Two thirds of the earth’s surface is covered by water and the human body consists of 75% of it. It is evidently obvious that water is one of the key elements responsible for life on earth. Contrary to the past, the current highly technological society has become destructive to this miracle of life. The natural heritage (rivers, seas and oceans) has been exploited, maltreated and polluted. Today, the water is contaminated with hundreds of toxins and pollutants and has become a chemical cocktail that is often inapt for human consumption. It is a strong perception that if water contamination continues (without any treatment of water to reuse it or purify it), then pure water may become the medicine of the future. Moreover, we not only need potable water, we also require water to be able to operate our daily processes and industry.
We can distinguish two major water treatment needs: 1) surface and ground water treatment for drinking water or process water production, 2) treatment or processing of different wastewaters for reuse/recycling of the water. In the following, the general characteristics of both types of feed water are briefly described.
Surface and ground waters
The wide range of contaminants discharged to surface waters can be grouped into broad classes, as shown in table 1. Domestic sewage and industrial wastes are point sources because they are usually collected by a network of pipes and conveyed to a single point of discharge into the receiving water. Urban and agricultural runoff is characterized by multiple discharge points, known as non-point sources. Contaminants frequently attach to soil and flow with runoff that drains to lakes and ponds. Due to its uncontrolled location, non-point source pollution presents the greatest hazard to surface water quality.
Table 1. Main water contaminants classifications and their major sources.
|Point sources||Non-point sources|
|Toxic organic chemicals||×||×||×|
The characterstics of waste water varies from location to location depending upon the population, land uses, ground water levels, and type of industry. Domestic waste water contains typical wastes from the kitchen, bathroom, and laundry etc.. Industrial waste water varies with the activity of that specific industry that generates the waste.
Usually, waste water is characterized in terms of its physical, chemical and biological properties.
Physically, waste water has, in the majority of cases, a gray color, a musty odor, and normally contains solids in a concentration of ~0.1% (~99.9% water content). The solids can be suspended as well as dissolved substances. Chemically, waste water is a solution of organics (carbohydrates, proteins, fats and greases, surfactants, oils, pesticides, phenols, etc.) and inorganics (heavy metals, nitrogen, phosphorus, inorganic acids, inorganic bases, sulfur, chlorides, alkalinity, etc.) as well as various gases (hydrogen sulfide, methane, ammonia, oxygen, carbon dioxide and nitrogen). Biologically, waste water can comprise various microorganisms that are classified as Protista (bacteria, fungi, protozoa, and algae), plants (ferns, mosses, seed plants and liverworts), and animals (invertebrates and vertebrates). Moreover, waste water may also contain many pathogenic organisms, which commonly originate from humans who are infected with disease or who are carriers of a disease.