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CE 445 Wastewater Reclamation and Reuse

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CE 445Wastewater Reclamation and Reuse
Dr. Mohab Kamal
ActivatedCarbon
Inwater reclamation, adsorption processes are sometimes used to remove dissolved constituents by accumulation on a solid phase.Activatedcarbon is a common adsorbent, which is employed as powdered activated carbon (PAC) with a grain diameter of less than 0.074 mm or granular activated carbon (GAC), which has a particle diameter greater than 0.1 mm.Duringwater reclamation, PAC can be added directly to the activated sludge process or solids contact processes, upstream of a tertiary filtration step.GACis used in pressure and gravity filtration.
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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ActivatedCarbon
Activatedcarbon is efficient for the removal of many regulated synthetic organic compounds as well as unregulated trace organic chemicals exhibiting properties of high and moderate hydrophobicity (e.g., steroid hormones,triclosan, bisphenol A) (Snyder et al., 2006a).AlthoughPAC needs to be disposed of after its adsorption capacity is reached, GAC can be regenerated either on- or offsite, providing this practice is more cost-effective than disposing it via landfills.OnsiteGAC regeneration is only cost-effective for large installations and is currently not practiced by any water reclamation facility in the United States.GACadsorbents are characterized by short empty-bed contact times (i.e., 5-30 min) and preferably a large throughput volume (i.e., bed volumes of 2,000 to 20,000 m3/m3)
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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BiologicalFiltration
For instance, simple aldehydes, ketones, and carboxylic acids are produced as ozone oxidizes organic matter in water.Theaggregate measurements commonly employed to assess the biodegradability of transformation products isassimilableorganic carbon (AOC) (HammesandEgli, 2005) and biodegradable dissolved organic carbon (BDOC) (Servaiset al., 1987).Thisreadily biodegradable carbon has been implicated in the acceleration and promotion of biofilm growth in distribution systems.Thus, drinking water treatment facilities usually employbiofiltrationafterozonationto reduce BDOC with the aid of indigenous bacteria present in thefeedwater.Additionally, the use ofbiofiltrationafter ozone also has been shown to reduce the formation of some byproducts formed during secondary disinfection with chlorine (Wert et al., 2007).Somestudies have also demonstrated that the byproducts fromozonationof trace organic chemicals, such as steroid hormones and pharmaceuticals, also are largely biodegradable (Stalteret al., 2010); therefore, there is growing support for the use ofbiofiltrationafter ozone or AOP.Althoughbiofiltrationalone may provide some direct benefit in terms of removing trace organic chemicals, it has generally been shown to be only marginally effective without a prior oxidation step (JuhnaandMelin, 2006).
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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Biological Filtration
Biological filtration can be accomplished using traditional media (i.e., sand/anthracite) or using activated carbon (biologically activated carbon [BAC]).Althoughsome studies have suggested that activated carbon is superior for supporting biological growth, mainly because of superior adherence of the biofilm to the GAC, there are some conflicting reports that show approximately equal performance using anthracite (Wert et al., 2008).Somestudies have demonstrated that BAC is capable of adsorption as well as biological degradation; however, the adsorptive capacity of the BAC will eventually be reduced as themicro-poresin the carbon structure become blocked and the adsorptive capacity subsequently becomes exhausted.
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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Biological Filtration
Somestudies have demonstrated that BAC is capable of adsorption as well as biological degradation; however, the adsorptive capacity of the BAC will eventually be reduced as themicro-poresin the carbon structure become blocked and the adsorptive capacity subsequently becomes exhausted.Atthis point, fresh GAC will be required to restore the adsorptive capacity, but effective biological activity as measured by reduction of AOC or BDOC will take time to establish.Theamount of time needed to develop a biologically active filter will depend on water quality, water temperature, and operational parameters.Animportant factor in establishing and maintaining an active biofilm is the backwash frequency with chlorinated water.
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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Biological Filtration
One major disadvantage of using biological filtration is the detachment of biofilm and likely detection of bacteria in filtered water.Althoughthese bacteria are not harmful, the detection of heterotrophic bacteria could in some cases lead to regulatory violations. In those cases,biofiltrationwould generally be followed by a disinfection step, such as chlorination or UV irradiation.
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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ChemicalOxidation
Chemical oxidation is commonly employed in water treatment to achieve disinfection, as described previously in this chapter; however, oxidants are also used to remove tastes, odors, and color and to improve the removal of metals (Singer andReckhow, 2010).Oxidantsused for water treatment include chlorine, chloramine, ozone, permanganate, chlorine dioxide, and ferrate.Advancedoxidation relies upon formation of powerful radical species, primarily hydroxyl radicals (OH·) and is rapidly gaining in use for the oxidation of more resistant chemicals, such as many trace organic chemicals and industrial solvents (Esplugaset al., 2007).Themost commonly employed advanced oxidation techniques in water reclamation use hydrogen peroxide coupled with UV light or ozone gas.TheUV light itself is not strictly an oxidant but it does selectively transform a small group of compounds sensitive to direct photolysis (e.g., NDMA,iohexol,triclosan, acetaminophen, diclofenac, sulfamethoxazole) (Pereira et al., 2007; Snyder et al., 2007; Yuan et al., 2009; andSancheset al., 2010).
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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ChemicalOxidation
Very few oxidative technologies are employed at operational conditions capable of mineralizing organic materials in water.Eventhe most promising advanced oxidation techniques using ozone and UV irradiation combined with peroxide will result in only a minor (if any) measurable reduction of dissolved organic carbon (DOC).Regardlessof the oxidation technique deployed and superior performance of trace organic chemical removal, some transformation products will result that are oftenuncharacterized.Themost commonly used oxidation methods for the removal of trace organic contaminants are described below.
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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ChemicalOxidationChlorine
Chlorine, defined here as the combination of chlorine gas,HOCl, andOCl–, reacts selectively with electron-rich bonds of organic chemicals (e.g., double bonds in aromatic hydrocarbons) (Minearand Amy, 1996).Recently, several reports have shown that many trace organic chemicals containing reactive functional groups can be oxidized by free chlorine (Adams et al., 2002;Debordeet al., 2004; Lee et al., 2004, Pinkston andSedlak, 2004;Westerhoffet al., 2005), while ketone steroids (e.g., testosterone and progesterone) are not as effectively oxidized (Westerhoffet al., 2005).However, the ability of chlorine to effectively oxidize trace organic chemicals, including steroid hormones, is a function of contact time and dose.Moreimportantly, chlorine is not expected to mineralize trace organic chemicals, but rather to transform them into new products (Vanderfordet al., 2008), which may in fact be more toxic than the original molecule.
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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Chemical OxidationChloramines
Chloramines are not nearly as effective as oxidants and thus play a much smaller role in trace organic chemical oxidation.Snyder(2007) demonstrated that a dose of 3 mg/L chloramines and a contact time of 24 hours was able to effectively oxidize phenolic steroid hormones (e.g.,estrone, estradiol,estriol,ethinylestradiol) as well astriclosanand acetaminophen; however, the vast majority of trace organic chemicals studied were not significant oxidized.Therefore, although chloramines play an important role in reduction of membrane fouling and disinfection, only minimal expected benefit in oxidation of trace organic chemicals will result.Moreover, careful evaluation of nitrosamine formation should be undertaken when using chloramines, considering the carcinogenic potency of these byproducts (see Choi et al., 2002; Mitch et al., 2003; Haas, 2010).
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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Chemical OxidationOzone
Ozone(O3) is a powerful oxidant and disinfectant that decays rapidly and leaves no appreciable residual in reclaimed water during storage and distribution.Ozone-enrichedoxygen is generally added to water through diffusers producing fine bubbles, and once dissolved in water, ozone quickly undergoes a cascade of reactions, including decomposition into hydroxyl radicals (OH·),hydroperoxylradical (HO2), and superoxide ion (O2–).Theseradicals along with molecular ozone will rapidly react with organic matter, carbonate, bicarbonate, reduced metals, and other constituents in water.Thereactions mediated by the hydroxyl radical are relatively nonselective, whereas molecular ozone is more selective (Elovitzet al., 2000).
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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Chemical OxidationOzone
Because of ozone’s ability to oxidize organic chemicals, it has been widely applied in water treatment for taste and odor control, color removal, and to reduce concentrations of trace organic chemicals.Atdosages commonly employed for disinfection, the vast majority of contaminants can be effectively converted into transformation products (Snyder et al., 2006c).Althoughseveral studies have shown that ozone effectively reduces estrogenic potency in reclaimed water (Snyder et al., 2006c), recent publications have suggested that biologically active filters be included after the ozone process in order to remove biodegradable byproducts formed duringozonation(Stalteret al., 2010).Forpotable reuse applications,ozonationcould also be applied after soil aquifer treatment (SAT), which combines the benefits of a more selective oxidation of remaining chemicals persistent to biodegradation and a lower ozone demand due to reduced DOC concentrations in the recovered water.
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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Chemical OxidationOzone
It is well known that in the presence of bromide, ozone can form bromate, a toxic byproduct. There are steps that can be employed to mitigate the formation of bromate, such as the use of chlorine and ammonia before ozone addition (vonGunten, 2003).Somereports have shown that ozone applied beforechloraminationalso results in the oxidation of nitrosamine precursors (Lee et al., 2007). However, ozone also has been shown to form some nitrosamines directly (vonGuntenet al., 2010).
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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Chemical OxidationOzone
Ozone can play an important role in water reclamation, but the process is more energy intensive and operationally complex than chlorination.Incases where trace organic chemical removal (e.g., pharmaceuticals, steroid hormones) is important, ozone is a viable option and does not result in a residuals stream like NF or RO membrane processes or in spent media as with activated carbon.However, ozone does not provide a complete barrier to trace organic chemicals, and there are certain chemicals that are not amendable to oxidation (e.g., chlorinated flame retardants; artificial sweeteners) (Snyder et al., 2006c).
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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Chemical OxidationUV Radiation
UVlight at doses commonly employed for disinfection (40–80mJ/cm2) is largely ineffective for trace organic chemical removal.Ina recent study that investigated the removal of trace organic chemicals from water, none of the target compounds investigated were well removed (>80 percent oxidized) using UV at disinfection doses (Snyder, 2007).However, when UV doses are significantly increased (generally by 10-fold) and high doses of hydrogen peroxide (5 mg/L and higher) are added, most trace organic chemicals were effectively oxidized (Snyder et al., 2006c).Activatedcarbon is sometimes employed to catalytically remove hydrogen peroxide, and other chemicals can be used to remove excess peroxide from the UV-AOP effluent.
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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Chemical OxidationUV Radiation
AlthoughUV-AOP does form transformation products (i.e., it does not result in mineralization of organic compounds), it does not form bromate.Additionally, UV alone at elevated dosages or in combination with hydrogen peroxide (UV-AOP) effectively removes NDMA.UV-AOP efficacy, however, is quite susceptible to water quality and requires proper pretreatment.Inmany potable reuse applications, UV-AOP is applied after RO treatment to negate the detrimental impacts of water quality, such as suspended and particulate matter and DOC.UV-AOPapplications generally will require extensive pretreatment to increase UV transmittance; however, recent studies have demonstrated that UV-AOP can be also effective in advanced-treated effluents (Rosario-Ortiz et al., 2010).
CE 445 Water Reclamation and Reuse (Dr. Mohab Kamal)
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CE 445 Wastewater Reclamation and Reuse