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: The work reported here describes the aerobic biodegradation of reduced sulfur compound mixtures in air streams by bioülters. Rates of removal of hydrogen sulüde as a sole substrate and in the presence of organo-sulfur compounds were determined to see if there were any inhibitory eþ ects of the organo-sulfur compounds on the rate of hydrogen sulüde removal. Experiments were conducted in three bench-scale bioülters packed with the mixtures of compost/perlite (4 : 1), hog fuel/ perlite (4 : 1), and compost/hog fuel/perlite (2 : 2 : 1), respectively. Hydrogen sulüde, the predominant odorous gas produced from kraft pulping processes, was used as the main pollutant (substrate). Other organo-sulfur species (dimethyl sulüde and dimethyl disulüde), also emitted from kraft pulp mills, were used as competing (secondary) substrates in the waste gas stream. To describe rates of removal a Michaelis-Menten type kinetic equation was modiüed to incorporate the plug ýow behavior of bioülters, and used in evaluating the pseudo-kinetic parameters, (the maximum removal rate) and V max (the half saturation concentration), for hydrogen sulüde biodegradation, and the type of macro-K m kinetic competition between hydrogen sulüde and the organo-sulfur compounds. No signiücant diþ erences in for the three bioülters were observed. The ranged between 136 and 147 g m-3 h-1, V max V max while the varied from 44 to 59 ppmv for the three bioülters. Hydrogen sulüde elimination capacity K m was not aþ ected by the presence of any of the organo-sulfur species in all of the three bioülters, conürming earlier results that hydrogen sulüde removal in bioülters is independent of the presence of organo-sulfur compounds mainly because of its easy biodegradability.

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A series of column studies, using site-specific soil and groundwater, were conducted to determine the feasibility of biologically active zone enhancement (BAZE) process for reductive biotransformation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in groundwater. This treatability study examined the use of four amendments (acetate, ethanol, soluble starch, and acetate plus ammonium), which served as electron donors. Triplicate columns, with groundwater residence time of about 27.5 h, were used for each amendment treatment and the amendment control. In treatment columns amendment dosing was 500 mg/L C for carbon sources and 100 mg/L N for ammonium. Each of the amendment treatments reduced RDX inlet concentrations of 100 g/L to less than 1 g/L. The highest first-order RDX biodegradation rate ranged between 0.140 and 0.447 h −1 for acetate amended columns as compared to 0.037 to 0.083 h −1 in control columns (no amendment). The addition of soluble starch resulted in increased toxicity (based on Microtox ® analysis) that was partially removed by biological activity in the columns. Ethanol addition itself did not result in increased toxicity but biological activity in this system did induce Microtox ® toxicity. Acetate did not have any Microtox ® toxicity associated with it. The addition of ammonium as a nitrogen source did not significantly increase the removal rate of RDX. Based on these observations acetate was selected for the field demonstration. Published by Elsevier B.V.

Sand-packed horizontal flow columns (5 cm i.d. x 65 cm)l were used in laboratory experiments to simulate in situ electrolytic and alkaline hybrid treatment zone for aqueous phase decomposition of RDX. An upgradient cathode and downgradient anode, spaced 35 cm apart were used to create alkaline reducing conditions followed by oxic, acidic conditions to degrade RDX by combination of alkaline hydrolysis and direct electrolysis. A preliminary experiment (25 mg/L RDX influent) with seepage velocity of 30.5 cm/day and current density of 9.9 A/m2 was used to determine the treatment feasibility and the aqueous products of RDX decomposition. Three additional column experiments (0.5 mg/L RDX influent) under the same conditions as the preliminary column were used to observe the treatment process repeatability and the alkaline treatment zone development. The results demonstrated approximately 95% decomposition of RDX in the column with an applied current density of 9.9 A/m2. Aqueous end-products formate, nitrite, and nitrate were detected in the effluent. Approximately 75% of the RDX was destroyed near the cathode, presumably by electrolysis, with 23% decomposed downstream of the cathode by alkaline hydrolysis. The preliminary column pseudo first order alkaline hydrolysis rate coefficient of 10.7 x 10(-3) min(-1) was used to estimate a treatment zone length less than 100 cm for RDX treatment below the EPA drinking water lifetime health advisory of 0.002 mg/L.