Most individuals find water at temperatures of 10-15°C most palatable. Groundwaters and waters from mountainous areas are normally within this range. Surface waters are, of course, subject to the effect of ambient temperatures and can be very warm during summer.
The temperature of water affects the efficiency of treatment units. For example, in cold temperatures, the viscosity increases. This, in turn, diminishes the efficiency of settling of the solids that the water may contain because of the resistance that the high viscosity offers to the downward motion of the particles as they settle. Pressure drops also increase in the operation of filtration units, again, because of the resistance that the higher viscosity offers.
Chlorides in concentrations of 250 mg/L or greater are objectionable to most people. Thus, the secondary standard for chlorides is 250 mg/L. Whether or not concentrations of 250 mg/L are objectionable, however, would depend upon the degree of acclimation of the user to the water. In Antipolo, a barrio of Cebu in the Philippines, the normal source of water of the residents is a spring that emerges along the shoreline between a cliff and the sea. As such, the fresh water is contaminated by saltwater before being retrieved by the people. The salt imparts to the water a high concentration of chlorides. Chloride contaminants could go as high as 2,000 mg/L; however, even with concentrations this high, the people continue to use the source and are accustomed to the taste.
The absence of fluorides in drinking water encourages dental caries or tooth decay; excessive concentrations of the chemical produce mottling of the teeth or dental fluorosis. Thus, managers and operators of water treatment plants must be careful that the exact concentrations of the fluorides are administered to the drinking water. Optimum concentrations of 0.7 to 1.2 mg/L are normally recommended, although the actual amount in specific circumstances depends upon the air temperature, since air temperature influences the amount of water that people drink. Also, the use of fluorides in drinking water is still controversial. Some people are against its use, while some are in favor of it.
Iron (Fe) and manganese (Mn) are objectionable in water supplies because they impart brownish colors to laundered goods. Fe also affects the taste of beverages such as tea and coffee. Mn flavors tea and coffee with a medicinal taste. The SMCLs (secondary MCLs) for Fe and Mn are, respectively, 0.3 and 0.05 mg/L.
Clinical, epidemiological, and toxicological studies have demonstrated that lead exposure can adversely affect human health. The three systems in the human body most sensitive to lead are the blood-forming system, the nervous system, and the renal system. In children, blood levels from 0.8 to 1.0 jg/L can inhibit enzymatic actions. Also, in children, lead can alter physical and mental development, interfere with growing, decrease attention span and hearing, and interfere with heme synthesis. In older men and women, lead can increase blood pressure. Lead is emitted into the atmosphere as Pb, PbO, PbO2, PbSO4, PbS, Pb(CH3)4, Pb(C2H5)4, and lead halides. In drinking water, it can be emitted from pipe solders.
The source of copper in drinking water is the plumbing used to convey water in the house distribution system. In small amounts, it is not detrimental to health, but it will impart an undesirable taste to the water. In appropriate concentrations, copper can cause stomach and intestinal distress. It also causes Wilson's disease. Certain types of PVC (polyvinyl chloride) pipes, called CPVC (chlorinated polyvinyl chloride), can replace copper for household plumbing.
Nitrate is objectionable for causing what is called methemoglobinemia (infant cyanosis or blue babies) in infants. The MCL is 10 mg/L expressed as nitrogen.
Before the establishment of stringent regulations, sludges from wastewater treatment plants were most often spread on lands and buried in ditches as methods of disposal. As the sludge decays, nitrates are formed. Thus, in some situations, these methods of disposal have resulted in the nitrates percolating down the soil causing excessive contaminations of the groundwater. Even today, these methods are still practiced. In order for these practices to be acceptable to the regulatory agencies, a material balance of the nitrate formed must be calculated to ascertain that the contamination of the groundwater does not go to unacceptable levels.
The presence of sodium in drinking water can affect persons suffering from heart, kidney, or circulatory ailments. It may elevate blood pressures of susceptible individuals. Sodium is plentiful in the common table salt that people use to flavor food to their taste. It is a large constituent of sea water; hence, in water supplies contaminated by the sea as in the case of Antipolo mentioned earlier, this element would be plentiful.
The sulfate ion is one of the major anions occurring naturally in water. It produces a cathartic or laxative effect on people when present in excessive amounts in drinking water. Its SMCL is 250 mg/L.
Zinc is not considered detrimental to health, but it will impart an undesirable taste to drinking water. Its SMCL is 5 mg/L.
Biochemical oxygen demand (BOD) is the amount of oxygen consumed by the organism in the process of stabilizing waste. As such, it can be used to quantify the amount or concentration of oxygen-consuming substances that a wastewater may contain. Analytically, it is measured by incubating a sample in a refrigerator for five days at a temperature of 20°C and measuring the amount of oxygen consumed during that time.
The substances that consume oxygen in a given waste are composed of carbonaceous and nitrogenous portions. The carbonaceous portion refers to the carbon content of the waste; carbon reacts with the dissolved oxygen producing CO2. On the other hand, the nitrogenous portion refers to the ammonia content; ammonia also reacts with the dissolved oxygen. Even though the term used is nitrogenous, nitrogen is not referred to in this context. Any nitrogen must first be converted to ammonia before it becomes the "nitrogenous."
Generally, two types of analysis are used to determine BOD in the laboratory: one where dilution is necessary and one where dilution is not necessary. When the BOD of a sample is small, such as found in river waters, dilution is not necessary. Otherwise, the sample would have to be diluted. Table 2.1 sets the criteria for determining the dilution required. This table shows that there are two ways dilution can be made: using percent mixture and direct pipetting into 300-mL BOD bottles. Normally, BOD analysis is done using 300-mL incubation bottles.
Because BOD analysis attempts to measure the oxygen equivalent of a given waste, the environment inside the BOD bottle must be conducive to uninhibited bacterial growth. The parameters of importance for maintaining this type of environment are
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