Application of high rate nitrifying trickling filters for potable water treatment

The interference of ammonia with chlorination is a prevalent problem encountered by water treatment plants located throughout South East Asia. The efficacy of high rate, plastic-packed trickling filters as a pre-treatment process to remove low concentrations of ammonia from polluted surface water was investigated. This paper presents the findings from a series of pilot experiments, which were designed to investigate the effect of specific conditions—namely low ammonia feed concentrations (0.5-5.0 mg NH₄-N L⁻¹), variations in hydraulic surface load (72.5-145 m³ m⁻² d⁻¹) and high suspended solid loads (51 ± 25 mg L⁻¹)—on filter nitrifying capacity. The distribution of nitrification activity throughout a trickling filter bed was also characterised. Results confirmed that high hydraulic rate trickling filters were able to operate successfully, under ammonia-N concentrations some 10- to 50-fold lower and at hydraulic loading rates 30-100 times greater than those of conventional wastewater applications. Mass transport limitations posed by low ammonia-N concentrations on overall filter performance were insignificant, where apparent nitrification rates (0.4-1.6 g NH₄-N m⁻² d⁻¹), equivalent to that of wastewater filters were recorded. High inert suspended solid loadings had no adverse effect on nitrification. Results imply that implementation of high rate trickling filters at the front-end of a water treatment train would reduce the ammonia-related chlorine demand, thereby offering significant cost savings.     

Operational experiences with structured plastic media filters: 10 years on

The performance of 10 cross flow structured plastic media trickling filter plants is discussed. The sites are arranged in a number of configurations with the plastic media filters operating as sole secondary process units, in parallel with other process units or in double filtration configuration. Data for 2003 and 2004 show that the plants are performing well. Data are presented for the plastic media filter stream where it is available. Two operational problems are discussed; overgrazing of nitrifying biofilms by excessive populations of snails and loss of nitrification performance in cold weather, particularly on smaller sites. Overgrazing by snails, identified as Lymnaea peregra has been controlled on one site by the annual treatment of an isolated filter with high ammoniacal nitrogen strength sludge dewatering liquors. On a second site suffering a similar problem the plastic media filter duty was changed from single filtration to being the primary filters in a double filtration system with existing stone media filters used for secondary filters. Loss of nitrification performance has been associated with excessive heat loss on some sites. Filters built as tower structures, with typically 4–5 m media depth allow easy control of airflow via restriction of the engineered ventilation openings at the base of the filter. This has been found to have a direct impact on the degree of cooling. However, airflow control on plastic media retrofitted into wide shallow stone media filter shells with 1.6–2 m media depth is more difficult. These structures offer less opportunity for control of airflow and associated heat losses.     

An energy-efficient two-stage passively aerated trickling filter for high-strength wastewater treatment and reuse

This work aimed to assess the technical and energetic feasibility of a passively aerated laboratory-scale trickling filter, configured as a two-stage system, to produce urban wastewater (UWW) reusable in agriculture. The trickling filter was fed continuously with high-strength UWW at four hydraulic retention times (HRTs), that is, 10, 5, 2 and 1 day, corresponding to organic loading rates (OLRs) of 0.1, 0.2, 0.5 and 0.9 kg COD/m³/d, respectively. The results revealed a good performance in organic load removal and nitrification at the four HRTs. The trickling filter showed high organic pollutant removal efficiencies of up to 93%, 94% and 98% for chemical oxygen demand (COD), BOD₅ and total suspended solid (TSS), respectively, as well as high ammonia nitrogen removal above 96% at the shortest HRT of 1 day. All physicochemical parameters were significantly lower than the allowable limits set out in ISO 16075 for category C (non-food crop irrigation) irrigation water. The reuse of treated UWW in irrigation led to germination indexes and growth parameters of triticale (Triticosecale Wittm.) almost equal to those obtained using tap water. Energy use was found to be about 0.2754 kWh/m³ of treated wastewater, making it competitive with trickling filter plants reported in the literature. The simplicity and energy efficiency of the developed trickling filter system, combined with its capacity for almost full nitrification, make it appealing for sewage treatment in small communities in developing countries.     

A design model for nitrification on structured cross flow plastic media trickling filters

An empirical model has been developed to predict the effluent ammoniacal nitrogen concentration from structured cross flow plastic media trickling filters operated over the range of BOD loadings 0.12–0.38 kg/m³/day and ammoniacal nitrogen loadings of 0.06–0.23 kg/m³/day. The model gives good predictions based on 24‐h average effluent concentrations over a range of filter depths, organic and hydraulic loading rates. When incorporated with suitable hydraulic models, effluent ammoniacal concentration can be predicted through the diurnal range. The data gathering for the model included depth profiles on three filters. These have shown that at all but the very highest BOD loadings, nitrification commences from the very top of the filter in the presence of soluble BOD loadings previously thought to preclude the development of nitrifying biomass. Several reasons have been proposed to explain this, with the key argument being that the efficient oxygen transfer afforded by the media design is sufficient to satisfy heterotroph and autotroph oxygen demand simultaneously.     

Estrogenic and AhR activities in dissolved phase and suspended solids from wastewater treatment plants

The distribution of estrogen receptor (ERα) and Aryl Hydrocarbon Receptor (AhR) activities between the dissolved phase and suspended solids were investigated during wastewater treatment. Three wastewater treatment plants with different treatment technologies (waste stabilization ponds (WSPs), trickling filters (TFs) and activated sludge supplemented with a biofilter system (ASB)) were sampled. Estrogenic and AhR activities were detected in both phases in influents and effluents. Estrogenic and AhR activities in wastewater influents ranged from 41.8 to 79 ng/L E₂ Eq. and from 37.9 to 115.5 ng/L TCDD Eq. in the dissolved phase and from 5.5 to 88.6 ng/g E₂ Eq. and from 15 to 700 ng/g TCDD Eq. in the suspended solids. For both activities, WSP showed greater or similar removal efficiency than ASB and both were much more efficient than TF which had the lowest removal efficiency. Moreover, our data indicate that the efficiency of removal of ER and AhR activities from the suspended solid phase was mainly due to removal of suspended solids. Indeed, ER and AhR activities were detected in the effluent suspended solid phase indicating that suspended solids, which are usually not considered in these types of studies, contribute to environmental contamination by endocrine disrupting compounds and should therefore be routinely assessed for a better estimation of the ER and AhR activities released in the environment.     

Quantification of denitrification potential in carbonaceous trickling filters

Biofilm samples from a carbonaceous trickling filter (TF) were evaluated in bench scale reactors to determine their maximum potential denitrification rates. Intact, undisturbed biofilms were placed into 0.6 L bench-scale reactors filled with sterilized, primary clarifier effluent spiked with nitrate to a final concentration of 16-18 mg/L as N. Dissolved oxygen concentrations were maintained between 2 and 4 mg/L in the bulk aqueous phase. Nitrate loss from the reactors was monitored over a 5h period. Denitrification rates of 3.09-5.55 g-N/m(2)day were observed with no initial lag period. This suggests that the capacity for denitrification is inherent in the biofilm and that denitrification can take place even when oxygen is present in the bulk aqueous phase. There were no significant differences in denitrification rates per unit area of media (g-N/m(2)day) either between (a). experimental runs or (b). sampling locations over the trickling filter. This suggests that denitrification potentials are uniform over the entire volume of the full-scale TF. For wastewater treatment plants with TFs that currently nitrify downstream, this approach may be used to meet less stringent permitted discharge concentrations and may allow some facilities to postpone or eliminate construction of additional unit processes for denitrification.     

Design of a nitrifying tertiary trickling filter based on theoretical concepts

A nitrification model for a tertiary trickling filter is developed based on stoichiometry, Fick's Law and Monod kinetics. The design of tertiary trickling filters for nitrification is discussed, with special emphasis on: residual ammonium concentration, recirculation, reactors in series, residual alkalinity, residual nitrite concentration and effects of temperature on reactor performance. Wherever possible the theoretical predictions are compared with experimental results.     

Particle size distribution in effluent of trickling filters and in humus tanks

Particles and aggregates from trickling filters must be eliminated from wastewater. Usually this happens through sedimentation in humus tanks. Investigations to characterize these solids by way of particle size measurements, image analysis and particle charge measurements (zeta potential) are made within the scope of Research Center for Science and Technology "Fundamentals of Aerobic biological wastewater treatment" (SFB 411). The particle size measuring results given within this report were obtained at the Ingolstadt wastewater treatment plant, Germany, which served as an example. They have been confirmed by similar results from other facilities. Particles flushed out from trickling filters will be partially destroyed on their way to the humus tank. A large amount of small particles is to be found there. On average 90% of the particles are smaller than 30 microm. Particle size plays a decisive role in the sedimentation behaviour of solids. Small particles need sedimentation times that cannot be provided in settling tanks. As a result they cause turbidity in the final effluent. Therefore quality of sewage discharge suffers, and there are hardly advantages of the fixed film reactor treatment compared to the activated sludge process regarding sedimentation behaviour.     

Operational aspects of the desulfurization process of energy gases mimics in biotrickling filters

Biological removal of reduced sulfur compounds in energy-rich gases is an increasingly adopted alternative to conventional physicochemical processes, because of economical and environmental benefits. A lab-scale biotrickling filter reactor for the treatment of high-H₂S-loaded gases was developed and previously proven to effectively treat H₂S concentrations up to 12,000 ppm_v at gas contact times between 167 and 180 s. In the present work, a detailed study on selected operational aspects affecting this system was carried out with the objective to optimize performance. The start-up phase was studied at an inlet H₂S concentration of 1000 ppm_v (loading of 28 g H₂S m⁻³ h⁻¹) and inoculation with sludge from a municipal wastewater treatment plant. After reactor startup, the inlet H₂S concentration was doubled and the influence of different key process parameters was tested. Results showed that there was a significant reduction of the removal efficiency at gas contact times below 120 s. Also, mass transfer was found to be the main factor limiting H₂S elimination, whereas performance was not influenced by the bacterial colonization of the packed column after the initial startup. The effect of gas supply shutdowns for up to 5 days was shown to be irrelevant on process performance if the trickling liquid recirculation was kept on. Also, the trickling liquid velocity was investigated and found to influence sulfate production through a better use of the supplied dissolved oxygen. Finally, short-term pH changes revealed that the system was quite insensitive to a pH drop, but was markedly affected by a pH increase, affecting both the biological activity and the removal of H₂S. Altogether, the results presented and discussed herein provide new insight and operational data on H₂S removal from energy gases in biotrickling filters.     

Leachate treatment with nitrification of ammonia

Results are presented on the treatment of leachate to remove ammonia by biological nitrification. Outdoor activated sludge and trickling filter pilot plants were operated for 2 years at a major co-disposal landfill. Leachate ammonia nitrogen concentrations ranged from 150 to 550 mg l^?1 while TOC concentrations ranged from 200 to 500 mg l^?1. Very little of the TOC was degradable and BOD: NH₃-N ratios were typically 1:3.Nitrification was successfully established in both plants, and curves were established for the response of the kinetics to different temperatures. Maximum ammonia removal rate in the activated sludge plant was at least 131 g N kg VSS^?1 day^?1 achieved at an average temperature of 13°C. Maximum removal rate in the trickling filter was 309 mg N m^?2 day^?1, at 16°C.Operating problems and strategies for full-scale treatment are discussed.     

The effects of media size on the performance of biological aerated filters

Biological aerated filters (BAFs) are an attractive process option, particularly when low land usage is required. They can combine BOD, solids and ammoniacal nitrogen removal and can be utilised at both secondary and tertiary stages of wastewater treatment. Media selection is critical in the design and operation of BAFs to achieve effluent quality requirements. Two size ranges, 1.5-3.5 and 2.5-4.5 mm, of a foamed clay called StarLight C were used in pilot-scale reactors. Both performed well as BAF media, with reactor loads up to 12 kg COD m(-3) d and 4 kg suspended solids m(-3) d (based on working volumes). The most consistent effluent was obtained using the smaller medium since, at flow rates above 0.41 min(-1), the BAF using the larger medium produced an effluent containing more than 20 mg l(-1) of suspended solids for over 30 min after backwashing. Up to 70% longer run times, as determined by reaching a set head loss, were recorded for the BAF containing the larger rather than the smaller medium. Additionally, the development of pressure above the smaller medium filter bed tended to be logarithmic rather than linear. Reactor profiles indicated that suspended solids removal did not occur over the full 2.3 m depth of the columns. The BAF containing the smaller medium utilised a mean depth of 1.7 +/- 0.3 m, whereas a mean depth of 2.1 +/- 0.3 m was used by the larger medium BAF. Both the head loss development data and the suspended solids removal profiles indicated that the smaller medium BAF was underperforming as a filter.     

Organic carbon removal and nitrification of high strength wastewaters using stratified sand filters

The current practice of spray irrigation of dairy parlour wastewaters is laborious and time consuming. Intermittent sand filtration systems may offer an alternative to spray irrigation when designed to remove organic carbon, nitrogen, phosphorus, coliforms and viruses from such wastewaters to allow discharge of the final effluent directly into receiving waters without damage to the environment. In this study two instrumented stratified sand filter columns (0.425 and 0.9 m deep, and both 0.3 m in diameter) were intermittently loaded for 439 days with synthetic dairy parlour washings at a number of hydraulic and organic loading rates. At a biochemical oxygen demand (BOD) loading of 22 g m(-2) d(-1), over 92% of the BOD and suspended solids in the wastewater was removed in the two filters and nitrification was complete. The 0.9 m column had a sustained ability to adsorb the influent phosphorus during the study period; however, the phosphorus adsorption capacity of the 0.425 m column began to decrease after approximately 30 days. Biomass, comprising hydrated extracellular polymers (exopolymers) and living and dead cells, accumulated in the 0.9 m column; it was assessed by sodium bromide tracer studies and by variations in the sand volumetric water contents using time domain reflectometry (TDR). The biomass growth increased the retention time of the wastewater in the filter media, and occurred mainly at the top of the first sand layer. Intermittent stratified sand filters appear to offer an effective and sustainable treatment process for the removal of BOD from high-strength wastewaters, and for the complete nitrification of ammonium.     

Operational Experience with Biological Aerated Filters1

Yorkshire Water has two full-scale biological aerated filters in operation. The first was installed at North Bierley sewage-treatment works for the tertiary nitrification of humus―tank effluent to secure consent compliance and ascertain if anticipated future standards could be achieved. The second was recently commissioned at Hedon sewage-treatment works for secondary treatment, as part of an evaluation of compact plant to meet the requirements of the urban waste water treatment Directive at coastal sites. The plant at North Bierley (near Bradford) is constructed mainly of steel and is designed to achieve an effluent quality of 10 mg/l suspended solids, 10 mg/l BOD, and 5 mg/l ammoniacal nitrogen. The plant at Hedon (near Hull) is constructed of concrete and is designed to achieve a 30 mg/l suspended solids and 25 mg/l BOD standard. Both plants have proved to be capable of meeting their respective effluent requirement. For each works, the paper describes (i) the identification of the problem, (ii) the reasons for selecting the biological aerated filter process, (iii) details of the plant, (iv) operating experiences, and (v) plant performance.     

Nitrogen removal assessment through nitrification rates and media biofilm accumulation in an IFAS process demonstration study

An IFAS demonstration study was conducted at the 76,000 m³/day (20MGD) James River Wastewater Treatment Plant (JRTP) located in Newport News, Virginia by converting one fully-aerobic conventional aeration basin with dedicated secondary clarification to a 7041 m³/day (8404 m³/day max month) IFAS train in a modified Ludzack-Ettinger (MLE) configuration. During the study, biomass concentrations on the biofilm carriers were monitored (weekly) as well as nitrogen species concentrations in the IFAS reactor to quantify the nitrogen transformations occurring within the demonstration tank. In a related effort, nitrification kinetics for ammonia and nitrite oxidizing bacteria were monitored on a weekly basis for IFAS media alone, IFAS process mixed liquor without media, and IFAS mixed liquor and media together in an effort to identify the location of nitrification activity (i.e. on the media or in the suspended culture) in the IFAS process. Biomass quantity on the media was generally observed to be inversely related to temperature except during a period when an auxiliary carbon source contaminated with fungi was introduced. Both ammonia oxidizing and nitrite oxidizing bacterial activity were elevated on the carriers compared to the suspended culture (AOB_media: 4.97 mgNOx/gMLSS/hr; AOB_suspended: 1.72 mgNOx/gMLSS/hr; NOB_media: 7.55 mgNOx/gMLSS/hr; NOB_suspended: 0.82 mgNOx/gMLSS/hr) during all periods of the study. In-basin nitrification rates calculated based on nitrogen profiling efforts averaged 0.90 mgNOx/m²/day which was in good agreement with the average of 0.89 mgNOx/m²/day for IFAS mixed liquor and media from batch testing.     

Removal of dissolved and particulate organic matter in high-rate trickling filters

The biochemical reaction is normally assumed to control the over-all purification rate in a trickling filter and the most commonly used mathematical models are based on first-order reaction kinetics. The substrate is assumed to consist of one single substance, normally measured as the biochemical or chemical oxygen demand.The result of this investigation indicates that the removal of dissolved organic matter in high-rate trickling filters is disturbed if fine suspended and colloidal matter is present in the influent to the filters. This is an important factor to be considered and further research on the influence of the substrate composition on the purification rate is needed. The result also indicates that liquid film diffusion might control the substrate removal rate. The efficiency of the filter could not be related to the specific surface of the plastic packing used. The configuration of the packing is obviously a more relevant factor, possibly affecting the turbulence and/or the wetted area.     

Effects of recirculation rate of nitrified liquor and temperature on biological nitrification–denitrification process using a trickling filter

In the modified Ludzack–Ettinger process, high‐energy input is required in a nitrification tank. To address this issue, a new biological nitrification–denitrification system was constructed with a trickling filter for nitrification. The effects of recirculation rate of nitrified liquor and temperature through the treatment of municipal wastewater were evaluated. The highest DN removal efficiency was observed at 6.5 h of hydraulic retention in the denitrification tank and 350% of recirculation rate of nitrified liquid against the influent flow rate. The DN removal efficiencies did not reach theoretical values for all conditions tested because the COD/N ratios in the influent often decreased to less than 5 g‐COD/g‐N and temperatures dropped to less than 15°C in winter. The former inhibited the denitrification process and the latter significantly decreased the bioactivity of nitrifying bacteria. As such, this system is suitable in tropical and subtropical areas with annual minimum temperatures of over 15°C.     

Phosphorus limitation in nitrifying groundwater filters

Phosphorus limitation has been demonstrated for heterotrophic growth in groundwater, in drinking water production and distribution systems, and for nitrification of surface water treatment at low temperatures. In this study, phosphorus limitation was tested, in the Netherlands, for nitrification of anaerobic groundwater rich in iron, ammonium and orthophosphate. The bioassay method developed by Lehtola et al. (1999) was adapted to determine the microbially available phosphorus (MAP) for nitrification. In standardized batch experiments with an enriched mixed culture inoculum, the formation of nitrite and nitrate and ATP and the growth of ammonia-oxidizing bacteria (AOB; as indicated by qPCR targeting the amoA-coding gene) were determined for MAP concentrations between 0 and 100 μg PO₄-P L⁻¹. The nitrification and microbial growth rates were limited at under 100 μg PO₄-P L⁻¹ and virtually stopped at under 10 μg PO₄-P L⁻¹. In the range between 10 and 50 μg PO₄-P L⁻¹, a linear relationship was found between MAP and the maximum nitrification rate. AOB cell growth and ATP formation were proportional to the total ammonia oxidized. Contrary to Lehtola et al. (1999), biological growth was very slow for MAP concentrations less than 25 μg PO₄-P L⁻¹. No full conversion nor maximum cell numbers were reached within 19 days. In full-scale groundwater filters, most of the orthophosphate was removed alongside with iron. The remaining orthophosphate appeared to have only limited availability for microbial growth and activity. In some groundwater filters, nitrification was almost totally prevented by limitation of MAP. In batch experiments with filtrate water from these filters, the nitrification process could be effectively stimulated by adding phosphoric acid.     

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.     

Ammoniacal Nitrogen Removal in Biological Aerated Filters: The Effect of Media Size

Recent legislation has led to stringent ammoniacal-nitrogen consents and the need for first-time sewage treatment in coastal areas where land is limited. This has led to the need to improve 'small footprint'sewage-treatment processes (such as biological aerated filters) which can be used for carbonaceous treatment, nitrification, or for combined treatment. The removal of ammoniacal nitrogen in filters containing different sizes of Lytag medium and operated for combined carbonaceous treatment and nitrification, was compared at different hydraulic and volumetric loading rates. The results suggest that filters containing the smallest media size (2–4 mm), gave optimum nitrification at ammoniacal-nitrogen loading rates up to 0.6 kg/m³. d. At higher loading rates there was a rapid decrease in nitrification for this size of medium but, with 2.8–5.6 mm medium, nitrification continued at loading rates up to 1 kg amm. N/m³ d. The filters containing larger media sizes (4–8 mm and 5.6–11.2 mm) exhibited low levels of nitrification above a loading rate of 0.2–0.4 kg amm. N/m³. d.     

Transport of nanoparticles with dispersant through biofilm coated drinking water sand filters

This article characterizes, experimentally and theoretically, the transport and retention of engineered nanoparticles (NP) through sand filters at drinking water treatment plants (DWTPs) under realistic conditions. The transport of four commonly used NPs (ZnO, CeO_2, TiO_2, and Ag, with bare surfaces and coating agents) through filter beds filled with sands from either acid washed and calcined, freshly acquired filter media, and used filter media from active filter media, were investigated. The study was conducted using water obtained upstream of the sand filter at DWTP. The results have shown that capping agents have a determinant importance in the colloidal stability and transport of NPs through the different filter media. The presence of the biofilm in used filter media increased adsorption of NPs but its effects in retaining capped NPs was less significant. The data was used to build a mathematical model based on the advection-dispersion equation. The model was used to simulate the performance of a scale-up sand filter and the effects on filtration cycle of traditional sand filtration system used in DWTPs.