Fate of dissolved organic nitrogen in two stage trickling filter process

Dissolved organic nitrogen (DON) represents a significant portion of nitrogen in the final effluent of wastewater treatment plants (WWTPs). Biodegradable portion of DON (BDON) can support algal growth and/or consume dissolved oxygen in the receiving waters. The fate of DON and BDON has not been studied for trickling filter WWTPs. DON and BDON data were collected along the treatment train of a WWTP with a two-stage trickling filter process. DON concentrations in the influent and effluent were 27% and 14% of total dissolved nitrogen (TDN). The plant removed about 62% and 72% of the influent DON and BDON mainly by the trickling filters. The final effluent BDON values averaged 1.8 mg/L. BDON was found to be between 51% and 69% of the DON in raw wastewater and after various treatment units. The fate of DON and BDON through the two-stage trickling filter treatment plant was modeled. The BioWin v3.1 model was successfully applied to simulate ammonia, nitrite, nitrate, TDN, DON and BDON concentrations along the treatment train. The maximum growth rates for ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria, and AOB half saturation constant influenced ammonia and nitrate output results. Hydrolysis and ammonification rates influenced all of the nitrogen species in the model output, including BDON.     

Oxygen microprofiles of trickling filter biofilms

Oxygen microprofiles of photosynthetic and non-photosynthetic biofilms of trickling filters from a sewage treatment plant were studied with Clark type oxygen microelectrodes. The oxygen profiles in photosynthetic biofilms exhibited pronounced changes with changing light conditions, and the profiles of both types of biofilm were affected by addition of nutrients. The existence of a 100–500 μm thick diffusive boundary layer in the water just above the biofilm was evident from all recordings. The O₂ gradient in this boundary layer was used to calculate diffusive fluxes of oxygen exchanged between the biofilms and the overlying water phase. The calculated fluxes were compared to the overall oxygen consumption rates measured experimentally and to the photosynthetic activity as measured with the microelectrodes. Approximately 60–70% of the oxygen produced in the algal films during photosynthesis was consumed within the films. At least one third of this consumption may be due to photorespiration. Dark/light and light/dark shifts demonstrated a very dynamic nature of the O₂ status of the algal films, showing an increase from anaerobic conditions to 500% air saturation and vice versa within 25 min. In the same regime, pH profiles showed a similar dynamic change, whereby pH varied between 8.1 and 9.7 in the same period.

The data obtained with the non-photosynthetic biofilms show that the oxygen respiration and oxygen penetration are mostly limited by diffusive oxygen transport through the boundary layer. The overall oxygen consumption of the heterotrophic biofilms equalled within ± 10% the estimates made from flux calculations.     

Field evaluation of the treatability of type A zeolite in a trickling filter plant

Type A zeolite is a synthetic aluminosilicate which can be used as a builder in laundry detergents. The treatability of this zeolite in wastewater was evaluated in a trickling filter plant under field conditions. The normal performance of the plant was established during a baseline period of three months, after which the zeolite was added to the raw wastewater for 7 months. The removal of the zeolite by the plant averaged 81% or more at an influent concentration of 10 mg 1⁻¹. Of the zeolite that passed into the secondary effluent, 92% was removed by a dual-media filter. Removal from raw influent to tertiary effluent was thus 99%. The presence of the zeolite in the wastewater had no effect on the performance of the plant, the production of gas by the anaerobic digester or the concentrations of Pb, Zn and Ni in the effluent.     

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.     

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.     

Biodegradability determinations in trickling filter units compared with the OECD Confirmatory Test

The “coupled units test”, i.e. the modification of the OECD Confirmatory Test for the application of non-specific parameters such as the carbon analysis was described in detail in a previous paper, while the present paper discusses the reproducibility of its results, the sensitivity of the method, and the merits and shortcomings of the non-specific analyses (COD and DOC) employed. The extension of the coupled units test principle to trickling filters, a new transinoculation procedure, some square wave feeding experiments and the mathematical separation of the main contributions to the tolerance limits, the analytical and biological variances, are presented.     

Distribution and activity of ammonia oxidizing bacteria in a large full-scale trickling filter

The biofilm in a full-scale nitrifying trickling filter (NTF) treating municipal wastewater has been investigated with microbiological methods using fluorescence in situ hybridization (FISH) with 16S rRNA oligonucleotide probes in combination with confocal laser scanning microscopy (CLSM) and mathematical modeling using a dynamic multi-species biofilm reactor model. Ammonia oxidizing bacteria (AOB) were found to belong to the genus Nitrosomonas at different depths in the NTF at every sampling occasion, corresponding to different long-term operational conditions for the NTF. Both the measurements and the corresponding simulated predictions showed the same general trend of a decrease with filter depth of the amount of biofilm, the proportion of AOB to all bacteria and the total amount of AOB. The latter decreased by several times from top to bottom of the NTF. Measurements and simulations of potential ammonium oxidizing activity in the biofilm also showed a decreasing activity with depth in the NTF, which generally was operating at close to complete nitrification. However, no difference was observed when the activity was normalized to the amount of biofilm, despite decreasing proportions of AOB to all bacteria with depth in the NTF. This could be explained by diffusion limitations in the biofilm from the upper parts of the NTF according to the biofilm reactor model. The relatively good agreement between the simulations and the measurements shows that the kind of biofilm reactor model used can qualitatively describe an averaged behavior and averaged composition of the biofilm in the reactor.     

Application of correlation-regression method for determination of coefficients for the eckenfelder trickling filter models

A correlation-regression method is developed for determination of the first order and the retardant reaction rate coefficients for the Eckenfelder mathematical models of trickling filtration process. The method allows to increase the accuracy of these coefficients estimation comparing to frequently used graphical techniques. This increase in accuracy determination of a given rate coefficient exerts an influence on dimensioning of a trickling filter.Computer programs are developed to perform the following functions: estimate reaction rate coefficients together with various correlation—regression terms for a given value of the exponent on hydraulic loading rate (n); select the reaction rate coefficient value with corresponding value of the exponent n for a maximum value of the correlation coefficient.Numerical examples are presented for the published data from pilot-scale plastic media trickling filters to illustrate this procedure.Higher values of the correlation coefficients have been obtained for the first order reaction model than for the retardant reaction model using BOD and TOC but opposite when COD was used to describe the performance of these trickling filters.In addition, different values of the exponent n have been obtained for soluble BOD, COD and TOC for the same type of filter medium indicating that the value of this exponent determined by the above method (or graphical techniques) is different from the value of the exponent n which modifies the effect that hydraulic loading has on the detention time.     

Structure of nitrifying biofilms in a high-rate trickling filter designed for potable water pre-treatment

This study examined the composition and structure of nitrifying biofilms sampled from a high-rate nitrifying trickling filter which was designed to pre-treat raw surface water for potable supply. The filter was operated under a range of feed water ammonia and organic carbon concentrations that mimicked the raw water quality of poorly protected catchments. The biofilm structure was examined using a combination of fluorescence in situ hybridisation and scanning electron microscopy. Biopolymers (carbohydrate and protein) were also measured. When the filter was operated under low organic loads, nitrifiers were abundant, representing the majority of microorganisms present. Uniquely, the study identified not only Nitrospira but also the less common Nitrobacter. Small increases in organic carbon promoted the rapid growth of filamentous heterotrophs, as well as the production of large amounts of polysaccharide. Stratification of nitrifiers and heterotrophs, and high polysaccharide were observed at all filter bed depths, which coincided with the impediment of nitrification throughout most of the filter bed. Observations presented here specifically linked biofilm structure with filter functionality, physically validating previous empirical modelling hypotheses regarding competitive interactions between autotrophic and heterotrophic bacteria in biofilms.     

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.     

The effectiveness of conventional trickling filter treatment plants at reducing concentrations of copper in wastewaters

Eight different sewage treatment works were sampled in the North West of England. The effectiveness of the conventional treatment processes (primary sedimentation and biological trickling filters) as well as various tertiary treatment units in terms of both total and dissolved copper removal was evaluated. The removal of total copper across primary sedimentation averaged 53% and were relatively consistent at all sites, however, at three sites the removal of dissolved copper also occurred at this stage of treatment. Removal of total copper by the biological trickling filters averaged 49%, however, substantial dissolution of copper occurred at two sites, which highlighted the unpredictability of this treatment process in the removal of dissolved copper. Copper removal during tertiary treatment varied considerably even for the same treatment processes installed at different sites, primarily due to the variability of insoluble copper removal, with little effect on copper in the dissolved form being observed. The proportion of dissolved copper increased significantly during treatment, from an average of 22% in crude sewages to 55% in the final effluents. There may be the potential to optimise existing, conventional treatment processes (primary or biological treatment) to enhance dissolved copper removal, possibly reducing the requirement for installing any tertiary processes specifically for the removal of copper.     

The effect of temperature on the growth of microbial film in a model trickling filter

The daily weight change of a microbial film in a model filter after the start of synthetic feed application was observed and the effect of temperature on the growth of the film was studied. The rate of BOD removal, the rate at which SS was washed out, the yield coefficient and the autolysis coefficient were chosen as the factors related to the growth of the film and the effects of temperature on them were examined.The growth pattern of the film can be divided into the lag-phase, growth-phase and stationary-phase. The growth equation of the film in the growth-phase was obtained by assuming that the rates of BOD removal and SS washed out were constant.In order to evaluate the growth of the film at various temperatures, the growth capacity and the mean growth rate were defined. The growth capacity is the film weight at the stationary-phase and expresses the maximum weight to which the film can increase in a given filter. The growth capacity increased as the temperature fell. This is due to the autolysis coefficient which becomes lower at low temperatures. The period necessary to reach the stationary-phase was shorter at high temperatures. The mean growth rate, which was defined as the rate when the film has reached half the growth capacity, was at its maximum at 15°C.     

3-nitrobenzenesulfonic acid and 3-aminobenzesulfonic acid in a laboratory trickling filter: Biodegradability with different activated sludges

The biodegradation of 3-nitrobenzenesulfonate (3-NBS) or 3-aminobenzenesulfonate (3-ABS) was examined in a laboratory trickling filter device containing one of six activated sludges as the biocatalyst. No activated sludge from four communal treatment plants could degrade 3-NBS or 3-ABS. In contrast, each of the sludges from two plants treating wastes from the textile industry was able to completely degrade 3-NBS or 3-ABS. Under certain conditions, communal activated sludge could acclimate to degrade 3-NBS, even though inoculation with a degradative sludge was a more efficient process. In the absence of a carbon source, the degradative ability of trickling filters was retained for at least 1 week; thereafter, an adaptation phase was required before rapid and extensive degradation of recovered 3-NBS. Degradation was monitored by global parameters (DOC and release of CO₂) and specific determinations of substrate (HPLC). The global parameters indicated incomplete metabolism of 3-NBS, but this effect was found to be due to the presence of a non-degraded impurity (5%), 4-NBS, found in most commercial preparations of 3-NBS.     

Sloughing of microbial film in trickling filters

A well established model for microbial film growth in trickling filters has been used to study the influence of sloughing on the performance characteristics of trickling filters under conditions of constant input. It has been argued that sloughing occurs when the substrate concentration at the support-microbial film interface falls below a critical value. Under these conditions the effluent BOD fluctuates in a fashion similar to that found in filters treating sewage. This is consequence of the time dependent variation of the microbial film thickness throughout the filter.The results obtained lead to suggestions for improved performance and indicate that without proper understanding of the sloughing process, optimal design and operation of trickling filters is unlikely. It also appears that design procedures based upon an average microbial hold-up are inadequate.     

灵感之泉涓涓不息

可以毫不夸张地说,作为世界级的设计宗师,菲利普．斯达克极大地影响了过去十年间浴室文化的成型。所以,在“菲利普．斯达克的浴室”问世的第十载,来自汉斯格雅的设计师品牌雅生理所当然地为它的雅生．斯达克系列增加了几个新的特点。米兰的家具博览会又一次为雅生斯达克提供了机会,来庆祝它经久不衰的生命力。     

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.     

Treating landfill leachate using passive aeration trickling filters; effects of leachate characteristics and temperature on rates and process dynamics

Biological ammoniacal-nitrogen (NH₄⁺-N) and organic carbon (TOC) treatment was investigated in replicated mesoscale attached microbial film trickling filters, treating strong and weak strength landfill leachates in batch mode at temperatures of 3, 10, 15 and 30 °C. Comparing leachates, rates of NH₄⁺-N reduction (0.126-0.159 g m^− 2 d^− 1) were predominantly unaffected by leachate characteristics; there were significant differences in TOC rates (0.072-0.194 g m^− 2 d^− 1) but no trend relating to leachate strength. Rates of total oxidised nitrogen (TON) accumulation (0.012-0.144 g m^− 2 d^− 1) were slower for strong leachates. Comparing temperatures, treatment rates varied between 0.029-0.319 g NH₄⁺-N m^− 2 d^− 1 and 0.033-0.251 g C m^− 2 d^− 1 generally increasing with rising temperatures; rates at 3 °C were 9 and 13% of those at 30 °C for NH₄⁺-N and TOC respectively. For the weak leachates (NH₄⁺-N < 140 mg l^− 1) complete oxidation of NH₄⁺-N was achieved. For the strong leachates (NH₄⁺-N 883-1150 mg l^− 1) a biphasic treatment response resulted in NH₄⁺-N removal efficiencies of between 68 and 88% and for one leachate no direct transformation of NH₄⁺-N to TON in bulk leachate. The temporal decoupling of NH₄⁺-N oxidation and TON accumulation in this leachate could not be fully explained by denitrification, volatilisation or anammox, suggesting temporary storage of N within the treatment system. This study demonstrates that passive aeration trickling filters can treat well-buffered high NH₄⁺-N strength landfill leachates under a range of temperatures and that leachate strength has no effect on initial NH₄⁺-N treatment rates. Whether this approach is a practicable option depends on a range of site specific factors.     

Dispersion in the inclined plane model of trickling filters

In this paper an attempt has been made to set up a relationship between the removal efficiency and the hydraulic regimes of biological filters. For this purpose an equation has been first derived to determine the dispersion number. Using this equation, effluent concentration has been calculated by means of dispersed plug flow model in the range of channelized flow, and for large hydraulic loadings. Around the minimum wetting rate, the removal efficiencies are computed with equation of complete mixing. The application of this theory to the experimental results reported in literature has also been shown and the ranges of validity of dispersed plug flows and mixflows are determined. It has been demonstrated that the predicted concentrations are in good agreement with the measured values.     

Nitrification in tertiary trickling filters followed by deep-bed filters

Based on 20 months of pilot experiments, tertiary plastic media trickling filters have shown to be a feasible and cost-saving solution for the enlargement of existing treatment plants for nitrification. The influence of several process variables such as hydraulic load, media characteristics, NH₄-load, concentration fluctuations, suspended solids, organic nutrients and biomass grazing on nitrification activity was evaluated. From performance analysis along the trickling filter depth, basic design informations were obtained. In addition to suspended solids removal, subsequent deep-bed filtration proved to be an excellent final treatment to further reduce and stabilize effluent ammonia and nitrite residuals.     

Effect of mass transport on BOD removal in trickling filters

The effect of liquid-phase mass transport on BOD removal efficiency in a trickling filter is presented based on an analytical model of the process. It is shown graphically that liquid-phase mass transport resistances can significantly affect BOD removal for a given trickling filter. The applicability of the results presented to the analysis of experimental data and trickling filter design is discussed.