Expert: underground sewage is the main culprit of groundwater pollution in China

Recently, the government of many places has launched a related investigation on the underground pollution from the network explosion. Whether the evidence of underground pollution of enterprises is solid or not, it is an indisputable fact that the groundwater pollution in China is serious. On this issue, the reporter of environment and life interviewed Wang Hao, an expert in hydrologic and water resources and academician of Chinese Academy of engineering.

Academician Wang Hao

60% of groundwater pollution in China is serious

Environment and life: you are an authoritative expert in groundwater research. Can you introduce the current situation of groundwater in China?

Wang Hao: more than 1.5 billion people around the world rely mainly on groundwater as drinking water. The groundwater resources in China account for 1/3 of the total water resources, which maintains 70% of the population drinking, 40% of farmland irrigation and 38% of industrial production.

Because of the discharge of industrial wastewater and domestic sewage, the use of excessive fertilizer and pesticide, the leaching of garbage dump and the leakage of underground oil tank, groundwater is suffering more and more serious pollution. Experts from China Geological Survey Bureau pointed out that 90% of groundwater in China suffered from different degrees of pollution and 64% of the pollution was serious.

The groundwater pollution is serious in the shallow groundwater in the plain area of 197000 square kilometers, which is evaluated by the national water resources survey, and in Taihu Lake, Liaohe, Haihe and Huaihe River.

Fertilizer and pesticide lead to the "three nitrogen" (i.e. ammonia nitrogen, nitrate, nitrite) in underground water exceeding the standard. The nitrate nitrogen in groundwater is found to exceed the standard in every province and province of the Yangtze River Delta.

There are still organic pollution in groundwater pollution. The domestic relevant departments have investigated and evaluated the groundwater pollution, and generally detected micro organic substances, and carcinogenic, teratogenic and mutagenic "three causing" substances have been detected to different degrees. These substances are not easily degraded by microorganisms in water, but are easily absorbed by organisms, and returned to human table through food chain. More than 100 pollutants have been detected in groundwater in Beijing, Tianjin and Hebei, many of which are "three causes".

In recent years, because of the large amount of groundwater over exploitation, a large area of groundwater funnel has been formed underground, so it is more important to pour the ground sewage into the groundwater. According to the official report, the groundwater in North China has exceeded 120billion cubic meters, which is equivalent to 200 Baiyangdian water. The continuous decline of groundwater level has formed a huge groundwater falling funnel area in the North China Plain. In these areas, not only will the shallow groundwater be polluted, but also with the continuous flow of shallow sewage to the deep, the deep groundwater is also easily polluted.

In short, groundwater pollution in China has been developing from point to surface, from east to west, from city to countryside, from local to regional.

The human body in the agricultural industry is the victim

Environment and life: what harm will such groundwater pollution cause?

Wang Hao: first, it directly affects the quality of drinking water. The hardness of groundwater is too high after being polluted. As a drinking water source, it is not only bitter and difficult to drink, but also may cause gastrointestinal dysfunction, and symptoms such as vomiting, diarrhea and flatulence. When groundwater is polluted, it will often cause changes of three nitrogen content in water. If the content of three nitrogen in water is too high, it will cause harm to human body (especially infants), and cause acute poisoning of nitrate. Trian can be transformed into nitrosamine, a carcinogen under specific conditions in human body, leading to cancer and even death. In addition, if the groundwater source is polluted by serious organic pollution or heavy metal pollution, the "three causes" substances produced in the water will cause greater harm to human health. In recent years, the "cancer villages" in Taihu and Chaohu have been gradually appearing, which has aroused widespread concern about the relationship between water pollution and the incidence rate of cancer.

Secondly, in the field of food safety, the impact of water pollution on agricultural products quality is also one of the hot topics.

Moreover, in China, especially in the north, groundwater accounts for a large proportion of industrial production water, and the pollution of groundwater will seriously affect industrial production. The increase of groundwater hardness will make the boiler and the pipe wall scale, which will not only waste fuel, but also directly affect the boiler life and even cause explosion; in the textile printing and dyeing industry, washing products with high hardness water slurry will not only consume a lot of detergent, but also produce inferior products or waste products; in addition, high hardness groundwater will also be used for many lines such as chemical industry, pharmaceutical industry, wine making, power generation and papermaking The industry causes harm. This forces some industries to soften and purify hard water, which increases production costs.

After the pollutants are discharged into rivers and lakes, in addition to the harm to natural fish and aquatic organisms in the water, excessive nitrate will acidize and corrode the water, affect the normal growth of water organisms and even cause extinction of some aquatic organisms.

Improper treatment of sewage and waste liquid in China

Environment and life: what role does underground sewage play in the current situation of groundwater pollution in China?

Wang Hao: the government has issued corresponding policies for the enterprise sewage discharge and sewage treatment standards to reduce the negative impact of industrial development on the environment to a small extent.

However, some illegal enterprises have discharged industrial wastewater containing highly toxic carcinogens (such as non degradable arsenic and mercury and other heavy metals or PAHs) into the ground. In addition to digging seepage pits and leaking wells, in order to avoid investigation and treatment, some pollution enterprises will directly inject a large amount of sewage into the ground with high-pressure pumps, and some enterprises in the South even discharge sewage into underground karst caves.

For example, the cadmium pollution in Guangxi, which was in full swing in February 2012, was caused by the discharge of cadmium pollutants by two enterprises through the cave.

The situation of sewage discharge through seepage pit and seepage well is common. This method provides low cost and easy operation conditions for surface water infiltration. These sewage often penetrate into the groundwater aquifer through sand gravel and rock with good permeability on the upper layer of groundwater, which causes groundwater pollution.

The common underground sewage discharge method in China is to use shallow well and water layer to discharge the untreated sewage into the groundwater through 300-500 meters deep well, which is usually the place where the groundwater can be drunk. Because of the improper treatment of sewage and waste water and the immature sewage technology in China, underground sewage has undoubtedly become the main culprit of groundwater pollution in China.

Source of data for an underground well in Eastern Fort Worth, Texas / EPA website

90% of the hazardous waste liquid is injected into the ground

Environment and life: it is understood that underground sewage is also used internationally. From the perspective of science and technology, what conditions do underground sewage need to have? Can the relevant management system be used for reference in China?

Wang Hao: from the international perspective, there are three types of underground sewage, the first two are the commonly used seepage well discharge and shallow well water layer discharge in China,

The third method, high pressure deep well discharge, also known as "deep well perfusion", has been adopted by many countries and proved to be a mature and leading treatment method for wastewater and waste liquid. The United States has started early in this regard. Since the 1930s, American oil companies have used this technology to treat the waste liquid from oil and natural gas production. More than 2.84 billion cubic meters of waste liquid are injected into the ground every year, and the number of pour wells has also exceeded 650000. About 89% of the hazardous industrial waste liquid that is difficult to be treated in the United States is disposed by deep well perfusion.

The advantage of deep well grouting is that the liquid is stored in deep geological layer, which can avoid pollutants entering the biosphere circulation system, reduce the environmental pressure on the atmosphere, water body and shallow stratum, and the safety factor is far higher than other waste disposal technologies.

However, as a safe underground sewage discharge method, deep well grouting requires high requirements for geological conditions, depth of excavation and safety protection of deep wells, and it is difficult to withstand the long-term test of crustal movement. First, in the location of the cast-in-place wells, it is necessary to have simple geological structure, no complex faults and folds, but also stable formation structure, less seismic activity or small impact of earthquake damage, and ensure that rock minerals can be compatible with sewage, and there are not many places to meet these conditions at the same time. Such countries as Japan, which are located in the joint of plates, are not suitable for deep well grouting, but There are many suitable places in China.

For this new type of underground sewage discharge, China is basically feasible in technology, but to achieve safe underground sewage discharge, it is necessary to establish corresponding implementation standards and regulatory measures.