Nutrient Removal Activated Sludge Systems Research Articles

Modeling nutrient removal and energy consumption in an advanced activated sludge system under uncertainty

Activated sludge models are widely used to simulate, optimize and control performance of wastewater treatment plants (WWTP). For simulation of nutrient removal and energy consumption, kinetic parameters would need to be estimated, which requires an extensive measurement campaign. In this study, a novel methodology is proposed for modeling the performance and energy consumption of a biological nutrient removal activated sludge system under sensitivity and uncertainty. The actual data from the wastewater treatment plant in Slupsk (northern Poland) were used for the analysis. Global sensitivity analysis methods accounting for interactions between kinetic parameters were compared with the local sensitivity approach. An extensive procedure for estimation of kinetic parameters allowed to reduce the computational effort in the uncertainty analysis and improve the reliability of the computational results. Due to high costs of measurement campaigns for model calibration, a modification of the Generalized Likelihood Uncertainty method was applied considering the location of measurement points. The inclusion of nutrient measurements in the aerobic compartment in the uncertainty analysis resulted in percentages of ammonium, nitrate, ortho-phosphate measurements of 81%, 90%, 78%, respectively, in the 95% confidence interval. The additional inclusion of measurements in the anaerobic compartment resulted in an increase in the percentage of ortho-phosphate measurements in the aerobic compartment by 5% in the confidence interval.The developed procedure reduces computational and measurement efforts, while maintaining a high compatibility of the observed data and model predictions. This enables to implement activated sludge models also for the facilities with a limited availability of data.

Full Scale SBR Municipal Wastewater Treatment Facility Utilization of Simultaneous Nitrification/Denitrification Coupled with Traditional Nitrogen Removal to Meet Water Criterion

Simultaneous nitrification denitrification (SND) is a well-established phenomenon in biological nutrient removal activated sludge systems. Study at a municipal wastewater treatment facility sought to determine nitrogen removal effectiveness within a full-scale sequential batch reactor (SBR) system utilizing SND in conjunction with traditional nitrogen removal. In addition to characterizing extent of SND, the research examined the ability of SND to meet state-based effluent water quality standards. At the selected facility, the average SND efficiency during a two-month sampling period was 52.8%, paralleling results from similar SBR municipal wastewater systems. The observed SBR system had removal efficiencies > 99% for the influent to effluent -N concentrations. The SND process also resulted in average NO3-NO2-N concentration that was 82% lower than the theoretical concentration under comparable circumstances. Overall, nitrogen removal for this SBR system was >99% which typified results in other SND systems, but at a higher Total Nitrogen removal rate.

Strategies for mitigating nitrous oxide production and decreasing the carbon footprint of a full-scale combined nitrogen and phosphorus removal activated sludge system

Nitrous oxide (N2O) emitted from biological nutrient removal activated sludge systems contributes significantly to the total carbon footprint of modern wastewater treatment plants. In the present study, N2O production and emissions were experimentally determined in a large-scale plant (220,000 PE) employing combined nitrogen (N) and phosphorus (P) removal. As a modelling tool, the Activated Sludge Model 2d (ASM2d) was extended with modules describing multiple N2O production pathways and N2O liquid-gas transfers. The new model was calibrated and validated using the results of laboratory experiments and full-scale measurements. Different operational strategies were evaluated following the proposed model-based procedure. Heterotrophic denitrification was found to be the predominant pathway of N2O production under both anoxic and aerobic conditions. This behaviour could primarily be attributed to the predominant abundance of heterotrophic denitrifiers over nitrifiers. Simulations revealed that the optimal solution for minimizing liquid N2O production is to set the dissolved oxygen concentration in the aerobic zone from 1 to 2 mg O2/L and to enhance the mixed liquor recirculation rate (MLR) (>500% of the influent flowrate) while not compromising effluent standards. Regarding the actual conditions, the potential reduction in the carbon footprint was estimated to be 10% by applying the proposed operational strategy. The results suggest that considerable improvements can be achieved without substantial upgrades and increased costs.

Data scarcity in modelling and simulation of a large-scale WWTP: Stop sign or a challenge

Data scarcity can be considered as the main limitation for a more widespread utilization of mathematical models in the design, optimization and control of biological nutrient removal activated sludge systems (BNRAS). High cost and demanding workload related to experimental data and sufficient sampling campaigns make the data collection process an unpleasant necessity for managing stakeholders in modelling projects. Complicated use of online-sensors leading to frequent erroneous readings and dynamic nature of wastewater treatment processes can intensify the data scarcity problems. This paper investigates the influence of data scarcity on the development and calibration of wastewater treatment plant (WWTP) models. A straightforward methodology is proposed to address the challenges associated with data quality and quantity problems in modelling of a BNRAS in the largest Italian WWTP located in Castiglione, Italy. The plant operational modes, weather condition and sensor performance during the sampling campaigns were the main sources of the data scarcity. Influent, biokinetic, aeration, hydraulic and transport, clarifier, energy consumption and effluent sub-models were calibrated by use of the proposed extensive step-wise calibration process. The Monte Carlo analysis was performed to quantify the uncertainty of the modelling results. The proposed methodology could be implemented in engineering practice to develop and calibrate the WWTP models while it increases the awareness about modelling robustness and its characterized uncertainty to avoid bad modelling practice.

Sludge disintegration model with finite disintegration rate

The activated sludge process is the most widely used biological wastewater treatment method for domestic and industrial wastewaters. One drawback of this process is the production of `sludge'. The expense for treating excess sludge accounts for 50-60% of the operating costs in a wastewater treatment plant. Traditional methods for disposing of excess sludge are increasingly regulated due to environmental concerns about the presence of potentially toxic elements in the sewage sludge. A promising method to reduce excess sludge production is to increase its biodegradability by disintegrating it within the bioreactor. We extend an earlier model by allowing the sludge disintegration reactions to occur at a finite rate. Furthermore, we include a more realistic model for the hydrolysis of particulate matter by allowing the rate of hydrolysis to saturate at high particulate concentrations. We analyze the steady-state operation of an activated sludge system incorporating a sludge disintegration unit to prevent excess sludge production. References A. Alharbi, M. I. Nelson, A. L. Worthy and H. Sidhu. Sludge formation in the activated sludge process with a sludge disintegration unit. In M. Nelson, T. Hamilton, M. Jennings and J. Bunder, Eds, Proceedings of the 11th Biennial Engineering Mathematics and Applications Conference, EMAC-2013, ANZIAM J. , 55:C348–C367, 2013. doi:10.21914/anziamj.v55i0.7803 P. S. Barker and P. L. Dold. Sludge production and oxygen demand in nutrient removal activated sludge systems. Water Sci. Technol. , 34(5–6):43–50, 1996. doi:10.1016/0273-1223(96)00627-0 A. Canales, A. Pareilleux, J. L. Rols, G. Goma and A. Huyard. Decreased sludge production strategy for domestic wastewater treatment. Water Sci. Technol. , 30(8):97–106, 1994. doi:10.1016/S0043-1354(03)00441-X C. P. Chu, W. C. Feng, B.-V. Chang, C. H. Chou, and D. J. Lee. Reduction of microbial density level in wastewater activated sludge via freezing and thawing. Water Res. , 33:3532–3535, 1999. doi:10.1645/0022-3395(2002)088[0718:EOFTEO]2.0.CO;2 E. Egemen, J. Corpening, and N. Nirmalakhandan. Evaluation of an ozonation system for reduced waste sludge generation. Water Sci. Technol. , 44(2–3):445–452, 2001. http://wst.iwaponline.com/content/44/2-3/445 M. Henze, C. P. L. Grady Jr, W. Gujer, G. V. R. Marais, and T. Matsuo. A general model for single-sludge wastewater treatment systems. Water Res. , 21(5):505–515, 1987. doi:10.1016/0043-1354(87)90058-3 M. I. Nelson and E. Balakrishnan. An analysis of an activated sludge process containing a sludge disintegration system. In F. Chan, D. Marinova, and R. S. Anderssen, Eds, 19th International Congress on Modelling and Simulation, MODSIM 2011, 331–337, 2011. http://www.mssanz.org.au/modsim2011/A3/nelson.pdf M. I. Nelson and T. C. L. Yue. A Mathematical Analysis of a Membrane Bioreactor Containing a Sludge Disintegration System . Chem. Eng. Commun. , 201(10):1384–1403, 2014. doi:10.1080/00986445.2013.809001 Y.-K. Oh, K.-R. Lee, K.-B. Ko, and I.-T. Yeom. Effects of chemical sludge disintegration on the performance of wastewater treatment by membrane bioreactor. Water Res. , 41:2665–2671, 2007. doi:10.1016/j.watres.2007.02.028 Z. Wang, L. Wang, B. Z. Wang, Y. F. Jiang, and S. Liu. Bench-scale study on zero excess activated sludge production process coupled with ozonation unit in membrane bioreactor. J. Environ. Sci. Heal. A , 43(11):1325–1332, 2008. doi:10.1080/10934520802177987 Y. Wei, R. T. Van Houten, A. R. Borger, D. H. Eikelboom, and Y. Fan. Minimization of excess sludge production for biological wastewater treatment. Water Res. , 37:4553–4467, 2003. doi:10.1016/S0043-1354(03)00441-X H. Yasui, K. Nakamura, S. Sakuma, M. Iwasaki, and Y. Sakai. A full-scale operation of a novel activated sludge process without excess sludge production. Water Sci. Technol. , 34(3–4):395–404, 1996. doi:10.1016/0273-1223(96)00604-X S.-H. Yoon. Important operational parameters of membrane bioreactor-sludge disintegration (MBR-SD) system for zero excess sludge production. Water Res. , 37:1921–1931, 2003. doi:10.1016/S0043-1354(02)00578-X S.-H. Yoon, H.-S. Kim, and S. Lee. Incorporation of ultrasonic cell disintegration into a membrane bioreactor for zero sludge production. Process Biochem. , 39(12):1923–1929, 2004. doi:10.1016/j.procbio.2003.09.023

Shift in microbial community structure of anaerobic side-stream reactor in response to changes to anaerobic solid retention time and sludge interchange ratio

A laboratory scale nutrient removal activated sludge system coupled with an anaerobic side-stream reactor was operated for 300 days treating real urban wastewater. A significant decrease in sludge production was obtained increasing the anaerobic solid retention time (SRTASSR) and decreasing the sludge interchange ratio (IR). In this study, the microbial community structure was analyzed and compared with the sludge reduction performance. Quantitative polymerase chain reaction analyses encoding 16 ribosomal RNA and functional genes revealed a wide diversity of phylogenetic groups in each experimental period, resulting from long solids retention time and recirculation of sludge under aerobic, anoxic and anaerobic conditions. However, decreasing SRTASSR from 10 to 2.5d and increasing IR from 27 to 100%, an increasing selection of both fermenting bacteria able to release extracellular polymeric substances and hydrolyze organic matter and slow growing bacteria involved in nutrient removal were detected and linked to the sludge reduction mechanisms.

Modeling the Effect of External Carbon Source Addition under Different Electron Acceptor Conditions in Biological Nutrient Removal Activated Sludge Systems.

The aim of this study was to expand the International Water Association Activated Sludge Model No. 2d (ASM2d) to predict the aerobic/anoxic behavior of polyphosphate accumulating organisms (PAOs) and "ordinary" heterotrophs in the presence of different external carbon sources and electron acceptors. The following new aspects were considered: (1) a new type of the readily biodegradable substrate, not available for the anaerobic activity of PAOs, (2) nitrite as an electron acceptor, and (3) acclimation of "ordinary" heterotrophs to the new external substrate via enzyme synthesis. The expanded model incorporated 30 new or modified process rate equations. The model was evaluated against data from several, especially designed laboratory experiments which focused on the combined effects of different types of external carbon sources (acetate, ethanol and fusel oil) and electron acceptors (dissolved oxygen, nitrate and nitrite) on the behavior of PAOs and "ordinary" heterotrophs. With the proposed expansions, it was possible to improve some deficiencies of the ASM2d in predicting the behavior of biological nutrient removal (BNR) systems with the addition of external carbon sources, including the effect of acclimation to the new carbon source.

Dissolved and colloidal organic nitrogen removal from wastewater treatment plants effluents and reject waters using physical-chemical processes.

Four physical-chemical processes were compared in terms of the efficiencies of dissolved and colloidal organic nitrogen (DON and CON) removal from the secondary effluents (SE) and reject water from full-scale biological nutrient removal activated sludge systems. Adsorption on activated carbon was most efficient and allowed removal from the SE of up to 80% and 100% of DON and CON, respectively. High efficiencies of DON removal from SE (up to 55%) were also obtained when using coagulation with iron(III) chloride and calcium hydroxide at final pH = 11.0-11.5. The efficiency of DON removal from thickening waste activated sludge (TWAS) reject water, obtained using coagulation with iron(III) chloride, was comparable with the efficiency for the SE. The efficiency of this process with regard to the sludge digester liquors (SDL) was significantly higher, i.e., 65-70% for both DON and CON. The ion exchange process with strongly acidic cation exchange resin (without pH correction) resulted in a relatively small efficiency of DON removal (<15%), and negligible efficiency of CON removal (<10%). Furthermore, ultrafiltration (0.015 μm) of SE and TWAS reject water resulted in a relatively low efficiency of DON removal (10-13% and 10-20% respectively). Ultrafiltration was found to be more effective for DON removal from SDL (41-68%).

The role of biodegradable particulate and colloidal organic compounds in biological nutrient removal activated sludge systems

The efficiency of denitrification and enhanced biological phosphorus removal in biological nutrient removal activated sludge systems is strongly dependent on the availability of appropriate carbon sources. Due to high costs of commercial compounds (such as methanol, ethanol, acetic acid, etc.) and acclimation periods (usually) required, the effective use of internal substrates is preferred. The aim of this study was to determine the effects of slowly biodegradable compounds (particulate and colloidal), as internal carbon sources, on denitrification, phosphate release/uptake and oxygen utilization for a full-scale process mixed liquor from two large wastewater treatment plants located in northern Poland. Since it is difficult to distinguish the effect of slowly biodegradable substrate in a direct way, a novel procedure was developed and implemented. Four types of one- and two-phase laboratory batch experiments were carried out in two parallel reactors with the settled wastewater without pre-treatment (reactor 1) and pre-treated with coagulation–flocculation (reactor 2). The removal of colloidal and particulate fractions resulted in the reduced process rates (except for phosphate release). The average reductions ranged from 13 % for the oxygen utilization rate during the second phase of a two-phase experiment (anaerobic/aerobic), up to 35 % for the nitrate utilization rate (NUR) during the second phase of a conventional NUR measurement.

Modeling hydrolysis of slowly biodegradable organic compounds in biological nutrient removal activated sludge systems

Hydrolysis is an important process in biological wastewater treatment and is known to be the rate-limiting step in organic carbon removal from municipal or industrial wastewater. The influence of the readily biodegradable chemical oxygen demand fraction in biological wastewater treatment systems has been extensively investigated, but little is known about the effects of slowly biodegradable substrate (XS) on denitrification and enhanced biological phosphorus removal. The biodegradation of XS is initiated by hydrolysis, which is an integral part of activated sludge models, such as the Activated Sludge Model no. 2d (ASM2d). This process is slower than heterotrophic growth and thus becomes the rate-limiting step for the biodegradation of organic compounds. The aim of this study was to evaluate different concepts of modeling the hydrolysis process using the original and modified version of ASM2d. Batch test results obtained at a large biological nutrient removal (BNR) plant in Gdansk (Poland) provided an experimental database for comparison of the two model predictions. Both models were compared in terms of their predictions for the most important process rates in BNR activated sludge systems. In comparison with the orginal ASM2d, the modified model had no or only minor effect on the predicted nitrate utilization rate, phosphate release rate and anoxic/aerobic phosphate uptake rate, but better predicted the oxygen uptake rate. The average ARDs (average relative deviations) were 19.0 and 29.3% (original ASM2d) vs. 13.4 and 20.4% (modified ASM2d), respectively, for the settled wastewater without pretreatment and after coagulation-flocculation.

A mechanistic model for fate and removal of estrogens in biological nutrient removal activated sludge systems

Two estrogen fate and transformation models were integrated with a comprehensive activated sludge model (ASM) to predict estrogen removal based on biomass and solids production. Model predictions were evaluated against published full-scale plant data as well as results from a laboratory-scale sequencing batch reactor (SBR) fed synthetic wastewater. The estrogen fate model relating the rate of total estrogen degradation to soluble estrogen concentrations successfully predicted estrogen removals when compared with measured concentrations. Model fit 17α-ethinylestradiol (EE2) biodegradation rate constant was 19 to 43% of the estrone (E1) value and 31 to 72% of the 17β-estradiol (E2) value.

A hypothesis on Microthrix parvicella proliferation in biological nutrient removal activated sludge systems with selector tanks

The objective of this study was to evaluate the ability of Microthrix parvicella for long-chain fatty acids uptake under anaerobic, anoxic, and aerobic conditions as well as its ability to utilize volatile fatty acids and long-chain fatty acids under anoxic and aerobic conditions. According to the results, a hypothesis on the competition between floc-forming microorganisms and M.parvicella for long-chain fatty acids uptake under aerobic, anoxic, and anaerobic conditions was formulated. According to this hypothesis, M.parvicella exhibits similar long-chain fatty acids uptake capacity with floc-forming microorganisms even at relatively high floc loading values that are very often imposed at selector tanks. Following this hypothesis, the failure of selector tanks to provide for an effective M.parvicella control is evidenced. Based on the experimental results, the ability of M.parvicella to utilize long-chain fatty acids with rates comparable to those of floc formers, even in anoxic conditions, in conjunction with its lower acetate utilization rates, provides a good explanation regarding its preference to slowly biodegradable organic carbon compounds.

Experimental and Model-Based Evaluation of the DON and CON Fate in Biological Nutrient Removal Activated Sludge Systems

Experimental and Model-Based Evaluation of the DON and CON Fate in Biological Nutrient Removal Activated Sludge Systems

The role and control of sludge age in biological nutrient removal activated sludge systems

The sludge age is the most fundamental and important parameter in the design, operation and control of biological nutrient removal (BNR) activated sludge (AS) systems. Generally, the better the effluent and waste sludge quality required from the system, the longer the sludge age, the larger the biological reactor and the more wastewater characteristics need to be known. Controlling the reactor concentration does not control sludge age, only the mass of sludge in the system. When nitrification is a requirement, sludge age control becomes a requirement and the secondary settling tanks can no longer serve the dual purpose of clarifier and waste activated sludge thickeners. The easiest and most practical way to control sludge age is with hydraulic control by wasting a defined proportion of the reactor volume daily. In AS plants with reactor concentration control, nitrification fails first. With hydraulic control of sludge age, nitrification will not fail, rather the plant fails by shedding solids over the secondary settling tank effluent weirs.

Development of a mechanistic model for biological nutrient removal activated sludge systems and application to a full‐scale WWTP

AbstractIn wastewater treatment plants (WWTPs) the production of nitrite as an intermediate in the biological nutrient removal (BNR) process has been widely observed, but not been taken into account by most of the conventional activated sludge models yet. This work aims to develop a mechanistic mathematical model to evaluate the BNR process after resolving such a problem. A mathematical model is developed based on the Activated Sludge Model No.3 (ASM3) and the EAWAG Bio‐P model with an incorporation of the two‐step nitrification–denitrification, the anoxic P uptake, and the associated two‐step denitrification by phosphorus accumulating organisms. The database used for simulations originates from a full‐scale BNR municipal wastewater treatment plant. The influent wastewater composition is characterized using batch tests. Model predictions are compared with the measured concentrations of chemical oxygen demand (COD), NH‐N, NO‐N, NO‐N, PO‐P, and mixed liquid volatile suspended solids. Simulation results indicate that the calibrated model is capable of predicting the microbial growth, COD removal, nitrification and denitrification, as well as aerobic and anoxic P removal. Thus, this model can be used to evaluate and simulate full‐scale BNR activated sludge WWTPs. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Transformations of Dissolved and Colloidal Organic Nitrogen in Biological Nutrient Removal Activated Sludge Systems

Transformations of Dissolved and Colloidal Organic Nitrogen in Biological Nutrient Removal Activated Sludge Systems

A general kinetic model for biological nutrient removal activated sludge systems: Model evaluation

Hu et al. (2007) presented a general kinetic model for biological nutrient removal (BNR) activated sludge (AS) systems in general, but for external nitrification (EN) BNRAS (ENBNRAS) systems in particular. In this article, this model is evaluated against a large number of experimental data sets. In this evaluation, the model is first used to simulate a wide variety of conventional internal nitrification (IN) BNRAS systems to evaluate its predictions and also evaluate the model parameters suggested by Hu et al. (2007), and to calibrate those constants for which values are not available in the literature. Simulation results indicate that the model, with appropriately calibrated parameters, is capable of predicting COD removal, nitrification and denitrification and two types of biological excess phosphorus removal (BEPR), namely aerobic and anoxic/aerobic P uptake BEPR. The model is then used to simulate the ENBNRAS systems to evaluate its capacity of simulating the behaviour of this system. Simulation results show that the model is capable of simulating the behaviour of the ENBNRAS systems, including COD, nitrification, denitrification and BEPR, particularly anoxic P uptake BEPR, with the values of kinetic and stoichiometric parameters obtained in modelling conventional BNRAS systems, except for micro(NIT), K(MP), eta(PAO) and eta(H) which required calibration.

A general kinetic model for biological nutrient removal activated sludge systems: Model development

In this article, a kinetic model is developed and presented for biological nutrient removal (BNR) activated sludge (BNRAS) systems in general, but for external nitrification (EN) BNRAS (ENBNRAS) systems in particular. The model is based on the UCTPHO model, but includes some significant modifications, such as anoxic P uptake and associated denitrification by phosphorus accumulating organisms (PAOs). Some key features of the model are described and discussed before the model is presented. Model evaluation will be addressed in another article (Hu et al., 2007).

Using respirometric techniques and fluorescent in situ hybridization to evaluate the heterotrophic active biomass in activated sludge

The separation and accurate quantification of active biomass components in activated sludge is of paramount importance in models, used for the management and design of waste water (WW) treatment plants. Accurate estimates of microbial population concentrations and the direct, in situ determination of kinetic parameters could improve the calibration and validation of existing models of biological nutrient removal activated sludge systems. The aim of this study was to obtain correlations between heterotrophic active biomass (Z(BH)) concentrations predicted by mathematical models and quantitative information obtained by Fluorescent in situ hybridizations (FISH). Respirometric batch test were applied to mixed liquors drawn from a well-defined parent anoxic/aerobic activated sludge system to quantify the Z(BH) concentrations. Similarly fluorescent labeled, 16S rRNA-targeted oligonucleotide probes specific for ammonia and nitrite oxidizers were used in combination with DAPI staining to validate the Z(BH) active biomass component in activate sludge respirometric batch tests. For the direct enumeration and simultaneous in situ analysis of the distribution of nitrifying bacteria, in situ hybridization with oligonucleotide probes were used. Probes (NSO 1225, NSR 1156, and NIT3) were used to target the nitrifiers and the universal probe (EUB MIX) was used to target all Eubacteria. Deducting the lithoautotrophic population from the total bacteria population revealed the Z(BH) population. A conversion factor of 8.49 x 10(-11) mg VSS/cell was applied to express the Z(BH) in terms of COD concentration. Z(BH) values obtained by molecular probing correlated closely with values obtained from the modified batch test. However, the trend of consistently poor correspondence of measured and theoretical concentrations were evident. Therefore, the focus of this study was to investigate alternative technology, such as FISH to validate or replace kinetic parameters which are invariably incorporated into models.

Kinetics of nitrogen removal in a MBR nutrient removal activated sludge system

The application of membrane bioreactor (MBR) technology to biological nutrient removal (BNR) activated sludge (AS) systems is limited and uncertainty exists as to the impact of the conditions induced by the membranes on the biologically mediated processes of nutrient removal. Two main conditions associated with MBRs are (1) high total suspended solids (TSS) concentrations (8–20 g/L) and (2) different selection pressures due to biomass retention not being based on settleability, compared with conventional systems with secondary settling tanks (SSTs). Recently, Ramphao et al. [1] concluded that incorporating membranes in BNR AS makes a profound difference to the design of the system. Previous investigations on aerobic AS have observed microscopically significant changes in the structure of the flocs and in the ratio between free suspended and aggregated cells, as well as different metabolic activities induced by membrane inclusion [2]. These observations would suggest that the introduction of membranes into BNR systems may cause associated changes in the kinetics of BNR. This will impact on the system performance and hence on the procedures and methods for design and simulation of MBR–BNR systems.