International Research on Recycling Living and Industrial Water (1)

Introduction

Natural water cycle

In nature, water, like energy, can neither be created nor lost, but can only be transformed from one form to another. In the natural water cycle, most of the rain falling on the ground returns to the atmosphere through the evaporation of vegetation. Some rainwater seeps into the aquifer, and some rainwater flows to the river as runoff and enters the ocean. It finally returns to the surface as rain by evaporation. A small part of the water used as drinking water for wildlife is purified through natural processes.

The water in the world is almost all saline (97%). In the remaining 3% of the water, 2/3 of the snow and ice exist in the polar and alpine regions. Only about 1% of the world's water exists in the form of liquid fresh water. Of these, more than 98% of freshwater is groundwater, and less than 2% of freshwater is available river and lake water, so liquid freshwater is a very limited resource. (Bouwer 2000)

Changed water cycle

Humans have imposed many new water cycle factors that have led to significant changes in the natural circulation of water. The imposed water circulation factors are as follows:

· Capture river and groundwater as town and agricultural water · Treated and untreated sewage return to the river · Recycled wastewater for beneficial recycling · Where fresh water is scarce Desalination of brine

Groundwater is the main water resource in many parts of the world. The rate of exploitation of groundwater often exceeds the rate of recharge, so groundwater levels are declining. The decline of salty sea surface in Central Asia due to the use of surface water for irrigation can be used as an extreme example to illustrate the problems associated with falling water levels. This place was once a prosperous fishing area, but now the Aral Sea has been reduced to a small part of its original size. The former seaside city is now thousands of kilometers away from the sea. It can be seen that the impact of this issue on the economy, society and the environment is serious.

The impact of urban development on the water cycle is also serious. Water withdrawal from the urban water supply reduces the flow of river water. At the same time, the discharge of rainwater and sewage that carry large amounts of pollutants causes the water quality of the river to decline. The water quality of highly developed rivers in urban areas in their catchment areas has become more severe.
The problem of the shortage of exposed water

The worldwide supply of fresh water is limited and is threatened by pollution. The increasing demand for agriculture, industry, and urban water supplies has led to a limited distribution of fresh water resources. In many countries, available freshwater resources have been heavily exploited and in some cases may have been overexploited. In order to avoid water crisis, many countries must protect water resources, manage water supply and demand, reduce pollution and reduce the environmental impact of a growing population (Hinichsen et al 1999). E.g:

• In the Nile Valley below the Aswan Dam, the current water demand exceeds the maximum water supply from the Aswan Dam. The shortage is supplemented by the reuse of sewage and discharged irrigation drainage (Croce 1998).

• The lack of adequate water supply is the most important limiting factor in the socio-economic growth of South Africa in the 21st century. Existing plans indicate that the demand for water after 2020 will exceed the available water supply (Odendaal et al 1998).

Water reuse meets world water demand

Water reuse is a valuable water resource. After the water is used up, it is no longer thrown away but it is treated rationally and reused for secondary use. This will reduce the need for high quality fresh water. The reuse of water improves the reliability of water supply, and it can meet the greater needs of mankind with less fresh water, thus alleviating the impact of human survival on the world's water environment. The conversion of the old "use once and then discharge" method into new sustainable "water-saving" methods of "protection, rational use, and recycling" will benefit the entire world.

Felicia Marcus, a former local EPA administrator in the arid western United States, said: "Water reuse is a key factor in managing our water resources. Through the protection and reuse of water, we can meet the needs of the environment, and Sustainable development and a successful economy."

Tom Hannigan is the chief executive officer (CEO) of California's Department of Water Resources. He describes water reuse as the "shining star" to meet California's future water needs. (to be continued)