COD Consumption Research Articles

Combination of electrocoagulation with advanced oxidation processes for the treatment of distillery industrial effluent

The treatment of distillery industrial effluent by means various combinations of electrocoagulation with Advanced Oxidation Processes (AOPs) such as ozonation, electrocoagulation, peroxi–electrocoagulation, photo–electrocoagulation, ozone–electrocoagulation and peroxi–photo–electrocoagulation process on the removal of percentage color, COD and energy consumption. The effects of various operating parameters such as ozone flow rate (5 to 15 LPM), initial effluent pH (2 to 10), current density (0.10 to 0.50A/dm2) and H2O2 concentration (50 to 500mg/L) on the removal of pollutant were studied in this study. Moreover comparison of all the processes in terms of color removal, COD removal and energy consumption was also carried out. The experimental results showed that100% of color and COD removal could be achieved by ozone–electrocoagulation process with an energy consumption of 5.7kWh/m3 within four hours of reaction time. The extent of color and COD removal was analyzed using a UV/vis spectrophotometer and closed reflux method.

Treatment of multicomponent aqueous solution of purified terephthalic acid wastewater by electrocoagulation process: Optimization of process and analysis of sludge

The present research work is based on degradation of major pollutants of purified terephthalic acid (PTA) wastewater by electrocoagulation (EC) process. Terephthalic acid (TPA), benzoic acid (BA) and para-toluic acid (p-TA) are the major pollutants of PTA wastewater. A central composite design (CCD) has been developed for maximum removal of TPA, BA, p-TA, COD and minimum consumption of energy. Effects of various process parameters viz. pH: (5–13), current density: (49.5–255.5 A/m2), supporting electrolyte concentration, NaCl: (0.25–2.25 g/L) and electrolysis time: (15–95 min) are studied on removal efficiencies of responses. Aluminium (Al) and iron (Fe) were selected as electrode materials. Maximum percentage removal of TPA: 56.21, 54.10; BA: 59.52, 53.84; p-TA: 45.71, 39.91, and COD: 49.91, 42.95 are achieved at optimum operating conditions by Al and Fe electrodes respectively. Operating cost of the process was calculated based on energy consumption, electrode consumption, sludge disposable, and transportation costs and found $13.64 and $14.46 per kg of COD removed by Al and Fe electrodes respectively. Sludge residues obtained after EC treatment at optimum operating conditions are analyzed by settling, sludge volume index (SVI), XRD, SEM/EDX, point of zero charge (PZC), FTIR and DGA/TGA.

Studies on various operating parameters for the removal of COD from pulp and paper industry using electrocoagulation process

This study describes a batch electrocoagulation process for treating pulp and paper industry wastewater using iron plates. The effect of various operating parameters such current density, initial effluent pH, initial COD concentration, electrode combination and interelectrode distance on the removal of percentage COD and power consumption were investigated. The experimental results showed that 85% COD removal with 5.16 kWh/m3 of power consumption was observed for initial COD concentration of 2,500 ppm with current density of 0.40 A/dm2, initial effluent pH of 7.0 with interelectrode distance 1 cm at the end of the 120 min of operation. It was observed that, an increase in current density, decrease in the effluent COD concentration, Fe/Fe electrode combination, and decrease in interelectrode distance improved the COD removal efficiency. Optimum initial effluent pH for highest COD removal was 7.0. Furthermore in this investigation, extraction of lignin from the pulp and paper industrial effluent also carried out and analyzed by FT-IR system.

Grey seal predation impairs recovery of an over‐exploited fish stock

Summary Grey seal predation has been blamed by fishers for the decline of Atlantic cod stocks and has led to calls for seal culls. In the West of Scotland, estimates of cod consumption by seals have exceeded reported catches and spawning biomass, focussing attention on the interaction between fishers and seals. Bayesian models making different assumptions about seal predation were used to estimate the size of the West of Scotland cod stock between 1985 and 2005 and the mortalities due to fishing and seal foraging. A simple population model was used to identify the likely direction of cod population change at recent mortality rates. All model configurations suggest that the total mortality of cod has remained fairly stable and high for many years regardless of the assumptions on seal predation. The high mortality explains the long‐term decline of the stock. The best‐fitting model suggests that mortality due to fishing reduced substantially in the decade up to 2005, but has been replaced by increased seal predation mortality on a smaller cod stock. Given total mortality estimates, the stock is unlikely to recover even at present reduced levels of fishing. Synthesis and applications. Our model offers a method of estimating seal predation mortality as part of routine stock assessments that inform fishery management. The analysis shows that predation by seals can be an important component of the total stock mortality. It also shows that assuming invariant natural mortality, as adopted in many standard fish stock assessments, may lead to incorrect perceptions of fishing mortality, over‐estimating the benefits of reducing fishing mortality when there is density‐dependent predation. It is essential to consider predation by top predators when formulating appropriate advice for managing the fishery.

Modeling of Anaerobic Digestion of Food Industry Wastes in Different Bioreactor Types

In the present study, modeling of the anaerobic digestion of food industry waste is examined. A very simple model was developed, assuming that the organic matter (in terms of COD) is composed of a hardly and an easily biodegradable COD fraction, which are consumed through different Monod kinetics towards methane production. Biochemical methane potential tests and continuous stirred tank experiments were carried out and used to estimate the values of the main kinetic parameters. In the sequel, the kinetic model is used to predict the behavior of a periodic anaerobic baffled reactor (PABR), also fed with the same waste. Only a single new parameter, the biomass retention factor is added in order to model the behavior of the high-rate reactor. Despite the structural and operational differences of the two anaerobic digesters, the simple model was able to satisfactorily predict methane production and COD consumption of both bioreactors over a wide range of operating conditions. Thus, the proposed modeling approach can be valuable in describing the behavior of different anaerobic digesters, using a minimal number of kinetic variables and kinetic/stoichiometric parameters.

Evaluating the possibility of using acetone-butanol-ethanol (ABE) fermentation wastewater for bacterial cellulose production by Gluconacetobacter xylinus.

To reduce the cost of bacterial cellulose (BC) production, the possibility of using acetone-butanol-ethanol (ABE) fermentation wastewater with high COD value (18050mgl(-1) ) for BC production by Gluconacetobacter xylinus was evaluated. After 7days of fermentation, the highest BC yield (1·34gl(-1) ) was obtained. The carbon sources including sugars (glucose and xylose), organic acids (acetic acid and butyric acid) and alcohol compounds (ethanol and butanol) were utilized by G.xylinus simultaneously during fermentation. Although the COD decrease ratio (about 14·7%) was low, the highest BC yield on COD consumption (56·2%, gg(-1) ) was relatively high and the remaining wastewater could be used for further BC fermentation. Besides, the environment of ABE fermentation wastewater showed small influence on the BC structure by comparison with the BC products obtained in traditional HS medium using field emission scanning electron microscope (FE-SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Overall, ABE fermentation wastewater is one promising substrate for BC production. The possibility of using acetone-butanol-ethanol (ABE) fermentation wastewater for bacterial cellulose (BC) production by Gluconacetobacter xylinus was evaluated in this study. This is the first time that ABE fermentation wastewater was used as substrate for BC fermentation. The results provide detail information of metabolism of G.xylinus in ABE fermentation wastewater and the influence of wastewater environment on the structure of BC samples. Overall, this bioconversion could reduce the cost of BC production greatly.

Electrocoagulation of Landfill Leachate with Monopolar Aluminum Electrodes

In this paper, the removal of COD from landfill using aluminum electrode by the electrocoagulation method was investigated. The studies were run with the parallel plate monopolar aluminum electrodes and the effect of pH and current density on removal efficiency of COD and energy consumption were determined. The initial COD concentration of 4100 mg/L was reduced to 1763 mg/L with the removal efficiency of 57% at the current density of 75 mA/cm 2 and pH 5. Index Terms—Aluminium electrode, landfill leachate, treatment. I. I NTRODUCTION The most common and desirable integral indispensable solid waste management strategy is sanitary landfilling because it is simple and has low exploitation and capital costs. Up to 95% of the total municipal solid waste collected in the world is disposed of in landfills (1). Physico-chemical and biological conversions are occurred during the landfilling process and a result of conversions degregated organic compounds that soluble in rainwater are formed. Any liquid material that drains from land material is called leachate and it is highly toxic liquid with dissolving organic compounds, heavy metals and different soluble materials derived from the material that it has passed through. The composition of from a landfill depends on the age of the landfill and the type of waste that it contains. Leachate can potentially contaminate nearby surface and ground water if left untreated. Therefore landfills require close environmental monitoring during their design, operation, and long-term post-closure period. Leachate must be treated before discharging to environment. Many different physico-chemical techniques such as adsorption (2), chemical precipitation (3), coagulation/flocculation (4), chemical oxidation (5) and biological methods (6) have been being applied for the treatment of landfill leachate. Electrocoagulation, one of the most useful electrochemical methods, is a comparatively new technique for wastewater treatment. Also, electrocoagulation has some advantages such as, short retention time, easy operation, not needed the chemical addition, simple equipment, high sedimentation velocity and possibility of complete automation (7).

Low-temperature anaerobic treatment of low-strength pentachlorophenol-bearing wastewater

The anaerobic treatment of low-strength wastewater bearing pentachlorophenol (PCP) at psychro-mesophilic temperatures has been investigated in an expanded granular sludge bed reactor. Using an upward flow rate of 4 m h(-1), a complete removal of PCP, as well as COD removal and methanization efficiencies higher than 75% and 50%, respectively, were achieved. Methanogenesis and COD consumption were slightly affected by changes in loading rate, temperature (17-28°C) and inlet concentrations of urea and oils. Pentachlorophenol caused an irreversible inhibitory effect over both acetoclastic and hydrogenotrophic methanogens, being the later more resistant to the toxic effect of pentachlorophenol. An auto-inhibition phenomenon was observed at PCP concentrations higher than 10 mg L(-1), which was accurately predicted by a Haldane-like model. The inhibitory effect of PCP over the COD consumption and methane production was modelled by modified pseudo-Monod and Roediger models, respectively.

Regulation of an Activate Sludge Wastwater Plant VIA Robust Active Control Design

The main task of this work is related with the design of a class of SISO robust control law for theregulation of substrate concentration (CDO) of an Industrial Activated Sludge Wastewater Plant. The controldesign is related with an uncertainty estimator (reduced order observer) based Active Control. Departing from the tracking error between the desired and the current substrate concentrations trajectories a control law is designed and the plant is regulated to the corresponding set point of the COD concentration. To be realizable the controller needs model information related with the kinetic term of COD consumption which is provides with a reduced order observer, these coupled structure (observer based controller) is robust against model uncertainties. The performance of the proposed control law is illustrated with numerical simulations employing a mathematical model of an Industrial Activated Sludge Wastewater Plant tuned with industrial data.

Role of electrode materials for the anodic oxidation of a real landfill leachate – Comparison between Ti–Ru–Sn ternary oxide, PbO2 and boron-doped diamond anode

In this paper the electrocatalytic properties of Ti–Ru–Sn ternary oxide (TiRuSnO2), PbO2 and boron-doped diamond (BDD) anodes have been compared for the electrochemical oxidation of a real landfill leachate from an old municipal solid waste landfill (average values of COD 780mgdm−3 and NH4+-N266mgdm-3). The experiments have been performed using an undivided flow cell equipped with a stainless steel cathode, under constant current of 2A and flow-rate of 420dm3h−1. The performance of the electrodes has been compared measuring the time evolution of aromatic compounds, COD, ammonium, colour removal, current efficiency and energy consumption. The experimental results indicated that after 8h of electrolyses TiRuSnO2 anode yields only 35% COD, 52% colour and 65% ammonium removal. Using PbO2 ammonium and colour were completely removed but a residual COD (i.e. 115mgdm−3) was present.On the contrary BDD enables complete COD, colour and ammonium removal due to the electrogeneration of hydroxyl radicals from water discharge and active chlorine from chloride ions oxidation. BDD also exhibits greater current efficiency along with a significantly lower energy cost than other electrodes. These results indicated that the electrochemical oxidation with BDD anode is an effective process for the treatment of landfill leachate.

ORP slope and feast–famine strategy as the basis of the control of a granular sequencing batch reactor treating winery wastewater

Winery wastewater is characterized by a high variability of its organic content, and flexible systems such as granular sequencing batch reactors (GSBRs) are required for its treatment. Despite the high load capacity inherent to these systems, the operation with a predetermined cycle length is not suitable to withstand high COD fluctuations. In this study, a control system able to automatically control the HRT depending on the actual organic load has been designed. The relation between ORP slope and DO profiles with the COD consumption together with a proper periodic starvation time are the basis of the control strategy. GSBR operation using the designed system led to an organic matter removal up to 95% for a wide range of organic matter concentrations (1–8g/L), optimizing cycle duration and avoiding unnecessary aeration costs. The reactor showed a high stability and a rapid response to sudden changes in the COD influent concentration. Biomass settleability remained almost constant around 95m/h and aggregates showed a Feret diameter of 4–6mm and sphericity up to 0.8.

Foraging performance of juvenile Atlantic cod Gadus morhua and profitability of coastal habitats

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 456:245-253 (2012) - DOI: https://doi.org/10.3354/meps09705 Foraging performance of juvenile Atlantic cod Gadus morhua and profitability of coastal habitats Anders Persson*, Peter Ljungberg, Magnus Andersson, Elin Götzman, P. Anders Nilsson Department of Biology, Aquatic Ecology, Lund University, Ecology Building, 223 62 Lund, Sweden *Email: anders.persson@biol.lu.se ABSTRACT: Overfishing and eutrophication affects coastal communities worldwide, leading to dwindling fish stocks and deteriorated habitats. Hence, attempts to rebuild overfished stocks to past fish productivities need to account for functional relations between habitat types and fish performance. Here we quantified resource availability, foraging performance, and anti-predator behavior of juvenile Atlantic cod Gadus morhua (hereafter ‘cod’) to assess the costs and benefits associated with different coastal habitats. In the laboratory, cod foraged more efficiently in sand habitats compared to the structurally more complex habitats of eelgrass Zostera marina and the canopy forming bladderwrack Fucus vesiculosus. Presence of chemical cues from a cannibal reduced cod consumption rates in all habitats, but most strongly in the sand habitat. Field observations in the 3 habitats showed highest resource density in the bladderwrack habitat and lowest in the sand habitat, irrespective of season. Habitat profitability, calculated by combining data from field estimates of prey density and experimental quantifications of foraging performance, revealed the bladderwrack habitat to be the most profitable, independent of season. The difference in profitability between the complex habitats was relatively small, suggesting that cod in the field contributed to drive habitat profitability towards equalization. The results strengthen the view that the ongoing loss of seagrass and macroalgae habitats may have significant ramifications for juvenile cod performance, which ultimately may lower the productivity of entire stocks. Consequently, future and ongoing rebuilding of commercial fish stocks should revise the expectations of stock productivity (and hence harvesting intensity) accordingly. KEY WORDS: Cod · Habitat choice · Macroinvertebrates · Functional response · Seagrass · Bladderwrack · Fucus vesicolosus · Zostera marina Full text in pdf format PreviousNextCite this article as: Persson A, Ljungberg P, Andersson M, Götzman E, Nilsson PA (2012) Foraging performance of juvenile Atlantic cod Gadus morhua and profitability of coastal habitats. Mar Ecol Prog Ser 456:245-253. https://doi.org/10.3354/meps09705 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 456. Online publication date: June 07, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Evaluation of a novel oxidation ditch system with dual DO control technology for biological nutrient removal by mass balance analysis

A novel pilot-scale oxidation ditch (OD) system with an anaerobic tank and dual dissolved oxygen (DO) control technology was used to treat raw domestic wastewater during 310 days of operation. Three intensive sampling sessions indicated that the dual DO control technology could create stable aerobic and anoxic zones along the main ditch, even with large influent fluctuations. Dramatic total nitrogen (TN), total COD, and total phosphorus removal efficiencies were achieved within ranges of 78–90%, 83–91%, and 69–82%, respectively. June nitrogen balance results revealed that 60% of influent TN was denitrified and that 92% denitrification occurred in the main OD, demonstrating the advantage of the dual DO controls. In addition, COD balance values showed that 67% of the mineralized COD was due to denitrification, and aerobic oxidation was minimized. With lower influent BOD/N ratios of 4.0–4.7, significant TN removal performances were obtained in this OD system. Maximizing COD for denitrification and minimizing aerobic degradation suggest that this novel OD system shows promise for highly effective sewage treatment with effective COD consumption.

Stable Isotope Evidence for Late Medieval (14th–15th C) Origins of the Eastern Baltic Cod (Gadus morhua) Fishery

Although recent historical ecology studies have extended quantitative knowledge of eastern Baltic cod (Gadus morhua) exploitation back as far as the 16th century, the historical origin of the modern fishery remains obscure. Widespread archaeological evidence for cod consumption around the eastern Baltic littoral emerges around the 13th century, three centuries before systematic documentation, but it is not clear whether this represents (1) development of a substantial eastern Baltic cod fishery, or (2) large-scale importation of preserved cod from elsewhere. To distinguish between these hypotheses we use stable carbon and nitrogen isotope analysis to determine likely catch regions of 74 cod vertebrae and cleithra from 19 Baltic archaeological sites dated from the 8th to the 16th centuries. δ13C and δ15N signatures for six possible catch regions were established using a larger sample of archaeological cod cranial bones (n = 249). The data strongly support the second hypothesis, revealing widespread importation of cod during the 13th to 14th centuries, most of it probably from Arctic Norway. By the 15th century, however, eastern Baltic cod dominate within our sample, indicating the development of a substantial late medieval fishery. Potential human impact on cod stocks in the eastern Baltic must thus be taken into account for at least the last 600 years.

Scale-up of B-doped diamond anode system for electrochemical oxidation of phenol simulated wastewater in batch mode

Scale-up of boron-doped diamond (BDD) anode system is critical to the practical application of electrochemical oxidation in bio-refractory organic wastewater treatment. In this study, the scale-up of BDD anode system was investigated on batch-mode electrochemical oxidation of phenol simulated wastewater. It was demonstrated that BDD anode system was successfully scaled up by 121 times without performance deterioration based on the COD and specific energy consumption ( E sp) models in bath mode. The COD removal rate and E sp for the scaled-up BDD anode system through enlarging the total anode area while keeping similar configuration, remained at the similar level as those before being scaled up, under the same area/volume value, current density, retention time and wastewater characteristics. The COD and E sp models used to describe the smaller BDD anode system satisfactorily predicted the performance of the scaled-up BDD anode system. Under the suitable operating conditions, the COD of phenol simulated wastewater was reduced from 540 mg l −1 to 130 mg l −1 within 3 h with an E sp of only 34.76 kWh m −3 in the scaled-up BDD anode system. These results demonstrate that BDD anode system is very promising in practical bio-refractory organic wastewater treatment.

Fermentative production of hydrogen from cassava processing wastewater by Clostridium acetobutylicum

This work reports on the effect of initial substrate concentration on COD consumption, pH, and H 2 production during cassava processing wastewater fermentation by Clostridium acetobutylicum ATCC 824. Five initial COD wastewater concentrations, namely 5.0, 7.5, 10.7, 15.0, and 30.0 g/L, were used. The results showed that higher substrate concentrations (30.0 and 15.0 COD/L) led to lower H 2 yield as well as less efficient substrate conversion into H 2. On the other hand, initial COD concentrations of 10.7, 7.5 and 5 g/L furnished 1.34, 1.2 and 2.41 mol H 2/mol glucose, with efficiency of glucose conversion into H 2 of 34, 30, and 60% (mol/mol), respectively. These results demonstrate that cassava processing wastewater, a highly polluting effluent, can be successfully employed as substrate for H 2 production by C. acetobutylicum at lower COD concentrations.

Long-term changes in trophic patterns of Iceland cod and linkages to main prey stock sizes

Abstract Pálsson, Ó. K., and Björnsson, H. 2011. Long-term changes in trophic patterns of Iceland cod and linkages to main prey stock sizes. – ICES Journal of Marine Science, 68: 1488–1499. Data on the diet composition of Iceland cod (Gadus morhua) were collected in March of the years 1981–2010 and in autumn of the years 1988–2010. Capelin, northern shrimp, and euphausiids dominate the diet in all years and may be classified as the stable food of Iceland cod. Overall, total consumption by the smallest cod (20–29 cm) remained stable over the three decades, whereas that of larger fish has declined since the mid-1990s. This decline may explain the reduced growth rate of cod in recent years. Long-term, prey-specific patterns were identified in consumption, and significant trophic links were found between cod consumption and stock sizes of capelin and northern shrimp. In March, the correlation between cod consumption on capelin and capelin stock size was highly significant, a type I functional feeding response, but not significant in autumn. The correlation deteriorated in the early to mid-1990s and in the early 2000s. Increased inflow of Atlantic water into north Icelandic waters, and associated changes in capelin distribution, may have contributed to this trend. The interaction between cod consumption on northern shrimp and shrimp stock size showed a highly significant type I functional feeding response in both seasons.

Effects of weight loss and seafood consumption on inflammation parameters in young, overweight and obese European men and women during 8 weeks of energy restriction

In vitro studies have shown that long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFAs) can affect inflammation; however, results from intervention studies in overweight or obese individuals are contradicting. The aim of this study was to investigate the effects of weight loss and seafood consumption on inflammation parameters during energy restriction. In this 8-week intervention trial, 324 subjects (aged 20-40 years, body mass index 27.5-32.5 kg/m(2) from Iceland, Spain and Ireland) were randomized to one of four energy-restricted diets (-30% relative to estimated requirements): salmon (3 x 150 g/week, 2.1 g LC n-3 PUFA per day); cod (3 x 150 g/week, 0.3 g LC n-3 PUFA per day); fish oil capsules (1.3 g LC n-3 PUFA per day); and control (sunflower oil capsules, no seafood). Body weight, high-sensitivity C-reactive protein (CRP), interleukin-6 (IL-6), glutathione reductase and prostaglandin F2 alpha (PGEF2alpha) were measured at baseline and end point. Subjects experienced weight loss (-5.2+/-3.2 kg, P<0.001). Taken together for all subjects, there were significant decreases in all inflammation parameters. On a group level, salmon consumption was most effective, three of the four inflammation parameters decreased in the salmon group (high-sensitivity CRP=-32.0%; IL-6=-18.4%; PGEF2alpha=-18.5%; all P<0.05). Cod consumption decreased high-sensitivity CRP and IL-6 (-21.5 and -10.8%, respectively, both P<0.05). Changes in the other two groups were not significant, which can be partly explained by the large s.d. The mean concentrations of inflammation parameters decreased during a period of weight loss and dietary intervention. In our study, salmon consumption was most effective, three of the four measured inflammation parameters decreased significantly in the salmon group.

Increased Consumption of Fatty and Lean Fish Reduces Serum C-Reactive Protein Concentrations but Not Inflammation Markers in Feces and in Colonic Biopsies1–4

Fish consumption is associated with a reduced colorectal cancer risk. A possible mechanism by which fish consumption could decrease colorectal cancer risk is by reducing inflammation. However, thus far, intervention studies investigating both systemic and local gut inflammation markers are lacking. Our objective in this study was to investigate the effects of fatty and lean fish consumption on inflammation markers in serum, feces, and gut. In an intervention study, participants were randomly allocated to receive dietary advice (DA) plus either 300 g of fatty fish (salmon) or 300 g of lean fish (cod) per week for 6 mo, or only DA. Serum C-reactive protein (CRP) concentrations were measured pre- and postintervention (n = 161). In a subgroup (n = 52), we explored the effects of the fish intervention on fecal calprotectin and a wide range of cytokines and chemokines in fecal water and in colonic biopsies. Serum CRP concentrations were lower in the salmon (−0.5 mg/L; 95% CI −0.9, −0.2) and cod (−0.4 mg/L; 95% CI −0.7, 0.0) groups compared with the DA group. None of the inflammation markers in fecal water and colonic biopsies differed between the DA group and the groups that consumed extra fish. In conclusion, increasing salmon or cod consumption for 6 mo resulted in lower concentrations of the systemic inflammation marker CRP. However, exploratory analysis of local markers of inflammation in the colon or feces did not reveal an effect of fish consumption.

Nitrogen transformations and mass balances in anaerobic/anoxic/aerobic batch experiments with full-scale biomasses from BNR activated sludge systems

The aim of this study was to investigate nitrogen mass balances occurring inside full-scale BNR activated sludge systems, with special attention to colloidal and dissolved organic nitrogen (CON and DON) transformations. For this purpose, laboratory experiments were carried out using process biomass from two large BNR plants in northern Poland. Two parallel batch reactors were operated in a 3-phase (anaerobic/anoxic/aerobic) cycle. In one reactor, the settled wastewater without any pretreatment was used, whereas the settled wastewater after coagulation-flocculation (to remove colloidal and particulate fractions) was added to another reactor. The chemical pretreatment of settled wastewater with ZnSO(4) did not adversely affect the observed nitrification rates in the (last) aerobic phase. It caused, however, a reduction of denitrification rates in the anoxic phase. Moreover, the chemical pretreatment did not appear to generally decrease DON but decreased CON. DON was explicitly produced in the aerobic phase and organic nitrogen conversion also occurred at a significant rate in the anoxic phase with biodegradable COD consumption and solids hydrolysis. The inorganic N mass balances revealed N losses up to approximately 10% which could be attributed to a few novel pathways of nitrogen removal, most likely aerobic denitrification or simultaneous nitrification/denitrification.