Control Biofilter Research Articles

A pilot study of Mn redox driven nitrogen removal in municipal tailwater: Nitrogen metabolic pathway and electron transport mechanism

Microbial-mediated manganese (Mn) cycle coupled with nitrogen removal in municipal tailwater has received increasing attention. Herein, this study successfully extended the application of this technique to an 800 L biofilter, achieving a daily capacity of 2.4 m3 for treating municipal tailwater with a low C/N ratio. The operation results over 180 days indicated that the MnOx biofilter performed more efficiently than gravel control biofilter, achieving ∼ 40.2 % for nitrate and ∼ 35.9 % for total nitrogen (TN) removal efficiencies, respectively, under the conditions of hydraulic retention time (HRT) of 4 ∼ 5 h and low temperature (6.3–10.5 °C). To better elucidate the potential mechanisms, various functional bacteria involved in nitrogen and Mn transformation were identified, including heterotrophic denitrifying bacteria, such as Denitratisoma, Thauera, and Anaerolineae (cumulative relative abundance: 16.94–23.14 % in MnOx system vs. 9.86–11.90 % in control system) and Mn(II) oxidizing denitrifying bacteria, such as Pseudomonas and Acinetobacter (12.90–18.13 % vs. 3.59–4.64 %). Furthermore, metagenomic analysis indicated that the Mn cycle enhanced the expression of genes responsible for electron generation in organics/Mn metabolic pathways (e.g. TCA cycle and Mn oxidation), promoted electron transfer by enriching the Mn(II)-oxidizing denitrifying bacteria, and improved the abundance of genes associated with electron utilization (e.g. nitrate and nitrite reduction). The enhancement of the electron generation-transport-utilization due to Mn circulation contributed to efficient nitrate removal. This study provides further guidance of large-scale application and expands the understanding of the nitrogen removal mechanism in the Mn cycle-mediated process in municipal tailwater.

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.

Bioaugmentation of Nitrifying Microorganisms to Increase the Efficiency of the Oxidation of Nitrogen Compounds during Wastewater Biofiltration

The efficiency of the bioaugmentation of nitrifying bacteria into biofilm microbiocenosis with 30 days of continuous biofiltration of a solution of municipal model wastewater has been assessed. The laboratory setup consisted of two parallel operating biofilters. Cultures of ammonium-oxidizing and nitrite-oxidizing bacteria of the Nitrobacter genus were sequentially introduced into one of them after the initial period. It was established that the bioaugmentation of ammonium-oxidizing bacteria into the biofilm microbiocenosis led to an increase in the efficiency of the removal of ammonium nitrogen by an average of 1.6 times as compared to the control biofilter. The subsequent bioaugmentation of nitrite-oxidizing bacteria caused an increase in the amount of nitrates in purified water by an average of two times. The bioaugmentation of nitrifying bacteria in the biofilm microbiocenosis intensified the nitrification process. The quantitative and qualitative identification of microorganisms via fluorescence in situ hybridization showed an increased number of nitrifying microorganisms in the biofilm of the experimental biofilter and a correlation between this characteristic and the biotransformation of nitrogen compounds, which confirms the efficiency of the introduction of microorganisms into the biofilm.

Determination of filter bed structure characteristics and influence on performance of a 3D matrix biofilter in gaseous chlorobenzene treatment

The structure characteristics of filter bed greatly affect biofilter performance. In this study, a three-dimensional (3D) matrix biofilter packed with perlite and high mechanical strength 3D matrix material was established. The structure characteristics of the filter bed and the performance of 3D matrix biofilter and control biofilter (packed with perlite) were investigated. The 3D matrix biofilter presented higher chlorobenzene removal performance and lower bed compaction and pressure drop than the control biofilter. The packing factor, which could be used to represent the resistance when the gas stream passed through the filter bed, of the 3D matrix biofilter (7.59 × 105 m−1) was smaller than that of the control biofilter (1.04 × 106 m−1). Moreover, the specific surface area obtained from the molecular residence time distribution curves in the 3D matrix biofilter was higher (1754.82 ± 35.82 m2/m3) than that in the control biofilter (1474.03 ± 25.52 m2/m3), indicating improvements in mass transfer and performance. The characteristic parameters for mass transfer coefficient estimation in the biofilters were determined based on Onda’s modified correlation. 3D matrix biofilter demonstrated higher mass transfer coefficients than the control biofilter due to its higher specific surface area.

Биоаугментация нитрифицирующих микроорганизмов для повышения эффективности окисления соединений азота в процессе биофильтрации сточных вод

The efficiency of nitrifying bacteria bio-augmentation into biofilm microbiocenosis during 30-day continuous biofiltration of municipal wastewater model solution has been assessed. The laboratory setup consisted of two parallel operating biofilters, in one of which, after start-up period, cultures of ammonium-oxidizing and nitrite-oxidizing bacteria of the Nitrobacter genus were sequentially introduced. It was established that the bio-augmentation of ammonium-oxidizing bacteria into the biofilm microbiocenosis led to an increase in the efficiency of ammonium nitrogen removal by an average of 1.6 times compared to the control biofilter. The subsequent bio-augmentation of nitrite-oxidizing bacteria caused an increase in the amount of nitrates in purified water by 2 times on average. As a result of bio-augmentation of nitrifying bacteria into the biofilm microbiocenosis, the nitrification process was intensified. Quantitative and qualitative identification of microorganisms via fluorescence in situ hybridization showed an increase in the number of nitrifying microorganisms in the biofilm of experimental biofilter, which confirms the efficiency of introduction of microorganisms and correlates with the data on biotransformation of nitrogen compounds. nitrifying microorganisms, wastewater biofiltration, biofilms, bio-augmentation, fluorescence in situ hybridization.

Investigation of ozone and peroxone impacts on natural organic matter character and biofiltration performance using fluorescence spectroscopy

Impacts of ozonation alone as well as an advanced oxidation process of ozone plus hydrogen peroxide (H2O2 + O3) on organic matter prior to and following biofiltration were studied at pilot-scale. Three biofilters were operated in parallel to assess the effects of varying pre-treatment types and dosages. Conventionally treated water (coagulation/flocculation/sedimentation) was fed to one control biofilter, while the remaining two received water with varying applied doses of O3 or H2O2 + O3. Changes in organic matter were characterized using parallel factors analysis (PARAFAC) and fluorescence peak shifts. Intensities of all PARAFAC components were reduced by pre-oxidation, however, individual humic-like components were observed to be impacted to varying degrees upon exposure to O3 or H2O2 + O3. While the control biofilter uniformly reduced fluorescence of all PARAFAC components, three of the humic-like components were produced by biofiltration only when pre-oxidation was applied. A fluorescence red shift, which occurred with the application of O3 or H2O2 + O3, was attributed to a relative increase in carbonyl-containing components based on previously reported results. A subsequent blue shift in fluorescence caused by biofiltration which received pre-oxidized water indicated that biological treatment readily utilized organics produced by pre-oxidation. The results provide an understanding as to the impacts of organic matter character and pre-oxidation on biofiltration efficiency for organic matter removal.

Simultaneous removals of nitrate and sulfate and the adverse effects of gravel-based biofilters with flower straws added as exogenous carbon source

The feasibility of adding straws of ornamental flowers as carbon source into gravel-based biofilters to enhance removals of nitrate and sulfate simultaneously, and the concomitant adverse effects were evaluated in this study. The straws were added into a perforated PVC pipe vertically inserted into each biofilter. Results showed that compared to the control biofilter with almost no removal capacity, the experimental systems effectively co-eliminated nitrate and sulfate from the wastewater, with a mean removal rate of 1.29–2.11g NO3−-Nm−3d−1 and 1.03–2.16g SO42−m−3d−1, and higher efficiencies achieved for carnation and lily straws than rose and violet. A significant positive correlation was detected between nitrate and sulfate removal efficiency, with the nitrate removal notably more efficient. Nitrate and sulfate removal rates both decreased gradually with the operation time due to the declining carbon supply, and could be augmented again by fresh straw addition even in winter season. The phosphorous removal capacity of the biofilter was low and just influenced limitedly by the straw addition. High contents of organic carbon and colored matter were determined in the effluent after the straw addition but sharp drops to low levels were followed, resulting in insufficient carbon source for the removals of nitrate and sulfate. Mild accumulations of nitrite and ammonium occurred, averaging 0.39–1.30 mgL−1 and 0.46–0.93 mgL−1 in the effluent, while the content of dissolved sulfide was low. The biofilter added with rose straw showed the lowest relative adverse effects despite of its low removal capacities, and good performance with moderate adverse effects were obtained when adding with the carnation straw. The biofilter can be potentially applied to co-alleviate nitrate and sulfate pollutions although further optimization of straw addition is still required.

MIB and 2,4‐D Removal by Biofilters During Episodic Loading

Episodic occurrences of trace organic contaminants may affect their removal by biofilters. Removal of the naturally occurring algal metabolite 2‐methylisoborneol (MIB) and the herbicide 2,4‐dichlorphenoxyacetic acid (2,4‐D) by seven biofilters with an average empty bed contact time (EBCT) of 8.7 min is presented under a range of intermittent exposure conditions with continuous presence of dissolved organic matter. An average 70% removal of both MIB and 2,4‐D was found under constant exposure conditions over seven months. With the use of a pseudo‐first‐order model, much of the variability in removal during this time could be explained by EBCT changes. Microorganisms in the biofilters retained the capacity to biodegrade MIB and 2,4‐D after non‐exposure periods of up to five months. However, after nine months of non‐exposure, the MIB and 2,4‐D removals were lower than with the control biofilter, although the biofilter began to quickly reacclimate to these contaminants.

Modelling and experimental investigation on the application of water super adsorbents in waste air biofilters

In this research work, a synthetic water super absorbent polymer was included in the bed of a perlite-based biofilter for the removal of ethanol from air. The performance of this biofilter was compared with the performance of a control perlite-based biofilter lacking the water super absorbent. With the empty bed residence time of 2 min, both biofilters were able to remove more than 90% of the entering pollutant with the concentration of 1 g /m3, when regular moistening was applied. After last irrigation on day 23, the performance of the control biofilter was unchanged until day 35. From day 36 onwards, the control biofilter lost its activity gradually and became totally inactive on day 45. The performance of the super absorbent containing biofilter, however, was unchanged until day 58 before starting to lose its activity. A mechanistic model was developed to describe the performance of a biofilter under drying effects. The model could predict the trends of experimental results reasonably well. The model was also applied to predict the trends of experimental data from a published paper on the removal of hexane in a perlite/super absorbent containing biofilter.

Hexane biodegradation in two-liquid phase biofilters operated with hydrophobic biomass: Effect of the organic phase-packing media ratio and the irrigation rate

The hexane removal performance of three compost-based biofilters containing silicone oil at 0% (control), 10% and 20% v/v, and inoculated with a hydrophobic hexane degrading consortium was comparatively assessed under different irrigation strategies. The addition of 10% of silicone oil to the biofilter significantly improved its abatement performance by 72% compared to the control biofilter. However, when 20% of silicone oil was added to the compost no removal enhancement was observed, likely due to a severe reduction of the water holding capacity of the packing media (which decreased by 71%) together with a silicone-oil mediated gas flow channeling. An optimum mineral salt medium irrigation rate of 100mLLpacking-1d-1 resulted in a superior and more stable hexane abatement performance. No significant losses of silicone oil were observed at the end of the experimental period (⩽2.5%).

Enhancing ethylbenzene vapors degradation in a hybrid system based on photocatalytic oxidation UV/TiO2–In and a biofiltration process

The use of hybrid processes for the continuous degradation of ethylbenzene (EB) vapors has been evaluated. The hybrid system consists of an UV/TiO2–In photooxidation coupled with a biofiltration process. Both the photocatalytic system using P25-Degussa or indium-doped TiO2 catalysts and the photolytic process were performed at UV-wavelengths of 254nm and 365nm. The experiments were carried out in an annular plug flow photoreactor packed with granular perlite previously impregnated with the catalysts, and in a glass biofilter packed with perlite and inoculated with a microbial consortium. Both reactors were operated at an inlet loading rate of 127gm−3h−1. The greatest degradation rate of EB (0.414ngm−2min−1) was obtained with the TiO2–In 1%/365nm photocatalytic system. The elimination capacity (EC) obtained in the control biofilter had values ∼60gm−3h−1. Consequently, the coupled system was operated for 15 days, and a maximal EC of 275gm−3h−1. Thus, the results indicate that the use of hybrid processes enhanced the EB vapor degradation and that this could be a promising technology for the abatement of recalcitrant volatile organic compounds.

The effects of a lower irrigation system on pollutant removal and on the microflora of a biofilter

Moisture control is one the most important parameters in biofilters for air pollution control. Biofilters tend to experience drying at the air inlet port, which causes decreased pollutant removal over time. In this study, the installation of an irrigation system within the lower part of the biofilter bed was proposed, and its effect was quantified in a laboratory scale biofilter operated side by side with a control biofilter. The removal of toluene vapours at short gas residence time (13.5 s) served as a model system. The results showed that the rate of toluene elimination in the biofilter with the lower irrigation system was 1.2–1.7 times greater than the rate of toluene elimination in the control biofilter. At the completion of the two‐month experiment, a detailed examination was conducted of the packing materials with the immobilized pollutant‐degrading culture. The results highlighted the effects of bed drying on cell viability in the control biofilter. They also revealed that the bottom segment of the biofilter with the lower irrigation system had a higher moisture content, a higher biomass density and a larger fraction of active biomass than the corresponding segment in the conventional biofilter. These detailed examinations explained why an increased toluene removal was observed in the system equipped with a lower irrigation system. Overall, this study demonstrates enhanced pollutant removal in biofilters equipped with a lower irrigation system through a better control of moisture.

Treatment of dynamic VOC mixture in a trickling-bed air biofilter integrated with cyclic adsorption/desorption beds

A dual-fixed adsorption system involving a two-step cycle, i.e., adsorption and desorption was evaluated for dampening load fluctuation of a mixture of volatile organic compounds (VOCs)—toluene, styrene, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK). The cyclic beds successfully performed its function as a buffering unit for the fluctuating inlet loadings. When the employed loading did not exceed the critical loading of 34.0 g/(m 3 h), the integrated system maintained consistent 99% removal efficiency regardless of the fluctuation in feeding conditions prior to the cyclic adsorption beds. However, the performance of a standalone biofilter (control biofilter) fluctuated with the fluctuation of the feeding conditions. Under loadings exceeding the critical loading capacity, the integrated system showed much higher and more stable performance than the control system although it could not maintain consistent 99% removal efficiency. The cyclic beds could also act as a feeding source during starvation periods of the system which greatly enhanced the re-acclimation time for the biofilter and at the same time will regenerate the adsorber beds.

A novel integrated UV-biofilter system to treat high concentration of gaseous chlorobenzene

A novel integrated UV-biofilter system using UV reactor as the pretreatment process was setup to treat high concentration of gaseous volatile organic compounds (VOCs). Another control biofilter without the UV pretreatment was also established to compare the performance of the two systems. Chlorobenzene was selected as a model compound. The two systems were operated in parallel under different inlet chlorobenzene concentrations (500, 1000, 1600, mg · m−3). The experimental results indicate that the integrated system could eliminate chlorobenzene completely (100% removal efficiency) at the inlet concentration of 500 mg · m−3, whereas only 60% removal efficiency was achieved for the control biofilter. Also the elimination capacity for the organic carbon of the integrated system was much higher than that of the control biofilter. On the basis of intermediates analysis by Ion Chromatography and Gas Chromatography-Mass Spectrometry, the UV pretreatment has been proven to be able to enhance the performance of the following biofilter by transferring the recalcitrant target to some more biodegradable and soluble organic products (such as formic acid and chlorophenol). Furthermore, the produced ozone, a harmful by-product from UV photo-degradation, could be easily eliminated by the following biofiltration process.

Biofiltration of hydrophobic VOCs pretreated with UV photolysis and photocatalysis

The effects of pretreatments on the biofiltration of gas phase α-pinene, a poorly water soluble Volatile Organic Compound (VOC), was evaluated in a controlled and long-term experimental investigation. Ultraviolet (UV) photolysis and photocatalysis were used and compared as pretreatment techniques. A control experiment involving biofiltration alone allowed for the direct evaluation of the coupled UV-biofiltration. α-Pinene contaminated streams with flow rates of 5?6.5 l/min and concentrations of up to 130 ppmv were passed through the systems. UV pretreatment on average converted between 20 and 50% of α-pinene into water soluble intermediates. When comparing the effectiveness of each pretreatment process, UV photocatalysis provided greater α-pinene conversion, especially at low retention times and high contaminant loading. The untreated α-pinene along with the by-products of UV photooxidation was then removed effectively in the biofiltration stage. The UV-biofiltration process offered 50?80% more α-pinene removal compared to the control biofilter. Regardless of their effectiveness at removing the contaminant, photolysis and photocatalysis pretreatments had similar synergistic impact on the performance of the downstream biofilter.

Effect of Methanol on pH and Stability of Inorganic Biofilters Treating Dimethyl Sulfide

The biofiltration of dimethyl sulfide (DMS) and other reduced sulfur compounds (RSC) results in acidification of biofilters due to the accumulation of the sulfuric acid in packing material. This may lead to a decrease in biofilter performance due to a drop in pH. Results obtained from continuous experiments using three bench-scale biofilters packed with inorganic material mixed with limestone show that methanol (MeOH) alleviates the pH drop and enhances the stability of biofilter performance and DMS removal. The pH drop in the biofilters treating DMS with MeOH is 4 fold slower than that in the control biofiler treating DMS only. For the biofilters with MeOH addition, the pH of the biofilters drops more gradually (0.044 pH units per day) when compared to the MeOH suspension periods when MeOH is not added (0.23 pH units per day). MeOH addition consumes oxygen and results in a lower conversion ratio of sulfide to sulfuric acid due to the formation of elemental sulfur, reducing acidification in the biofilters. Nitrification was found to be actively taking place in the control biofilter treating DMS without MeOH addition, contributing to the significant pH drop in the reactor. It is proposed that MeOH prevents acid production from nitrification likely by limiting oxygen and nutrients to nitrifying bacteria in the MeOH-fed biofilters.

Two Liquid Phase Biofiltration for Removal of n-Hexane from Polluted Air

Two equal-size biofilters with perlite as the packing material were used to investigate the effect of amending silicone oil to the bed of a biofilter for removal of n-hexane from a contaminated air stream. The bed particles of one of the biofilters were partially coated with silicone oil. An n-hexane degrading bacterial culture was used as a biocatalyst in both biofilters. The biofilters operated in parallel under the same conditions for 70 days. The results showed that the silicone oil amended biofilter performed better than the other consistently during the period of investigation. The maximum elimination capacity for the silicone oil amended biofilter was 167 g · m−3 bed · h−1 compared to 114.9 g · m−3 bed · h−1 for the control biofilter. Sorption capacity of a biofilter plays an important role in damping shock changes at entering concentration. To determine how the amended oil could affect the sorption capacity of the biofilter, the responses of the biofilters to step and pulse changes at the inlet concentrations were investigated. A new steady state was established within several minutes after a change at the inlet concentrations. The outlet concentrations of the biofilters increased almost in parallel after a step increase at the inlet concentrations. For a step decrease at the inlet concentrations, the outlet concentration of the oil-amended biofilter was higher than the other for a short period of time due to the desorption phenomenon. The oil-amended biofilter damped a pulse increase at the inlet concentration much more effective than the control biofilter.

H2S degradation is reflected by both the activity and composition of the microbial community in a compost biofilter

In this study, 16S rRNA- and rDNA-based denaturing gradient gel electrophoresis (DGGE) were used to study the temporal and spatial evolution of the microbial communities in a compost biofilter removing H(2)S and in a control biofilter without H(2)S loading. During the first 81 days of the experiment, the H(2)S removal efficiencies always exceeded 93% at loading rates between 4.1 and 30 g m(-3) h(-1). Afterwards, the H(2)S removal efficiency decreased to values between 44 and 71%. RNA-based DGGE analysis showed that H(2)S loading to the biofilter increased the stability of the active microbial community but decreased the activity-based diversity and evenness. The most intense band in both the RNA- and DNA-based DGGE patterns of the H(2)S-degrading biofilter represented the sulfur oxidizing bacterium Thiobacillus thioparus. This suggested that T. thioparus constituted a major part of the bacterial community and was an important primary degrader in the H(2)S-degrading biofilter. The decreasing H(2)S removal efficiencies near the end of the experiment were not accompanied by a substantial change of the DGGE patterns. Therefore, the decreased H(2)S removal was probably not caused by a failing microbiology but rather by a decrease of the mass transfer of substrates after agglutination of the compost particles.

Disinfection effectiveness of ultraviolet (UV) light for heterotrophic bacteria leaving biologically active filters

Research Article| December 01 2004 Disinfection effectiveness of ultraviolet (UV) light for heterotrophic bacteria leaving biologically active filters Alexander A. Mofidi; Alexander A. Mofidi 1Metropolitan Water District of Southern California, 700 Moreno Avenue, La Verne, CA 91750-3399, USA Tel.:+1-909-392-5463 Fax:+1-909-392-5166; E-mail: amofidi@mwdh2o.com Search for other works by this author on: This Site PubMed Google Scholar Karl G. Linden Karl G. Linden 2Duke University, Department of Civil and Environmental Engineering, 121 Hudson Hall, Durham, NC 27708, USA Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2004) 53 (8): 553–566. https://doi.org/10.2166/aqua.2004.0044 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Twitter LinkedIn Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation Alexander A. Mofidi, Karl G. Linden; Disinfection effectiveness of ultraviolet (UV) light for heterotrophic bacteria leaving biologically active filters. Journal of Water Supply: Research and Technology-Aqua 1 December 2004; 53 (8): 553–566. doi: https://doi.org/10.2166/aqua.2004.0044 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Biologically operated filters are known to reduce elevated levels of biodegradable organic matter produced by the ozonation process, but they also consistently release high-levels of heterotrophic bacteria. An acceptable disinfection strategy for biofilter effluent bacteria is necessary to maintain distributed water quality. The efficiencies of various strategies for disinfecting naturally occurring heterotrophic bacteria in the effluent from an ozone/biofiltration plant treating California surface waters were compared. Bench-scale tests were conducted in the laboratory, using ultraviolet (UV) light (low-pressure and medium-pressure lamps), and the results were compared with those for the disinfection efficiency of free chlorine and chloramines. Inactivation efficiencies provided by the low- and medium-pressure UV lamps were similar (k⋍0.47 cm2 mJ−1). To consistently reduce biofilter effluent bacteria levels to <10 colony-forming units per millilitre (CFU ml−1) prior to distribution, this study showed that contact with either 1 min of free chlorine or 60 min of monochloramine (both at 2.5 mg l−1, pH=8, 20°C) would be necessary, compared with a UV dose of 15 mJ cm−2 from either lamp. To evaluate bacterial regrowth potential following UV treatment, samples were incubated at 20°C in a dark environment to mimic transport/storage in the distribution system. Without residual disinfection, bacteria treated by 60 and 140 mJ cm−2 of UV were able to regrow to untreated biofilter effluent levels within 3 and 7 days, respectively. Samples treated with 20 mJ cm−2 of UV and 2.5 mg l−1 of chloramines maintained bacteria at levels of <10 CFU ml−1 for up to 7 days. To investigate the plausibility of bench-scale results, a full-scale UV reactor (treating 3 million gallons per day (0.13 m3 s−1) was operated to treat the biofilter effluent at the large-scale treatment plant for a period of 8 months. Continuous UV treatment was observed to provide long-term control of the biofilter effluent bacteria to levels similar to those afforded by bench-scale treatment. However, towards the end of the study, the number of bacteria leaving the UV reactor increased to levels exceeding 102 CFU ml−1. It was observed that 2.5 mg l−1 monochloramine residual (no free-chlorine contact) applied at the inlet of a 60-min clearwell downstream from the UV reactor kept bacteria at a level of <10 CFUml−1 at the clearwell effluent. Based on these results, it is recommended that utilities using UV to control biofilter effluent bacteria apply a residual disinfectant (such as chloramines) to maintain low bacteria levels during distribution. bacteria, chloramines, chlorine, disinfection, heterotrophic, ultraviolet light This content is only available as a PDF. © IWA Publishing 2004 You do not currently have access to this content.

The effect of silicone oil on biofiltration of hydrophobic compounds

AbstractThis paper documents an investigation on the effect of using silicone oil in the bed of a perlite biofilter for removal of a mixture of hydrophobic compounds. Two bench‐scale biofilters, one with silicone oil and the other without silicone oil as a control, were used for the investigations. Results showed, at low inlet concentrations, the difference in performance between the silicone oil‐treated biofilter and the control biofilter were insignificant, while at high concentrations, the biofilter with silicone oil performed slightly better. The maximum elimination capacities obtained in this research were 20.41 g/(m3bed.h) and 18.83 g/(m3bed.h) for the silicone oil‐added biofilter and the control biofilter, under the same conditions, respectively.