What Is Groundwater Remediation?

Groundwater remediation refers to the use of extraction, gas stripping, bioremediation, and infiltration reaction walls to restore contaminated groundwater to its original water quality. Groundwater resources are an important part of water resources. At present, groundwater pollution in our country occurs from time to time. Groundwater pollution control and remediation work is of great significance to the sustainable use of groundwater resources ^[1] .

Groundwater is a valuable freshwater resource for human beings. However, with the continuous development of social industrialization, wastewater discharge, industrial waste residues, agricultural irrigation, landfill leakage, damage to transportation pipelines and storage tanks for petrochemical raw materials may cause groundwater pollution. The original shortage of water resources is more serious, and it poses a serious threat and challenge to human health, food safety, drinking water safety, regional ecological environment, sustainable economic and social development, and even social stability. And social concerns.

Remediation technologies for contaminated groundwater include extraction technology, gas extraction technology, air stripping technology, bioremediation technology, osmotic reaction wall technology, in-situ chemical repair, and so on.

Groundwater Remediation Extraction Technology

The extraction treatment is to use a water pump to extract the groundwater, get a reasonable purification treatment on the ground, and re-inject the treated water into the ground or discharge into the surface water body. This treatment method can efficiently remove pollutants in the extracted water, but it cannot guarantee that all the pollutants in groundwater, especially rock formations, are effectively removed.

Groundwater remediation gas stripping technology

Vacuum pumps and wells are used to induce negative or positive pressure in the polluted area to generate airflow. The pollutants in the adsorbed, dissolved, or free phase are converted to the gas phase, pumped to the surface, and then collected and processed. Typical gas stripping systems include extraction wells, vacuum pumps, humidity separation devices, gas collection devices, gas purification treatment devices, and auxiliary equipment.

The main advantages of gas stripping technology include: can be operated in situ, relatively simple, and has little interference to the surroundings; effective removal of volatile organic compounds; can handle more contaminated groundwater within an acceptable cost range; the system is easy Installation and transfer; Easy to combine with other technologies. In the United States, gas stripping has almost become the "standard" technology for repairing groundwater and soil contaminated by gas stations. Gas stripping technology is suitable for formations with better permeability and homogeneity.

Groundwater remediation air blowoff technology

Air blow-off is the injection of compressed air into a contaminated area under certain pressure conditions, driving out volatile compounds dissolved in groundwater, compounds adsorbed on the surface of soil particles, and compounds blocked in soil voids. Air stripping involves three processes: on-site air stripping; volatilization of volatile organic compounds; aerobic biodegradation of organic compounds. In comparison, blow-off and volatilization proceed faster, while the biodegradation process is slow. In practical applications, air blowoff technology and air stripping technology are usually combined to obtain effects that cannot be achieved by a single technology.

Groundwater remediation technology

Bioremediation is a technology that uses microorganisms to degrade pollutants in groundwater and eventually convert them into inorganic substances. It is divided into in situ enhanced bioremediation and bioreactor methods. In situ enhanced bioremediation is the treatment between the in situ and the residue-sustaining parts without the contaminated soil being stirred. This system mainly combines the extraction groundwater system and the reinjection system (injected air or H ₂ O ₂ , nutrients and domesticated microorganisms) to enhance the biodegradation of organic pollutants. The bioreactor treatment method is an improvement of enhanced bioremediation methods, that is, the process of pumping groundwater to the above-ground part for treatment with the bioreactor. In recent years, the types of bioreactors have been greatly developed. Pump-type bioreactors, continuous circulating upflow bed reactors, and mud bioreactors have already achieved initial results in the repair of contaminated groundwater.

PRB Groundwater Remediation Infiltration Reaction Wall (PRB) Technology

Infiltration reaction wall technology is a rapidly developing in-situ remediation technology suitable for groundwater pollution in recent years. It is also called an active infiltration wall. It is to set a highly permeable active material wall downstream of the pollutant area, so that the pollutants in the pollution plume are trapped and treated, and the groundwater is purified. The United States Environmental Protection Agency (UNEP) defines PRB as a passive reaction zone filled with active materials. When groundwater containing pollutants passes through a pre-designed medium under a natural hydraulic gradient, dissolved organic matter, metals, nuclides and other pollutants Can be degraded, adsorbed, precipitated or removed. The barrier contains reducing agents that degrade volatile organic compounds, metal-fixing (chelating) agents, nutrients needed for microbial growth and reproduction, and oxygen or other substances. Among them, the selection of active materials is the key to good or bad PRB repair effect. Active materials typically require the following characteristics:

Strong ability to adsorb and degrade pollutants and maintain activity for a long time;

Maintain stability under natural groundwater conditions;

wall deformation is small;

Good corrosion resistance;

The material has good stability and good ecological safety, and cannot cause harmful by-products to enter the groundwater.

At present, the active materials researched in the laboratory include: activated carbon, zeolite, and organic clay for physical adsorption; phosphate, limestone, zero-valent iron, and biologically active microbial materials for chemical adsorption. Currently, the most commonly used material is zero-valent iron.

Compared with traditional groundwater treatment technology, PRB technology is a passive system without additional power. In particular, the operation of the processing system is performed underground and does not take up floor space, which is more economical and convenient than the original pumping technology. Once the PRB is installed, except for the need to replace the wall reaction material in some cases, almost no other operating and maintenance costs are required. Practice shows that compared with the traditional groundwater extraction and reprocessing method, the basic operation cost is saved by at least 30%.

Groundwater remediation

Chemical reduction and repair technology is a method that uses chemical reducing agents to reduce and remove pollutants in the polluted environment. It is mostly used for groundwater pollution control. It is newly emerging in developed countries such as Europe and the United States to remove harmful components in polluted water in situ The method mainly repairs pollutants sensitive to reduction, such as chromate, nitrate and some chlorinating reagents, in the groundwater. The reaction zone is usually located below the contaminated soil or in the aquifer layer near the pollution source. According to the different reducing agents used, chemical reduction repair methods can be divided into active metal reduction methods and catalytic reduction methods. The former uses iron, aluminum, zinc and other metal elements as reducing agents, and the latter uses hydrogen, formic acid, and methanol as reducing agents. Generally, a catalyst must be present to make the reaction proceed. Commonly used reducing agents are SO ₂ , H ₂ S gas and zero-valent Fe colloids. Among them, zero-valent Fe colloid is a strong reducing agent, which can reduce nitrate to nitrite, nitrogen or ammonia nitrogen. Zero-valent Fe colloids can remove chloride ions from many chlorinating reagents and convert the transportable oxygen-containing anions and oxygen-containing cations into a difficult-to-migrate state. Zero-valent Fe can be injected through a well, or it can be placed on the route through which pollutants flow, or micron or even nano-sized zero-valent Fe colloids can be injected directly into the natural aquifer.

Groundwater Remediation Electrokinetic Remediation Technology

Electrochemical dynamic repair technology is a new green repair technology that uses the principle of electrodynamics to repair the soil and groundwater environment. It can be used to remove some organic pollutants and heavy metal ions. It has environmental compatibility, multifunctional applicability, and high selection. It is suitable for automatic control and low running cost. During the electric repair process, the metal and charged ions undergo directional migration under the action of an electric field, and then undergo centralized processing in a set processing area; at the same time, an electrolytic reaction occurs on the electrode surface, and the anode electrolysis generates hydrogen and hydroxide ions. Cathodic electrolysis produces hydrogen ions and oxygen, while most non-polar organic pollutants are removed by electrodialysis. In recent years, electrochemical dynamic repair technology has been increasingly combined with other technologies or auxiliary materials, such as ultrasound technology ^[2] .