Farhad Nadim

Optimizing acid-hydrolysis: a critical step for production of ethanol from mixed wood chips

Abstract Ethanol can be produced from renewable lignocellulosic materials such as various types of natural woods. The cellulose contents of wood can be converted to ethanol in a two-step process where acid-hydrolysis converts cellulose to glucose sugars by hydrolysis (saccharification) and the resulting sugars can be converted to ethanol by fermentation. The main challenge of producing fuel ethanol from renewable lignocellulosic biomass through acid-hydrolysis and fermentation is overcoming the cost-limiting factors associated with various stages of this technology. In this study, sugar recovery rates from a mixture of wood chips were investigated through three sets of acid-hydrolysis experiments. Wood chips were sorted to include equal ratios (by weight) of softwood and hardwood. Acid concentration and the heating period were the two main factors affecting dextrose yields. It was found that with the use of 26% by weight sulfuric acid, highest dextrose yields could be reached within 2 h of heating time. This corresponds to overall conversion efficiency of mixed wood chip cellulose to dextrose in the range of 78–82% based on theoretical values.

Atmospheric mercury monitoring survey in Beijing, China.

With the aid of one industrial, two urban, two suburban, and two rural sampling locations, diurnal patterns of total gaseous mercury (TGM) were monitored in January, February and September of 1998 in Beijing, China. Monitoring was conducted in six (two urban, two suburban, one rural and the industrial sites) of the seven sampling sites during January and February (winter) and in four (two urban, one rural, and the industrial sites) of the sampling locations during September (summer) of 1998. In the three suburban sampling stations, mean TGM concentrations during the winter sampling period were 8.6, 10.7, and 6.2 ng/m3, respectively. In the two urban sampling locations mean TGM concentrations during winter and summer sampling periods were 24.7, 8.3, 10, and 12.7 ng/m3, respectively. In the suburban-industrial and the two rural sampling locations, mean mercury concentrations ranged from 3.1-5.3 ng/m3 in winter to 4.1-7.7 ng/m3 in summer sampling periods. In the Tiananmen Square (urban), and Shijingshan (suburban) sampling locations the mean TGM concentrations during the summer sampling period were higher than winter concentrations, which may have been caused by evaporation of soil-bound mercury in warm periods. Continuous meteorological data were available at one of the suburban sites, which allowed the observation of mercury concentration variations associated with some weather parameters. It was found that there was a moderate negative correlation between the wind speed and the TGM concentration at this suburban sampling location. It was also found that during the sampling period at the same site, the quantity of TGM transported to or from the sampling site was mainly influenced by the duration and frequency of wind occurrence from certain directions.

The mechanism and applicability of in situ oxidation of trichloroethylene with Fenton’s reagent

Fentons reagent is the result of reaction between hydrogen peroxide (H(2)O(2)) and ferrous iron (Fe(2+)), producing the hydroxyl radical (-*OH). The hydroxyl radical is a strong oxidant capable of oxidizing various organic compounds. The mechanism of oxidizing trichloroethylene (TCE) in groundwater and soil slurries with Fentons reagent and the feasibility of injecting Fentons reagent into a sandy aquifer were examined with bench-scale soil column and batch experiment studies. Under batch experimental conditions and low pH values ( approximately 3), Fentons reagent was able to oxidize 93-100% (by weight) of dissolved TCE in groundwater and 98-102% (by weight) of TCE in soil slurries. Hydrogen peroxide decomposed rapidly in the test soil medium in both batch and column experiments. Due to competition between H(2)O(2) and TCE for hydroxyl radicals in the aqueous solutions and soil slurries, the presence of TCE significantly decreased the degradation rate of H(2)O(2) and was preferentially degraded by hydroxyl radicals. In the batch experiments, Fentons reagent was able to completely dechlorinate the aqueous-phase TCE with and without the presence of soil and no VOC intermediates or by-products were found in the oxidation process. In the soil column experiments, it was found that application of high concentrations of H(2)O(2) with addition of no Fe(2+) generated large quantities of gas in a short period of time, sparging about 70% of the dissolved TCE into the gaseous phase with little or no detectable oxidation taking place. Fentons reagent completely oxidized the dissolved phase TCE in the soil column experiment when TCE and Fentons regent were simultaneously fed into the column. The results of this study showed that the feasibility of injecting Fentons reagent or H(2)O(2) as a Fenton-type oxidant into the subsurface is highly dependent on the soil oxidant demand (SOD), presence of sufficient quantities of ferrous iron in the application area, and the proximity of the injection area to the zone of high aqueous concentration of the target contaminant. Also, it was found that in situ application of H(2)O(2) could have a gas-sparging effect on the dissolved VOC in groundwater, requiring careful attention to the remedial system design.

Detection and remediation of soil and aquifer systems contaminated with petroleum products: an overview

Fate of organic chemicals in the subsurface strata is not very well understood. It has only been a decade or two that environmental scientists are focusing their attentions on remediating sites that are contaminated with organic chemicals. Different routes of soil and groundwater contamination by petroleum hydrocarbon compounds and their partitioning into gaseous, aqueous and pure phases in the subsurface strata are discussed. A summary of the techniques used for treating hydrocarbon-contaminated soil and groundwater and their application limitations are presented. United States Environmental Protection Agencys (US-EPA) methods 8260, 8270 and 418.1 for detection and quantitation of petroleum range hydrocarbon in soil and aqueous samples and some recently developed mathematical models used to predict the fate and transport of petroleum range compounds in aquifer systems are briefly discussed. Results of some toxicological studies on light and heavy petroleum hydrocarbon are presented. It is concluded that reaching an environment free of hydrocarbon contamination needs broad public understanding of the risks associated with these compounds. Proper management and careful handling of petroleum products reduces the possibility of spills. Replacing old and leaking underground storage tanks with new double wall tanks equipped with leak detectors and cathodic protection could significantly improve the quality of our precious and fragile groundwater resources.

United States experience with gasoline additives

Abstract History, benefits and problems associated with gasoline additives in the United States were reviewed. To reduce air toxics and ozone in highly air-polluted areas of the country, oxygenates will continue to be added to gasoline until an alternative is sought and approved by the Congress of the United States. In near future, the use of methyl tert butyl ether (MTBE) will be reduced from its present magnitude and could be replaced by ethanol or other oxygenates that are less harmful to the environment. With rising oil prices, global warming and other environmental issues in the horizon, it is very likely that in the future, hydrogen will substitute gasoline to power electrically driven motors in automobiles. Nevertheless, hydrogen has to be extracted from a readily available source such as gasoline. If gasoline is going to be used as a source of hydrogen, it has to be reformulated from its present form and there will be no need for any additives.

Identifying the potential sources of di-(2-ethylhexyl) phthalate contamination in the sediment of the Houjing River in southern Taiwan

Sediment samples were analyzed for di-(2-ethylhexyl) phthalate (DEHP), an organic endocrine disruptor, in Houjing River in southern Taiwan. The average DEHP concentration at 10 sampling locations, spanning from upper, middle, and lower segments of the stream, was calculated at 3.81+/-6.36mgkg(-1)drywt. Highest concentration was recorded at the Jhongsing Bridge (20.22mgkg(-1)drywt.) near the Dashe Industrial Park, followed by the Renwu Bridge (8.93mgkg(-1)drywt.) near the Renwu Industrial Park. The surface sediment concentration of DEHP was found to be higher in the dry season (October and December), and lower in the wet (flood) season (August), indicating that sources of DEHP remained active and continued to recharge the Houjing River. Vertical sediment core analysis revealed that highest concentration occurred at the depth of 40-60cm, indicating that historical discharges of DEPH may have been higher than recent years. Domestic comparison of DEHP concentrations in sediment from highest to lowest could be categorized as northern, southern, central, and eastern Taiwan, respectively, and seemed to be positively correlated with population density and/or industrial activity. Compared to other countries, DEHP concentration of the Houjing River was relatively higher than rivers studied in Japan, Germany, Italy, and Malaysia, and was relatively lower than the Aire and Trent Rivers in the United Kingdom.

Long-term investigation of atmospheric mercury contamination in Connecticut

Atmospheric mercury was monitored from January 1997 through the end of December 1999 in eight sampling locations in Connecticut. Four sampling locations were chosen along the shores of Long Island Sound and four were chosen in interior sections of Connecticut. Sampling locations were chosen to represent both rural and urban sectors. Average concentrations of gaseous and particulate mercury were found to be 2.06 ng/m3 and 10.5 pg/m3, respectively. The weekly average wet deposition fluxes of mercury and methylmercury over the three-year sampling period were measured to be 611 and 11 microg/ha/week, respectively. Concentrations of gaseous, particulate and wet flux of mercury were found to be significantly higher in urban areas than the rural sampling locations. There was, however, no significant difference between the mean gaseous and particulate concentrations of mercury in coastal and inland sampling locations. No significant difference was observed either between the wet fluxes of total mercury in coastal and inland sampling locations and there was no spatial gradient for mercury concentration and deposition. The data of this study suggest that vehicular traffic and localized emission sources in urban areas play a significant role in determining the atmospheric concentration of mercury in Connecticut.

The influence of clay on K2CO3/Co–MoS2 catalyst in the production of higher alcohol fuel

The K2CO3/Co–MoS2/clay catalyst was synthesized and its productivity and selectivity toward higher alcohol synthesis (HAS) fuel were tested at temperature and pressure ranges of 290–320 °C, H2/CO=1.1 syngas, GHSVavg=1800 h−1, and 13 790 kPa, respectively. Highest oxygenates productivity (0.32 kg/kg catalyst/h) was obtained at 310 °C with an oxygenates selectivity of 70%. Under the above conditions, the major oxygenates produced were ethanol, 1-propanol, methanol, and isobutanol, respectively. Increasing the reaction temperature for K2CO3/Co–MoS2/clay catalyst led to a decreasing trend in the selectivity of oxygenates. However, at higher temperatures, the clay-combined catalyst produced more hydrocarbons and CO2. The results indicated that clay had a significant impact on higher alcohol synthesis when K2CO3 was incorporated into the Co–MoS2, and acted as a modifier of the catalyst serving to increase the activity and selectivity to higher alcohol fuel in the temperature range of 290–310 °C.

Estimation of wet, dry and bulk deposition of atmospheric nitrogen in Connecticut

Atmospheric nitrogen species including NO3-, NH4+ and total nitrogen in air and precipitation samples were collected with low-volume filter packs and wet deposition collectors from March 1999 through the end of December 2000 in seven sampling locations in Connecticut. Three sampling locations were chosen along the shores of Long Island Sound and four were chosen in interior sections of Connecticut. Sampling sites were chosen to represent both rural and urban sectors. Wet deposition flux of nitrogen species was calculated using wet concentrations, the volume of collected precipitation and the opening surface area of the Aerochemetrics wet deposition collector. The dry deposition flux of nitrogen species was estimated with the application of the dry deposition inferential model (DDIM). Bulk deposition of nitrogen was collected with the aid of a device based on the Swedish IVL Sampler. The dry deposition fluxes of NO3-, NH4+ and total nitrogen were found to be significantly higher in urban areas than the rural sampling locations. There was, however, no significant difference between the wet deposition fluxes of different nitrogen species in rural and urban sampling locations. When inland and coastal sites were compared, the dry deposition fluxes of NH4+ and total nitrogen were significantly higher in inland locations and there was no significant difference between coastal and inland sampling locations for wet deposition fluxes of nitrogen species. No significant difference was observed between the bulk deposition and the sum of the wet and dry deposition fluxes of total nitrogen at rural sampling locations. In urban sampling locations, the bulk deposition flux of total nitrogen was significantly lower than the sum of dry and wet deposition fluxes. There appears to be a similar seasonal trend in wet and dry deposition fluxes of total nitrogen in Connecticut with high and low deposition fluxes occurring in summer and winter periods, respectively.

Desorption rate limitation in the extraction of organic molecules from unsaturated soils during soil venting operations

Abstract A microscale mathematical model is developed to analyze the desorption rate limited extraction of volatile organic compounds in a soil column. By solving the diffusion equation in the liquid layer around the soil particles and incorporating the effects of slow desorption from the soil surfaces, it is found that the concentration of organics in the effluent is eventually given by the sum of two separate contributions. The first represents the removal of the compounds initially dissolved in the liquid layer by diffusion, providing an exponentially decaying concentration in the effluent. The second represents the removal of the organics, initially adsorbed onto the solid surfaces, by slow desorption producing the long-time tail which has been observed in the effluent concentration during soil vapor extraction. This model was applied to two bench-scale columns packed with soil contaminated by volatile organic compound (VOC) contaminated soil. The simplified results of the mathematical model allow such parameters as the effective diffusion length, area of gas-liquid contact, the desorption rate constant and the equilibrium partition coefficient, for trichloroethylene in the two soil columns to be determined.