The role of emergy in the analysis of water consumption in an industrial complex

Water stress is one of the most serious challenges facing the industrial sector in the near future. According to some estimates, about 48 countries will experience water stress by the year 2025. Furthermore, in a recent paper in Nature, Rockstrom and coworkers estimated that global water use has increased dramatically since the industrial revolution, to a current level of about 2,600 cubic kilometer per year, as compared to an estimated sustainable limit of 4000 cubic kilometers per year. In addition, the problem is compounded by climate change, which threatens to significantly change the geographic distribution of water supplies for industrial activities. Thus, the prospect of rising water cost and declining availability leads to serious economic concerns for industrial companies. This issue has led to increased research in process integration methodology to reduce their freshwater consumption, and improve industrial water utilization efficiency. The Middle East is one of the regions which faces water scarcity due to lack of rainfall; as a result, many of the countries there face the threat of chronic water shortage. An example is my home country, Iran, where insufficient supply and improper location of industries, as well as sporadic precipitation, make it among the most arid countries of the world. Apart from that, rapid increase in population from 10 million in 1925 to 68 million in 2005 causes the country to face serious challenges about water conservation as well as modification in current consumption trend. These trends make planning for efficient use of water resources important.

Many researchers have developed approaches to optimum water integration, based on either pinch analysis or mathematical programming. Recently, many researchers in various countries have also studied interplant or eco-industrial approaches for water and resource conservation. An eco-industrial park (EIP) consists of several plants which cooperate with one another through resource exchange to achieve common environmental goals such as reducing resource consumption or greenhouse gas emissions. Some studies, notably that of Marian Chertow in 2007, also discussed the importance of water as a starting point for more complex exchanges in EIPs. It is because wastewater exchange may facilitate developing trust among different companies within the EIP. Eventually, mature EIPs may deal with exchange of materials, in addition to water, among several firms. Although implementing an EIP could be costly, and even if it might be difficult to convince companies to participate, designing an optimum EIP with appropriate metrics for sustainability could maximize environmental benefits.

There are several methods which have been implemented to achieve optimum EIP design. However, most of these techniques design the optimum networks with some of the EIP streams based on minimizing water consumption or monetary cost, while few of them have dealt directly with “total” environmental impacts. For example, in 2008, the Korean researchers Lim and Park made use of carbon footprint as basis to design EIP networks. In 2003 in the USA, Lou et al. developed an approach for material exchange in EIP networks using the concept of “emergy,” a concept proposed by Howard Odum which computes the cumulative energy used directly and indirectly to produce a product or service. The purpose of emergy is to quantify the “true value” of a commodity based on natural resource flows, thus emergy can be used as a thermodynamically based measure of sustainability (for more information you can visit www.emergysystems.org). One implicit assumption is that most natural processes on earth are driven indirectly by solar energy. Thus, one of the most important reasons for using emergy in EIP is to consider externalities (e.g. natural inputs, environmental impacts) which are neglected in normal monetary computations used in conventional approaches.

Although some researchers criticize emergy as simplistic or misleading, it is undeniable that the natural resources are the basic components of any production and commodity. In my work at De La Salle University under the tutelage of Dr. Anthony Chiu and Dr. Raymond Tan, I use emergy as a basis to design optimum EIP for water reuse network. Actually, there were many researchers who have done related work previously; however, none of them have considered environmental activities as part of the whole system. In other words, there are other activities and inputs for EIP such as natural resource inputs for water, electricity, pipeline and wastewater treatment while the economic performance was the only attribute that is considered in most prior studies.  

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Mohammad Sadegh Taskhiri is a former research assistant at the Industrial Engineering Department of De La Salle University, Manila. He received his BS in Industrial Engineering from the Islamic Azad University of the Iran in 2006, and recently completed his MS in Industrial Engineering at De La Salle University. His current research work focuses on the role of emergy as means of measurement of the externalities and use of eco-efficiency to optimize natural resource consumption and green house gas (GHG) mitigation in industrial ecosystems. He now has six international conference papers, as well as one paper based on his thesis accepted for publication in the journal Clean Technologies and Environmental Policy. E-mail him at [email protected].