Water problems in the future will become more intense and more complex. Our increasing population will tremendously increase wastes, primarily sewage (污物). On tile other hand, increasing demands for water will decrease substantially the amount of water available for diluting (稀释) wastes. Rapidly expanding industries which involve more and mine complex chemical processes will produce large volumes of liquid wastes, and many of these will contain chemicals which are noxious. To feed our rapidly expanding population, agriculture will have to be intensified. This will involve ever-increasing quantities of agricultural chemicals. From this, it is apparent that drastic steps must be taken immediately to develop correct measures for the pollution problem.
There are two ways by which this pollution problem can be solved. The first way is to de- crease their pollution hazard. This involves the processing of solid wastes "prior to" disposal and the treatment of liquid wastes.
A second approach is to develop an economic use for all or a part of the wastes. Farm manure (肥料) is spread in fields as a nutrient or organic supplement. Effluents (废液) from sewage disposal plants are used in some areas both for irrigation and for the nutrients contained. Effluents from other processing factories may also be used as a supplemental source of water. Many industries, such as meat and poultry processing factories, are currently changing former waste products into marketable by-products. Other industries are economic uses for waste products.
By writing the passage, the author wants to ______