This study presents the experimental results obtained during long-term operation of two biofilters treating two alcohols: methanol and ethanol. The biofilters used for this purpose were previously packed with a compost material made from tobacco processing residues. The alcohols concentrations tested lay between 0.40 and 3.20 g/m 3 for methanol, and 0.55 and 5.05 g/m 3 for ethanol. The empty bed residence time in each biofilter was 60 s. Biofilter inlet loads of less than 190 and 300 g/m 3 /h for the methanol and ethanol additions respectively, were thereafter evaluated. In addition, the concentrations of nutrient nitrogen were also varied, from 0.1 to 2.0 g-N/l and from 0.3 to 11.3 g-N/l for the ethanol and the methanol, respectively. The results thus obtained have made it possible to select the optimal nitrogen concentrations which, for the cases examined, turn out to be 0.3 g-N/l and between 2 and 3.8 g-N/l for the ethanol and methanol substrates, respectively. The maximum elimination capacities obtained in this study were 82 and 150 g/m 3 /h, respectively for the methanol and ethanol cases. It was therefore concluded that, for a readily biodegradable compound such as ethanol, the nitrogen requirement is substantially lower than that needed for the methanol degradation, the latter appearing to be more difficult to degrade biologically under similar operating conditions. The production rate of the co-product carbon dioxide during methanol and ethanol biofiltration was also investigated. Also, a good correlation was found to exist between the temperature and the conversion achieved in the biofilter.

Volatile organic compounds (VOCs) are pollutants that are responsible for the formation of the tropospheric ozone, one of the precursors of smog. VOCs are emitted by various industries including chemical plants, pulp and paper mills, pharmaceuticals, cosmetics, electronics and agri-food industries. Some VOCs cause odor pollution while many of them are harmful to environment and human or animal health. For the removal of VOCs, biofiltration, a biological process, has proved to be reliable when properly operated. This process has therefore been widely applied in Europe and North America. The main advantages associated with the use of biofiltration are related to its set-up, maintenance, and operating costs which are usually lower than those related to other VOCs control technologies and because it is less harmful for the environment than conventional processes like incineration. In the present paper, the main parameters (type, moisture, pH, and temperature of filter bed, microbial population, nutrients concentrations, and VOCs' inlet load) to be controlled during the biofiltration are identified and described in detail. The main phenomena involved in biofiltration are also discussed. For improving the efficiency of VOC control biotechnology, new techniques are now proposed that include the use of membranes, biphasic reactors, UV photolysis, and many others.

Soil contaminated with persistent pesticides, such as DDT, poses a serious risk to humans and to wildlife. A surfactant-aided soil-washing technique was studied as an alternative method for remediation of DDT-contaminated soil. An ex situ soil washing method was investigated using nonionic and anionic surfactants due to the clayey structure of the contaminated soil. A mixture of 1 percent nonionic surfactant (Brij 35) and 1 percent anionic surfactant (SDBS) removed more than 50 percent of DDT from soil in a flow-through system, whereas individual surfactants or other combinations of the surfactants had a lower removal efficiency. The soil-washing technique was improved using a mixing system. The mixture of surfactants was optimized in the mixing system, and the combination of 2 percent Brij 35 and 0.1 percent SDBS was found to be optimum, removing 70 to 80 percent of DDT. Prewashing of the soil with tap water decreased the adsorption of surfactants INTRODUCTIONIn many locations in Canada and elsewhere around the world, soil contamination represents a serious risk to both humans and the environment (Harris et al., 2000). Contamination with organochlorines is considered to be of particular importance since organochlorines are persistent substances that may represent a continuing source of contamination for decades. Among the organochlorines, dichloro-diphenyl-trichloroethane (DDT) is one of the most notorious synthetic pesticides since it continues in use to this day, although use of DDT has been widely restricted in application since 1972 (Hitch & Day, 1992;Martijn et al., 1993;Turusov et al., 2002). Concerns with worldwide spraying of DDT eventually led to use of DDT being banned in most countries in 1972. Also, DDT was subsequently banned for agricultural use worldwide, but its limited use in disease vector control continues to this day in some parts of the world (Vieira et al., 2001).DDT and its metabolites-breakdown or by-products of DDT, including 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD) and 1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene (DDE)-are extremely persistent in the environment and may accumulate in the food chain (Veith et al., 1979) 119 Remediation of DDT-Contaminated Soil Using Optimized Mixtures of Surfactants and a Mixing Systemhealth, and they are known carcinogens (Kashyap et al., 1977). As a consequence, lands contaminated with DDT are limited in their development potential (e.g., change of land use from agricultural to residential may be disallowed). It is highly likely, for example, that significant expanses of agricultural land continue to have levels of DDT and its metabolites that are elevated in concentration, although only limited testing has been carried out to date. Environmental agencies, such as the U.S. Environmental Protection Agency and the Ontario Ministry of the Environment (MOE), have established standards and guidelines, exceedance of which precludes specific land use. Hence, due to the long half-life of DDT and its metabolites in natural environmental conditions, co...

Soil contamination with persistent pesticides such as dichloro-diphenyl-trichloroethane (DDT) is a major issue at many brownfield sites. A technology that can be used to treat DDT-contaminated soil using surfactants is to enhance the migration of the contaminants from the soil phase to the liquid phase, followed by the dechlorinating of the mobilized DDT in the liquid phase using zerovalent iron (ZVI). The DDT degradation using ZVI occurs under anaerobic conditions via reductive reactions. The effect of the iron concentration on the dechlorination rate is assessed in the range of 1 to 40 percent (weight to volume) for remediation of a DDT-contaminated site in Ontario, Canada. The optimum percentage of iron is found to be 20 percent at which the dechlorination rates of DDT and 1,1-dichloro-2,2-bis( p-chlorophenyl)ethane (DDD) were 4.5 and 0.6 mg/L/day, respectively. While mixing of the reaction solution is shown to be important in providing the iron surface available for the dechlorination reaction throughout the reaction solution, there is no significant difference between batch and fed-batch mode of adding iron to the dechlorination process. Low pH values (pH INTRODUCTIONSoil contamination by organic compounds is a widespread and serious problem throughout the world and represents risks to both humans and the environment. The exposure problems become even more important in the situation of organochlorines since the organochlorines are persistent substances and, thus, be considered a continuing source of contamination for decades (Chapman et al., 1981; Martjin et al., 1993;Vieira et al., 2001). Among the organochlorines, dichloro-diphenyl-trichloroethane (DDT) is one of the most notorious synthetic pesticides and continues to be widespread (Turusov et al., 2002), although use of DDT has been widely restricted in application since 1972 (Hitch & Day, 1992). Concerns with indiscriminate spraying of DDT eventually led to the banning of most uses of DDT in Canada and the United States in 1972. Also, DDT was subsequently banned for agricultural use worldwide, but its limited use in disease vector control continues in parts of the world (Kapp, 2004). In 2001, 91 countries signed the Stockholm convention on persistent organic pollutants to protect humans and the environment from toxic chemicals, including DDT (Walker et al., 2003 (Klöpffer, 1994). Also, DDT and its metabolites have been shown to possess carcinogenic properties (Kashyap et al., 1977).As a consequence of the issues indicated, the challenges of DDT and its metabolites in contaminated soils continue to be a major issue. There are many sites, or portions of land, that are not able to be developed for subsequent uses (e.g., change of land use from agricultural to residential) because of contamination with DDT, DDD, and DDE at concentrations exceeding environmental guidelines. For example, at a site in Ontario, Canada, current levels of DDT in the case-study site area exceed the Ontario Ministry of Environment (MOE) standards for residential exposures by 10 to...