环境保护论文代写:After effects of man-made chemicals
2.4 Effects of Soil Contamination
Soil contamination can cause severe health problems for human beings, other animals as well as environment. Some of the effects of the soil contamination on environment as well as human beings are listed below.
- Reduced soil fertility & nitrogen fixation.
- Deposition of silt in tanks and reservoirs
- Reduced crop yield and increased erosion.
- Ecological imbalance & reduced vegetation
- Release of pollutant gases and radioactive rays causing health risks.
- Entrance of dangerous chemicals underground water.
- Clogging of drains and Inundation of areas.
- Release of gases & Foul smell.
- Waste management problems.
2.5 Health Risks
The major issue is that there are lots of sensitive land uses where people are in direct contact with soils like parks, residences, schools and playgrounds. Other contact mechanisms include inhalation of soil contaminants which have been vaporized or contamination of drinking water. There is a very large set of health risks from vulnerability to soil contamination depending on type ofpollutant, pathway of attack and vulnerability of the exposed population. Following are the risks:
- Contaminated soil can be discharged to municipal waterways. Thus, it accumulates in water used by human being for various purposes.
- Hazardous substances which are eluted from contaminated soil may get ingested through groundwater.
- There can be direct ingestion of contaminated soil including soil particulate.
- Hazardous substances which are emitted by contaminated soil to atmosphere may get inhaled and cause serious health issues.
- Hazardous substances on crops & the livestock on contaminated land can get accumulated and ingested by human beings.
2.6 Control Measures for Soil Contamination
Due to increased soil pollution and rising adverse effects on the environment and risk in safety, control measures are required for checking this problem. Following are the few:
- Recycling of plastic waste & purification of wastewater.
- Waste landfill control & ban on deforestation.
- Industries provided with adequate prevention and protection measures.
- Newer sewer networks as far as possible.
- Liquid manure storage basin provided as far as possible.
3. REMEDIAL SOULTIONS
3.1 Soil Remediation
Soilremediationis the collective term for various strategies that are used to purify and regeneratesoil. It is part of a wider effort i.e. environmental remediation, which also includes efforts to purify the air and the damage done to the ecological balance of the planet.
3.2 Soil Remediation Technologies
There are two distinct classes of soil remediation: in-situ, or on-site, and ex-situ, or off- site. On-site cleanup measures are generally preferred as they are cheaper. Ex-situ remediation has the added incentive of taking the mass of contaminants off-site before they can spread further.More caustic chemicals can be used & acid leaching can be done ex-situ without any harm to the environment.
In-situ situations are limited as only the topside of the soil is accessible. The environmental limitations force in-situ remediation to fall into three categories: bioremediation, washing & venting.
Off-site facilities have the opulence of complete control over the cleaning chemical measures. Isolation of soil is easily possible in a controlled environment, without weather problems.
3.3 IMPORTANT REMEDIAL SOLUTIONS
3.3.1 Solidification and Stabilization
Stabilization/Solidificationis a remediation technology which relies on the reaction between a binder and soil to prevent the mobility of contaminants.
Stabilization – requires the addition of reagents to a contaminated material (e.g. soil or sludge) to obtain more chemically stable constituents.
Solidification – involves the addition of reagents to a contaminated material to give physical stability and to contain the contaminants in a solid product and abridge access by external agents (e.g. air, rainfall).
However, the uptake of S/S technologies has been relatively modest, and a number of barriers have been identified including:
- The relatively low cost and widespread use of disposal to landfill;
- Uncertainty over the durability and rate of contaminant release from S/S-treated material;
- Experiences of past poor practice in the application of cement stabilization processes used in waste disposal in the 1980s and 1990s.
- Residual liability associated with immobilized contaminants remaining on-site, rather than their removal or destruction.
3.3.2 Excavation or Dredging
Excavation processes can be very simple such as hauling the contaminated soil and maintain a regulated landfill. The process of aeration is applicable to Volatile Organic Compounds (VOCs). Dredging of bay mud or other silty clays containing contaminant can be carried out in case of contamination of a river soil or bay bottom.
Nowadays, because of the advance processes like “bio-augmentation” and “bio-stimulation” of the excavated material, it is possible to remediate semi-volatile compounds (SVOCs) onsite.
3.3.3 In-Situ Oxidation
This technology has become very popular and widely accepted due to its application for a wide range of soil and groundwater contaminants. Various types of oxidants such as hydrogen peroxide, potassium permanganate, ozone gas are injected in the process of chemical oxidation. Oxygen gas can also be used in the process. But also, the injected gases can cause the contamination to spread faster than normal.
3.3.4 Pump and treat
Pump and treat involves pumping out contaminated groundwater with the use of a submersible or vacuum pump, and allowing the extracted groundwater to be purified by slowly proceeding through a series of vessels that contain materials designed to adsorb the contaminants from the groundwater. For petroleum-contaminated sites this material is usually activated carbon in granular form.
Depending on geology and soil type, pump and treat may be a good method to quickly reduce high concentrations of pollutants. It is more difficult to reach sufficiently low concentrations to satisfy remediation standards, due to the equilibrium of absorption (chemistry)/desorption processes in the soil.
3.3.5 Soil Vapor Extraction
Soil vapor extraction (SVE) is an in situ unsaturated zone soil remediation technology in which a vacuum is applied to the soil to induce the controlled flow of air and remove volatile and some semi volatile contaminants from the soil. The gas leaving the soil may be treated to recover or destroy the contaminants, depending on local and state air discharge regulations
Granular activates carbon is used as a filter for water. This activated carbon is positively charged and thus removes the negative ions such as ozone, chlorine, fluorides. This carbon must be replaced periodically. It is not that much effective in removing heavy metals.