation, solidification/stabilization, pyrometallurgical separation, chemical stabilization, electrokinetic remediation, soil replacement and turning, soil washing and bioremediation (including phytoremediation). However, each measure has certain application limitations and more or less other problems, some of which are even insurmountable technical difficulties. 'Once heavy metals enter the soil, remediation becomes very difficult and requires a great deal of time and money,' said Chen Shibao.
In addition, many other factors must be taken into account in actual engineering applications.
Industry experts unanimously agree that the top priority is to control source pollution. 'In heavy metal pollution prevention, source control must be combined with process blocking and end-of-pipe treatment, of which source control is the key. We must never take the old path of polluting first and treating later. This is also one of the core elements of the ecological civilization that China currently advocates,' said Chen Shibao.
