Optimisation-based methodology for the design and operation of sustainable wastewater treatment facilities

The treatment of municipal and industrial wastewaters in conventional wastewater treatment plants (WWTPs) requires a significant amount of energy in order to meet ever more stringent discharge regulations. However, the wastewater treatment industry is undergoing a paradigm shift from a focus on waste-stream treatment and contaminant removal to a proactive interest in energy and resource recovery facilities, driven by both economic and environmental incentives. The main objective of this thesis is the development of a decision-making tool in order to identify improvement opportunities in existing WWTPs and to develop new concepts of sustainable wastewater treatment/recovery facilities. The first part of the thesis presents the application of a model-based methodology based on systematic optimisation for improved understanding of the tight interplay between effluent quality, energy use, and fugitive emissions in existing WWTPs. Plant-wide models are developed and calibrated in an objective to predict the performance of two conventional activated sludge plants owned and operated by Sydney Water, Australia. In the first plant, a simulation-based approach is applied to quantify the effect of key operating variables on the effluent quality, energy use, and fugitive emissions. The results show potential for reduced consumption of energy (up to 10-20%) through operational changes only, without compromising effluent quality. It is also found that nitrate (and hence total nitrogen) discharge could be signficantly reduced from its current level with a small increase in energy consumption. These results are also compared to an upgraded plant with reverse osmosis in terms of energy consumption and greenhouse gas emissions. In the second plant, a systematic model-based optimisation approach is applied to investigate the effect of key discharge constraints on the net power consumption. The results show a potential for reduction of energy (20-25%), without compromising the current effluent quality. The nitrate discharge could be reduced from its current level to less than 15 mg/L with no increase in net power consumption and could be further reduced to <5 mg/L subject to a 18% increase in net power consumption upon the addition of an external carbon source. This improved understanding of the relationship between nutrient removal and energy use for these two plants will feed into discussions with environmental regulators regarding nutrient discharge licensing.The second part of the thesis deals with the application of a systematic, model-based methodology for the development of wastewater treatment/resource recovery systems that are both economically and environmentally sustainable. With the array of available treatment and recovery options growing steadily, a superstructure modeling approach based on rigorous mathematical optimisation provides a natural approach for tackling these problems. The development of reliable, yet simple, performance and cost models is a key issue with this approach in order to allow for a reliable solution based on global optimisation. it is argued that commercial wastewater simulators can be used to derive such models. The superstructure modeling framework is also able to account for wastewater and sludge treatment in an integrated system and to incorporate LCA with multi-objective optimisation to identify the inherent trade-off between multiple economic and environmental objectives. This approach is illustrated with two case studies of resource recovery from industrial and municipal wastewaters. The results establish that the proposed methodology is computationally tractable, thereby supporting its application as a decision support system for selection of promising wastewater treatment/resource recovery systems whose development is worth pursuing. Our analysis also suggests that accounting for LCA considerations early on in the design process may lead to dramatic changes in the configuration of future wastewater treatment/recovery facilities.Open Acces

Towards the synthesis of wastewater recovery facilities using enviroeconomic optimization

The wastewater treatment industry is undergoing a major shift towards a proactive interest in recovering materials and energy from wastewater streams, driven by both economic incentives and environmental sustainability. With the array of available treatment technologies and recovery options growing steadily, systematic approaches to determining the inherent trade-off between multiple economic and environmental objectives become necessary, namely enviroeconomic optimization. The main objective of this chapter is to present one such methodology based on superstructure modeling and multi-objective optimization, where the main environmental impacts are quantified using life cycle assessment (LCA). This methodology is illustrated with the case study of a municipal wastewater treatment facility. The results show that accounting for LCA considerations early on in the synthesis problem may lead to dramatic changes in the optimal process configuration, thereby supporting LCA integration into decision-making tools for wastewater treatment alongside economical selection criteria

Model-based methodology for plant-wide analysis of wastewater treatment plants: Industrial case study

© IWA Publishing 2015.This paper presents the application of a model-based methodology for improved understanding of the tight interplay between effluent quality, energy use, and fugitive emissions in wastewater treatment plants. Dynamic models are developed and calibrated in an objective to predict the performance of a conventional activated sludge plant owned and operated by Sydney Water, Australia. A scenario-based approach is applied to quantify the effect of key operating variables on the effluent quality, energy use, and fugitive emissions. Operational strategies that enable a reduction in aeration energy by 10-20% or a reduction of total nitrogen discharge down to 3 mg L-1 are identified. These results are also compared to an upgraded plant with reverse osmosis in terms of energy consumption and greenhouse gas emissions. This improved understanding of the relationship between nutrient removal, energy use, and emissions will feed into discussions with environmental regulators regarding nutrient discharge licensing

Preparation and characterization of biocomposite film made of activated carbon derived from microalgal biomass: An experimental design approach for basic yellow 1 removal

The adsorbent is typically used in the form of a fine powder, which can pose challenges when attempting to recover from the liquid after use. This issue has been addressed by encapsulating the fine powder in a biopolymeric material to create a biocomposite film. In this study, activated carbon (AC) powder derived from microalgal biomass and pectin were used to produce this biocomposite film. This film was employed as an adsorbent to remove basic yellow 1 (BY) dye from a liquid solution. The biocomposite film underwent characterization using a gas sorption analyzer, Fourier transform infrared spectrometry, and field emission scanning electron microscopy. The point of zero charge and mechanical properties were also determined. The impact of various factors, including contact time, initial pH, initial dye concentration, and temperature, on BY uptake were investigated. The BY uptake reached equilibrium at 540 min, and the monolayer BY uptake was 57.75 mg/g. Experimental design and response surface methodology were utilized to identify the key factors affecting BY uptake and determine the optimal levels of these factors for maximum BY uptake. Statistical analysis of the derived model yielded an R2 of 0.9997 and a p-value of 9.89 × 10−5, indicating that the optimal conditions were achieved under specific conditions: a solution pH of 2.0, an initial BY concentration of 250 mg/L, and operating temperature of 320 K. These results suggest that the low-cost biocomposite film developed in this study has the potential to effectively remove BY from industrial wastewater