Treatment of Paint Spray Booth Off-Gases in a Fungal Biofilter

Biological processes, most notably biofilters and biotrickling filters, are increasingly used to remove and biodegrade a wide variety of volatile organic compounds (VOCs) present in gas streams emitted from industrial operations. In the research described herein, a laboratory-scale biofilter was operated for a period of more than 180 days to treat a waste gas comprised of a four-component VOC mixture representative of solvents present in off-gases emitted by painting operations. The biofilter, packed with a cubed polyurethane foam media and initially inoculated with a pure culture of the fungus Cladosporium sphaerospermum, was maintained under acidic conditions throughout the duration of the experiments. The system was supplied with a mixture of n-butyl acetate, methyl ethyl ketone, methyl propyl ketone, and toluene with influent concentrations of 124, 50.5, 174, and 44.6 mg?m?3, respectively. The biofilter’s empty bed residence time (EBRT) was varied from 2.0 min to 15 s. When the influent gas stream was properly humidified, the system exhibited stable long-term performance with an average total VOC removal greater than 98% even with an EBRT as low as 15 s. Under the loading condition tested, this corresponds to an average elimination capacity of 92 g?m?3?h?1. VOC concentration profiles measured along the height of the biofilter revealed a distinct VOC degradation pattern that was observed under all loading conditions tested. Although the column was initially inoculated with only Cladosporium sphaerospermum, several additional species of fungi tentatively identified as Penicillium brevicompactum, Exophiala jenselmei, Fusarium oxysporum, Fusarium nygamai, Talaromyces flavus, and Fonsecaea pedrosi were found growing attached to the packing medium by the end of experiment. Results demonstrate that fungal biofilters can consistently maintain high removal efficiency for paint VOC mixtures over extended periods of operation. The results also indicate that it would be difficult and likely unnecessary to maintain specific species in full-scale fungal biofilters treating paint spray booth emissions.     

Removal of EATX from Waste Gases by a Trickle-Bed Air Biofilter

The trickle-bed air biofilter performance for treating mixtures of ethylacetate (EA), toluene (T), and xylene (X) volatile organic compounds (VOCs) was evaluated under different influent VOC loadings. The EA removal efficiencies were significantly higher than those for T and X, indicating that EA is a preferred substrate in the EATX waste gas. More than 80% removal efficiencies could be achieved under influent loadings below 77 g EA∕m3∕h, 8 g T∕m3∕h, and 10 g X∕m3∕h. The trickle-bed air biofilter appears efficient for controlling EATX emission with medium EA loadings and low TX loadings. The elimination capacities of EA, T, and X for a pure VOC feed were higher than for a mixed VOC feed and the differences increased with increased influent VOC loading.     

Treatment of MTBE-Contaminated Water in Fluidized Bed Bioreactor

Methyl tertiary-butyl ether (MTBE) biodegradation was evaluated in a laboratory-scale granular activated carbon (GAC)-based fluidized bed bioreactor system. The reactor was operated in seven distinct phases during which the MTBE loading rate, hydraulic retention time, cocontaminant loading [butyl, toluene, ethylbenzene, and xylene (BTEX) and tertiary-butyl alcohol (TBA)] and temperature were varied. The reactor was able to treat MTBE to less than 20 ug/L at 25°C and total organic carbon (TOC) loading rates between 0.01 and 1.1 kg/m3 of expanded GAC bed per day (kg/m3?day). Net biomass yield in the reactor under high loading conditions was approximately 0.55 g of total suspended solids (TSS) per gram of TOC consumed. This high yield under the higher loading rates necessitated that biomass be removed from the reactor to control bed expansion. At a loading rate of 1.5 kg/m3?day, MTBE effluents exceeded 20 ug/L. Reactor performance decreased as the reactor temperature was reduced from 25 to 15°C, but even at the lower temperatures MTBE removal efficiency exceeded 99%. Methyl tertiary-butyl ether treatment efficiency was not affected by the addition of TBA or BTEX under the conditions evaluated. Results of this study demonstrate that fluid bed bioreactors inoculated with an appropriate microbial culture can efficiently treat MTBE-contaminated water.     

Biodegradation of benzene, toluene, ethylbenzene, and o-xylene by a coculture of Pseudomonas putida and Pseudomonas fluorescens immobilized in a fibrous-bed bioreactor

A fibrous-bed bioreactor containing the coculture of Pseudomonas putida and P. fluorescens immobilized in a fibrous matrix was developed to degrade benzene (B), toluene (T), ethylbenzene (E), and o-xylene (X) in synthetic waste streams. The kinetics of BTEX biodegradation by immobilized cells adapted in the fibrous-bed bioreactor and free cells grown in serum bottles were studied. In general, the BTEX biodegradation rate increased with increasing substrate concentration and then decreased after reaching a maximum, showing substrate-inhibition kinetics. However, for immobilized cells, the degradation rate was much higher than that of free cells. Compared to free cells, immobilized cells in the bioreactor tolerated higher concentrations (> 1000 mg l-1) of benzene and toluene, and gave at least 16-fold higher degradation rates for benzene, ethylbenzene, and o-xylene, and a 9-fold higher degradation rate for toluene. Complete and simultaneous degradation of BTEX mixture was achieved in the bioreactor under hypoxic conditions. Cells in the bioreactor were relatively insensitive to benzene toxicity; this insensitivity was attributed to adaptation of the cells in the bioreactor. Compared to the original seeding culture, the adapted cells from the fibrous-bed bioreactor had higher specific growth rate, benzene degradation rate, and cell yield when the benzene concentration was higher than 100 mg l-1. Cells in the fibrous bed had a long, slim morphology, which is different from the normal short-rod shape found for suspended cells in solution.     

Load Dampening System for Vapor Phase Bioreactors

Vapor phase bioreactors are receiving increasing attention as a cost-effective treatment method for air contaminated with volatile organic compounds (VOCs). In this study, a novel absorption and humidification system was evaluated for its ability to dampen transient VOC loads, and to reduce their detrimental effects on a downstream bioreactor. A model based on the mass transfer characteristics of two target compounds (acetone and toluene) was developed and takes into account a closed water recirculation loop that minimizes fugitive emissions and simultaneously humidifies the inlet gas stream. When water is used as the scrubbing liquid, model and experimental results indicate that the system effectively dampens hydrophilic compounds and segregates them from the hydrophobic compounds in the waste gas stream. The response of a vapor phase bioreactor to the pretreated stream has also been assessed, and results indicate that the load dampening system works effectively for hydrophilic, but not hydrophobic, VOCs. However, when an organic cosolvent is used in conjunction with water, hydrophobic VOCs can also be dampened efficiently.     

Empirical Model for Biofiltration of Toluene

In this study the toluene removal efficiency of a composted pine bark biofilter was determined at loading rates ranging from 9.04 to 54.21 g m?3 h?1, retention times of 0.25–3.0 min, and at various bed heights. Toluene removal efficiencies exceeding 90% were obtained when the biofilter was subjected to a gas retention time in excess of 0.32 min (19.2 s) and loading rates below 42 g m?3 h?1. The data obtained were used to develop an empirical model. The empirical model successfully described the overall removal efficiency with an R2 value of 0.98. The influence of oxygen concentration on the removal efficiency was also evaluated. Reduced biofilter performance was observed at oxygen concentrations below 5%. A wide range of microorganisms were isolated from the biofilter, which included Corynebacterium jeikeium A, Corynebacterium nitrilophilus, Micrococcus luteus, Pseudomonas mendocina, Sphingobacterium thalphophilum, and Turicella otitidis.     

Single-Submerged Attached Growth Bioreactor for Simultaneous Removal of Organics and Nitrogen

The use of a single-unit, single-zone submerged attached growth bioreactor (SAGB) for the combined removal of carbonaceous organics and nitrogen from a municipal wastewater was demonstrated. A nitrification efficiency of 97% was achieved at a total organic loading of 3.47?kg?bCOD/m3?day. The total nitrogen loading varied from 0.2?to?0.3?kg?N/m3?day and resulted in effluent total nitrogen concentrations ranging from 4.2?to?8.5?mg/L. Concurrent denitrification was achieved at rates ranging from 0.077?to0.29?kg?N/m3?day. This single-unit SAGB, by providing dual treatment capacities, represents a cost-effective option that is particularly attractive for facilities with limited space and budget for system upgrade.     

Cultured astrocytes express proteins involved in vesicular glutamate release

The objective of this study is to analyze volatile organic compound (VOC) concentrations in Taiwan's drinking water supply. Focusing on Taiwan's three major metropolitan areas--Taipei, Taichung and Kaohsiung (in the north, middle and south, respectively)--171 samples were taken from tap water and 68 from boiled water. Tests showed VOC concentrations were highest in Kaohsiung. This is due to different water sources and methods of treatment. Except for bromoform, trihalomethane (THM) concentrations were highest. Detection rates of toluene and 1,2-dichloroethane were slightly higher than other VOC compounds. VOC concentrations decreased significantly after water was boiled. THMs had a removal rate from 61% to 82%. The authors conclude that the three metropolitan areas contain significantly different levels of VOCs and that boiling can significantly reduce the presence of VOCs. Other sources of pollution that contaminate drinking water such as industrial plants and gas stations must be further investigated.     

Novel Hybrid Filter for the Treatment of Septic Tank Effluent

Intermittent sand filtration is a common and effective method for treating septic tank effluent. However, if the loading rate is too high, clogging and ponding of the sand filter surface layer can occur due to the accumulation of excessive biomass and the deposition of suspended solids. This ponding limits the practicality of sand filtration as it makes it necessary to take the filter out of service for maintenance. The objective of this study was to develop and test, on-site, a new hybrid filter system that would reduce the risk of clogging at an organic loading rate substantially greater than the maximum recommended loading rate for intermittent sand filters. The system comprised a 0.6?m deep horizontal flow biofilm reactor (HFBR) over a 0.85?m deep stratified sand filter. The HFBR consisted of a stack of 20 horizontal corrugated polyvinyl chloride sheets, at 32?mm vertical spacings. The sheets were arranged so that the wastewater flowed over and back along alternate sheets down through the stack. The main biofilm growth formed on these sheets. The hybrid filter was loaded with septic tank effluent from an office/garage complex at the rate of 206?L/m2?day for a period of 400 days in two phases. During the first phase, the effluent volume of 600?L/day was applied in 24 doses/day for 10?min/dose, and during the second phase in 6 doses/day for 40?min/dose. Biofilms in the HFBR substantially reduced the organic and suspended solids loads that reached the sand filter surface and allowed an average total biochemical oxygen demand (BODT) loading rate, based on HFBR plan area, of 37?g?BODT/m2?day to be applied to the system without clogging. This rate was substantially greater than the maximum recommended loading rate of 24?g?BODT/m2?day for intermittent sand filters. During both loading phases a BODT removal of 94% was achieved and nitrification was nearly complete. The average effluent BODT was 12±4?mg/L during both phases. The hybrid filter system appeared to perform better in terms of suspended solids handling and nitrification during the more frequent dosing phase. The hybrid filtration system offers a more compact alternative to intermittent sand filtration on its own with little risk of clogging.     

Membrane Bioreactor for Cometabolism of Trichloroethene Air Emissions

Biofilters have been of limited use for cometabolism of chlorinated organic compounds, such as trichloroethene (TCE), due to enzyme inhibition or toxicity effects. A hollow fiber membrane bioreactor was investigated that involves a bundle of polypropylene fibers through which volatile organic compound contaminated air passes. The fibers are immersed in a recirculating nutrient/cosubstrate solution. Batch culture experiments were performed with a mixed culture that could cometabolize TCE with toluene as a primary substrate. No inhibition or inquiry to the toluene degrading ability was observed at up to 15 mg L?1 toluene or up to 1.5 mg L?1 TCE. The culture was inoculated into the hollow-fiber membrane bioreactor. Initially toluene was supplied to the reactor to build a sufficient biomass density on the fibers. After steady-state toluene removal was achieved, TCE was added to the gas phase of the reactor. Toluene was added in three different configurations: (1) As a mixture with TCE in the gas phase; (2) by pulsing into the gas phase; or (3) to the liquid phase. This paper investigates which reactor configuration is most favorable for cometabolism of toluene and TCE.     

Biotrickling Filtration for Control of Volatile Organic Compounds from Microelectronics Industry

This study investigated the transient and steady-state performance of a bench-scale biotrickling filter for the removal of an organic mixture (acetone, toluene, and trichloroethylene) typically emitted by the microelectronics industry. The microbial consortium consisting of seven bacterial strains that were fully acclimated prior to inoculation onto activated carbon media. Among the seven strains, the Pseudomonas and Sphingomonas strains appeared to be the major groups degrading toluene (>25?ppmv/h?108 cell) and trichloroethylene (>2.3?ppmv/h?108 cell), while Mycobacteria and Acetobacteriaceae strains were the primary decomposers of acetone (>90?ppmv/h?108 cell). The column performance was evaluated by examining its responses to the fluctuating influent total hydrocarbon concentrations, which varied from 850 to 2,400 ppmv. Excellent steady-state removal efficiencies greater than 95% were consistently observed, and system recovery was typically within two days after a significant increase in the inlet loading was experienced. The overall mass-transfer rate and the biokinetic constants were determined for each organic component. Mathematical simulations based on these parameters demonstrated that the removal of acetone was kinetically limiting, whereas the removals of toluene and trichloroethylene were at least partially mass-transfer limiting.     

Model Study Based on Experiments on Toluene Vapor Removal in a Biofilter

A study on the prediction of toluene vapor removal in a biofilter using an acclimated mixed-culture was carried out on the basis of experimental data obtained under various states of inlet vapor concentrations, flow rates or empty bed retention time, and biofilter temperature. Variations of removal performance and parameters with biofilter temperature and vapor organic load were examined. Several kinetic models such as a first-order reaction equation and mathematical models of Ottengraf, Ottengraf-van den Oever, van Lith et al., and Kornegay-Andrews were applied and examined with respect to the prediction performance of toluene vapor removal under pseudo-steady-state conditions. Limitations of the models were investigated, and optimal operating conditions and various design parameters such as degradation rate constant, maximum elimination capacity, and removal efficiency were also determined.     

Performance of a Biofilm Airlift Suspension Reactor for Synthetic Wastewater Treatment

Performance stability of a biofilm airlift suspension reactor (BASR) was studied using ethanol as a substrate. The main objective of this research was to investigate the applicability of the reactor as a wastewater treatment process by examining the effects of soluble chemical oxygen demand (SCOD) loading rate and hydraulic retention time (HRT) on the performance of the reactor. SCOD removal of 90% or higher was achieved at an HRT of 45 min with loading rates from 10 to 18 kg SCOD/m3?day. Similar results were obtained at HRTs of 60 and 90 min and a SCOD loading rate of 10 kg SCOD/m3?day. Nitrification occurred in the system when the ratio of SCOD to ammonia nitrogen was changed from 10:1 to 6:1. The morphology of the biofilm in the BASR was denser and thicker when nitrifiers grew in the biofilm. Filamentous overgrowth was observed from time to time and proper chlorine dose successfully suppressed its growth. The oxygen uptake rate was an effective tool for monitoring the effect of chlorination.     

Granular Bed Baffled Reactor (Grabbr): Solution to a Two-Phase Anaerobic Digestion System

A single unit anaerobic granular bed baffled reactor (GRABBR) is proposed as an alternative to a separately operated two-phase anaerobic digestion system. This overcomes the problems related to wastewater treatment at high loading rates which usually results in accumulation of intermediate acid products, and consequently inhibits methanogenesis. This study was carried out to evaluate the stability of a five compartment GRABBR system when treating synthetic glucose wastewater at various operational conditions. The reactor was started with volumetric organic loading rate (OLR) of 1 kg chemical oxygen demand (COD)/m3?day, equivalent to 120 h hydraulic retention time (HRT), and loading rates were gradually increased at suitable intervals to up to 20 kg COD/m3?day (6 h HRT). At steady state, the overall soluble COD (SCOD) removal was over 95% under all applied loading conditions. At lower loadings, the reactor operated as a completely mixed system, and most of the treatment was achieved in the first compartment. At higher loadings, the entire system transformed into different phases, acidogenesis being dominant near the influent point, whilst methanogenesis was the main activity in the compartments near the effluent point. Granule breaking and flotation was observed in the acidogenic zone, whilst the methanogenic zone retained its original granular form. High assimilation rate of influent nitrogen was observed in the first compartment with the formation of nongranular biomass, identified as Klebsiella pneumoniae. The success of GRABBR as a single unit two-phase anaerobic digestion system could save the cost of an extra unit traditionally employed to achieve similar goals in treatment of high strength wastewaters.     

Electrocoagulation of Silica Nanoparticles in Wafer Polishing Wastewater by a Multichannel Flow Reactor: A Kinetic Study

A simplistic and systematic procedure has been developed for the design and upscaling of a multichannel, continuous-flow electrocoagulation reactor of monopolar configuration for the removal of submicron particles from wastewater. Using wastewater generated from the chemical-mechanical planarization process as the target wastewater, a series of laboratory-scale studies were conducted to determine the required operating conditions for the efficient removal of the ultrafine silica particles. These operating criteria included charge loading ( ≥ 8?F/m3), current density ( ≥ 5.7?A/m2), hydraulic retention time ( ≥ 60?min), as well as the initial pH (7–10). Furthermore, a steady-state transport equation with second-order reaction kinetics was employed to describe the rate of coagulation as the rate-limiting factor. The actual kinetic constant determined from the laboratory-scale experiments was approximately 1.2×10?21?m3/s, which was three orders of magnitude smaller than that calculated based on Brownian coagulation. The model was subsequently validated with a series of experiments using a pilot-scale electrocoagulation reactor geometrically similar to the laboratory-scale reactor with nearly 20 times volumetric scaleup.     

Evaluation of Slip Feed System for Vapor-Phase Bioreactors

This study evaluated the ability of a slip feed system to maintain the pollutant-degrading activity of biomass in a vapor phase bioreactor during periods of little or no contaminant feed. Three slip feed fractions (1, 5, and 9% by mass) were investigated in a bioreactor treating toluene-contaminated air. Results indicate that the slip feed system improved the contaminant degradation capacity in the carbon-deprived bioreactor zones by approximately 30% regardless of the slip feed fraction supplied. This yielded a 10–20% improvement in toluene removal efficiency when the entire bioreactor column was subjected to a sudden threefold spike in toluene loading. When a 12% slip feed was supplied to the bioreactor during a short-term (3 days) or longer-term (1 week) shutdown period, it reduced the reacclimation time required following restart by as much as 70%. These results indicate that as long as the biomass receives at least a trace of the pollutant by means of a slip feed system, it can maintain sufficient pollutant degrading capacity to respond quickly to pollutant loadings upon restart.     

Removal of Methyl Isobutyl Ketone From Contaminated Air by Trickle-Bed Air Biofilter

A laboratory-scale trickle-bed air biofilter was evaluated for the removal of methyl isobutyl ketone (MIBK) from a waste gas stream. Six-millimeter (6?mm) Celite pellets (R-635) were used as the biological attachment medium. Effects of MIBK volumetric loading rates on removal efficiency, biofilter reacclimation, biomass growth, and removal kinetics were studied under three different operating conditions, namely, backwashing and two intermittent periods (off chemical—no MIBK input; and off flow-no flow input). Backwashing of the biofilter once a week with full-medium fluidization removed the excess biomass and attained stable long-term performance with over 99% removal efficiency for loading rates less than 3.26?kg chemical oxygen demand (COD)/m3?day. The two intermittent periods could also sustain high removal efficiency for loading rates up to 1.09?kg?COD/m3?day without any backwashing. The recovery time increased with an increase in loading rates. Furthermore, the intermittent operations required a longer time to recover than backwashing. The pseudo-first-order removal rate constant decreased with an increase in volumetric loading rate. The removal kinetics showed an apparent dependency on the experimental operating conditions.     

Changes in Polyhydroxy-Alkanoates (PHAs) during Enhanced Biological Phosphorus Removal with Dairy Industrial Wastewater

Using the industrial wastewater from a dairy plant, the performance of enhanced biological phosphorus removal (EBPR) with complex organic substances was evaluated. A laboratory-scale sequencing batch reactor (SBR) was operated and the organic loading rate in total chemical oxygen demand (tCOD) increased gradually from 200–600?g-tCOD?m?3?cycle?1 in three steps. As the organic loading increased, the food to microorganism ratio (F/M) increased from 0.16–0.27 (g-tCOD/g-MLVSS d). When it increased over 600?g-tCOD?m?3?cycle?1, the effluent phosphorus concentration fluctuated, showing an unstable EBPR activity. During the anaerobic condition, higher fraction of poly-3-hydroxyvalerate (PHV) was observed and the ratio of PHV to poly-3-hydroxybuyrate (PHB) production (ΔPHV/ΔPHB) ranged 1.2 ～ 3.4?mM-C/mM-C. PHV was produced faster and used later than PHB. By applying fluorescent in situ hybridization (FISH) technique, the percentage of Rhodocyclus-related bacteria to the total cell counts was monitored as an indicator of phosphorus accumulating organisms (PAOs). The population accounted for 38.3±16.2% at low organic loading rate and stayed at the same level as the organic loading rate increased.     

High Rates of Ammonia Removal in Experimental Oxygen-Activated Nitrification Wetland Mesocosms

While constructed treatment wetlands are very efficient at polishing nitrate from secondary effluent, they are much less effective at removing ammonia. A key factor that limits ammonia oxidation via biological nitrification in vegetated wetlands is low levels of dissolved oxygen. This study evaluated the effectiveness of side-stream oxygenation to enhance ammonia removal in replicate surface-flow experimental mesocosms containing wetland sediment and plants (Typha spp.). Mesocosms had a water volume of 29.5 L, a hydraulic retention time of 5 days, and a hydraulic loading rate of 4.3 cm/d, and were loaded with synthetic secondary effluent contain 10 mg-N/L of ammonia. Relative to nonoxygenated controls, oxygenation increased ammonia removal rates by an order of magnitude. Areal removal rates increased from 40?mg-N/m2/d to 450?mg-N/m2/d, concentration removal efficiency increased from 10 to 95%, and area-based first-order removal rates increased from <2?m/year to 50–75 m/year. Ammonia removal rates in oxygenated mesocosms were 2- to 4-fold higher than rates reported for full-scale constructed wetlands treating secondary effluent. Results show that oxygen-activated nitrification wetlands, a hybrid of conventional oxygenation technology and wetland ecotechnology, hold promise in economically enhancing rates of ammonia removal and shrinking the wetland area needed to polish ammonia-dominated secondary effluent. Further study is needed to confirm that oxygenation can promote high rates of ammonia removal at the field scale.