Issues in Potable Reuse The Viability of Augmenting Drinking Water Supplies with Reclaimed Water (1998) / Chapter Skim
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2 Chemical Contaminants in Reuse Systems
2 Chemical Contaminants in Reuse Systems
Pages 45-73
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From page 45... ...
The mix of chemicals in wastewater varies depending on what types of industries and land uses the service area includes, the nature of the wastewater collection system, and the effectiveness of industrial pretreatment and source control programs. As summarized in Table 2-1, wastewaters contain known inorganic chemicals and minerals that are present naturally in the potable water supply; chemicals from industrial, commercial, and other human activities in the wastewater service area; and chemicals added or generated during water and wastewater treatment and distribution.
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From page 46... ...
However, the potential hazards they pose to downstream consumers remain manageable because these minerals and salts can be accurately quantified in water, and well-established treatment processes can usually reduce their concentrations to levels complying with national drinking water standards or recommended limits. Levels of phosphate and nitrogen, two other chemicals commonly found in wastewater, are often monitored at treatment plants because of their potential effects on the ecology of receiving waters.
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From page 47... ...
For instance, removals of some priority pollutants and other potentially toxic organic compounds in wastewater treatment plants have been reported by a number of researchers, including Richards and Shieh (1986) , Hannah et al.
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From page 48... ...
Drinking Constituent Water Standards San Diego Tampa Denver Physical TOC 0.27 1.88 0.2 TDS 500 42 461 18 Turbidity (NTU) 0.27 0.05 0.06 Nutrients Ammonia-N 0.8 0.03 5 Nitrate-N 0.6 0 0.1 Phosphate-P 0.1 0 0.02 Sulfate 250 0.1 0 1 Chloride 250 15 0 19 TKN 0.9 0.34 5 Metals Arsenic 0.05 <0.0005 oa NDb Cadmium 0.005 <0.0002 oa ND Chromium 0.1 <0.001 oa ND Copper 1.0 0.011 oa o.oog Lead c 0.007 oa ND Manganese 0.05 0.008 oa ND Mercury 0.002 <0.0002 oa ND Nickel 0.1 0.0007 0.005 ND Selenium 0.05 <0.001 oa ND Silver 0.05 <0.001 oa ND Zinc 5.0 0.0023 0.008 0.006 Boron 0.29 0 0.2 Calcium <2.0 1.0 Iron 0.3d 0.37 0.028 0.02 Magnesium <3.0 0 0.1 Sodium 11.9 126 4.8 NOTES: NTU = nephelometric turbidity units; TDS = total dissolved solids; TKN = total Kjeldahl nitrogen; TOC = total organic carbon.
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From page 49... ...
The Denver reuse project conducted an organic challenge study in which 15 different organic compounds were dosed at approximately 100 times the normal levels found in the reuse plant influent (Lauer et al., 1991~. Table 2-3 shows the initial doses and removal rates of these compounds for four different treatment processes.
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From page 50... ...
Effective source control programs, enforcement and monitoring of water quality standards, and reliability of water and wastewater treatment systems are standard measures for the protection of public health. Although a water reclamation plant could fail, monitoring at the water treatment plant would probably identify elevated levels of a regulated contaminant if such events occurred with some frequency.
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From page 51... ...
These interceptor sewers typically divert predominately residential wastewater to the water reclamation plants or route industrial wastewater around the reclamation plants to the wastewater treatment plant for ocean disposal. Thus, the water reclamation plants treat mainly residential and commercial waste, with less than 10 percent of the influent coming from industrial sources.
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From page 52... ...
Table 2-5 summarizes the concentrations of certain priority organic pollutants following secondary biological treatment in four different municipal districts as of 1987: Washington, D.C.; Orange County, California; Phoenix, Arizona; and Palo Alto, California. The Palo Alto system receives wastewater from a typical residential/commercial community as well as from a major university and from several electronics industries.
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From page 53... ...
The concentrations would be higher for many of the contaminants in the wastewater itself. Table 2-5 also contains a comparison of data from Orange County for two different time periods to illustrate the effects of using different biological treatment processes and of segregating wastewaters to reduce the industrial contribution to reclaimed water.
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From page 54... ...
THMs and HAAs are the most thoroughly studied and probably the dominant chlorinated DBPs that form under "normal" disinfection conditions used to treat drinking water and municipal wastewater. Such compounds typically account for between 30 and 50 percent of the total halogen incorporated into organic
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From page 55... ...
The reclaimed water studied came from five wastewater plants in southern California using secondary biological treatment, Vitrification, filtration, and chlorine disinfection (using a concentration x time value of 450 mg/liter x min)
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From page 56... ...
Acronyms are as follows: CH = chloral hydrate; CNC1 = cyanogen chloride; CP = chloropicrin; DOC = dissolved organic carbon; HAAs = haloactetic acids; HANs = haloacetonitriles; HKs = haloketones; TOC = total organic carbon; THMs = trihalomethanes; TSS = total suspended solids. generally meet the current standards for drinking water of 100 ,ug/liter, the levels found may be considered high if these reclaimed waters were to be used to augment potable supplies.
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From page 57... ...
formed per unit of dissolved organic carbon in the sample in
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From page 58... ...
. As in reclaimed water, TOX production in natural water varies considerably depending on the nature of the dissolved organic carbon.
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From page 59... ...
Concentration, Isolation, and Identification Methods Considerable effort has been expended over the past two decades to identify and characterize the complex mixture of chemicals in pristine natural waters, municipal wastewaters, and treated wastewaters. Most of this effort has been directed at organic compounds.
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From page 60... ...
Positive and Tentative Identification Peak or Compound Class 60 ISSUES IN POTABLE REUSE TABLE 2-7 Positive and Tentative Identifications and Estimated Concentrations of Organic Residues from GAC and Chlorinated GAC Effluents Estimated Concentration (,ug/liter)
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From page 61... ...
for in vitro and in viva toxicity testing of reclaimed water. Substantial advances in these techniques can be attributed to improvements in three areas: 1.
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From page 62... ...
could recover from 74 to 94 percent of the dissolved organic carbon in natural water samples, with the average recovery approaching 90 percent. They pretreated the water by passing it through a cation exchange resin to replace polyvalent cations with either H+ or Na+, thereby reducing the likelihood of coagulation or precipitation of the organics in the RO concentrate.
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From page 63... ...
For instance, the universality of basic metabolic pathways for the degradation of organic material ensures that most of the biologically generated organic matter from these different sources will have a great deal in common. Indeed, biological treatment processes in wastewater plants have been developed using natural systems as models, with the engineering aimed largely at compressing the time and volume required for the natural processes to occur.
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From page 64... ...
Further, natural organic matter in reclaimed water has been subjected to more microbial activity than natural organic matter in unperturbed water, and microbial activity increases its solubility. Presumably for the same reason, the specific ultraviolet absorbance (or absorbance per unit mass of organic carbon)
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From page 65... ...
residues; from sewage and industrial sources Adsorbable halogen-containing organic compounds, including by-products from chlorination of DOC and synthetic organic compounds, solvents, and pesticides; from multiple natural and anthropogenic sources Natural biochemical compounds found predominantly in human and livestock wastes; primary source is domestic sewage and feedlot runoff Complex mixture of compounds, many of which are priority pollutants; from multiple sources associated with combustion of fuels Table continues on next page
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From page 66... ...
. Over the last two decades, Giger and various colleagues have extensively studied the fate of the detergent compounds and their metabolites in wastewater treatment systems and downstream (e.g., Abel et al., 1994a, 1994b, 1996; Field et al., 1995; Giger et al., 1981, 1984~.
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From page 67... ...
General removal of TOC in advanced wastewater treatment systems would probably reduce concentrations of these compounds, but this issue has not been examined. As more organic chemicals are identified in wastewater at lower concentrations and as their biochemical effects are better understood, these health issues will arise more frequently.
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From page 68... ...
Another approach is to establish a quantifiable limit of a surrogate or composite parameter that would provide some information on the concentration or behavior of unknown or suspected target compounds. The total organic carbon concentration, for instance, is widely used as a practical evaluator of water and wastewater treatment processes.
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From page 69... ...
CONCLUSIONS Municipal wastewater contains many chemicals that present known or potential health risks if ingested and that must be removed or reduced before such water is reused to augment a drinking water supply. Such chemical contaminants fall into three groups: (1)
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From page 70... ...
Nevertheless, in the absence of contravening data, one can generally assume that reducing the concentration of general categories of contaminants, such as TOC, also reduces risks posed by specific contaminants. If the proper controls and monitoring of wastewater inputs are in place, the health concerns associated with total organic carbon of wastewater origin should diminish as its overall contribution to the water supply diminishes.
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From page 71... ...
1995. Fate of secondary alkane sulfonate surfactants during municipal wastewater treatment.
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From page 72... ...
1993. Removal of DOX and DOX precursors in municipal wastewater treatment plants.
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From page 73... ...
1995. Using reverse osmosis to obtain organic matter from surface and ground waters.
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