Remediation, chemical procedures

For the sake of environment remediation, the procedures that decrease pollutant emissions or those that enable the elimination of pollutants already discharged into the environment are still of the highest interest. For that purposes, physical (filtration, adsorption), chemical (oxidation, catalytic conversions, ozonization in the presence of a catalyst or without one) or biological methods are available. The choice of particular method depends on the nature and the concentration of pollutant, and on its physical state. AU mentioned processes are permanently objects of further development. 

The practice of free-phase NAPL recovery, soil vapor extraction, and hydraulic containment at remediation sites almost always generates some volume of water contaminated with dissolved fractions. Depending on the size of the facility and the scale of the recovery and restoration project, the amount of groundwater coproduced can possibly exceed 1000 gal/min. Handling of these volumes of contaminated water can be very expensive if treatment is required prior to disposal or reinjection. Treatment of water derived from sites contaminated by other organic chemicals will involve adaptations of these procedures to the specific situation. 

Certain basic chemical reactions can sometimes be used to remediate organic chemical contaminants in the unsaturated zone. Introduction of reacting chemicals to alter the Eh (oxidation state/electron availability), the pH (hydrogen ion availability), or a contaminant to an immobile state occasionally presents a viable remedial option. This procedure can be rather expensive in dealing with organic chemicals, and typically is only used in specific situations. 

What is the criterion that determines whether a decontamination procedure was effective It is not the absolute absence of any chemical contaminants in the equipment blank. Important for the project are only the contaminants of concern and their concentrations. For site investigations, when no information is available on existing pollutants, it may be important that no contaminants of concern are present in equipment blank samples above the laboratory PQLs. On the other hand, for site remediation projects, the presence of contaminants of concern in equipment blank samples may be acceptable, if these concentrations are only a fraction of the action levels. The decision to decontaminate equipment and the selection of the acceptability criteria for equipment blanks are made in the DQO process based on the intended use of the data. 

Speciation science seeks to characterise the various forms in which PTMs occur or, at least, the main metal pools present in soil. This chapter provides a review of the single and sequential chemical extraction procedures that have been more widely applied to determine the plant and the human bioavailability of PTMs from contaminated soil and their presumed geochemical forms. Examples of complementary use of chemical and instrumental techniques and applications of PTMs speciation for risk and remediation assessment are illustrated. 

Environmental samples often contain swathes of different chemicals in mixtures. An important question for risk assessment, regulation, and remediation is to establish whether the majority of chemicals contribute to the overall mixture effect, or whether joint toxicity can be traced back to a few substances. This issue has been the topic of considerable research efforts in the field of ecotoxicology. Its resolution has required whole mixture approaches, where environmental samples were subjected to extraction procedures, followed by fractionation and chemical analysis (toxicity identification evaluation (TIE), bioassay-directed fractionations). There are interesting examples in the literature where such approaches were combined with component-based mixture assessments with the aim of identifying chemicals that contribute to mixture effects (see Chapter 4). 

Mortar joints between the brick will recede due to wear and adverse chemical and thermal effects. This is normally a relatively slow, progressive phenomenon. The condition is remedied by raking any loose or deteriorated mortar from the joint and repointing with furan mortar. This is a maintenance procedure which will be done many times during the lining life. 

A valuable review (Hamby 1996) has been given that summarizes chemical and physical treatments of soils, and contaminated ground and surface waters. Some procedures for chemical destruction of selected xenobiotics have been given in Chapter 4, Section 4.1.1 and 4.1.3, comments on sequential microbial and chemical reactions in Chapter 4, Section 4.2.3, and an example of combined biological and chemical remediation is given in Section 8.2.1. 

Soil and groundwater contaminated with hazardous materials create special challenges for chemists and chemical engineers. Determination of the composition and mobility of the contaminants, and the risks they pose to humans and the environment, often requires specialized analytical techniques. In some cases the hazardous nature of the contaminants may be reduced by natural attenuation due to chemical or biological activity in the soil, and a better understanding of the mechanism of attenuation can help to predict or accelerate the rate of hazard reduction. When remediation of the site is deemed necessary, cleanup or containment procedures must be tailored to the specific characteristics of the site. 

Materials with acidic sites have to replace strong acids in the hydrolysis of MTBE and other fuel oxygenates, as using acids would cause strongly acidic effluents and corrosion. Catalytic materials used in MTBE remediation need to have the following properties insolubility in water and therefore easy separation of the catalyst from the treated water, chemical stabiUty, and feasibility for regeneration. Possible appHcations of these materials include PRBs as well as packed-bed reactors in pump-and-treat procedures. 

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