Simplification of Complex WWTP Models into Simple Design and Evaluative WRRF Tool

Wastewater treatment plant (WWTP) steady-state models have been used, historically, by consulting engineers and researchers for design, process optimisation, and to study and evaluate various operating scenarios. These models have, however, been generally developed for single unit process which limits their use. In addition, there have been three recent shifts in the past two decades from conventional design and modelling of WWTPs. Firstly, the shift from single unit to plant-wide modelling. Secondly, WWTPs are considered as water and resource recovery facilities (WRRFs). Lastly, there has been a growing interest to use the developed plant-wide steady-state models by stakeholders i.e., plant operators, designers and decision-makers who have limited technical expertise in WWTP modelling. These stakeholders use these models for design, evaluation and optimisation of scenarios. The later shift has raised the debate of complexity versus simplicity of the developed steady-state models. In addition to the aforementioned shifts, there has been limited research on the impact of sludge return liquors on the overall plant performance especially in the context of South African WWTPs. Wastewater treatment plants treat influent wastewater to a specified effluent quality, through several processes, before discharging it into the receiving water bodies. One of the by-products of these treatment processes is a nitrogen (N) and phosphorus (P) rich dewatering liquor (DWL). Generally, South African WWTPs recycle the DWL to the mainstream treatment process without first undergoing any side-stream treatment process (SSTP). The recycling of such N and P rich DWLs to the mainstream process, without first going through any SSTP and/or addition of organics to the mainstream process (organics have a role to play in nutrient removal, through the provision of substrate for biomass growth and provision of electron donors in the process of denitrification) poses a problem to the treatment process. Consequently, the reactor is overloaded with nutrients without sufficient organics to remove them; hence, the plant produces poor effluent quality i.e., high N and P concentrations at high operational cost. A simplified full-scale steady-state WWTP simulation tool, namely, plant performance evaluation tool (PPET), with a user-friendly interface was developed, based on principles of sound mass balance and kinetic and stoichiometric relations over the full-scale plant, to bridge the gap between the complexity of WWTP models and the lack of technical expertise of the stakeholders. This simulation tool analyses the impact of recycling sludge dewatering liquors on the overall plant performance. Furthermore, it gives the user a platform to analyse different scenarios and provides uncompromised results that enable the user to make better design and operation decisions. The bio-augmentation batch enhanced (BABE) and struvite precipitation SSTPs, and plant performance indices i.e., effluent quality and operational cost indices, EQI and OCI, respectively, were incorporated into PPET to analyse case studies on South African plants. It was found that there are added benefits of using a SSTPs to mitigate the detrimental impacts of recycled DWL when the capacity of the plant has been exceeded. However, both BABE and struvite precipitation processes achieve different results based on the composition of the DWL that is being treated i.e., for DWL from an anaerobic digester treating waste activated sludge that is not P rich (with low EBPR), then the recommended SSTP operation would be BABE process rather than struvite precipitation. Due to the different treatment systems (i.e., with variations in influent loads, system configurations and priority end products required - energy, water, phosphorus, etc.), further investigations are required on strategies for implementation of the various SSTPs

High-Loaded Activated Sludge - Improvement of a Solids Retention Time Controlled System

Although 100 years old, the activated sludge system remains inevitable for modern wastewater treatment. Advancements within the development of mainstream nitrogen removal techniques based on anaerobic ammonium-oxidising bacteria have renewed the interest in traditional, high-loaded activated sludge systems for COD removal only. In order for activated sludge plants to be efficient in terms of energy use, methane production and areal footprint, the retention time for the active organisms, or analogously the solids retention time, needs to be kept low and precisely regulated. At Sjölunda wastewater treatment plant, Sweden, an automated solids retention time control system at one of the activated sludge lines was recently implemented. Operation of the experimental line with solids retention time set to 1.2 days with the controller was compared to a manually regulated line, operated at a higher solids retention time (aboutThe Sjölunda wastewater treatment plant faces the challenge of tougher demands for the quality of the water leaving the plant and entering the Öresund strait between Denmark and Sweden. At the same time, the population of Malmö with neighbourhood is growing rapidly, which means an increase in the loading on the plant. The residence time for the active microbes, the “sludge”, in the first biological treatment step has important implications for the treatment efficiency and also for the energy balance at the plant. Consequently, the “sludge age” must be determined and precisely controlled

Municipal Wastewater Management

Taking the papers’ collection of this Special Issue as a whole, it is clear that “Municipal Wastewater Management” is an ongoing field of research with the ability to incorporate current environmental and human health challenges. The use of municipal sewage to monitor COVID-19 virus circulation in communities and the estimation of possible outbreaks, even before clinical cases have been identified, is a fact that justifies this. In light of the Coronavirus pandemic, the interest of the impact that research on municipal wastewater management can have on improving humans’ health and protecting the environment is being rethought. In respect to this, there is an essential need for scientific publications that present varieties of case studies and discuss best practices, so as wastewater treatment plants to be seen not only as sites of pollutants removal but also as places where energy is efficiently used and environmental sustainability is being practiced, in close relation to the needs of the community. Viewed in this way, the papers’ collected in this Special Issue are looking forward to reach a broad readership that can gain awareness and understanding of their topics and be stimulated into future research and collaborations that would improve all stakeholders engagement in promoting a sustainable municipal wastewater management

Modelling and model-based optimization of N-removal WRRFs : reactive settling, conventional & short-cut N-removal processes

La détérioration des ressources en eau et la grande quantité d'eau polluée générée dans les sociétés industrialisées donnent une importance fondamentale aux procédés de traitement des eaux usées pour préserver les ressources, conformément à l'objectif 6 des 17 objectifs de développement durable des Nations Unies. Le rejet de nutriments tels que l'ammoniac par les eaux usées est un problème important, l'élimination de l'azote (N) est donc l'un des processus critiques de toute station de récupération des ressources en eau (StaRRE). L'objectif de ce projet de recherche doctoral est d'améliorer la compréhension des mécanismes d'élimination de l'azote dans le traitement biologique des eaux usées grâce à la modélisation, et d'optimiser les StaRRE existantes pour réduire la consommation d'énergie et de ressources. Dans ce cadre, 3 études différentes ont été réalisées. Tout d'abord, un modèle de décanteur réactif unidimensionnel a été développé. Celui-ci prédit le comportement de décantation de boues à des concentrations élevées de boues ainsi que les conversions biocinétiques dans le processus de décantation secondaire (DS). Il a été constaté qu'une description précise des réactions biocinétiques dans la DS impose des défis de calibration élevés pour le modèle de décantation, car ce dernier doit capturer les profils de concentration complets de la biomasse active dans la couverture de boues. Le modèle calibré a pu prédire avec précision les profils de concentration des effluents et du lit de boues dans la DS. Le modèle développé peut être utilisé pour le contrôle et la simulation des StaRRE afin d'obtenir de meilleures prédictions des concentrations d'effluents et des boues de retour, et aussi de calculer correctement le bilan massique d'azote d'une StaRRE. Deuxièmement, un modèle à l'échelle de l'usine a été mis en place pour un système de pré-dénitrification conventionnel pour la StaRRE pilEAUte à l'échelle pilote. Une méthodologie de calibration du modèle par étapes a été adoptée en fusionnant les principaux protocoles de calibration de modèle, tout en mettant l'accent sur le modèle biocinétique. Le modèle de la StaRRE pilEAUte, y compris le décanteur réactif développé, a été calibré et validé pour simuler les variables de modèle sélectionnées, puis utilisé pour une analyse de scénarios plus approfondie de l'optimisation de la consommation d'énergie et des ressources. Les résultats de l'analyse des scénarios ont montré le potentiel d'optimisation du système conventionnel d'élimination d'azote grâce à la réduction de l'aération et du retour interne des nitrates. Ils ont également démontré que la dénitrification dans le décanteur secondaire peut avoir une contribution significative à la capacité globale d'élimination d'azote d'une StaRRE lorsque la liqueur mixte peut traverser le lit de boues. Troisièmement, l'étude visait à évaluer l'applicabilité des stratégies de commande continu et intermittent du rapport de l'ammoniac par rapport aux NOX-N (commande AvN) sur la StaRRE pilEAUte. Les stratégies de commande de l'aération par AvN sont appliquées en amont d'un réacteur de désammonification, qui est un processus d'élimination efficace d'azote avec un besoin de ressources réduit (en termes d'aération et carbone) par rapport aux systèmes conventionnels. Les deux stratégies de commande testées pourraient être réalisées grâce à une commande automatique. Cependant, le maintien du rapport AvN dans l'effluent à la valeur souhaitée (1) dépend fortement des conditions opérationnelles telles que les variations de l'affluent, le temps de rétention des boues et la fiabilité des capteurs. Même si la recherche est guidée par les études de StaRRE à l'échelle pilote, les méthodologies développées pour démontrer et modéliser les processus et les conditions opérationnelles économes en énergie et en ressources sont applicables et transférables à d'autres études de cas à plein échelle.Deterioration of water resources and the large amount of polluted water generated in industrialized societies gives fundamental importance to waste water treatment processes to preserve resources in accordance with goal 6 of the 17 sustainable development goals of the United Nations. Discharge of nutrients such as ammonia with waste water is a significant issue, thus nitrogen (N) removal is one of the critical processes of any water resource recovery facilities (WRRF). The objective of this PhD research project was to improve the understanding of N-removal mechanisms in biological treatment of wastewater through modelling and to optimize existing WRRFs to reduce energy and resource consumption. Within this context, 3 different studies were carried out. First, a one dimensional reactive settler model was developed that predicts the settling behaviour at high sludge concentrations together with biokinetic conversions in the secondary settling process. It was found that an accurate description of biokinetic reactions in the SST puts high calibration requirements on the settling model as it must properly capture the full concentration profiles of active biomass in the sludge blanket. The calibrated model was able to accurately predict the effluent and sludge blanket concentration profiles in the SST. The developed model can be used for control and simulation of WRRFs for better predictions of SST effluent and underflow concentrations and also properly calculate the nitrogen mass balance of a WRRF. Second, a plant-wide model was set up for a conventional pre-denitrification system for the pilot-scale pilEAUte WRRF. A step-wise model calibration methodology was adopted by merging main existing model calibration protocols while placing emphasis on the biokinetic model. The pilEAUte model, including the developed reactive settler, was calibrated and validated to simulate the selected model variables and used for further scenario analysis for energy and resource optimization. The scenario analysis results showed the optimization potential of conventional N removal systems through application of reduced aeration and internal nitrate recycling. It also demonstrated that denitrification in the secondary settler can contribute significantly to the overall N removal capacity of the WRRF when mixed liquor can pass through the sludge blanket. Third, it was aimed to evaluate the applicability of continuous and intermittent Ammonia vs NOₓ-N (AvN) control strategies on the pilEAUte WRRF. The AvN aeration control strategies are applied prior to a deammonification stage which is a short-cut N removal process with reduced resource (aeration and carbon) requirements in comparison to conventional systems. Both strategies could be achieved through automatic control. However, keeping the AvN ratio in the effluent on the desired value highly depends on operational conditions such asinfluent variations, sludge retention time and the sensor's measurement reliability

A study of the effect of substrate composition on the microbial ecology of activated sludge

Eighty percent of all biologically treated waste waters in Europe are oxidised by the activated sludge process. Bulking sludge caused by the proliferation of filamentous organisms is the primary cause of failure of this system. The effect of various substrates in both laboratory scale, fully mixed and sequencing batch (SBR) reactor configurations were used to assess their combined effect on activated sludge microbial ecology and hence sludge settlement. Five different substrate types were used ; synthetic sewage, a basic monosaccharide, disaccharides, polysaccharides and amino acids. In all cases using the fully mixed reactor, bulking occurred while, good settling sludge was produced in the sequencing batch reactor. The cause of this bulking was deemed to be due to the lack of so called "selector effect" within the fully mixed reactor characterised by :- i) high rates of substrate consumption ii) high oxygen (or generally: electron acceptor) up take rate iii) enhanced growth of zoogleal bacteria iv) increased metabolic diversity This laboratory work was compared and contrasted with a pure oxygen activated sludge (VITOX) system treating a high strength pea processing waste water. This fully mixed system had proved difficult to operate since its installation and in the first two years of this study suffered bulking caused by low dissolved oxygen levels. In the third year a combination of a hydraulic problem and subsequent lack of control led to filamentous bulking. This particular bulking incident was controlled by the addition of chlorine to the aeration tank which was selectively toxic to the filamentous organisms present. Due to the studies carried out at both laboratory and full scale an initial contact zone was installed within the main aeration tank prior to the 4th year of this study so as to create an area of high floc loading and high substrate uptake. This initial anoxic contact zone proved successful in preventing the development of a poorly settling sludge and is in line with common practice for the elimination of filamentous bulking reported in the literature. Oxidation Reduction Potential (ORP) proved a reliable and appropriate monitor of conditions of low to zero D.O. experienced in the laboratory scale reactors and at full scale in the anoxic contact zone. It was also found that ORP could be used to detect when D.O. levels became completely depleted and monitor reductions in nitrate levels

Effects of power level, organic loading and temperature on the performance of facultative aerated lagoons

PhD ThesisFacultative aerated lagoons are aerated lagoons operated at low power levels and are wastewater stabilization ponds with artificial aeration. These lagoons are used more commonly than aerobic aerated lagoons because a satisfactory effluent can be produced with a lower power input. The power level applied to facultative aerated lagoons is sufficient only to satisfy the oxygen demand but not adequate to keep all the solids in suspension and settled solids will decompose aerobically and anaerobically. In the study reported, laboratory-model facultative aerated lagoons of 81 litres volume, aerated with diffused air, were used to study the performance of such lagoons in the treatment of municipal wastewater. Different combinations of four power levels, 0.25,0.5,1 and 2.0 W/m3, three different organic loadings, 20,33 and 62 g BOD5/m3d. , and two temperature levels, 20°C and 30°C, were applied in twenty four experimental runs. Influent and effluent were sampled on a regular basis and their characteristics were determined. The effluent from the model facultative aerated lagoons was always of reasonable quality, with respect to BOD5, COD and suspended solids. This was achieved with no provision for effluent settling or additional treatment. Removals of 91 percent BOD5 and 67 percent COD could be achieved for unfiltered samples. Effluent BOD5 of 13 mg/l in the filtered samples and 31 mg/l in the unfiltered samples was attainable in these lagoons. Effluent suspended solids levels as low as 41 mg/i were also obtained. Thus facultative aerated lagoons will provide both biological and physical treatment operations in a single earthen tank. Because suspended solids in the effluent from facultative aerated lagoons are low, no sludge disposal or processing is needed on a continuous basis. Other performance criteria; nitrogen, phosphorus, iii chlorophyll "a", Escherichia. coli and faecal streptococci, are reported on in the thesis. It was observed that the level of power introduced into the facultative aerated lagoon had positive and significant effects on some performance parameters, including BOD5 and COD filtered removal rate coefficients, removal efficiencies for BOD5 and COD (except for COD removal in facultative aerated lagoons operated at high temperature, 30°C) and effluent suspended solids and negative and significant effects for others, such as suspended solids removal efficiency. The effect of power was insignificant for other parameters, especially BOD5 and COD unfiltered removal rate coefficients. The effect of power level on filtered removal efficiencies was higher than on unfiltered ones. BOD5 and COD removal efficiencies were negatively affected by organic loading (or positively by retention time) and the effect was found to be significant. The organic loading effect was significant and positive on filtered BOD5 and both filtered and unfiltered COD removal rate coefficients whereas it was negative on unfiltered BOD5 removal rate coefficients. Temperature had significant and positive effects on some parameters, including removal rate coefficients both filtered BOD5 and COD as well as unfiltered BOD5 and BOD5 and COD removal efficiencies, and insignificant effects on others, such as unfiltered COD removal rate coefficient. The effect of temperature on the removal rate coefficients, except the unfiltered COD removal rate coefficient, was higher at higher organic loadings (shorter retention times) whereas its effect on BOD5 and COD removals efficiencies was higher at lower power levels. The temperature correction coefficient for BOD5 at low power levels was higher than at higher levels of power. iv The effect of power level on the temperature correction coefficient was significant whereas the organic loading (or retention time) effect was insignificant. Relationships between the individual operating parameters and performance parameters are presented in the form of empirical equations and the combined effects of these operating parameters and performance parameters were also modelled. High organic loading (short retention time) in facultative aerated lagoons operated at low power levels proved to remove more organic material per day per unit of power introduced into the lagoon. Therefore, the optimum conditions of organic loading and power level at which a single facultative aerated lagoon used as a sole treatment process for treating settled sewage should be operated are 0.25 W/m3 for power level and 62 g BOD5 /m3. d for organic loading (3 to 4 days retentiom time). The effect of mixing, represented by the parameters in a simulation model, on performance was also modelled in the form of empirical equations. Nitrogen, phosphorus, Escherichia coli and faecal streptococci removals were considerable. Variations of their removal performance as well as algal concentration variations with the operating parameters were also studied and discussed. A mathematical equation was developed for the determination of the mean solids retention time (SRT) in facultative aerated lagoons. The relationship between SRT and power level and organic loading was determined and represented by an empirical equation. A power level of around 0.5 W/m3 was the threshold for settleable solids suspension below which no significant decrease in effluent or mixed liquor suspended solids concentration would take place.Umm Al-Qura University, Makkah (Saudi Arabia

Anaerobic Co-Digestion of Lignocellulosic Waste

Some terms, such as eco-friendly, circular economy and green technologies, have remained in our vocabulary, because the truth is that mankind is altering the planet to put its own subsistence at risk. Besides, for rationalization in the consumption of raw materials and energy, the recycling of waste through efficient and sustainable processes forms the backbone of the paradigm of a sustainable industry. One of the most relevant technologies for the new productive model is anaerobic digestion. Historically, anaerobic digestion has been developed in the field of urban wastes and wastewater treatments, but in the new challenge, its role is more relevant. Anaerobic digestion is a technologically mature biological treatment, which joins bioenergy production with the efficient removal of contaminants. This issue provides a specialized, but broad in scope, overview of the possibilities of the anaerobic digestion of lignocellulosic biomass (mainly forestry and agricultural wastes), which is expected to be a more promising substrate for the development of biorefineries. Its conversion to bioenergy through anaerobic digestion must solve some troubles: the complex lignocellulosic structure needs to be deconstructed by pretreatments and a co-substrate may need to be added to improve the biological process. Ten selected works advance this proposal into the future

Nutrient recovery from bio-digestion waste: from field experimentation to model-based optimization

The increasing awareness of natural resource depletion, the increasing demand of nutrients and energy for food production, and the more and more stringent nutrient discharge and fertilization levels, have resulted in an increased attention for nutrient recovery from municipal and agricultural wastes. This PhD dissertation aims at stimulating the transition to a bio-based economy by providing (tools to develop) sustainable strategies for nutrient recovery from organic wastes following bio-energy production through anaerobic digestion (= bio-digestion waste). Particular attention is paid to the valorization of the recovered products as renewable substitutes for chemical fertilizers and/or as sustainable organo-mineral fertilizers in agriculture. Three complementary research phases were conducted: 1) technology inventory and product classification, 2) product value evaluation, 3) process modelling and optimization. In the first phase, a systematic technology review and product classification was performed. In phase 2, product characterizations and mass balance analyses at full-scale waste(water) resource recovery facilities (WRRFs) were executed. An economic and ecological evaluation of different bio-based fertilization scenarios was conducted and the most sustainable scenarios were selected for subsequent agronomic evaluation at field and greenhouse scale. In phase 3, a generic nutrient recovery model library was developed aiming at fertilizer quantity and quality as model outputs. Increased insights in unit process performance and interactions were obtained through global sensitivity analyses. The models were successfully used as a tool for treatment train configuration and optimization. Based on all acquired knowledge, a generic roadmap for setting up nutrient recovery strategies as function of fertilizer markets, legislations, and waste characterization was established. As such, the present dissertation further develops the concepts of maximally closing nutrient cycles in a cradle-to-cradle approach. The work reveals important evidence of the positive impact of recovered products on the economy, agronomy, and ecology of intensive plant production. Moreover, it provides the fundamental information and tools to facilitate the implementation and optimization of sustainable nutrient recovery strategies. All of this may open up new opportunities for sustainable and more bio-based economic growth and thus create a win-win situation for the environment, the society, and the economy in Belgium, Canada, and beyond

Book of abstracts of the 10th International Chemical and Biological Engineering Conference: CHEMPOR 2008

This book contains the extended abstracts presented at the 10th International Chemical and Biological Engineering Conference - CHEMPOR 2008, held in Braga, Portugal, over 3 days, from the 4th to the 6th of September, 2008. Previous editions took place in Lisboa (1975, 1889, 1998), Braga (1978), Póvoa de Varzim (1981), Coimbra (1985, 2005), Porto (1993), and Aveiro (2001). The conference was jointly organized by the University of Minho, “Ordem dos Engenheiros”, and the IBB - Institute for Biotechnology and Bioengineering with the usual support of the “Sociedade Portuguesa de Química” and, by the first time, of the “Sociedade Portuguesa de Biotecnologia”. Thirty years elapsed since CHEMPOR was held at the University of Minho, organized by T.R. Bott, D. Allen, A. Bridgwater, J.J.B. Romero, L.J.S. Soares and J.D.R.S. Pinheiro. We are fortunate to have Profs. Bott, Soares and Pinheiro in the Honor Committee of this 10th edition, under the high Patronage of his Excellency the President of the Portuguese Republic, Prof. Aníbal Cavaco Silva. The opening ceremony will confer Prof. Bott with a “Long Term Achievement” award acknowledging the important contribution Prof. Bott brought along more than 30 years to the development of the Chemical Engineering science, to the launch of CHEMPOR series and specially to the University of Minho. Prof. Bott’s inaugural lecture will address the importance of effective energy management in processing operations, particularly in the effectiveness of heat recovery and the associated reduction in greenhouse gas emission from combustion processes. The CHEMPOR series traditionally brings together both young and established researchers and end users to discuss recent developments in different areas of Chemical Engineering. The scope of this edition is broadening out by including the Biological Engineering research. One of the major core areas of the conference program is life quality, due to the importance that Chemical and Biological Engineering plays in this area. “Integration of Life Sciences & Engineering” and “Sustainable Process-Product Development through Green Chemistry” are two of the leading themes with papers addressing such important issues. This is complemented with additional leading themes including “Advancing the Chemical and Biological Engineering Fundamentals”, “Multi-Scale and/or Multi-Disciplinary Approach to Process-Product Innovation”, “Systematic Methods and Tools for Managing the Complexity”, and “Educating Chemical and Biological Engineers for Coming Challenges” which define the extended abstracts arrangements along this book. A total of 516 extended abstracts are included in the book, consisting of 7 invited lecturers, 15 keynote, 105 short oral presentations given in 5 parallel sessions, along with 6 slots for viewing 389 poster presentations. Full papers are jointly included in the companion Proceedings in CD-ROM. All papers have been reviewed and we are grateful to the members of scientific and organizing committees for their evaluations. It was an intensive task since 610 submitted abstracts from 45 countries were received. It has been an honor for us to contribute to setting up CHEMPOR 2008 during almost two years. We wish to thank the authors who have contributed to yield a high scientific standard to the program. We are thankful to the sponsors who have contributed decisively to this event. We also extend our gratefulness to all those who, through their dedicated efforts, have assisted us in this task. On behalf of the Scientific and Organizing Committees we wish you that together with an interesting reading, the scientific program and the social moments organized will be memorable for all.Fundação para a Ciência e a Tecnologia (FCT