Up-flow Biological Aerated Filter Research Articles

Bioaugmentation of nitrifying bacteria in up-flow biological aerated filter's microbial community for wastewater treatment and analysis of its microbial community

Bioaugmentation is a bioremediation approach involving the seeding of the competent microbial consortia to improve nitrogen removal from wastewater. The discharge of nitrogen-saturated wastewater into freshwater results in cultural eutrophication and huge outbreak of harmful algal bloom. The purpose of this study was to relate the population size of bioaugmented ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) with nitrification performance in an experimental up-flow biological aerated filter (UBAF) for domestic wastewater treatment. Fluorescent in situ hybridization (FISH) was used to enumerate the portions of AOB and NOB in UBAFs. The FISH method disclosed that nitrifying bacteria represented 31.3% of the total population. The AOB (16.6%) outcompeted NOB (14.6%) after 15 days of bioaugmentation. Additionally, AOB/NOB ratio (1.13) showed a higher nitrification process. The average effluent from experimental UBAF exhibited high nitrogen and nutrients removal, the averaged removal efficiencies for NH4+-N, NNO3-, COD, BOD5 and phosphate were 85.2%, nitrate accumulation (2.2 times), 67.3%, 75.6%, and 58.3%, respectively. Therefore, an increase in the number of nitrifying microorganisms confirms the efficacy of microbial seeding and correlates with the physical-chemical data on bioconversion of nitrogenous compounds. However, on day 35, there was a disparate distribution pattern of the nitrifying bacteria (AOB, NOB) in the experimental UBAF, which in turn declined the nitrification performance.The study demonstrated the importance of monitoring the shifts of the nitrifying bacterial population in UBAF. Moreover, the bioaugmentation of nitrifying bacteria in UBAF packed with cost-effective and eco-friendly ceramsite could be a promising alternative technique for the domestic wastewater treatment.

Characteristic on pollutant removal and extracellular polymeric substances distribution in different periods of an up-flow biological aerated filter

The up-flow biological aerated filter (UBAF) reactor was established to explore the pollutant removal and the extracellular polymeric substances (EPS) distribution at the initial stage of biofilm, maturity of biofilm, and stable operation periods. The parallel factor (PARAFAC) model was applied to analyze the three-dimensional fluorescence characteristics of EPS. Canonical correlation analysis (CCA) was used to study the correlation between the distribution of EPS and pollutant removal. The results showed that the removal efficiency of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), and total phosphorus (TP) at the maturity of biofilm were higher than other periods, and reached to 95.68%±0.87%, 73.48%±4.32%, and 63.80%± 14.27%, respectively. The operation period had a significant correlation with EPS distribution. All of biofilm samples detected four kinds of fluorescent substance of tryptophan-like (C1), protein-like (C2), humilic acid (C3), and humic acids-like (C4). The CCA result showed that NH4+-N removal had a very significant positive correlation with EPS concentration and composition (R≥0.9261).

Enhanced removal of organic matter and typical disinfection byproduct precursors in combined iron–carbon micro electrolysis-UBAF process for drinking water pre-treatment

The organic matter and two types of disinfection byproduct (DBP) precursors in micro-polluted source water were removed using an iron–carbon micro-electrolysis (ICME) combined with up-flow biological aerated filter (UBAF) process. Two pilot-scale experiments (ICME-UBAF and UBAF alone) were used to investigate the effect of the ICME system on the removal of organic matter and DBP precursors. The results showed that ICME pretreatment removed 15.6% of dissolved organic matter (DOM) and significantly improved the removal rate in the subsequent UBAF process. The ICME system removed 31% of trichloromethane (TCM) precursors and 20% of dichloroacetonitrile (DCAN) precursors. The results of measurements of the molecular weight distribution and hydrophilic fractions of DOM and DBP precursors showed that ICME pretreatment played a key role in breaking large-molecular-weight organic matter into low-molecular-weight components, and the hydrophobic fraction into hydrophilic compounds, which was favorable for subsequent biodegradation by UBAF. Three-dimensional fluorescence spectroscopy (3D-EEM) further indicated that the ICME system improved the removal of TCM and DCAN precursors. The biomass analysis indicated the presence of a larger and more diverse microbial community in the ICME-UBAF system than for the UBAF alone. The high-throughput sequencing results revealed that domination of the genera Sphingomonas, Brevundimonas and Sphingorhabdus contributed to the better removal of organic matter and two types of DBP precursors. Also, Nitrosomonas and Pseudomonas were beneficial for ammonia removal.

Effect of Aeration Rates and Filter Media Heights on the Performance of Pollutant Removal in an Up-Flow Biological Aerated Filter

The biological aerated filter (BAF) is an effective biological treatment technology which removes the pollutants in municipal wastewater secondary treatment. However, we still know little about the interaction between the pollutants removal and microbes within the BAF. In this study, we used an up-flow BAF (UBAF) reactor to investigate the relationships between the pollutants removal and microbial community structure at different aeration rates and filter media heights. The microbial community of biofilm was analyzed by Illumina pyrosequencing. Our results showed that the UBAF achieved a better removal efficiency of chemical oxygen demand (COD), NH4+-N, NO3−-N, and total phosphorus (TP) at an aeration rate of 65 L/h. In addition, the COD and NH4+-N removal mainly occurred at 0–25 cm height of filter media. The microbial community structure in the UBAF demonstrated that the relative abundance of the Planctomycetes and Comamonadaceae at 10 cm height of filter media were 11% and 48.1%, respectively, proportions significantly higher than those under others treatments. Finally, the changes in relative abundance of Proteobacteria, Planctomycetes, and Nitrospirae likely explained the mechanism of nitrogen and phosphorus removal. Our results showed that suitable conditions could enhance the microbial community structure to achieve a high pollutants removal in the UBAF.

Analysis of extracellular polymeric substances (EPS) and ciprofloxacin-degrading microbial community in the combined Fe-C micro-electrolysis-UBAF process for the elimination of high-level ciprofloxacin

Extracellular polymeric substances (EPS) and ciprofloxacin-degrading microbial community in the combined Fe-C micro-electrolysis and up-flow biological aerated filter (UBAF) process for the treatment of high-level ciprofloxacin (CIP) were analyzed. The research demonstrated a great potential of Fe-C micro-electrolysis-UBAF for the elimination of high-level CIP. Above 90% of CIP removal was achieved through the combined process at 100 mg L−1 of CIP loading. In UBAF, the pollutants were mainly removed at 0–70 cm heights. Three-dimensional fluorescence spectrum (3D-EEM) was used to characterize the chemical structural of loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) extracted from biofilm sample in UBAF. The results showed that the protein-like substances in LB-EPS and TB-EPS had no clear change in the study. Nevertheless, an obvious release of polysaccharides in EPSs was observed during long-term exposure to CIP, which was considered as a protective response of microbial to CIP toxic. The high-throughput sequencing results revealed that the biodiversity of bacteria community became increasingly rich with gradual ciprofloxacin biodegradation in UBAF. The ciprofloxacin-degrading microbial community was mainly dominated by Proteobacteria and Bacteroidetes. Microorganisms from genera Dechloromonas, Brevundimonas, Flavobacterium, Sphingopyxis and Bosea might take a major role in ciprofloxacin degradation. This study provides deep theoretical guidance for real CIP wastewater treatment.

Biochemical characteristic along UBAF in a one-stage autotrophic nitrogen removal reactor.

The Up-flow biological aerated filter (UBAF) based on a one-stage autotrophic nitrogen removal process has been widely investigated nowadays. In this work, the biochemical characteristic along the volcanic-filled UBAF reactor had been studied. The results indicate that short-rod, spherical and elliptical (averaged 0.2-1.0 μm) microorganisms with a specific irregular cauliflower profile existed in the system. Species identification showed Nitrosococcus- and Nitrosomonas-related aerobic ammonium-oxidizing bacteria (AerAOB) and Candidatus Kuenenia stuttgartiensis-like anaerobic ammonium-oxidizing bacteria (AnAOB) were the predominant functional bacteria that mixed with each other and showed no distinct niche in the system. However, the bioactivity of functional microorganisms displayed differently at different filter layers, with a better pollutant-removal activity in the lower parts than in the upper parts of the UBAF. In the lower parts, compact and small zooglea formed, whereas it trended to be larger and looser along the filter. Moreover, there was better biodiversity of AerAOB in the lower part, while AnAOB showed stable and low biodiversity along the filter.

Synthesis, application and evaluation of non-sintered zeolite porous filter (ZPF) as novel filter media in biological aerated filters (BAFs)

A zeolite porous filter (ZPF) was prepared using mixed raw zeolite, cement, and aluminum powder through steam curing and used as a novel filter medium in biological aerated filter (BAF). The performances of ZPF and commercially available ceramsite (CAC) in two laboratory scale upflow BAFs were compared. Results showed that the interconnected porous structure of ZPF was conducive to microbial biofilm growth. ZPF featured a total porosity of 29.55%, a compressive strength of 41–47N, and a specific surface area of 59.53m2/g. BAF containing ZPF showed more effectively the removal of organic carbon, ammonia nitrogen, nitrogen, and phosphorus compared to BAF containing CAC. The hydraulic retention time (HRT) was 7h at an air/water (A/W) ratio of 3:1. The amounts of total nitrogen removed were 59.89% with ZPF and 35.96% with CAC. Moreover, the amount of phosphorus removed was 83.80% with ZPF, whereas that of CAC was only 31.50%. ZPF was more suitable for the attached growth of heterobacteria and nitrobacteria to attain simultaneous nitrification and denitrification performance in the BAF. Therefore, ZPF is a novel suitable filter medium for simultaneous removal of nitrogen and phosphorus in BAFs.

Effect of novel sludge and coal cinder ceramic media in combined anaerobic–aerobic bio-filter for tetracycline wastewater treatment at low temperature

Two novel ceramic media were prepared by sludge, coal cinder and straw. Their characteristics such as physical property, total porosities and crystal components were studied. Moreover, their application on the combined up-flow anaerobic bio-filter (UAF) and up-flow biological aerated filter (UBAF) system to treat the synthetic wastewater containing tetracycline (TET) were studied at low temperature of 16°C. To be specific, first, chemical oxygen demand (COD) and ammonia (NH4-N) were measured to determine the start-up time. Then in the steady operation stage, influence of nitrogen and TET on the removals of COD, NH4-N, total nitrogen, total phosphorus and TET were investigated. Results showed that two new ceramics possessed high total porosity, roughness surface, low bulk and grain density. Due to the novel ceramics fillers, the start periods of the UAF and UBAF were shortening to 42 and 10days. Moreover, compared to conventional reactor, the new system had advantages of high processing efficiency, high organic load, strong shock and tetracycline resistance. When original influent COD, NH4-N and TET were 4000, 200 and 45mg/L, the total COD, NH4-N and TET reductions could reach to 97%, 99% and 89%. Furthermore, the low temperature did not influence the system.

Development and application of Palygorskite porous ceramsite in a biological aerated filter (BAF)

Novel filter Palygorskite porous ceramsite (PC) was prepared using Palygorskite clay, pore-forming material sawdust, and sodium silicate with a mass ratio of 10:2:1 after sintering at 700°C for 180 min. PC was characterized with X-ray diffraction, X-ray fluorescence, scanning electron microscopy, elemental, and porosimetry. PC had a total porosity of 67% and specific surface area of 61 m2/g. In order to assess the usefulness of PC as a medium for biological aerated filters (BAF), PC and (commercially available ceramsite) CAC were used to treat wastewater city in two laboratory-scale upflow BAFs. The results showed that the reactor containing PC was more efficient than the reactor containing CAC in terms of total organic carbon (TOC), ammonia nitrogen (NH3-N), and the removal of total nitrogen (TN) and phosphorus (P). This system was found to be more efficient at water temperatures ranging from 20 to 26°C, an air–water (A/W) ratio of 3:1, dissolved oxygen concentration >4.00 mg/L, and hydraulic retention time (HRT) ranging from 0.5 to 7 h. The interconnected porous structure produced for PC was suitable for microbial growth, and primarily protozoan and metazoan organisms were found in the biofilm. Microorganism growth also showed that, under the same submerged culture conditions, the biological mass in PC was significantly higher than in CAC (34.1 and 2.2 mg TN/g, respectively). In this way, PC media can be considered suitable for the use as a medium in novel biological aerated filters for the simultaneous removal of nitrogen and phosphorus.

Cosmetic wastewater treatment by a combined anaerobic/aerobic (ABR+UBAF) biological system

The cosmetics industry has been growing steadily for the past several years in China, yet very few researches exist on cosmetic wastewater treatment system. This study gave new insight to develop a combined anaerobic baffled reactor (ABR) and upflow biological aerated filter (UBAF) system for the treatment of cosmetic wastewater. The chemical oxygen demand (COD) removal efficiency in the cosmetic wastewater was mainly investigated in the front two compartments of ABR reactor, while it was treated by the same reactor with six compartments. When the influent COD load was set at 1.5g COD/L.d, the COD removal efficiency reached a maximum in the No. 1 compartment. The highest COD removal efficiency achieved 2.0g COD/L.d for the complete ABR reactor. The optimal hydraulic retention time (HRT) of the ABR was 48 h. A UBAF reactor was applied to advanced treatment for ABR effluent. The coke powder with the diameter of 0.5–1.0mm and the gas-water ratio of 7:1 were chosen the optimal experimental conditions. Under the above-optimal experimental conditions, the COD removal efficiency of UBAF was 69.5–82.6%. After the combined treatment by ABR and UBAF, the cosmetic wastewater effluent can effectively supply the discharge standard in China.

Remediation of Iron, Manganese, and Organic Pollutants in Lignite‐Derived Water Using an Upflow Biological Aerated Filter

AbstractA large amount of lignite‐derived water is created during the process of refining lignite. The concentration of Fe, Mn, phenol, and some other organic pollutants of the lignite‐derived water is above the discharge permit or circulating cooling water reuse standard in China. A laboratory‐scale upflow biological aerated filter (UBAF) was developed to treat this lignite‐derived water. Three kinds of coke powders, as waste products in the coal chemical industry with 0.1–0.4 mm, 0.5–1.0 mm, and 1.0–2.0 mm in diameter, were tested as the UBAF's carrier materials. A comparative study of gas–water ratio for the UBAF is presented. The studies presented in this paper demonstrate that with coke powder diameter of 0.5–1.0 mm and gas/water ratio of 7:1, the UBAF reactor can achieve optimal removal efficiency. After the UBAF treatment, the removal efficiency of Fe, Mn, and phenol was found to be 38.4–62.5%, 56.6–74.3%, and 89.5–94.3%, respectively. The lignite‐derived water can meet the discharge permit to surface water and reuse standard for circulating cooling water after the treatment by UBAF. The coke powder, as a waste material, can be used as a support material for UBAF very well.

The removal of 1,4-dioxane from polyester manufacturing process wastewater using an up-flow Biological Aerated Filter (UBAF) packed with tire chips

1,4-Dioxane is one of the by-products from the polyester manufacturing process, which has been carelessly discharged into water bodies and is a weak human carcinogen. In this study, a laboratory-scale, up-flow biological aerated filter (UBAF), packed with tire chips, was investigated for the treatment of 1,4-dioxane. The UBAF was fed with effluent, containing an average of 31 mg/L of 1,4-dioxane, discharged from an anaerobic treatment unit at H Co. in the Gumi Industrial Complex, South Korea. In the batch, a maximum of 99.5 % 1,4-dioxane was removed from an influent containing 25.6 mg/L. In the continuous mode, the optimal empty bed contact time (EBCT) and air to liquid flow rate (A:L) were 8.5 hours and 30:1, respectively. It was also found that the removal efficiency of 1,4-dioxane increased with increasing loading rate within the range 0.04 to 0.31 kg 1,4-dioxane/m3·day. However, as the COD:1,4-dioxane ratio was increased within the range 3 to 46 (mg/L COD)/(mg/L 1,4-dioxane), the removal efficiency unexpectedly decreased.

The characteristics and application of grain-slag media in a biological aerated filter (BAF)

Novel filter media-grain slag particles were prepared using waste material-grain slag, clay and pore-forming material with a mass ratio of 3:2:1. Compared with haydite, grain-slag had higher total porosity, larger total surface area and lower bulk and apparent density. Tests of heavy metal elements in lixivium proved that grain-slag were safe for wastewater treatment. In order to ascertain the application of grain-slag, grain-slag and haydite were applied as the media of biological aerated filters (BAF) to treat municipal wastewater in two lab scale upflow BAFs. The results showed that grain-slag reactor brought a relative superiority to haydite reactor in terms of chemical oxygen demand (CODcr) and ammonia nitrogen (NH3-N) removal at the conditions of water temperature ranging from 20°C to 26°C and DO ≥4.00mgL−1 when hydraulic retention time (HRT) ranging from 1h to 5h. In addition, the detection of the amount of hetero bacteria and nitrobacteria of two biological aerated filters in three HRTs also showed that grain-slag medium was more suitable to the attached growth of nitrobacteria, which is helpful to the improvement of nitrification performance in grain-slag BAF. Therefore, grain-slag application in BAF, as a novel process of treating wastes with wastes, provided a promising way in grain slag waste material utilization.

Biochemical Characteristics of UBAF in Different Influent NH<sub>4</sub><sup>+</sup>-N Concentration under Yellow River Condition

The upflow biological aerated filter(UBAF) filled with grain slag was applied in Yellow River treatment. The aim is to study the reactor’s ability withstanding ammonia nitrogen volumetric loading in Yellow River water treatment. As influent NH4+-N concentration increases from 0.2mg/L to 3.0mg/L, the average removal rate of turbidity, CODMn and NH4+-N were 82%, 27% and 97% respectively, and removal of NH4+-N occurs mainly in the filter layer depth changing from 150cm to 210cm. The nitrification performance improves when PO43- -P concentration in water reach 60μg/L, and the removal of NH4+-N occurs mainly in the filter media layer depth shortened from 210cm to 90cm.

The Characteristics and Application of Water Quenched Slag Particles (WQSP) as Filter Media

Novel filter media-water quenched slag particles (WQSP) were prepared using waste material- Water quenched slag, clay and pore-forming material with a mass ratio of 3:2:1. Compared with haydite, WQSP had higher total porosity, larger total surface area and lower bulk and apparent density. Tests of heavy metal elements in lixivium proved that SGSP were safe for wastewater treatment. In order to ascertain the application of WQSP ，WQSP and haydite were applied as the media of biological aerated filters (BAF) to treat municipal wastewater in two lab scale upflow BAFs. The results showed that WQSP reactor brought a relative superiority to haydite reactor in terms of chemical oxygen demand (CODcr) and ammonia nitrogen (NH3-N) removal at the conditions of water temperature ranging from 200C to 260C and DO ≥4.00 mg·L-1. Therefore, WQSP application, as a novel process of treating wastes with wastes, provided a promising way in water quenched slag utilization.

Study of municipal wastewater treatment with oyster shell as biological aerated filter medium

Oyster shell and plastic ball were applied as the media of biological aerated filters (BAF) to treat municipal wastewater in two lab scale upflow BAFs. The results indicated that oyster shell BAF and plastic ball BAF had average chemical oxygen demand (COD) removals of 85.1% and 80.0%, when hydraulic retention time (HRT) was longer than 4 h, and 65.7% and 68% with HRT of 2 h, respectively. In terms of removing ammonia nitrogen (NH 3-N), oyster shell BAF and plastic ball BAF had average removals of 98.1% and 93.7% for HRT longer than 4 h, and 47.2% and 65.1% for HRT of 2 h, respectively. Total phosphorus (TP) removals of oyster shell BAF were increased to 79.9% and 90.6% as the pH increased to 9 and 10, respectively, while no improvement was observed for plastic ball BAF. The effluent pH of oyster shell BAF was higher and buffered compared with that of the influent, mainly due to the CaCO 3 released from the shell. The oyster shell may also be the main reason to support the BAF a higher NH 3-N removal efficiency when HRT was longer than 4 h, compared with plastic ball BAF.

Advanced treatment of landfill leachate by a new combination process in a full-scale plant

Advanced treatment of mature landfill leachate from a municipal landfill located in southern China (Jiangmen) was carried out in a full-scale plant using a new process. The combined process has a sequencing batch reactor (SBR) serving as the primary treatment, with polyferric sulfate (PFS) coagulation coupled with a Fenton system as secondary treatment, and a pair of upflow biological aerated filters (UBAFs) in parallel as tertiary treatment. The overall removal efficiency of chemical oxygen demand (COD) in this process was 97.3%, with an effluent COD less than 100 mg/L. Up to 99% ammonia (N–NH 3) removal efficiency was achieved in the SBR, with an effluent of less than 3 mg/L, which meets the discharge standard (≤25 mg/L) with only primary treatment. The total phosphorus (TP) and suspended solids (SS) in the final effluent were reduced to less than 1 mg/L and 10 mg/L, respectively. The experience gained in the operation and maintenance will lead to a more stable performance of this combined process. An economic analysis shows that the overall operating cost of the advanced treatment was $2.70/m 3. This new combination process was proved to be highly compatible and efficient in a small-scale landfill leachate treatment plant and is recommended for small-scale landfill leachate treatment plants.

Treatment of wastewater containing azo dye reactive brilliant red X-3B using sequential ozonation and upflow biological aerated filter process

In this work, the treatment of wastewater containing azo dye reactive brilliant red X-3B using sequential ozonation and upflow biological aerated filter process has been studied. Decolorization was almost complete after 120 min with an ozone concentration of 34.08 mg/L, the biological oxygen demand for 5 days (BOD 5)/chemical oxygen demand (COD) ratio increased from 0.102 to 0.406, which was more effective for the subsequent upflow biological aerated filter (UBAF) to reduce COD concentration. Under the conditions of gas/liquid = 3, hydraulic load = 4.8 m 3/m 3.d, T = 20–25 °C, the mass ratio of ozone to dye = 4.5, pH 11, the COD and color of the effluent were less than 40 mg/L and 20 Pt–Co units, respectively, and the average decolorization and COD removal efficiency were 97% and 90%, respectively. The experimental results showed that the combination of ozone oxidation and upflow biological aerated filter was a promising technique to treat wastewater containing azo dye.

Comparing cost and process performance of activated sludge (AS) and biological aerated filters (BAF) over ten years of full sale operation

In the early 1990s, the Wastewater Treatment Plant (WWTP) of Frederikshavn, Denmark, was extended to meet new requirements for nutrient removal (8 mg/L TN, 1.5 mg TP/L) as well as to increase its average daily flow to 16,500 m(3)/d (4.5 MGD). As the most economical upgrade of the existing activated sludge (AS) plant, a parallel biological aerated filter (BAF) was selected, and started up in 1995. Running two full scale processes in parallel for over ten years on the same wastewater and treatment objectives enabled a direct comparison in relation to operating performance, costs and experience. Common pretreatment consists of screening, an aerated grit and grease removal and three primary settlers with chemical addition. The effluent is then pumped to the two parallel biological treatment stages, AS with recirculation and an upflow BAF with floating media. The wastewater is a mixture of industrial and domestic wastewater, with a dominant discharge of fish processing effluent which can amount to 50% of the flow. The maximum hydraulic load on the pretreatment section as a whole is 1,530 m(3)/h. Approximately 60% of the sewer system is combined with a total of 32 overflow structures. To avoid the direct discharge of combined sewer overflows into the receiving waters, the total hydraulic wet weather capacity of the plant is increased to 4,330 m(3)/h, or 6 times average flow. During rain, some of the raw sewage can be directed through a stormwater bypass to the BAF, which can be modified in its operation to accommodate various treatment needs: either using simultaneous nitrification/denitrification in all filters with recirculation introducing bottom aeration with full nitrification in some filters for storm treatment and/or post-denitrification in one filter. After treatment, the wastewater is discharged to the Baltic Sea through a 500 m outfall. The BAF backwash sludge, approximately 1,900 m(3) per 24 h in dry weather, is redirected to the AS plant. Primary settler sludge and the combined biosolids from the AS plant are anaerobically digested, with methane gas being used for generation of heat and power. On-line measurements for the parameters NO3, NO2, NH4, temperature as well as dissolved oxygen (DO) are used for control of aeration and external carbon source (methanol). Dosing of flocculants for P-removal is carried out based on laboratory analysis and jar tests. This paper discusses the experience gained from the plant operation during the last ten years, compiling comparative performance and cost data of the two processes, as well as their optimisation.

Long Term Full Scale Comparison of Activated Sludge (AS) with Biological Aerated Filter (BAF)

The Wastewater Treatment Plant (WWTP) of Frederikshavn, Denmark, was extended in the early nineties to increase its average daily flow to 4,5 MGD (16,500 m³/d) and meet new requirements for nutrient removal (8 mg/l TN, 1,5 mg TP/l). A parallel biological aerated filter (BAF) was the selected as the most economical upgrade of the existing activated sludge plant (AS), and started up in 1995. Running two full scale processes in parallel on the same wastewater and treatment objectives for over ten years enabled a direct comparison in relation to operating performance, costs and experience. After screening, a combined grit and grease chamber and 3 primary settlers, the effluent is pumped to the bio-treatment, consisting of AS with recirculation (Modified Lutzack-Ettinger – MLE) and an upflow BAF with floating media. The wastewater is a mixture of industrial and domestic wastewater, with a dominant discharge of fish processing effluent which can amount to 50 % of the flow. The maximum hydraulic load on the pretreatment section as a whole is 10 MGD (1,530 m3/h) . Approx. 60% of the sewer system is combined with a total of 32 overflow structures. To avoid the direct discharge of combined sewer overflows into the receiving waters, the total hydraulic capacity of the plant is increased during rain to 27 mgd (4,330 m³/hour) or 6 times average flow. During rain, this is achieved by directing some of the raw sewage through a stormwater bypass to the BAF and switching all six BAF to full nitrification. After final biotreatment, the wastewater is conveyed through a 500 m sea outfall. The operation of the BAF can be modified to accommodate various treatment needs: - either using simultaneous nitrification/denitrification in all filters with recirculation - bottom aeration with full nitrification in all filters for stormwater treatment - or post-denitrification in 1 filter. On-line measurements for the parameters NO3, NO2, NH4 and PO4 as well as dissolved oxygen (DO) are used for control of aeration and for addition of flocculants for P-removal and external carbon source (methanol). The BAF backwash sludge, approx. 0.5 MGD (1.900 m³/d) once every 24 h in dry weather, is redirected to the AS plant. Sludge from primary settlers and the combined biosolids from the AS plant are anaerobically digested, with methane gas being used for generation of heat and power. This paper discusses the experience gained from the plant operation during the last ten years, compiling comparative performance and cost data of the two processes.