Water problem in the future will become more intense and more complex. Our increasing population will tremendously increase urban wasters, primarily sewage. On the other hand, increasing demands for water will decrease substantially the amount of water available for processing wasters. Rapidly expanding industries which involve more and more complex chemical processes will produce larger volume of liquid wasters, 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 serious steps must be taken immediately to develop corrective measures for the pollution problem. There are two ways by which this pollution problem can be settled. The first relates to the treatment of wastes to decrease their pollution danger. This involves the processing of solid wasters prior to disposal and the treatment of liquid wasters to permit the reuse of the water or minimize pollution upon final disposal. 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. Wastes from sewage disposal plants are used in some areas both for irrigation and for the nutrients contained. Wastes from other processing plants may also be used as a supplemental source of water. Many industries, such as meat and poultry processing plants, are currently converting former waste products into marketable byproducts. Other industries are exploring potential economic uses for their waste products. The phrase "prior to" in Paragraph 2 probably means______.