Altaf H. Wani

Biofiltration: A promising and cost‐effective control technology for Odors, VOCs and air toxics

Abstract Biofiltration, a relatively recent air pollution control technology, has been identified as a promising method of odor, VOC and air toxic removal form waste‐gas streams because of low capital and operating costs, low energy requirements and an absence of residual products requiring further treatment or disposal. Biofiltration units are microbial systems incorporating microorganisms grown on a porous solid media like compost, peat, soil or mixture of these materials. The filter media and the microbial culture are surrounded by a thin film of water called biofilm. Waste‐gases containing biodegradable VOCs and inorganic air toxics are vented through this biologically active material, where soluble contaminants partition into the liquid film and are biodegraded by the resident microorganisms in the biofilm. The technology has been successfully applied to a wide range of industrial and public sector sources for the abatement of odors, VOCs and air toxics, with an elimination efficiency of more than 90...

Biofiltration control of pulping odors - hydrogen sulfide : Performance, macrokinetics and coexistence effects of organo-sulfur species

The work reported here describes the aerobic biodegradation of reduced sulfur compound mixtures in air streams by biofilters. Rates of removal of hydrogen sulfide as a sole substrate and in the presence of organo-sulfur compounds were determined to see if there were any inhibitory effects of the organo-sulfur compounds on the rate of hydrogen sulfide removal. Experiments were conducted in three bench-scale biofilters packed with the mixtures of compost/perlite (4:1), hog fuel/ perlite (4:1), and compost/hog fuel/perlite (2:2:1), respectively. Hydrogen sulfide, the predominant odorous gas produced from kraft pulping processes, was used as the main pollutant (substrate). Other organo-sulfur species (dimethyl sulfide and dimethyl disulfide), 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 modified to incorporate the plug flow behavior of biofilters, and used in evaluating the pseudo-kinetic parameters, Vmax (the maximum removal rate) and Km (the half saturation concentration), for hydrogen sulfide biodegradation, and the type of macrokinetic competition between hydrogen sulfide and the organo-sulfur compounds. No significant differences in V max for the three biofilters were observed. The V max ranged between 136 and 147 g m−3 h −1, while the Km varied from 44 to 59 ppmv for the three biofilters. Hydrogen sulfide elimination capacity was not affected by the presence of any of the organo-sulfur species in all of the three biofilters, confirming earlier results that hydrogen sulfide removal in biofilters is independent of the presence of organo-sulfur compounds mainly because of its easy biodegradability. © 1999 Society of Chemical Industry

Degradation Kinetics of Biofilter Media Treating Reduced Sulfur Odors and VOCs

A lab-scale study was conducted to determine the rate and extent of decomposition of three biofilter media materials-compost, hog fuel, and a mixture of the two in 1:1 ratio-used in biofiltration applied to removal of reduced sulfur odorous compounds from pulp mill air emissions. The rate of carbon mineralization, as a measure of biofilter media degradation, was determined by monitoring respiratory CO2 evolution and measuring the changes in carbon and nitrogen fractions of the biofilter materials over a period of 127 days. Both ambient air and air containing reduced sulfur (RS) compounds were used, and the results were compared. After 127 days of incubation with ambient air, about 17% of the media carbon was evolved as CO2 from compost as compared to 6 and 12% from hog fuel and the mixture, respectively. The decomposition showed sequential breakdown of carbon moieties, and three distinct stages were observed for each of the biofilter media. First-order rate kinetics were used to describe the decomposition stages. Decomposition rates in the initial stages were at least twice those of the following stages. Carbon mineralization showed close dependence on the C/N ratio of the biofilter material. Media decomposition was enhanced in the presence of RS gases as a result of increased bioactivity by sulfur-oxidizing bacteria and other microorganisms, thus reducing the media half-life by more than 50%. At higher concentrations of RS gases, the CO2 evolution rates were proportionally lower than those at the low concentrations because of the limited acid buffering capacity of the biofilter materials.

Electrolytic Alkaline Decomposition of a Munition Constituent (RDX) Contaminated Groundwater

Combined use of electrolysis and alkaline hydrolysis is explored for in-situ decomposition of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in laboratory experiments with simulated groundwater. Alkaline medium generated by water electrolysis at the cathode under direct electric currents will develop a permeable alkaline barrier for in-situ decomposition of RDX. Pseudo-first order transformation rate coefficients were developed from alkaline hydrolysis and electrolytic batch experiments for RDX decomposition with time. The results provided a target pH of 12 and a current density of 1 mA/cm 2 for treatment of RDX under groundwater flow column experiment. The results from the one-dimensional sand-filled alkaline hydrolysis columns (5-cm ID) were used to develop reaction rate coefficients used in designing a large scale-up one-dimensional column to test the electrolytic generation of hydroxide (10-cm ID). The rate coefficient from the 5-cm alkaline columns (0.46 per hr) was used to calculate a column length (160 cm) for complete removal of RDX and its nitroso-substituted products under groundwater flow rate of 30 cm/day. Effluent RDX concentrations from the 10-cm scale-up column (4,000 µg/L influent) were less than 0.1 µg/L for 36 days of treatment. The study concludes that cathodes placed at the down-gradient of groundwater RDX plume can perform as an effective permeable alkaline hydrolysis barrier for decomposition of RDX to levels below EPA drinking water advisory limits.

Direct Electrolytic Reduction of Energetic Compounds (hexahydro-1,3,5-trinitro-1,3,5-triazine and 2,4,6-trinitrotoluene) in Groundwater

Electrolytic reactive barriers (e-barriers) consist of closely spaced permeable electrodes installed across a groundwater contaminant plume in a permeable reactive barrier format. Application of sufficient potential to the electrodes results in sequential oxidation and reduction of the target contaminant. The objective of this study was to quantify the mass distribution of compounds produced during sequential electrolytic oxidation and reduction of ordinance related compounds (ORCs) in a laboratory analog to an e-barrier. In this study, a series of column tests were conducted using RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) and TNT (2,4,6-trinitrotoluene) as representative ORCs. The experimental setup consisted of a plexiglass column packed with quart-feldspar sand to simulate aquifer conditions. A single set of porous electrodes consisting of expanded titanium-mixed metal oxide mesh was placed at the midpoint of the soil column as a one-dimensional analog to an e-barrier. Constant current of 20 mA (variable voltage) was applied to the electrode set. Initial studies involved quantification of reaction products using unlabeled RDX and TNT. The results indicated approximately 70% of the influent concentration was transformed, in one pass, through sequential oxidation-reduction for both contaminants. Following the unlabeled studies, 14 C labeled ORCs were introduced to conduct the mass balance. An activity balance of up to 95.5% was achieved for both 14 C-RDX and 14 C-TNT. For both contaminants, approximately 21% of the influent activity was mineralized to 14 CO 2 . The proportion of the initial activity in the dissolved fraction was different for the two test contaminants. Approximately 30% of the initial 14 C-RDX was recovered as unreacted in the dissolved phase. The balance of the 14 C-RDX was recovered as non-volatile, non-nitroso transformation products. None of the 14 C-RDX was sorbed to the column sand packing. For 14 C-TNT approximately 51% of the initial activity was recovered in the dissolved phase, the majority of which was unreacted TNT. The balance of the 14 C-TNT was either sorbed to the sand packing (approximately 23.7 %) or dissolved/mineralized as unidentified ring cleavage products (4.5%).