Integrated Water Networks Research Articles

Global optimization for large‐scale water network synthesis based on dynamic partition and adaptive bound tightening

AbstractThe synthesis of large‐scale integrated water networks is typically formulated as nonconvex mixed‐integer quadratic constrained programming (MIQCP) or QCP problems. With the complexity arising from bilinear terms in modeling mass flows of contaminants and binary variables representing the presence of units or streams, numerous local optima exist, thus presenting a significant optimization challenge. This study introduces a deterministic global optimization algorithm based on mixed‐integer programming (MIP) to tackle such problems. The approach involves dynamically strengthening the relaxed problems to converge towards the original problems. A simultaneous partition strategy is proposed combining locally uniform division with dynamic partitioned variables choosing. Furthermore, several adaptive bound contraction schemes are introduced to efficiently manage the size of the relaxed problems, assisting in accelerating the solution process. The algorithm's effectiveness and robustness are demonstrated with a large test set, showing superior performance compared to commercial solvers specifically on MIQCP problems.

Water network integration for industrial park based on numerical indicators

This paper presents a numerical approach for water network integration of industrial park. A new numerical indicator General Treatment Potential (GTP) is proposed to reflect the general potential of the source streams to be treated by the treatment unit. To design the public distributed treatment system, the source streams are arranged in descending order of their GTP values, and treated in turn. To design the reused network in each plant, the treated streams are added into the plant as source streams, and reused by the demand streams. The final integrated water network can be obtained in several iterations. Three examples with two cases, network retrofitting and network design, are investigated to show the proposed approach. The results show that the proposed design procedure can reduce the freshwater consumption, cut down the annualized cost, or simplify the structure of the water network in industrial park.

Graph neural network for integrated water network partitioning and dynamic district metered areas

Water distribution systems (WDSs) are used to transmit and distribute water resources in cities. Water distribution networks (WDNs) are partitioned into district metered areas (DMAs) by water network partitioning (WNP), which can be used for leak control, pollution monitoring, and pressure optimization in WDS management. In order to overcome the limitations of optimal search range and the decrease of recovery ability caused by two-step WNP and fixed DMAs in previous studies, this study developed a new method combining a graph neural network to realize integrated WNP and dynamic DMAs to optimize WDS management and respond to emergencies. The proposed method was tested in a practical case study; the results showed that good hydraulic performance of the WDN was maintained and that dynamic DMAs demonstrated excellent stability in emergency situations, which proves the effectiveness of the method in WNP.

Heat Integrated Water Regeneration Network Synthesis via Graph-Theoretic Sequential Method

The integration of multiple resources conservation networks is necessary to attain the ever-stringent sustainable goals. This work takes initiatives to develop a heat integrated water network via a proposed P-graph-based sequential methodology. In the first step, a set of feasible water regeneration networks is generated using the conventional P-graph framework. Then, the obtained feasible networks will be used as the inputs in the second stage which aims to generate various sets of feasible heat exchanger networks. It is worth noting that the second model is solved by an extended P-graph framework (P-HENS) for combinatorial process network optimization. The solutions are then ranked based on the total network cost. To demonstrate the effectiveness of the proposed method, a typical water regeneration network (three sources and three sinks) with multi-contaminants is used. The results show a total of 103 feasible water network structures (water network cost ranging from 0.76 M$/y to 1.18 M$/y). Thereafter, a list of feasible HIWRN can be determined using P-HENS. The top four HIWRNs which offer similar total network cost (~1.639 M$/y) are demonstrated. This proposed method provides valuable insights that allow decision-makers to further select the optimal solution which may be more beneficial as compared to the one obtained via conventional methods.

Ekonomski aspekt ekološko održivih procesa i implementacija koncepta nulte emisije u hemijskoj industriji

One of the key issues in the field of process systems engineering is the issue of sustainability. In addition to economic and energy efficiency, the processes must also be environmentally sustainable, which will minimize the harmful impact on the environment. For this purpose, various methods are used that are based on the use of process heuristics, thermodynamic analysis and mathematical programming. In a systematic way, they enable the identification of places of inefficient use of raw materials, water and energy, as well as minimizing the discharge of waste streams from the process, while respecting the principles of reuse, regeneration, recirculation and prevention of pollution at source. From all the above, it can be concluded that systemic methods are of great importance in the development of environmentally sustainable processes and the implementation of the concept of zero emissions in the chemical industry. The paper presents the possibility of obtaining a conceptual solution in which the complete integration of water in the process (zero liquid discharge) is achieved on a concrete example of designing and optimizing an integrated water network based on superstructure and mathematical programming.

Integrated Water Management at the Peri-Urban Interface: A Case Study of Monterey, California

Climate change, drought, and chronic overdraft represent growing threats to the sustainability of water supplies in dry environments. The Monterey/Salinas region in California exemplifies a new era of integrated or “one water” management that is using all of the water it can get to achieve more sustainable supplies to benefit cities, agriculture, and the environment. This program is the first of its kind to reuse a variety of waters including wastewater, stormwater, food industry processing water, and agricultural drainage water. This study investigates the partnerships, projects, and innovations that shape Monterey’s integrated water network in order to better understand the challenges and opportunities facing California communities as they seek to sustainably manage peri-urban water supplies. Water reuse in the Monterey region produces substantial economic and environmental benefits, from tourism and irrigation of high-value crops to protection of groundwater and increases in environmental flows and water quality. Water resource managers in other communities can learn from Monterey’s success leveraging local needs and regional partnerships to develop effective integrated water solutions. However, key challenges remain in resolving mismatched timing between water availability and demand, funding alternative water supplies, and planning effectively under uncertainty. Opportunities exist to increase Monterey’s recycled water supply by up to 50%, but this requires investment in seasonal storage and depends on whether desalination or additional recycling forms the next chapter in the region’s water supply story. Regulatory guidance is needed on seasonal subsurface storage of tertiary-treated recycled water as distinct from potable recharge. By increasing the supply of recycled water to Monterey’s indirect potable use system, the region’s potential need for seawater desalination may be delayed as much as 30 years, resulting in cost and energy savings, and giving the opportunity to resolve present planning concerns.

Design of heat integrated water networks with multiple contaminants

The heat integrated water networks have the features of complex network structure and high costs. To overcome the problems, this paper presents a new design method for heat integrated water networks with simple structure and low costs. The proposed method includes two steps: the water-using network is designed first by considering the concentration specifications of water-using processes, which is reflected by the values of concentration potentials. Then, the heat exchanger network can be designed based on the water network obtained in the first step. Self heating strategy is adopted in the design of heat exchanger network to reduce the complexity of the network. Examples are illustrated to demonstrate the effectiveness of the proposed method. The network structures obtained by using the proposed design method are simple, and the total annual costs calculated in this paper are comparable to that of literature results.

Energy and Water Management for Industrial Large-Scale Water Networks: A Systematic Simultaneous Optimization Approach

Water and energy management issues in process industries are generally related to the synthesis of heat integrated water networks (HIWN), because water and energy are inextricably intertwined in process water networks. The aim of this study is to present a novel mathematical programming model for HIWN synthesis problems and develop an efficient solution strategy. This research is an extension of our previous work, where the targeting of heat integrated water-using networks (HIWUN) has been addressed. In this model, wastewater treatment units and multiple contaminants are embedded, and the total annual cost (TAC) is optimized rather than targeting a simplified TAC. What is more, a three-step solution strategy is proposed to guarantee obtaining promising solutions. The freshwater consumption, the relaxed TAC (rTAC), and the TAC are optimized successively. Good initial points for the rigorous HIWN model in the last step can be generated by the minimizing the rTAC. Four examples including two large-scale exam...

Sequential synthesis of heat integrated water networks: A new approach and its application to small and medium sized examples

This paper presents a new step-wise sequential solution strategy for the synthesis of heat integrated water networks (HIWNs) comprising of two mathematical models. The first model minimizes water and energy costs. The optimal freshwater and water flow rates within the HIWN are determined from this model. Using these optimal flow rates, different configurations of HIWN are evaluated for the purpose of heat integration. The second model is the stage-wise heat exchanger network (Yee and Grossmann, 1990), which is solved for each of the evaluated network configuration in a sequential manner. Using this proposed strategy, a set of locally optimal HIWNs are produced and the best one is chosen based on the minimum total annual cost (TAC). The proposed sequential strategy is applied to small and medium sized examples in the literature. The results show that the proposed new sequential solution strategy can be successfully applied to small and medium sized HIWN problems.

An automated composite table algorithm considering zero liquid discharge possibility in water regeneration–recycle network

In this study, a novel Automated Composite Table Algorithm (ACTA) is developed for targeting the water regeneration–recycle network of single contaminant problem. The ACTA is based on Pinch Analysis, but is automated by taking into consideration the possibility of zero liquid discharge (ZLD) for the water network. In the existing literature, the targeting procedure for ZLD network is based on the graphical tool of Limiting Composite Curve (LCC). However, identification of key parameters (i.e. freshwater, wastewater, regenerated water flowrates, along with pre-regeneration concentrations) is very tedious for highly integrated water network system. The magnification around the turning point of LCC is required to identify the correct pinch points and targeting procedure is done iteratively until the reliable network targets can be determined. These limitations are now overcome by the ACTA, which is an improved version of Composite Table Algorithm that is capable of identifying key parameters algebraically for a given post-regeneration concentration. The newly developed ACTA is capable of handling a wide range of problems including ZLD and non-ZLD network, for both fixed load and fixed flowrate problems.

Optimal Synthesis of Refinery Property-Based Water Networks with Electrocoagulation Treatment Systems

This paper presents an optimization approach to the incorporation of electrocoagulation in the design of integrated water networks for oil refineries. A disjunctive programming formulation is developed to minimize the cost of the water-management system while including the characteristics of process water streams, recycle, reuse, and treatment of wastewater streams, performance of candidate technologies, and composition and property constraints for the process units and the environmental discharges. The performance of electrocoagulation was related to temperature pH and the concentration of phenols and sodium chloride. Ancillary units including pH adjustment, reverse osmosis, and heat exchangers were used to support the electrocoagulation unit. Two case studies are presented to show the applicability of the proposed model and the feasibility of using electrocoagulation as part of an integrated water management scheme for oil refineries.

Simultaneous optimization of water and energy within integrated water networks

This contribution presents the synthesis of heat-integrated water-using and wastewater treatment networks (HIWTNs). The superstructure proposed includes process water-using units, wastewater treatment (regeneration) units, and heat exchangers (HEs) as well as all the new opportunities for water and heat integration within the overall network. A two-step solution strategy is proposed for the subsequent solving of two nonlinear models and the identifying of a set of good locally optimal solutions. The targeting model is solved during the first synthesis step thus minimising the operating cost of the network and providing an initialisation, as well as good upper-bounds for freshwater and utilities consumption for the second model. The objective of the second synthesis step is to synthesise HIWTNs simultaneously by minimising total annual cost (TAC). This research was an extension of our previous works and a follow-up on our recent studies, where we addressed the synthesis problems of HIWTNs but now using a different superstructure (e.g. multiple choices mixing and the splitting of streams allowing for additional heat integration within the overall network) and a more efficient solution strategy from the point of generating of multiple solutions. We solved two literature and two newly introduced examples in order to demonstrate the applicability of the proposed strategy. Improvements in the results were achieved using the studied literature examples of HIWTNs.

Fixed-flowrate total water network synthesis under uncertainty with risk management

Abstract This work addresses the problem of integrated water network synthesis under uncertainty with risk management. We consider a superstructure consisting of water sources, regenerators, and sinks that leads to a mixed-integer quadratically-constrained quadratic program (MIQCQP) for a fixed-flowrate total water network synthesis problem. Uncertainty in the problem is accounted for via a recourse-based two-stage stochastic programming formulation with discrete scenarios that gives rise to a multiscenario MIQCQP comprising network design in the first stage and its operation in the second stage acting as recourse. In addition, we extend the model to address risk management using the Conditional Value-at-Risk (CVaR) metric. Because a large number of scenarios is often required to capture the underlying uncertainty of the problem, causing the model to suffer from the curse of dimensionality, we propose a stepwise solution strategy to reduce the computational load. We illustrate this methodology on a case study inspired from the water network of a petroleum refinery in Malaysia. The presence of nonconvex bilinear terms necessitates the use of global optimization techniques for which we employ a new global MIQCQP solver, GAMS/GloMIQO and verify the solutions with BARON. Our computational results show that total water network synthesis under uncertainty with risk management problems can be solved to global optimality in reasonable time.

A master–slave solving method with adaptive model reformulation technique for water network synthesis using MINLP

A unified mixed-integer nonlinear programming (MINLP) model is developed for process synthesis of integrated water networks, where water-using processes and treatment operations are combined in a single network. Pump and pipe costs and different treatment technologies can also be included in the unified MINLP model. A master–slave solving method is proposed along with a heuristic method dealing with integer variables in the outer loop and a gradient-based method optimizing nonlinear programming (NLP) in the inner loop. An adaptive model reformulation module is developed in the middle layer to bridge the inner and outer loops. By exploiting the structure knowledge of the MINLP model for the water network (WN) synthesis, this module automatically simplifies the NLP model in both dimensionality and complexity. It helps to generate the most concise NLP model for the inner loop optimization. Good performance of the proposed method is demonstrated through examples.

System analysis of total water systems for water minimization

System-wide analysis of water systems to minimize water use in process industries has been carried out when charges for effluents from the process are simultaneously considered with cost of freshwater intake and in-house water treatment in the design of water and effluent systems. It has been demonstrated that the degree of wastewater regeneration and recycling is heavily dependent on the charges associated wastewater effluent. The reusability of water and its techno-economic impacts are examined with both a graphic-based manual technique and an automated design method using mathematical optimization, with which conceptual insights are sought in a systematic manner to evaluate different integrated options including water reuse, regeneration and recycling. For the optimization model, new solution strategy has been proposed for solving the MINLP problem of total water systems which carries out rigorous economic trade-offs existed in an integrated water network, together with wastewater charges.

Integrated water networks optimisation under uncertainty

An automated design method for the water networks under uncertain process conditions has been developed. To deal with the uncertainty problem, the installation of buffer tank and the installation of supplementing pipelines are systematically considered in the design of water networks. The cost-effective and feasible distribution and reuse of water within the network is identified from the superstructure-based optimisation model, with which all the operational constraints and fluctuating operating characteristics for water-using operations are fully and simultaneously reflected. The optimisation framework provides rigorous economic evaluation of the network through trade-off between operating and capital costs under uncertainty. The conceptual insight related to the design of water networks is incorporated in developing a reliable solution strategy which can effectively deal with the difficulty in solving the mixed-integer nonlinear programming problem. Case studies are given to validate the proposed model and demonstrate the importance of considering uncertain process conditions in the design and optimisation of water networks.

Energy and Water Optimization in Biofuel Plants

In this paper we address the topic of energy and water optimization in the production of bioethanol from corn and switchgrass. We show that in order for these manufacturing processes to be attractive, there is a need to go beyond traditional heat integration and water recycling techniques. Thus, we propose a strategy based on mathematical programming techniques to model and optimize the structure of the processes, and perform heat integration including the use of multi-effect distillation columns and integrated water networks to show that the energy efficiency and water consumption in bioethanol plants can be significantly improved. Specifically, under some circumstances energy can even be produced and the water consumption can be reduced below the values required for the production of gasoline.

Optimization of Total Networks of Water-Using and Treatment Units by Genetic Algorithms

The optimization of an integrated network of water-using (WU) and treatment (TU) units is addressed in this paper, by targeting for maximum treated water reuse as a considerably better alternative to fresh water consumption. An optimal integrated water network (WN) is an oriented graph, starting with inlet contaminant free WUs and then the other WUs ranked by a certain criteria. The outlet wastewater streams are either split to be reused by the next WUs in sequence or sent to treatment. The mathematical model of the integrated WN is based upon total and contaminant species mass balances for each and every WU/TU which is restricted with respect to the inlet and outlet contaminant concentrations. The performance of the approach is tested on a synthetic example. Several scenarios were used, the results being analyzed in connection with the reduction of fresh water consumption and the increase of internal and treated water reuse.

Achieving Low Unaccounted-For-Water through Reliable Supply to Customers and Efficient Network Management

Since the early 1980s, PUB has been conscious of the need to manage the water supply network efficiently and to account for the amount of water distributed through the network. This concern is primarily motivated by PUB's goal to provide a high level of service to customers with reliable supply of water at affordable cost. With the strong support of the top management and the active participation of everyone in PUB, an Integrated Water Network Management System has been adopted to ensure that leakage in new networks is kept to a minimum through proper planning, design and the use of good quality materials that are installed with good workmanship. Losses in existing network are reduced through network management and leakage controls as well as accounting for water distributed with full and accurate metering. Consequently, these deliberate efforts have enabled Singapore to achieve one of the lowest Unaccounted-For-Water in the world (below 5%).

Synthesis of non-isothermal heat integrated water networks in chemical processes

This paper presents a new approach for the simultaneous synthesis and optimization of heat integrated water networks. A new superstructure for heat exchanger network (HEN) synthesis is proposed. The procedure is based on mixed integer non-linear mathematical programming (MINLP). Four relevant examples are presented to illustrate various aspects of the proposed approach.