Biomass Control via UV Lamp Application and Nutrient Supply Restriction in the Biofiltration of Gaseous VOCs

Biofiltration may have clogging problems owing to excess biomass growth during the treatment of gaseous pollutants.In this study,we employed an UV(Ultraviolet)lamp and controlled the nutrient supply to conduct a biofiltration process for treating 2-butanone(MEK:Methyl Ethyl Ketone)and toluene in a gas stream.Two methods of UV lamp usage(direct and indirect irradiation)and several nutrient supply methods were tested.However,no clear effect was observed with either UV usage.Under the optimal conditions,97%of the MEK and 69%of the toluene gases were removed after 29 s of EBRT(Empty Bed Retention Time).The inlet loads were 18 and 19 mg/(m^(3)·h)for MEK and toluene,respectively.Under these conditions,23 g-N/(m^(3)·day)of nitrate-nitrogen was consumed.Excess biomass growth occurred during simultaneous excess nutrient supply and a persistent irrigation schedule.In this study,we demonstrated the effective use of a dense nitrate solution to deliver an appropriate amount of nutrients and moisture,and the optimal irrigation frequency was four times per week.

Performance of rotating drum biofilter for volatile organic compound removal at high organic loading rates

Uneven distribution of volatile organic compounds （VOCs） and biomass, and excess biomass accumulation in some biofilters hinder the application of biofiltration technology. An innovative multilayer rotating drum biofilter （RDB） was developed to correct these problems. The RDB was operated at an empty bed contact time （EBCT） of 30 s and a rotational rate of 1.0 r/min. Diethyl ether was chosen as the model VOC. Performance of the RDB was evaluated at organic loading rates of 32,1, 64.2, 128, and 256 g ether/（m^3·h） （16.06 g ether/（m^3·h） ≈ 1.0 kg chemical oxygen demand （COD）/（m^3·d））. The EBCT and organic loading rates were recorded on the basis of the medium volume. Results show that the ether removal efficiency decreased with an increased VOC loading rate. Ether removal efficiencies exceeding 99% were achieved without biomass control even at a high VOC loading rate of 128 g ether/（m^3·h）. However, when the VOC loading rate was increased to 256 g ether/（m^3·h）, the average removal efficiency dropped to 43%. Nutrient limitation possibly contributed to the drop in ether removal efficiency. High biomass accumulation rate was also observed in the medium at the two higher ether loading rates, and removal of the excess biomass in the media was necessary to maintain stable performance. This work showed that the RDB is effective in the removal of diethyl ether from waste gas streams even at high organic loading rates. The results might help establish criteria for designing and operating RDBs.

Modeling the formation of soluble microbial products(SMP) in drinking water biofiltration

Both a theoretical and an empirical model were developed for predicting the formation of soluble microbial products （SMP） during drinking water biofiltration. Four pilot-scale biofilters with ceramsite as the medium were fed with different acetate loadings for the determination of SMP formation. Using numerically simulated and measured parameters, the theoretical model was developed according to the substrate and biomass balance. The results of this model matched the measured data better for higher SMP formation but did not fit well when SMP formation was lower. In order to better simulate the reality and overcome the difficulties of measuring the kinetic parameters, a simpler empirical model was also developed. In this model, SMP formation was expressed as a function of fed organic loadings and the depth of the medium, and a much better fit was obtained.

Performance of two biofilters with neutral and low pH treating off-gases

Two different functional biofilters were carried out and compared for the treatment of off-gas containing multicomponent odors and volatile organic compounds (VOCs) in this study. The effects of pH values and the empty bed retention time (EBRT) on the performance of the bioreactors were studied; and the characteristics of microbial populations in the two biofilters were also determined. The experimental results indicated that the removal effciencies of hydrophilic compounds such as butyric acid and ammonia ...

Removal of eutrophication factors and heavy metal from a closed cultivation system using the macroalgae,Gracilaria sp.(Rhodophyta)

In this study, the ability of macroalgae Gracilaria sp. of removing eutrophication factors and toxic heavy metals A1, Cr, and Zn in a closed cultivation system is reported. The results show that the concentration of the three heavy metals decreased significantly during the experimental period in an algal biomass dependent manner. The biofiltration capacity of the alga for A1, Cr, and Zn is 10.1%-72.6%, 52.5%-83.4% and 36.5%,91.7%, respectively. Using more materials resulted in stronger heavy metal removal. Additionally, the concentration of chl-a, TN, TP and DIN of water samples fxom aquariums involving large, medium, and small algal biomass cultivation increased first and then decreased during the experiment. COD value of all three groups decreased with time and displayed algal biomass dependency： more algae resulting in a greater COD value than those of less biomass. Furthermore, changes in COD reflect an obvious organic particles deprivation process of algae. This is the first report on heavy metal removal effect by Gracilaria species. The results suggest that macroalgae can be used as a biofilter for the treatment of nutrient-enriched or heavy-metal polluted water, to which an appropriate time range should be carefully determined.

Relationship between Moisture Behavior and Gaseous Volatile Organic Compounds Removal in a Biofiltration System

Studies on the relationship between moisture behavior and gaseous VOCs （Volatile Organic Compounds） removal efficiency of packed tower biofilters are limited. In this research, the nutrient holding capacity, moisture evaporation rate and gaseous toluene and MEK （Methyl Ethyl Ketone） removal efficiencies of bioreactors with porous synthetic resin as the packing material were simultaneously observed. The nutrient holding capacity in one of the reactors was higher than those of the other two because its packing layer was frequently supplied with a nutrient solution by soaking. This reactor exhibited the highest toluene removal efficiency. However, excessive biomass growth was observed in this reactor. The reactor with a less frequent supply of nutrient solution by soaking showed a slightly lower toluene removal efficiency, possibly due to lack of nutrients in the packing layer. The reactor that was fed with the nutrient solution by spraying it onto the packing layer （a common method for supplying moisture） had the lowest toluene removal efficiency, mainly because of the uneven distribution of nutrients. Moreover, the moisture evaporation rate in the packing layer during moisture supply and heat balance were determined.

Soil-Based Biofiltration for Air Purification:Potentials for Environmental and Space LifeSupport Application

Soil biofiltration, also known as soil bed reactor (SBR), technology was originally developed in Germany to take advantage of the diversity in microbial mechanisms to control gases producing malodor in industrial processes. The approach has since gained wider international acceptance and continues to see improvements to maximize microbial and process efficiency and extend the range of problematical gases for which the technology can be an effective control. We review the basic mechanisms which underlay microbial soil processes involved in air purification, advantages and limitations of the technology and the current research status of the approach. Soil biofiltration has lower capital and operating/energetic costs than conventional technologies and is well adapted to handle contaminants in moderate concentrations. The systems can be engineered to optimize efficiency though manipulation of temperature, pH, moisture content, soil organic matter and airflow rates. Soil air biofiltration technology was modified for application in the Biosphere 2 project, which demonstrated in preparatory research with a number of closed system testbeds that soil could also support crop plants while also serving as soil filters with airpumps to push air through the soil. This Biosphere 2 research demonstrated in several closed system testbeds that a number of important trace gases could be kept under control and led to the engineering of the entire agricultural soil of Biosphere 2 to serve as a soil filtration unit for the facility. Soil biofiltration, coupled with food crop production, as a component of bioregenerative space life support systems has the advantages of lower energy use and avoidance of the consumables required for other air purification approaches. Expanding use of soil biofiltration can aid a number of environmental applications, from the mitigation of indoor air pollution, as a method of reducing global warming impact of methane (biogas), improvement of industrial air emissions and prevention of accidental release of toxic gases.

Improving Removal Efficiency of Organic Matters by Adding Phosphorus in Drinking Water Biofiltration Treatment

Objective To investigate phosphorus limitation and its effect on the removal efficiency of organic matters in drinking water biological treatment. Methods Bacterial growth potential (BGP) method and a pair of parallel pilot-scale biofilters were used for the two objectives, respectively. Results The addition of phosphorus could substantially increase the BGPs of the water samples and the effect was stronger than that of the addition of carbon. When nothing was added into the influents, both CODMn removals of the parallel biofilters (BF1 and BF2) were about 15%. When phosphate was added into its influent, BF1 performed a CODMn removal, 6.02 percentage points higher than the control filter (BF2) and its effluent had a higher biological stability. When the addition dose was <20μg. L-1, no phosphorus pollution would occur and there was a good linear relationship between the microbial utilization of phosphorus and the removal efficiency of organic matters. Conclusions Phosphorus was a limiting nutrient and its limitation was stronger than that of carbon. The addition of phosphate was a practical way to improve the removal efficiency of organic matters in drinking water biological treatment.

Modification of Grey Water Treatment Using Combination of Cascade Aeration and Biofiltration

A combination of cascade aeration and biofiltration systems is one of the available ecological treatments to reduce the concentration of pollutants in grey water and resolve the problem of acute water crisis supply in Iraq. An experimental constructed grey water treatment system has been installed at AI-Mustansiriya University, College of Engineering during the period from January to December 2012. The performance of the treatment schemes has been evaluated by monitoring the quality of the raw grey water and effluent on these samples which are： pH, COD （chemical oxygen demand）, TSS （total suspended solids）, TDS （total dissolved solids）, PO43 （phosphates）, NO32 （nitrates）, NO （nitrites）, oils ＆ grease, NH3-N （ammonia-nitrogen） and some anions and cations. The average removal rate of COD was more than 60% that of NH3-N, NO3-N, NO2-N, TDS and TSS that were 55%-89%, 59%-74%, 79%-98%, 17%-52% and 51%-87%, respectively. Also the results indicate that the removal efficiency of ions concentrations such as Ca2＋, Mg2＋, Na＋, K＋ were 78%-96%, 73%-97%, 14%-47% and 44%-64%, respectively, while for cations such as SO42, Cl and PO43-, the removal efficiencies were 33%-79%, 27%-61% and 81%-99%, respectively. Finally oils ＆ grease was 79%-88%.

Role of Fungal Biomass in N-Hexane Biofiltration

The biofiltration of n-hexane is studied to optimize determinants factors of hydrophobic VOC filtration efficiency. Four trickle-bed air biofilters (TBABs) were employed;two of which were supplied with nutrients buffered at a neutral pH, while another two at an acidic pH of 4 to induce and enhance fungal growth. The loading rate of n-hexane was kept constant in all TBABs at 13 g/m3/h. At each pH levels studied, the biomass of the TBABs was pre-acclimated using different ratios of n-hexane and methanol. The fungal biomass responsible for the degradation of n-hexane was then examined and quantified. Dichloran Rose Bengal Chloramphenicol agar was used for fungi quantification, and optical microscopy for classification. Effluent biomass was validated by measuring volatile suspended solids. Fungal counts resulting from n-hexane biodegradation were related to nitrate and carbon consumption. It was found that n-hexane elimination capacity closely followed biomass growth, and reached a steady-state at an optimum biomass density of roughly 3000 cfu/ml. Major shifts in fungal species were observed in all TBABs. Dominant fungal species grew slowly to become the most numerous, and were found to provide maximum elimination capacity, although TBABs pre-acclimated to higher methanol concentrations took less time to reach this steady-state. It was concluded, therefore, that steady and monitored growth of TBAB biomass is an essential factor in maximizing fungi’s ability to metabolize VOCs and that a new ecological biofiltration model may be the most effective at VOC purification.

Purification Potential of Local Media in the Pre-Treatment of Greywater Using Vertical Biofilters under Sahelian Conditions

Several on-site greywater treatment systems are under development including biofiltration, whose efficiency is influenced by the filter media. Therefore, the main objective of this study was to evaluate the influence of the type of filter media and their grain size in the removal of organic and microbial pollutants from greywater. Hence, three types of local filter media of different grain size were used for the pre-treatment of greywater. Their removal potential and clogging time were evaluated and compared. The results indicated that the type of filter media and the grain size have an influence on the elimination of organic and microbial pollution from greywater. Indeed, sand of 1 - 2 mm in size obtained the highest removal efficiencies of organic pollutants (67.35% and 78.04% for COD and BOD5 respectively) and microbial indicators (2.07, 1.77 and 2.27 log. units for E. coli, fecal coliforms and enterococci respectively). Although media of fine texture enhanced the removal efficiencies, they experienced significant clogging problems. To overcome these limitations while enhancing the removal efficiency, 1) pre-treatment stage with coarse materials followed by a treatment with finer materials or 2) the use of a combination of fine and coarse materials should be considered.

INDOOR AIR QUALITY(IAQ)IMPROVEMENTS USING BIOFILTRATION IN A HIGHLY EFFICIENT RESIDENTIAL HOME

INTRODUCTION Americans spend the majority of their time indoors where levels of pollutants may run two to five times-and occasionally more than 100 times-higher than outdoor levels[1].Many of these pollutants can cause adverse health reactions in building occupants,which can contribute to lower worker productivity and increased sick leave.Traditional methods of indoor pollutant control in sealed buildings involve the use of outdoor ventilation.Outdoor ventilation requires the intake of outdoor air,which must be heated or cooled to meet indoor temperature and humidity requirements.This represents between 10-20%of the total energy consumption of a building[2].

Performance of biotrickling filters packed with structured or cubic polyurethane sponges for VOC removal

Two identical bench-scale biotrickling filters （BTFs）, BTF 1 and BTF 2, were evaluated for toluene removal at various gas empty bed contact times （EBCTs） and organic loadings. BTF 1 and BTF 2 were packed with structured and cubic synthetic polyurethane sponges, respectively. At a constant toluene loading of 16 g/（m3.hr）, toluene removal efficiencies decreased from 98.8% to 64.3% for BTF 1 and from 98.4% to 74.1% for BTF 2 as gas EBCT decreased from 30 to 5 sec. When the toluene loading increased from 35 to 140 g/（m3.hr） at a gas EBCT of 30 sec, the removal efficiencies decreased from 99.1% to 77.4% for BTF 1 and from 99.0% to 81.5% for BTF 2. The pressure drop for both BTFs increased with increased air flow rate, and did not significantly vary while the toluene loading was increased under similar operation conditions. BTF 1 and BTF 2 could start up successfully within 19 and 27 days, respectively, when packed with fresh sponge media, and the performances could be restored in 3-7 days after biomass was removed and wasted from the media. BTF 2 displayed higher removal efficiency even under shorter EBCT or higher loading rate than BTF1 when other operation conditions were similar, while it showed lower pressure drop than BTF 1 during the whole period of operation. These results demonstrated that both BTFs could treat waste gas containing toluene effectively.

Combined process of biofiltration and ozone oxidation as an advanced treatment process for wastewater reuse

The effluent of a wastewater treatment plant was treated in a pilot plant for reclaimed water production through the denitrification biofilter （DNBF） process, ozonation （O3）, and biologic aerated filtration （BAF）. The combined process demonstrated good removal performance of conventional pollutants, including con- centrations of chemical oxygen demand （27.8 mg·L^-1） and total nitrogen （9.9 mg·L^-1） in the final effluent, which met the local discharge standards and water reuse purposes. Micropollutants （e.g., antibiotics and endocrine-disrupting chemicals） were also significantly removed during the proposed process. Ozonation exhibited high antibiotic removal efficiencies, especially for tetracycline （94%）. However, micropollutant removal efficiency was nega- tively affected by the nitrite produced by DNBF. Acute toxicity variations of the combined process were estimated by utilizing luminescent bacteria. Inhibition rate increased from 9% to 15% during ozonation. Carbonyl compound concentrations （e.g., aldehydes and ketones） also increased by 58% as by-products, which consequently increased toxicity. However, toxicity eventually became as low as that of the influent because the by-products were effectively removed by BAR The combined DNBF/O3/ BAF process is suitable for the advanced treatment of reclaimed water because it can thoroughly remove pollutants and toxicity.

Biofiltration and disinfection codetermine the bacterial antibiotic resistome in drinking water:A review and meta-analysis

The bacterial antibiotic resistome(BAR)is one of the most serious contemporary medical challenges.The BAR problem in drinking water is receiving growing attention.In this study,we focused on the distribution,changes,and health risks of the BAR throughout the drinking water treatment system.We extracted the antibiotic resistance gene(ARG)data from recent publications and analyzed ARG profiles based on diversity,absolute abundance,and relative abundance.The absolute abundance of ARG was found to decrease with water treatment processes and was positively correlated with the abundance of 16S rRNA(r=0.963,/?<0.001),indicating that the reduction of ARG concentration was accompanied by decreasing biomass.Among treatment processes,biofiltration and chlorination were discovered to play important roles in shaping the bacterial antibiotic resistome.Chlorination exhibited positive effects in controlling the diversity of ARG,while biofiltration,especially granular activated carbon filtration,increased the diversity of ARG.Both biofiltration and chlorination altered the structure of the resistome by affecting relative ARG abundance.In addition,we analyzed the mechanism behind the impact of biofiltration and chlorination on the bacterial antibiotic resistome.By intercepting influent ARG-carrying bacteria,biofilters can enrich various ARGs and maintain ARGs in biofilm.Chlorination further selects bacteria co-resistant to chlorine and antibiotics.Finally,we proposed the BAR health risks caused by biofiltration and chlorination in water treatment.To reduce potential BAR risk in drinking water,membrane filtration technology and water boiling are recommended at the point of use.

Removal of odors and VOCs in municipal solid waste comprehensive treatment plants using a novel three-stage integrated biofilter:Performance and bioaerosol emissions

A novel three-stage integrated biofilter(TSIBF)composed of acidophilic bacteria reaction segment(ABRS),fungal reaction segment(FRS)and heterotrophic bacteria reaction segment(HBRS)was constructed for the treatment of odors and volatile organic compounds(VOCs)from municipal solid waste(MSW)comprehensive treatment plants.The performance,counts of predominant microorganisms,and bioaerosol emissions of a flill-scale TSIBF system were studied.High and stable removal efficiencies of hydrogen sulfide,ammonia and VOCs could be achieved with the TSIBF system,and the emissions of culturable heterotrophic bacteria,fungi and acidophilic sulfur bacteria were relatively low.The removal efficiencies of different odors and VOCs,emissions of culturable microorganisms,and types of predominant microorganisms were different in the ABRS,FRS and HBRS due to the differences in reaction conditions and mass transfer in each segment.The emissions of bioaerosols from the TSIBF depended on the capture of microorganisms and their volatilization from the packing.The rational segmentation,filling of high-density packings and the accumulation of the predominant functional microorganisms in each segment enhanced the capture effect of the bioaerosols,thus reducing the emissions of microorganisms from the bioreactor.

Evaluation of co-metabolic removal of trichloroethylene in a biotrickling filter under acidic conditions

This study investigated the removal of hydrophobic trichloroethylene（TCE） in the presence of methanol（co-metabolite） in a biotrickling filter,which was seeded with fungi at pH 4.Starvation was chosen as the biomass control strategy.Two systems,Biofilter I（methanol：TCE 70：30） and Biofilter II（methanol：TCE 80：20） were run in parallel,each with varying composition ratios.The TCE loading rates for both biofilters ranged from 3.22 to 12.88 g/m^3/hr.Depending on the ratio,methanol concentrations varied from 4.08 to 27.95 g/m^3/hr.The performance of the systems was evaluated and compared by calculating removal kinetics,carbon mass balance,efficiencies and elimination capacities.Methanol was observed to enhance TCE removal during the initial loading rate.However,methanol later inhibited TCE degradation above 6.44 g TCE/m^3/hr（Biofilter I） and 3.22 g TCE/m^3/hr（Biofilter II）.Conversely,TCE did not impede methanol removal because over 95% methanol elimination was consistently achieved.Overall,Biofilter I was able to outperform Biofilter II due to its greater resistance towards methanol competition.

Removal of multicomponent VOCs in off-gases from an oil refining wastewater treatment plant by a compost-based biofilter system

Waste gases from oil refining wastewater treatment plants are often characterized by the presence of multicomponent and various concentrations of compounds.An evaluation of the performance and feasibility of removing multicomponent volatile organic compounds(VOCs)in off-gases from oil refining wastewater treatment plants was conducted in a pilot-scale compost-based biofilter system.This system consists of two identical biofilters packed with compost and polyethylene(PE).This paper investigates the effects of various concentrations of nonmethane hydrocarbon(NMHC)and empty bed residence time(EBRT)on the removal efficiency of NMHC.Based on the experimental results and practical applications,an EBRT of 66 s was applied to the biofilter system.The removal efficiencies of NMHC were within the range of 47%–100%.At an EBRT of 66 s,the average removal efficiency of benzene,toluene,and xylene were more than 99%,99%,and 100%,respectively.The results demonstrated that multicomponent VOCs in off-gases from the oil refining wastewater treatment plant could be successfully removed in the biofilter system,which may provide useful information concerning the design criteria and operation of full-scale biofilters.