Biological Nutrient Removal Systems Research Articles

Algal Nutrient Removal During Wastewater Treatment

While major improvements in wastewater treatment using enhanced biological nutrient removal (BNR) systems have reduced nutrient loading to natural receiving waters, current limits of technology preclude further nutrient reductions using established, traditional BNR processes. New, cost-efficient and easily adaptable approaches to wastewater treatment must be designed to reduce total nitrogen (N) and phosphorus (P) in effluents from water resource recovery facilities (WRRFs) further. The goal of this research is to develop phycoremediation strategies that employ phytoplankton to remove N (and P) from treated effluents prior to discharge at a lower cost. To make phycoremediation viable within municipal WRRFs that operate at high flow rates and have short in-plant hydraulic residence times (< 8 h), “wash out” of algal biomass must be prevented, algae must be easily separated and removed from the treated effluent before discharge, and sufficient algal biomass must be retained within or returned to the reactor to ensure stable algal populations within the plant. For these reasons, this research employed encapsulation techniques that allow for ease of removal of the algae while removing nutrients at high rates. Results show removal efficiencies up to 100% for nitrate, nitrite, and phosphate with a hydraulic retention time of 6.5 h. These high reduction efficiencies were achieved by incorporating wavelength specific submersible LEDs, maintaining a constant pH, and with constant mixing. This title belongs to WERF Research Report Series ISBN: 9781780406749 (eBook)

Investigation of microbial community structure in an advanced activated sludge side-stream reactor process with alkaline treatment

An advanced side-stream reactor process with alkaline treatment (SIPER) has been demonstrated excellent sludge reduction potential and nutrient removal in the previous pilot-scale studies. The microbial community characteristic of the process was investigated in this study. The results indicated that the return of alkaline-treated sludge did not influence microbial activity of the activated sludge containing a higher diversity of bacteria in the SIPER process. Sludge in the biological nutrient removal (BNR) system and in the side-stream reactor (SSR) showed significantly different microbial composition, although two systems were connected via sludge recycle. The unique bacterial community was attributed to high pH environment in the SSR. Sequences represented by predominant DGGE bands were affiliated with Proteobacteria, Firmicutes, Bacteroidetes, Chloroflexi, and Chlamydiae. The predominant bacteria in the system were nitrifying, denitrifying, and hydrolytic acid producing bacteria. The hydrolytic acid producing bacteria played an important role in achieving lysis-cryptic growth of cells while nitrifying and denitrifying bacteria laid the foundation for effective nitrogen removal. Plenty of nitrifying and denitrifying bacteria existed in the SSR, which improved the utility of the supernatant of alkaline-treated sludge as an additional carbon source and enhanced nitrogen removal of the system.

A logistic model for the remediation of filamentous bulking in a biological nutrient removal wastewater treatment plant.

Biological nutrient removal (BNR) systems across the globe frequently experience bulking and foaming episodes, which present operational challenges such as poor sludge settling due to excessive filamentous bacteria. A full-scale BNR plant treating primarily domestic wastewater was monitored over a period of 1 year to investigate filamentous bacterial growth response under various plant operating parameters. Identification of filamentous bacteria by conventional microscopy and fluorescent in situ hybridisation indicated the dominance of Eikelboom Type021N, Thiothrix spp., Eikelboom Type 1851 and Eikelboom Type 0092. A cumulative logit model (CLM) was applied to elucidate significant relationships between the filamentous bacteria and plant operational parameters. The model could predict the potential abundance of dominant filamentous bacteria in relation to wastewater treatment plant operational parameters. Data obtained from the model corroborated with previous findings on the dominance of most filaments identified, except for Type 0092, which exhibited some unique traits. With further validation, the model could be successfully applied for identifying specific parameters which could contribute towards filamentous bulking, thus, providing a useful tool for regulating specific filamentous growth in full-scale wastewater treatment plants.

The removal of N and P in aerobic and anoxic-aerobic digestion of waste activated sludge from biological nutrient removal systems

Biological nutrient removal (BNR) activated sludge (AS) systems produce a waste activated sludge (WAS) that is rich in nitrogen (N) and phosphorus (P). When this sludge is thickened to 3–6% total suspended solids (TSS) and digested (aerobic or anaerobic), a high proportion of N and P are released to the bulk liquid resulting in high concentrations of ammonia/nitrate and orthophosphate up to several hundred mg/ℓ (without denitrification or P precipitation). This research investigates P removal by P precipitation in anoxic-aerobic digestion of P-rich BNR system WAS. The experimental setup for this work was a lab-scale membrane UCT BNR system fed real settled sewage with added acetate, orthophosphate, and cations Mg and K to increase biological excess P removal. This WAS was fed to batch aerobic digesters at various TSS concentrations, and to two 20-day retention time continuous anoxic-aerobic digesters (AnAerDig) with aeration cycles of 3-h air on and 3-h air off, one fed concentrated WAS (20 g TSS/ℓ ) and the other fed diluted WAS (3 g TSS/ℓ). Nitrogen removal has been discussed in the previous paper. This paper focuses on the P removal by P precipitation observed in the batch tests and continuous systems. The rate of polyphosphate release (bGP) during batch aerobic digestion at low TSS without P precipitation was found to be 2.5 times faster than the endogenous respiration rate (bG) of phosphorus accumulating organics (PAO), i.e. bGP = 0.1/d. This rate was then applied to the high-TSS aerobic batch tests and continuous anoxic-aerobic digesters to estimate the P precipitation at various TSS concentrations, with and without additional Mg or Ca dosing. Newberyite (MgHPO4·3H2O) and amorphous tricalcium phosphate (ACP or TCP, Ca3(PO4)2·xH2O) are found to be the most common phosphate precipitates.Keywords: biological excess phosphorus removal, waste activated sludge, anoxic-aerobic digestion, phosphaterelease, mineral precipitation

Nutrient release, recovery and removal from waste sludge of a biological nutrient removal system

The uncontrolled release of nutrients from waste sludge results in nitrogen and phosphorus overloading in wastewater treatment plants when supernatant is returned to the inlet. A controlled release, recovery and removal of nutrient from the waste sludge of a Biological Nutrient Removal system (BNR) are investigated. Results showed that the supernatant was of high mineral salt, high electrical conductivity and poor biodegradability, in addition to high nitrogen and phosphorus concentrations after the waste sludge was hydrolysed through sodium dodecyl sulphate addition. Subsequently, over 91.8% of phosphorus and 10.5% of nitrogen in the supernatants were extracted by the crystallization method under the conditions of 9.5 pH and 400 rpm. The precipitate was mainly struvite according to X-ray diffraction and morphological examination. A multistage anoxic–oxic Moving Bed Biofilm Reactor (MBBR) was then adopted to remove the residual carbon, nitrogen and phosphorus in the supernatant. The MBBR exhibited good performance in simultaneously removing carbon, nitrogen and phosphorus under a short aeration time, which accounted for 31.25% of a cycle. Fluorescence in situ hybridization analysis demonstrated that nitrifiers presented mainly in floc, although higher extracellular polymeric substance content, especially DNA, appeared in the biofilm. Thus, a combination of hydrolysis and precipitation, followed by the MBBR, can complete the nutrient release from the waste sludge of a BNR system, recovers nutrients from the hydrolysed liquor and removes nutrients from leftovers effectively.

Development of the anaerobic baffled reactor-membrane bioreactor (ABR-MBR) as a biological nutrient removal system for high-rise building wastewater recycling

A novel anaerobic baffled reactor-membrane bioreactor (ABR-MBR) system has been developed as a compact combined biological treatment system and membrane separation unit for wastewater recycling from high-rise buildings. Here, the anaerobic baffled reactor (ABR) compartment had five baffles and served as anaerobic degradation zone, followed by the aerobic membrane bioreactor (MBR) compartment for further aerobic degradation of organic residues. The total operating hydraulic retention time (HRT) of the ABR-MBR system was 3 h (2 h for ABR compartment and 1 h for aerobic MBR compartment). The wastewater used in the study came from Charoen Wisawakam Building, Faculty of Engineering, Chulalongkorn University, located in Bangkok city, Thailand. The results showed that treated effluent quality was quite good and highly promising for water reuse purposes. The average permeate flux of the membrane was kept at 30 L/m2-h. The ABR-MBR system could remove more than 90% COD, total nitrogen, and total phosphorus from building wastewater at total operating HRT of only 3 h. Specific phosphorus uptake rate obtained in the aerobic MBR compartment is calculated to be 4.82 mgP/gMLSS h. Moreover, a rapid phosphorus uptake phenomenon in the MBR compartment implies that PAOs biomass seems to respond for biological phosphorus removal by the ABR-MBR system. The research suggests that the ABR-MBR system can be a promising system for water reuse and reclamation for high-rise buildings in the near future.

Optimization of A2O BNR Processes Using ASM and EAWAG Bio‐P Models: Model Performance

This paper presents the performance of an optimization model for a biological nutrient removal (BNR) system using the anaerobic-anoxic-oxic (A(2)O) process. The formulated model simulates removal of organics, nitrogen, and phosphorus using a reduced International Water Association (IWA) Activated Sludge Model #3 (ASM3) model and a Swiss Federal Institute for Environmental Science and Technology (EAWAG) Bio-P module. Optimal sizing is attained considering capital and operational costs. Process performance is evaluated against the effect of influent conditions, effluent limits, and selected parameters of various optimal solutions with the following results: an increase of influent temperature from 10 degrees C to 25 degrees C decreases the annual cost by about 8.5%, an increase of influent flow from 500 to 2500 m(3)/h triples the annual cost, the A(2)O BNR system is more sensitive to variations in influent ammonia than phosphorus concentration and the maximum growth rate of autotrophic biomass was the most sensitive kinetic parameter in the optimization model.

Uptake by Algae of Dissolved Organic Nitrogen from BNR Treatment Plant Effluents

The importance of dissolved organic nitrogen (DON) in wastewater treatment effluent has dramatically increased as permitted effluent total nitrogen (TN) concentrations have been decreased to very low levels in response to problems with impaired surface water quality from eutrophication. For conventional secondary treatment, DON typically accounts for less than 10% of the effluent TN, but it is a major component (>50%) in effluents from advanced biological nutrient removal (BNR) treatment plants, for which most of the inorganic nitrogen species and effluent suspended solids are removed. DON persists in effluents from BNR systems and little is known about the potential impact of the effluent DON from these facilities on surface water quality. Of particular interest is what portion of DON is readily available for algae consumption or can be converted to forms to support algal growth, and what type of substances compose DON. To develop a better understanding of the occurrence and bioavailability of DON in effluents from advanced BNR systems, a new protocol was developed for measuring the readily bioavailable DON and forms of DON that are not readily taken up by algae (recalcitrant DON). An anion exchange resin was used to remove nitrate while an XAD-8 resin was used to remove hydrophobic forms of DON. To assess the bioavailability of wastewater-derived DON, algal growth assays were performed in the presence of bacteria in effluents from ten municipal BNR wastewater treatment plants. The results showed only minor difference in the algal growth and DON consumption between the untreated and XAD-8 treated samples. Growth of algae and DON consumption were not observed in the eluent from XAD-8 resins, despite the fact that this fraction contained up to approximately 30% of the DON. These findings indicate that the hydrophobic DON retained on the XAD-8 resin is not bioavailable to algae over periods of several weeks and that the XAD-8 treatment combined with an anion exchange resin can be used to quantify and separate this recalcitrant form of DON from bioavailable DON and nitrate. This title belongs to WERF Research Report Series . ISBN: 9781780401386 (eBook)

Characterisation of raw sewage and performance assessment of primary settling tanks at Firle Sewage Treatment Works, Harare, Zimbabwe

The need for more stringent effluent discharge standards as prescribed by the Environmental Management Act 20:27 to protect the environment can be sustainably achieved with the aid of Activated Sludge Models. Thus, the researchers believe it is time to re-evaluate wastewater characteristics at Firle Sewage Treatment Works (STW) and make use of activated sludge simulators to address pollution challenges caused by the sewage plant. Therefore, this paper characterizes raw sewage and assesses settled and unsettled sewage in order to evaluate the performance of the primary treatment system and the suitability of the settled sewage for treatment by the subsequent Biological Nutrient Removal (BNR) system at Firle STW. Parameters studied included COD, BOD, TKN, TP, NH3, TSS, pH and Alkalinity. Composite samples were collected over a 9-day campaign period (27 June to 6 July 2012), hourly grab samples over 24hrs and composite samples on 6 March 2012 which were then analysed in the lab in accordance with Standard Methods for the Examination of Water and Wastewater to support the City of Harare 2004–2012 lab historical records. Concentrations for unsettled sewage in mg/L were COD (527±32), BOD (297±83) TKN (19.0±2.0), TP (18±3), NH3 (24.0±12.9), TSS (219±57), while pH was 7.0±0 and Alkalinity 266±36mg/L. For settled sewage the corresponding values in mg/L were COD (522±15), BOD (324±102), TKN (21.0±3.0), TP (19.0±2.0), NH3 (25.6±11.2), TSS (250±66), while pH was 7.0±0 and Alkalinity 271±17mg/L. The plant design values for raw sewage are COD (650mg/L), BOD (200mg/L), TKN (40mg/L) and TP (11mg/L). Thus, COD and nitrogen were within the plant design range while BOD and TP were higher. Treatability of sewage in BNR systems is often inferred from the levels of critical parameters and also the ratios of TKN/COD and COD/TP. The wastewater average settled COD/BOD, COD/TP and TKN/COD ratio were 1.7±0.5, 27.1±3.1 and 0.04±0.01 respectively and corresponding unsettled ratios were 1.8±0.5, 30.77±6.8 and 0.04±0 respectively. Thus, treatability by the 3-stage BNR system appears highly feasible for nitrogen and is likely to be complex for phosphorous. Fractionation of COD, TP and TN is recommended to appropriately advise further steps to optimise the plant operations.

The variation of volatile fatty acid compositions in sewer length, and its effect on the process design of biological nutrient removal

The potential of enhanced biological phosphorus removal (EBPR) in biological nutrient removal (BNR) systems critically depends on the availability and types of volatile fatty acids (VFAs) in sewage. Although the characteristics of VFAs in sewage are strongly related with the biochemical transformations in the sewer system, they have not been studied thoroughly in terms of BNR process design. We have investigated the characteristics of VFAs in influent of nine sewage treatment plants which represent typical small to very large sewer systems in Korea. We found that influent total VFACOD (VFA as chemical oxygen demand) concentrations ranged from 20.4 to 65.2 mg/L. Acetic acid was a predominant VFA in sewage, and the propionic acid (HPr) portion averaged 38.7% of total VFACOD. However the sewage from longer sewer systems showed more HPr content, indicating that type of VFA varied with the total sewer length. The finding is a particularly important consideration for BNR process design since availability of HPr positively behaved to suppress the unfavorable growth of glycogen-accumulating organisms. The implication of these findings for BNR process design is discussed in this paper.

Assessment of Urban Source Metal Levels in Influent, Effluent, and Sludge of Two Municipal Biological Nutrient Removal Wastewater Treatment Plants of Bursa, an Industrial City in Turkey

AbstractRemoval of Al, As, Cd, total Cr (Tot. Cr), Cu, Total Fe (Tot. Fe), Mn, Ni, Pb, Sb, Sn, and Zn from urban effluent by wastewater treatment plants (WWTPs) operated under five‐stage Bardenpho® process were investigated and water soluble metals in the dewatered sludge were quantified. Samples were collected from two WWTPs on a weekly basis over an approximately 2.5‐year time span. Tot. Fe and Al were the most abundant, As, Pb, Ni, Cu, and Cd were the least abundant metals in the influents of both WWTPs. Removal efficiencies above 75% were achieved for Tot. Cr, Tot. Fe, Al, and Cu, whereas, no significant removal was observed for As, Cd, Pb, Sb, and Sn. Removal of Tot. Cr, Cu, Tot. Fe, Zn, Al, Mn, and Ni were influenced by influent suspended solids concentrations, and of Tot. Cr, Zn, and Cd were influenced by their initial content in the influent. Zn removal efficiency of biological nutrient removal (BNR) system in this study was higher and Cd removal efficiency was lower than that of conventional activated sludge reported in the literature. No remarkable difference for metals such as Cu, Mn, Ni, and Pb was observed between the removal efficiencies of conventional system and BNR system.

Changes of pH in A&lt;sup&gt;2&lt;/sup&gt;O Process System and its Impact on Nitrogen and Phosphorus Removal

Simulate sewage were used in an anaerobic-anoxic-aerobic biological nutrient removal system(A2O process), by observing the pHs in different compartments and its reflected changes in nitrogen and phosphorus removal, studied on the effects of different pHs on the removal of pollutants. The experiments indicates that the anaerobic phosphorus release showed the main performance of the decline of pH, denitrification in anoxic zone caused the rise of pH, uptake of phosphate in the aerobic zone mainly caused the continuous rise of pH. There is no evidently changes in COD removal, ammonia nitrogen get the highest removal as the pH value was between 8.0-8.5, when pH was at 6.5-7.5, the TN have the maximum removal rate, TP can keep in a high level when the pH was above 6.0.

Lamellar 이차침전지에서의 침강 특성 파악

Where an activated sludge system needs to be converted to biological nutrient removal(BNR) system, the secondary clarifier must handle higher MLSS from bioreactor since nitrification in BNR system that requires higher SRTs than activated sludge system. Either increase the clarifier size or modification of clarifier physical structure is required to cope with MLSS surge. One of recommended structural modification is the insertion of Lamellar within clarifier. In this study, two clarifiers - one has Lamellar structure inserted and the other does not - were used to compare the effect of Lamellar in solid/liquid separation. Same MLSS was fed to both clarifiers and concentrations of MLSS were varied. With all MLSS concentrations, attachment of MLSS on Lamellar was observed and it was found that detached MLSS caused the higher effluent SS concentrations than that of non-Lamellar clarifier effluent. From these results, Lamellar should not be inserted in clarifier to handle MLSS from BNR processes and the recommendation must be withdrawn.

Molecular Characterization of Denitrifying Bacteria Isolated from the Anoxic Reactor of a Modified DEPHANOX Plant Performing Enhanced Biological Phosphorus Removal

Enhanced Biological Phosphorus Removal (EBPR) under anoxic conditions was achieved using a Biological Nutrient Removal (BNR) system based on a modification of the DEPHANOX configuration. Double-probe Fluorescence in Situ Hybridization (FISH) revealed that Polyphosphate Accumulating Organisms (PAOs) comprised 12.3 +/- 3.2% of the total bacterial population in the modified DEPHANOX plant. The growing bacterial population on blood agar and Casitone Glycerol Yeast Autolysate agar (CGYA) medium was 16.7 +/- 0.9 x 10(5) and 3.0 +/- 0.6 x 10(5) colony forming units (cfu) mL(-1) activated sludge, respectively. A total of 121 bacterial isolates were characterized according to their denitrification ability, with 26 bacterial strains being capable of reducing nitrate to gas. All denitrifying isolates were placed within the alpha-, beta-, and gamma-subdivisions of Proteobacteria and the family Flavobacteriaceae. Furthermore, a novel denitrifying bacterium within the genus Pseudomonas was identified. This is the first report on the isolation and molecular characterization of denitrifying bacteria from EBPR sludge using a DEPHANOX-type plant.

Distillery wastes as external carbon sources for denitrification in municipal wastewater treatment plants

In this study, by-products from alcohol production were examined in terms of their potential application as external carbon sources for enhancing denitrification in biological nutrient removal systems. Three types of batch tests were used to compare the effects of the distillery by-products, such as fusel oil, syrup and reject water, on the non-acclimated activated sludge. Much higher nitrate utilization rates (NURs) were observed for the latter two carbon sources. In the conventional NUR measurements (one-phase experiments), the observed NURs with syrup and reject water were 3.2-3.3 g N/(kg VSS h) compared with 1.0 g N/(kg VSS h) obtained for fusel oils from two different distilleries. When the carbon sources were added at the beginning of the anoxic phase preceded by an anaerobic phase (two-phase experiments), the NURs were 4.2 g N/(kg VSS h) (syrup and reject water) and 2.4-2.7 g N/(kg VSS h) (fusel oils). The heterotrophic yield coefficient, determined based on the conventional OUR measurements, varied in a relatively narrow range (0.72-0.79 g COD/g COD) for all the examined carbon sources. Due to advantageous composition (much higher COD concentrations and COD/N ratios), fusel is a preferred carbon source for practical handling in full-scale wastewater treatment plants.

Minimizing nitrous oxide in biological nutrient removal from municipal wastewater by controlling copper ion concentrations

In this study, nitrous oxide (N(2)O) production during biological nutrient removal (BNR) from municipal wastewater was reported to be remarkably reduced by controlling copper ion (Cu(2+)) concentration. Firstly, it was observed that the addition of Cu(2+) (10-100 μg/L) reduced N(2)O generation by 54.5-73.2 % and improved total nitrogen removal when synthetic wastewater was treated in an anaerobic-aerobic (with low dissolved oxygen) BNR process. Then, the roles of Cu(2+) were investigated. The activities of nitrite and nitrous oxide reductases were increased by Cu(2+) addition, which accelerated the bio-reductions of both nitrite to nitric oxide (NO (2) (-) → NO) and nitrous oxide to nitrogen gas (N(2)O → N(2)). The quantitative real-time polymerase chain reaction assay indicated that Cu(2+) addition increased the number of N(2)O reducing denitrifiers. Further investigation showed that more polyhydoxyalkanoates were utilized in the Cu(2+)-added system for denitrification. Finally, the feasibility of reducing N(2)O generation by controlling Cu(2+) was examined in two other BNR processes treating real municipal wastewater. As the Cu(2+) in municipal wastewater is usually below 10 μg/L, according to this study, the supplement of influent Cu(2+) to a concentration of 10-100 μg/L is beneficial to reduce N(2)O emission and improve nitrogen removal when sludge concentration in the BNR system is around 3,200 mg/L.

Internal Behavior of Biological Nutrient Removal System for Advanced Wastewater Treatment

 Abstract—The purpose of this research was develop a biological nutrient removal (BNR) system which has low energy consumption, sludge production, and land usage. These indicate that BNR system could be a alternative of future wastewater treatment in ubiquitous city(U-city). Organics and nitrogen compounds could be removed by this system so that secondary or tertiary stages of wastewater treatment satisfy their standards. This system was composed of oxic and anoxic filter filed with PVDC and POM media. Anoxic/oxic filter system operated under empty bed contact time of 4 hours by increasing recirculation ratio from 0 to 100 %. The system removals of total nitrogen and COD were 76.3% and 93%, respectively. To be observed internal behavior in this system SCOD, NH3-N, and NO3-N were conducted and removal shows range of 25~100%, 59~99%, and 70~100%, respectively. Keywords—BNR, nitrification, denitrification, organics removal, anoxic, oxic, advanced treatment. I. INTRODUCTION ATER/SEWAGE facility, one of the urban base facilities constituting a city, is an important infrastructure, and to manage it the nation has a systematic system established for a long time. In the mean time, recently the nation has recognized the importance of an ubiquitous environment to lead the future society and established 'u-Korea ' plan, and each local government is expanding the promotion of u-city construction projects connected to the ubiquitous environment (1). At the same time, low-carbon green growth, a national project, and water quality standards of discharged water(2) continuously reinforced to improve the water quality of rivers has presented a new paradigm trend composed of improvement of existing wastewater treatment plants, application of advanced treatment technology and distributed wastewater treatment for tertiary treatment. Thus, cases for application of the biological nutrient removal system (BNR) have been on the rise to reduce the installation site, produce high quality treated water, and save labor and operating costs with automated operation (3). The BNR system which has been developed mainly in Europe not only can maintain SRT (4) for a long time without separate operation and make free load changes but also does not require the secondary sedimentation tank and can secure high-concentration microbes, providing due to the shorter reaction time a higher degree of intensity for site requirement than the existing suspended growth process. Thus, the BNR system is advantageous in application to wastewater treatment

Upgrading the efficiency of an external nitrification BNR system – The modified Dephanox process

Two types of external nitrification biological nutrient removal (BNR) plants were successively operated for municipal wastewater treatment. The first plant configuration was based on the conventional Dephanox design. Basic operational parameters were chosen as variables in order to assess their impact on the plant efficiency. The experimental results indicated that minimization of the aerobic mass fraction to values as low as 11% was practically feasible, resulting to high nutrient removal percentages, of 81% and 83%, respectively for nitrogen and phosphorus. However, the activated sludge characteristics with pin flocs formation and the absence of protozoa, led to increased total suspended solids concentration in the plant effluent (42 mg TSS/L in average). By increasing the aerated mass fraction to 16–17%, the sludge quality characteristics were improved and the pin flocs phenomenon was moderated. The increase in the aerated mass fraction was achieved “indirectly”, because of the lower biomass concentration in the anaerobic reactor, by establishing an additional mixed liquor recirculation flow in the conventional Dephanox design. This new configuration, referred as the modified Dephanox process, allowed for maintaining high anoxic P uptake extend with simultaneous enhancement of the plant denitrification potential. Fluorescence in situ hybridization (FISH) demonstrated that the well-known Phosphorus Accumulating Organism (PAO), Candidatus Accumulibacter phosphatis, was present in both the conventional and modified Dephanox process. The new configuration was proven to be more efficient regarding nutrient removal, being an interesting modification of the typical Dephanox design.

The influence of fundamental design parameters on ciliates community structure in Irish activated sludge systems

The protozoan community in eleven activated sludge wastewater treatment plants (WWTPs) in the greater Dublin area has been investigated and correlated with key physio-chemical operational and effluent quality parameters. The plants represented various designs, including conventional and biological nutrient removal (BNR) systems. The aim of the study was to identify differences in ciliate community due to key design parameters including anoxic/anaerobic stages and to identify suitable bioindicator species for performance evaluation. BNR systems supported significantly different protozoan communities compared to conventional systems. Total protozoan abundance was reduced in plants with incorporated anoxic and anaerobic stages, whereas species diversity was either unaffected or increased. Plagiocampa rouxi and Holophrya discolor were tolerant to anoxic/anaerobic conditions and associated with high denitrification. Apart from process design, influent wastewater characteristics affect protozoan community structure. Aspidisca cicada was associated with low dissolved oxygen and low nitrate concentrations, while Trochilia minuta was indicative of good nitrifying conditions and good sludge settleability. Trithigmostoma cucullulus was sensitive to ammonia and phosphate and could be useful as an indicator of high effluent quality. The association rating assessment procedure of Curds and Cockburn failed to predict final effluent biological oxygen demand (BOD5) indicating the method might not be applicable to treatment systems of different designs.

Modeling organic nitrogen conversions in activated sludge bioreactors

For biological nutrient removal (BNR) systems designed to maximize nitrogen removal, the effluent total nitrogen (TN) concentration may range from 2.0 to 4.0 g N/m(3) with about 25-50% in the form of organic nitrogen (ON). In this study, current approaches to modeling organic N conversions (separate processes vs. constant contents of organic fractions) were compared. A new conceptual model of ON conversions was developed and combined with Activated Sludge Model No. 2d (ASM2d). The model addresses a new insight into the processes of ammonification, biomass decay and hydrolysis of particulate and colloidal ON (PON and CON, respectively). Three major ON fractions incorporated are defined as dissolved (DON) (<0.1 µm), CON (0.1-1.2 µm) and PON (41.2 µm). Each major fraction was further divided into two sub-fractions - biodegradable and non-biodegradable. Experimental data were collected during field measurements and lab experiments conducted at the ''Wschod'' WWTP (570,000 PE) in Gdansk (Poland). The accurate steady-state predictions of DON and CON profiles were possible by varying ammonification and hydrolysis rates under different electron acceptor conditions. With the same model parameter set, the behaviors of both inorganic N forms (NH4-N, NOX-N) and ON forms (DON, CON) in the batch experiments were predicted. The challenges to accurately simulate and predict effluent ON levels from BNR systems are due to analytical methods of direct ON measurement (replacing TKN) and lack of large enough database (in-process measurements, dynamic variations of the ON concentrations) which can be used to determine parameter value ranges.