Full-scale Filter Research Articles

Biological iron oxidation by Gallionella spp. in drinking water production under fully aerated conditions

Iron oxidation under neutral conditions (pH 6.5–8) may be a homo- or heterogeneous chemically- or a biologically-mediated process. The chemical oxidation is supposed to outpace the biological process under slightly alkaline conditions (pH 7–8). The iron oxidation kinetics and growth of Gallionella spp. – obligatory chemolithotrophic iron oxidizers – were assessed in natural, organic carbon-containing water, in continuous lab-scale reactors and full-scale groundwater trickling filters in the Netherlands. From Gallionella cell numbers determined by qPCR, balances were made for all systems. The homogeneous chemical iron oxidation occurred in accordance with the literature, but was retarded by a low water temperature (13 °C). The contribution of the heterogeneous chemical oxidation was, despite the presence of freshly formed iron oxyhydroxides, much lower than in previous studies in ultrapure water. This could be caused by the adsorption of natural organic matter (NOM) on the iron oxide surfaces. In the oxygen-saturated natural water with a pH ranging from 6.5 to 7.7, Gallionella spp. grew uninhibited and biological iron oxidation was an important, and probably the dominant, process. Gallionella growth was not even inhibited in a full-scale filter after plate aeration. From this we conclude that Gallionella spp. can grow under neutral pH and fully aerated conditions when the chemical iron oxidation is retarded by low water temperature and inhibition of the autocatalytic iron oxidation.

Assessment of nitrification in groundwater filters for drinking water production by qPCR and activity measurement

In groundwater treatment for drinking water production, the causes of nitrification problems and the effectiveness of process optimization in rapid sand filters are often not clear. To assess both issues, the performance of a full-scale groundwater filter with nitrification problems and another filter with complete nitrification and pretreatment by subsurface aeration was monitored over nine months. Quantitative real-time polymerase chain reaction (qPCR) targeting the amoA gene of bacteria and archaea and activity measurements of ammonia oxidation were used to regularly evaluate water and filter sand samples. Results demonstrated that subsurface aeration stimulated the growth of ammonia-oxidizing prokaryotes (AOP) in the aquifer. Cell balances, using qPCR counts of AOP for each filter, showed that the inoculated AOP numbers from the aquifer were marginal compared with AOP numbers detected in the filter. Excessive washout of AOP was not observed and did not cause the nitrification problems. Ammonia-oxidizing archaea grew in both filters, but only in low numbers compared to bacteria. The cell-specific nitrification rate in the sand and backwash water samples was high for the subsurface aerated filter, but systematically much lower for the filter with nitrification problems. From this, we conclude that incomplete nitrification was caused by nutrient limitation.

Development of testing procedure for ceramic disc filters

Small-scale laboratory tests for sizing and designing disc filters are typically performed by using leaf test equipment. Although the basic tests are fairly simple and quick, the accuracy and repeatability of the results may be poor due to various reasons. In addition to errors caused by variations in the structure of the equipment, also the skills and experience of the person performing the tests is of great importance. This paper introduces an experimental study carried out for defining the most important sources of errors in these kinds of laboratory tests and for estimating their influence on the final test results. The results obtained in this study were utilized for designing an improved version of the test equipment and also for creating a standard procedure for performing the tests. The results acquired with the small-scale laboratory tests were in good agreement with the performance results obtained from full-scale ceramic disc filters operating in industrial processes.

Assessing granular media filtration for the removal of chemical contaminants from wastewater

Granular media filtration was evaluated for the removal of a suite of chemical contaminants that can be found in wastewater. Laboratory- and pilot-scale sand and granular activated carbon (GAC) filters were trialled for their ability to remove atrazine, estrone (E1), 17α-ethynylestradiol (EE2), N-nitrosodimethylamine (NDMA), N-nitrosomorpholine (NMOR) and N-nitrosodiethylamine (NDEA). In general, sand filtration was ineffective in removing the contaminants from a tertiary treated wastewater, with the exception of E1 and EE2, where efficient removals were observed after approximately 150 d. Batch degradation experiments confirmed that the removal of E1 was through biological activity, with a pseudo-first-order degradation rate constant of 7.4 × 10 −3 h −1. GAC filtration was initially able to effectively remove all contaminants; although removals decreased over time due to competition with other organics present in the water. The only exception was atrazine where removal remained consistently high throughout the experiment. Previously unreported differences were observed in the adsorption of the three nitrosamines, with the ease of removal following the trend, NDEA > NMOR > NDMA, consistent with their hydrophobic character. In most instances the removals from the pilot-scale filters were generally in agreement with the laboratory-scale filter, suggesting that there is potential in using laboratory-scale filters as monitoring tools to evaluate the performance of pilot- and possibly full-scale sand and GAC filters at wastewater treatment plants.

Observations on the Performance and Modeling of Glycerin- and Methanol-fed Denitrification Filters

Observations on the Performance and Modeling of Glycerin- and Methanol-fed Denitrification FiltersThe objective of this investigation was to utilize the full-scale denitrification filter data from five treatment plants to explore the significance of the following variables on nitrate removal rate: (a) nitrate loading rate (NLR), (b) hydraulic loading rate (HLR), (c) temperature, and (d) PO4- P:NO3-N ratio. Much of this data was gathered in prior studies (Bilyk et al. 2008 and 2011; Ledwell et...Author(s)Katya BilykPeter DoldSamuel LedwellRon LatimerPaul PittMary SadlerSourceProceedings of the Water Environment FederationSubjectSession 32: Supplemental Carbon for DenitrificationDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2011ISSN1938-6478SICI1938-6478(20110101)2011:15L.1598;1-DOI10.2175/193864711802713405Volume / Issue2011 / 15Content sourceWEFTECFirst / last page(s)1598 - 1614Copyright2011Word count112Subject keywordsDenitrificationfiltercarbonmethanolglyceringlycerolmodelingphosphorus limitation

Active slag filters—simple and sustainable phosphorus removal from wastewater using steel industry byproduct

Active filtration, where effluent is passed through a reactive substrate such as steel slag, offers a simple and cost-effective option for removing phosphorus (P) from effluent. This work summarises a series of studies that focused on the world's only full-scale active slag filter operated through to exhaustion. The filter achieved 75% P-removal during its first 5 years, reaching a retention capacity of 1.23 g P/kg slag but then its performance sharply declined. Scanning electron microscopy, X-ray diffraction, X-ray fluorescence, and chemical extractions revealed that P sequestration was primarily achieved via adsorption onto iron (Fe) oxyhydroxides on the slag's surface. It was concluded that batch equilibrium tests, whose use has been repeatedly proposed in the literature, cannot be used as an accurate predictor of filter adsorption capacity because Fe oxyhydroxides form via chemical weathering in the field, and laboratory tests don't account for this. Research into how chemical conditions affect slag's P retention capacity demonstrated that near-neutral pH and high redox are optimal for Fe oxyhydroxide stability and overall filter performance. However, as Fe oxyhydroxide sites fill up, removal capacity becomes exhausted. Attempts to regenerate P removal efficiency using physical techniques proved ineffective contrary to dogma in the literature. Based on the newly-developed understanding of the mechanisms of P removal, chemical regeneration techniques were investigated and were shown to strip large quantities of P from filter adsorption sites leading to a regenerated P removal efficiency. This raises the prospect of developing a breakthrough technology that can repeatedly remove and recover P from effluent.

Evaluation of Biological Air Filters for Livestock Ventilation Air by Membrane Inlet Mass Spectrometry

Biological air filters have been proposed as a cost-effective technology for reducing odor emissions from intensive swine production facilities. In this work we present results from the application of membrane inlet mass spectrometry (MIMS) for continuously monitoring the removal of odorous compounds in biological air filters. The sensitivity and selectivity were tested on synthetic samples of selected odorous compounds, and linearity and detection limits in the lower ppb range were demonstrated for all compounds tested (methanethiol, dimethyl sulfide, carboxylic acids, 4-methylphenol, aldehydes, indole, and skatole) except trimethylamine. The method was applied in situ at two full-scale filters installed at swine houses. The results have been compared with analyses by thermal desorption gas chromatography-mass spectrometry (TD-GC/MS), and odor was measured by olfactometry. By comparison with TD-GC/MS, observed MIMS signals were assigned to 4-methylphenol, 4-ethylphenol, indole, skatole, the sum of volatile reduced organic sulfur compounds (ROS), and three subgroups of carboxylic acids. The removal rates were observed to be related to air-water partitioning with removal efficiencies in the range of 0 to 50% for low-soluble organic sulfur compounds and high removal efficiencies (typically 80-100%) for more soluble phenols and carboxylic acids. Based on the results and published odor threshold values, it is estimated that the low removal efficiency of ROS is the main limitation for achieving a higher odor reduction.

A full-scale treatment of freeway toll-gate domestic sewage using ecology filter integrated constructed rapid infiltration

To explore an economical and manageable wastewater treatment process, a full-scale ecology filter integrated constructed rapid infiltration (Eco-CRI) was conducted and applied to treat freeway toll-gate domestic sewage, and the performances of Eco-CRI were investigated to evaluate its technical and economical suitability. The results showed that chemical oxygen demand, suspended solids, ammonia, and phosphorus could be removed efficiently when 1.0 m d −1 of the hydraulic loading rate and 2 h of dosing and 6 h of resting of feed regime were operated, respectively. Clogging, which was by far the biggest operational concern for the soil-based treatment systems, was not observed during the whole operation over a period of 14 months. Based on the results of economical analysis, electrical power consumption of per m 3 wastewater treated was only 0.13 kWh. Besides maintenance of dosing pump, regular maintenance of Eco-CRI was just harvesting reeds and earthworms once a year. The facts indicated that Eco-CRI was a cost-effective and technically feasible process for freeway toll-gate domestic sewage treatment, and might serve as an attractive option for wastewater treatment in remote areas where regular maintenance was not feasible and/or in present developing countries like China where uneconomical approaches were not acceptable due to the local socioeconomic situation.

Performance of High-Rate Biotrickling Filter Under Ultra-High H<SUB>2</SUB>S Loadings at a Municipal WWTP

Performance of High-Rate Biotrickling Filter Under Ultra-High H2S Loadings at a Municipal WWTPA full-scale biotrickling filter (BTF) was installed at the JEA Buckman Water Reclamation Facility in Jacksonville, Florida. The objective was to determine the effect of very low empty bed residence times (EBRTs) ( 300 g H2S/m3.hr) on the BTF's performance. The BTF uses structured synthetic EcoBase™ media and it was treating air from the biosolids building.The inlet and outlet H2S...Author(s)Louis D. le RouxMatthew E. JohnsonSourceProceedings of the Water Environment FederationSubjectArticlesDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2010ISSN1938-6478SICI1938-6478(20100101)2010:3L.691;1-DOI10.2175/193864710802768334Volume / Issue2010 / 3Content sourceOdors and Air Pollutants ConferenceFirst / last page(s)691 - 701Copyright2010Word count186Subject keywordsBiotrickling filterhydrogen sulfide removalbiological odor control

Comparison of batch sorption tests, pilot studies, and modeling for estimating GAC bed life

Saint Paul Regional Water Services (SPRWS) in Saint Paul, MN experiences annual taste and odor episodes during the warm summer months. These episodes are attributed primarily to geosmin that is produced by cyanobacteria growing in the chain of lakes used to convey and store the source water pumped from the Mississippi River. Batch experiments, pilot-scale experiments, and model simulations were performed to determine the geosmin removal performance and bed life of a granular activated carbon (GAC) filter–sorber. Using batch adsorption isotherm parameters, the estimated bed life for the GAC filter–sorber ranged from 920 to 1241 days when challenged with a constant concentration of 100 ng/L of geosmin. The estimated bed life obtained using the AdDesignS model and the actual pilot-plant loading history was 594 days. Based on the pilot-scale GAC column data, the actual bed life (>714 days) was much longer than the simulated values because bed life was extended by biological degradation of geosmin. The continuous feeding of high concentrations of geosmin (100–400 ng/L) in the pilot-scale experiments enriched for a robust geosmin-degrading culture that was sustained when the geosmin feed was turned off for 40 days. It is unclear, however, whether a geosmin-degrading culture can be established in a full-scale filter that experiences taste and odor episodes for only 1 or 2 months per year. The results of this research indicate that care must be exercised in the design and interpretation of pilot-scale experiments and model simulations for predicting taste and odor removal in full-scale GAC filter–sorbers. Adsorption and the potential for biological degradation must be considered to estimate GAC bed life for the conditions of intermittent geosmin loading typically experienced by full-scale systems.

GAC adsorption filters as barriers for viruses, bacteria and protozoan (oo)cysts in water treatment

Granular Activated Carbon (GAC) adsorption filtration is commonly used in drinking water treatment to remove NOM and micro-pollutants and on base of the process conditions a certain capacity to eliminate pathogenic micro-organisms was expected. The experiences with the mandatory quantitative microbial risk assessment of Dutch drinking water revealed a lack of knowledge on the elimination capacity of this process for pathogens. The objective of the current study was to determine the capacity of GAC filtration to remove MS2, Escherichia coli and spores of Clostridium bifermentans as process indicators for pathogens and more directly of (oo)cysts of Cryptosporidium parvum and Giardia lamblia. Challenge tests with fresh and loaded GAC were performed in pilot plant GAC filters supplied with pre-treated surface water at a contact time which was half of the contact time of the full-scale GAC filters. MS2 phages were not removed and the removal of E. coli and the anaerobic spores was limited ranging from ≤0.1–1.1 log. The (oo)cysts of C. parvum and G. lamblia, however, were removed significantly (1.3–2.7 log). On base of the results of the experiments and the filtration conditions the removal of the indicator bacteria and (oo)cysts was largely attributed to attachment. The model of the Colloid Filtration Theory was used to describe the removal of the dosed biocolloids in the GAC filters, but the results demonstrated that there is a lack of quantitative knowledge about the influence of collector characteristics on the two major CFT parameters, the single collector and the sticking efficiency.

Technical and economical study of a full-scale biotrickling filter for H2S removal from biogas

The present study evaluates the technical and economical feasibility of the H2S elimination from an energy-rich gas using a full-scale biotrickling filter installed in a municipal waste water treatment plant. The study analyzes the continuous operation of a 4.5 months period, treating 80 m3 h-1 of biogas with an average H2S concentration of 3000 ppmv. The bioreactor was operated at a gas contact time of 180 seconds and maximum elimination capacities of 170 g H2S m-3 h-1 were obtained without any occurrence of neither biological nor mass transfer limitation. Elemental sulfur and sulfate were the main detected byproducts of the H2S treatment. The main drawback observed during the studied period was related to the air flow supply. This caused a removal efficiency decrease and an excess of sulfur production. A comparative cost-benefit analysis of the more applied chemical oxidation processes with the biological treatment was performed. Savings chemicals indicated that the payback time of the substitution treatment was about 4.5 years. Cost savings ranged between 11000€ per year, or 2.6€ per kg H2S treated. The results of this study have shown how to solve the main operational problems detected in the proposed system and the cost-benefit analysis suggests a significant benefit by replacing the current chemical treatment by the biological alternative not only from an environmental point of view, but also from an economical perspective.

Dynamic Modeling of Bentazon Removal by Pseudo-Moving-Bed Granular Activated Carbon Filtration Applied to Full-Scale Water Treatment

A model for the removal of pesticides by granular activated carbon (GAC) filtration in full-scale water treatment is presented. The model describes GAC filtration in a pseudo-moving-bed configuration, where two filters are operated in series and after breakthrough the first filter is regenerated and becomes the second filter. The influent of the second filter is changing due to gradual breakthrough of the first filter. Therefore, a dynamic model is developed based on kinetics, equilibrium, and mass balance equations. The model is calibrated and validated on data of full-scale and pilot plants. Operational strategies are evaluated of two different cases. From this study it can be concluded that a dynamic mathematical model can be successfully used to evaluate the performance and operation of full-scale GAC filters for pesticide removal and can be used for operational decision support. Data obtained from practice can be used for calibration without additional laboratory work.

On-line monitoring of gas-phase bioreactors for biogas treatment: hydrogen sulfide and sulfide analysis by automated flow systems

Biogas is produced by biological processes under anaerobic conditions and may contain up to 20,000 ppm(v) hydrogen sulfide (H(2)S), a corrosive substance that attacks power engines and can affect the health of the industrial staff. H(2)S must be removed from the biogas, especially in co-generation facilities where the biogas is burnt for energy production. Nowadays, biofiltration is being studied and considered as an interesting alternative for removing H(2)S from the biogas besides classical chemical processes. The novelty of this work is the design and construction of an automated H(2)S on-line analyser to assess the composition of the liquid and gas phases of gas-phase bioreactors. The analyser is made of two parallel flow configurations which share the same detection device. The first configuration is a single-channel flow injection analyser (FIA) to detect S(2-) in the liquid phase. The second configuration is a continuous flow analyser (CFA) with a gaseous diffusion step (GD-CFA) for detecting H(2)S in the gas phase. The diffusion step enables separation of the H(2)S((g)) from the sample and its conversion into a detectable chemical species (S(2-)). S(2-) detection was performed with an Ag(2)S ion-selective electrode (ISE) selective to S(2-)(aq). The main response parameters of the FIA system are a linear range between 3 x 10(-5) and 1 x 10(-1) mol L(-1) S(2-) (0.61-3,200 mg L(-1)), with a sensitivity of 27.9 mV decade(-1) and a detection limit of 1.93 x 10(-5) mol L(-1) S(2-). The GD-CFA configuration presents a linear range between 400 and 10,000 ppm(v) H(2)S((g)) with a sensitivity of 26.1 mV decade(-1) and a detection limit of 245 ppm(v) H(2)S. The proposed analyser was used by analysing real gas and liquid samples with optimal results at a full-scale biotrickling filter for biogas treatment at a municipal wastewater treatment plant.

Rapid and direct estimation of active biomass on granular activated carbon through adenosine tri-phosphate (ATP) determination

Granular activated carbon (GAC) filtration is used during drinking water treatment for the removal of micropollutants such as taste and odour compounds, halogenated hydrocarbons, pesticides and pharmaceuticals. In addition, the active microbial biomass established on GAC is responsible for the removal of biodegradable dissolved organic carbon compounds present in water or formed during oxidation (e.g., ozonation and chlorination) processes. In order to conduct correct kinetic evaluations of DOC removal during drinking water treatment, and to assess the state and performance of full-scale GAC filter installations, an accurate and sensitive method for active biomass determination on GAC is required. We have developed a straight-forward method based on direct measurement of the total adenosine tri-phosphate (ATP) content of a GAC sample and other support media. In this method, we have combined flow-cytometric absolute cell counting and ATP analysis to derive case-specific ATP/cell conversion values. In this study, we present the detailed standardisation of the ATP method. An uncertainty assessment has shown that heterogeneous colonisation of the GAC particles makes the largest contribution to the combined standard uncertainty of the method. The method was applied for the investigation of biofilm formation during the start-up period of a GAC pilot-scale plant treating Lake Zurich water. A rapid increase in the biomass of up to 1.1×10 10 cells/g GAC dry weight (DW) within the first 33 days was observed, followed by a slight decrease to an average steady-state concentration of 7.9×10 9 cells/g GAC DW. It was shown that the method can be used to determine the biomass attached to the GAC for both stable and developing biofilms.

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 75–82 μg/L, which illustrates the potential of THM cometabolism to have a significant impact on treated water quality.

Using Pilot-Scale Investigations to Estimate the Remaining Geosmin and MIB Removal Capacity of Full-Scale GAC-Capped Drinking Water Filters

Abstract Pilot tests were conducted to investigate the removal of geosmin and 2-methylisoborneol (MIB) by new and semi-exhausted granular activated carbon (GAC) extracted from full-scale filters located in the City of Toronto's drinking water treatment facilities. Four pilot filters containing core-sampled GAC and new sand were fed with settled water from a full-scale plant and operated under conditions similar to those employed at full-scale. None of the pilot filters appeared to be capable of reducing geosmin and MIB concentrations to below the commonly cited threshold odour limits of 4 ng/L for geosmin and 9 ng/L for MIB at the influent levels tested. When operated at a 5-min empty bed contact time (EBCT) with geosmin influent concentrations in the range of about 70 to 110 ng/L, removals ranged from 10 to 38% in filters with 25 to 30 cm of used GAC. In the filter with 25 cm of new GAC, removal was 83%. When operated with a 7.5-min EBCT, the filter containing 95 cm of used bituminous GAC removed 78% of the geosmin present in the influent. For both geosmin and MIB, the effluent concentration and the amount removed increased as influent concentration increased, as was expected. In general, geosmin was better removed than MIB.

Multivariate Online Monitoring of a Full-Scale Biological Anaerobic Filter Process Using Kernel-Based Algorithms.

Multivariate statistical process control such as principal component analysis (PCA) and partial least squares (PLS) has been effectively utilized to analyze large databases accumulated in industrial plants in order to improve process performance and product quality. However, because both PCA and PLS are basically linear methods, nonlinearity in most chemical and biological processes is still a significant problem for their practical applications. Kernel-based algorithms are potentially very efficient for monitoring process disturbances and predicting key quality variables of nonlinear processes by mapping an original input space into a high-dimensional feature space. Nonlinear data structure in the original space is most likely to be linear at the high-dimensional feature space. Kernel-based methods essentially require only linear algebra, making them as simple as linear multivariate projection methods, and can handle a wide range of nonlinearities because of their ability to use different kernel functions. In this work, kernel-based algorithms such as kernel PCA (KPCA) and kernel PLS (KPLS) are applied to a full-scale biological anaerobic filter process treating highstrength organic wastewater in a petrochemical plant. KPCA is applied to detect process disturbances in real-time and KPLS to predict inferentially key process variables in the anaerobic filter process. The proposed kernel-based approaches could effectively capture the nonlinear relationship in the process variables and show far better performance in process monitoring and prediction of quality variables compared to the conventional PCA and PLS methods.

Vertical distribution of nitrifying populations in bacterial biofilms from a full‐scale nitrifying trickling filter

Cryosectioned biofilm from three depths (0.5, 3.0 and 6.0 m) in a full-scale nitrifying trickling filter (NTF) were studied using fluorescence in situ hybridization (FISH). A large number of sections were used to determine how the biofilm thickness, structure and community composition varied with depth along the ammonium concentration gradient in the NTF, and how the ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were distributed vertically within the biofilm. Both the biofilm thickness and relative biomass content of the biofilm decreased with depth, along with structural differences such as void size and surface roughness. Four AOB populations were found, with two Nitrosomonas oligotropha populations dominating at all depths. A smaller population of Nitrosomonas europaea was present only at 0.5 m, while a population of Nitrosomonas communis increased with depth. The two N. oligotropha populations showed different vertical distribution patterns within the biofilm, indicating different ecophysiologies even though they belong to the same AOB lineage. All NOB were identified as Nitrospira sp., and were generally more associated with the biofilm base than the surface-associated dominating AOB population. Additionally, a small population of anaerobic ammonia-oxidizers was found at 6.0 m, even though the biofilm was well aerated.

Tertiary Denitrification and Very Low Phosphorus Limits: A Practical Look at Phosphorus Limitations on Denitrification Filters

Deep-bed denitrification filters have been successfully used for over 25 years to meet total nitrogen (TN) limits of 3 mg/L and even lower. In some cases, the wastewater treatment plants (WWTPs) also have had moderate total phosphorus (TP) limits, in the range of 0.5 to 2 mg/L. More recently, some WWTPs are required to meet very low TN and TP limits simultaneously. For example, as the result of the development of total maximum daily loads (TMDL) for the Chesapeake Bay, many WWTPs in Maryland and Virginia will be required to meet limits of 3 mg/L TN and 0.3 mg/L TP on a 12-month average basis. A number of these plants have even more stringent phosphorus limits of 0.18 mg/L monthly average. This has raised practical operating concerns with respect to the ability of these WWTPs to meet low TP limits without additional treatment downstream of the filters. In addition, a certain amount of phosphorus is required to support the growth of denitrifying bacteria and it may be difficult to ensure there is sufficient phosphorus to promote denitrification if too much is removed in upstream processes. This paper will examine phosphorus requirements for denitrification, and expands upon earlier information presented at the International Water Association Biofilm Systems VI Conference in September 2006. Operating data from several full-scale and pilot denitrification filters operating for low TN and TP simultaneously will be presented and evaluated to determine when low phosphorus concentrations actually impact denitrification, and identify strategies for ensuring reliable performance.