Fixed Film Processes Research Articles

Enhanced mainstream nitrogen removal from synthetic wastewater using gel-immobilized anammox in fluidized bed bioreactors: Process performance and disintegration mechanisms

Anammox retention, which is crucial for successful nitrogen removal because of slow growth, is still a major challenge. Fixed film processes or gel-immobilization techniques can minimize biomass washout. However, the detachment mechanisms from gel-immobilized beads are still unclear. Despite the widely known advantages of fluidized bed reactor (FBR) with respect to biomass retention, the technology has not been investigated for anammox processes, and thus, the current study evaluated the feasibility of using immobilized anammox gel beads as a carrier media in anammox fluidized bed reactor (AFBR), with a particular focus on understanding detachment mechanisms. The study optimized the packing ratio in AFBR and compared holed and non-holed beads. The optimum packing ratio (on a volumetric basis) was 30% (v/v) with a nitrogen removal rate (NRR) of 0.40 kg N/m3-d at a volumetric nitrogen loading rate (NLR) of 0.51 kg N/m3-d. Biomass detachment rates increased linearly with specific anammox activity (SAA). The fluidized bed reactor employing holed (more porous) anammox gel beads (HFBR) exhibited 20% lower biomass detachment rates than the non-holed fluidized bed reactor (NHFBR). Moreover, the HFBR achieved a maximum NRR of 0.81 kg N/m3-d at NLR of 1.01 kg N/m3-d after 35 days without operational problems, whereas the NHFBR with non-holed anammox gel beads failed after 30 days. The hindrance to diffusion of the generated nitrogen gas was the main mechanism of beads breakup and biomass washout, and thus, the sustainability of the beads hinges on increased external porosity. Therefore, developing microporous gel beads is critical for achieving a high rate stable anammox process that overcomes the limitations of the current technologies.

Production and removal of soluble organic nitrogen by nitrifying biofilm

This study investigated soluble organic nitrogen (sON) activity in batch reactors mimicking nitrifying moving bed biofilm reactors (MBBRs). This work was divided into two objectives focusing on the production and degradation of sON, respectively. For the first objective, a synthetic feed that did not contribute any organic nitrogen was used and results indicated that irrespective of the presence of influent organic carbon (0 versus 400 mg COD/L) in the reactors, sON was contributed by the biofilm during nitrification. Although net production of sON was observed, both production and ammonification coexisted which regulated the sON concentration. For the second objective, actual wastewater was fed to the reactors to investigate sON degradation under different carbon to nitrogen (C/N) ratios. A higher concentration of sON was biodegraded in the reactor when fed with influent containing a lower C/N ratio. Overall results suggested that organic carbon bioavailability and/or ammonia concentration influenced the production and ammonification of sON. This study is the first to explore the sON activity by MBBR biofilm and findings from this work could extend the knowledge on the fixed film process with respect to sON activity to regulate and optimize reactor operation in meeting stringent total nitrogen discharge limits.

Phenol biodegradation in an aerobic fixed-film process using conductive bioelectrodes: Biokinetic and kinetic studies

Phenol biodegradation in an aerobic fixed-film process using conductive bioelectrodes: Biokinetic and kinetic studies

Microbial Structure and Functions of Biofilm During Wastewater Treatment in the Dairy Industry

ABSTRACTThe microbial structure and activity of biofilm are two important parameters for the successful operation and control of fixed film processes in wastewater treatment. However, the constant interaction between fixed and suspended biomass requires the parallel investigation of these two biological components. The aim of the present article is to study the key microbiological and enzymological parameters of biofilm and suspended biomass from an anaerobic sequencing batch biofilm reactor for dairy wastewater treatment. The effectiveness of organic matter (measured as COD) removal and nitrates removal was determined. The microbial structure of biofilm and suspended biomass was investigated by the quantity of anaerobic heterotrophs, anaerobic spore-forming microorganisms and denitrifying bacteria. The total dehydrogenase activity and the nitrate reductase activity were used as indicators for biomass activity. The obtained data showed that the enzyme activity of the fixed biomass was higher in comparison with that of the suspended biomass. This result is related to the more heterogenic media of the inert carrier and more dynamic conditions in the biofilm inner layers. The total dehydrogenase activity of the fixed biomass was four times higher and the nitrate reductase activity of the fixed biomass was two times higher than that of the suspended biomass during stable biofilm functioning. The investigated biological system mineralized the organic matter with high effectiveness (to 90%) and removed 67% of the nitrates from dairy wastewater as a result of the controlled water treatment process.

Biodegradation of Coir Geotextiles Attached Media in Aerobic Biological Wastewater Treatment

Coir is a hard and tough organic fibre, rich in cellulose and lignin, and possesses high specific area and wetting ability - factors which are important for bacterial adhesion in fixed film processes. Few studies have been reported on the durability of coir geotextiles, when used in Civil Engineering applications such as slope protection works. However, its durability when used as the media in biofilters, for wastewater treatment extensively has not been studied yet. Durability of coir geotextiles has been assessed by keeping it in wet condition and measuring the tensile strength of the fibres, at different times. In the present study, coir geotextiles that were used as the attachment media in a biofilter, for treatment of organic rich wastewater was tested for durability. The units were operated as aerobic, gravity flow filters. Different wastewater parameters were employed in each of these runs. Tensile strength of the fibres was determined after each run. Results show that loss of tensile strength (or degradation) is influenced by the characteristics of the effluent wastewater to the filter, due to the growth of microorganisms which depends upon the concentration of substrates in the wastewater. Permeability studies shows reduction in permeability, is influenced by the organic loading rate on the filters and the duration of filter operation. SEM studies and E-DAX analysis shows the biodegradation of the fibres constituents, influenced by the substrate concentration.

Modeling Fixed Film Processes: Practical Considerations and Current Limitations from a Consulting Viewpoint

Modeling Fixed Film Processes: Practical Considerations and Current Limitations from a Consulting Viewpoint

Remediation of bromate-contaminated groundwater in an ex situ fixed-film bioreactor

Use of a pilot-scale fixed-film bioreactor was investigated for remediation of bromate contamination within groundwater. Bromate reduction with stoichiometric production of bromide was observed, providing supporting evidence for complete reduction of bromate with no production of stable intermediates. Reduction of 87–90% bromate from an influent concentration of 1.1 mg L − 1 was observed with retention times of 40–80 h. Lower retention times led to decreases in bromate reduction capability, with 11.5% removal at a 10 h retention time. Nitrate reduction of 76–99% from a 30.7 mg L − 1 as NO 3 − influent was observed at retention times of 10–80 h, although an increase in nitrite production to 2.7 mg L − 1 occurred with a 10 h retention time. Backwashing was not required, with the large plastic packing media able to accommodate biomass accumulation without decreases in operational efficiency. This study has provided proof of concept and demonstrated the potential of biological bromate reduction by fixed-film processes for remediation of a bromate contaminated groundwater source.

Development of an empirical model for domestic wastewater treatment by biological aerated filter

An empirical model for wastewater treatment by biological aerated filters (BAF) was developed in the study, which relates influent soluble chemical oxygen demand (sCOD) to effluent sCOD and medium bed height in order to simply engineering design and verify experimentally the suitability of this model and ascertain the relationship between the constant values calculated with the model and reactor performance. The theoretical model was based on design of contact oxidation process and conventional biofilter because these fixed-film processes show similar flow pattern. Firstly, the two parallel BAF systems packed with lava medium and expanded clay medium, respectively, were run for actual domestic wastewater at different hydraulic loading rates during the experiment. A great deal of data was then used to the empirical model, which was based on a first-order reaction, to calculate the empirical values of n (medium constant) and K (overall process constant). The experimental results show that the treatment efficiency of lava medium exceed to that of expanded clay medium, which just conform to what the model predict, the higher value of K the greater efficiency of sCOD removal, and the lower value of n the greater variation of sCOD removal indicating a poor resistance to shock loading. Next, the effect of suspended solid (SS) on model was estimated by simulated domestic wastewater to verify its feasibility.

Use of the methane yield to indicate the metabolic behaviour of methanogenic biofilms

Methane yield ( Y C H 4 ) is the result of the balance between the flows of organic carbon to catabolism and anabolism in methanogenic ecosystems. In anaerobic biofilm processes, it can be easily obtained to be used to characterize the behaviour of the biofilm in important transient phases. Thus, at the beginning of the start-up period, Y C H 4 is very low, indicating an important anabolic activity of the microorganisms to build the biofilm. Then, its value increases upto a stable level corresponding to the end of the biofilm formation. The time course of Y C H 4 describes the three phases of biofilm formation with the induction, the growth and the steady state. Therefore, it is possible to compare different start-up strategies and define the best operating conditions to grow the methanogenic biofilm. In steady state operations, Y C H 4 expresses the balance of the dynamic system between the net growth of the fixed cells and the biomass detachment, depending on the shear stress and on the capacity of the solid support to retain biomass. It also reflects the detachment rate evolution in anaerobic fixed film processes.

DENITRIFICATION FILTERS: A COMPARISON OF MANUFACTURERS AND REVIEW OF PERFORMANCE, PATENT AND BIDDING ISSUES

DENITRIFICATION FILTERS: A COMPARISON OF MANUFACTURERS AND REVIEW OF PERFORMANCE, PATENT AND BIDDING ISSUESWith the development of total maximum daily loads for nutrient discharges to address water quality concerns, many wastewater treatment plants are facing stringent nutrient limits. Deepbed denitrification filters are a well-proven technology for meeting low total nitrogen limits. Concurrent denitrification and solids removal in a deep-bed filter was first patented in 1973, and then followed by a...Author(s)C. deBarbadilloM. LambertD. ParkerW. WellsR. WilletSourceProceedings of the Water Environment FederationSubjectSession 67: Fixed Film Processes—New ApproachesDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2004ISSN1938-6478SICI1938-6478(20040101)2004:10L.435;1-DOI10.2175/193864704784131365Volume / Issue2004 / 10Content sourceWEFTECFirst / last page(s)435 - 457Copyright2004Word count189

The impact of temperature on nitrification rate in fixed film biofilters

The impact of temperature on nitrification rate was evaluated in this study through experimental tests, mathematical modeling and sensitivity analysis. The results show that the impact of temperature on fixed film nitrification rate is less significant than that predicted by the van't Hoff–Arrhenius equation. In a fixed film biofilter, the impact of temperature on nitrification rate due to DO (dissolved oxygen) limitation is different from that due to TAN (total ammonia nitrogen) limitation. Sensitivity analysis indicated that a temperature increment at 20 °C resulted in nitrification rate increase of 1.108% per °C and 4.275% per °C under DO and TAN limited conditions, respectively. Diffusion mass transport plays an important role in fixed film nitrification processes. Consequently, the effect of temperature on nitrification rate due to bacterial growth rate change in fixed film processes is greatly reduced compared with that of suspended growth processes. When oxygen is limited, the decrease in saturation DO concentration as temperature increases results in a negative temperature impact upon the nitrification rate.

Influence of the nutrient balance on biofilm composition in a fixed film process

An attached fungal growth has appeared in a fixed biofilm process at the waste water treatment plant of the City of Oulu, Finland. Due to the filamentous morphology of the fungi, biofilm support material is easily washed out. The appearance is believed to be the result of the unbalanced availability of nutrients, where phosphorus has been identified as the key component. Experimental work concentrated on the influence of phosphorus on the fungal growth. Bench scale experiments showed that a higher uptake of phosphorus for the removal of organic material is possible, which also resulted in a suppression of the fungal growth by bacterial biomass. The results were confirmed by experimentation in a full-scale biofilter. Addition of extra phosphoric acid to the biofilter influent resulted in a biofilm where the fungal growth is less pronounced. The fungal growth is believed to be competitive with the desired bacterial growth. It is possible to keep the fungal growth within limits by changing the conditions in favour of the bacterial growth, thus avoiding the operational problems connected with the filamentous fungi.

Computer programs for estimating substrate flux into steady‐state biofilms from pseudoanalytical solutions

AbstractFixed‐film processes employing microorganisms attached to an inert surface (biofilms) are widely used for biological treatment of municipal and industrial wastewater. For optimal design and analysis of these processes, mathematical models are necessary that describe the dynamics of contaminant transport within these biofilms and the associated contaminant utilization by the microorganisms. However, these governing equations that typically involve Fickian diffusion for contaminant transport and Monod kinetics for contaminant utilization are inherently nonlinear and have no closed form solutions except under special conditions. This can restrict their use in the classroom as cumbersome numerical techniques must be used for their solution. This problem is well documented in the literature and several authors have presented pseudoanalytical solutions that replace numerical solutions with algebraic equations. In the present study, we present pseudoanalytical solution‐based computer programs for estimating substrate flux and biofilm thickness for a steady‐state biofilm. Depending upon the intended end use, these programs can either partially or totally automate the solution process. In the partial automation mode, they can serve to enhance student understanding of important concepts related to steady‐state biofilms, while complete automation can help bring more challenging and realistic problems associated with steady‐state biofilms into the classroom. The programs have been tested on MATLAB version 5.0 and are available as freeware for educational purposes. © 2002 Wiley Periodicals, Inc. Comput Appl Eng Educ 10: 26–32, 2002; Published online in Wiley InterScience (www.interscience.wiley.com.); DOI 10.1002/cae.10017

Analysis of organic removal rates in the aerated submerged fixed film process

Performance data from a pilot-plant employing the four-stage aerated submerged fixed film (ASFF) process treating domestic wastewater were analyzed to examine the organic removal rates. The process has shown high BOD removal efficiencies (> 90%) over a wide range of hydraulic loading rates (0.04 to 0.68 m3/m2·d). It could also cope with high hydraulic and organic loadings with minimal loss in efficiency due to the large amount of immobilized biomass attained. The organic (BOD and COD) removal rate was influenced by the hydraulic loadings applied, but organic removal rates of up to 104 kg BOD/ m2·d were obtained at a hydraulic loading rate of 0.68 m3/m2·d. A Semi-empirical model for the bio-oxidation of organics in the ASFF process has been formulated and rate constants were calculated based on statistical analysis of pilot-plant data. The relationships obtained are very useful for analyzing the design and performance of the ASFF process and a variety of attached growth processes.

Etude Microbiologique D'un Biofiltre a Lit Ruisselant: Representativite des Eaux de Lavage et Distribution Verticale des Bactéries Heterotrophes Aerobies Microbiological Study of a Trickling Biofiltration Process: Representativeness of Washwaters and Vertical Distribution of Heterotrophic Aerobic Bacteria

Many methods exist to monitor the microbial activity of a biological treatment process. These methods have been used mostly for suspended biomass rather than for fixed film processes: the sampling of the biomass in the latter case is more difficult, especially for a full scale plant. For the biofiltration processes, this difficulty can be avoided by the use of the washwaters which however have to be proven to be representative of the biofilter's biomass. The objective of this paper is to assess the microbiological representativity of the washwaters when compared to the fixed biomass of a full scale biofiltration process, Biodrof®. The organisms selected to compare washwaters and fixed biomass are: heterotrophic aerobic bacteria (HAB), Pseudomonas, Flavobacterium, Aeromonas, moulds and yeasts. The vertical distribution of HAB has also been evaluated across the biofilter in order to verify if a vertical stratification occurred in this kind of process. The results showed no significant differences between mean counts (t-Test) of microorganisms in washwaters and fixed on the media suggesting the representativenness of the washwaters with the fixed biomass. No vertical distribution of HAB was observed from the different depths (0–25cm, 45–70cm, 90–115cm) across the biofilter: the same mean counts (statistic Anova) are observed at each depth suggesting an homogeneous vertical distribution of microorganisms in the Biodrof® process studied.

Deicing Fluid Treatment in Batch-Loaded Aerobic Fluidized Bed Reactor

This study demonstrates the feasibility of treating storm water contaminated with airport deicing fluid (ethylene glycol) in a batch-loaded aerobic fluidized bed reactors. In addition, the removal rates were measured for batch-loaded and continuously loaded fluidized bed reactors. These values were compared with each other and with more conventional wastewater treatment processes. Treating the contaminated storm water in batches eliminated the operational problems common to a continuously loaded aerobic fluidized bed reactor. Most significantly, excess biofilm growth and the accompanying maintenance and operational problems were controlled through endogenous respiration. Ethylene glycol and chemical oxygen demand removal rates of 710 and 2,200 g/m{sup 3}/day, respectively, were achieved in the batch-loaded reactor. The resulting batch-loaded full-scale installation is expected to be two to three times larger than a continuously operated fluidized bed reactor; however, it is expected to be equal to or much smaller than more conventional activated sludge and fixed film process installations. An additional benefit of the batch-loaded process is the low quantity of sloughed biofilm, which results in a low level of effluent solids (16 mg/L total suspended solids). As a result, secondary clarification and associated sludge treatment might not be required.

Analysis of organic removal rates in the aerated submerged fixed film process

Performance data from a pilot-plant employing the four-stage aerated submerged fixed film (ASFF) process treating domestic wastewater were analyzed to examine the organic removal rates. The process has shown high BOD removal efficiencies (> 90%) over a wide range of hydraulic loading rates (0.04 to 0.68 m3/m2 A). It could also cope with high hydraulic and organic loadings with minimal loss in efficiency due to the large amount of immobilized biomass attained. The organic (BOD and COD) removal rate was influenced by the hydraulic loadings applied, but organic removal rates of up to 104 kg BOD/ m2-d were obtained at a hydraulic loading rate of 0.68 m3/m2 A. A Semi-empirical model for the bio-oxidation of organics in the ASFF process has been formulated and rate constants were calculated based on statistical analysis of pilot-plant data. The relationships obtained are very useful for analyzing the design and performance of the ASFF process and a variety of attached growth processes.

Modelling biological aerated filters for wastewater treatment

Biological aerated filters (BAFs) are submerged three-phase fixed-media reactors for wastewater treatment. A major characteristic of BAF reactors is the use of granular media which allows solids separation as well as secondary or tertiary biological treatment in one unit. The aim of this work was to design a simple empirical model relating influent soluble chemical oxygen demand (sCOD) to effluent sCOD and reactor height, verify experimentally the suitability of this model and ascertain the relationship between model constants and reactor performance. The theoretical model was based on that designed for trickling filters as both fixed-film processes show a similar plug flow pattern. Two reactors were set up to run parallel treating settled domestic sewage using media identical in size and shape, except one was less dense than water (relative density 0.92) and the other was denser than water (relative density 1.05). The reactors were run upflow with liquid flowrates of 0.29–0.58 m 3 d −1 (0.2–0.5 litres min −1) and an air:liquid ratio of 10:1. After 4 weeks from start-up, steady-state was reached. From this point, samples were taken at different heights along the reactors at timed intervals and profiles of sCOD removal against reactor height were produced. This analysis was repeated for a number of different flowrates and organic loadings (0.57–1.40 kg sCOD m −3 d −1). The resulting data was then used with the empirical model, which was based on a first-order reaction, to calculate the values of k∗ (overall process constant) and n (media factor). A higher value of k∗ was found for the floating media (55) compared with the value found for the sunken media (33). This indicated the greater efficiency of sCOD removal in the floating media. The values of the media constants were similar, showing the similarity in the media shape and size.

Discussion: VOCS in Fixed Film Processes. I: Pilot Studies

Discussion: VOCS in Fixed Film Processes. I: Pilot Studies

Closure to “VOCS in Fixed Film Processes. I: Pilot Studies” by Wayne J. Parker, Hugh D. Monteith, and Henryk Melcer

Closure to “VOCS in Fixed Film Processes. I: Pilot Studies” by Wayne J. Parker, Hugh D. Monteith, and Henryk Melcer