972 PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS INTRODUCTION The substances in domestic and industrial wastewater having significance in water-pollution control, disposal, and reuse are (1) dissolved decomposable organic substances result- ing in dissolved oxygen depletion in streams and estuaries and/or causing taste and odor; (2) suspended organic solids resulting in dissolved oxygen depletion; (3) inert suspended solids (SS) causing turbidity and resulting in bottom sedi- ment deposits; (4) toxic synthetic organic substances and heavy metals; (5) oil, grease, and floating materials; (6) acids and alkalis; and (7) dissolved salts, including nutrients like phosphorus and nitrogen. Conventional wastewater-treatment practices have been oriented to the removal of grit and floating matter followed by the removal of suspended and dissolved organic matter. The removal of suspended matter has been achieved by sedimentation, and the bulk of the soluble organic matter is removed by biological oxidation and flocculation. These processes, when carried out in combination, have proved to be economical and effective means for remov- ing organic matter from wastewaters. However, there are certain disadvantages associated with them. These include the following: 1. Biological process require considerable operating control and often generate operating problems of a complex nature. 2. Biological processes are easily upset by shock loads and require time to regain efficient operation. 3. Biological processes are unable to remove certain nutrients, heavy metals, and inorganic salts, when- ever there is a requirement for their removal. 4. Many waste streams contain certain compounds that do not respond to biological treatment or, alternatively, require extensive pretreatment. In the last decades, physical-chemical treatment of waste- water has been studied both on laboratory and pilot-plant scales with important industrial and municipal wastewater- treatment applications. This type of treatment is used either as a pretreatment, tertiary treatment, or advanced treatment given to the effluent from secondary treatment, or as a substitute for conventional biological treatment. In the latter case, it is found to produce effluent of a quality at least equal to that produced by conventional biological treatment. The first study on the treatability of raw wastewater by physical-chemical processes was reported by Rudolfs and Trubnick in 1935. In this study, solids were removed by chemical coagulation with ferric chloride followed by absorption of dissolved impurities with activated carbon. Stander and Van Vuuren (1969) investigated the treat- ment of raw wastewater in a pilot plant where solids removal was achieved by primary sedimentation and chemical coagu- lation with lime, and adsorption with activated carbon. Rizzo and Schade (1969) have also reported results on the pilot- plant treatment of raw wastewater with chemical coagulation and anionic polymer and adsorption with activated carbon. Zuckerman and Molof (1970) studied the efficiency of a treatment system in which raw wastewater was lime-clarified at high pH and then activated-carbon-treated: their results showed that the chemical oxygen demand (COD) values of the final effluent were significantly lower than those associ- ated with good conventional treatment. Moreover, they con- cluded that the removal of soluble organics with activated carbon was enhanced because of the hydrolytic breakdown of high-molecular-weight organic compounds, at a higher pH value, which are absorbed more readily by activated carbon. Weber et al. (1970) investigated the chemical clarifi- cation of primary effluent with ferric chloride followed by activated-carbon adsorption. Their results showed that 65% of the organic matter present in primary effluent was removed by chemical treatment with ferric chloride. Overall removal of biochemical oxygen demand (BOD) was reported as being consistently in the range of 95 to 97%. Final effluent from the system contained approxi- mately 5 mg/l BOD as compared to 30 mg/l for the same wastewater treated conventionally. In another study, Villiers et al. (1971) showed that the treatment of primary effluent by lime clarification and acti- vated carbon, in a steady flow system, produced an efflu- ent with total organic carbon (TOC) averaging 11 mg/l and turbidity averaging less than 2. Phosphates and SS removal were consistently 90% or better. These product characteris- tics are comparable to those associated with products from well-operated conventional treatment plants. Shuckrow (1971) had developed a sewage-treatment process involving chemical coagulation for SS removal, fol- lowed by adsorption of soluble organics on powdered carbon. The advantages cited for this process were (1) a total treat- ment time of less than one hour, (2) a high-quality effluent, C016_005_r03.indd 972 11/22/2005 11:25:15 AM © 2006 by Taylor & Francis Group, LLC PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS 973 (3) lower initial plant cost, (4) ability to remove nitrogen and phosphorus, and (5) a final sludge reduction to sterile ash in a centrifuge-incineration process combined with a chemical regeneration step to recover both the coagulant and the carbon. While the estimated operational costs were high, the overall costs during a 20-year plant life were considered to be signifi- cantly less than costs for comparable biological facilities. Ecodyne Corporation’s first complete physical-chemical treatment plant in Rosemount, Minnesota, with 0.04 to 0.08 m 3 /sec peak capacity, consisted of bar screening, phos- phate removal with sludge recirculation, dual media filtration, carbon absorption to remove dissolved organics, secondary filtration, and ammonia removal by ion exchange with zeo- lite. The plant included facilities for regenerating the carbon, recovering ammonia, and regenerating brine from the ion- exchange system (Ecodyne, 1972). Examples of more recent research include an exhaustive review on the treatment of pulp- and paper-mill wastewa- ter published by Pokhrel and Viraraghavan in 2004. This includes the different processes involved with their effluents, the different methods for treatment of these effluents, the integration of biological and physico-chemical processes, a comparison of them, and conclusions from this review. An article by Van Hulle and Vanrolleghem (2004) presents the development, calibration, and application of a model for the simulation and optimization of a wastewater-treatment plant. The constructed model proved to be able to predict large variations in influent composition. This could be an important tool for production scheduling when applied to industrial wastewater-treatment plants. Recent research in specific areas is included in for each process. The number of water-treatment facilities in the United States by treatment capacities is presented in Table 1. Many of these facilities include some sort of physical-chemical treatment technology. A diagram of alternative technologies for wastewater treatment is shown in Figure 1; it includes most of the processes to be discussed in the next section. As environmental regulations, space availability, and cost fac- tors affect the treatment of waste streams, more and more physical-chemical treatment will be needed to meet these constraints. This is an important research area that will con- tinue to grow in the next years. PHYSICAL AND CHEMICAL PROCESSES USED IN WASTEWATER TREATMENT The following important unit operations and unit processes involved in the physical and chemical treatment of wastewater are discussed in detail: Flow equalization and neutralization Chemical coagulation, flocculation, and sedimentation Filtration Gas stripping Ion exchange Adsorption Flotation Chemical processes Oxidative, photochemical, and electron-beam processes Flow Equalization and Neutralization Both domestic and industrial wastewater flows show con- siderable diurnal variation, and it is considered necessary to significantly dampen these variations in inflow to relieve hydraulic overload on both biological and physical-chemical plants. This process will also smooth out variations in influent characteristics. Flow-equalization basins are basically flow-through or side-line holding tanks, and their capacity is determined by plotting inflow and outflow mass curves. These tanks are generally located after preliminary treatment and should be designed as completely mixed basins, using either diffused air or mechanical surface aerators, to prevent settling of sus- pended impurities. If decomposable organic matter is present in the wastewater, aeration will prevent septicity. The pre- aeration can also reduce the BOD on subsequent treatment units. Flow-equalization basins can also be used to neutral- ize the acidity or alkalinity in incoming wastewater. The neutralizing chemicals are added to the inflow wastewater stream before entering the flow-equalization basins, and the retention period in these basins provides sufficient time for reaction. Any precipitates produced during neutralization are separated in subsequent sedimentation basins. Chemical Coagulation, Flocculation, and Sedimentation The use of chemical treatment appeared early in the devel- opment of sewage- and wastewater-treatment technology. Aluminum sulfate, lime, and ferrous sulfate, when used in the manner usually adopted for water clarification, were successful in producing an effluent of quality better than that obtained by plain sedimentation. An effluent that is generally fairly clear, with only very fine suspended or col- loidal solids but with practically all of the dissolved solids remaining, can be produced. Under most favorable condi- tions and with skilled operation, SS may be reduced in an amount of up to 90% and BOD up to 85%. However, the TABLE 1 Number of wastewater-treatment facilities in the United States (1996) Flow ranges m 3 /s Number of facilities Total existing flowrate m 3 /s 0–0.00438 6444 12.57 0.0044–0.0438 6476 101.78 0.044–0.438 2573 340.87 0.44–4.38 446 511.12 4.38 47 443.34 Other 38 — Total 16204 1409.68 Source: Adapted from Tchobanoglous et al., 2003. C016_005_r03.indd 973 11/22/2005 11:25:15 AM © 2006 by Taylor & Francis Group, LLC 974 PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS cost of the coagulants and the difficulty of disposing of the larger amount of the sludge produced by this process caused it to be abandoned. The revival of chemical treatment can be attributed to a number of factors that accumulated as a result of continuous investigations and reevaluation of the process. These are (1) the decrease in cost of chemicals; (2) better understanding of floc formation and the factors affecting it; (3) the development of methods of sludge filtration and processing that overcome, in part, the difficulty of greater sludge bulk; and (4) the establishment of the relationship between eutrophication in streams and nutrients, particularly phosphorus, nitrogen oxides, and organic matter. This rela- tion establishes the need of final effluent wastes free of such pollutants regardless of the cost of additional treatment. The settling velocities of finely divided and colloidal particles in wastewaters are so small that removing them in a settling tank under ordinary conditions is impossible unless very long detention periods are provided. Therefore, it has been necessary to devise means to coagulate these very small particles into larger ones that will have higher settling velocities. The aggregation of dispersed particles in wastewater is induced by addition of chemical coagulants to decrease the effects of stabilizing factors such as hydration and zeta potential, and by agitation of the medium to encour- age collisions between particles. Because of the greater amount of suspended matter in sewage, the doses for chemical coagulants are generally con- siderably greater. Therefore, in order to keep costs down, it is important that the chemical reaction involved with each coagulant should be known and enhanced and that optimum pH values be obtained by adjustment with acid or base to get more efficient coagulation and clarification with least sludge production. Coagulation Coagulation is a process in which chemicals are added to an aqueous system for the purpose of creat- ing rapid-settling aggregates out of finely divided, dispersed matter with slow or negligible setting velocities. The poten- tial applications of this process in treating wastewater are: (1) direct coagulation of organic matter present mostly as colloidal particles in wastewater; (2) the removal of colloi- dal substances prior to such tertiary treatment processes as ion exchange, carbon adsorption, and sand filtration; (3) the removal of colloidal precipitates formed in phosphate pre- cipitation processes; and (4) the removal of dispersed micro- organisms after a brief biooxidation process. The majority of colloids in domestic wastewater or in organic wastes are of a hydrophilic nature; that is, they have an affinity for water. The affinity of hydrophilic particles for water results from the presence of certain polar groups such as −COOH and −NH 2 on the surface of the particles. These groups are water-soluble and, as such, attract and hold a sheath of water firmly around the particle. The primary charge on hydrophilic colloidal particles may arise from ionization of the chemical groups present at the surface of the particles, e.g., car- boxyl, amino, sulfate, and hydroxyl. This charge is dependent upon the extent to which these surface groups ionize, and thus the particle charge depends upon the pH. Equalization Raw wastewater Spill pond Filtration Precipi- tation Oxidation/ reduction Heavy metals Process wastewaters Organic chemicals Organics, ammonia In-plant treatment Centrifugation Drying Sludge disposal Incineration Lagooning Land disposal Sludge digestion Filtration Gravity thickening Dissolved-air flotation Sludge dewatering Air or steam stripping To discharge or POTW GAC adsorption Oxi- dation Neutralization Coagulation Filtration Anaerobic treatment Activated sludge Ozonation PAC coagulant PACT Nitrification/ denitrification RBC Aerated lagoon Trickling filter To publicly owned treatment works (POTW) Primary treatment Acid or alkali Chemicals Flotation Sedi- mentation Filtration GAC adsorption Discharge to receiving water Secondary treatment Tertiary treatment Biological roughing Wastewater Return flows Sludge GAC and PAC: granular and powdered activated carbon RBC: rotating biological contractor FIGURE 1 Alternative technologies for wastewater treatment (From Eckenfelder, 2000. Reprinted with permission from McGraw-Hill.) C016_005_r03.indd 974 11/22/2005 11:25:16 AM © 2006 by Taylor & Francis Group, LLC PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS 975 The precise zeta potential that yields optimum coagu- lation must be determined for a given wastewater by actual correlation with jar test or plant performance. The control point has been reported to be in the range of 0 to −10 mV when raw sewage is coagulated by alum. It is important that coagulants contribute polyvalent ions of charge opposite to the zeta potential of the dispersion. On a molar basis, biva- lent ions seem to be about 10 to 50 times and trivalent ions about 300 to 700 times as effective as monovalent ions for destabilization of dispersion in wastewater (Rich, 1963). The zeta potential is unaffected by pH in the range of 5.5 to 9.5 (Eckenfelder, 2000). Since most dispersions encountered in wastewaters are stabilized by negative charges, coagulants required are polyvalent cations such as aluminum, ferric, ferrous, or cal- cium. Organic polyelectrolytes are also effective coagulants. Dispersions stabilized principally by electrostatic force are in general amenable to coagulation inasmuch as addition of small doses of suitable electrolytes may effect a significant change in zeta potential of the particles. The most widely used chemicals for coagulation of wastewater are the salts of aluminum and iron. Lime alone has also been used for precipitation of phosphates. Aluminum Sulfate In order to form flocs, aluminum sulfate requires the presence of alkalinity, which, if naturally present in wastewater in the form of bicarbonate, would lead to the following reaction: Al 2 (SO 4 ) 3 .xH 2 O 3Ca(HCO 3 ) 2 → 2Al(OH) 3 ↓ 3CaSO 4 xH 2 O 6CO 2 (1) In case of insufficient alkalinity in the wastewater, lime is generally added, and the reaction with alum becomes: Al 2 (SO 4 ) 3 .xH 2 O 3Ca(OH) 2 → 2Al(OH) 3 ↓ 3CaSO 4 xH 2 O (2) In the presence of phosphate, the following reaction also occurs: Al 2 (SO 4 ) 3 .xH 2 O 2PO 4 -2 → 2AlPO 4 ↓ 3SO 4 -2 xH 2 O (3) Aluminum hydroxide flocs are least soluble at a pH of approximately 7.0. The floc charge is positive below pH 7.6 and negative above pH 8.2 (Eckenfelder, 1966). The solubil- ity of AlPO 4 is related to the pH and the equilibrium con- stant for the salt. Stumm and Morgan (1970) state that the solubility of aluminum phosphate is pH-dependent, and the optimum pH for phosphorus removal lies in the range of 5.5 to 6.5. Generally, at pH above 6.3, the phosphate removal occurs either by incorporation in a complex with aluminum or adsorption on the aluminum hydroxide flocs. According to Yuan and Hsu (1970), the reaction mechanism for precipita- tion of phosphates by aluminum hydroxide is very complex. They have proposed that the positively charged hydroxy- aluminum polymers are the species that accounts for the precipitation of phosphates and that effective phosphate pre- cipitation can occur only when the positive charges on the polymers are completely neutralized. It is also reported that the effectiveness of aluminum is related to the nature and concentration of the foreign components present and to the ratio of phosphate to aluminum. Alum has been used extensively for phosphate removal in raw wastewaters. Bench-scale tests of alum addition were conducted at Springfield, Ohio, and Two Rivers, Wisconsin (Harriger and Hoffman, 1971 and 1970, respectively). Raw wastewater at Springfield required an average Al:P mass ratio of 1.9:1 to achieve 80% removal, while at Two Rivers the average mass ratio was 0.93:1 to obtain phosphate removal of 85%. The stoichiometric equation (3) indicates that each kilogram of phosphorus requires 0.87 kg of aluminum for complete precipitation. Ferrous Sulfate and Lime If ferrous salts are used for wastewater coagulation, addition of a small amount of base, usually sodium hydroxide or lime, is essential. The required dosage is related to the alkalinity of water. Ferrous sulfate reacts with calcium bicarbonate in water, but this reaction is much delayed and therefore cannot be relied on (Steel, 1960). Caustic alkalinity, due to the addition of lime to the wastewater, produces a speedy reaction. The lime is added first, and the following reaction takes place: FeSO 4 .7H 2 O Ca(OH) 2 → Fe(OH) 2 CaSO 4 7H 2 O (4) The ferrous hydroxide is not an efficient floc, but it can soon be oxidized by the dissolved oxygen in wastewater as ferric hydroxide: 4Fe(OH) 2 O 2 2H 2 O → 4Fe(OH) 3 ↓ (5) An insoluble hydrous ferric oxide is produced over a pH range of 3 to 13. The floc charge is positive in the acid range and negative in the alkaline range, with a mixed charge over a pH range of 6.5 to 8.0. This process is usually cheaper than the use of alum but needs greater skill to dose with the two chemicals. Ferric Chloride Ferric chloride has been used successfully for wastewater coagulation because it works well in a wide pH range (Steel, 1960; Wuhrmann, 1968). The reactions of ferric chloride with bicarbonate alkalinity and lime are, respectively: 2FeCl 3 3Ca(HCO 3 ) 2 → 2Fe(OH) 3 ↓ 3CaCl 2 6CO 2 (6) 2FeCl 3 3Ca(OH) 2 → 2Fe(OH) 3 ↓ 3CaCl 2 (7) Wuhrmann (1968) was successful in removing phosphates from sewage effluent by precipitation with a mixture of ferric salt and lime. The ferric dosages varied between 10 and 20 mg/l and the lime dosages from 300 to 350 mg/l in order to raise the pH to values between 8 and 8.3. The actual lime dosage required is related to the alkalinity of C016_005_r03.indd 975 11/22/2005 11:25:16 AM © 2006 by Taylor & Francis Group, LLC 976 PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS the water. According to Wuhrmann, the dominant reaction product between the phosphate ion and the ferric ion at pH above 7 is believed to be FePO 4 , with a solubility product of about 10 23 at 25°C. The colloidal particle size of the FePO 4 requires a sufficient excess of ferric ion for the formation of a well-flocculating hydroxide precipitate, which includes the FePO 4 particles and acts as an efficient adsorbent for other phosphorous compounds. It has been reported that for efficient phosphorus removal (85 to 95%), the stoichiometric amount of 1.8 mg/l Fe required per mg/l P should be supplemented by at least 10 mg/l of iron for hydroxide formation. Also, the use of anionic polymer is considered desirable in order to produce a clear supernatant (Wukash, 1968). Lime Lime reacts with the bicarbonate alkalinity of waste- water to form calcium carbonate, which precipitates, under normal conditions: Ca(OH) 2 Ca(HCO 3 ) 2 → 2CaCO 3 ↓ 2H 2 O (8) Normally, 70 to 90% of the phosphorus in domestic sewage is in the form of orthophosphates or polyphosphates that may hydrolyze orthophosphates. The remaining phosphorus is present in the form of organic-bound phosphorus. The removal of phosphorus can be achieved by direct adsorption on the surface of calcium carbonate particles. Orthophosphates can also be precipitated in the alkaline range by reaction with cal- cium salts to form hydroxyapatite, according to the following reaction: 10Ca(OH) 2 6H 3 PO 4 → 10Ca (PO 4 ) 6 (OH) 2 ↓ 18H 2 0 (9) Schmid and McKinney (1969) observed that hydroxyapatite was present in soluble form at a pH value above 9.5. They also found that at pH values of 9.5 or less, phosphorus was adsorbed onto the growing faces of calcium-carbonate par- ticles, thereby inhibiting their growth. Buzzell and Sawyer (1967) have shown that at pH levels of 10 to 11 in the primary sedimentation tanks, BOD removal of 55 to 70%, nitrogen removal of 25%, phosphate removal of 80 to 90%, and coli- form removal of 99% can be expected. Bishop et al. (1972) have reported that precipitation of domestic wastewater with lime removed approximately 80% of the TOC, BOD, and COD; 91% of the SS; 97% of the total phosphorus; and 31% of the total nitrogen. Phosphates from secondary effluent have been removed successfully at Lake Tahoe by precipitation with lime (Slechta and Culp, 1967). Albertson and Sherwood (1967) found that by recirculating calcium-phosphate solids, previously formed due to the addition of lime, it was possible to reduce the lime dosage by about 50%. Galarneau and Gehr (1997) present experimental results of their studies on phosphorous using aluminum hydroxide. de-Bashan and Bashan (2004) present an extensive review of recent advances in phosphorous removal from wastewaters and its separation for use as a fertilizer or as an ingredient in other products. In wastewater-treatment practices, it is detrimental to form large floc particles immediately in the flocculation step because it reduces the available floc surface area for adsorp- tion of phosphorus. Therefore, it is essential to maintain fine pinpoint flocs in order to get a maximum phosphate removal by surface adsorption, and this can be achieved by minimizing the time of their flocculation. This is not the case if the goal is one of colloidal-solids removal, as is often the case in water treatment. The process of coagulation and flocculation in wastewater treatment can be summarized in the following three steps: 1. As the coagulant dissolves, positive aluminum and ferric ions become available to neutralize the negative charges on the colloidal particles includ- ing organic matter. These ions may also react with constituents in solution such as hydroxides, car- bonates, phosphates, sulfides, or organic matter to form complex gelatinous precipitates of colloidal dimensions that are termed “microflocs.” This is the first stage of coagulation, and for greatest effi- ciency a rapid and intimate mixing is necessary before a second reaction takes place. 2. After the positively charged ions have neutralized a large part of the colloidal particles and the zeta potential has been reduced, the resulting flocs are still too small to be seen or to settle by gravity. The treatment, therefore, should be flocculation, slow stirring so that very small flocs may agglomerate and grow in size until they are in proper condition for sedimentation. Some evidence suggests that aggregation of microflocs with dispersed waste con- stituents is the most important mechanism affecting coagulation in water treatment (Riddick, 1961). 3. During the third phase, surface adsorption of parti- cles takes place on the large surface area provided by the floc particles. Some of the bacteria present will also become entangled in the floc and carried to the bottom of the tank. Electrocoagulation Electrocoagulation is a process in which the coagulating ions are produced by electrolytic oxidation of sacrificial electrodes. This technique has been successfully used in the removal of metals, suspended particles, colloids, organic dyes, and oils. An interesting review of this technique is presented by Mollah et al. (2001). In it the advantages and disadvantages of electrocoagulation are presented as well as a description and comparison with chemical coagulation. His group studied its use in the treatment of a synthetic-dye solu- tion with a removal of 99% under optimal conditions (Mollah, Morkovsky, et al., 2004). Another publication (Mollah, Pathak, et al., 2004) presents the fundamentals of electrocoagulation and the outlook for the use of this process in wastewater treat- ment. Lai and Lin (2003) studied the use of electrocoagulation for the treatment of chemical mechanical polishing wastewater, obtaining a 99% copper removal and 96.5% turbidity reduction in less than 100 minutes. C016_005_r03.indd 976 11/22/2005 11:25:16 AM © 2006 by Taylor & Francis Group, LLC PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS 977 Sedimentation Sedimentation basins are important compo- nents in water- and wastewater-treatment systems, and their performance greatly depends upon proper design. In chemical treatment of wastewater, the separation of chemically coagu- lated floc depends on the characteristics of the floc in addition to the factors normally considered in the design of conven- tional primary and secondary clarifiers. Field experience indi- cates that the usual values for surface overflow rates used in separating chemical floc in water-treatment plants must be reduced in order to obtain a good efficiency in the removal of floc from chemically coagulated wastewater (Weber et al., 1970; Convery, 1968; Rose, 1968; Kalinske and Shell, 1968). In wastewater-treatment practices, the recommended overflow rate for removal of alum floc is 30 m/day, while with use of lime or iron salts, it can be increased up to 40 m/day. Filtration Filtration of wastewater can be accomplished by the use of (1) microscreens, (2) diatomaceous earth filters, (3) sand fil- ters, (4) mixed media filters, or (5) membranes. The filtration of sludges, on the other hand, is achieved by sand beds or vacuum filters. The filtration characteristics of the solids found in a bio- logical treatment plant effluent are greatly different from those of the floc formed during chemical coagulation for the removal of organic matter and phosphates. Tchobanoglous and Eliassen (1970) have noted that the strength of the bio- logical floc is much greater than that of the flocs resulting from chemical coagulation. Accordingly, biological flocs can be removed with a coarser filter medium at higher filtration rates than can the weaker chemical flocs, which may shear and penetrate through the filter more readily. Lynam et al. (1969) had observed that the chemical floc strength can be controlled, to some degree, with the use of polymers as coagulant aids. Their experi- ments yielded higher SS removal by filtration when 1 mg/l of anionic polymer A-21 was used along with alum. The filterability of solids in a conventional biological plant effluent is dependent upon the degree of flocculation achieved in the biological process. For example, filtration of the effluent from a trickling-filter plant normally cannot yield more than 50% removal of the SS due to the poor degree of biological flocculation in trickling filters. On the other hand, the activated sludge process is capable of a much higher degree of biological flocculation than the trickling-filter pro- cess. The degree of biological flocculation achieved in an activated sludge plant was found to be directly proportional to the aeration time and inversely proportional to the ratio of the amount of organic material added per day to the amount of SS present in the aeration chamber (Culp and Hansen, 1967a). It has also been reported that up to 98% of the SS found in the effluent from a domestic sewage-treatment plant after a 24-hour aeration time could be removed by filtration without the use of coagulants (Culp and Hansen, 1967b). Microscreening Microscreens are mechanical filters in which flow is passed through a special metallic filter fabric placed around a drum. The filter traps the solids and rotates with the drum to bring the fabric under backwash water sprays fitted to the top of the machine, in order to wash the solids to a hopper for gravity removal to disposal. The rate of flow through the microscreen is determined by the applied head, normally limited to about 150 mm or less, and the concentration and nature of the SS in the effluent. Extensive tests at the Chicago Sanitary District showed that microscreens with a 23 µm aperture could reduce the SS and BOD of a good-quality activated sludge effluent, 20–35 mg/l SS and 15–20 mg/l BOD, to 6–8 mg/l and 3.5– 5 mg/l, respectively (Lynam et al., 1969). It was noted that the microscreens were more responsive to SS loading than to hydraulic loading and that the maximum capacity of the microscreens was reached at the loading of 4.3 kg/m 2 /day at 0.27 m/min. Diatomaceous Earth Filtration Diatomite filters found their widest application in the production of potable waters, where the raw water supply was already of a relatively good quality, i.e., of low turbidity. Operating characteristics of diatomite filters can now be predicted under a wide range of operat- ing conditions by utilizing several mathematical models (Dillingham et al., 1966, 1967). Several investigators have studied the filtration of secondary effluent by diatomite filters whose ability to produce an excellent-quality effluent is well established (Shatto, 1960; R. Eliassen and Bennett, 1967; Baumann and Oulman, 1970). However, the extremely high cost and their inability to tolerate significant variations in SS concentration limit the usage of diatomite filters in sewage- treatment practices. Sand Filtration Sand filters have been operated as slow sand filters or as rapid sand filters made with one or more media. A slow sand filter consists of a 150- to 400-mm-thick layer of 0.4-mm sand supported on a layer of a coarser mate- rial of approximately the same thickness. The underdrainage system under the coarser material collects the filtrate. The rate of flow through the filter is controlled at about 3 m/day. This rate is continued until the head loss through the bed becomes excessive. Then the filter is thrown out of service and allowed to partially dry, and 25 to 50 mm of the sand layer, which includes the surface layer of sludge, is manually scraped from the top for washing. Disadvantages of slow sand filtration system are: (1) the filters may become inoper- ative during the cold winter weather, unless properly housed; (2) slow sand filters may not be effective due to the rapid clogging of filters (the normal frequency of cleaning filters varies from once to twice a month; Truesdale and Birkbeck, 1996); (3) the cost of slow sand filtration is three times the cost of rapid sand filters and twice the cost of microscreens (anonymous, 1967); and (4) the large space requirement. Rapid sand filters consist of about a 400-mm-thick layer of 0.5- to 0.65-mm sand supported on coarser gravel. The rate of filtration ranges between 80 and 120 mm/min. At this high filtration rate, the filter beds need backwashing when the head loss becomes excessive. C016_005_r03.indd 977 11/22/2005 11:25:17 AM © 2006 by Taylor & Francis Group, LLC 978 PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS Lynam et al. (1969) reported results of detailed tests con- ducted on filtration of secondary effluent from an activated sludge plant of the Chicago Sanitary District. They used a filter bed of 0.85-mm-effective-size sand in a 280-mm depth and a filtration rate of 120 mm/min, and analyzed the data in terms of both hydraulic and SS loadings. Poor correlations were obtained between effluent quality and hydraulic load- ing, effluent quality and solids loading, and solid removal and hydraulic loading. However, an excellent correlation existed between SS loading and SS removals. It was also observed that the sand filtration of alum-coagulated solids was no better than that of uncoagulated solids, and the opti- mum SS removal was obtained by alum and polymer coagu- lation in combination with sand filtration. A review of the retention of pathogenic bacteria in porous media is presented by Stevik et al. (2004). The review includes the factor affecting bacteria retention and the factors that effect elimination of bacteria from porous media. The authors also suggest priority areas of research in this field. Multimedia Filtration The limitation of the single medium rapid sand filter follows from its behavior as a surface filtra- tion device. During filter backwashing, the sand is graded hydraulically, with the finest particles rising to the top of the bed. As a result, most of the material removed by the filter is retained at or very near the surface of the bed. When the secondary effluent contains relatively high solids concen- trations, the head loss increases very rapidly, and SS clog the surface in only a few minutes. One approach to increase the effective filter depth is to use dual-media beds consisting of a discrete layer of coarse coal placed above a layer of fine sand. More recently, the concept of mixed-media filters has been introduced in order to achieve a filter performance that very closely approaches an ideal one. In this case a third layer of a very heavy and fine material, garnet (with specific gravity of 4.2) or illmenite (with specific gravity of 4.5), is placed beneath the coal and sand. Conley and Hsiung (1965) have suggested the optimum design values for these filters. The selection of media for any filtration application should be based on the floc characteristics. An example of a typical dual-media filter is shown in Figure 2. Moving-Bed Filters These types of filters were put on the market by the Johns-Manville Corporation in the late 1960s. It is a continuous sand filter in which influent wastewater passes through the bed and becomes product water. Solids trapped on the filter face and within the bed move with the filter media, countercurrent to the liquid. Solids and small amounts of filter media regularly removed from the filter face are educted to the filter media tower without stopping operations. Solids are scrubbed from the media and dis- charged as a waste sludge, while the washed media is fed back into the bed. The filter medium usually used is 0.6- to 0.8-mm sand with a maximum sand-feed rate of 5 mm/min and maxi- mum filtration rate of 85 m/day (2100 U.S. gal/day/ft 2 ). The advantages claimed for this system are (1) automatic and continuous operation, (2) that the filter allows much higher and variable solids loadings than is permissible with a sand bed, and (3) that through an efficient use of coagulant chemi- cals, the system has the flexibility to reduce turbidity, phos- phorus, SS, and BOD to the desired level (Johns-Manville Corporation, 1972). Membrane Filtration Membrane filtration is being applied more extensively as membrane materials are becoming more resistant and affordable. Fane (1996) presents a description of membrane technology and its possible applications in water and wastewater treatment. An extensive study on microfiltra- tion performance of membranes with constant flux for the treatment of secondary effluent was published by his research group in 2001 (Parameshwaran et al., 2001). Kentish and Stevens (2001) present a review of technologies for the recy- cling and reuse of valuable chemicals from wastewater, par- ticularly from solvent-extraction processes. A feasibility study on the use of a physico-chemical treatment that includes nanofiltration for water reuse from printing, dyeing, and finishing textile industries was per- formed by Bes-Pia et al. (2003). In this work jar tests were conducted for flocculation using commercial polymers fol- lowed by nanofiltration. Their results show that the combina- tion reduces COD from 700 to 100 mg/l. Another treatment approach by the same authors (2004) uses ozonation as a pretreatment for a biological reactor with nanofiltration as a final step. A combined approach is presented by Wyffels et al. (2003). In this case a membrane-assisted bioreactor for the treatment of ammonium-rich wastewater was used, showing this to be a reliable technology for these effluents. Galambos et al. (2004) studied the use of nanofiltration and reverse osmosis for the treatment of two different waste- waters. For their particular case the use of reverse osmosis was more convenient due to the high quality of the effluent, but the permeate of the nanofiltration can only be released into a sewer line or would have to be treated, resulting in an eco- nomic compromise. A comparison between a membrane bio- reactor and hybrid conventional wastewater-treatment systems at the pilot-plant level is presented by Yoon et al. (2004). The removal of volatile organic compounds (VOCs) using a stripper-membrane system was studied by Roizard et al. (2004). Their results show that this hybrid system can be used for the removal of toluene or chloromethane with a global efficiency of about 85%. Vildiz et al. (2005) investigated the use of a coupled jet loop reactor and a membrane for the treatment of high- organic-matter-content wastewater. The main function of the membrane is the filtration of the effluent and the recycle of the biomass to the reactor. One advantage of the system is its reduced size as compared with traditional treatment systems, as well as a better-quality effluent. A comprehensive review on the use of nanofiltration membranes in water and wastewater use, fouling of these membranes, mechanisms of separation, modeling, and the use of atomic force microscopy for the study of surface mor- phology is presented by Hilal et al. (2004). The future of C016_005_r03.indd 978 11/22/2005 11:25:17 AM © 2006 by Taylor & Francis Group, LLC PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS 979 membranes and membrane reactors in green technology and water reuse was published by Howell (2004). In it, water problems in different regions of the world are discussed, different membrane systems are presented, and different approaches for new research are introduced. Reverse Osmosis There are several reverse-osmosis units cur- rently in use to produce freshwater from seawater. With recent improvements in membranes, this process is also being used for purification of wastewater. Substantial removal of BOD, COD, total dissolved solids, phosphate, and ammonia by this process has been reported (Robinson and Maltson, 1967). In a reverse-osmosis process, wastewater containing dis- solved materials is placed in contact with a suitable semi- permeable membrane in one of the two compartments of the tank. The pressure on this compartment is increased to exceed the osmotic pressure for that particular waste in order to cause the water to penetrate the membrane, carrying with it only a small amount of dissolved materials. Therefore, the dissolved material in the wastewater gets concentrated con- tinuously, while highly purified water collects in the other compartment. The performance of the reverse-osmosis process depends mainly on (1) the membrane semipermeability or its effi- ciency to separate dissolved material from the wastewater, and (2) the membrane permeability or the total amount of water that can be produced with appropriate efficiency for the removal of dissolved materials. It has been reported that the conventional cellulose-acetate membranes give adequate separation efficiency, but the flow rate of water is too small to be of practical interest. However, cellulose-acetate mem- branes allow a much higher flow rate of product water, at the same separation efficiency, which makes it applicable in wastewater-treatment practices (Goff and Gloyne, 1970). The operating pressure, as well as the rejection perfor- mance of the membrane, is dependent on the membrane porosity. Rejection performances of three graded mem- branes with secondary sewage effluent were investigated by Bray et al. (1969). Merten et al. (1968) evaluated the performance of an 18.9 m 3 /day pilot reverse-osmosis unit in removing small amounts of organic material found in the effluent of carbon columns treating secondary effluent. With a feed pressure of 2760 kPa and water recovery of 80 to 85%, 84% removal of COD present in the carbon column effluent, averaging 10.8 mg/l, was achieved. Problems of clogging have occurred when operating with waters containing high concentrations of bicarbonate, and as such, adjustment of pH to prevent calcium-carbonate precipitation is normally required. Sadr Ghayeni et al. (1996) discuss issues such as flux control and transmission in microfiltration membranes and biofouling in reverse-osmosis membranes in their use for the reclamation of secondary effluents. The process used for the study consisted of a microfiltration membrane fol- lowed by a reverse-osmosis membrane. The performance of this combined system was evaluated by Sadr Ghayeni et al. (1998b), as was the study of the adhesion of bacteria to reverse-osmosis membranes (1998a). Effluent Transfer pipe Storage compartment Filter compartment Collection chamber Air Underdrain nozzles Recycle Backwash Equalization tank Drain Sump Coal Sand Filter backwash Polymer Three-way valve Water level Alum Influent Filter Backwash FIGURE 2 Typical dual-media filter (From Eckenfelder, 2000. Reprinted with permission from McGraw-Hill.) C016_005_r03.indd 979 11/22/2005 11:25:18 AM © 2006 by Taylor & Francis Group, LLC 980 PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS A study on the processing of composite industrial effluent by reverse osmosis was published by Sridhar et al. in 2003. The effluent used in the study was from combined bulk drug and pharmaceutical companies, obtaining a removal of 88% of dissolved solids, COD, and BOD, with reasonable water recovery. They also present a comparison between aerobic and reverse-osmosis treatment for this effluent. A physical-chemical process for the treatment of chemi- cal mechanical polishing process wastewater is presented by Lin and Yang (2004). In it the authors used chemical coagula- tion using different coagulants followed by reverse osmosis, obtaining water capable of being reused in the process due to its characteristics. Electrodialysis Electrodialysis involves the removal of inorganic ions from water by creating an electrical potential across two electrodes dipped in water. One of the two strips serves as a cathode and the other as an anode. The treatments that can be achieved by electrodialysis include: 1. Removal of inorganic ions: Under the effect of applied potential, cations and anions migrate to the cathode and anode, respectively. By alternat- ing membranes, a series of concentrating and diluting compartments can be created. For a long run and better efficiency, it is essential that turbid- ity, SS, colloids, and trace organics are removed from the wastewater before it enters the electrodi- alysis unit. 2. Effective bacteria reduction in wastewater: Most of the municipal wastewaters contain a high con- centration of chloride ions. Oxidation of chloride at the anode produces chlorine, hypochlorite, or chloramines, depending on the nature of the wastewater. Chlorine in these forms is a good dis- infectant and also provides an effective means of reducing soluble BOD. In order to reduce the operating cost of the electrodialysis pro- cess, the eroding anodes made of aluminum or iron are now being replaced by nonconsumable noble anodes, which appear to have more potential in wastewater treatment (Culp and Culp, 1971). The cost of disinfection by electrodialysis is reported to be 0.053 $/m 3 of wastewater as compared to 0.095 $/m 3 for the conventional chlorination (unpublished proposal, 1970). However, some other sources have reported that the cost of electrolytic treatment of wastewater was too high for the removal of a large percentage of secondary effluent COD. Grimm et al. (1998) present a review of electro-assisted methods for water purification, including electrodialysis. Fukumoto and Haga (2004) applied this technique for the treatment of swine wastewater with removal rates for NO 3 − and PO 4 −3 ions of 99% and an average color reduction of 58%. Gas Stripping In domestic wastewaters, most of the nitrogen that gets converted to ammonia during biological degradation is present either as ammonia or in organic form. When the carbon concentration in wastewater becomes low and the nitrifying bacteria are populous, this ammonia can be oxi- dized by bacteria to nitrites and nitrates in the presence of dissolved oxygen. The stripping process can be employed either before or after secondary treatment for removing high levels of nitrogen that is present as ammonia. If it is to be used as pretreatment prior to a biological system, enough nitrogen, N:BOD 5:150, must be left in the efflu- ent to satisfy the nutritional requirement (Eckenfelder and Barnhart, 1963). In wastewater, ammonium ions exist in equilibrium with ammonia and hydrogen ions: NH 4 ↔ NH 3 ↑ H (10) At pH levels of 6 to 8, ammonia nitrogen is mostly present in the ionized form NH 4 . Increasing the pH to above 10 changes all the nitrogen to ammonia gas, which is remov- able by agitation. The stripping of ammonia from wastewater is carried out with air. In this operation, wastewater is agi- tated vigorously in a forced-draft countercurrent air-stripping tower when the ammonia is driven out from the solution and leaves with the air exhausted from the tower. The efficiency of ammonia removal in the stripping process depends upon the pH, airflow rate, tower depth, and hydraulic loading to the tower. Slechta and Culp (1967) have shown experimentally that the efficiency of the ammonia-stripping process is dependent on the pH of the wastewater for pH values up to 10.8. However, no significant increase in ammonia removals was achieved by elevating the pH above 10. Kuhn (1956) had come to the same conclusion. It has also been reported that the efficiency of the ammonia-stripping process depends on maximizing the air–water contact within the stripping tower. Higher ammo- nia removals and lower air requirements were obtained with a 40 50-mm packing than with a 100 100-mm packing. Increased tower depth, which provides additional air–water contact, results in greater ammonia removals and lower air requirements. Ammonia removals of 90%, 95%, and 98% were obtained at airflow rates of 1875, 3000, and 6000 m 3 per cubic meter of wastewater, respectively. Gas stripping is also used for removal of H 2 S and VOCs from wastewater. Ion Exchange The ion-exchange process has been adopted successfully in wastewater-treatment practice for removing most of the inorganic dissolved salts. However, the cost of this method for wastewater treatment cannot be justified unless the efflu- ent water is required for multiple industrial municipal reuse. One of the major applications of this technique is the treat- ment of plating-industry wastewater, where the recovery of chrome and the reuse of water make it an attractive choice (Eckenfelder, 2000). Gaffney et al. (1970) have reported that the modified DESAL process, developed for treating acid mine drainage C016_005_r03.indd 980 11/22/2005 11:25:18 AM © 2006 by Taylor & Francis Group, LLC PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS 981 waters, can be applied successfully to the treatment of sec- ondary sewage effluent. This process consists of passing secondary sewage-plant effluent upflow through an ion- exchange unit filled with a weak base anion exchange resin, Amberlite IRA-68, operated on a bicarbonate cycle. The effluent with a pH of 6.0 is then treated with a small quan- tity of bentonite and cationic flocculant, Prima floc C-7, fol- lowed first by aeration to drive out carbon dioxide, and then lime softening in proportion to its hardness concentration. A dosage of 30 mg/l of bentonite, 3 to 5 mg/l of polyelec- trolyte, and normal lime levels are required. The effluent that is partially desalinated and essentially free of nitrates, phosphates, chlorides, alkyl benzene sulfonate (ABS), and COD can be produced. If the salinity is too high, it may be reduced further by passing a portion of the effluent through a weak acid cation, Amberlite IRC-84. It has been observed that IRA-68 can remove much of the organic contents and COD, thereby eliminating or markedly reducing the need for carbon treatment. Slechta and Culp (1967) tested a cationic resin, Duolite C-25, for the removal of ammonia nitrogen from the carbon column effluent that was containing ammonia nitrogen in the range of 18 to 28 mg/l as nitrogen. A 100-mm-diameter Plexiglas cylinder filled to a depth of 700 mm with the resin served as the pilot ion-exchange column. The rate of appli- cation of influent waste to the ion-exchange column was 0.4 m 3 /min per cubic meter of resin. Following breakthrough of the ammonia nitrogen to 1 mg/l, the bed was backwashed and the resin was regenerated. On the average, about 400 bed volumes of carbon column effluent had been passed through the ion-exchange resin prior to a breakthrough to 1 mg/l ammonia nitrogen. However, considering the operating and capital costs, they concluded that the ammonia-stripping process was more efficient. Nitrate nitrogen, present in the effluent from the acti- vated sludge process, has been removed by anion exchange regenerated with brine by R. Eliassen and Bennett (1967). This ion-exchange process also removes phosphates and some other ions; however, pretreatment by filtration is essential. The resin is restored by treatment with acid and methanol. The removal of heavy metals with Mexican clinoptilo- lite was studied by Vaca Mier et al. (2001). In this study the interactions of lead, cadmium, and chromium competed for the ion-exchange sites in the zeolite. The authors also stud- ied the influence of such factors as the presence of phenol and the pH of the solution to be treated. Adsorption Application of adsorption on granular active carbon, in columns of counterflow fluidized beds, for the removal of traces or organic pollutants, detergents, pesticides, and other substances in wastewater that are resistant to biological deg- radation has become firmly established as a practical, reliable, and economical treatment (Slechta and Culp, 1967; Weber, 1967; Parkhurst et al., 1967; Stevens and Peters, 1966; Presecan et al., 1972). Adsorption can also be accomplished with powdered carbon (Davies and Kaplan, 1964; Beebe and Stevens, 1967), which is mixed in wastewater, flocculated, and ultimately settled. However, there are certain problems associated with the use of powdered carbon. These are: (1) that large quanti- ties of activated carbon are needed in wastewater treatment, because it is used only on a once-through basis, and han- dling of such large quantities of carbon also creates a dust problem, and (2) problems in disposal of precipitated carbon unless it is incinerated along with the sewage sludge. Carbon-Adsorption Theory Less polar molecules, includ- ing soluble organic pollutants, are removed by adsorption on a large surface area provided by the activated carbon. Smaller carbon particles enhance the rate of pollutant removal by providing more total surface area for adsorption, partial deposition of colloidal pollutants, and filtration of larger particles. However, it is almost always necessary to remove finely divided suspended matter from wastewater by pretreatment prior to its application on a carbon bed. Depending on the direction of flow, the granular carbon beds are either of the downflow-bed type or upflow-bed type. Downflow carbon beds provide the removal of suspended and flocculated materials by filtration beside the absorption of organic pollutants. As the wastewater passes through the bed, the carbon nearest the feed point eventually becomes sat- urated and must be replaced with fresh or reactivated carbon. A countercurrent flow using multiple columns in series is considered more efficient. The first column is replaced when exhausted, and the direction of flow is changed to make that column the last in the series. Full countercurrent operation can best be obtained in upflow beds (Culp and Culp, 1971). Upflow carbon columns for full countercurrent opera- tions may be either of the packed-bed type or expanded- bed type. Packed beds are well suited to treatment of wastes that contain little or no SS, i.e., turbidity less than 2.5 JTU. However, the SS invariably present in municipal and indus- trial wastewaters lead to progressive clogging of the carbon beds. Therefore, expanded-bed upflow columns have certain potential advantages in operation of packed-bed adsorbers for treating wastes that contain SS. In expanded-bed-type adsorbers, water must be passed with a velocity sufficient to expand the bed by about 10%, so that the bed will be self-cleaned. Experiments conducted by Weber et al. (1970) have shown that expanded-bed and packed-bed adsorption sys- tems have nearly the same efficiency with regard to the removal of soluble organic materials from trickling-filter effluent, under otherwise similar conditions. The packed- bed system was found to be more effective for removal of SS, but the clogging that resulted from these solids required higher pumping pressure and more frequent cleaning of the carbon beds. Because of the time elapsed in cleaning, the expanded-bed production was about 9% more than the packed-bed production. The Lake Tahoe Water Reclamation Facilities, described by Slechta and Culp (1967), included pretreatment of second- ary effluent by chemical clarification and filtration, thereby C016_005_r03.indd 981 11/22/2005 11:25:19 AM © 2006 by Taylor & Francis Group, LLC [...]... pre -treatment Desalination, 167, 387–392 Bes-Pia, A., Mendoza-Roca, J.A., Alcaina-Miranda, M.I., Iborra-Clar, A., and Iborra-Clar, M.I (2003) Combination of physico -chemical treatment and nanofiltration to reuse wastewater of a printing, dyeing and finishing textile industry Desalination, 157(1–3), 73–80 Bhatkhande, D.S., Pangarkar, V.G., and Beenackers, A.A.C.M (2001) Photocatalytic degradation for environmental. .. Eductor High-pressure water Quench tank Eductor High-pressure water Eductor Wet scrubber High-pressure water FIGURE 3 Carbon-adsorption process diagram (From Eckenfelder, 2000 Reprinted with permission from McGraw-Hill.) © 2006 by Taylor & Francis Group, LLC PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS of PACT in municipal wastewater treatment resulted from the inability of the physical- chemical treatment. .. Quality Improvement by Physical and Chemical Processes, Water Resources Symposium No 3, University of Texas Press, Austin and London, 104 Beebe, R.L and Stevens, J.I (1967) Activated carbon system for wastewater renovation Water and Waste Engineering, 4(1), 43 Bes-Pia, A., Iborra-Clar, A., Mendoza-Roca, J.A., Iborra-Clar, M.I., and Alcaina-Miranda, M.I (2004) Nanofiltration of biologically treated... TREATMENT OF WASTEWATERS segregation by effluent type; evaluation of the pretreatment steps; and modeling of the individual steps involved Aiyuk et al (2004) propose a chemically enhanced primary treatment followed by a UASB reactor for the treatment of domestic wastewater The chemical pretreatment consisted of the addition of FeCl3 or Al2(SO4)3 and polymers in a mixing tank, and a posttreatment of the biologically... R16 Chung, Y.-C., Ho, K.-L., and Tseng, C.-P (2003) Hydrogen sulfide gas treatment by a chemical- biological process: chemical absorption and biological oxidation steps Journal of Environmental Science and Health, Part B—Pesticides, Food Contaminants, and Agricultural Wastes, 38(5), 663–679 © 2006 by Taylor & Francis Group, LLC Conley, W.R., Jr and Hsiung, K (1965) Design and application of multimedia... Journal of Chemical Technology and Biotechnology, 78(11), 1149–1156 Lin, S.H and Yang, C.R (2004) Chemical and physical treatments of chemical mechanical polishing wastewater from semiconductor fabrication Journal of Hazardous Materials, 108(1–2), 103–109 Lynam, B., Ettelt, G., and McAloon, T (1969) Tertiary treatment at Metro Chicago by means of rapid sand filtration and microstrainers Journal of the... a review Pure and Applied Chemistry, 76(4), 801–813 PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS Gehr, R., Wagner, M., Veerasubramanian, P., and Payment, P (2003) Disinfection efficiency of peracetic acid, UV and ozone after enhanced primary treatment of municipal wastewater Water Research, 37(19), 4573–4586 Getoff, N (1996) Radiation-induced degradation of water pollutants—state of the art Radiation... Physics and Chemistry, 47(4), 581–593 Getoff, N (2002) Factors influencing the efficiency of radiation-induced degradation of water pollutants Radiation Physics and Chemistry, 65(4–5), 437–446 Ghoreishi, S.M and Haghighi, R (2003) Chemical catalytic reaction and biological oxidation for treatment of non-biodegradable textile effluent Chemical Engineering Journal, 95(1–3), 163–169 Goff, D.L and Gloyne,... 30 granular activated-carbon plants were designed in the United States for use at municipal wastewater -treatment plants (DeJohn and Edwards, 1981) Thirteen of the plants are classed as physical- chemical and 15 as tertiary treatment plants, and 4 use carbon to dechlorinate According to the authors, there have been some problems encountered at certain physical- chemical and tertiary treatment plants, but... 41(2), 247 Mantzavinos, D and Psillakis, E (2004) Enhancement of biodegradability of industrial wastewaters by chemical oxidation pre -treatment Journal of Chemical Technology and Biotechnology, 79(5), 431–454 Matatov-Meytal, Y.I and Sheintuch, M (1998) Catalytic abatement of water pollutants Industrial and Engineering Chemistry Research, 37(2), 309–326 Meidl, J.A (1981) Application of PACT to municipal . Mendoza-Roca, J.A., Alcaina-Miranda, M.I., Iborra-Clar, A., and Iborra-Clar, M.I. (2003). Combination of physico -chemical treat- ment and nanofiltration to reuse wastewater of a printing, dyeing and. & Francis Group, LLC PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS 983 of PACT in municipal wastewater treatment resulted from the inability of the physical- chemical treatment process to. compo- nents in water- and wastewater -treatment systems, and their performance greatly depends upon proper design. In chemical treatment of wastewater, the separation of chemically coagu- lated