Wastewater reuse: a new approach to screen for designs with minimal total costs

Current process integration tools dealing with the generation of optimal wastewater reuse designs require a lot of effort for data acquisition and frequently suggest designs which are rejected by the process owners due to the ignored constraints or expensive piping needs. In this paper we present a mixed integer linear programming (MILP) model that overcomes both criticisms. Only easily accessible data such as process location, current water demand, and binary information on the reuse possibilities of wastewater streams are required. The total costs, comprising operating costs (freshwater, wastewater treatment, pumping) and investment costs (piping, holding tanks), are minimised for a given time horizon. One characteristic of calculating the piping cost is that splitting and merging of pipes are taken into account. The model was applied to an industrial case study for which several reuse designs were generated and discussed with regard to economical (payback time, investment costs), ecological (total flow rate), and technical aspects.     

水系统集成技术在甲醇厂的应用

水系统集成技术是把整个工业用水系统作为一个整体来看待,并考虑水质、水量的分配,从而使系统用水的重复利用率达到最大,同时废水排放量最小。甲醇企业是用水和废水排放的大户,将水系统集成技术应用于甲醇工业,具有重要意义。文中结合水系统集成技术的工业应用现状,总结了水系统集成技术在工业企业中应用的一般步骤,具体分为以下几步:选定目标系统,明确水源水阱,确定关键污染物组分和极限进出口浓度,生成初始网络和用水网络调优。并以某甲醇厂简化的用水系统为实例,采用文中所提出的一般应用步骤,对用水网络进行了优化,获得了新鲜水节水率达34.5%的节水效果。     

Optimal design of single‐contaminant regeneration reuse water networks with process decomposition

Water network with regeneration schemes (e.g., regeneration reuse, regeneration recycling) can reduce freshwater consumption further than water network merely with direct reuse. Regeneration reuse, compared with regeneration recycling, can additionally avoid unexpected accumulation of contaminants. Owing to these features, process decomposition can help to reduce freshwater usage and wastewater discharge of regeneration reuse water systems and achieve the results, which graphical method delivers. In this article, the effect of decomposition on water‐using process and further on regeneration reuse water system is briefly analyzed on the concentration‐mass load diagram. Then a superstructure and three sequential mathematical models, which take process decomposition into account, are in turn developed to optimize single contaminant regeneration reuse water systems. By several examples, the reliability of the models is verified. Moreover, several decomposition strategies are summarized to realize the regeneration reuse water network, which attains the targets from graphical method. The results indicate that postregeneration concentration has a major impact on the scheme of process decomposition. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Wastewater minimization in multipurpose batch plants with a regeneration unit: Multiple contaminants

Wastewater minimization can be achieved by employing water reuse opportunities. This paper presents a methodology to address the problem of wastewater minimization by extending the concept of water reuse to include a wastewater regenerator. The regenerator purifies wastewater to such a quality that it can be reused in other operations. This further increases water reuse opportunities in the plant, thereby significantly reducing freshwater demand and effluent generation. The mathematical model determines the optimum batch production schedule that achieves the minimum wastewater generation within the same framework. The model was applied to two case studies involving multiple contaminants and wastewater reductions of 19.2% and 26% were achieved.     

Mathematical modelling of sustainable wastewater reuse networks considering CO<Subscript>2</Subscript> emissions

Water resource management poses a challenge in the process industry because a large amount of water must be used, even when prices increase. Companies struggle to minimize consumption by reusing wastewater, and the resulting water-reuse-network problem has been actively investigated. With the rising impact of global climate change, it is necessary to develop a sustainable methodology to reduce carbon dioxide emissions in the process industry. This paper proposes a mathematical model for sustainable water reuse networks that explicitly considers CO₂ emissions. To construct a sustainable network, emissions due to the construction and operation of the water network and additional water demand due to CO₂ capture facilities are incorporated. Actual case studies of steel manufacturing processes and eco-industrial parks are presented to illustrate the applicability of the model.     

Positive and negative effects of excessive water reuse to be considered in water network synthesis

Water network synthesis has focused on maximizing water reuse to minimize freshwater consumption, even though the adverse effect of water use has not been examined until now. This study evaluates and analyzes the positive and negative effects of excessive water reuse on the environmental and economic performance of a water network system. Life cycle assessment and life cycle costing are used to evaluate the environmental impacts and economic costs of the three water systems with the different levels of water reuse. Networking for low water reuse enhances both environmental and economic performance of a water system. However, networking for excessive water reuse deteriorates the economic performance of the water system, even though this networking enhances its environmental performance. Therefore, the positive and negative effects of excessive water reuse should be taken into account in developing new pinch analysis methodologies and mathematical optimization models for water network synthesis.     

Simulation of mass exchange networks using modified genetic algorithms

The optimum water usage network leads to both a minimum of freshwater consumption and a minimum of generated wastewater. This work is to develop a mass-exchange networks (MENs) module for a minimum freshwater usage target. This module works as an interface to retrieve supplemental data of chemical processes from a process simulator and to communicate this to the genetic algorithm optimizer. A reuse system and a regeneration/recyclingsystem with a single contaminant are considered as approaches for freshwater minimization. In the formulated model, as mixed integer nonlinear programming (MINLP), all of the variables are divided into independent and dependent variables. The values of independent variables come from randomization, whereas the values of dependent variables come from simultaneous solutions of a set of equality constraints after assigning the values of independent variables. This method is applied to the steps of initialization, crossover and mutation. The MENs module is validated with a tricresylphosphate process consisting of five unit operations. Water is used to remove a fixed content of cresol. From the result, the module gives a reliable solution for freshwater minimization, which can satisfy mass balance and constraints. The results show that reuse and regeneration/recycling strategies can reduce freshwater consumption, including wastewater generated. Reuse cannot decrease the mass load of the contaminant, while regeneration/recycling can. In addition, regeneration requires less freshwater than the reuse process.     

水夹点分析与数学规划法相结合的用水网络优化设计

提出了水夹点分析和数学规划法相结合的用水网络最优设计法。水夹点分析基于对过程用水的理解,获得新鲜水用量目标并给出用水网络设计的基本规则。在此基础上建立过程使用新鲜水、排放废水和回用的各种可能匹配方案的用水网络超结构及其MINLP模型。既避免了用水夹点综合设计用水网络得不到真正意义上的最优解,又在一定程度上防止超结构规模过大,MINLP维数太高,求解困难。采用通用代数建模系统GAMS得到用水网络最优设计方案。文献中的应用实例表明,本文所提方法可充分发挥水夹点分析确定新鲜水用量或回用结构的简洁实用性和超结构MINLP寻求最佳方案的优点。     

Technical efficiency and cost analysis in wastewater treatment processes: A DEA approach

In light of the growing importance of water reuse as an alternative source of water resources in many regional areas, the objective of this paper is to analyse the efficiency of wastewater treatment plants as a basic requisite to improve the potential of the water reuse. The analytical benchmarking methodology Data Envelopment Analysis (DEA) is used to calculate efficiency measurements. An efficiency index is obtained for each plant by means of mathematical programming techniques, aiming to minimise the inputs used in the water treatment process. This indicator is used as a reference to analyse plants' activity through a series of variables including the size of the plant or its cost structure. Given the importance of wastewater treatment in the Valencia Region (Spain), empirical research has been carried out for 338 plants located in this area. We verify the fact that the largest plants run more efficiently than smaller plants, as was to be expected. At the same time, there is evidence that a series of representative variables in the treatment process are clearly linked to efficiency. Maintenance and waste management costs are the most important factors to explain the differences between plants in terms of efficiency. Finally, the benchmarking methodology (Data Envelopment Analysis) is confirmed as a very useful management tool for the study of wastewater sector.     

Synthesis of Water Utilization System Using Concentration Interval Analysis Method （Ⅱ） Discontinuous Process

The first part of the series of this article proposed a systematic method for the synthesis of continuous water-using system involving both non-mass-transfer-based and mass-transfer-based operations.This article,by extending the method,proposes a time-dependent concentration interval analysis（CIA）method to solve the problems associated with the synthesis of discontinuous or batch water-using systems involving both non-mass-transfer-based and mass-transfer-based operation.This method can effectively identify the possibility of water reuse and the amount of water reused under time constraints for minimizing the consumption of freshwater in single or repeated batch/discontinuous water-using systems.Moreover,on the basis of the heuristic method adapted from concentration interval analysis method for the continuous process network design,the network design for the discontinuous or batch process can be obtained through the designs for every time interval.Case study illustrates that the method presented in this article can simultaneously minimize the freshwater consumption in single or repeated batch/discontinuous water system and can determine a preferable storage tank capacity for some problems.     

基于浓度间隔分析的用水系统集成(Ⅱ)不连续过程

The first part of the series of this article proposed a systematic method for the synthesis of continuous water-using system involving both non-mass-transfer-based and mass-transfer-based operations.This article,by ex- tending the method,proposes a time-dependent concentration interval analysis(CIA)method to solve the problems associated with the synthesis of discontinuous or batch water-using systems involving both non-mass-transfer-based and mass-transfer-based operation.This method can effectively identify the possibility of water reuse and the amount of water reused under time constraints for minimizing the consumption of freshwater in single or repeated batch/discontinuous water-using systems.Moreover,on the basis of the heuristic method adapted from concentra- tion interval analysis method for the continuous process network design,the network design for the discontinuous or batch process can be obtained through the designs for every time interval.Case study illustrates that the method presented in this article can simultaneously minimize the freshwater consumption in single or repeated batch/discontinuous water system and can determine a preferable storage tank capacity for some problems.     

THE USE OF NONLINEAR PROGRAMMING TO OPTIMAL WATER ALLOCATION

Environmental protection, shortage of fresh-water and rising costs for wastewater treatment are all convincing motives for reducing fresh-water consumption and wastewater discharge of the chemical, petrochemical, petroleum refining and other process industries. Maximizing water reuse, regeneration re-use, and regeneration recycling within the chemical plant, as well as optimal distribution of waste streams for end-of-pipe treatment can reduce fresh-water usage and wastewater discharge, while they are also significant in shrinking capital investment in wastewater treatment systems.

Optimal assignment and design of water consuming, regenerating, and treatment systems is a complicated task that can be mathematically formulated as mixed integer non-linear programming (MINLP). In the present article the superstructure based 'Cover and Eliminate' approach with NLP is applied with the tools of the GAMS/M1NOS/CONOPT package and compared to previous results. After introducing the problem in the context of chemical process synthesis, a mathematical model is described and the use of the methodology is explained. Experience with the use of GAMS is discussed. Several case studies are solved including basic examples from the literature and their variants.

The main conclusion is that the application of the mathematical programming for the optimal water allocation problem is essential owing to the broad variety of the specification opportunities. The complex nature of re-use, regeneration re-use, and recycling with multiple pollutants and multiple treatment processes cannot be simultaneously taken into account by conceptual approaches. It is also shown that the assumption on the independency of contamination rates, generally applied in earlier works, are not necessarily valid; and the NLP approach can deal with the more reliable specifications.     

Energy and water supply,Orange County,California

In the service area of the Orange County Water District in Southern California there are 1.5 million people who rely upon a complex water supply system composed of local groundwater and imported water from the Colorado River and from Northern California. Every gallon of water distributed in the area requires the expenditure of energy to place the water at the point of demand. The water is either energized to pressure from groundwater or pumped great distances over the Mohave Desert or the length of the San Joaquin Valley and over the Tehachapi Mountains. Southern California is in a chronic drought condition, as the local supply can furnish only one-third of the annual demand. Because of the intense competition for supplemental water supplies throughout the state and the West in recent years, there has been a growing interest in recycling wastewater as a supplement for use in irrigation and groundwater recharge. This supply will also require energy for treatment and distribution.The purpose of this paper is to evaluate the energy requirements of all available water sources so as to provide our communities with a continuing supply at a reasonable cost. The energy necessary to produce a potable supply through wastewater reclamation and reuse, as practiced at Water Factory 21, is compared to the energy necessary to transfer water great distances through challenging terrains, such as that required by the Colorado River and State Water Project aqueduct systems. As energy supplies lessen and the costs of those remaining energy supplies increase, it is apparent that the incremental costs of energy to supply water will be the controlling factor in future water resource economics.     

Integrated concepts in water reuse: managing global water needs

Communities across the world face water supply challenges due to increasing demand, drought, depletion and contamination of groundwater, and dependence on single sources of supply. Water reclamation, recycling, and reuse address these challenges by resolving water resource issues and creating new sources of high-quality water supplies. The future potential for reclaimed treated effluent is enormous. Although water reclamation and reuse is practiced in many countries around the world, current levels of reuse constitute a small fraction of the total volume of municipal and industrial effluent generated. In addition, to meet their growing water supply needs, communities are considering other non-traditional sources of water such as agricultural return flows, concentrate and other wastewater streams, storm water, co-produced water resulting from energy and mining industries, as well as the desalination of seawater and brackish groundwater. Water reuse provides a wide range of benefits for communities, which translates into creating immense value for the public and the environment. The benefits of water reuse, however, can be difficult to quantify and often go unrecognized. One of the most significant benefits of water reuse is the value created by the inclusion of water reuse in integrated water resources planning and other aspects of water policy and the implementation of water projects resulting in the long-term sustainability of our water supplies. These integrated concepts, which involve the convergence of diverse areas such as governance, health risks, regulation, and public perception, also present a significant challenge to water reuse. These complex connections can assert equal influences on both the benefits and challenges associated with water reuse. In addressing these complex integrated issues, a number of significant barriers and impediments to the widespread implementation of water reuse projects arise. Numerous examples exist of barriers experienced by current water reuse projects around the world, including: the need for innovative technologies, technology transfer, and novel applications; the need for public education and increased public acceptance; better documentation of the benefits of water reuse; the lack of available funding for water reuse projects; working with the media; and the need for support by regulators and politicians. Integrated concepts can also be factors in a number of trends affecting water reuse globally. Current trends include addressing emerging pollutants of concern, the use of advanced wastewater treatments including membranes, indirect potable reuse, public perception, understanding the economics of water reuse, groundwater recharge and aquifer storage and recovery, salinity management (including concentrate disposal), increase in the use of “alternative sources”, environmental or natural system restoration, innovative uses of nonpotable water reuse, and decentralized and satellite systems. Since these trends are emerging developments in the field of water reclamation and reuse, there are a number of research needs associated with these topics. Research is needed to better understand the issues, to develop innovative technologies, and to develop tools and other assistance for communities and water agencies to implement successful water reclamation and reuse projects.     

污水回用网络优化设计的研究

在工业生产的各个用水过程中会产生大量污水，使污水最小化的一个有效的方法就是设计污水回用网络，以便使污水得到最大程度的回用，这样在满足用水要求的同时使新鲜水消耗最少，利用自适应模拟退火遗传算法对用水网络进行最优设计。     

Integrated water resource management through water reuse network design for clean production technology: State of the art

This article considers new and existing technologies for water reuse networks for water and wastewater minimization. For the systematic design of water reuse networks, the theory of the water pinch methodology and the mathematical optimization are described, which are proved to be effective in identifying water reuse opportunities. As alternative solutions, evolutionary solutions and stochastic design approaches to water system design are also illustrated. And the project work flow and an example in a real plant are examined. Finally, as development is in the forefront in process industries, this paper will also explore some research challenges encountered in this field such as simultaneous water and energy minimization, energy-pinch design, and eco-industrial parks (EIP).     

Process‐based graphical approach for simultaneous targeting and design of water network

A new process‐based graphical approach (PGA) is presented for the simultaneous targeting and design of water network. The PGA is extended from the limiting water profile which was developed for flow rate targeting for a water network. Via PGA procedure, apart from locating the minimum freshwater and wastewater flow rate targets, the water network that corresponds to the minimum flow rate targets is also synthesized simultaneously. The proposed approach handles both fixed load (including operations with water loss and/or gain) and fixed flow rate problems equally well. In addition, the approach can be used to synthesize direct reuse/recycle, regeneration reuse/recycling, and total water network. Furthermore, the proposed approach is applicable for water network with multiple freshwater sources. Three literature examples are presented to illustrate the proposed approach. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Synthesis of water networks considering the sustainability of the surrounding watershed

This paper presents a new mathematical programming model for the optimal synthesis of recycle and reuse networks considering simultaneously the integration of the water network system and the surrounding watershed to satisfy process and environmental constraints. The model considers the optimal location of the new industrial facility to integrate its wastewater discharge to the environment with the surrounding watershed through a disjunctive formulation. The pollutants discharged for the new plant are tracked simultaneously with the other discharges to the watershed (i.e., residential, sanitary, industrial and extractions), and the natural phenomena that affect the composition of the watershed (i.e., evaporation, filtration, etc.), in addition to the chemical reactions that are carried out in the rivers. The objective function consists in minimizing the total annual cost that is constituted by the installation of the new plant cost (including the transportation for raw materials, products and services, as well as the land cost), the wastewater treatment costs (including the piping cost) and the fresh sources cost. Two example problems were used to show the applicability of the proposed methodology.     

水挟点技术研究进展

废水减量是通过改进流程尽量以减少废水生成量而节约水资源的环保课题。在国外，水挟点技术（简写为ＷＰＴ），用于废水减量问题的研究，已经发展到一定深度，并已成功地用于多个工厂的废水减量问题。但是，在国内这方面的研究尚处于空白阶段。为了使广大科技工作者了解这方面的研究进展，本文着重介绍了水挟点技术的基本原理、发展过程、现状及展望。     

UASB-CASS-BAF工艺用于屠宰废水的中水回用

为了满足屠宰废水处理后的中水回用要求,实现屠宰废水的零排放,本工程采用UASB-CASS-BAF工艺对该废水进行治理。运行结果表明,该工艺处理效率高,出水水质稳定而且明显优于《肉类加工工业水污染排放标准》(GB 13457—1992),符合中水回用要求。