Contaminated Land (Essay Sample)

Contaminated land
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 The use of permeable reactive barriers for the remediation of dissolved phase inorganic pollutants in groundwater plumes
Permeable reactive barrier are one of the latest technologies that is being used in remediation of polluted groundwater. It is a technology that utilizes the permeable zone in cleaning up contaminated groundwater plume through transformation of pollutants into less harmful products.in this technology, the flow of water is intercepted by reactive materials that exchange contaminants with the flow of water. The PRBS technology can be used as replaceable units, semi-permanent or permanent units. During this process various pollutants are degraded, precipitated, exchanged and sorbed in the reactive layer. The materials may be both organic and inorganic compounds (Gavaskar, 1999).
There are various inorganic compounds which can be treated in using the prb. Some of these inorganic compounds include, cr, TCE, Ni, Pb, cd, as, Zn, Cu. in order for the prb process to be effective the choice of reactive materials is important. The selection of these reactive materials is controlled by several factors which include reactivity, stability, availability, cost and environmental compatibility of the materials. The concentration of inorganic compounds such as ca, mg and Na, usually determine the formation and deposition of the precipices formed on the surface of the reactive medium. Therefore the performances of reactive materials are also affected by these concentrations. Any changes in the hydraulic conductivity of the reactive barriers may affect the workability of this process. The clogging of the iron surface alters the flow of the plume in the underground wastewater flow. This may dip further down to the aquifer. In prbs, geochemical models may be used to determine the possible mineral phases that will be formed under certain conditions. The parameter for longevity of the process is the amount of dissolved oxygen .it is for this that the pretreatment zones are constructed to prevent dissolved oxygen from entering the zero valet zones.
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One of the most common reactive material used PRB is the granular zero valet iron. The zero-valet iron is used as amended Fe 2+ or plated with Cu, Ni and Pd. Iron is mainly used due to its ability to degrade several inorganic compounds such as the chromium nickel, lead sulfate, phosphate and arsenic. The rate of degradation of depends on the specific surface are of iron. The cheapest metallic media which can be used as a reactive material is the granular iron.
In many field applications, studies have shown that inorganic constituents are a barrier themselves to degradation. This leads to mineral precipitates as CaCO3, FeCO 3 and MgCO3 to be formed.
HCO3 CO3 +H+
This is because of the increase in pH. However, the existence of the species does not affect the reactivity of the iron wall. The reactions of bimetallic systems such as iron and copper or iron and nickel have accelerated degradation rates compared to other metals. Some of the common reactions of inorganic compounds in prbs include:
According to Blowes et al (1995) the Reduction of toxic Cr (for example Cro4) to Cr and other precipitates can be summarized as follows
CrO4 + Fe + 8H -Fe + Cr+4 H2O
(1-x) fFe3+ + (x) Cr 3+2H2 O – FeCrOOH+ 3H
Fe+ CrO4 + 4 H 2O – (Fe, Cr) (OH) 3 + 5OH
The iron bearing oxhydoxides and iron bearing aluminosilicates minerals may also conduct the reduction and precipitation of cr. However, the reaction rate will be greater when FE is used. During the removal of cr, PH increases significantly from 6.5 to around 9. The chromium concentration is reduced to less than 0.01mg/l.
BOF -oxide is one of the materials that are abundantly present in the waste products. It is fine and contains oxidized materials such as, iron, calcium, magnesium and arsenic. BOF I is used in the remediation of arsenic .Arsenic is one of the inorganic compounds that are treated in this technology.it is found in ground water as 3+. The compound is mainly mobile and is highly toxic. The toxicity of these inorganic compounds arises from the redox reaction that take place in the compound. In the reactions the ions are hydrolyzed forming h3AsO3 an H3AsO4. The redox conditions that prevail at the surface of these reactions are different from those shown in the effluent quality. The initial concentration of arsenic is reduced while the PH maintained at the same levels.
The reduction and precipitation of selenium
HSeO4+ 3Fe + 7H - 3Fe + Se + 4H2O
The reaction showed above shows how selenium is removed from wastes.
The reductive precipitation of U
Fe + UO2 - Fe +UO2
The removal of UO2, MoO4, TcO4 and CrO4 using iron occurs with the following priorities UO2, MoO4, TcO4 and cro4. In this removal process, the UO2 is adsorbed on the newly formed iron oxide with both reduction and precipitation occurs concurrently. The other electro active metals that are treatable during the reaction process are hg and cu (Joo & Ching, 2000).
The removal of peat and iron will also lead to reductive of precipitation of other inorganic elements such as uranium. Through mobilization of carbonate solutions, the reduced species could also be re-oxidized if there are favorable conditions. Reduction of NO3- to NH4
Gianluca (2004) explains that in the permeable reactive barrier, studies have shown that NO3 is initially reduced to NO2 and then to NH4. This process undergoes a kinetic evaluation that is very high. 4Fe +NO3+ 10H+ - 4Fe + NH4 + 3H2O(p.42)
Alumina is chemically produced as one of the porous dehydrated aluminum components. It has a high surface retention capacity for inorganic cation and anions such as, as, PO4and Sr. This is due to its surface adsorption capacity. Alumina absorbs almost 99 % of Sr. In conclusion, PRB technologies will continue being used for treatment of groundwater remediation. The technology offers a simple and effective way of treating waste water in a cost effective manner. This technology is also easy to use for a variety of landscapes.
Field chemical analysis techniques for contaminated land investigations
There are various chemical analysis techniques which can be used for contaminated land investigations. The choice and use of every technique depends on the type of contamination, the level of contamination and nature of the ground. One of the most common technique for testing ground water and soil is the use of colometric test kits. These kits utilize micro titrations techniques to find the level of ground water contamination or sill contamination. The titrant is added drop wise to a small amount of soli collected in the field that contains an indicator. The colometric test kits utilize colometric reactions whereby color is measured against a photometer.
Colometric test kits have an advantage over other forms due to their speed of analysis and their portability. They are also low in the cost of purchase. Several contaminants can be analyzed in using the same test kits. In colometric test kits techniques, paper strips are used. These test strips are dipped into the sample to be analyzed. The color formed on the test strip is then analyzed is then compared to chart accompanying the test kit. Some of the contaminants that can be analyzed by the colometric test kit include arsenic, copper, iron and ammonia. Some of the colometric test kits can analyze as many as 20 compounds in one test. The kits are portable. Test kits have the ability to analyze VOHS in the fields. They facilitate ground water plume chasing activities.
During remediation, the concentration of iron in ground water or soils can be accurately monitored using test kits .test kits are depended on the colometric or turbid metric reactions in the soils or ground water. The color or turbidity change of the ground water is the response for the presence of any contaminate in the soil or ground water. The operation involves sealed glass tubes that are filled with the sample in from the field. If the target material is present in the soil or ground water, the color will change. Reagent kits are designed for both analyses of soil and water samples in the field. These kits are small and require operation of a single person. Some of the reagent kits use chemical reactions specific to certain materials in the soil to produce color in the visible spectrum. Therefore, any changes in color indicate particular presence of the material. The intensity of the color shows the concentration of the materials in the sample (Thompson & Nathanial, 2003).


Another field testing technique is the use of gas chromatography combined with mass spectrometry. This provides an analytical tool that is definite of various samples that are present in the sample. Filed portable chromatography equipment is used in areas that require quick identification of the sample materials and a high degree of accuracy. The gas chromatography test kits are designed to be used in the field and are portable. They are easy to use and do not require complex skills while operating the machines. However while using this technique it is advisable that one should take a lot much care while handling the instruments and the analytes.
In samples that have oils as contaminants for soil or ground water some of the techniques used include the colometric analyzers. In this technique, the sample is placed dried and cleaned using a syringe that is mounted on the drying column of the testing kit. The inorganic chloride that is dried is filtered and analyzed using a two point calibration measurement. The hanby filed test kit can also be used for testing this sample. This is a test kit test for aromatic compounds found in the petroleum oils. The test kit is based on the Fridell –crafts alkylation process that leads to ...