Review of Greywater Reuse by Amit Gross, Adi Maimon, Yuval Alfiya, and Eran Friedler

According to a United Nations estimate (2007), approximately one-fifth of the world’s population is facing water shortage. In reality, this figure is much higher, depending on how water shortage in defined. Further, water shortage is going to become much more severe in the years ahead because of increasing population; rising standard of living; growing need for greater food production, energy generation, and industrial production; urbanization and land use change; higher waste disposal requirements; and climate change. Sustainable water availability requires efficient water use and reuse. Days of wastage of water are long gone. The search for efficient water use practices motivated the authors to explore greywater. To that end, treatment facilities were examined, treatment systems were developed, and environmental and health risks due to greywater at different treatment levels were quantified. Although millions of people use greywater for irrigation and flushing toilets, and scores of companies have developed recycling schemes, information on greywater reuse is still scanty for public consumption and information on the Internet is not always reliable. Reviewing scores of studies on greywater reuse from around the world, the authors have produced a unique and comprehensive book on greywater reuse. The book is a great contribution and the authors ought to be applauded for this excellent work. Providing a short introduction about the book and clarifying that it has Israeli slant, the contents of the book are described in seven chapters.

Chapter 1 deals with greywater characteristics. It first discusses the factors that influence the nature of greywater, including flows contained in greywater, source of greywater, cultural variables and characteristics of occupants, climate and geographic variables, supply pipes and greywater collection piping, and quality of the source water. It then goes on to discussing physical and chemical characteristics, sources of greywater, diurnal pattern of greywater flows, diurnal changes in greywater characteristics, and synthetic greywater. The chapter is concluded with a brief summary. This is a very comprehensive and well-written chapter.

Greywater treatment constitutes the subject matter of Chapter 2. Outlining the challenges in treating greywater, it first discusses treatment principles encompassing physical treatment, chemical treatment, biological treatment, nitrogen removal, and phosphorus removal; then discusses treatment technologies, including the use of untreated greywater, constructed wetlands, activated sludge, rotating biological contactor, and membrane bioreactor. Next it discusses disinfection, including disinfectant concentration and contact time, disinfection with chlorine, disinfection using ozone, disinfection using stabilized hydrogen peroxide, disinfection using ultraviolet (UV) radiation, and factors affecting disinfection efficiency. The chapter is concluded with a discussion of comparison of different technologies. On the whole the chapter is well written and is highly informative.

Chapter 3 deals with greywater usages. It discusses greywater reuse for flushing toilets and garden irrigation. It is a short chapter but highly informative and useful. The authors emphasize that proper planning is the key to greywater reuse and will significantly reduce potential hazards to human health and environment.

Risk assessment and management are described in Chapter 4. The chapter starts out with a discussion of risk management comprising five components: hazard identification, setting tolerable risk levels and associated targets, risk assessment, measures for achieving targets, and critical control points. It then goes on to discussing each of these components in detail. It is a very well-written chapter.

Chapter 5 deals with policy and legislation. Providing a brief background to legislative and political issues associated with greywater reuse, it first provides a comparative review of greywater legislation with an attempt to reconcile differing regulatory messages, including the U.S. experience, Australian experience, and European experience. Then, it discusses setting standards and strategies to manage risk involved in greywater, including management strategies, enforcement and supervision, and standardization and technical aspects of greywater treatment system and greywater reuse. International regulations versus risk assessment and legislation in Israel are discussed next. The chapter is concluded with an appendix tabulating legislation in Australia, Great Britain, and three U.S. states. The treatment in the chapter is quite comprehensive.

Perceptions and attitudes toward greywater recycling are reviewed in Chapter 6. Beginning with a discussion of the importance of public attitudes and perceptions regarding greywater recycling, it goes on to discussing the key factors that shape these attitudes and perceptions with a review of literature from around the world, including Great Britain, Spain, Oman, Australia, and Israel. For Australia, the review includes water recycling as a whole and gives factors that explain the disparity between the overwhelming support and the much lower rate of actual wastewater recycling technology adoption and reuse. The authors deal with the Israel case more thoroughly, which includes issues such as low contact but high support; not healthy, no thanks; not in my backyard; high economic gain equals high support; awareness does not equal support; I will make my own decision, thanks; do not know but support; population; and rationalization for support. The chapter is concluded with an outline of future research.

The last chapter, Chapter 7, is on technoeconomic aspects of greywater reuse. It discusses basic considerations, calculation of annual cost of greywater separation and treatment, comparison of three biological treatment technologies as a case study, benefit, examination of economic feasibility of greywater treatment and reuse; and examination of the payback period of the initial investment in the system. The chapter provides a comprehensive discussion.

The book is summarized with a restatement of its aim of pooling together scientific information on greywater and its reuse. It reinforces that with proper planning greywater can significantly contribute to alleviating water shortages at individual, regional, and national levels. This is an excellent book with a thorough treatment of greywater and its reuse. The book will be useful to those who would want to understand greywater and its many facets, such as policy makers, lawyers, economists, agriculturists, and engineers.