Treatment of a colored groundwater by ozone-biofiltration: pilot studies and modeling interpretation

Pilot studies investigated the fates of color, dissolved organic carbon (DOC), and biodegradable organic matter (BOM) by the tandem of ozone plus biofiltration for treating a source water having significant color (50 cu) and DOC (3.2 mg/l). Transferred ozone doses were from 1.0 to 1.8 g O3/g C. Rapid biofilters used sand, anthracite, or granular activated carbon as media with empty-bed contact time (EBCT) up to 9 min. The pilot studies demonstrated that ozonation plus biofiltration removed most color and substantial DOC, and increasing the transferred ozone dose enhanced the removals. For the highest ozone dose, removals were as high as 90% for color and 38% for DOC. While most of the color removal took place during ozonation, most DOC removal occurred in the biofilters, particularly when the ozone dose was high. Compared to sand and anthracite biofilters, the GAC biofilter gave the best performance for color and DOC removal, but some of this enhanced performance was caused by adsorption, since the GAC was virgin at the beginning of the pilot studies. Backwashing events had no noticeable impact of the performance of the biofilters. The Transient-State, Multiple-Species Biofilm Model (TSMSBM) was used to interpret the experimental results. Model simulations show that soluble microbial products, which comprised a significant part of the effluent BOM, offset the removal of original BOM, a factor that kept the removal of DOC relatively constant over the range of EBCTs of 3.5-9 min. Although improved biofilm retention, represented by a small detachment rate, allowed more total biofilm accumulation and greater removal of original BOM, it also caused more release of soluble microbial products and the build up of inert biomass in the biofilm. Backwashing had little impact on biofilter performance, because it did not remove more than 25% of the biofilm under any condition simulated.     

Modeling of trihalomethane cometabolism in nitrifying biofilters

The computer program AQUASIM was used to model biofilter experiments seeded with Lake Austin, Texas mixed-culture nitrifiers. These biofilters degraded four trihalomethanes (THMs) (trichloromethane (TCM) or chloroform, bromodichloromethane (BDCM), dibromochloromethane (DBCM), tribromomethane (TBM) or bromoform) commonly found in treated drinking water. Apparent steady-state data from the biofilter experiments and supporting batch experiments were used to estimate kinetic parameters for TCM, DBCM and ammonia degradation. Subsequently, the model was verified against other experimental biofilter data. To allow for full-scale simulations, BDCM and TBM rate constants were estimated using data from batch kinetic studies. Finally, the model was used to simulate full-scale filter performance under different filter surface loading rates and THM speciation seen in practice. Overall, total THM removals ranged from 16% to 54% in these simulations with influent total THM concentrations of 75-82microg/L, which illustrates the potential of THM cometabolism to have a significant impact on treated water quality.     

Measurement of biomass activity in drinking water biofilters using a respirometric method

A simple respirometric method was developed and applied for the measurement of biomass activity in bench-scale drinking water biofilters. The results obtained with the new method, i.e. biomass respiration potential (BRP), indicated a high sensitivity allowing the quantification of the activity of low amounts of biomass. The analysis of duplicate samples showed a reasonable reproducibility, i.e. average coefficient of variation of 14% (n = 19). The calculation of the ratio between biomass activity and the amount of viable biomass (phospholipid) at different filter depths indicated a substantial increase of this ratio with filter depth. This indicated an increased biomass activity per unit amount of viable biomass deeper in the biofilters, where biofilm thickness is low. The comparison of the filter profiles of biomass activity and dissolved biodegradable organic matter (BOM), expressed as theoretical oxygen demand, showed a high correlation between these profiles. Consequently, BRP results appear to be good indicators of the BOM removal capacity of the filter biomass. Therefore, BRP results can potentially be used in certain cases instead of BOM measurements for the assessment of the BOM removal capacity of drinking water biofilters, operated under different conditions. This is important because of the relative complexity of the measurements of BOM surrogates, e.g. assimilable organic carbon and biodegradable dissolved organic carbon, and BOM components.     

Comparative measurements of microbial activity in drinking water biofilters

Tetrazolium reduction assays, phospholipid analysis, and 16S rRNA (rDNA) sequence analysis were applied to assess the distribution, composition and activity of microbial communities developing in biofilters treating non-ozonated and ozonated drinking water. The response of media-attached biomass to both operating temperature (3 degrees C vs. > 12 degrees C) and ozone application point was assessed. As judged by 2-(p-iodo-phenyl)-3-(p-nitrophenyl)-s-phenyl tetrazolium chloride (INT) reduction, the dehydrogenase activity in biofilter systems that were operated with non-ozonated water was 55% lower than in identical filters operating with ozonated water. There was no significant difference between the microbiological activity measured in a biofilter series treating ozonated water and an identical series where ozonated water was introduced at an intermediate point. The biomass levels in biofilter systems that were operated with ozonated water were 47% higher on average than identical systems operated with non-ozonated water. Operating temperature had no significant impact on total biomass levels; however, specific dehydrogenase activity was 70% higher in systems operated at ambient temperatures (> 12 degrees C) than in systems held at 3 degrees C. Phospholipid and rDNA analysis suggests that there was a community structure response to ozone application and operating temperature, but no response to different ozone application points.     

Hydrodynamic behaviour and comparison of technologies for the removal of excess biomass in gas-phase biofilters

The hydrodynamic behaviour of a biofilter fed toluene and packed with an inert carrier was evaluated on start-up and after long-term operation, using both methane and styrene as tracers in Residence Time Distribution experiments. Results indicated some deviation from ideal plug flow behaviour after 2-year operation. It was also observed that the retention time of VOCs gradually increased with time and was significantly longer than the average residence time of the bulk gas phase. Non-ideal hydrodynamic behaviour in packed beds may be due to excess biomass accumulation and affects both reactor modeling and performance. Therefore, several methods were studied for the removal of biomass after long-term biofilter operation: filling with water and draining, backwashing, and air sparging. Several flow rates and temperatures (20-60 degrees C) were applied using either water or different chemicals (NaOH, NaOCl, HTAB) in aqueous solution. Usually, higher flow rates and higher temperatures allowed the removal of more biomass, but the efficiency of biomass removal was highly dependent on the pressure drop reached before the treatment. The filling/draining method was the least efficient for biomass removal, although the treatment did basically not generate any biological inhibition. The efficiency of backwashing and air sparging was relatively similar and was more effective when adding chemicals. However, treatments with chemicals resulted in a significant decrease of the biofilter's performance immediately after applying the treatment, needing periods of several days to recover the original performance. The effect of manually mixing the packing material was also evaluated in duplicate experiments. Quite large amounts of biomass were removed but disruption of the filter bed was observed. Batch assays were performed simultaneously in order to support and quantify the observed inhibitory effects of the different chemicals and temperatures used during the treatments.     

Calibration and validation of an ASM3-based steady-state model for activated sludge systems--part I: Prediction of nitrogen removal and sludge production

The steady-state model from Siegrist and Gujer (1994) which can be used for the design and optimisation of nitrogen-removing activated sludge plants is applied to the stoichiometrics and kinetics of a validated Activated Sludge Model No. 3. It considers the wastewater composition, the effect of the electron acceptor on the average sludge production, the oxygen input into anoxic volumes, denitrification in the secondary clarifier, the temperature and various operating conditions. The organic substrate for denitrification originates from readily degradable substrate from the influent, from the hydrolysis of slowly degradable particulate substrate along the activated sludge plant and from the endogenous respiration of the biomass. The model is calibrated and validated with data from long-term full-scale and pilot-plant experiments for Swiss municipal wastewater. The most sensitive parameters as well as the uncertainty of the model prognosis for various COD-to-nitrogen ratios from inlet water and anoxic volume fractions were calculated with the aid of sensitivity analyses and Monte-Carlo simulations. Excel spreadsheets of the model for different flow schemes are available from the corresponding author.     

Non-steady state simulation of BOM removal in drinking water biofilters: model development

A numerical model was developed to simulate the non-steady-state behavior of biologically-active filters used for drinking water treatment. The biofilter simulation model called "BIOFILT" simulates the substrate (biodegradable organic matter or BOM) and biomass (both attached and suspended) profiles in a biofilter as a function of time. One of the innovative features of BIOFILT compared to previous biofilm models is the ability to simulate the effects of a sudden loss in attached biomass or biofilm due to filter backwash on substrate removal performance. A sensitivity analysis of the model input parameters indicated that the model simulations were most sensitive to the values of parameters that controlled substrate degradation and biofilm growth and accumulation including the substrate diffusion coefficient, the maximum rate of substrate degradation, the microbial yield coefficient, and a dimensionless shear loss coefficient. Variation of the hydraulic loading rate or other parameters that controlled the deposition of biomass via filtration did not significantly impact the simulation results.     

Effect of Organic Carbon on Tertiary Denitrification of the Secondary Effluent in Biofilters Packed with Suspended Carriers

Denitrifying biokinetics in biofilters packed with suspended carriers were evaluated under different empty bed residence times (EBRT) with ethanol or acetate as the electron donor. The two denitrifying biofilters removed nitrate (NO₃^––N) effectively after only 3–4 days operation. At EBRT of 30; 15 and 7.5 min, the NO₃^––N removal percentage was 84; 72 and 59% in the ethanol biofilter, and was 89; 70 and 62% in the acetate biofilter, respectively. With the influent NO₃^––N loading rate ranged from 0.4 to 1.8 g/(m²·d), the NO₃^––N removal loading rate increased with increasing influent NO₃^––N loading rates, and the system was substrate limited. While when the influent nitrate loading rate was above 3 g/(m²·d), the system was biomass limited. The half-order coefficients were 0.162; 0.175 and 0.274 (mg/L)^1/2/min for the ethanol biofilter with the influent NO₃^––N concentration of 7.3–7.7 mg/L, and were 0.107; 0.165 and 0.303 (mg/L)^1/2/min for the acetate biofilter with the influent NO₃^––N concentration of 6.8–8.0 mg/L. Denitrification efficiency varied slightly during the backwashing cycle, and the effect of backwashing on the effluent turbidity was relatively large, especially for the biofilter with ethanol as the organic carbon.     

Impact of temperature on nitrification in biological activated carbon (BAC) filters used for drinking water treatment

The impact of temperature on nitrification in biological granular activated carbon (GAC) filters was evaluated in order to improve the understanding of the nitrification process in drinking water treatment. The study was conducted in a northern climate where very cold water temperatures (below 2 degrees C) prevail for extended periods and rapid shifts of temperature are frequent in the spring and fall. Ammonia removals were monitored and the fixed nitrifying biomass was measured using a method of potential nitrifying activity. The impact of temperature was evaluated on two different filter media: an opened superstructure wood-based activated carbon and a closed superstructure activated carbon-based on bituminous coal. The study was conducted at two levels: pilot scale (first-stage filters) and full-scale (second-stage filters) and the results indicate a strong temperature impact on nitrification activity. Ammonia removal capacities ranged from 40 to 90% in pilot filters, at temperatures above 10 degrees C, while more than 90% ammonia was removed in the full-scale filters for the same temperature range. At moderate temperatures (4-10 degrees C), the first stage pilot filters removed 10-40% of incoming ammonia for both media (opened and closed superstructure). In the full-scale filters, a difference between the two media in nitrification performances was observed at moderate temperatures: the ammonia removal rate in the opened superstructure support (more than 90%) was higher than in the closed superstructure support (45%). At low temperatures (below 4 degrees C) both media performed poorly. Ammonia removal capacities were below 30% in both pilot- and full-scale filters.     

The effect of nitrate on VOC removal in trickle-bed biofilters

In response to the growing concern over volatile organic compounds (VOCs), biofiltration is becoming an established economical air pollution control technology for removing VOCs from waste air streams. Current research efforts are concentrating on improving control over key parameters that affect the performance of gas phase biofilters. This study utilized diethyl ether as a substrate, nitrate as the sole nutrient nitrogen source within two co-currently operated trickle-bed biofilters, for over 200 days. The two pelletized medium biofilters were operated at a low empty bed contact time of 25 s, inlet gas flow rates of 8.64 m³/day, nutrient liquid flow rates of 1 liter/day, and COD loading rates of 1.8 and 3.6 kg/m³ per day, respectively. Operational parameters including contaminant concentration in the gas phase, nutrient nitrate concentration in the aqueous phase, and the frequency of biomass removal were considered. Special attention was given to the effect and the role of nitrate on VOC removal. Throughout the experiment, nitrate persisted in the liquid effluent and the ether removal efficiencies improved with increasing influent nitrate concentration, which suggest that the nitrate diffusion into the biofilms is rate determining. By increasing the concentration of oxygen in the feed to this biofilter from 21% (ambient air) to 50 and 100%, while maintaining an influent ether concentration of 133 ppmv and a feed nitrate concentration of 67 mg-N/liter, the performance of the biofilter was not significantly affected. These results suggest that nitrogen was rate limiting as a growth nutrient rather than as an electron acceptor for the respiration of ether. The results also indicated that removal of excess biomass is necessary to maintain long-term performance. However, the required frequency of biomass removal depends on operating parameters such as loading.     

固定化微生物强化生物滤池处理硝基苯和苯胺废水

利用复合微生物菌群BCP35,对自制的大孔功能化载体FPU进行微生物的固定化,并与厌氧生物滤池和好氧生物滤池联用处理含高浓度硝基苯和苯胺的废水,研究了固定化微生物强化生物滤池处理污染物的运行效果、硝基苯和苯胺的降解特征,比较了固定化微生物和游离态微生物的除污性能,同时分析了载体上微生物的状态和生物量.结果表明,固定化微生物强化生物滤池工艺对硝基苯、苯胺具有很好的去除效果,对硝基苯和苯胺的降解率可分别达到99.8%和99.9%;同时生物滤池还对污染物浓度变化具有较强的抗冲击负荷能力;与游离态微生物相比,固定化微生物在去除COD、硝基苯、苯胺等方面更具优势;生物滤池内的微生物浓度较高,可达到38g/L.     

生物滤塔处理含三甲胺气体的研究

研究了分别填充堆肥和污泥的生物滤塔对含三甲胺气体的处理能力.结果表明,两种生物滤塔均能有效处理含三甲胺的气体,对三甲胺的去除率几乎达到了100%,三甲胺被生物降解并生成氨.堆肥生物滤塔各段填料中的硝态氮含量随时间的延长呈显著提高的趋势,但pH值出现下降,说明其中发生了氨的硝化作用.而在污泥生物滤塔中,随着氨的积累则各填料层的pH值迅速升高,并且没有观察到亚硝态氮以及硝态氮含量的增加,因此其不具备进一步降解氨的能力.     

Performance and biofilm activity of nitrifying biofilters removing trihalomethanes

Nitrifying biofilters seeded with three different mixed-culture sources removed trichloromethane (TCM) and dibromochloromethane (DBCM) with removals reaching 18% for TCM and 75% for DBCM. In addition, resuspended biofilm removed TCM, bromodichloromethane (BDCM), DBCM, and tribromomethane (TBM) in backwash batch kinetic tests, demonstrating that the biofilters contained organisms capable of biotransforming the four regulated trihalomethanes (THMs) commonly found in treated drinking water. Upon the initial and subsequent increased TCM addition, total ammonia nitrogen (TOTNH₃) removal decreased and then reestablished, indicating an adjustment by the biofilm bacteria. In addition, changes in DBCM removal indicated a change in activity related to DBCM. The backwash batch kinetic tests provided a useful tool to evaluate the biofilm’s bacteria. Based on these experiments, the biofilters contained bacteria with similar THM removal kinetics to those seen in previous batch kinetic experiments. Overall, performance or selection does not seem based specifically on nutrients, source water, or source cultures and most likely results from THM product toxicity, and the use of GAC media appeared to offer benefits over anthracite for biofilter stability and long-term performance, although the reasons for this advantage are not apparent based on research to date.     

Laboratory modelling of manganese biofiltration using biofilms of Leptothrix discophora

Laboratory biofilters (pilot-scale, 20 l and laboratory-scale, 5l) were constructed in order to model the bioaccumulation of manganese (Mn) under flow conditions similar to those occurring in biofilters at groundwater treatment sites. The biofilters were operated as monocultures of Leptothrix discophora, the predominant organism in mature Mn oxidising biofilms. Biologically mediated Mn bioaccumulation was successfully modelled in both filter systems. The data obtained showed that in the small-scale biofilter, the Mn concentrations that gave the highest rate of Mn bioaccumulation, shortest maturation time, highest optical density (biomass) and growth rate were between 2000 and 3000 microg x l(-1). The non-problematic scale-up of the process from the laboratory-scale to the pilot-scale biofilter model suggests that Mn biofilters may be 'seeded' with laboratory grown cultures of L. discophora. By initially operating the biofilter as a re-circulating batch culture, with an initial Mn concentration of approximately 2500 microg x l(-1), it is hoped to reduce the filter maturation time from months to days.     

Effect of air-assisted backwashing on the performance of an anaerobic fixed-bed bioreactor that simultaneously removes nitrate and arsenic from drinking water sources

Contaminant removal from drinking water sources under reducing conditions conducive for the growth of denitrifying, arsenate reducing, and sulfate reducing microbes using a fixed-bed bioreactor may require oxygen-free gas (e.g., N₂ gas) during backwashing. However, the use of air-assisted backwashing has practical advantages, including simpler operation, improved safety, and lower cost. A study was conducted to evaluate whether replacing N₂ gas with air during backwashing would impact performance in a nitrate and arsenic removing anaerobic bioreactor system that consisted of two biologically active carbon reactors in series. Gas-assisted backwashing, comprised of 2 min of gas injection to fluidize the bed and dislodge biomass and solid phase products, was performed in the first reactor (reactor A) every two days. The second reactor (reactor B) was subjected to N₂ gas-assisted backwashing every 3-4 months. Complete removal of 50 mg/L NO₃⁻ was achieved in reactor A before and after the switch from N₂-assisted backwashing (NAB) to air-assisted backwashing (AAB). Substantial sulfate removal was achieved with both backwashing strategies. Prolonged practice of AAB (more than two months), however, diminished sulfate reduction in reactor B somewhat. Arsenic removal in reactor A was impacted slightly by long-term use of AAB, but arsenic removals achieved by the entire system during NAB and AAB periods were not significantly different (p > 0.05) and arsenic concentrations were reduced from approximately 200 μg/L to below 20 μg/L. These results indicate that AAB can be implemented in anaerobic nitrate and arsenic removal systems.     

Impact of water boundary layer diffusion on the nitrification rate of submerged biofilter elements from a recirculating aquaculture system

Total ammonia nitrogen (TAN) removal by microbial nitrification is an essential process in recirculating aquaculture systems (RAS). In order to protect the aquatic environment and fish health, it is important to be able to predict the nitrification rates in RAS's. The aim of this study was to determine the impact of hydraulic film diffusion on the nitrification rate in a submerged biofilter. Using an experimental batch reactor setup with recirculation, active nitrifying biofilter units from a RAS were exposed to a range of hydraulic flow velocities. Corresponding nitrification rates were measured following ammonium chloride, NH₄Cl, spikes and the impact of hydraulic film diffusion was quantified.The nitrification performance of the tested biofilter could be significantly increased by increasing the hydraulic flow velocity in the filter. Area based first order nitrification rate constants ranged from 0.065 m d⁻¹ to 0.192 m d⁻¹ for flow velocities between 2.5 m h⁻¹ and 40 m h⁻¹ (18 °C). This study documents that hydraulic film diffusion may have a significant impact on the nitrification rate in fixed film biofilters with geometry and hydraulic flows corresponding to our experimental RAS biofilters. The results may thus have practical implications in relation to the design, operational strategy of RAS biofilters and how to optimize TAN removal in fixed film biofilter systems.     

Biological nitrogen removal from municipal landfill leachate: low-cost nitrification in biofilters and laboratory scale in-situ denitrification

The slow leaching of nitrogen from solid waste in landfills, resulting in high concentrations of ammonia in the landfill leachate, may last for several decades. The removal of nitrogen from leachate is desirable as nitrogen can trigger eutrophication in lakes and rivers. In the present study, a low-cost nitrification-denitrification process was developed to reduce nitrogen load especially in leachates from small landfills. Nitrification was studied in laboratory and on-site pilot aerobic biofilters with waste materials as filter media (crushed brick in upflow filters and bulking agent of compost in a downflow filter) while denitrification was studied in a laboratory anoxic/anaerobic column filled with landfill waste. In the laboratory nitrification filters, start-up of nitrification took less than 3 weeks and over 90% nitrification of leachate (NH4-N between 60 and 170mg N l(-1), COD between 230 and 1,300 mg l(-1)) was obtained with loading rates between 100 and 130 mgNH4-N l(-1) d at 25 degrees C. In an on-site pilot study a level of nitrification of leachate (NH4-N between 160 and 270 mg N l(-1), COD between 1,300 and 1,600 mg l(-1)) above 90% was achieved in a crushed brick biofilter with a loading rate of 50mg NH4-N l(-1) d even at temperatures as low as 5-10 degrees C. Ammonium concentrations in all biofilter effluents were usually below the detection limit. In the denitrification column. denitrification started within 2 weeks and total oxidised nitrogen in nitrified leachate (TON between 50 and 150mg N l(-1)) usually declined below the detection limit at 25 degrees C, whereas some ammonium, probably originating from the landfill waste used in the column, was detected in the effluent. No adverse effect was observed on the methanation of waste in the denitrification column with a loading rate of 3.8 g TON-N/t-TS(waste) d. In conclusion, nitrification in a low-cost biofilter followed by denitrification in a landfill body appears applicable for the removal of nitrogen in landfill leachate in colder climates.     

Nutrient and sediment removal by stormwater biofilters: a large-scale design optimisation study

A large-scale column study was conducted in Melbourne, Australia, to test the performance of stormwater biofilters for the removal of sediment, nitrogen and phosphorus. The aim of the study was to provide guidance on the optimal design for reliable treatment performance. A variety of factors were tested, using 125 large columns: plant species, filter media, filter depth, filter area and pollutant inflow concentration. The results demonstrate that vegetation selection is critical to performance for nitrogen removal (e.g. Carex appressa and Melaleuca ericifolia performed significantly better than other tested species). Whilst phosphorus removal was consistently very high (typically around 85%), biofilter soil media with added organic matter reduced the phosphorus treatment effectiveness. Biofilters built according to observed 'optimal specifications' can reliably remove both nutrients (up to 70% for nitrogen and 85% for phosphorus) and suspended solids (consistently over 95%). The optimally designed biofilter is at least 2% of its catchment area and possesses a sandy loam filter media, planted with C. appressa or M. ericifolia. Further trials will be required to test a wider range of vegetation, and to examine performance over the longer term. Future work will also examine biofilter effectiveness for treatment of heavy metals and pathogens.     

Effect of nitrogen limitation on performance of toluene degrading biofilters

The literature reports conflicting observations regarding the need for nutrient addition to biofilters treating contaminated gases. Such conflicts are often based on quasi-steady-state performance data collected on biofilters operated under continuous loading conditions. In the studies described herein, the impact of nitrogen limitations on two toluene-fed biofilters was assessed over a 97-day period. The biofilters were packed with polyurethane foam medium and contained different initial levels of nitrate-nitrogen. Toluene and CO2 concentration profiles were monitored during both normal steady loading conditions and short-term, unsteady-state transient loading conditions (e.g., shock loads). Packing medium samples were periodically removed and analyzed to quantify changes in nitrate-nitrogen content over time. Data are presented which show that over long-time periods (several months), nutrient-induced kinetic limitations diminished biofilter performance during transient, unsteady-state conditions even when performance during normal steady loading was not adversely affected. Elemental analysis of biomass removed from the biofilters support nitrate-nitrogen and CO2 concentration profile data and clearly illustrate how kinetically limited biofilters fail during shock loads even when there is an overall stoichiometric excess of nutrients.     

Impact of support media in an integrated biofilter-submerged membrane system

The impact of a support material on an integrated biofilter-membrane system, simulating a difficult-to-treat surface water, was examined in terms of membrane fouling rate and water quality parameters. The support media in the membrane tanks did not generally affect any of the water quality parameters measured; however, there was an observable difference in the membrane fouling rates between the two processes with the support media system fouling at least two times slower than the non-support system. Total organic carbon (TOC) removals at around 60% were observed for two integrated biofilter-immersed membrane processes with the majority of the TOC removal occurring in the biofilters. One of the membrane tanks contained a support media (Process A) while the other did not (Process B). The feedwater contained humic acid (65% w/w) and readily biodegradable carbons (35% w/w) in the forms of acetic acid, formic acid and formaldehyde. The influent TOC values were between 3.35 and 3.94 mg/L. Acetate removals varied between 66 and 83%, while over 90% of the formate was removed and the formaldehyde was completely removed in the biofilters. There was a decrease in the UV absorbance values by over 70% for both processes.