Biofilter Operation Research Articles

Inhibition of disinfection byproducts formation and microbial stress responses by Cu-Al/coconut shell activated carbon biofiltration: The key role of Al species

The effects of biological activated carbon treatment using CuAl bimetallic modified coconut shell activated carbon (CAAC) were investigated on the formation of disinfection by-products (DBPs) and microbial stress responses with unmodified granular coconut shell activated carbon (GAC) as a reference. In the long-term biological filtration process, the formation potentials of trihalomethanes and haloacetic acids in the effluent of CAAC filter (ACW) was reduced by 63.58 % compared to the effluent of GAC filter (CW). After the 6th day of biofilter operation, the dissolved organic carbon concentration of ACW rapidly decreased to around 1.03 mg/L and was consistently lower than that of CW. Under the enhanced biological flocculation by Al species, the extracellular polymeric substances (EPS) on the CAAC surface exhibited higher content and stronger flocculation efficiency, making the biofilm denser and more difficult to detach into ACW. In addition, the developed biofilms on CAAC surface promoted the biodegradation of organic compounds including DBPs precursors. Interestingly, the coexistence of Cu and Al mitigated the stimulatory effect of Cu, resulting in less intracellular reactive oxygen species and EPS. Our findings revealed that as a biofilter carrier filler, CAAC can effectively improve water quality and continuously control the risk of DBPs in the subsequent transmission and distribution process. More importantly, the introduction of Al species can provide new ideas to promote the realistic application of various modified treatment materials that are stressful to microorganisms.

Technical solution for purifying emissions of climate-active gases

The rising demand for food products and subsequent increase in agricultural production leads to heightened quantities of waste and by-products, particularly within the livestock industry. Traditional methods of livestock by-product disposal encompass intensive processing, including biodestruction processes. However, these processes tend to generate significant emissions of climate-active gases such as carbon dioxide, methane, nitrous oxide, and ammonia. To mitigate environmental impacts, it is proposed to integrate an advanced gas-air emission purification system into the existing livestock by-product processing lines. (Research purpose) The objective is to develop a system for purifying emissions of climate-active gases, particularly ammonia, produced during the intensive biotechnological processing of livestock by-products. (Materials and methods) Based on the properties of the primary pollutants, possible methods for their removal from emissions were determined. Such methods include dry, wet, condensation, and biological treatment. The biopurification method was selected for its efficacy and optimal performance. (Results and discussion) As a technical solution, a sequential gas-air emission purification process was developed using biofilters equipped with a polymer carrier and organic substrates as fillers. The system is equipped with digital sensors for monitoring and controlling the operational workflow. A special feature of the proposed system design is the use of replaceable filter cartridges and an active irrigation system. (Conclusions) The research helped to identify main types, parameters and methods for purifying emissions of climate-active gases with a focus on ammonia. Emission purification with a digital workflow control system is carried out sequentially in a shell-and-tube condenser and a biofilter. The specific cooling surface is 1.09∙10–3 square meters per 1 cubic meter, the specifi c refrigerant consumption is 0.7 liters per 1 cubic meter. Optimal biofilter performance was attained at the temperature of 30 degrees Celsius, with 45-55 percent humidity, active acidity of 8-8.4 units, and residence time of 15-30 seconds in the filter layer. These conditions ensure a high degree of ammonia purification and long-term biofilter operation.

IoT Water Quality Monitoring and Control System in Moving Bed Biofilm Reactor to Reduce Total Ammonia Nitrogen.

Traditional aquaculture systems appear challenged by the high levels of total ammoniacal nitrogen (TAN) produced, which can harm aquatic life. As demand for global fish production continues to increase, farmers should adopt recirculating aquaculture systems (RAS) equipped with biofilters to improve the water quality of the culture. The biofilter plays a crucial role in ammonia removal. Therefore, a biofilter such as a moving bed biofilm reactor (MBBR) biofilter is usually used in the RAS to reduce ammonia. However, the disadvantage of biofilter operation is that it requires an automatic system with a water quality monitoring and control system to ensure optimal performance. Therefore, this study focuses on developing an Internet of Things (IoT) system to monitor and control water quality to achieve optimal biofilm performance in laboratory-scale MBBR. From 35 days into the experiment, water quality was maintained by an aerator's on/off control to provide oxygen levels suitable for the aquatic environment while monitoring the pH, temperature, and total dissolved solids (TDS). When the amount of dissolved oxygen (DO) in the MBBR was optimal, the highest TAN removal efficiency was 50%, with the biofilm thickness reaching 119.88 μm. The forthcoming applications of the IoT water quality monitoring and control system in MBBR enable farmers to set up a system in RAS that can perform real-time measurements, alerts, and adjustments of critical water quality parameters such as TAN levels.

Assessing macroscopic and microscopic performance of fungal-based biofilters for methane abatement

Fungi have recently been shown to increase the performance of biofiltration in removing hydrophobic compounds like methane (CH4). The effectiveness of fungal-based biofiltration for treating low-concentrated (2% v/v) CH4 emissions was assessed in three biofilters (BFs) packed with expanded clay or compost and inoculated with fungal strains. The BFs were operated under different conditions of empty bed residence time (EBRT), pH of the mineral medium and irrigation. No CH4 removal was recorded in the BF inoculated with Candida subhashii and packed with expanded clay. Similarly, low CH4 abatement performances were observed for BF-1 and BF-2 inoculated with Fusarium solani and packed with expanded clay, with maximum removals of ∼36% when irrigated with MSM at a pH of 7 and operated at an EBRT of 42 min. Opposite, BF-3 packed with compost and inoculated with F. solani achieved average removals ranging from 80.3% (EC of 19 g m−3 h−1) at an EBRT of 34 min to 52.0% (EC of 22 g m−3 h−1) when decreasing the EBRT to 18 min. Amplicon metagenomics showed that CH4-degrading bacteria natural of compost were representative in BF-3. It also showed the importance of biostimulation in biofiltration for promoting methanotrophic growth. The fungal characterization revealed that a key factor on fungal BFs is the dominant fungi present. In this sense, Fusarium and clade LKM11 promoted methanotrophic growth. This knowledge can be applied to the operation of fungal BFs subjected to the treatment of CH4 via controlled bioaugmentation and biostimulation.

Establishment and optimization of sulfur-based autotrophic-heterotrophic denitrification biofilters for advanced post-anaerobic treatment of effluent from kitchen wastewater and landfill leachate under low temperature

Landfill leachate treatment is a major challenge in wastewater treatment. In this study, two sulfur-based autotrophic-heterotrophic denitrification biofilters (Ra biofilter with room-temperature molded filler and Rb biofilter with melt molded filler) were used to treat kitchen-landfill leachate at low temperatures. The effects of reflux ratio, concentrations of NaHCO3, and Na2S2O3 on the total nitrogen removal efficiency were analyzed, and based on response surface methodology, the optimum parameters were determined. After optimization, the total nitrogen removal efficiency for the Ra and Rb biofilters increased by 83% and 81%, respectively. Moreover, sulfur-based autotrophic denitrification accounted for more than 70% of the nitrogen removal in both biofilters. Based on high-throughput sequencing results, the functional bacteria exhibited high abundance in the Ra biofilter, indicating that the room-temperature molded filler favored the enrichment of functional bacteria. These findings were important for optimizing the operation of sulfur autotrophic-heterotrophic denitrification biofilters at low temperatures.

Bioaerosols released from multistage biofilter for gaseous benzene removal: Escape behavior and pathogenicity

Biological deodorization systems are widely used to control odors and volatile organic compounds. However, the secondary contamination of bioaerosol emissions is a noteworthy issue in the operation of biofilters for off-gas purification. In this study, a multistage biofilter for benzene treatment was utilized to investigate the bioaerosol emissions under different flow rates and spray intervals. At the outlet of the biofilter, 99–7173 CFU/m3 of bioaerosols were detected, among which pathogens accounted for 8.93–98.73 %. Proteobacteria and Firmicutes dominated bioaerosols at the phylum level. The Mantel test based on the Bray-Curtis distance revealed strong influences of flow rate introduced to the biofilter and biomass colonized on the packing materials (PMs) on bioaerosol emissions. The non-metric multidimensional scaling results suggested a correlation between the bioaerosol community and bacteria on the PMs. Bacillus and Stenotrophomonas were the two main genera stripped from the biofilm on PMs to form the bioaerosols. SourceTracker analysis confirmed that microorganisms from the PMs near outlet contributed an average of 22.3 % to bioaerosols. Pathogenic bacteria carried by bioaerosols included Bacillus, Serratia, Stenotrophomonas, Achromobacter, Enterococcus, and Pseudomonas. Bioaerosols were predicted to cause human diseases, with antimicrobial drug resistance and bacterial infectious disease being the two main pathogenic pathways. Stenotrophomonas sp. LMG 19833, Pseudomonas sp., and Stenotrophomonas sp. were the keystone species in the bioaerosol co-occurrence network. Overall, results of present study promote the insight of bioaerosols, particularly pathogen emissions, and provide a basis for controlling bioaerosol contamination from biofilters.

Start‐up and operation of anammox biofilter in treating low‐strength ammonia wastewater prepared by tail water from a municipal wastewater treatment plant

AbstractBACKGROUNDEconomic technology of advanced nitrogen removal of municipal wastewater is urgently needed. In this study, anammox biofilter (A‐BF) as a carbon‐ and energy‐saving advanced nitrogen removal process was tested under the conditions of sewage secondary effluent.RESULTSThe results showed that A‐BF could be successfully started up under total nitrogen (TN) of both 25 and 75 mg L−1 within 30 days at 25 °C. It achieved a nitrogen removal rate of 0.62 ± 0.08 kg‐N m−3 d−1 with nitrogen loading rate of 1.35 kg‐N m−3 d−1 at TN of 17 mg L−1. The ceramsite bed was conducive to the formation of biofilm and enrichment of functional microorganisms. The volatile suspended solid reached 1.39–7.33 g L−1, in which the abundance of the typical anammox bacteria Candidatus_Brocadia and Candidatus_Kuenenia occupied 0.96–1.35% and 0.29–0.92%, respectively.CONCLUSIONSOverall, under low TN concentration and high nitrogen load, A‐BF could be a candidate technique for advanced nitrogen removal of municipal sewage. © 2023 Society of Chemical Industry.

Fixed-bed biofilter for polluted surface water treatment using chitosan impregnated-coconut husk biochar

Pelletizing biochar enables its use as a biofilter medium for polluted canal water treatment. Coconut husk biochar pellets and their modification with chitosan (CHC) were compared with conventional activated carbon pellets and gravel. The biofilter columns with these media were operated with a hydraulic loading rate of 0.1 m3/m2∙h. CHC showed the highest potential to reduce phosphate and nitrogen, via the adsorption process in the first week of filtration and later enhanced by biodegradation, to achieve removal efficiencies of 61.70 and 54.37% for these two key nutrients, respectively, over five weeks of biofilter operation. The predominant bacteria in the biofilter communities were characterized at the end of the experiments by next generation sequencing and quantitative polymerase chain reaction analysis. The biofilter communities included ammonium oxidizing, nitrite oxidizing, denitrifying, polyphosphate accumulating and denitrifying phosphate-accumulating bacteria that benefit nutrient removal. The CHC biofilter also effectively removed micropollutants, including pharmaceuticals.

Prolonged operation of a methane biofilter from acclimation to the failure stage

ABSTRACT Global warming needs immediate attention to reduce major greenhouse gas emissions such as methane (CH4). Bio-oxidation of dilute CH4 emissions in packed-bed bioreactors such as biofilters has been carried out over recent years at laboratory and large scales. However, a big challenge is to keep CH4 biofilters running for a long period. In this study, a packed-bed lab-scale bioreactor with a specialized inorganic-based filter bed was successfully operated over four years for CH4 elimination. The inoculation of the bioreactor was the active leachate of another CH4 biofilter which resulted in a fast acclimation and removal efficiency (RE) reached 80% after seven weeks of operation for CH4 inlet concentrations ranging from 700 to 800 ppmv and an empty bed residence time (EBRT) of 6 min. During four years of operation, the bioreactor often recorded REs higher than 65% for inlet concentrations in the range of 1900–2200 ppmv and an EBRT of 6 min. The rate and interval of the nutrient supply played an important role in maintaining the bioreactor’s high performance over the long operation. Forced shutdowns were unavoidable during the 4-year operation and the bioreactor fully tolerated them with a partial recovery within one week and a progressive recovery over time. In the end, the bioreactor’s filter bed started to deteriorate due to a long shutdown of twelve weeks and the extended operation of four years when the RE dropped to below 8% with no sign of returning to its earlier performance.

Изучение процесса очистки сточных вод при работе биофильтра в периодическом режиме

The article presents the study results of the performance of the experimental unit with a plastic film load working in a periodic mode of wastewater supply at high initial loads. The kinetics of the process and changes in the efficiency of wastewater treatment over time are considered. As it was revealed, an increase in the load on the bio-filter caused a corresponding increase in the rate of contaminants` removal over the entire range of tested loads, while biomass saturation with the substrate was not observed. This characterizes a high adaptive capacity of the attached biomass to high salvo loads. It is shown that the process of organic contaminants` removal on bio-filter under the conditions of periodic tests has a staged character, indicating the possibility of bio-filter operation in the modes of incomplete and complete biological treatment of wastewater, as well as for nitrification processes. The beginning of the nitrification process and its speed depended on the load on the bio-filter for organic pollution and the degree of wastewater treatment, and the change in the rate of nitrification was autocatalytic. An indicator of the non-oxidizable part of organic pollutants in wastewater is taken into consideration, which can be used in the evaluation of the bio-filter performance.

Zero additional maintenance stormwater biofilters: from laboratory testing to field implementation

Abstract Stormwater biofilters are one of the most widely used nature-based solutions for urban water management. In the last 20 years, biofilters have been extensively studied for their pollutant removal performance; however, their application in the field is limited by high maintenance requirements. In this work, we propose the concept of zero additional maintenance (ZAM) biofilters as a solution to this challenge. To understand the design and operation of ZAM biofilters, a three-stage research programme was conducted to (i) examine filter media configurations that could protect against surface clogging, (ii) test the pollutant removal performance of a variety of lawn grasses, and (iii) validate the laboratory findings through field monitoring. The results showed that a protective filter media layer delayed the onset of clogging. Five lawn grasses – Kenda Kikuyu, Empire Zoysia, Santa Ana Couch, Village Green Kikuyu and Palmetto Soft Leaf Buffalo – were found to effectively reduce nitrogen concentrations and meet other local pollution reduction requirements. Monitoring of three field-scale ZAM biofilters confirmed their high nutrient and heavy metal removal performance. Overall, the findings of these three studies confirm the potential for well-designed ZAM biofilters to achieve stormwater management requirements with no additional maintenance compared with standard street landscaping.

Performance and neural modeling of a compost-based biofilter treating a gas-phase mixture of benzene and xylene

Biofilter (BF) has been regarded as a versatile gas treatment technology for removing volatile organic compounds (VOCs) from contaminated gas streams. In order for BF to be utilized in the industrial setting, it is essential to conduct research aimed at removing VOC mixtures under different inlet loading conditions, i.e. as a function of the gas flow rate and inlet VOC concentrations. The main aim of this study was to apply artificial neural networks (ANN) and determine the relationship between flow rate (FR), pressure drop (PD), inlet concentration (C), and removal efficiency (RE) in the BF treating gas-phase benzene and xylene mixtures. The ANN model was trained and tested to assess the removal efficiency of benzene (REB) and xylene (REX) under the influence of different FR, PD and C. The model's performance was assessed using a cross-validation method. The REb varied from 20% to >60%, while the REx varied from 10% to 70% during the different experimental phases of BF operation. The causal index (CI) technique was used to determine the sensitivity of the input parameters on the output variables. The ANN model with a topology of 4-4-2 performed the best in terms of predicting the RE profiles of both the pollutants. Furthermore, the effect was more pronounced for xylene because an increase in the benzene concentration reduced xylene removal (CI = −25.7170) more severely than benzene removal. An increase in the xylene concentration had a marginally positive effect on the benzene removal (CI = +0.1178).

Inhibiting effect of quorum quenching on biomass accumulation: A clogging control strategy in gas biofilters

Controlling excessive biomass is essential for maintaining the long-term stable operation of gas biofilters. Current methods based on physical and chemical technologies can reduce removal efficiency. In this study, we developed a new method using enzymatic-quorum quenching (QQ) to simultaneously control biomass and maintain a stable removal efficiency. A 70-d biofilter operation showed that clogging was controlled with the application of enzymatic-QQ, thereby maintaining a stable operation performance. The pressure drop of the biofilter with QQ enzyme (QQBF) was 75 Pa m−1, while that of the control biofilter (BF) was 156 Pa m−1. Moreover, the biomass accumulation of QQBF was only 130.58 kg m−3, while that of BF was 218.50 kg m−3. Further analysis indicated that enzymatic-QQ decreased biofilm adhesion strength. Accordingly, the biofilm inside the QQBF detached more easily from the filler surface than that in the BF. The 16S rDNA gene sequencing results suggested that the enzymatic-QQ regulated the related functional genes, thereby changing the biofilm characteristics. Moreover, the reduced biofilm thickness and lower inactivated microbes in QQBF enhanced the metabolic activity. Overall, our results demonstrated that QQ is a promising technology for regulating biofilm characteristics and controlling the clogging of gas biofilters.

Basic Research for the Development of a Vegetation Biofilter Operation Algorithm in a Subway Station

Background and objective We measured the particulate matter (PM) reduction rate when the vegetation biofilter operated for 1 hour every 6 hours. As a result of data analysis, PM concentrations in the subway station showed a high correlation with the train stop duration depending on the service frequency of train operations, and the reduction rate was high in the section where PM concentrations as well as the change rates were high. Therefore, in order to maximize PM reduction using the biofilter, it is necessary to optimize the performance of the biofilter in various environments by designing an intelligent algorithm that takes the frequency of train operations into account. Methods We collected PM10 and PM2.5 data for 2 weeks in position 5 (POS5) and POS6. The multi-module vegetation biofilter was installed in POS6, whereas it was not in POS5. The average hourly data for PM concentrations were obtained, and the change in concentrations was analyzed every 24 hours. Results PM in subway stations is known to spread from the tracks to waiting areas as the train moves. Therefore, the change in PM concentrations by time zone has a high correlation of about 0.8 with the sum of the stop duration depending on the frequency of train operations. The vegetation biofilter is operated 4 times a day for 1 hour every 6 hours. The reduction rate reached up to 30% in 6–8 hours, where the PM concentrations increased sharply. Conclusion We came up with an algorithm to maximize the PM reduction effect by identifying the effect using the vegetation biofilter as a means for air purification in public use facilities such as subway stations. To this end, there is a need for a method that can dynamically select the section where the PM concentrations increase rapidly and set the biofilter operation time.

Denitrification performance and mechanism of biofilter constructed with sulfur autotrophic denitrification composite filler in engineering application

Sulfur autotrophic denitrification (SAD) is a promising technology due to its low cost and low sludge production. Based on previous studies on SAD materials as well as the denitrification mechanism of SAD technology, this study constructed two biofilters with a sulfur autotrophic denitrification composite filler (SADCF) to investigate the application potential of SAD technology. The feasibility of a SADCF-based biofilter was demonstrated, with a maximum nitrate volume load of 0.75 kg N/(m3·d) and low accumulation of nitrite and ammonium. In addition, an improved backwashing method (air–water backwashing) was obtained by comparing two different backwashing methods. Furthermore, some iron reducing bacteria (0.4% Geothrix) along with a rapid proliferation of the main sulfur-oxidizing bacteria (23.0% Thiobacillus and 27.7% Ferritrophicum) were found under real-world operating conditions. Overall, the results of this study provide a case reference for the operation of SADCF-based biofilters and the application of SAD technology in engineering.

Microbial community assembly and metabolic function in top layers of slow sand filters for drinking water production

Slow sand filters (SSFs) are widely applied to treat potable water; the removal of contaminants (e.g., particles, organic matter, and microorganism) occurs primarily in the top layer. However, the development of the microbial community and its metabolic function is still poorly understood. In the present study, we analyzed the microbial quantity and community of the influents sampled from the effluent of the last step (rapid sand filtration) and of the top layers of SSFs (Schmutzdecke, 0–2 cm, 4–6 cm, 8–10 cm) sampled near terminal head loss when the Schmutzdecke (SCM) was most developed in two full-scale drinking water treatment plants (DWTPs). The two DWTPs use the same artificially recharged groundwater source. The biomass in the filter, quantified by flow cytometric intact cell counts (ICC) and adenosine triphosphate (ATP), decreased rapidly along the depth till 8–10 cm (>1 log TCC; >75% ATP); the decrease was most pronounced from the SCM to the surface sand layer (0–2 cm), after which the biomass stabilized quickly at lower depths (2–10 cm). Remarkably, beta diversity showed that SSFs layers of the same depth in two DWTPs with distinctive filter age and plant location clustered together, which indicated their insignificant effects in shaping microbial communities in SSFs. The alpha diversity indices followed the trend of the biomass, suggesting more active and diverse communities in SCM layer. PICRUSt-based function prediction revealed significant over-representation of metabolism and degradation of complex organic matters (e.g., butanoate, propanoate, xenobiotic, D-Alanine, chloroalkene, and bisphenol) in SCM layer, the functional importance of which was confirmed by the co-occurrence patterns of the dominant taxa and metabolic functions. Using an island biogeography model, we found that microbial communities in SSFs were strongly assembled by selection (68 OTUs, 50.0% sequences), rather than by simple accumulation of the microbial communities in the influents (120 OTUs, 44.8% sequences). Our findings enhance the understanding of microbial community assembly and of metabolic function in the top layers of SSFs, and constitute a valuable contribution to optimizing the design and operation of biofilters in full-scale DWTPs.

Development of a feedback control system for a differential biofilter degrading toluene contaminated air

In this study, a proportional – integral feedback control system was implemented on a lab-scale differential biofilter to control the gas phase toluene concentration in the soil bed through online manipulation of the inlet toluene concentration. The feedback control system was based on a cascade controller that manipulated the setpoint of an air bath diffusion system to manipulate the inlet toluene concentration. The controller performed well for toluene concentrations in the reactor of 10 – 300 ppm for both setpoint changes and disturbance rejections; however, the system was nonlinear requiring different tuning parameters at different outlet concentrations. Feedback control of the toluene concentration in the differential reactor was used to explore the impact of concentration on start-up and long-term biofilter operation in a rigorous fashion. Starting at an reactor concentration of 20 ppm and then increasing to 65 ppm increased the toluene removal rate (33 ± 1.6 g m−3h−1) compared to starting the reactor at an outlet concentration of 81 ppm before settling at 65 ppm (42 ± 0.9 g m− 3h−1). The toluene removal rate increased with increasing outlet toluene concentration and then eventually decreased when reaching the inhibitory toluene concentration (ranged from 80 to 250 ppm).

Removal of Trace Organic Chemicals during Long-Term Biofilter Operation

Removal of trace organic chemicals (TOrCs) at environmentally relevant concentrations was investigated in technical sand and biological activated carbon (BAC) biofilters processing nearly 90000 bed...

Biofilters for the co-treatment of volatile organic compounds and odors in a domestic waste landfill site

Volatile organic compounds (VOCs) and odors are two important gaseous pollutants escaped from landfill, which are harmful to human health and the surrounding environment. In this study, biofilter was used to control VOCs and odors from an actual landfill. The operating efficiency and mechanism of biofilters on the sealing zone and leachate treatment zone were respectively analyzed and compared. The results found that components of gaseous pollutants from these two zones are different. Hydrogen sulfide (572.96 μg/m3), ammonia (479.28 μg/m3), and dimethyl sulfide (279.81 μg/m3) were mainly detected in sealing zone, and dichloromethane (3573.97 μg/m3), triethylamine (1818.21 μg/m3), benzene (1809.11 μg/m3), and chlorobenzene (1286.81 μg/m3) were main components of gaseous pollutants in leachate treatment zone. Although the types and concentrations of gaseous pollutants in these two zones were significantly different, the biofilters showed good removal efficiencies. The average removal rate of the total VOC (TVOC), sulfides, and amines in both biofilters exceeded 80%. The outlet concentrations meet the level-3 standard of the Emission standards for odor pollutants (GB 14544–93). This is mainly related to the evolution of bacterial population during the operation of biofilters. In the inoculums, the dominant bacterial genus is Brevibacillus (58.84%), and bacteria with Bacillus and Pseudomonas only occupied 2.67% and 1.77%. With the extension of operation time, the dominant bacteria of biofilter in the sealing zone gradually evolved into Mycobacterium (67.82%) and Bacillus (27.90%), while the dominant bacteria of biofilter in the leachate treatment zone evolved into Bacillus (72.69%) and Pseudomonas (21.59%). These results indicated that identification of gaseous pollutant components and design of appropriate treatment systems based on their components will further improve the operating efficiency of biofilters in the actual landfill.

Evaluation of bioaerosols by flow cytometry and removal performance in a biofilter treating toluene/ethyl acetate vapors

The removal efficiency (RE) and bioaerosol emission of a perlite biofilter treating vapors of toluene (T) and/or ethyl acetate (EA) were assessed, under different operating conditions, during 171 days. Under the first stages of operation, a mixture of EA and T was treated, with equivalent inlet loads (ILs) of each compound (ranging from 26 to 84 g m−3 h−1), achieving a 100% RE of EA, and a maximum elimination capacity (EC) of T of 58.7 g m−3 h−1. An inhibition of T removal was noted in presence of EA, as T was treated subsequently to EA, along biofilter depth. A 17 days starvation period induced no global deterioration of performance regarding EA removal, but a 50% lower RE of T. Suspension of one contaminant, with interspersed feeding of only one component of the mixture, caused a permanent drop of the RE of EA (to 87.3%), after a T only feeding of 41 days. Flow cytometry (FC) was applied for quantification of bioaerosols, allowing for differentiation between viable, dead and damaged cells. During the overall biofilter operation, bioaerosol emission was not statistically different from bioaerosol retention. However, the biofilter significantly emitted bioaerosols (mostly viable cells) during start-up and IL increase, whereas a global retention of dead cells was observed during the interspersed feeding of one contaminant. Bioaerosols measured by FC (107 Cells m−3) were three orders of magnitude greater than with plate counting dishes, indicating that FC does not underestimate bioaerosols as culture dependent techniques.