I. Pollution sources of industrial "three wastes"

Industrial "three wastes" (waste water, waste gas and waste residue) are one of the main factors of groundwater pollution.

(I) Industrial wastewater

For example: (1) industrial electroplating wastewater, the main pollutants are CN, Cr, Cd, Ni, Zn, Hg and "three acids" (HCL, HSO4, HNO3); (2) industrial pickling wastewater, the main component of which is triacid; (3) Metallurgical industrial wastewater, the main pollutants are metal pollutants such as copper, aluminum, zinc, nickel and cadmium; (4) Light industrial wastewater, the main pollutants are alkali, fat, alcohol, aldehyde, ammonia nitrogen, dyes, sulfur, etc. (5) Petrochemical organic wastewater, pollutants are composed of various nitro groups, amino compounds, oils, phenols, alcohols, acids and bases, chlorides, cyanides, various metal compounds, organic compounds, aromatic hydrocarbons and their derivatives. If these toxic and harmful wastewater are directly discharged into urban sewers, rivers, lakes and seas without treatment, or directly discharged into ditches and large seepage pits, it is the main cause of chemical pollution of groundwater.

(2) Industrial waste gas

Some typical industrial waste gases, such as SO2, H2S, CO, CO2, nitrogen oxides and benzopyrene, will cause serious smoke pollution to the atmosphere. These pollutants will fall with the rainfall and enter the water cycle through surface runoff, causing secondary pollution to surface water and groundwater.

(III) Industrial waste residue

Industrial waste residue includes blast furnace slag, steel slag, fly ash, pyrite slag, calcium carbide slag, red mud, coal washing sludge, ferrosilicon slag, tailings from concentrator and sludge from sewage treatment plant. For example, the metallurgical industry produces waste containing cyanide, and the paper industry produces waste containing sulfite; The electronic industry produces mercury-containing garbage; Polychlorinated biphenyls produced by petrochemical industry; Pesticide waste contains phenol, phenol tar waste and waste rich in mineral oil and hydrocarbon solvents; Dust leaching from coal-fired power plants produces arsenic, chromium, selenium and chlorine. Some of these waste residues are naturally accumulated, and some are buried underground. In the stratum with poor waterproof performance, toxic and harmful substances such as heavy metals, volatile phenol and cyanide enter the water body and soil after wind and rain. Part of it directly infiltrates with precipitation, and part of it migrates downstream, and infiltrates with surface runoff, thus causing surface and linear pollution to groundwater. For example, in Shenyang, Jinzhou, Jilin and other cities, chromium slag piles up like mountains, forming an important source of groundwater pollution.

Second, the pollution sources of urban life

For a long time, municipal domestic sewage has been directly discharged without any treatment, and only the self-purification ability of surface water body is used to eliminate pollutants, but the self-purification ability of water body is limited. According to statistics, more than 80% of rivers in China are polluted, and some rivers are so polluted that they can't even be used to irrigate farmland, and at the same time, they also pollute groundwater sources.

(1) Domestic sewage

Domestic sewage mainly includes SS (suspended solids), BOD (biochemical oxygen demand), NH4-N (ammonia nitrogen), ABS (synthetic detergent), P, CL and bacteria. The pollutants contained in domestic sewage and wastewater discharged from hospitals are mostly ammonia nitrogen, phosphorus, synthetic detergents, anaerobic bacteria, volatile phenol, mercury, viruses and radioactive substances, and most of them are discharged into rivers, ditches or seepage pits, polluting surface water and groundwater. Untreated domestic garbage piled up at random is leached by wind and precipitation, and toxic and harmful substances in it enter the water body, polluting surface water and groundwater.

(2) Domestic garbage

Domestic garbage is generally disposed by landfill. With the erosion of the sun, rain and surface runoff, the dissolved substances in the garbage buried around the city will slowly penetrate into the ground and pollute the underground aquifer. Domestic waste is rich in organic matter and salts, which are decomposed into organic nitrogen → ammonia nitrogen → nitrite nitrogen → nitrate nitrogen under the action of microorganisms, so the detection rate of three nitrogen in groundwater is 10% ~ 46%, and the detection rate of total bacteria and coliforms is 10% ~ 26%. Therefore, domestic garbage and septic tanks in residential areas are the main channels that cause organic pollution.

Three. Agricultural pollution source

The main sources of groundwater pollution caused by agricultural activities are residual pesticides, fertilizers, decomposition of animal and plant remains and unreasonable sewage irrigation. They cause the water quality of shallow groundwater to deteriorate in a large area, the most important of which is the increase of NO3-N and the pollution of pesticides and fertilizers.

agricultural chemical pollution

Pesticide pollution has carcinogenic, teratogenic and mutagenic effects on humans and animals. It is reported that this pesticide still exists in the groundwater where DDT was used 30 years ago. In some places, the DDT content per liter of groundwater exceeds the standard by thousands of times. Pesticides widely used now, leached by atmospheric precipitation, pollute groundwater in a large area in the form of "source".

(B) Chemical fertilizer pollution

On the one hand, excessive application of nitrogen fertilizer will increase the NO3 content, permanent hardness and salinity of water; On the other hand, it will cause eutrophication of water bodies. When the content of inorganic nitrogen exceeds 300mg/m3 and the total phosphorus exceeds 20mg/m3, eutrophication will occur, causing a large number of aquatic organisms to die.

(3) Sewage irrigation

Many sewage contains toxic elements and compounds, which often leads to serious groundwater pollution in sandy soil areas with shallow groundwater burial and good permeability of vadose zone. For example, six sewage reservoirs and more than 20 sewage ponds in Xi 'an have more than 300,000 m3 of water storage, which has caused extensive pollution to the first and second terraces of Weihe River.

Four, heavy metals and radioactive pollution sources

Mercury, cadmium, lead, chromium, zinc, cobalt, nickel, tin and other heavy metals and metalloid arsenic, among which mercury, cadmium, chromium and arsenic are the most prominent pollution; Radioactive pollution is a kind of special pollution mainly containing radioactive nuclear elements, including radioactive water pollution. Natural radioactive nuclear elements, fallout from nuclear weapons tests, radioactive waste water and wastes from other industries will pollute groundwater and lead to cancer and genetic diseases.

Groundwater pollution control technologies can be summarized as physical treatment, hydrodynamic control, extraction treatment and in-situ treatment.

1. 1 physical method

Physical method is a method to treat polluted groundwater by physical means, which can be summarized as follows:

① shielding method

This method is to set up various physical barriers underground to intercept polluted water and prevent pollutants from spreading further. The commonly used mortar curtain method is to pour mortar into the ground through pressure to form a curtain around the polluted water body, thus intercepting the polluted water body. Other physical barrier methods include mud retaining wall, vibrating pile retaining wall, sheet pile retaining wall, block replacement, membrane and synthetic material curtain trap method, etc. Its principle is similar to that of mortar curtain method. Generally speaking, physical shielding method can only be considered as a permanent sealing method when dealing with a small range of highly toxic and refractory pollutants. In most cases, it is only used as a temporary control means in the initial stage of groundwater pollution control.

② passive collection method

This method is to dig a ditch deep enough downstream of the groundwater flow, and arrange a collection system in the ditch to collect pollutants floating on the water surface, such as oil pollutants, or collect all the polluted groundwater for treatment. Passive collection method is generally effective for treating light pollutants (such as oil). ), has been widely used in the United States to control groundwater oil pollution.

1.2 hydrodynamic control method

Hydrodynamic control method is to use well group system to artificially change the hydraulic gradient of groundwater by pumping water or injecting water into aquifer, thus separating polluted water from clean water. According to the different arrangement of well group systems, hydraulic control methods can be divided into upstream watershed method and downstream watershed method. The upstream watershed method is to arrange a row of water injection wells upstream of the polluted water body, and inject fresh water into the aquifer through the water injection wells to form an underground watershed at the water injection wells, thus preventing the upstream clean water body from replenishing the polluted water body downwards; At the same time, a row of pumping wells are arranged downstream to pump out the polluted water for treatment. The downstream watershed rule is to arrange a row of water injection wells downstream of the polluted water body to inject water, form a watershed downstream to prevent the pollution plume from spreading downstream, and arrange a row of pumping wells upstream to extract clean water and send it to the downstream for injection. Similarly, in the initial stage of groundwater pollution control, hydrodynamic control method is generally used as a temporary control method to prevent the spread of pollutants.

1.3 extraction processing method

Extraction treatment is a widely used method at present, which can be selected according to the types of pollutants and treatment costs, and can be roughly divided into three categories:

① Physical methods. Include adsorption, gravity separation, filtration, reverse osmosis, blowing and incineration.

② Chemical methods. Include coagulation and precipitation, redox, ion exchange and neutralization.

③ Biological methods. Include activated sludge method, biofilm method, anaerobic digestion method and soil disposal method. The treatment method after pumping polluted groundwater is the same as that of surface water. It should be pointed out that the establishment of well group system is the key to extract polluted groundwater, and well group system should be able to control the flow of the whole polluted water body. The treated groundwater has two destinations, one is direct utilization and the other is recharge. It is used for recharge because recharge can dilute the polluted water body and scour the aquifer; On the other hand, it can also accelerate the circulating flow of groundwater, thus shortening the remediation time of groundwater.

1.4 in-situ treatment method

In-situ treatment is the focus of groundwater pollution control technology research, which not only saves the treatment cost, but also reduces the surface treatment facilities, minimizes the exposure of pollutants and reduces the disturbance to the environment. This is a promising groundwater pollution control technology. In-situ treatment technology includes physical and chemical treatment and biological treatment.

1.4. 1 physical and chemical treatment method

① Administration method. Inject chemicals into the polluted water body through the well group system, such as injecting neutralizer to neutralize acidic or alkaline leachate, adding oxidant to degrade organic matter or precipitate inorganic compounds, etc.

② Osmotic treatment bed. Osmotic treatment bed is mainly suitable for thin and shallow aquifer, and is generally used for harmless treatment of landfill leachate. The specific method is to dig a ditch downstream of the pollution plume, and the ditch reaches the bedrock or impermeable clay layer at the bottom of the aquifer, and then fill the ditch with a permeable medium that can react with pollutants. After the polluted groundwater flows into the ditch, it reacts with the medium to generate harmless products or sediments, which are removed. Commonly used filling media are: a. limestone, which is used to neutralize acidic groundwater or remove heavy metals; B. Activated carbon is used to remove nonpolar pollutants, carbon tetrachloride, benzene, etc. ; C zeolite and synthetic ion exchange resin are used to remove dissolved heavy metals.

③ Soil modification methods. Using the clay layer in the soil, the clay in the soil is transformed into organic clay by in-situ injection of surfactants and organic modified substances through injection wells. Modified organoclay can effectively adsorb organic pollutants in groundwater.

1.4.2 biological treatment method

The principle of in-situ bioremediation is actually an artificial enhancement of natural biodegradation process. It stimulates the growth of in-situ microorganisms by taking artificial measures, including adding oxygen and nutrients, thus strengthening the natural biodegradation process of pollutants. Usually, the process of in-situ bioremediation is: firstly, the ability of in-situ microorganisms to degrade pollutants is determined through experimental research, then the oxygen demand and nutrient ratio that can promote the growth of microorganisms to the greatest extent are determined, and finally the research results are applied to practice. All kinds of in-situ bioremediation technologies currently in use are based on various strengthening measures, such as strengthening oxygen supply technology, which are roughly as follows:

① Bio-air impact technology. This technology is similar to the air washing technology in the in-situ physicochemical method, which injects air into the bottom of the polluted area, but the difference is that the air supply of biological air washing is smaller, as long as it can stimulate the growth of microorganisms.

② dissolved air water oxygen supply technology. This technology was developed by researchers at Virginia Tech. It can be made into dissolved gas-water composed of 2/3 gas and 1/3 water, and the bubble diameter can be as small as 55 μ m. Injecting this gas-water mixture into the polluted area can greatly improve the oxygen transfer efficiency.

③ Hydrogen peroxide oxygen supply technology. In this technology, hydrogen peroxide is injected into polluted groundwater as an oxygen source, and hydrogen peroxide decomposes to produce oxygen for microbial growth. Hydrogen peroxide is often injected with catalyst, which is used to control the decomposition rate of hydrogen peroxide to make it consistent with the oxygen consumption rate of microorganisms.

Hope to adopt.