RESEARCH ON WATER COMPONENTS

The Biochemical oxygen demand (BOD) is the oxygen required for the biochemical decomposition of the organic matter in wastewater. It is determined by measuring the amount of oxygen used by decay microorganisms in a sample of the wastewater over a specific period of time, usually five days, at a specific period of time, usually five days, at a specific temperature, generally 68-degree farenheight or 20 degree Celsius.

The BOD is indicative of the impact that the wastewater can be expected to make on the oxygen content of the stream receiving the waste. The per capita contribution in the United States is about one sixth of a pound (0.075 kg) per day. In 100 gallons (378 liters) of wastewater per capita per day, the BOD amounts to a concentration of about 200 milligrams per liter (11.5 grams per gallon), nearly to 200 parts per million.

Suspended Solids

On the average, about one fifth of a pound (0.09kg) of suspended solids is added to wastewaters per capita per day in the United States. This results in a concentration of about 240 milligrams per liter (14 grains per gallon). The suspended solids are a burden in the receiving streams because of the BOD that the organic particles exert, because of the turbility the particles impart to the receiving water and because of the sludge deposits that may build up in the stream. The handling and disposal of the solids removed in treatment constitute a major function of wastewater treatment plants.

Suspended solids in wastewater are classified as either fixed or volatile. The fixed solids are essentially inert and the volatile solids make up the organic fraction that is suitable for biological degradation or incineration. Suspended solids may also be classified as either settleable or nonsettleable. The settleable solids can be readily removed by a period of quiescence in a sedimentation tank (primary treatment). The nonsettleable solids can be removed by other means (secondary treatment).

pH

pH is the negative logarithm of the effective hydrogen-ion concentration. In simple terms, pH refers to whether the water is acidic or alkaline. The pH scale goes from 0 to 14, with a pH of 7 generally considered neutral. Water with a pH below 7 is considered acid while that with a pH of above 7 is considered alkaline.

With respect to acidity or alkalinity, domestic wastewaters are generally neutral. Industrial wastes, however, may make the water too acidic or too basic. When this happens, special pretreatment is needed before the waters undergo biological treatment, because extremes of acidity or alkalinity are toxic to the microorganisms responsible for biological treatment.

Certain areas lacking limestone are notorious for having low pH (acidic water). It corrodes the metal parts of the plumbing system and as a result, high levels of lead may be found when water stands in the pipes overnight. Typically, waters with a low pH is very low in hardness and is considered naturally soft.

The Environmental Protection Agency (EPA) considers pH to be a secondary contaminant with an acceptable range of 6.5 to 8.5. In some countries, private wells nearly always have pH problems. If non-corrosive, plastic piping is used in the home, low pH has no adverse effects; however, if copper tubing is used, low pH will shorten its life span. Neutralizers, which are available from water treatment companies, can adjust the pH to the desired level.

Microorganism

Most natural water contains a wide variety of microorganisms, some of which are capable of producing disease in humans and other animals. Some bacteria and protozoans occur naturally in water; others as well as viruses, are introduced by contamination. Many viruses and other microorganisms, particularly the enteric organisms that live in the intestines of man and other warm-blooded animals, are found in large numbers in wastewaters.

Most waterborne bacteria diseases result from drinking unpurified water and results in gastrointestinal infection. The two most serious types are cholera and typhoid fever. Epidemics of these two diseases are usually due to contamination of flesh water supplies by the feces of sufferers.

Unusual conditions can cause some wells to be contaminated with bacteria. On the other hand, wells that have been contaminated by surface water may not show a problem now, again, due to unusual weather conditions. This emphasizes the need for regular testing of well water. Since human feces discharged each day contains about one million coliform organisms per capita, all wastewaters are heavily loaded with coliforms and their numbers are indicative of the overall degree of water contamination.

The drinking water standards of the US Public Health Service require that drinking water contain an average of no more than one coliform organism per 100 milliliters of water, about 10 per quart. This low concentration suggests that pathogenic organisms are not likely to be present. Ordinary wastewater may have hundreds of thousands of coliform organisms per milliliter, and because conventional wastewater treatment can remove only from 99.0% to 99.9% of them, chemical disinfection is required for complete safety if the water is to be reused.

Lead

Lead is a toxic metal known to be harmful to human health if inhaled or ingested. Important sources of lead exposure include ambient air, soil and dust, food and water. On average, it is estimated that lead in drinking water contributes between 10 and 20 percent of total lead exposure in young children. In the last few years, federal controls on lead in gasoline have significantly reduced people's exposure to lead.

The degree of harm depends upon the level of exposure. Known effects of exposure to lead range from subtle biochemical changes at low levels of exposure, to severe neurological and toxic effects or even death at extremely high levels. Young children, infants and fetuses will adsorb any lead they consume more readily and therefore are more vulnerable. A child's mental and physical development can be irreversibly stunned by over-exposure to lead. The most common cause is corrosion. Dissolved oxygen, low pH (acidity) and low mineral content in water are common causes of corrosion. All kinds of water, however, may have high level of lead. Lead- contaminated drinking water is most often a problem in houses that are either very old or very new. The use of lead solder with copper pipes is widespread and experts regard this lead solder as the major cause of lead contamination of household water in US home today.

Since you cannot see, taste or smell lead dissolved in water, testing is the only sure way of telling whether or not there is harmful quantities of lead in your drinking water. Federal standards initially limited the amount of lead in water to 50 parts per billion (ppb). In light of new health and exposure data, EPA has set an action level of 15ppb. If tests show that the level of lead in your household water is in the area of 15 ppb or higher, it is advisable to reduce the lead level in your tap water as much as possible.

Chlorine Demand

The chlorine demand of wastewaters is important where the water is to be disinfected, because chlorine is the most commonly used disinfectant. The higher the degree of wastewater treatment, the less the chlorine demand of the treated effluent is likely to be. Chlorine requirements may range from 20 to 200 pounds (9-90kg) per million gallons (3.78 million liters) of wastewater to be treated.

Nutrients

Nutrients, particularly nitrogen and phosphorus compounds, are present in significant concentrations in all domestic wastewaters, chiefly from human excreta and detergents. The nutrients in wastewaters as well as those from fertilizers used on cultivated fields encourage the growth of large populations of algae and other aquatic organisms in the receiving waters. This enrichment, called eutrophication, may interfere with the normal ecological balance of the receiving water.

Heavy Metals and Synthetic Organic Chemicals

Heavy metals and synthetic organic chemicals pose special problems in wastewaters. High concentrations of them may interfere with the treatment processes.

The heavy metals, particularly lead and mercury, are toxic to man and other animals. Mercury pollution in lakes and streams has seriously endangered many fish as well as the people who eat the fish. Some synthetic organic compounds, such as the chlorinated hydrocarbons, may also be toxic if they get into the water supplies or into the food chain. The identification and determination of the concentration of these chemicals are difficult, but where industrial wastes and agricultural run-offs containing heavy metals and synthetic organic compounds are known to find their way into the wastewater collection system, their detection is important.