Wastewater management decision-making: A literature review and synthesis.

Wastewater management decision-making is complicated because of: (1) a complex regulatory structure, (2) the wide variety of conflicting expectations by stakeholders external and internal to the responsible utility, and (2) constrains including regulatory requirements, available technologies and practices, and customer willingness to pay. This review synthesizes the results from over 200 papers published since 2000 and presents a decision-making structure and process which is (1) science and fact-based, (2) reflects sustainability, (3) clear and transparent, (4) inclusive, (5) produces an objective-oriented decision, (6) scalable, (7) repeatable, and (8) efficient. Tools supporting the decision-making process are reviewed, including Multi-Criteria Decision Analysis (MCDA), Data Envelopment Analysis (DEA), Analytic Hierarchy Process (AHP), process modeling, economic assessments, Life Cycle Assessment (LCA), and Social Life Cycle Assessment (SLCA). Ultimately it was determined that engagement of decision-makers and relevant stakeholders to assess their values and preferences, coupled with supporting data and analyses, is necessary to reach a decision that, critically, has the support needed for it to be implemented. The results demonstrate that an understanding of the components of the decision process, coupled with an orderly process, enables good wastewater management decision-making. PRACTITIONER POINTS: A decision-making structure and process leading to the selection of implementable solutions is presented. The process possesses the following attributes: (1) science and fact-based, (2) reflect sustainability, (3) clear and transparent, (4) inclusive, (5) produce an objective-oriented decision, (6) scalable, (7) repeatable, and (8) efficient An extensive summary and analysis of tools supporting the decision process are provided, including Multi-Criteria Decision Analysis (MCDA), Data Envelopment Analysis (DEA), Analytic Hierarchy Process (AHP), process modeling, economic assessments, Life Cycle Assessment (LCA), and Social Life Cycle Assessment (SLCA). The critical role of internal and external stakeholders and differentiating their involvement relative to decision-makers is emphasized.

Smoothing the Phosphorus Resource Stress under the Socioeconomic Development in China.

Phosphorus (P) is the key in maintaining food security and ecosystem functions. Population growth and economic development have increased the demand for phosphate rocks. China has gradually developed from zero phosphate mining to the world's leading P miner, fertilizer, and agricultural producer since 1949. China released policies, such as designating phosphate rock as a strategic resource, promoting eco-agricultural policies, and encouraging the use of solid wastes produced in mining and the phosphorus chemical industry as construction materials. However, methodological and data gaps remain in the mapping of the long-term effects of policies on P resource efficiency. Here, P resource efficiency can be represented by the potential of the P cycle to concentrate or dilute P as assessed by substance flow analysis (SFA) complemented by statistical entropy analysis (SEA). P-flow quantification over the past 70 years in China revealed that both resource utilization and waste generation peaked around 2015, with 20 and 11 Mt of mined and wasted P, respectively. Additionally, rapidly increasing aquaculture wastewater has exacerbated pollution. The resource efficiency of the Chinese P cycle showed a U-shaped change with an overall improvement of 22.7%, except for a temporary trough in 1975. The driving force behind the efficiency decline was the roaring phosphate fertilizer industry, as confirmed by the sharp increase in P flows for both resource utilization and waste generation from the mid-1960s to 1975. The positive driving forces behind the 30.7% efficiency increase from 1975 to 2018 were the implementation of the resource conservation policy, downstream pollution control, and, especially, the circular agro-food system strategy. However, not all current management practices improve the P resource efficiency. Mixing P industry waste with construction materials and the development of aquaculture to complement offshore fisheries erode P resource efficiency by 2.12% and 9.19%, respectively. With the promotion of a zero-waste society in China, effective P-cycle management is expected.

Achieving Carbon Mitigation with Economic Benefits through High-Resolution Analysis of Renewable Resource Integration in Global Coastal Cities.

Coastal regions, home to more than half of the global population and contributing over 50% to the global economy, possess vast renewable resources, such as seawater and solar energy. The effective utilization of these resources, through the seawater-cooled district cooling system (SWDCS), seawater toilet flushing (SWTF), and rooftop solar photovoltaic system (RTPV), has the potential to significantly reduce carbon emissions. However, implementing these technologies in different geographic contexts to achieve the desired carbon and economic outcomes at the city level lacks a clear roadmap. To address this challenge, we comprehensively analyzed 12 coastal megacities worldwide by integrating geospatial building data. Our study evaluated the potential energy savings, carbon mitigation, and levelized carbon abatement costs (LCACs) from a life cycle perspective. The results revealed that using seawater and solar energy within urban boundaries can reduce electricity consumption from 1 to 24% across these cities. The spatial distribution of the LCAC for seawater-based systems exhibited more variation compared to the RTPV. By applying specific LCAC thresholds ranging from 0 to 225 USD/tCO2e, all cities could achieve both carbon reductions and economic benefits. These thresholds resulted in up to 80 million tonnes of carbon emission reductions and 5 billion USD of economic benefits, respectively. Our study provides valuable insights into integrating renewable resource systems, enabling coastal cities to achieve carbon and economic advantages at the city scale simultaneously.

Optimizing Air Scouring Energy for Sustainable Membrane Bioreactor Operation by Characterizing the Combination of Factors Leading to Threshold Limiting Conditions.

Key operating variables to predict the necessary scour air flowrate in full-scale Membrane Bioreactor (MBR) systems are identified, aiming to optimize energy consumption while avoiding the limiting condition (i.e., rapid increasing total resistance). The resulting metric, referred to here as the K value, was derived by balancing hydrodynamic conditions between the particle deposit rate imposed by permeate flux normalized by fouling condition and its removal by shear stress induced from air scouring. The metric includes air scouring flow, permeate flow, Mixed Liquor Suspended Solids (MLSS) concentration, Mixed Liquor (ML) viscosity, membrane packing density, and total resistance. Long-term (year-long) data from two full-scale MBR plants were analyzed. The value of K corresponding to limiting operational operation and referred to as the limiting K value, KLim, is estimated by detecting the occurrence of threshold limiting flux from the data stream and calculating the resulting value for K. Then, using KLim, the minimum required specific air demand per permeate (SADp,Crit) is calculated, indicating a potential reduction of over half the air scouring energy in typical operational conditions. The results from this data driven analysis suggest the feasibility of employing KLim to predict the adequate scour air flowrate in terms of dynamically varying operational conditions. This approach will lead to the development of energy-efficient algorithms, significantly reducing scour air energy consumption in the full-scale MBR system.

Monitoring biofilm thickness using the membrane aerated biofilm reactor (MABR) fingerprint soft sensor to optimize nitrogen removal.

The ongoing commercialization and installation of full-scale membrane aerated biofilm reactors (MABRs) stimulate the increasing need to monitor biofilm development. Biofilm thickness in MABRs can be assessed indirectly by plotting the exhaust oxygen purity versus bulk ammonia concentration, defined here as the MABR fingerprint soft sensor. Dynamic simulations with diurnal flow variations of an MABR unit model were implemented over a broad range of biofilm thicknesses and influent conditions consisting of variable C/N ratios and applied ammonia fluxes to assess the utility of the MABR fingerprint. Results show that the continuously decreasing trend of the MABR fingerprint plot slopes can be employed as a useful signal for biofilm thickness control in nitrogen removal processes. This technique is useful in a wide range of influent conditions and is helpful for MABR operators and designers to arrange biofilm thickness control events efficiently and determine where in an overall treatment process the technique can be applied to control biofilm thickness and optimize process performance. PRACTITIONER POINTS: The linear relationship between exhaust oxygen purity and bulk ammonia concentration is defined as the MABR fingerprint plot. MABR fingerprint plots are generated for a given biofilm thickness with diurnal flow or short-term loading variations implemented. Continuously decreasing trends of the MABR fingerprint plot slopes are useful signals for biofilm control in nitrogen removal. The MABR fingerprint is useful over a wide range of influent conditions regarding C/N ratios and applied ammonia fluxes. MABR practitioners can use the fingerprint plots to determine when biofilm control measures should be taken.

Exposure of the static magnetic fields on the microbial growth rate and the sludge properties in the complete-mix activated sludge process (a Lab-scale study).

BACKGROUND: In this study, the effect of static magnetic fields (SMFs) on improving the performance of activated sludge process to enhance the higher rate of microbial growth biomass and improve sludge settling characteristics in real operation conditions of wastewater treatment plants has been investigated. The effect of SMFs (15 mT), hydraulic retention time, SRT, aeration time on mixed liquor suspended solids (MLSS) concentrations, mixed liquor volatile suspended solids (MLVSS) concentrations, α-factor, and pH in the complete-mix activated sludge (CMAS) process during 30 days of the operation, were evaluated. RESULTS: There were not any differences between the concentration of MLSS in the case (2148.8 ± 235.6 mg/L) and control (2260.1 ± 296.0 mg/L) samples, however, the mean concentration of MLVSS in the case (1463.4 ± 419.2 mg/L) was more than the control samples (1244.1 ± 295.5 mg/L). Changes of the concentration of MLVSS over time, follow the first and second-order reaction with and without exposure of SMFs respectively. Moreover, the slope of the line and, the mean of α-factor in the case samples were 6.255 and, - 0.001 higher than the control samples, respectively. Changes in pH in both groups of the reactors were not observed. The size of the sluge flocs (1.28 µm) and, the spectra of amid I' (1440 cm-1) and II' (1650 cm-1) areas related to hydrogenase bond in the case samples were higher than the control samples. CONCLUSIONS: SMFs have a potential to being considered as an alternative method to stimulate the microbial growth rate in the aeration reactors and produce bioflocs with the higher density in the second clarifiers.

The hybrid MABR process achieves intensified nitrogen removal while N2O emissions remain low.

The hybrid membrane aerated biofilm reactor (MABR) process represents a full-scale solution for sustainable municipal wastewater treatment. However, most of the existing hybrid MABR processes retain large aerobic bioreactor volumes for nitrification, which is undesirable for energy and carbon savings. In this study, we used the plant-wide modeling approach with dynamic simulations to examine a novel hybrid MABR configuration with aeration controls that change the anoxic and aerobic fractions of the bioreactor volume. Result showed that the novel hybrid MABR showed "swinging" nitrification and denitrification capacities in response to diurnal loadings, achieving intensified nitrogen removal performance under both warm and cold temperature scenarios. N2O emissions from the hybrid MABR were only 1/5 of the emissions from the conventional activated sludge. The model predicted higher CH4 emissions from the hybrid MABR than the activated sludge process due to the methanogen growth in the oxygen-depleted MABR biofilm layer. Future measurements for CH4 emission are needed to obtain a holistic picture of the carbon footprint of the hybrid MABR process.

Diagnosing and characterizing the mechanisms of biological phosphorus removal at the Great Lakes Water Authority (GLWA) water resource recovery facility (WRRF).

Previous research has demonstrated that biological phosphorus removal (bio-P) occurs in the Great Lakes Water Authority (GLWA) water resource recovery facility (WRRF) high purity oxygen activated sludge (HPO-AS) process, suggesting that sludge fermentation in the secondary clarifier sludge blanket is key to bio-P occurrence. This study, combining batch reactor testing, the development of a process model for the HPO-AS process using Sumo21 (Dynamita), and the analysis of eight and a half years of plant operating data, showed that bio-P consistently occurs at the GLWA WRRF. This occurrence is attributed to the unique configuration of the HPO-AS process, which has a relatively large secondary clarifier compared to the bioreactor, and the characteristics of the influent wastewater, primarily particulate matter with limited concentrations of dissolved biodegradable organic matter. The volatile fatty acids (VFAs) needed for polyphosphate accumulating organisms (PAOs) growth are produced in the secondary clarifier sludge blanket, which provides more than four times the anaerobic biomass inventory compared to the anaerobic zones in the bioreactor, thus facilitating bio-P in the current system. Opportunities exist to further optimize the phosphorus removal performance of the HPO-AS process and reduce the amount of ferric chloride used. These findings may be of interest to researchers investigating biological phosphorus removal in similar systems. PRACTITIONER POINTS: Fermentation in the clarifier sludge blanket an essential component of bio-P process at this facility. Results suggest simple adjustments to the system could lead to further improvements in bio-P. It is possible to decrease the use of chemical phosphorus removal methods (i.e., ferric chloride) while simultaneously increasing bio-P. Determining the phosphorus mass balance from sludge streams provides insight into evaluating the effectiveness of the phosphorus recovery system.

Biological and physical selectors for mobile biofilms, aerobic granules, and densified-biological flocs in continuously flowing wastewater treatment processes: A state-of-the-art review.

There have been significant advances in the use of biological and physical selectors for the intensification of continuously flowing biological wastewater treatment (WWT) processes. Biological selection allows for the development of large biological aggregates (e.g., mobile biofilm, aerobic granules, and densified biological flocs). Physical selection controls the solids residence times of large biological aggregates and ordinary biological flocs, and is usually accomplished using screens or hydrocyclones. Large biological aggregates can facilitate different biological transformations in a single reactor and enhance liquid and solids separation. Continuous-flow WWT processes incorporating biological and physical selectors offer benefits that can include reduced footprint, lower costs, and improved WWT process performance. Thus, it is expected that both interest in and application of these processes will increase significantly in the future. This review provides a comprehensive summary of biological and physical selectors and their design and operation.

Granule formation mechanism, key influencing factors, and resource recycling in aerobic granular sludge (AGS) wastewater treatment: A review.

The high-efficiency and additionally economic benefits generated from aerobic granular sludge (AGS) wastewater treatment have led to its increasing popularity among academics and industrial players. The AGS process can recycle high value-added biomaterials including extracellular polymeric substances (EPS), sodium alginate-like external polymer (ALE), polyhydroxyfatty acid (PHA), and phosphorus (P), etc., which can serve various fields including agriculture, construction, and chemical while removing pollutants from wastewaters. The effects of various key operation parameters on formation and structural stability of AGS are comprehensively summarized. The degradable metabolism of typical pollutants and corresponding microbial diversity and succession in the AGS wastewater treatment system are also discussed, especially with a focus on emerging contaminants removal. In addition, recent attempts for potentially effective production of high value-added biomaterials from AGS are proposed, particularly concerning improving the yield, quality, and application of these biomaterials. This review aims to provide a reference for in-depth research on the AGS process, suggesting a new alternative for wastewater treatment recycling.

Flushing Toilets and Cooling Spaces with Seawater Improve Water-Energy Securities and Achieve Carbon Mitigations in Coastal Cities.

Exploring alternative water sources and improving the efficiency of energy uses are crucial approaches to strengthening the water-energy securities and achieving carbon mitigations in sub(tropical) coastal cities. Seawater use for toilet flushing and district cooling systems is reportedly practical for achieving multiaspect benefits in Hong Kong. However, the currently followed practices are yet to be systematically evaluated for scale expansions and system adaptation in other coastal cities. The significance of using seawater to enhance local water-energy securities and carbon mitigations in urban areas remains unknown. Herein, we developed a high-resolution scheme to quantify the effects of the large-scale urban use of seawater on a city's reliance on non-local and non-natural water and energy supplies and its carbon mitigation goals. We applied the developed scheme in Hong Kong, Jeddah, and Miami to assess diverse climates and urban characteristics. The annual water and energy saving potentials were found to be 16-28% and 3-11% of the annual freshwater and electricity consumption, respectively. Life cycle carbon mitigations were accomplished in the compact cities of Hong Kong and Miami (2.3 and 4.6% of the cities' mitigation goals, respectively) but not in a sprawled city like Jeddah. Moreover, our results suggest that district-level decisions could result in optimal outcomes supporting seawater use in urban areas.

Comparative analysis of floc characteristics and microbial communities in anoxic and aerobic suspended growth processes.

A fully anoxic suspended growth process is an appealing alternative to conventional activated sludge (AS) due to considerable aeration reduction and improved carbon processing efficiency for biological nutrient removal (BNR). With development of the hybrid membrane aerated biofilm reactor (MABR) technology, implementation of a fully anoxic suspended growth community in BNR facilities became practical. To better understand potential limitations with the elimination of aeration, we carried out microscopic examination and 16S rRNA gene-based microbial community profiling to determine how an anoxic suspended growth would differ from the conventional aerobic process in floc characteristics, microbial diversity, microbial temporal dynamics, and community assembly pattern. Fewer filamentous populations were found in the anoxic mixed liquor, suggesting easily sheared flocs. The anoxic microbial community had distinct composition and structure, but its diversity and temporal dynamics were similar to the conventional aerobic community. A variety of well-studied functional guilds were also identified in the anoxic community. The anoxic microbial community assembly was more stochastic than the conventional aerobic community, but deterministic assembly was still significant with a large core microbiome adapted to the anoxic condition. PRACTITIONER POINTS: Flocs developed under the anoxic conditions had less filamentous backbones, implying reduced flocculation capacity and easily sheared flocs. Knowledge about the ecophysiology of Thauera, Thiothrix, and Trichococcus can help achieve good properties of the anoxic flocs. A diverse microbial community sustainably adapted to the fully anoxic condition, containing a variety of filaments, denitrifiers, and PAOs. The anoxic microbial community displayed a similar degree of diversity and temporal dynamics compared to the aerobic counterpart. The anoxic community's assembly was more stochastic, so it may be less subject to changes in environmental variables.

Available online sensors can be used to create fingerprints for MABRs that characterize biofilm limiting conditions and serve as soft sensors.

Membrane aerated biofilm reactors (MABRs) are a promising biological wastewater treatment technology, whose industrial applications have dramatically accelerated in the last five years. Increased popularity and fast industrial adaptation are coupled with increased needs to monitor, optimize, and control MABRs with available online sensors. Observations of commercial scale MABR installations have shown a distinctive and repetitive pattern relating oxygen purity in MABR exhaust gas to reactor ammonia concentrations. This provides an obvious opportunity for process monitoring and control which this paper investigates with the help of modeling. The relationship plots between the bulk ammonia concentration and the oxygen purity are defined as MABR fingerprint plots, which are described in the form of steady-state curves and dynamic trajectories. This study systematically investigated, analyzed, and explained the behaviors and connections of steady-state curves and dynamic trajectories with a MABR model in SUMO®, and proposed a hypothesis about utilizing the MABR fingerprint plots to characterize MABR system performance, identify the limiting factor of biofilms, and possibly develop a soft senor for MABR biofilm thickness monitoring and control.

Design methodologies to determine optimal staging of membrane-aerated biofilm reactors for mainstream treatment with anammox.

Partial nitritation anammox (PNA) membrane-aerated biofilm reactors (MABRs) can be used in mainstream nitrogen removal to help facilities reduce their energy consumption. Previous PNA MABR research has not investigated the impacts of staging, i.e. arraying MABRs in series, on their nitrogen removal performance, operation, and ability to suppress nitrite oxidizing bacteria. In this paper, a mathematical model simulated PNA MABR performance at different influent total ammonia concentrations and loadings. A design methodology for staging PNA MABRs was created and found that the amount of membrane surface area is dependent upon the total ammonia-nitrogen concentration and loading, and the air loading to the membrane must be proportional to the total ammonia-nitrogen loading to maximize the total inorganic nitrogen (TIN) removal rate. This led to approximately equal-sized stages that each had a TIN removal percentage of 71% of the influent total ammonia nitrogen. Staging a treatment train resulted in 9.8% larger total ammonia and 9.3% larger total nitrogen removal rates when compared with an un-staged reactor. The un-staged reactor also was not able to produce an effluent total ammonia concentration below 5 mg N/L which would be necessary for many facilities' permits.

A mobile-organic biofilm process for wastewater treatment.

The mobile-organic biofilm (MOB) process includes mobile biofilms and their retention screens with a bioreactor and liquid and solid separation. The MOB process is inexpensive and easy to integrate with wastewater treatment (WWT) processes, and it provides for high-rate WWT in biofilm or hybrid bioreactors. This paper describes three modes of MOB process operation. The first mode of operation, Mode I, has a mobile-biofilm reactor and a mobile-biofilm retention screen that is downstream of and external to a bioreactor and upstream of liquid and solid separation. Modes II and III have a hybrid (i.e., mobile biofilms and accumulated suspended biomass) bioreactor and liquid and solid separation. Mode II includes a mobile-biofilm retention screen that is downstream of and external to a hybrid bioreactor and upstream of liquid and solid separation. Mode III includes mobile-biofilm retention screening that is external to a hybrid bioreactor and liquid and solid separation, receives waste solids, and relies on environmental conditions and wastewater characteristics that are favorable for aerobic-granular sludge formation. This paper presents a mechanistic approach to design and evaluate MOB processes and describes MOB process: (1) modes of operation, (2) design and analysis methodology, (3) process and mechanical design criteria, (4) mathematical modeling, (5) design equations, and (6) mobile-biofilm settling characteristics and return. A mathematical model was applied to describe a fixed bioreactor volume and secondary-clarifier area with Modes I, II, and III. The mathematical modeling identified key differences between MOB process modes of operation, which are described in this paper. PRACTITIONER POINTS: MOB is a municipal and industrial wastewater treatment (WWT) process that reduces bioreactor and liquid and solids separation process volumes. It may operate with a mobile-biofilm reactor or a hybrid (mobile biofilms and suspended biomass) bioreactor. This paper provides a mechanistic basis for the selection and design of a MOB process mode of operation, and it describes MOB process modes of operation, design criteria, design equations, mathematical modeling, and mobile-biofilm settling characteristics. MOB integrated WWT plants exist at full scale and reliably meet their treatment objectives. The MOB process is an emerging environmental biotechnology for cost-effective WWT.

Automating process design by coupling genetic algorithms with commercial simulators: a case study for hybrid MABR processes.

The development of commercial software and simulators has progressed to assist engineers to optimize design, operation, and control of wastewater treatment processes. Commonly, manual trial-and-error approaches combined with engineering experience or exhaustive searches are used to find candidate solutions. These approaches are becoming less favorable because of the increasingly elaborate process models, especially for new and innovative processes whose process knowledge is not fully established. This study coupled genetic algorithms (GAs), a subfield of artificial intelligence (AI), with a commercial simulator (SUMO) to automatically complete a design task. The design objective was the upgrade of a conventional Modified Ludzack-Ettinger (MLE) process to a hybrid membrane aerated biofilm reactor (hybrid MABR). Results demonstrated that GAs can (1) accurately estimate five influent wastewater fractions using eleven typical measurements - 3 out of 5 estimated fractions were nearly the same and the other two were within 7% relative errors and (2) propose reasonable designs for the hybrid MABR process that reduce footprint by 17%, aeration by 57%, and pumping by 57% with significantly improved effluent nitrogen quality (TN<3 mg-N/L). This study demonstrated that tools from AI promote efficiency in wastewater treatment process design, optimization and control by searching candidate solutions both smartly and automatically in replacement of manual trial-and-error methods. The methodology in this study contributes to accumulating process knowledge, understanding trade-offs between decisions, and finally accelerates the learning pace for new processes.

Material biosynthesis, mechanism regulation and resource recycling of biomass and high-value substances from wastewater treatment by photosynthetic bacteria: A review.

The environmental-friendly and economic benefits generated from photosynthetic bacteria (PSB) wastewater treatment have attracted significant attention. This process of resource recovery can produce PSB biomass and high-value substances including single cell protein, Coenzyme Q10, polyhydroxyalkanoates (PHA), 5-aminolevulinic acid, carotenoids, bacteriocin, and polyhydroxy chain alkyl esters, etc. for application in various fields, such as agriculture, medical treatment, chemical, animal husbandry and food industry while treating wastewaters. The main contents of this review are summarized as follows: physiological characteristics, mechanism and application of PSB and potential of single cell protein (SCP) production are described; PSB wastewater treatment technology, including procedures and characteristics, typical cases, influencing factors and bioresource recovery by membrane bioreactor are detailed systematically. The future development of PSB-based resource recovery and wastewater treatment are also provided, particularly concerning PSB-membrane reactor (MBR) process, regulation of biosynthesis mechanism of high-value substances and downstream separation and purification technology. This will provide a promising and new alternative for wastewater treatment recycling.

Recent progress using membrane aerated biofilm reactors for wastewater treatment.

The membrane biofilm reactor (MBfR), which is based on the counter diffusion of the electron donors and acceptors into the biofilm, represents a novel technology for wastewater treatment. When process air or oxygen is supplied, the MBfR is known as the membrane aerated biofilm reactor (MABR), which has high oxygen transfer rate and efficiency, promoting microbial growth and activity within the biofilm. Over the past few decades, laboratory-scale studies have helped researchers and practitioners understand the relevance of influencing factors and biological transformations in MABRs. In recent years, pilot- to full-scale installations are increasing along with process modeling. The resulting accumulated knowledge has greatly improved understanding of the counter-diffusional biological process, with new challenges and opportunities arising. Therefore, it is crucial to provide new insights by conducting this review. This paper reviews wastewater treatment advancements using MABR technology, including design and operational considerations, microbial community ecology, and process modeling. Treatment performance of pilot- to full-scale MABRs for process intensification in existing facilities is assessed. This paper also reviews other emerging applications of MABRs, including sulfur recovery, industrial wastewater, and xenobiotics bioremediation, space-based wastewater treatment, and autotrophic nitrogen removal. In conclusion, commercial applications demonstrate that MABR technology is beneficial for pollutants (COD, N, P, xenobiotics) removal, resource recovery (e.g., sulfur), and N2O mitigation. Further research is needed to increase packing density while retaining efficient external mass transfer, understand the microbial interactions occurring, address existing assumptions to improve process modeling and control, and optimize the operational conditions with site-specific considerations.

An adaptive real-time grey-box model for advanced control and operations in WRRFs.

Grey-box models, which combine the explanatory power of first-principle models with the ability to detect subtle patterns from data, are gaining increasing attention in wastewater sectors. Intuitive, simple structured but fit-for-purpose grey-box models that capture time-varying dynamics by adaptively estimating parameters are desired for process optimization and control. As an example, this study presents the identification of such a grey-box model structure and its further use by an extended Kalman filter (EKF), for the estimation of the nitrification capacity and ammonia concentrations of a typical Modified Ludzack-Ettinger (MLE) process. The EKF was implemented and evaluated in real time by interfacing Python with SUMO (Dynamita™), a widely used commercial process simulator. The EKF was able to accurately estimate the ammonia concentrations in multiple tanks when given only the concentration in one of them. In addition, the nitrification capacity of the system could be tracked in real time by the EKF, which provides intuitive information for facility managers and operators to monitor and operate the system. Finally, the realization of EKF is critical to the development of future advance control, for instance, model predictive control.