Biological Nutrient Removal Wastewater Treatment Research Articles

Deactivation of internal recirculation in a full-scale Biological Nutrient Removal (BNR) Wastewater Treatment Plant (WWTP) reveals outstanding microeukaryotic bioindicators

The bioindicator potential of the microeukaryotic community in a full-scale A2O wastewater treatment process was assessed after deactivating the internal recirculation in one of the two parallel treatment lines of the plant. The deactivation of the internal recirculation in one of the lines (NIR-line), led to a strong decrease in nitrogen removal efficiency (53 % ammonia-uptake in the NIR-line versus 97 % in the unaltered line or IR-line), as well as to a lower organic matter removal (95 % BOD5 removal versus 97 % in the IR-line). The microeukaryote community structure changed greatly confirming trends observed in experimental studies and showed a decrease in abundance and richness in the NIR-line. However, this line showed a significant higher abundance of certain ciliate species, such as Epistylis camprubii and Vorticellides infusionum, which are common species in conventional activated sludge. Conversely, the IR-line showed useful indicators of internal recirculation, associated with much higher ammonium and BOD5 removal. These results show that identification to ciliate species level provides a more reliable bioindication in nutrient removal systems, supporting the importance of research on biological parameters, mainly protists, as simple and useful tools for plant operators to manage nutrient removal processes. These observations extend the current boundaries of bioindication.

Application of machine learning techniques to model a full-scale wastewater treatment plant with biological nutrient removal

A full-scale biological nutrient removal wastewater treatment process was simulated using artificial intelligence. In wastewater treatment plants, adaptive machine learning models can reduce process disruptions and generate savings through optimized operation. Machine learning is also useful when simulating processes that are particularly complex and where the physio-chemical interactions are not well understood, such as biological nutrients removal. Current models in literature only focus on the prediction of a small number of effluent parameters using a direct input-output approach. This paper presents a machine learning ensemble model that combines artificial neural networks, adaptive neuro-fuzzy inference systems, and support vector regression to predict 15 process parameters that include biomass properties, operation parameters, and effluent characteristics. A historical dataset between 2010 and 2020 was used to develop and validate the model. The model features a six-stage modular model structure where each parameter was predicted using a separate model and based on the preceding predicted parameters. The average correlation coefficient, normalized root mean square error, and symmetric mean absolute error of 69%, 0.06%, and 7.5%, respectively. The ensemble approach improved the average prediction accuracy over individual base models by 5%. The model developed in this study was more versatile than other machine learning models in the literature and relatively reduced the ambiguity of black-box data-driven models.

Incorporation of the complete ammonia oxidation (comammox) process for modeling nitrification in suspended growth wastewater treatment systems

The newly discovered process complete ammonia oxidation (comammox) has changed the traditional understanding of nitrification. In this study, three possible concepts of comammox were developed and incorporated as part of an extended two-step nitrification model. For model calibration and validation, two series of long-term biomass washout experiments were carried out at 12 °C and 20 °C in a laboratory sequencing batch reactor. The inoculum biomass was withdrawn from a large biological nutrient removal wastewater treatment plant. The efficiency of the examined models was compared based on the behaviors of ammonia, nitrite, and nitrate in the studied reactor. Predictions of the conventional approach to comammox, assuming the direct oxidation of ammonia to nitrate, were slightly better than the two other approaches. Simulation results revealed that comammox could be responsible for the conversion of >20% of the influent ammonia load. Therefore, the role of commamox in the nitrogen mass balance in activated sludge systems should not be neglected and requires further investigation. Furthermore, sensitivity and correlation analysis revealed that the maximum growth rates (μ), oxygen half-saturation (KO), and decay rates (b) of the canonical nitrifiers and comammox were the most sensitive factors, and the highest correlation was found between μ and b among all considered kinetic parameters. The estimated μ values by the best model were 0.57, 0.11, and 0.15 d−1 for AOB, NOB, and comammox bacteria, respectively.

Estimation of greenhouse gas and odour emissions from a cold region municipal biological nutrient removal wastewater treatment plant

Seasonal temperature variations in cold regions worldwide lead to variable gas emissions from municipal wastewater treatment plants (MWTPs) due to changing wastewater temperatures in open-to-air treatment processes. The objective of this study was to determine the greenhouse gas (including carbon dioxide, CO2; methane, CH4; and nitrous oxide, N2O) and odour (including ammonia, NH3; and hydrogen sulphide, H2S) emission rate estimates (EREs) from the open-to-air processes of a biological nutrient removal (BNR) type MWTP in Saskatoon, SK, Canada. This MWTP experiences seasonal temperatures from −40 °C to 30 °C with the resultant wastewater temperatures considered herein of 13 °C and 17 °C being chosen based on monitoring data for winter and summer, respectively. Laboratory-scale reactors simulating anaerobic, anoxic, aerobic, and settling treatment processes were used to monitor gas EREs using wastewater samples taken from the analogous MWTP processes during the winter and summer seasons. Results indicated that the overall winter EREs for CO2, CH4, and N2O were 45,129 kg CO2/d, 21.9 kg CH4/d, and 3.20 kg N2O/d, respectively, while the H2S EREs were insignificant. The higher temperature for the summer samples resulted in increased EREs for CH4, N2O, and H2S EREs of 33.0 kg CH4/d, 3.87 kg N2O/d, and 2.29 kg H2S/d, respectively. However, the CO2 EREs were reduced to 37,794 kg CO2/d. Overall, the aerobic reactor was the dominant source of the GHG emissions for both seasons. In addition, studied changes in the aerobic reactor aeration rates (in reactor) and BNR treatment configurations (from site) further impacted the EREs.

Identification of Transformation Products for Benzotriazole, Triclosan, and Trimethoprim by Aerobic and Anoxic-Activated Sludge

This study identified biotransformation products formed from three anthropogenic trace organic compounds (TOrCs) (benzotriazole, triclosan, and trimethoprim) in aerobic and anoxic sludge from a biological nutrient removal (BNR) wastewater treatment system. Liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (LC-QTOF) was used to identify intermediate transformation products. A user-defined compound library was used to target unknowns in samples with a mix of TOrCs without requiring chemical standards and developed using EAWAG-BDD predictive software, which included 37 potential transformation products. Biotransformation batch experiments were conducted using activated sludge from anoxic and aerobic redox regimes of a BNR treatment plant located in Southern Nevada, United States. Four intermediates were observed for benzotriazole in both aerobic and anoxic activated sludge, which consisted of two isomers of hydroxy benzotriazole and two isomers of methoxy benzotriazole. Four intermediates were observed for trimethoprim under aerobic conditions, which formed 2,4-diaminopyrimidin-5-yl)(3,4,5-trimethoxyphenyl)methanol (TMP 306) and 2,6-diamino-5-hydroxy-5-(3,4,5-trimethoxybenzyl)-5,6-dihydropyrimidin-4(1H)-one (TMP 324) and two demethylation isomers of desmethyl trimethoprim. Triclosan had one confirmed transformation product, triclosan-o-sulfate, formed in both conditions. The identification of these transformation products will allow for more thorough risk assessments to be performed for the target TOrCs.

The impact of the art-ICA control technology on the performance, energy consumption and greenhouse gas emissions of full-scale wastewater treatment plants

Advanced real time – Instrumentation, Control, and Automation (Art-ICA) controllers are an advanced control solution for biological nutrient removal wastewater treatment plants. Art-ICA has been previously shown to be capable of enhancing nutrient removal performance in BNR plants, at lower energy expenditures. However, the impact that this control solution has on the greenhouse gas emissions from full-scale wastewater treatment plants has not previously been addressed. This work addresses the effect of art-ICA on the performance, energy consumption and greenhouse gas emissions of two full-scale WWTPs, Chelas and Castelo Branco (Portugal). The raw wastewater, nitrous oxide emissions, energy consumption and water discharges were quantified in two independent trains operated under different operational modes, conventional operation and art-ICA control. The implementation of the art-ICA strategy improved the effluent quality and reduced the operational costs, resulting in a better performance of these WWTPs. The art-ICA controllers activation led to a reduction of 54% and 7–10% of the total nitrogen effluent and in the specific energy consumption, respectively. Moreover, process control with art-ICA did not have a negative impact on the N2O emissions of the plants, and contributed to lower global warming potential by the facilities. The lower indirect carbon dioxide production due to lower energy consumption contributes to the observation that art-ICA control is environmentally preferable to conventional control.

Modeling nitrous oxide production by a denitrifying-enhanced biologically phosphorus removing (EBPR) activated sludge in the presence of different carbon sources and electron acceptors

In this study, the IWA Activated Sludge Model No. 2d (ASM2d) was expanded to identify the most important mechanisms leading to the anoxic nitrous oxide (N2O) production in the combined nitrogen (N) and phosphorus (P) removal activated sludge systems. The new model adopted a three-stage denitrification concept and was evaluated against the measured data from one/two-phase batch experiments carried out with activated sludge withdrawn from a local, large-scale biological nutrient removal wastewater treatment plant. The experiments were focused on investigating the effects of different external carbon sources (acetate, ethanol) and electron acceptors (nitrite, nitrate) on the mechanisms of N2O production in enhanced biological P removal by polyphosphate accumulating organisms (PAOs) and external carbon-based denitrification by ordinary heterotrophic organisms (OHOs). The experimental results explicitly showed that N2O production was predominantly governed by the presence of nitrite in the reactor regardless of the examined carbon source and the ratio COD/N in the reactor. The model was capable of accurately predicting (with R2 > 0.9) the behavior of not only N2O-N, but also NO3-N, NO2-N, soluble COD, and PO4-P. The simulation results revealed that only OHOs were responsible for N2O production, whereas the present denitrifying PAOs reduced only nitrate to nitrite.

Comparison of nutrient solubilisation and dewatering by freeze/thaw processing of sludge from Biological Nutrient Removal (BNR) and Non-BNR wastewater treatment plants.

Natural freeze/thaw processing is a simple, practical and low-cost solid-liquid separation method, which can effectively dewater wastewater sludge in Northern Canadian communities located in cold climate conditions. This method is especially effective when used in small treatment plants in remote and cold regions as typical dewatering methods require complex and expensive equipment, skilled operators and special maintenance. The objective of this research was to evaluate freeze/thaw processing as a method for dewatering, nutrient solubilisation and organics separation of wastewater sludge originating from two different wastewater treatment facilities: a Biological Nutrient Removal (BNR) plant and non-BNR plant. The results of experiments showed the effectiveness of this method for sludge dewatering and solubilisation of organics and nutrients. The sludge solid content increased approximately 10-fold after freeze/thaw processing. The treatment solubilised 15.2%, 33.5% and 21.5% of the initial total nitrogen, total phosphorus and total chemical oxygen demand, respectively for the non-BNR sludge. These values were 6.3%, 80.0% and 16.5%, respectively for the BNR sludge. The released phosphorus and nitrogen in the water can be recovered and used as fertilizer for agricultural purposes, supporting northern food production.

Nitrite oxidizing bacteria (NOB) dominating in nitrifying community in full-scale biological nutrient removal wastewater treatment plants

Nitrification activities and microbial populations of ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were investigated in 10 full-scale biological nutrient removal wastewater treatment plants in Xi’an, China. Aerobic batch tests were used to determine the nitrifying activities while fluorescence in situ hybridization was used to quantify the fractions of AOB and NOB in the activated sludge. The results showed that nitrifying bacteria accounted for 1–10% of the total population. Nitrosomonas and Nitrospira were the dominant bacteria for AOB and NOB respectively. Moreover, the average percentage of AOB was 1.27% and that of NOB was 4.02%. The numerical ratios of NOB/AOB varied between 1.72 and 5.87. The average ammonium uptake rate and nitrite uptake rate were 3.25 ± 0.52 mg (NH4+–N)/g(VSS) h and 4.49 ± 0.49 mg (NO2−–N)/g(VSS) h, respectively. Correspondingly, the activity of NOB was 1.08–2.00 times higher than that of AOB. Thus, NOB was the dominating bacteria in nitrifying communities. The year-round data of Dianzicun (W6) also expressed a similar trend. Since NOB had higher activities than that of AOB, a large nitrite oxidation pool could be formed, which guaranteed that no nitrite would be accumulated. Therefore, stable nitrification could be achieved. A conceptual model was proposed to describe the population variation of AOB and NOB in a nitrifying community.

Dewatering Biosolids with a Volute Press at two Biological Nutrient Removal Wastewater Treatment Plants in Montana

Dewatering Biosolids with a Volute Press at two Biological Nutrient Removal Wastewater Treatment Plants in Montana

Fate and Forms of Selenium in a Biological Nutrient Removal Wastewater Treatment Plant

Fate and Forms of Selenium in a Biological Nutrient Removal Wastewater Treatment Plant

Strategies for achieving energy neutrality in biological nutrient removal systems - a case study of the Slupsk WWTP (northern Poland).

The paper presents a model-based evaluation of technological upgrades on the energy and cost balance in a large biological nutrient removal (BNR) wastewater treatment plant (WWTP) in the city of Slupsk (northern Poland). The proposed upgrades include chemically enhanced primary sludge removal and reduction of the nitrogen load in the deammonification process employed for reject water treatment. Simulations enabled to estimate the increased biogas generation and decreased energy consumption for aeration. The proposed upgrades may lead the studied WWTP from the energy deficit to energy neutrality and positive cost balance, while still maintaining the required effluent standards for nitrogen. The operating cost balance depends on the type of applied coagulants/flocculants and specific costs of electric energy. The choice of the coagulant/flocculent was found as the main factor determining a positive cost balance.

Determination of the Fate of Dissolved Organic Nitrogen in the Three Wastewater Treatment Plants, Jordan

This research aimed to assess the composition of total dissolved nitrogen (TDN) species, particularly dissolved organic nitrogen (DON), over the traditional wastewater treatment operations in three biological nutrient removal (BNR) wastewater treatment plants (WWTPs) in Jordan. It had been found that the DON percentage was up to 30% of TDN within the effluent plant;which restricted the plant’s ability to eliminate nitrogen to minimal amounts. Effluent DON levels from the three plants varied from 11.7 to 34.8 mg N/L and would not fluctuate substantially, even if there seemed to be a substantial difference inside influent organic nitrogen levels. The main transforming of DON and biodegradable dissolved organic nitrogen (BDON( along the treatment train had been noticed in the aerobic method. More than 70% of effluent DON was consisting of hydrophilic materials, which promote algal growth. The research presented significant information for foreseeable future improving of WWTPs or the choice of DON elimination techniques to satisfy additional challenging nitrogen release limits.

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.

Assessment of the removal of estrogenicity in biological nutrient removal wastewater treatment processes

The removal of estrogenicity in a University of Cape Town-biological nutrient removal (UCT-BNR) wastewater treatment process was investigated using pilot and bench scale systems, batch experiments and mathematical modeling. In the pilot BNR process, 96±5% of the estrogenicity exerted by the influent wastewater was removed by the treatment process. The degradation efficiencies in the anaerobic, anoxic and aerobic zones of the pilot BNR bioreactor were 11±9%, 18±2% and 93±10%, respectively. In order to further understand the performance of the BNR process in the removal of estrogenicity from wastewater, a bench scale BNR process was operated with synthetic wastewater dosed with E1 and E2. The removal of estrogenicity in the bench scale system (95±5%) was comparable to the pilot BNR process and the degradation efficiencies were estimated to be 8±0.8%, 38±4% and 85±22% in the anaerobic, anoxic and aerobic zones, respectively. A biotransformation model developed to predict the fate of E1 and E2 in batch tests using the sludge from the BNR process was calibrated using the data from the experiments. The biotransformation rate constants for the transformation of E2 to E1 were estimated as 71±1.5, 31±3.3 and 1±0.9LgCOD−1d−1 for the aerobic, anoxic and anaerobic batch tests, respectively, while the corresponding biotransformation rate constants for the transformation of E1 were estimated to be 7.3±1.0, 3±2.0, and 0.85±0.6L·gCOD−1d−1. A steady state mass balance model formulated to describe the interactions between E2 and E1 in BNR activated sludge reasonably described the fate of E1 and E2 in the BNR process.

Quantification method of N2O emission from full-scale biological nutrient removal wastewater treatment plant by laboratory batch reactor analysis

This study proposes a simplified method for the quantification of N2O emission from a biological nutrient removal wastewater treatment plant (WWTP). The method incorporates a laboratory-scale batch reactor which had almost the same operational (wastewater and sludge flow rates) condition of a unit operation/process of the WWTP. Cumulative N2O emissions from the batch reactor at the corresponding hydraulic retention times of the full-scale units (primary and secondary clarifiers, pre-anoxic, anaerobic, anoxic and aerobic basins) were used for the quantification of N2O emission. The analysis showed that the aerobic basin emitted 95% of the total emission and the emission factor (yield) reached 0.8% based on the influent nitrogen load. The method successfully estimated N2O emission from the WWTP and it has shown advantages in measurement time and cost over the direct field measurement (floating chamber) method.

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

Removal 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.

Characteristics and fate of organic nitrogen in municipal biological nutrient removal wastewater treatment plants

The aim of this study was to investigate the occurrence and fate of colloidal and dissolved organic nitrogen (CON and DON) across biological nutrient removal (BNR) activated sludge bioreactors. Primary and secondary effluent total nitrogen (TN) measurements and component fractionation, CON and DON concentration profiles across BNR bioreactors, and laboratory batch experiments with the process mixed liquor were carried out at several full-scale BNR plants in northern Poland. The organic nitrogen (ON) components were divided into high CON, low CON, and DON based on sequential filtration through 1.2, 0.45 and 0.1 μm pore-size filters. The average influent DON0.1μm (<0.1 μm) concentrations ranged from 1.1 g N/m3 to 3.9 g N/m3 and accounted for only 4–13% of total organic nitrogen. In the effluents, however, this contribution increased to 12–45% (the DON0.1μm concentrations varied in a narrow range of 0.5–1.3 g N/m3). Conversions of ON inside the bioreactors were investigated in more detail in two largest plants, i.e. Gdansk (565,000 PE) and Gdynia (516,000 PE). Inside the two studied bioreactors, the largest reductions of the colloidal fraction were found to occur in the anaerobic and anoxic compartments, whereas an increase of DON0.1μm concentrations was observed under aerobic conditions in the last compartment. Batch experiments with the process mixed liquor confirmed that DON0.1μm was explicitly produced in the aerobic phase and significant amounts of ON were converted in the anoxic phase of the experiments.

Fate of Organic Nitrogen in Four Biological Nutrient Removal Wastewater Treatment Plants

This study investigated the fate of nitrogen species, especially organic nitrogen, along the mainstream wastewater treatment processes in four biological nutrient removal (BNR) wastewater treatment plants (WWTPs). It was found that the dissolved organic nitrogen (DON) fraction was as high as 47% of soluble nitrogen (SN) in the low-SN effluent plant, which limited the plant's capability to remove nitrogen to very low levels. A lower DON fraction was observed in high-SN effluent plants. Effluent DON concentrations from the four plants ranged from 0.5 to 2 mg N/L and did not vary significantly, even though there was a large variation in the influent organic nitrogen concentrations. Size fractionation of organic nitrogen by serial filtration through 1.2-, 0.45-, and 0.22-microm pore-sized membrane filters and the flocculation-and-filtration with zinc sulfate (ZnSO4) method was investigated. The maximum colloidal organic nitrogen (CON) fractions found were 68 and 45% in the primary effluent and final effluent, respectively. The experimental results showed that effluents after filtration through the 0.45-microm pore-sized filter contain significant colloidal fractions; hence, the constituents, including organic nitrogen, are not truly dissolved. A high CON fraction was observed in wastewater influents and was less significant in effluents. The flocculation and filtration method removed the colloidal fraction; therefore, the true DON fraction can be determined.

Nitrous oxide generation in full-scale biological nutrient removal wastewater treatment plants

International guidance for estimating emissions of the greenhouse gas, nitrous oxide (N 2O), from biological nutrient removal (BNR) wastewater systems is presently inadequate. This study has adopted a rigorous mass balance approach to provide comprehensive N 2O emission and formation results from seven full-scale BNR wastewater treatment plants (WWTP). N 2O formation was shown to be always positive, yet highly variable across the seven plants. The calculated range of N 2O generation was 0.006–0.253 kgN 2O–N per kgN denitrified (average: 0.035 ± 0.027). This paper investigated the possible mechanisms of N 2O formation, rather than the locality of emissions. Higher N 2O generation was shown to generally correspond with higher nitrite concentrations, but with many competing and parallel nitrogen transformation reactions occurring, it was very difficult to clearly identify the predominant mechanism of N 2O production. The WWTPs designed and operated for low effluent TN (i.e. <10 mgN L −1) had lower and less variable N 2O generation factors than plants that only achieved partial denitrification.