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.     

Effect of gas empty bed contact time on performances of various types of rotating drum biofilters for removal of VOCs

The effects of gas empty bed contact time (EBCT), biofilter configuration, and types of volatile organic compounds (VOCs) were evaluated to assess the performance of rotating drum biofilters (RDBs), especially at low EBCT values. Three types of pilot-scale RDBs, a single-layer RDB, a multi-layer RDB, and a hybrid RDB, were examined at various gas EBCTs but at a constant VOC loading rate. Diethyl ether, toluene, and hexane were used separately as model VOC. When EBCT increased from 5.0 to 60s at a constant VOC loading rate of 2.0kgCOD/(m(3)day), ether removal efficiency increased from 73.1% to 97.6%, from 81.6% to 99.9%, and from 84.0% to 99.9% for the single-layer RDB, the multi-layer RDB, and the hybrid RDB, respectively, and toluene removal efficiency increased from 76.4% to 99.9% and from 84.8% to 99.9% for the multi-layer RDB and the hybrid RDB, respectively. When hexane was used as the model VOC at a constant loading rate of 0.25kgCOD/(m(3)day), hexane removal efficiency increased from 31.1% to 57.0% and from 29.5% to 50.0% for the multi-layer RDB and hybrid RDB, respectively. The single-layer, multi-layer, and hybrid RDBs exhibited, respectively, the lowest, middle, and highest removal efficiencies, when operated under similar operational loading conditions. Hexane exhibited the lowest removal efficiency, while diethyl ether displayed the highest removal efficiency. The data collected at the various EBCT values correlated reasonably well with a saturation model. The sensitivity of removal efficiency to EBCT varied significantly with EBCT values, VOC properties, and biofilter configurations. Process selection and design for RDB processes should consider these factors.     

Accumulation and fate of green fluorescent labeled Escherichia coli in laboratory-scale drinking water biofilters

Biological filters combining microbial activity and rapid sand filtration are used in drinking water treatment plants for enhanced biodegradable organic matters (BOM) removal. Biofilms formed on filter media comprised of bacteria enclosed in a polymeric matrix are responsible for the adsorption of BOM and attachment of planktonic microorganisms. This study investigated the removal of Escherichia coli cells injected into laboratory-scale biofilters and the role of biofilm in retaining the injected E. coli. Green fluorescent protein was used as a specific marker to detect and quantify E. coli in the biofilms. About 35% of the total injected E. coli cells were observed in the filter effluents, when initial cell concentrations were measured at 7.4 x 10(6) CFU/mL and 1.6 x 10(7) CFU/mL in two separate experiments. The results from real-time PCR and plate count analysis indicated that 95% of the E. coli retained inside the filters were either non-viable or could not be recovered by colony counting techniques. Injected cells were unevenly distributed inside the filter with more than 70% located at the top 1/5 of the filter. Images obtained from an epifluorescent microscope showed that E. coli cells were embedded inside the biofilm matrix and presented mainly as microcolonies intertwined with other microorganisms, which was consistent with findings from standard plate count methods and qPCR.     

Development of biomass in a drinking water granular active carbon (GAC) filter

Indigenous bacteria are essential for the performance of drinking water biofilters, yet this biological component remains poorly characterized. In the present study we followed biofilm formation and development in a granular activated carbon (GAC) filter on pilot-scale during the first six months of operation. GAC particles were sampled from four different depths (10, 45, 80 and 115 cm) and attached biomass was measured with adenosine tri-phosphate (ATP) analysis. The attached biomass accumulated rapidly on the GAC particles throughout all levels in the filter during the first 90 days of operation and maintained a steady state afterward. Vertical gradients of biomass density and growth rates were observed during start-up and also in steady state. During steady state, biomass concentrations ranged between 0.8-1.83 x 10⁻⁶ g ATP/g GAC in the filter, and 22% of the influent dissolved organic carbon (DOC) was removed. Concomitant biomass production was about 1.8 × 10¹² cells/m²h, which represents a yield of 1.26 × 10⁶ cells/μg. The bacteria assimilated only about 3% of the removed carbon as biomass. At one point during the operational period, a natural 5-fold increase in the influent phytoplankton concentration occurred. As a result, influent assimilable organic carbon concentrations increased and suspended bacteria in the filter effluent increased 3-fold as the direct consequence of increased growth in the biofilter. This study shows that the combination of different analytical methods allows detailed quantification of the microbiological activity in drinking water biofilters.     

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.     

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.     

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.     

Performance of a fungal biofilter treating gas-phase solvent mixtures during intermittent loading

Biological treatment processes used to remove and degrade volatile organic compounds (VOCs) from contaminated gases emitted by industrial operations or waste treatment processes are almost always subjected to transient loading conditions because of the inherently unsteady-state nature of contaminant generating processes. In the study presented here, a laboratory-scale biofilter populated by a mixed culture of fungi was used to study the transient response to various periods of no contaminant loading in a system treating a model waste gas stream containing a mixture of commonly used solvents. The biofilter, packed with cubed polyurethane foam media and operated with an empty bed residence time of 15s, was supplied with a four-component mixture of n-butyl acetate, methyl ethyl ketone, methyl propyl ketone, and toluene at target influent concentrations of 124, 50.5, 174, and 44.6 mg/m(3), respectively. This corresponds to a total VOC loading rate of 94.3g/(m(3)h). Biofilter performance was evaluated over a 94-day period for three loading conditions intended to simulate processes generating contaminated gases only during daytime operation, daytime operation with weekend shutdown periods, and with long term (9-day) shutdown. Results indicate that fungal biofilters can be an effective alternative to conventional abatement technologies for treating solvent contaminated off-gases even under discontinuous loading conditions.     

Non-steady state simulation of BOM removal in drinking water biofilters: applications and full-scale validation

A biofilter model called "BIOFILT" was used to simulate the removal of biodegradable organic matter (BOM) in full-scale biofilters subjected to a wide range of operating conditions. Parameters that were varied included BOM composition, water temperature (3.0-22.5 degrees C), and biomass removal during backwashing (0-100%). Results from biofilter simulations suggest a strong dependence of BOM removal on BOM composition. BOM with a greater diffusivity or with faster degradation kinetics was removed to a greater extent and also contributed to shorter biofilter start-up times. In addition, in simulations involving mixtures of BOM (i.e. readily degradable and slowly degradable components), the presence of readily degradable substrate significantly enhanced the removal of slowly degradable material primarily due to the ability to maintain greater biomass levels in the biofilters. Declines in pseudo-steady state BOM removal were observed as temperature was decreased from 22.5 to 3 degrees C and the magnitude of the change was significantly affected by BOM composition. However, significant removals of BOM are possible at low temperatures (3-6 degrees C). Concerning the impact of backwashing on biofilter performance, BOM removal was not affected by backwash resulting in biomass removals of 60% or less. This suggests that periodic backwashing should not significantly impact biofilter performance as observed biomass removals from full-scale biofilters were negligible. In general, the simulation results were in good qualitative and quantitative agreement with experimental results obtained from full-scale biofilters.     

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.     

Biocenosis of BAC(F)s used for groundwater treatment

The studies on the biocenosis of biologically active carbon filters (BAC(F)) used in treatment of Miocene water revealed the presence of protozoa of the group of flagellates and ciliates (Glaucoma sp., Opercularia sp.), saprophytic bacteria, phase I and II nitrifying bacteria, Fe(II) and Mn(II) oxidizing bacteria of the family Siderocapsaceae, Leptothrix ochracea and Pedomicrobium sp., as well as microscopic fungi. The stratification of biofilter colonisation by these microorganisms was found to be similar to that occurring in biofilters applied in sewage treatment. A hypothetical model of microbiological transformations in BAC(F)s, brought about by various physiological groups of microorganisms, is presented. It is shown that ozone pre-treatment of water dosed to the biofilter reduces the number of saprophytic bacteria and moulds in its upper layer, as well as Fe(II) oxidizing bacteria of the family Siderocapsaceae across the full section of the biofilter; it does not, however, influence the abundance of nitrifying phase I and II autotrophic bacteria and Mn(II) oxidizing bacteria of the family Siderocapsaceae. The abundance of microorganisms in the biofilter outflow is increased in comparison with that in untreated water; they do not, however, create a health hazard for human beings.     

The effect of biofilter loading rate on the removal of organic ozonation by-products

The effect of biofilter loading rate on the removal of organic ozonation by-products (OBPs) was studied in three biofilters used for the pretreatment of drinking water. One of the biofilters contained plastic biofilm media (KMT) and the two others contained expanded clay aggregates (Filtralite). Tests were carried out with ozonated humic water at several OBP concentration levels using empty bed contact times (EBCTs) from 6.2 to 48 min. The sum of aldehyde (formaldehyde, acetaldehyde, glyoxal and methyl glyoxal) and acetone concentrations ranged from 21 to 77 μg l⁻¹ in the ozonated water. The total ketoacid (glyoxylic, pyruvic, and ketomalonic acids) concentrations varied from 92 to 521 μg l⁻¹. The results were modelled using a first-order model including parameter for minimum substrate concentration (S_min). The OBPs showed different sensitivities to decreasing EBCT. Formaldehyde and pyruvic acid had the highest specific removal rates and their removal was little affected by increased loading rate. Ketomalonic acid had the lowest specific removal rate and its removal efficiency was reduced most with decreasing EBCT. The other studied OBPs had specific removal rates close to each other. The ketoacids had higher S_min concentrations than aldehydes and the S_min concentrations were influenced by the influent OBP concentrations. The biofilter media did not have a significant effect on OBP removal efficiency. Generally, over 80% removal efficiency was obtained for OBPs at EBCTs over 20 min. The significance of OBP concentrations close to S_min for the biological stability of drinking water needs to be determined.     

Nutrient gradients in a granular activated carbon biofilter drives bacterial community organization and dynamics

The quality of drinking water is ensured by hygienic barriers and filtration steps, such as ozonation and granular activated carbon (GAC) filtration. Apart from adsorption, GAC filtration involves microbial processes that remove biodegradable organic carbon from the ozonated ground or surface water and ensures biological stability of the treated water. In this study, microbial community dynamics in were monitored during the start-up and maturation of an undisturbed pilot-scale GAC filter at 4 depths (10, 45, 80 and 115 cm) over a period of 6 months. New ecological tools, based on 16S rRNA gene-DGGE, were correlated to filter performance and microbial activity and showed that the microbial gradients developing in the filter was of importance. At 10 cm from the top, receiving the freshly ozonated water with the highest concentration of nutrients, the microbial community dynamics were minimal and the species richness remained low. However, the GAC samples at 80-115 cm showed a 2-3 times higher species richness than the 10-45 cm samples. The highest biomass densities were observed at 45-80 cm, which corresponded with maximum removal of dissolved and assimilable organic carbon. Furthermore, the start-up period was clearly distinguishable using the Lorenz analysis, as after 80 days, the microbial community shifted to an apparent steady-state condition with increased evenness. This study showed that GAC biofilter performance is not necessarily correlated to biomass concentration, but rather that an elevated functionality can be the result of increased microbial community richness, evenness and dynamics.     

Influence of intermittent wetting and drying conditions on heavy metal removal by stormwater biofilters

Biofiltration is a technology to treat urban stormwater runoff, which conveys pollutants, including heavy metals. However, the variability of metals removal performance in biofiltration systems is as yet unknown. A laboratory study has been conducted with vegetated biofilter mesocosms, partly fitted with a submerged zone at the bottom of the filter combined with a carbon source. The biofilters were dosed with stormwater according to three different dry/wet schemes, to investigate the effect of intermittent wetting and drying conditions on metal removal.Provided that the biofilters received regular stormwater input, metal removal exceeded 95%. The highest metal accumulation occurs in the top layer of the filter media. However, after antecedent drying before a storm event exceeding 3–4 weeks the filters performed significantly worse, although metal removal still remained relatively high. Introducing a submerged zone into the filter improved the performance significantly after extended dry periods. In particular, copper removal in filters equipped with a submerged zone was increased by around 12% (α = 0.05) both during wet and dry periods and for lead the negative effect of drying could completely be eliminated, with consistently low outflow concentrations even after long drying periods.     

Manganese removal during bench-scale biofiltration

As biological manganese (Mn) removal becomes a more popular water treatment technology, there is still a large gap in understanding the key mechanisms and range of operational characteristics. This research aimed to expand on previous bench-scale experiments by directly comparing small filtration columns inoculated with indigenous biofilms from a Mn filtration plant and filtration columns inoculated with a liquid suspension of Leptothrix discophora SP-6. Batch tests found that in the absence of manganese oxidizing bacteria Mn was not removed by air alone, whereas a mixed population and Leptothrix strain achieved greater than 90% removal of Mn. The bench-scale biofiltration experiments found that biological filters can be inoculated with a pure culture of L. discophora SP-6 and achieve a similar removal of indigenous biofilm. While Mn oxidizing bacteria (MOB) seem to be necessary for the auto-catalytic nature of these biological filters, Mn removal is achieved with a combination of adsorption to Mn oxides and biological oxidation. Additionally, it was demonstrated that biological Mn removal is possible over a broader “field of activity” (e.g., Mn removal occurred at a pH level as low as 6.5) than has previously been reported. The ability of this treatment technology to work over a broader range of influent conditions allows for more communities to consider biological treatment as an option to remove Mn from their drinking water.     

滤料粒径对地下水中铁、锰、氨氮、浊度去除效果的影响

滤料粒径是生物滤池设计的一个重要参数。采用滤料粒径分别为0. 8~1. 0、3~4、8~10 mm的3根成熟生物滤柱处理地下水,考察滤料粒径对铁、锰、氨氮、浊度去除效果的影响。结果表明,1^#、2^#、3^#滤柱出水的总铁平均浓度分别为0. 020、0. 037、0. 078 mg/L,锰平均浓度分别为0. 003 0、0. 005 1、0. 006 7 mg/L,氨氮平均浓度分别为0. 022、0. 030、0. 050 mg/L,浊度均值分别为0. 28、0. 69、1. 32 NTU,除3^#滤柱出水浊度不达标外,其余指标均满足国家标准。随着滤料粒径的增大,铁、锰、氨氮的沿程浓度明显升高,去除区域向下延伸,浊度主要在0~0. 4 m滤层被去除。     

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.     

Influence of filter media depth and vegetation on Faecal Coliform removal by stormwater biofilters

Biofilters are promising technologies that widely applied in the treatment of urban stormwater. However, the microbial removal capacity performance depends greatly on the design of biofilters. Hence, this laboratory study attempts to investigate the influence of filter media depths (i.e. 150, 250, 350 and 450 mm) and the variation of native plants, that is, Cow Grass (Axonopus compressus) and Pearl Grass (Axonopus compressus, dwarf) in removing stormwater microorganism particularly Faecal Coliform (FC). Findings showed that a minimum media depth of 300 mm was required to achieve >1 log FC removal. The mean removal of FC at 450 mm depth filter exceeded 2 log for both Cow and Pearl grass biofilter columns. Results showed that there was no statistically significant difference in vegetation type on the performance of FC removal, however, Cow grass biofilter column revealed higher FC mean log removal compared to Pearl grass biofilter column.     

Estimating nitrifying biomass in drinking water filters for surface water treatment

The objective of this work is to estimate active nitrifying biomass and its main influencing factors in low-loaded biofilters based on operational data. An analytical approach based on balancing growth, decay and biomass removed by backwashing is proposed. The method is developed and applied in pilot-scale rapid sand filters for drinking water treatment. Decay rate was measured directly in the filter for different temperatures. To assess the amount of active biomass in backwash water, a technique based on respiration measurements was used. Backwash losses increased overproportional with balanced biomass in the filter. The impact of both parameters on active biomass is quantified exemplarily for a given constant nitrification rate.     

Mixing in upflow anaerobic filters and its influence on performance and scale-up

Tracer studies were carried out in laboratory-scale and pilot-scale upflow anaerobic filters to determine the effect of liquid velocity, gas production and media depth on mixing patterns. A computer simulation model was developed to analyse tracer-response curves. In water studies at laboratory scale, gas production was shown to have a significantly greater effect on mixing than liquid upflow velocity. A reduction in the quantity of media also resulted in greater mixing due to the greater void space in which synthetic gas bubbles could cause turbulence. In the presence of sludge during reactor operation, at pilot and laboratory-scale, gas production had a significant influence on mixing. However, liquid velocity played an important role in solids distribution in the filter, in conjunction with media depth. At pilot-scale, at a low solids concentration, a high liquid velocity lifted the sludge “bed”, raising the source of gas production. The absence of gas below the sludge bed resulted in a plug flow regime which the incoming substrate entered. A reduction in the quantity of media increased the degree of mixing for a given liquid velocity and gas surface load. Lower liquid upflow velocities are required at a reduced media depth to prevent excessive biomass loss. Shear rates increase at high liquid and gas velocities, resulting in detachment of solids from the media and biomass washout. A close correlation was established between mixing and process performance which led to the development of a programme for start-up and operation of the filter to maintain optimum biomass/substrate contact. A strategy for scale-up was proposed through the development of correlations obtained from laboratory-scale filter studies which were used to predict pilot-scale mixing characteristics. This research highlighted the important factors influencing mixing patterns and scale-up in anaerobic upflow filters.