Sources of Individual Organic Compounds
The individual compounds of concern can be grouped into several categories: (1) priority pollutants, (2) volatile organic compounds (VOCs), (3) disinfection byproducts, (4) pesti- cides and agricultural chemicals, and (5) unregulated trace organic compounds. The sources of priority pollutants are primarily from commercial and industrial discharges and, to a very limited extent, from products used in domestic applications. Volatile organic compounds are derived primarily from commercial and industrial sources. Pesticides and agricultural chemicals found in wastewater are primarily from surface runoff from agricul- tural, vacant, and park lands. Unregulated trace organic compounds in question are derived, in large part, from (1) human and veterinary antibiotics, (2) human prescription and nonprescription drugs, (3) industrial and household wastewater products, and (4) sex and steroidal hormones.
Priority Pollutants
The U.S. EPA initially identified 129 priority pollutants in 65 classes to be regulated by categorical discharge standards; three were removed in 1981 (Federal Register, 1982).
Priority pollutants (both inorganic and organic) were selected on the basis of their known or suspected carcinogenicity, mutagenicity, teratogenicity, or high acute toxicity. Many of the organic priority pollutants are also classified as volatile organic compounds (VOCs).
Two types of standards are used to control pollutant discharges to public-owned treatment works (POTWs). The first, “prohibited discharge standards,” applies to all commercial and industrial establishments which discharge to POTWs. Prohibited standards restrict the discharge of pollutants that may create a fire or explosion hazard in collection systems or treatment works, are corrosive (pH , 5.0), obstruct flow, upset treatment processes, or increase the temperature of the wastewater entering the plant to above 40°C. “Categorical Standards” apply to industrial and commercial discharges in 25 industrial categories (“categorical industries”) and are intended to restrict the discharge of priority pollutants.
It is anticipated that this list will continue to be updated in future.
Volatile Organic Compounds (VOCs)
Organic compounds that have a boiling point less than or equal to 100°C or a vapor pres- sure greater than 1 mm Hg at 25°C are generally considered to be volatile organic com- pounds (VOCs). For example, vinyl chloride, which has a boiling point of 213.9°C and a vapor pressure of 2548 mm Hg at 20°C, is an example of an extremely volatile organic compound. Volatile organic compounds are of great concern because (1) once such com- pounds are in the vapor state they are much more mobile and, therefore, more likely to be released to the environment; (2) the presence of some of these compounds in the atmo- sphere may pose a significant public health risk; and (3) they contribute to a general increase in reactive hydrocarbons in the atmosphere, which can lead to the formation of photochemical oxidants. The release of these compounds in collection systems and at treatment plants, especially at the headworks, is of particular concern with respect to the health of the collection system and treatment plant workers. The physical phenomena involved in the release and control of VOCs is considered in more detail in Chap. 16.
Disinfection Byproducts
It has been found that when chlorine is added to water containing organic matter several organic compounds containing chlorine are formed. Collectively, these compounds, along with others, are known as disinfection byproducts (DBPs). Although generally present in low concentrations, they are of concern because many of them are known or suspected
2–7 Individual Organic Compounds
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potential human carcinogens. Typical classes of compounds include trihalomethanes (THMs), haloacetic acids (HAAs), trichlorophenol, and aldehydes.
In the last decade N-Nitrosodimethylamine (NDMA) has been found in the effluent from wastewater treatment plants. The reason for concern over this compound is because as a group of compounds, nitrosamines are among the most powerful carcinogens known (Snyder, 1995). These compounds are also known to be carcinogenic to various fish spe- cies at low concentrations. The U.S. EPA action limit for NDMA is two parts per trillion.
Based on the results of recent studies, NDMA appears to be formed during the chlorination process. In treated effluent, the nitrite ion can react with hydrochloric acid, present as result of the use of chlorine for disinfection, to form nitrous acid. In turn, nitrous acid can react with dimethylamine to form NDMA (Hill, 1988). The compound dimethylamine is common in wastewater and surface waters, being found in urine, feces, algae, and plant tissues. Dimethylamine is also part of some polymers used for water treatment (such as polydiallyl dimethylamine) and for ion exchange resins. The formation of NDMA under basic and alkaline conditions has been reported by Wainwright (1986).
Because of the concern over the formation of DBPs and NDMA, considerable atten- tion has been focused on the use of ultraviolet (UV) disinfection as a possible replacement for chlorine. In addition, considerable attention has been focused on the modifications to conventional treatment processes to improve the treatment of these compounds and to advanced treatment processes for the removal of these substances. The use of UV radiation for disinfection and the destruction of NDMA is considered in Chap. 12.
Pesticides and Agricultural Chemicals
Pesticides, herbicides, and other agricultural chemicals, are toxic to many organisms and, therefore, can be significant contaminants of surface waters. Concentrations of these chemicals can result in fish kills, in contamination of the flesh of fish that decreases their value as a source of food, and in impairment of water supplies. These chemicals are not common constituents of domestic wastewater.
Unregulated Trace Organic Compounds
In addition to the compounds discussed above for which requirements have been estab- lished, varieties of new unregulated (often referred to as emerging, trace or micropollutant compounds) compounds have been identified in many of the nation’s water supplies and in treated wastewater effluents at low ng/L or low ug/L concentrations. The compounds in ques- tion are derived, in large part, from (1) human and veterinary antibiotics, (2) human prescrip- tion and nonprescription drugs, (3) industrial and household wastewater products, and (4) sex and steroidal hormones. Typical examples of types of compounds involved are reported in Table 2–16. As more becomes known about the health impacts of these compounds, it is anticipated that discharge limits may be developed for a number of these compounds. Given that over 30 million organic compounds are known to exist, it is clear that the list of emerg- ing compounds will continue to grow as analytical techniques continue to improve.
Analysis of Individual Organic Compounds
The analytical methods used to determine individual organic compounds require the use of sophisticated instrumentation capable of measuring trace concentrations in the range of 10212 to 1023 mg/L. Gas chromatographic (GC) and high-performance liquid chromato- graphic (HPLC) methods are used most commonly to detect individual organic com- pounds. Different types of detectors are used with each method, depending on the nature of the compound being analyzed. Typical detectors used in conjunction with gas chroma- tography include electrolytic conductivity, electron capture (ECD), flame ionization (FID),
(continued ) Veterinary and human antibiotics
Carbadox Norfioxacin Sulfamethazine
Chlortetracycline Oxytetracycline Sulfamethiazole
Ciprofloxacin Roxarsone Sulfathiazole
DoIcycline Roxithromycin Sulfamethoxazole
Enrofloxacin SarafIoxacin Tetracycline
Erythromycin Spectinomycin Trimethoprim
Erythromycin-H2O SulfachIorpyridazine TyIosin
Ivermectin SuIfadimethoxine Virginiamycin
Lincomycin Sulfamethazine
Sex and steroidal hormones
Cis-androsternone Estrone Mestranol
3-b-coprostanol Estriol 19-norethisterone
Cholesterol 17a-estradiol Progesterone
Equilenin 17b-estradiol Testosterone
Equilin 17a-ethynylestradiol
Human prescription and non-prescription drugs (general use) Acetominophen (antipyretic) Fluoxetine (antidepressant)
Albuterol (antiasthmatic) Furosemide (diuretic)
Amoxicillin (antibiotic) GemfibroziI (lipotropic agent)
Caffeine (stimulant) Ibuprofen (anti-inflammatory)
Carbamazepine (anticonvulsant) Mefformin (antidiabetic agent)
Cimetidine (antacid) Paroxetine (paxil metabolite)
Codeine (analgesic) Paraxanthine (caffeine metabolite)
Cotinine (nicotine metabolite) Ranitidine (antacid) Dehydronifedipine (antianginal) Salbutamol (antiasthmatic) Digoxigenin (digoxin metabolite) Sulfamethoxazole (antibiotic) Diltiazem (antihypertensive) Trimethoprim (antibiotic) Diphenhydramine (antihistamine) Warfarin (anticoagulant) Enalaprillat (antihypertensive)
Industrial and Household Wastewater Products (general use)
Acetophenone (fragrance) Lindane (pesticide)
Anthracene (PAH)b Methyl parathion (pesticide)
Benzo(a)pyrene (PAH) Napthalene (PAH)
Benzophenone (used in plastics) NPEO1 – total (detergent metabolite) 2,6-di-tert-para-benzoquinone (antioxidant) NPEO2 – total (detergent metabolite) 5methyI 1 H benzotriazole (antioxidant) OPEO1 (detergent metabolite)
Table 2–16