Refractory organic pollutants

The efficient use of current supplied during the oxidation of bio-refractory organic pollutants by electrochemical treatment imposes to adopt an electrocatalytic material such as boron-doped diamond (BDD) that produces hydroxyl radicals. At the end of electrochemical treatment, a low transfer of pollutants occurs toward the hydroxyl radicals due to the reduced concentration of pollutants in the bulk, and this condition reduces the degree of utilization of BDD anodes. Ex-cell-mediated oxidation (via persulfate) of organic pollutants can be applied after electrochemical treatment, and its effects are a higher utilization of BDD anodes and an efficient removal of pollutants at the end of treatment, when their concentrations achieve low values. This oxidation consists of various steps after the electrochemical production of a precursor of active oxidants, it is initially mixed with the wastewater and successively activated by thermal or ultraviolet energy in order to generate active oxidants that efficiently oxidize the pollutants. 

Over the past decade, water pollution control has progressed from an art to a science. Increased emphasis has been placed on the removal of secondary pollutants, such as nutrients and refractory organics, and on water reuse for industrial and agricultural purposes. This in turn has generated both fundamental and appHed research, which has improved both the design and operation of wastewater treatment faciUties. 

Activated carbon has high specific surface area with respect to its volume, and thus has high adsorption capacity. Activated carbon adsorption is considered to be one of the most versatile treatment technologies and can remove classical pollutants such as COD, TOC, BOD, and nitrogen, as well as toxic pollutants such as phenol, refractory organic compounds, VOCs, and soluble heavy metals.38 Activated alumina and peat have also demonstrated similar abilities. 

Surfactant concentrations in polluted natural water bodies interfere with the self-purification process in several ways. First, certain detergents such as ABS are refractory or difficult to biodegrade and even toxic or inhibitory to microorganisms, and influence the BOD exhibited by organic pollution in surface waters. On the other hand, readily biodegradable detergents could impose an extreme short-term burden on the self-purification capacity of a water course, possibly introducing anaerobic conditions. 

Pitt, W. W. Jolley, R. L. Katz, S. Automated Analysis of Individual Refractory Organics in Polluted Water SERL. U.S. Environmental Protection Agency. U.S. Government Printing Office Washington, DC, 1974 EPA 660/2-74-076. 

Full-scale ozonation systems have been used to treat waste waters, such as landfill leachates, as well as waste waters from the textile, pharmaceutical and chemical industries (FTGAWA, 1997 Bohme, 1999). The main pollutants associated with these waters are refractory organics, which can be characterized as (Masten and Davies, 1994) ... 

Temperature will affect the degradation rate of different organic pollutants. Weir et al. (1987) reported that benzene and hydrogen peroxide are insensitive to temperature because photochemically induced reactions often have low activation energies. Koubek (1975) stated that temperature has little effect on the oxidation of refractory organics however, Sundstrom et al. (1986) observed that the decomposition rates of some halogenated aliphatics increased with temperature. 

Uses of high-resolution analytical systems in other types of research can also be envisioned. For example, the molecular pollutants, especially the refractory organic compounds, in the effluents of sanitary sewage plants have not been well established. Preliminary results from analysis of primary and secondary effluents from conventional sanitary sewage plants show that up to 80 UV-absorbing constituents can be monitored by the UV-analyzer (Fig. 21). Obviously, such analytical systems would be useful in monitoring the effectiveness of various processing steps. 

Considering some practical aspects, it has to be remarked that the EB is best used as a pre-treatment step to integrate a conventional bio-, and physico-chemical plant. Under such conditions a dose of 2 kGy allows the destruction of most organic pollutants with unmatched success even in case of bio-refractory compounds. Simultaneously, disinfection of wastewater is achieved. When only disinfection is required, the dose may be reduced to... 

Selective extraction was used to operationally determine the quantitative and qualitative distributions of PCB 8 and saturated hydrocarbons among free lipid (FL), humic acid (HA), and humin (HU) fractions of four contaminated estuarine sediments. In all samples, over 90% of the total sedimentary PCB s and hydrocarbons were extracted with FL fractions. Bound (HA and HD) and free assemblages of these compounds may have derived from different sources. Two polar, chlorinated pollutants also detected In this study, hexachlorophene (HCP) and pentachlorophenol (PCP), were proportionately more concentrated In bound fractions than the non-polar compounds HCP was detected only In HA fractions and was probably chemically hound to refractory organic matter. Selective extraction Is a promising technique for Investigating strongly bound polar pollutants, such as HCP, which apparently are not recovered by conventional solvent extraction. 

Polar pollutants, such as chlorinated phenols, can occur largely as chemically bound components of refractory organic matter. 

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