Gaseous ammonia uptake in compost biofilters as related to compost water content

Sewage sludge and yard waste compost were used as biofilter materials and tested with respect to their capacity for removing ammonia from air at different water contents. Ammonia removal was measured in biofilters containing compost wetted to different moisture contents ranging from air dry to field capacity (maximum water holding capacity). Filters were operated for 15 days and subsequently analyzed for NH3/NH4+, NO2-, and NO3-. The measured nitrogen species concentration profiles inside the filters were used to calculate ammonia removal rates. The results showed that ammonia removal is strongly dependent on the water content in the filter material. At gravimetric water contents below 0.25 g H2O g solids(-1) for the yard waste compost and 0.5 g H2O g solids(-1) ammonia removal rates were very low but increased rapidly above these values. The sewage sludge compost filters yielded more than twice the ammonia removal rate observed for yard waste compost likely because of a high initial concentration of nitrifying bacteria originating from the wastewater treatment process and a high airwater interphase surface area that facilitates effective ammonia dissolution and transport to the biofilm.     

Removal of ammonia by biofilters: a study with flow-modified system and kinetics

The characteristics of ammonia removal by two types of biofilter (a standard biofilter with vertical gas flow and a modified biofilter with horizontal gas flow) were investigated. A mixture of organic materials such as compost, bark, and peat was used as the biofilter media based on the small-scale column test for media selection. Complete removal capacity, defined as the maximum inlet load of ammonia that was completely removed, was obtained. The modified biofilter showed complete removal up to 1.0 g N/kg dry material/day. However, the removal capacity of the standard biofilter started to deviate from complete removal around 0.4 g N/kg dry material/day, indicating that the modified biofilter system has higher removal efficiency than the standard upflow one. In kinetic analysis of the biological removal of ammonia in each biofilter system, the maximum removal rate, Vm, was 0.93 g N/kg dry material/day and the saturation constant, Ks, was 32.55 ppm in the standard biofilter. On the other hand, the values of Vm and Ks were 1.66 g N/kg dry material/day and 74.25 ppm, respectively, in the modified biofilter system.     

Biofiltration of gasoline vapor by compost media

Gasoline vapor was treated using a compost biofilter operated in upflow mode over 4 months. The gas velocity was 6 m/h, yielding an empty bed retention time (EBRT) of 10 min. Benzene, toluene, ethylbenzene and xylene (BTEX) and total petroleum hydrocarbon (TPH) removal efficiencies remained fairly stable approximately 15 days after biofilter start-up. The average removal efficiencies of TPH and BTEX were 80 and 85%, respectively, during 4 months of stable operation. Biodegradation portions of the treated TPH and BTEX were 60 and 64%, respectively. When the influent concentration of TPH was less than 7800 mg TPH/m3, approximately 50% of TPH in the gas stream was removed in the lower half of the biofilter. When the influent concentration of BTEX was less than 720 mg BTEX/m3, over 75% of BTEX in the gas stream was removed in the lower half of the biofilter. Benzene removal efficiency was the lowest among BTEX. A pressure drop could not be detected over a 1-m bed height at a gas velocity of 6 m/h after approximately 4 months of operation. Results demonstrated that BTEX in gasoline vapor could be treated effectively using a compost biofilter.     

Carbonyl Sulfide Removal with Compost and Wood Chip Biofilters,and in the Presence of Hydrogen Sulfide

Abstract

Carbonyl sulfide (COS) is an odor-causing compound and hazardous air pollutant emitted frequently from wastewater treatment facilities and chemical and primary metals industries. This study examined the effectiveness of biofiltration in removing COS. Specific objectives were to compare COS removal efficiency for various biofilter media; to determine whether hydrogen sulfide (H₂S), which is frequently produced along with COS under anaerobic conditions, adversely impacts COS removal; and to determine the maximum elimination capacity of COS for use in biofilter design. Three laboratory-scale polyvinyl chlo-ride biofilter columns were filled with up to 28 in. of biofilter media (aged compost, fresh compost, wood chips, or a compost/wood chip mixture). Inlet COS ranged from 5 to 46 parts per million (ppm) (0.10–9.0 g/m³fihr). Compost and the compost/wood chip mixture produced higher COS removal efficiencies than wood chips alone. The compost and compost/wood chip mixture had a shorter stabilization times compared with wood chips alone. Fresh versus aged compost did not impact COS removal efficiency. The presence of H₂S did not adversely impact COS removal for the concentration ratios tested. The maximum elimination capacity is at least 9 g/m³·hr for COS with compost media.     

Characterization of compost biofiltration media.

The effect of compost quality on performance of biofiltration media was investigated. Three types of compost media were characterized in terms of their key properties, including pH, total organic carbon (TOC) and nitrogen, moisture content, oxygen uptake rates and heterotrophic and fungal plate counts. Laboratory-scale biofilter columns were each filled with a different compost medium mixed with buffer and a bulking agent. The columns were operated with a volatile organic compound (VOC) mixture consisting of ethyl alcohol, butyraldehyde, ethyl acetate, and 1,1-diethoxybutane and subjected to various operating conditions. After 13 months, the columns were sampled and post-characterization of the media was performed. A mixture of biosolids/horse manure compost, which had a high initial microbial activity, had the shortest acclimation period. Best overall performance, however, was observed with yard waste compost, which was the most stable medium. Media hydrophobicity was a key factor in long-term performance. Significant changes in compost structure, moisture content, pH, volatile solids, oxygen uptake rates, and microbial population densities were observed over the course of the study. Analyses of organic nitrogen content showed that significant amounts of nitrogen were not depleted from the media.     

Gaseous Ammonia Uptake in Compost Biofilters as Related to Compost Water Content

Abstract

Sewage sludge and yard waste compost were used as biofilter materials and tested with respect to their capacity for removing ammonia from air at different water contents. Ammonia removal was measured in biofilters containing compost wetted to different moisture contents ranging from air dry to field capacity (maximum water holding capacity). Filters were operated for 15 days and subsequently analyzed for NH₃/NH₄ ⁺, NO₂ ^-, and NO₃ ^-. The measured nitrogen species concentration profiles inside the filters were used to calculate ammonia removal rates. The results showed that ammonia removal is strongly dependent on the water content in the filter material. At gravimetric water contents below 0.25 g H₂O g solids^-1 for the yard waste compost and 0.5 g H₂O g solids^-1 ammonia removal rates were very low but increased rapidly above these values. The sewage sludge compost filters yielded more than twice the ammonia removal rate observed for yard waste compost likely because of a high initial concentration of nitrifying bacteria originating from the wastewater treatment process and a high air-water interphase surface area that facilitates effective ammonia dissolution and transport to the biofilm.     

Backfitting Electrostatic Precipitators: Gas Velocity and Reliability Considerations

Abstract

The kinetic behavior of the toluene biofiltration process was investigated in this research. Toluene was used as a model compound for less water-soluble gas pollutants. The limiting factor in the overall toluene biofiltration process was determined by analyzing the effectiveness factor of the biofilm along the biofilter. Experiments were conducted in three laboratory-scale biofilters packed with mixtures of chaff/compost, D.E. (diatomaceous earth)/compost and GAC (granular activated carbon)/compost, respectively. A mathematical model previously proposed was verified in this study as being applicable to these biofilters packed with different filter materials. Both the experimental and theoretical results confirmed that the biodegradation rate along the biofilter followed the zero order, fractional order to first order kinetics as toluene concentration decreased. Moreover, at higher toluene concentration, biodegradation rate and mass flux of toluene were lower near the bottom of the biofilter due to substrate inhibition. Analysis of the effectiveness factor indicated that biofiltration of a less soluble compound such as toluene should not be operated at high gas flow rates (low gas residence times) due to the mass transfer limitation of such a system. At an approximate constant inlet toluene concentration of 0.9 g/m³, the toluene removal efficiency in these three biofilters would drop below 90% when the gas residence time decreased to 2.5, 2.5, and 2.0 min, respectively.     

Sulfur toxicity and media capacity for H2S removal in biofilters packed with a natural or a commercial granular medium

Two types of media, a natural medium (wood chips) and a commercially engineered medium, were evaluated for sulfur inhibition and capacity for removal of hydrogen sulfide (H2S). Sulfate was added artificially (40, 65, and 100 mg of S/g of medium) to test its effect on removal efficiency and the media. A humidified gas stream of 50 ppm by volume H2S was passed through the media-packed columns, and effluent readings for H2S at the outlet were measured continuously. The overall H2S baseline removal efficiencies of the column packed with natural medium remained >95% over a 2-day period even with the accumulated sulfur species. Added sulfate at a concentration high enough to saturate the biofilter moisture phase did not appear to affect the H2S removal process efficiency. The results of additional experiments with a commercial granular medium also demonstrated that the accumulation of amounts of sulfate sufficient enough to saturate the moisture phase of the medium did not have a significant effect on H2S removal. When the pH of the biofilter medium was lowered to 4, H2S removal efficiency did drop to 36%. This work suggests that sulfate mass transfer through the moisture phase to the biofilm phase does not appear to inhibit H2S removal rates in biofilters. Thus, performance degradation for odor-removing biofilters or H2S breakthrough in field applications is probably caused by other consequences of high H2S loading, such as sulfur precipitation.     

生物滤池处理城市污水工艺中恶臭和微生物气溶胶的填料选择简

采用实验室规模的生物滤池对含硫化氢、氨和微生物气溶胶的气体进行处理,并对海绵、陶粒、堆肥和空心塑料小球4种物质作为反应器填料的性能进行比较。结果表明,不同填料生物滤池对硫化氢、氨和微生物气溶胶的去除效率明显不同,去除效率从高到低的顺序依次为海绵、陶粒、堆肥和空心塑料小球生物滤池。海绵和陶粒生物滤池出气异养细菌和真菌主要以小粒径粒子为主。在同样的进气和运行条件下,堆肥填料层的压力降最大,其次是陶粒和空心塑料小球填料层,海绵填料层的压力降最小。对4种填料的性能进行综合比较,海绵和陶粒较适宜作为处理硫化氢、氨和微生物气溶胶的生物滤池填料。     

Ammonia removal from compost leachate using zeolite. II. A study using continuous flow packed columns

Bench-scale packed zeolite columns were set up and operated to investigate the continuous removal of ammonium ions from compost leachate. The effects of hydraulic retention time (HRT), and particle size of the zeolite on the ammonia adsorption capacity were studied. For both the coarse particle and the powdered zeolite columns, higher ammonia removal efficiencies were achieved with longer HRT (i.e., lower influent flow rate) tests. At the same HRT, ammonia removal efficiencies from tests with powdered zeolite were generally 20% higher than tests with the coarse particle zeolite. A HRT of 6 hours was found appropriate for efficient ammonia removal, and an operating capacity of 1.31 mg N/g zeolite was obtained. Over 98% of the ammonia input from the influent was consistently removed for over 5 bed volumes (BV) of compost leachate flowing through the zeolite column. Zeolite proved to have a great potential as a medium for ammonia removal in treating composting leachate.     

AMMONIA REMOVAL FROM COMPOST LACHATE USING ZEOLITE. II. A STUDY USING CONTINUOUS FLOW PACKED COLUMNS

Bench-scale packed zeolite columns were set up and operated to investigate the continuous removal of ammonium ions from compost leachate. The effects of hydraulic retention time (HRT), and particle size of the zeolite on the ammonia adsorption capacity were studied. For both the coarse particle and the powdered zeolite columns, higher ammonia removal efficiencies were achieved with longer HRT (i.e., lower influent flow rate) tests. At the same HRT, ammonia removal efficiencies from tests with powdered zeolite were generally 20% higher than tests with the coarse particle zeolite. A HRT of 6 hours was found appropriate for efficient ammonia removal, and an operating capacity of 1.31 mg N/g zeolite was obtained. Over 98% of the ammonia input from the influent was consistently removed for over 5 bed volumes (BV) of compost leachate flowing through the zeolite column. Zeolite proved to have a great potential as a medium for ammonia removal in treating composting leachate.     

生物滤池处理城市污水工艺中恶臭和微生物气溶胶的填料选择

采用实验室规模的生物滤池对含硫化氢、氨和微生物气溶胶的气体进行处理,并对海绵、陶粒、堆肥和空心塑料小球4种物质作为反应器填料的性能进行比较。结果表明,不同填料生物滤池对硫化氢、氨和微生物气溶胶的去除效率明显不同,去除效率从高到低的顺序依次为海绵、陶粒、堆肥和空心塑料小球生物滤池。海绵和陶粒生物滤池出气异养细菌和真菌主要以小粒径粒子为主。在同样的进气和运行条件下,堆肥填料层的压力降最大,其次是陶粒和空心塑料小球填料层,海绵填料层的压力降最小。对4种填料的性能进行综合比较,海绵和陶粒较适宜作为处理硫化氢、氨和微生物气溶胶的生物滤池填料。     

Effect of gas velocity and influent concentration on biofiltration of gasoline off-gas from soil vapor extraction

This study was conducted to evaluate the effects of gas inlet concentration and velocity on the biofiltration of gasoline vapor. Gasoline vapor was treated using a compost biofilter operated in an upflow mode for about 3 months. The inlet concentration of gasoline total petroleum hydrocarbon (TPH) ranged from about 300 to 7000 mgm(-3) and gas was injected at velocities of 6 and 15 mh(-1) (empty bed residence time (EBRT)=10 and 4 min, respectively). The maximum elimination capacities of TPH at 6 and 15 mh(-1) found in this research were over 24 and 19 gm(-3) of filling material h(-1), respectively. TPH removal data was fit using a first-order kinetic relationship. In the low concentration range of 300-3000 mg m(-3), the first-order kinetic constants varied between about 0.10 and 0.29 min(-1) regardless of gas velocities. At TPH concentrations greater than 3000 mgm(-3), the first-order kinetic constants were about 0.09 and 0.07 min(-1) at gas velocities of 6 mh(-1) and 15 mh(-1), respectively. To evaluate microbial dynamics, dehydrogenase activity, CO2 generation and microbial species diversity were analyzed. Dehydrogenase activity could be used as an indicator of microbial activity. TPH removal corresponded well with CO2 evolution. The average CO2 recovery efficiency for the entire biofilter ranged between 60% and 70%. When the gas velocity was 6 mh(-1), most of the microbial activity and TPH removal occurred in the first quarter of the biofilter. However, when the gas velocity was 15 mh(-1), the entire column contributed to removal. Spatial and temporal variations in the biofilter microbial population were also observed. Nearly 60% of the colonies isolated from the compost media prior to biofiltration were Bacillus. After 90 days of biofiltration, the predominant species in the lower portion (0-50 cm) of the filter were Rhodococcus, while Pseudomonas and Acinetobacter dominated the upper portion (75-100 cm).     

A hybrid biological process of indoor air treatment for toluene removal

Bioprocesses, such as biofiltration, are commonly used to treat industrial effluents containing volatile organic compounds (VOCs) at low concentrations. Nevertheless, the use of biofiltration for indoor air pollution (IAP) treatment requires adjustments depending on specific indoor environments. Therefore, this study focuses on the convenience of a hybrid biological process for IAP treatment. A biofiltration reactor using a green waste compost was combined with an adsorption column filled with activated carbon (AC). This system treated a toluene-micropolluted effluent (concentration between 17 and 52 µg/m³), exhibiting concentration peaks close to 733 µg/m³ for a few hours per day. High removal efficiency was obtained despite changes in toluene inlet load (from 4.2 × 10^?3 to 0.20 g/m³/hr), which proves the hybrid system’s effectiveness. In fact, during unexpected concentration changes, the efficiency of the biofilter is greatly decreased, but the adsorption column maintains the high efficiency of the entire process (removal efficiency [RE] close to 100%). Moreover, the adsorption column after biofiltration is able to deal with the problem of the emission of particles and/or microorganisms from the biofilter.

ImplicationsIndoor air pollution is nowadays recognized as a major environmental and health issue. This original study investigates the performance of a hybrid biological process combining a biofilter and an adsorption column for removal of indoor VOCs, specifically toluene.     

Biotreatment of H2S- and NH3-containing waste gases by co-immobilized cells biofilter

Gas mixture of H2S and NH3 in this study has been the focus in the research area concerning gases generated from the animal husbandry and the anaerobic wastewater lagoons used for their treatment. A specific microflora (mixture of Thiobacillus thioparus CH11 for H2S and Nitrosomonas europaea for NH3) was immobilized with Ca-alginate and packed inside a glass column to decompose H2S and NH3. The biofilter packed with co-immobilized cells was continuously supplied with H2S and NH3 gas mixtures of various ratios, and the removal efficiency, removal kinetics, and pressure drop in the biofilter was monitored. The results showed that the efficiency remained above 95% regardless of the ratios of H2S and NH3 used. The NH3 concentration has little effect on H2S removal efficiency, however, both high NH3 and H2S concentrations significantly suppress the NH3 removal. Through product analysis, we found that controlling the inlet ratio of the H2S/NH3 could prevent the biofilter from acidification, and, therefore, enhance the operational stability. Conclusions from bioaerosol analysis and pressure drop in the biofilter suggest that the immobilized cell technique creates less environmental impact and improves pure culture operational stability. The criteria for the biofilter operation to meet the current H2S and NH3 emission standards were also established. To reach Taiwan's current ambient air standards of H2S and NH3 (0.1 and 1 ppm, respectively), the maximum inlet concentrations should not exceed 58 ppm for H2S and 164 ppm for NH3, and the residence time be kept at 72 s.     

Effects of residence time distribution and packing on methanol oxidation in biotrickling filter

The effects of residence time distribution (RTD) on biotrickling filter systems and the comparison of the maximum elimination capacity (EC) and poisoning limits as functions of loadings of two packing media, Celite Biocatalyst Carrier R-635 and a subituminous coal, were studied. To alter the RTD patterns in the two reactor columns, two baffle designs were chosen. The RTD tests were done under dry conditions, over a range of airflow rates, with zero baffle, one baffle, and two baffles added into each column. Mixed culture from compost was used to acclimate the bed for the methanol removal efficiency study. No nutrients were added in the coal column. To study the poisoning limit, the inlet methanol concentration was randomly increased until a severe drop in removal efficiency occurred. From the RTD tests and the removal efficiency runs, which did not result in 100% conversion, number of tank-in-series (N) values, maximum EC values, and rate constants of each column with different baffle configurations could be obtained. Results from duplicate runs showed that addition of baffles decreased the N values of the columns and increased the back mixing in both systems. Maximum EC values, critical loadings, and poisoning limits also increased with increasing back mixing. Coal was superior to Celite Biocatalyst Carrier R-635 because it gave good conversions without additional nutrients. In all runs, the rate of methanol removal was controlled by a zero order process.     

Removal of low concentrations of carbon tetrachloride in compost-based biofilters operated under methanogenic conditions.

Research was performed to demonstrate the removal of carbon tetrachloride (CT) using compost biofilters operated under methanogenic conditions. Biofilters were operated at an empty-bed residence time of 2.8 minutes using nitrogen as the atmosphere. Hydrogen and carbon dioxide were supplied as an electron donor and carbon source, respectively, during acclimation of the bed medium microbes. Once methanogenesis was demonstrated, CT flow to the biofilter was established. Biofilters were operated over a CT concentration range from 20 to 700 ppbv for 6 months. Bed medium microbes were able to remove up to 75% of the inlet CT. At excessively high CT concentrations (> 500 ppmv), methane production and hydrogen utilization by the bed medium microbes appeared to be inhibited. CT removal by the biofilter decreased when the hydrogen supply was removed from the biofilter inlet, indicating that hydrogen acted as the electron donor for reductive dechlorination. The removal efficiency and relatively low empty bed residence times demonstrated by these laboratory-scale biofilters indicate that anaerobic biofiltration of CT may be a feasible full-scale process.     

VOC elimination in a compost biofilter using a previously acclimated bacterial inoculum.

A comparison of biodegradation efficiencies was done for volatile benzene, toluene, ethylbenzene, m-xylene, p-xylene, and o-xylene elimination in a compost biofilter. The column was first exposed to a synthetic mixture and then a free phase product mixture containing these compounds at increasing pollutant loads. The optimal moisture content of the system was determined, and this was used in the biodegradation experiments. An acclimated culture was used as an inoculum for the biofilter, the matrix of which consisted of composted forestry products, composted sewage sludge, lime, and perlite. Inlet and outlet concentrations were measured, and pollutant loads, elimination capacities, and removal efficiencies were determined for each of the compounds. Optimal moisture content for this system was found to be 40%, and the short lag times (one to five days) in acclimating to the compounds was ascribed to the presence of the well-acclimated inoculum. The compounds in the synthetic mixture had higher removal efficiencies (80-99%) even at the higher pollutant loads experienced, with the exception of o-xylene. Dynamic removal efficiencies and acclimation periods were seen in the free phase product mixture, with a removal efficiency range from 70 to 95%. This was attributed to the presence of chlorinated aliphatics in the free phase product.     

Sulfur Toxicity and Media Capacity for H2S Removal in Biofilters Packed with a Natural or a Commercial Granular Medium

Abstract

Two types of media, a natural medium (wood chips) and a commercially engineered medium, were evaluated for sulfur inhibition and capacity for removal of hydrogen sulfide (H₂S). Sulfate was added artificially (40, 65, and 100 mg of S/g of medium) to test its effect on removal efficiency and the media. A humidified gas stream of 50 ppm by volume H₂S was passed through the media-packed columns, and effluent readings for H₂S at the outlet were measured continuously. The overall H₂S baseline removal efficiencies of the column packed with natural medium remained >95% over a 2-day period even with the accumulated sulfur species. Added sulfate at a concentration high enough to saturate the biofilter moisture phase did not appear to affect the H₂S removal process efficiency. The results of additional experiments with a commercial granular medium also demonstrated that the accumulation of amounts of sulfate sufficient enough to saturate the moisture phase of the medium did not have a significant effect on H₂S removal.

When the pH of the biofilter medium was lowered to 4, H₂S removal efficiency did drop to 36%. This work suggests that sulfate mass transfer through the moisture phase to the biofilm phase does not appear to inhibit H₂S removal rates in biofilters. Thus, performance degradation for odor-removing biofilters or H₂S breakthrough in field applications is probably caused by other consequences of high H₂S loading, such as sulfur precipitation.     

Ethylbenzene removal in a multiple-stage biofilter

In practice, biofilters are often conceived as entire, single-unit systems. However, the activity of a biofilter varies greatly over its depth. For a given period, each stage of the biofilter dominates ethylbenzene removal. Ethylbenzene was continuously removed in a mixed-medium biofilter. The overall removal efficiency of the ethylbenzene ranged from 70% to greater than 99%. In the upflow biofilter, the most dominant ethylbenzene degrading stage shifted consecutively from the bottom to the top of the reactor. Average water content throughout the biofilter media was relatively consistent. However, the water content of each stage fluctuated dramatically and was correlated with the ethylbenzene removal rate. Without any water addition, the biofilter was operated for 62 days above the target removal efficiency of 80%. A 9-month slow-release fertilizer, mixed with composting media, was an effective way to eliminate the nutrient deficiency in the biofilter operation.