awwa seminar ROCEED1NG/ Minimizing and Recycling Water Plant Sludge Presented at the AWWA Conference, May 13,1973 No. 20123 ------- U,S,EPAU IIIMII1" .. — RXOODQD^773 ------- PROCEEDINGS AWWA SEMINAR ON MINIMIZING AND RECYCLING WATER PLANT SLUDGE Presented by EDUCATION COMMITTEE OF AMERICAN WATER WORKS ASSOCIATION AND UNITED STATES ENVIRONMENTAL PROTECTION AGENCY Water Supply Division Las Vegas, Nevada May 13, 1973 ------- FOREWORD All materials and information contained herein are published in the exact form as presented to AWWA by the seminar speakers. Per AWWA policy for publication of "Proceedings," no attempt is made on the part of the American Water Works Association to edit, reformat, or alter the material provided except where obvious errors or discrep- ancies have been detected. Any statements or views here presented are totally those of the speakers and are neither condoned nor re- jected by the American Water Works Association or its members. Copyrighted 1973 by American Water Works Association 2 Park Ave., New York, N.V, ii ------- CONTENTS Title of Paper Paper Number Waste Discharge Regulations and Turbidity Standards I Use of Organic Polymers and Sludge Volume Reduction II High Energy Mixing and Flocculation III Direct Filtration vs. Oxidation IV Magnesium Carbonate Recycling V Practice in MgCO^ Recovery and Reuse VI iii ------- WASTE DISCHARGE REGULATIONS AND TURBIDITY STANDARDS* Gordon G. Robeck** Edgar A. Jeffrey*** INTRODUCTION The Federal government through EPA has many new responsibilities as a result of Public Law 92-500 on pollution control, and it may soon be establishing new drinking water standards that would apply to all Community Water Supply Systems. These standards will be essentially an updating or revising of the existing PHS 1962 Drinking Water Standards. PROPOSED NEW TURBIDITY STANDARD We in the Water Supply Research Lab are always anxious to demonstrate how a high-quality water can be delivered to the consumer's tap economically. Hence, much effort has gone into developing data to show that many surface sources can be treated by non-conventional arrangements at less than the usual costs. In reviewing the literature and our experience with evaluating Interstate Carrier Water Supplies, we noticed several systems have had trouble controlling coliform when certain biological blooms and silt loads enter the transmission or distribution lines. Increasing chlorination many times seems to temporarily suppress the presence of growth of coliform, but other times it has not been successful, particularly if there are open finished water reservoirs. Filtration will usually allow post chlorination to be more effective, but we are mainly responsible for suggesting a performance standard, not *For presentation at Seminar, May 13, 1973, Las Vegas, Nevada. Jointly sponsored by AWWA Education Committee and Water Supply Div., USEPA. **Director, Water Supply Research Laboratory, NERC-CI, USEPA. ***Water Supply Technical Advisor, Water Supply Division, USEPA. 1-1 ------- create a how-to-do policy so we developed a rationale for supporting a turbidity limit of 1 at the consumers tap. The Public Advisers suggested some changes including having the limit applied at the point of entry into the distribution system. The compromise proposal now reads as follows: "4. 22 2 3 TURBIDITY Approval Limit (Health) - 1 Til Turbidity in drinking water shall not exceed one turbidity unit at the point where water enters the distribution system except where it can be demonstrated that a higher turbidity not exceeding 5TU does not: (1) interfere with disinfection, (2) cause tastes and odors upon disinfection, (3) prevent the maintenance of an effective disinfection agent throughout the distribution system, (4) result in deposits in the distribution system, and (5) cause consumers to question the safety of their drinking water. " The Federal Technical Review Committee prepared the following rationale to support the turbidity limit: "Drinking water should be low in turbidity prior to disinfection and at the consumer's tap for the following reasons: 1) Several studies have demonstrated that the presence of particulate matter in water interferes with effective disinfection. Neefe, Baty, Reinhold, and Stokes^ added from 40 to 50 ppm of feces containing the causative agent of infectious hepatitis to distilled water. They then treated this water by varying techniques and fed the resultant liquid to human volunteers. One portion of the water that was disinfected to a total chlorine residual after 30 minutes of 1. 1 mg/l caused hepatitis in 2 of the 5 volunteers. A similar experiment, in which the water was first coagulated and then filtered, prior to disinfection to the same concentration of total residual, produced no 1-2 ------- hepatitis in 5 volunteers. This was repeated with 7 additional volunteers, and again no infectious hepatitis occurred. (2) Chang, Woodward and Kabler showed that nematode worms can ingest enteric bacterial pathogens as well as virus, and that the nematode-born organisms are completely protected against chlorin- ation even when more than 90 percent of the carrier worms are immobilized. Walton^ analyzed data from three waterworks treating surface waters by chlorination only. Coliform bacteria were detected in the chlorinated water at only one waterworks, the one that treated a Great Lakes water that usually did not have turbidities greater than 10 TU, but occasionally contained turbidities as great as 100 TU. (4) Sanderson and Kelly studied an impounded water supply receiving no treatment other than chlorination. The concentration of free chlorine residual in samples from household taps after a minimum of 30 minutes contact time varied from 0. 1 to 0. 5 mg/l and the total chlorine residual was between 0, 7 and 1 mg/l . These samples consistently yielded confirmed coliform organisms. Turbidities in these samples varied from 4 to 84 TU, and microscopic examination showed iron rust and plankton to be present. They concluded ". . .coliform bacteria were imbedded in particles of turbidity and were probably never in contact with the active agent. Viruses, being smaller than bacteria, are much more likely to escape the action of chlorine in a natural water. Thus, it would be essential to treat water by coagulation and filtration to nearly zero turbidity if chlorination is to be effective as a viricidal process. " (^ Hudson reanalyzed the data of Walton, above, relating them to the hepatitis incidence for some of the cities that Walton studied. 1-3 ------- A summary of his analysis is shown in Table I. TABLE 1 FILTERED-WATER QUALITY AND HEPATITIS INCIDENCE, 1953 Final City Average Turbidity TU Chlorine Residual mg/1 Hepatitis eases/100, G 0. 15 0. 1 3. 0 C 0. 10 0. 3 4. 7 H 0. 25 0. 3 4. 9 B 0. 2 - 8. 6 M 0. 3 0. 4 31.0 A 1.0 0. 7 130 / c j Tracy, Camarena, and Wing noted that during 1963, in San Francisco, California, 33 percent of all the coliform samples showed 5 positive tubes, in spite of the presence of chlorine residual. During the period of greatest coliform persistence, the turbidity of this unfiltered supply was between 5 and 10 TU. (7) Finally, Robeck, Clarke, and Dostal showed that virus penetration through a granular filter was accompanied by a break- through of floe, as measured by an increase in effluent turbidity above 0. 5 turbidity unit in a pilot unit seeded with an abnormally high dose of virus. These 7 studies show the importance of having a low turbidity water prior to disinfection and entrance into the distribution system. / o\ 2) The 1969 Community Water Supply Survey revealed that unpleasant tastes and odors were among the most common customer complaints. While organics and inorganics in finished water do cause tastes and odors, these problems are often 1-4 ------- aggravated by the reaction of chlorine with foreign substances. Maintenance of a low turbidity will permit disinfection with less likelihood of increasing taste and odor problems. 3) Regrowth of microorganisms in a distribution system is often stimulated if organic matter (food) is present. An example (9) of this possibility occurred in a Pittsburgh hospital. One source of this food is turbidity created by algae and other biological forms. Therefore, the maintenance of low turbidity water will reduce the level of this microbial food and maintain a cleanliness that will help prevent regrowth of bacteria and the growth of other microorganisms. 4) The purpose of maintaining a chlorine residual in a distribution system is to have a biocidal material present throughout the system so that the consumer will be protected if the integrity of the system is violated. Because the material causing the turbidity can exert a chlorine demand, the maintenance of a low turbidity water throughout the distribution system will facilitate the provision of proper chlorine residual. For these reasons, the approval limit (health) for turbidity is one (1) Turbidity Unit (TU) as the water enters the distribution system, although a properly operated water treatment plant employing coagulants and granular filtration should consistently produce a finished water with a turbidity of less than 0. 5 T. U." The Public Advisers have suggested some changes be made in this statement, but any re-write will probably still say essentially the same thing. Because of the change in the turbidity standard, some surface sources may have to be managed in a slightly different way in order 1-5 ------- to meet the new limit. Filtration, for example, may have to be used to remove most of the particulates. In that case, flocculants may also be necessary and thus sludge will be formed and have to be processed. Thus we would seem to be complicating the water utility man's life while striving for a better quality product. Although new problems are being formed, we think there are various designs and operating procedures that will create far less sludge than conventional treatment, so we have invited several speakers here today to explain how they have been minimizing sludge production or re-cycling to reduce disposal problems. We in the Water Supply Research Laboratory of EPA have some ideas about modified treatment, but we can bring these oat later during the discussion period. WASTE DISCHARGE REGULATIONS The question of discharge permits has received increasing interest as more water companies are being forced to confront the problem of waste sludge and brine disposal. The fact is that water plant wastes have been considered as industrial by many states for many years. The entrance of the Federal government into the permit program is fairly recent, and has not as yet been fully felt by many industries, including water treatment plants. The history of Federal involvement is rather interesting and perhaps worthy of a few comments before discussing briefly the Standards and Enforcement Section of Public Law 92-500 - "Federal Water Pollution Control Act Amendments of 1972." In 1966, in a case of the U.S. Government vs. Standard Oil, the court ruled, in a case involving an oil spill, that oil in a river 1-6 ------- as a result of a spill is refuse. The Oil Company had contended that it was a valuable product and should not be defined as waste. Once it was defined as a refuse, it became subject to the 1899 Refuse Act. .Section 13 of this ACT prohibits the discharge or deposit of any waste in a waterway. The law authorizes the Chief of the Corps of Engineers to grant permits for the discharge of waste that will not be harmful, etc. Environmentalists immediately saw this as a way to control the discharge of wastes to rivers and in 1970, EPA was appointed as the technical advisor to the Corps of Engineers on the issuance of these discharge permits. There had been no federal permit system prior to 1970. Since then very few permits have been issued because of the Kalur vs Itesor case. In this case, the courts handed down a decision that required an environmental impact statement to be issued before a permit could be issued. This required that the Corps of Engineers issue an environmental impact statement for each waste discharge. This was an extremely difficult task, and the Corps of Engineers was reluctant to start to issue many permits because its staff was just not equal to it numerically. In addition, there was strong evidence that pending water pollution legislation would override the Kalur decision and release the Corps of Engineers of the responsi- bility of both issuing permits and making environmental impact statements. So, during the period between the Kalur decision and the passage of the 1972 Amendments to the Water Pollution Control Act, the Federal permit program had been in a state of suspended animation. 1-7 ------- An Act, cited as, "Federal Water Pollution Control Act Amendments of 1972," was passed on October 18, 1972. It did relieve the Corps of Engineers of regulatory responsibilities for permit issuances and charged the Administrator of USEPA with these responsibilities. During this period, it should be remembered that the states had their own water quality regulations, and many had permit regulations that included all waste discharges, including water treatment plant wastes. The states, as well as the Corps of Engineers and EPA, were initially interested in the major dis- charges, and in many instances, water treatment plants were not included in this category. In some cases they were, and many larger plants have been aware of these permit regulations for many years. All will probably be aware of the regulations shortly. FEDERAL STANDARDS AND PERMIT REGULATIONS The 1972 law requires the issuance of permits for all discharges to surface waters. There are no exceptions. Industries that discharge to sewage collection systems are not included, except that their wastes are implicit in the waste treatment plant permit. The parts of the Act (Public Law 92-500)that are of most interest are Title III - "Standards and Enforcement" and Title IV - "Permits and Licenses." The specific sections are 301, 302, 307, 318, 402, and 404. These sections are in the Appendix. They are written with a lawyer's flair for prosaic verbosity. What they say in summary is the following: 1. The discharge of any pollutant by anyone is unlawful, with certain exceptions. 1-8 ------- 2. By July 1, 1977, effluent limitations for point sources must be achieved based on, "the best practicable control technology currently available, " as defined by the EPA Administrator. Limitations for publicly owned treatment works will be based on secondary treatment, as defined by the Administrator. 3. By July 1, 1983, limitations must be achieved based on the "best available technology economically achievable, " as determined by the Administrator for yet to be defined categories and classes of industries - all to result in reasonable progress toward the national goal of eliminating all pollutants. 4. The Administrator is authorized to set water quality- related effluent limitations following public hearings. 5. Requires the Administrator to set pretreatment standards for introduction of pollutants into treatment works. 6. The Act provides for criminal penalties of from $2500 to $25, 000/day, or one year in prison, or both; double these amounts for the second offense; and civil penalties of up to $10, 000/day. 7. Requires essentially that all dischargers obtain a federal permit, contingent upon attaining a certificate from state, interstate agencies, or EPA, showing that they are in compliance with the law. 8. The EPA Administrator is authorized to issue permits for pollutant discharge under certain conditions; among these is a compliance timetable. 1-9 ------- 9. Authorizes EPA to approve state programs for conducting their own permit programs. 10. Where state standards are more stringent than required federal standards, the state standards will control. EFFECTS ON SLUDGE DISPOSAL PROCEDURES The Act applies to the discharge of any pollutant. In many states, "pollutant" has come to embrace back-wash water as well as sludge from settling and presettling reservoirs. This is to be expected since state water quality standards are generally related to effluent type standards that prohibit the degradation of the quality of the surface water receiving the discharge. The situation at Cincinnati may serve as an example of the extremes that some utilities may have to go to. The water works is embarking on a program that will eventually relieve the Ohio River of the onus of any Cincinnati water plant waste discharge. A $400, 000 pro ject that should be completed in three to four months, will permit them to recycle the backwash water to presettling reservoirs. Iron sludge that accumulates in the secondary settling basins is recycled through the presettling reservoirs. About once a year it is necessary to clean one of the two primary settling reservoirs. This sludge is now returned to the Ohio River. The prospect is that the water plant will be prohibited in the near future from making these returns. As a solution, the water works officials plan to construct a storage reservoir that will receive these annual discharges from the settling reservoirs. The storage reservoir is going to be built on part of a nearby golf course, and the water works will acquire the land in early 1974. Following construction of the reservoir, the water works will have no return 1-10 ------- discharge of any kind to the Ohio River, except perhaps the super- natant from the sludge storage reservoir. There is some question now as to whether this can be returned. It depends on the final definition and EPA approval of a clause in the ORSANCO Standards which requires "substantially complete removal of settleable solids," and "substantial reduction of suspended solids and also any other material to such a degree that these materials will not affect the turbidity, color, or odor of the River or impart taste or odor to water supplies, or taint the fish." If it is ruled that the supernatant cannot be discharged to the river, then it will probably be recycled through the primary reservoirs. The ultimate disposal of the sludge solids may have to be by centrifugation. These statements and actions being taken by water plants indicate that the handwriting is on the wall. They are shaped by legislation, both federal and state. Special consideration will probably be given to plants having particular problems, but over-all it appears that there will be little or no return discharge to the surface waters unless it meets the State's effluent standards. Checking with the EPA Regional Office or State Pollution Control Agency is, no doubt, the best way to acquire details that apply to your own situation. We only hope that citing the new regulations will help you to understand why the material to be presented in this seminar plus the information already in the AWWA Journal is important to you. 1-11 ------- Neefe, J. R., Baty, J. B., Reinhold, J. G., and Stokes, J. "Inactivation of the virus of infectious hepatitis in drinking water." Am. Jour, of Public Health, 37, 365-372 (Apr. 1947). Chang, S. L., Woodward, R. L., arid Kabler, P. K. "Survey of free-living nematodes and amoebas in municipal supplies." Jour. AWWA, 52, 5, 613-618 (May 1960). Walton, G. "Effectiveness of water treatment processes as measured by coliform reduction." U. S, Dept. of Health, Education, and Welfare, Public Health Service, Publ. No. 898, 68 pp. (1961). Sanderson, W. W. and Kelly, S. Discussion of "Human enteric viruses in water; source, survival and removability" by Clarke, N. A., Berg, G., Kabler, P.K., and Chang, S. L. Internat. Conf. on Water Poll. Res., 536-541, London, September 1962. Pergamon Press. (1964). Hudson, H. E., Jr. "High-quality water production and viral disease." Jour. AWWA, 54, 10, 1265-1272 (Oct. 1962). Tracy, H. W., Camarena, V. M., and Wing, F. "Coliform persistence in highly chlorinated water. " Jour. AWWA, 58, 1151 (1966). Robeck, G. G., Clarke, N. A., and Dostal, K, A. "Effectiveness of water treatment processes in virus removal." Jour. AWWA, 54, 1275-1290 (Oct. 1962). McCabe* L. J., Symons, J. M., Lee, R, D., and Robeck, G. G. "Survey of community water supply systems," Jour. AWWA, 62, 670-687 (Nov. 1970). Roueche, B. Annals of Medicine. Three sick babies. The New Yorker, Oct. 5 (1968). Kispert, Edward C., Private Communication, April 13, 1973. 1-12 ------- APPENDIX 1-13 ------- "TITLE III—ST.VXD.VUDS AXD EXFOUCEMENT Pub. Law 92-500 "kffi.uext limitations October 18, 1972 "Sv.c. SOI. (a) Except as in compliance with this section and sec- tions 302, 300, 307, 318, 402, mul 404 of this Act, the discharge of any pollutant by a 113- person shall be unlawful. "(b) I11 "order to carry out the objective of this Act there shall Ix. achieved— 66 STAT. , "(1)(A) not later than July 1, 1077, efiluent limitations for point sources, other than publicly owned treatment works, (i) which shn.lt require the application of the best practicable control technology currently available as defined by the Administrator pursuant to section '104(b) of this Act, or (ii) in the case of a dis- charge into a publicly owned treatment works which meets the requirements of subparagraph ( B) of this paragraph, which shall require compliance with any applicable pretreatment requirements and any requirements under section 307 of this Act; and "(B) for publicly owned treatment works in existence on July 1, 1077, or approved pursuant to section 203 of this Act prior to June 30,1974 (for which construction must be completed within four years of approval), effluent limitations based upon secondary treatment us defined by the Administrator pursuant to section 304(d) (1) of this Act; or, "(C) not later than July 1, 1977, any more stringent limitation, including those necessary to meet water quality standards, treat- ment standards, or schedules of compliance, established pursuant to any State law or refill at ions (under authority preserved by sec- tion 510) or any other Federal hsw or regulation, or required to implement nny applicable water quality standard established pur- suant to this Act. "(2) (A) not later than July 1, 1083. efiluent limitations for categories and classes of point sources, other than publicly owned treatment works, which (i) shall require application of the best available technology economically achievable for such category or class, which will result in reasonable further progress toward the national goal of eliminating the discharge of all pollutants, as determined in accordance, with regulations issued by the Admin- istrator pursuant to section 304(b)(2) of this Act, which such elltuent limitations shall require the elimination of discharges of all pollutants if the Administrator finds, on the basis of informa- tion available to him (including information developed pursuant to section 315), that such elimination is technologically and eco- nomically achievable for a categorv or class of point sources as determined in accordance with regulations issued bv the Adminis- trator pursuant to section 304(b) (2) of this Act. or (ii) in the case of the introduction of a pollutant into a publicly owned treatment works which meets the requirements of subparagraph (B) of this paragraph, shall require compliance with any applicable pretreat- ment requirements and any other requirement under section 307 of this Act; and "(B) not later than Julv t, 1083, compliance by all publicly owned treatment works with the requirements set forth in sec- tion 201 (g) (2) (A) of this Act. 1-14 ------- "(c) The Administrator may modify the requirements of subsection (b) (2) (A) of this section with respect to unv point source for which a permit application is filed sifter July 1. 1977. upon a showing by the owner or operator of such point source satisfactory to the Administra- tor that such modified requirements (1) will represent the maximum use of technology within the economic capability of the owner or operator; and (2) will result in reasonable further progress toward the elimination of the discharge of pollutants. "(d) Any effluent limitation required by paragraph (2) of subsec- tion (b) of this section shall be reviewed at least every five years and, if appropriate, revised pursuant to the procedure established under such paragraph. "(e) Effluent limitations established pursuant to this section or sec- tion 302 of this Act shall be applied to all point sources of discharge of pollutants in accordance with the provisions of this Act. 66 STAT. 846 "(f) Notwithstanding any other provisions of this Act it shall be unlawful to discharge any radiological, chemical, or biological war- fare agent or high-level radioactive waste into the navigable waters. "WAT Kit QUALITY liKl.ATH) EFFLUENT LIMITATIONS "Sec. 30-2. (a) Whenever, in the judgment of the Administrator, dis- clm rges of pollutants from a point source or group of point sources, with the application of effluent limitations required under section 301 (b) (-2) of this Act. would interfere with the attainment or mainte- nance of that wilt el- quality in a specific portion of the navigable waters winch shall assure protection of public water supplies, agricultural and industrial uses, and the protection and propagation of a balanced population of shellfish, fisfi and wildlife, and allow' recreational activi- ties in and on the water, effluent limitations (including alternative eflluent control strategies) for such point source or sources shall be established which can reasonably be expected to contribute to the, attainment or maintenance of such water quality. "(b) (1) Prior to establishment of any effluent limitation pursuant Public hearing, to subsection (a) of this section, the Administrator shall issue notice of intent to establish such limitation and within ninety days of such notice hold a public hearing to determine the relationship of the eco- nomic and social costs of achieving any such limitation or limitations, including any economic or social dislocation in the affected community or communities, to the social and economic benefits to be obtained (including the attainment of the objective of this Act) and to deter- mine whether or not such eflluent limitations can be implemented with available technology or other alternative control strategies. ¦'('2) If a person affected by such limitation demonstrates at such hearing that (whether or not such technology or other alternative con- trol strategies are available) there is no reasonable relationship between the economic and social costs and the benefits to be obtained (including attainment of the objective of this Act), such limitation shall not become effective and the Administrator shall adjust such limitation as it applies to such person. "(c) The establishment of eflluent limitations under this section shall not, oiMM'ate to delay the application of any effluent limitation estab- lished under sect ion :!D1 of this Act. 1-15 ------- ''TOXIC ANI) l'HKTKKATMEN'f FITI.UKNT STANDARDS "Svr.c. 307. (a) (1) Thy Administrator shall, within ninety days after the date of enactment of this title. publish (and from time to time thereafter revise") a list which includes any toxic pollutant or combina- tion of such pollutants for which an effluent standard (which may include a prohibition of the discharge of such pollutants or combina- tion of such pollutants) will ho established under this section. The Administrator in publishing such list shall take into account the toxic- ity of the pollutant, its persistence, degradability.the usual or potential presence of the affected organisms in any waters, the importance of the affected organisms and the nature and extent of the effect of the toxic pollutant on such organisms. il('2) "Within one hundred and eighty days after the date of pub- Proposed lication of any list, or revision thereof, containing toxic pollutants or effluent combination of pollutants under paragraph (1) of this subsection, the standard. Administrator, in accordance with section Soft of title o of the I'nited Publication. States Code, shall publish a proposed effluent standard (or a prohibi- 80 Stat. 38 3. tion) for such pollutant or combination of pollutants which shall take into account the toxicity of the pollutant, its persistence, degradability, 86 STAT. B57 the usual or potential presence of the affected organisms in any waters, the importance of the affected organisms and the nature and Hearing. extent of the effect of the toxic pollutant on such organisms, and he shall publish a notice for a public hearing on such proposed standard to be held within thirty days. As soon as possible after such hearing, but not later than six months after publication of the proposed effluent standard (or prohibition), unless the Administrator finds, on the record, that a modification of such proposed standard (or prohibition) is justified based upon a preponderance of evidence adduced at such hearings, such standard (or prohibition) shall be promulgated. Revised '"(¦*) If after a public hearing the Administrator finds that a modi- effluent fication of such proposed standard (or prohibition) is justified, a standard. revised ellluent standard (or prohibition) for such pollutant or com- bination of pollutants shall be promulgated immediately. Such stand- ard (or prohibition) shall be reviewed and, if appropriate, revised at least every three years. "(4) Anv diluent standard promulgated under this section shall bo at that level which the Administrator determines provides an ample margin of safety. "(5) When proposing or promulgating any effluent standard (or prohibition) under this section, the Administrator shall designate the category or categories of sources to which the elllnent standard (or prohibition) shall apply. Any disposal of dredged material may be included in such a category of sources after consultation with the Secretary of the Army. Efreotive "(6) Any ellluent standard (or prohibition) established pursuant to date, this section shall take effect on such date or dates as specified in the order promulgating such standard, but in no case more than one year from the date of such promulgation. "(7) Prior to publishing any regulations pursuant to this section the Administrator shall, to the maximum extent practicable within the time provided, consult with appropriate advisory committees, States, independent experts, and Federal departments and agencies. Pretreatment "(b)(1) The Administrator shall, within one hundred and eighty standards, days after the date of enactment of this title and from time to time proposed thereafter, publish proposed regulations establishing pretreatment regulations, standards for introduction of pollutants into treatment works (as publloatlon, defined in section 212 of this Act) which are, publicly owned for those pollutants which are determined not to be susceptible to treatment by such treatment works or which would interfere with the operation of such treatment works. Not later than ninety days after such publica- tion, and after opportunity for public hearing, the Administrator shall 1-16 ------- promulgate such pri'tieatinent standards. Pretmitnieiit standards under this subsection shall specify a time for com pi in nee. not to exceed three years from the date of promulgation and shall be established to prevent the discharge of anv pollutant through treatment works (as defined in section 212 of this Act) which are publicly owned, which pollutant interferes with, passes through, or otherwise is incompatible with such works. "(2) The Administrator shall, from time to time, as control tech- nology, processes, operating methods, or other alternatives change, revise" such standards following the procedure established by this sub- section for promulgation of such standards. "(3) When proposing or promulgating nnv pretreatment standard under this section, the Administrator shall designate the category or categories of sources to which such standard shall apply. "(4) Nothing in this subsection shall affect any pretreatment requirement established by any State or local law not in conflict with any pretreatment standard established under this subsection. "(c) In order to insure that any source introducing pollutants into a publicly owned treatment works, which source would be a new source subject to section 300 if it were to discharge pollutants, will not cause a violation of the ellluent limitations established for any such treatment works, the Administrator shall promulgate pretreatment standards for the category of such sources simultaneously with the promulgation of standards of performance under section 300 for the equivalent category of new sources. Such pretreatment standards shall prevent the dis- charge of any pollutant into such treatment works, which pollutant ' ire with, pass through, or otherwise be incompatible with "(d) After the effective date of any ellluent standard or prohibition or pretreatment standard promulgated under this section, it shall be unlawful for any owner or operator ol any source to operate any source in violation of any such ctiluent standard or prohibition or pretreat- ment standard. "Sec. 318. (a) The Administrator is authorized, after public hear- ings, to permit the discharge of a specific pollutant or pollutants under controlled conditions associated with an approved aquacultnre proj- ect under Federal or State supervision. "(b) The Administrator shall by regulation, not later than Janu- ary 1, 1974. establish anv procedures and guidelines ho deems neces- sary to carry out this section. "NATIONAL POU.CTANT D1SCHAHUE >',1.1 >11 NATION SYSTEM "Sec. 402. (a) (1) Except as provided in sections 318 and 404 of this Permits, Act, the Administrator may, after opportunity for public hearing, issuance, issue, a pennit for the discharge of any pollutant, or combination of pollutants, notwithstanding section 3<)i(u), upon condition that such discharge will meet cither all applicable requirements under sections 301, 302. 306, 307, 308, and 403 of this Act, or prior to the taking of necessary implementing actions relating to all such requirements, such conditions as the Administrator determines arc necessary to carry out the provisions of this Act. 66 STAT. 858 "aquacci.turk 1-17 ------- "(:!) The Administnitor shall prescribe conditions for such permits to assure compliance with the requirements of paragraph (1) of this subsection, including conditions on data mid information collection, reporting njui such other requirements «s he deems Appropriate. "(3) The permit program of the Administrator under paragraph (1) of this subsection, and jjermits issued thereunder, shall be subject to the same terms, conditions. am! requirements as npplv to a Statu permit program and ]K'rniiIs issued thereunder under subsection (b) of this sect-ion. "(4) All permits for discharges into the navigable watoi-s issued pursuant to section 1.'! of the, Act of March :i. 18!>!1. shall be deemed to 30 Stat, 1152, be permits issued under this title, and Hermits is-ued under this title 33 LSC 407. shall be deemed to be permits issued under section IS of the Act of Mnrch 'i. 1K!)<). and shall continue in force and effect for their term unless revoked, modified, or suspended in accordance with the pro- visions of this Act, "(5) No permit for a discharge, into the navigable waters shall be issued under section 5:S of the Act of March 3, after the date of enactment of this title. Knell application for a permit under section 111 of the Act of March ;i. 1K!)<), pending on the date of enactment of this Act .shall be deemed to be ad application for a permit under this section. The Administrator shall authorize a State, which he, deter- mines has the capability of administering a permit program which will carry out the object ive of this Act. to issue pennits for discharges into the navigable waters within the jurisdiction of such State. The Administrator may exercise the authority granted him bv the pre- ceding sentence only during the period which begins on the date, of enactment of this Act and ends either on the ninetieth day after the date of the first promulgation of guidelines required by section .'Wit {li) (-J) of this Act. or the date of approv al by the Administrator of tl permit program for such State under subsection (b) of this sec- tion. whichever date first occurs, and no such mithoriy.it'ion io a State shall extend beyond the last day of such period. Each such permit shall be subject to such conditions as the Administrator determines all1, necessary to carry out the provisions of this Act. Xo such perm t shall issue if the Admi uist rator objects to such issuance. "(b) At any time after the promulgation of the guidelines reqni;od State pennit by sui.r. f'tioti (h) (2) of section .'iO-t of this .Vet, tlie (ioventor of each progrv 3. Slate. des'-ing to administer its own permit program for discharges 66 S'fAT. 931 __ into navigable waters within its jurisdiction may submit to the Admin- istrator a full and complete description of the program it proposes to establish and administer under State law or under an interstate compact. In addition, such State shall submit ft statement from the attorney general (or the attorney for those State water pollution con- trol agencies which have independent legal counsel), or from the chief legal officer in the, case of an interstate agency, that the laws of such State, or the interstate compact, as the case may be, provide Approval adequate authority to carry out the described program. The Admin- oondltionu, istrator shall approve, each such submitted program unless he deter- mines that ndcqniite authority does not exist: *'(1) To issue permits which— l" (A) apply, and insure compliance with, any applicable require- ments of sections jiUl. 30-2, 30(5. ;507, and 40!i; "(B) are for fixed terms not exceeding five years; nnd "(C) cun be terminated or modified for cause including, but not limited to, the following: "(i) violation of any condition of the permit; "(ii) obtaining a permit by misrepresentation, or failure to disclose fully all relevant facts; 1-18 ------- " (iii) change in any condition that requires either a tempo- rary or permanent. reduction or elimination of tlie permitted discharge; "(D) control the disposal of pollutants into wells; "('2) (A) To issue permits which apply, and insure compliance with, all applicable requirements of section ;$08 of this Act, or li( It) To inspect, monitor, enter, and require reports to at least the same extent as required in section :108 of this Act; "(3) To insure that the public, and any other State the waters of which may be atl'eeted. receive, notice of each application for a permit and to provide an opportunity for public hearing before a ruling on each such application; " (4) To insure that the Administrator receives notice of each appli- cation (including a copy thereof) for a permit; "(5) To insure that nny State (other than the permitting State), whose, waters may be atl'eeted by the issuance of a permit may submit written recommendations to the permitting State (and the Adminis- trator) with respect to any permit application and, if any part of such written recommendations are not accepted by the. permitting State, that the permitting State w ill notify such affected State, (and the Administrator) in writing of its failure to so accept such recommenda- tions together with its reasons for so doing; "(0) To insure that no permit will be issued if, in the judgment of the Secretary of the Army acting through the Chief of Engineers, after consultation with the Secretary of the department in which the Coast Guard is operating, anchorage and navigation of any of the navigable waters would lie substantially impaired thereby; "(7) To abate violations of the permit or the permit program, including civil and criminal penalties and other ways and means of enforcement; "(8) To insure that any permit for a discharge from a publicly owned treatment works includes conditions to require adequate notice to the, permitting agency of (A) new introductions into such works of pollutants from any source which would be ft new source as defined in section liOti if such source were discharging pollutants, (11) new introductions of pollutants into such works from a source which would 1)0 subject to section -501 if it were discharging such pollutants, or (C) a substantial change in volume or character of pollutants being introduced into such works by a source introducing pollutants into 86 STAT. BB2 such works at the time of issuance of the permit. Such notice shall include information on the quality and quantity of etHuent to be introduced into such treatment works and any anticipated impact of such change in the quantity or quality of effluent to be discharged from such publicly owned treatment works; and "(0) To insure that any industrial user of any publicly owned treatment works will comply with sections 201(b), 307, and 308. "(c) (1) Not later than ninety days after the date on which a State has submitted a program (or revision thereof) pursuant to subsec- tion (b) of this section, the Administrator shall suspend the issuance of permits under subsection (a) of this section as to those navigable waters subject to such program unless ho determines that the State permit jirogrnm does not meet the, requirements of sul»section (b) of this section or docs not conform to the guidelines issued under section 304(h)(2) of this Act. If the Administrator so determines, he shall notify the State of any revisions or modifications necessary to con- form to such requirements or guidelines. "(2) Any State permit program under this section shall at all times be in accordance with this section and guidelines promulgated pursuant to section 1104(h) (2) of this Act. 1-19 ------- 86 STAT. 683 Publia Information, ''(3) Whenever the Administrator determines after public hearing that « State is not administering a program approv ed under this sec- tion in accordance with requirements oi this section, he shall so notify the State nnd, if appropriate corrective action is not taken within a reasonable time, not to exceed ninety days, the Administrator shall withdraw approval of such program. The Administrator shall not withdraw approval of any such program unless he shall first have, notified the State, and made public, in writing, the reasons for sue)) withdrawal. "(d) (J) Kucli State shall transmit to the Administrator a copy of each permit application received by audi State and provide notice to the Administrator of every action related to the consideration of sncli permit application, including each permit proposed to be issued by such State. "(2) No permit shall issue (A) if the Administrator within ninety days of the date of his notification under subsection (b)(5) of this section objects in writing to the. issuance of such permit, or (B) if the. Administrator wit hin ninety days of the. date of transmittal of the proposed permit by the State objects in writing lo the issuance of such permit its being outside the guidelines and requirements of this Act. "(3) The Administrator may, as to any permit application, waive paragraph ('2) of this subsection. "(e) In accordance with guidelines promulgated pursuant to sub- section (h) (2) o{ section "04 of this Act, the Administrator is author- ized to waive the requirements of subsection (d) of this section at the time lie approves a program pursuant to-subsection (h) of this section for any category (including any class, type, or size within such category) of jx>int sources within the State submitting such program. "(f) The Administrator shall promulgate regulations establishing categories of point sources which lie determines shall not be subject to the requirements of subsection (d) of this section in any State with a program approved pursuant to subsection (b) of this section. The Administrator may distinguish among classes, types, and sizes within apy category of point sources. ft(g$ Any permit issued under this section for the discharge of pol- lutants into the navigable waters from a vessel or other floating craft shall be subject, to any applicable regulations promulgated bv the Secretary of the department in which the Coast Guard is operating, request for the purpose of reproduct ion, "(k) Compliance with a. permit issued State peimit program, approval withdrawal. Administrator, notifioatl&n. Waiver authority. Point aouroes, DS.tegorieB, establishing specifications for safe transportation, handling, carriage, storage, and stowage of pollutants. "(h) In the event any condition of a permit for discharges from a. treatment works (as defined in section 212 of this Act) which is publicly owned is violated, a State with a program approved under subsection (b) of this section or the Administrator, where no State program is approved, may proceed in a court of competent jurisdiction to restrict or prohibit the introduction of any pollutant into euch treatment works by a source not utilizing such treatment works prior to the finding that such condition was violated. " (i) Nothing -in this section shall be construed to limit the author- ity of the Administrator to take action pursuant to section 309 of this Act. "(j) A copy of each permit application nnd each permit issued under this section shall be available to the public. Such permit appli- cation or permit, or portion thereof, shall further be available on pursuant to this section shall be deemed compliance, for purposes of sections 309 and 505, with sec- tions 301, 302, 306, 307, and 403. except any standard imposed under section 307 for a toxic pollutant injurious to human health. Until 1-20 ------- December 31,1074, in any case where a. permit for discharge has been applied for pursuant to t>)iis section, but final administrative disposition of such application hns not been made, such discharge shall not be a violation of (1) section 301, ,106, or 40'2 of this Act, or (2) section 13 stat. 1152. of the Act of March 3, 189!), unless the Administrator or-other plain- use 407. tiff proves that final administrative disposition of such application has not Wen made because, of the failure ot the applicant to furnish infor- mation reasonably required or requested in order to process the Applica- tion. For the 180-day period beginning on the date of enactment of the te, p. 816. Federal \Vtiter Pollution Control Act Amendments of 1972, in the case of any point source discharging any pollutant or combination of pol- lutants immediately prior to such date of enactment which source 13 not subject to sectio"n 13 of the Act of March 3, 1899, the discharge by such source shall not be a violation of this Act if such a source applies for a permit for discharge pursuant- to this section within such 180-day period. "permits fob dredged or fill jtaterial "Sec. 404. (a) The Secretary of the Army, acting through the Chief No*1'*! hearing of Engineers, may issue permits, after notice and opportunity for opportunity, public nearings for the discharge of dredged or fill material into the navigable waters at specified disposal sites. "(d) Subject to subsection (c) of this section, each such disposal si to shall bo specified for each such permit by the Secretary of the Army (1) through the application of guidelines developed by the Adminis- trator, in conjunction with the Secretary of the Army, which guide- lines shall be based ujktn criteria comparable to the criteria applicable to the territorial seas, tlwcontiguous zone, and the ocean under section 403(c), and (2) in anv case where such guidelines under clause (1) alone would prohibit the specification of a site, through the applica- tion additionally of the economic impact of the site on navigation and anchorage. "(c) The Administrator is authorized to prohibit the specification (including tho withdrawal of specification) of any defined area as a disposal site, and he ia authorized to deny or restrict the use of any defined area for specification (including the withdrawal of specifica- tion) ns a disposal site, whenever he determines, after notice ana oppor- tunity for public hearings, that tho discharge of such materials into such area will have an unacceptable adverse effect on municipal water supplies, shellfish beds and fishery areas (including spawning and brooding aveas), wildlife, or recreational areas. Before making such determination, the Administrator shall consult with the Secretary of the Army. The Administrator shall set forth in writing and make Pi ridings of public his findings and his reasons for making any determination Administrator, under this subsection. publioation. Disposal slt«j speolfioation prohibition* 1-21 ------- USE OF ORGANIC POLYMERS AND SLUDGE VOLUME REDUCTION by Lee Streicher Water Purification Engineer The Metropolitan Water District of So. Calif. Los Angeles, California Disposal of sludge or other process wastes has always been a part of water treatment plant operation. Ten or 20 years ago, however, it was more of a nuisance than a problem as most treatment plants returned the sludge to their source of water supply, whether river or lake, downstream or distant from the treatment plant intake so that it did not interfere with their plant operation. This was a very simple and inexpensive way to dispose of the sludge, and was used by 92 percent of the water treatment plants surveyed in 1953; Table 1. In recent years, and particularly since pollution control and protection of our environment have become subjects for almost daily discussion in newspapers and at public meetings, various state and local government agencies have passed regulations to control the discharge of potential pollutants into natural bodies of water or watercourses. Public Law 92-500, enacted in October 1972 as an amendment to the Federal Water Pollution Control Act, prohibits the discharge of pollutants into a waterway unless such discharge is authorized by a permit issued by the U.S. Environmental Agency or by an approved State Agency. Under these various regulations, sludge disposal is becoming a problem rather than the nuisance it was just a few years ago. Il-l ------- What, then, can be done to ease the burden of this problem? Several approaches to a solution can be considered. First, methods of treatment which might reduce the quantity of sludge produced should be investigated. If clarification without softening is required, the recently developed organic polymers may assist in the attainment of this goal. These polymers are long-chain, high-molecular-weight organic chemicals that are available in three types: (a) cationic, or positively charged; (b) anionic, or negatively charged; and (c) nonionic, or neutral in charge. As the suspended matter found in natural waters is usually negatively charged, the cationic polymers are generally the type most suitable for use as primary coagulants. If the suspended matter is of such a nature that these polymers can be used successfully as primary coagulants, the dosage required will probably fall within the range of 0.5 to 2.0 ppm. Compared with a dosage of 15 to 30 ppm or more of alum that might be required to achieve comparable clarification of the same water, the reduction in the quantity of sludge produced as a result of polymer use can be quite significant. Furthermore, unlike the gelatinous and voluminous aluminum hydroxide sludges, the polymer sludges are relatively dense and easier to dewater for subsequent handling and disposal. Although the unit cost of the cationic polymers is 10 to 15 times higher than the cost of alum, the dosages required for treatment are reduced by an even greater ratio, so the 11-2 ------- actual cost of chemicals for coagulation is less with polymers than with alum. It is important to point out that not all waters can be treated with equal success with the same polymer — or the same dosages. Jar tests should be run with several different dosages of the various polymers available to determine the specific material and range of dosages best suited for each water supply. In addition, for treatment of potable waters, only the polymers approved by the EPA for use in such water treatment should be considered. Even though a cationic polymer alone can, at times, produce a strong and readily settleable floe, at other times the floe may be weaker and less dense. A nonionic polymer may be helpful under these conditions as a coagulant aid. The nonionic polymer may act as a bridging material between fine particles of coagulated material, causing them to agglomerate into larger and stronger floe that will settle more readily and also be more easily filtered from the water. The dosage required to aid coagulation is about 0.1 to 0.25 ppm, so very little is added to the quantity of sludge produced. The cationic and nonionic polymers also appear to be effective as filter aids. In this application they appear to bridge between the fine particles carried over from the settling basins and produce a larger, and more readily filterable material. In fact, these materials may be very effective filter aids even with a water that has not been previously coagulated and flocculated. II-3 ------- Thus, if a natural water of moderately low turbidity (say less than 5 JTU) is to be clarified and coagulation is not mandatory, it may be possible to produce a high quality filtered water simply by using a polymer as a filter aid. The dosage required may range from about 10 to 30 parts per billion if a nonionic polymer is used, or from 30 to 90 ppb if a cationic polymer is used. Obviously, elimination of the prior coagulation and flocculation will further reduce the quantity of sludge produced for disposal, thereby limiting it to essentially the suspended matter removed from the water. Occasionally, with changes in the quantity and character of the suspended matter in a water supply, the usual range of dosages of the normally successful cationic polymer, even with the help of a nonionic coagulant aid, may fail to produce a good floe. It has been found that a very low dosage (about 4 ppm) of alum used in conjunction with the polymers may promote satisfactory flocculation. Although this results in an increase in the quantity of sludge produced and to some degree introduces the undesirable characteristics of aluminum hydroxide, the quantity is still substantially less than if 20 to 30 ppm of alum were used instead, and the alum- polymer sludge is still easier to handle and dewater than the alum sludge alone. Jar tests have indicated that a properly conditioned polymer sludge, when recirculated to the raw water channel to increase the suspended solids prior to II-4 ------- coagulation, can improve floe formation and clarification. For these tests, the sludge was conditioned by thorough agitation with about 50 ppm of cationic polymer. This made the sludge very dense and strong, and so heavy that it settled almost immediately when agitation was stopped. When enough conditioned sludge was added to the raw water to produce a turbidity of about 100 JTU, the floe formed following coagulation was much denser and the clarifica- tion of the water more complete than when no recirculated sludge was used. This proved to be the case even when the dosage of cationic polymer used for primary coagulation was reduced from 1.0 or 1.5 ppm to 0.5 ppm. At the time of writing, this recirculation had not yet been tried on a full plant scale but work has been started for such a test in the relatively near future. No matter what treatment methods or chemicals are used, if suspended matter has been removed from the water some sludge residue is left for ultimate disposal. As discharge to waterways has been or is being phased out, other methods must be considered. Sludge lagoons will continue to be used as long as land is available at moderate cost within a reasonable distance of the treatment plant. Landfill operations, too, will accept properly prepared sludge materials. Sewer systems may accept some sludges, but this merely shifts the burden for subsequent handling and ultimate disposal from the water treatment plant to the wastewater treatment plant. Polymer sludges are also suitable for use as soil II-5 ------- conditioners, which would be a desirable disposal method if a demand for such use could be developed. Incineration would appear to be a very practical way of reducing the quantity of sludge to an absolute minimum for ultimate disposal. This method is used with some sewage sludges, and it should be applicable to some water treatment plant sludges as well. If the suspended solids removed from the water are predominantly organic matter, and polymers are used for coagulation, then the sludge cake produced may be readily combustible provided that it is adequately dewatered. The ash remaining after incineration will represent only 5 to 10 percent of the original quantity of sludge. Furthermore, the ash should be easy to handle, it would not be subject to decompo- sition when applied to a landfill operation, and it may possibly be suitable for use as a filter aid (instead of diatomaceous earth) if needed during dewatering of the sludge prior to incineration. On the other hand, alum sludges and softening plant sludges are not well suited for incineration, as they are primarily non-combustible mineral matter and would permit very little volume reduction. Furthermore, the fuel requirement for these sludges would be much higher than for organic sludges. From the foregoing, it would appear that the use of the right polymers at the right dosages could help in the production of better water, perhaps even with a saving in chemical costs, and result in a substantial II-6 ------- reduction in the amount of sludge (and an improvement in the character of the sludge) produced for disposal. Unfortunately, however, some treatment plants have been unable to find a polymer or combination of polymers that would provide effective clarification with their waters. Until new polymers which can perform satisfac- torily with those waters are developed, those plants will continue to use alum (or, in some cases, iron salts) for coagulation. What can they do to relieve their sludge disposal problems? A reduction in the volume of sludge produced may be attainable if polymers can be used' as coagulation aids. It was mentioned eaflier that during times when polymers alone failed to produce a good floe, the addition of 4 ppm of alum helped to solve the immediate problem. In the same manner, the addition of 0,2 to 1.5 ppm of polymers may permit a substantial reduction in the alum dosage required to achieve satisfactory flocculation. This reduction in alum dosage will, of course, be reflected in a reduction in the quantity of sludge produced. But what if polymers are not helpful in the treatment of certain waters and higher dosages of alum must be used to obtain satisfactory clarification? If tests confirm the economic feasibility, recovery of alum or sodium aluminate from the aluminum hydroxide sludge might deserve consideration. Alum recovery is not practiced very widely and, where it is, the efficiency of II-7 ------- recovery appears to be only about 60 percent. In addition, if heavy metals are present, they will build up in concentration with each alum recovery operation. These factors have tended to discourage wider use of alum recovery from aluminum hydroxide sludge. Figure 1 shows a flow diagram of a typical alum recovery system, and Figure 2 shows a flow diagram of a modified recovery system which, in small pilot plant tests, yielded 80 to 93 percent recoveries of filtered alum. The modified system also requires less equipment, less lime (or calcium carbonate) for pH adjustment of the sludge cake left after filtration, and leaves less residue for ultimate disposal. Further tests of this system might be warranted to investigate its economic feasibility. An alkaline recovery system (using sodium hydroxide rather than sulfuric acid) has also been tried experimentally. This results in the recovery of sodium aluminate instead of alum. As the heavy metal hydroxides are not redissolved at the high pH levels maintained in this recovery process, there is no continuous build-up of these contaminants. However, the sodium aluminate alone is not a good primary coagulant, so alum, carbon dioxide, or other acidic material must be used with it to achieve proper coagulation. These recovery processes will, or course, reduce the quantity of sludge left for ultimate disposal. On the other hand, if alum or sodium aluminate recovery is not practicable, other methods for reducing the sludge II-8 ------- disposal problem should be considered. Alum sludge is very gelatinous and difficult to dewater, so it is not as suitable for lagooning as other sludges are. Here, again, polymers may be useful, in this instance as sludge conditioning agents to aid in the dewatering process. Drying beds, if used, must be shallow to permit cracking to the bottom of the sludge layer; otherwise the bottom material will remain wet for a long time. Discharge into a sewer system is a very simple means for disposal, but some sewage plants are reluctant to accept such sludge because when it is mixed with sewage sludge the mixture is much more difficult to dewater than sewage sludge alone and this, coupled with the voluminous nature of the alum sludge, tends to tax their digester capacity. Alum sludge is also less suited for landfill disposal because of its failure to compress into a hard, dense fill. Freezing and thawing may be the best way to reduce the quantity and improve the characteristics of an alum sludge, particularly if climatic conditions permit natural freezing. In this process the alum sludge is first thickened to about 3.5 to 4 percent solids and then slowly frozen. The ice crystals formed squeeze the water from the sludge and compress the particles to about one-sixth of their original volume. The process is irreversible and, when thawed, the particles are like a brown powder or sand. These granules could be used as soil conditioners, or, possibly, as fillers in some commercial products, but it is questionable whether a II-9 ------- sufficient demand for this material could be developed. However, disposal of the greatly reduced volume and easier to handle sand-like residue would be much easier than disposal of the original alum sludge. If softening, rather than just clarification, is desired in the treatment process, then the sludge produced will be either calcium carbonate or a mixture of calcium carbonate and aluminum hydroxide when lime or lime-soda ash softening is used. Calcium carbonate forms a dense, granular sludge which is easy to dewater and quite easy to handle. Magnesium hydroxide, like aluminum hydroxide, is voluminous and difficult to dewater. With any substantial degree of softening a great volume of sludge is produced. In the operation of large treatment plants, recovery of lime from calcium carbonate sludge may be practicable. Table 2 lists a number of plants in the U.S. where lime recovery is practiced. If the sludge contains a mixture of calcium carbonate and magnesium hydroxide, the two can be separated by centrifugation. (Or the process to be described later today by Kinman and Thompson may be applicable.) By passing through the steps of thickening, dewatering, flash drying, and calcination, the calcium carbonate sludge can be converted to lime. Generally, about 50 percent more lime can be recovered than was used in the treatment process, if a market can be found for this surplus lime, part of the cost of the reclamation process can be recovered. 11-10 ------- If the sludge is dried by not recalcined, it may be suitable for soil conditioning. If it is also low in organic matter, it could be used for road stabilization, neutralization of acid wastes, as a filler in rubber or other products, or possibly as a pigment in whitewash paints. If no use is found for the sludge, it can be much more easily dewatered and handled than alum sludge and thus is suitable for lagooning or for landfill disposal. It has been suggested that the sludge could assist in phosphate removal during sewage treatment, so that discharge into a sewer might be acceptable, but some sewage treatment plants have reported that the sludge interfered with anaerobic digestion or that it plugged the digesters. As mentioned earlier, unlike polymer sludges neither alum nor lime sludges are suited to incineration for volume reduction, so either recovery of treatment chemicals or application to other beneficial uses must be relied upon if the quantity of sludge left for ultimate disposal is to be reduced. Therefore, it appears that at this time the use of polymers, if applicable, will result in the production of minimal quantities of sludge or residue for final disposal. 11-11 ------- TABLE 1 Methods for Disposal of Water Treatment Plant Sludges Point of Disposal Percent of Plants Using Indicated Disposal Methods Softening (Lime) Sludge 1953* 1969 Coagulation (Alum) Sludge 1953* 1969 Stream or lake Sewer or drain Dry Creek Landfill Lagoons Recycled 92 4 1 0 3 39 6 11 11 33 92 4 1 0 3 49 21 6 6 18 * No distinction made between lime and alum sludges. Note: 1953 based upon responses from about 1,600 plants: 1969 data based upon responses from about 80 plants (mainly large plants). ------- TABLE 2 Recalcination Plants Location Water Plant Lime Sludge- Construction Type of Capacity Type of Capacity Feed to-Lime Date Fumace(l) ton/day Dewatering(2) mgd Ib/mg Ratio Plant Cost(3] $10* M M I M U> Miami, Fla, 1948 Lansing, Mich. 1954 Dayton, Ohio 1960 San Diego, Calif. 1961 S.D. Warren Company Muskegon, Mich. 1963 Ann Arbor, Mich. 1968 St. Paul, Minn. 1969 RK FB RK RK FB FB FB SO 30 150 25 70 24 SO c c c c VF c c 60 20 96 1,800 2,200 2,460 2.27 2.5 793 1,500 534 100 992 2.4 1,750 (1) RK = rotary kiln; FB = fluidized-bed incinerator. (2) C = centrifuge: VF = vacuum filter. (3) Construction cost at date of construction. ------- Figure 1 Flow Diagram of Typical Alum Recovery Installation Sulfuric Acid Lime and Sludge Mixing Acta ir Sludge i—j ' i—i Mixing \_J \_J M laked Lime Thickeners Sludge from Settling Basins Filter C Sludge Receiving Basin Recla j Tied Alum Tanks o> Trucked away to c To poJntr. of alum application site for disposal ------- Figure 2 Flow Diagram of Experimental Alum Recovery Installation ^^_£uifuric Acid Acid and Sludge Mixing Powdered Lime Pressure FiIters M i f—1 Filter Cake Sludge from Settling Basins Pug Mill Neutralised cake To points of Reclaimed aluia application hauled to dur.o site Alum for disposal ------- HIGH ENERGY MIXING AND FLOCCULATIQN By James H. Sullivan, Jr.*, Herbert L. Kaufman**, Wayne Eakins*** In water treatment plant operations we are always looking at ways to provide the customer with the highest quality product at the lowest possible price. In conventional coagulation plants a significant portion of the capital and operating cost is in the settling basins. Attempts to accomplish savings here have taken the form of minimizing the size consistent with the settling characteristics of the floe produced and/or the utilization of tube settlers. Both these concepts are consistent with the basic assumption that the floe volume after rapid mix and flocculation is sufficiently large to require a separation by gravity sedimentation prior to filtration. In recent years this basic assumption has been challenged at at least two points. First, the advent of organic polyelectrolytes offered the ability to reduce the absolute amount of coagulant re- quired to produce a comparable amount of destabilization of colloidal particles by an order of magnitude or more. This correspondingly resulted in a decrease in total floe volume. ~Vice President, Water and Air Research,Inc., Gainesville, Florida **Partner, Clinton Bogert Associates, Fort Lee, New Jersey ***Principal Associate, Clinton Bogert Associates,Fort Lee, New Jersey iii-i ------- (1 2) The second challenge grew out of the work of Camp ' 'in which he suggested that by proper regulation of rapid mixing conditions floe density could be greatly increased. Camp spoke in terms of floe volume concentration in which lower values correspond to more dense material. Using alum and ferric sulfate he demonstrated floe volumes ranging from less than 50 to over 700 vpm. Floe volumes were determined by visual examination under a 40 power microscope. Both these developments suggested that compact floe particles could be produced. If they could be maintained in this condition it might be possible to eliminate the sedimentation process altogether and go directly to filtration. Such floe would penetrate into the filter bed rather than create a blinding layer on the filter surface. Because of its small size it might be possible to store a considerable amount of material in the filter thereby achieving practical filter run durations. To be effective in reducing the volume of waste sludge, still yet another criteria would have to be met. That is, the floe so produced and removed by the filter must remain 1n a compact condition through the filter backwash process and settle in a short time to a relatively high solids concentration. That is the point we are dealing with in this seminar. Is the final volume of floe to be disposed of reduced by utilizing the direct filtration process? For comparison purposes we should examine what happens in a conventional plant. In reviewing both his own work as well as that III-2 ------- (3) of others, Hudson concluded that floe volumes entering a settling basin are in the range of 2,000 to 7,000 vpm. However, upon settling, the floe begins to compact and the floe volume decreases. Neubauer^ has reported values of 1,230 and 2,660 vpm for waste sludge from upflow clarifiers. How- ever, it was also noted that this sludge was "readily settleable" to floe volumes of 520 and 1,140 respectively. Data from plants having settling basins that waste sludge on a batch basis have reported sludge volumes ranging from 200 to 26,000 vpm. Other sources^ report only the solids content of the waste sludge. Typical values range from slightly less than one percent solids up to five percent or even higher. These are values in the settled sludge mass however and do not represent the concentration which will result when the basin is taken out of service and cleaned. When this occurs the overlying water as well as the settled sludge is wasted together and the resultant sludge concentration 1s lower. Even so, it is likely that the average sludge volume actually wasted 1s less on a volume per volume of raw water basis than the sludge volumes continuously wasted from upflow clarifiers. How- ever, batch operations suffer in that the waste occurs in slugs which can make ultimate disposal more troublesome. Filter backwash water in conventional plants contains a small fraction of the total solids load but can present disposal problems due to high solids content. Against this background let us consider the comparable conditions if the direct filtration process is utilized. This past summer and fall we III-3 ------- evaluated the direct filtration process for use by the City of Lynn, Massachusetts. The characteristics of the raw water are shown in Table 1. In addition to the obvious potential problems with color, turbidity, iron, and manganese the water has from time to time strong taste and odor. A pilot plant was constructed and operated at Lynn inter- mittently from August 1972 to April 1973. Raw water temperature ranged from 3 to 20° C. A total of 76 filter runs were made. A schematic of the pilot plant is shown in Figure 1. As can be seen, the pilot plant consisted of up to four stages of rapid mix with an average detention time per stage of 0.77 minutes. The flocculators which followed could be either bypassed, operated as a single unit, or operated as two units in series. The small holding basin prior to the filters simulated the retention of water that occurs above the actual filter bed iri a full-scale filter. Table 1 Typical Raw Water Quality at Lynn, Mass. Turbidity 1 - 3 Color 35 - 50 pH 7.1-7.3 Alkalinity,mg/l as CaCO^ 15 - 25 Hardness, mg/1 as CaCC^ 45 - 55 Iron, mg/1 0,15 Manganese, mg/1 0.05 III-4 ------- Constant Head Standpipe Alum Backwash 'lJr^n Waste Chlorine Polymer Lime \ I f I | Raw i Water ~ t± J—J J L_ L__ Rapid Mix Basins (may be by-passed) Pump r~i Flocculators (may be by-passed) Filter Holding Basin Filtered Water Tank Backwash Pump Scale: None Figure 1. Pilot Plant Set-up ------- The filters consisted of 6 inch diameter plexiglass tubes, with appropriate connections for measuring head loss to various depths in the bed. The early work was all done with dual-media anthracite-sand beds. Both declining rate and constant rate modes of operation were utilized. In the latter portion of the study a three media filter was operated in parallel with one of the dual media units. The goals selected for finished water quality were less than 0.2 FTU turbidity (preferably less than 0.1 FTU) and color less than 5 units. These goals are considerably more stringent than the 1962 U. S. Public Health Service standards of 5 turbidity and 15 color and are only slightly less stringent than the AWWA goals of 0.1 and 3 respectively. Alum was used as the primary coagulant throughout the study. How- ever, it was found to prevent breakthrough of color and turbidity, the addition of a small amount of a non-ionic polyelectrolyte as a filter aid was required. With 30 mg/1 of alum, a pol.yelectro7yte dose of about 0.05 to 0.25 mg/1 was found to be sufficient. Increasing the dosage of the non-ionic polyelectrolyte allowed no significant decrease in alum dosage. Filter runs were in the range of 5-10 hours depending on the filter operating conditions. Allowing for backwash water and backwash time, the most productive mode of operation was to operate declining rate beginning at 6 gpm/ft , Table 2 shows the relative amounts of water produced under four modes of operation. It may be significant that higher filtration rates produced more water per run, at no deterioration in quality, although the runs were shorter. III-6 ------- Table 2 Comparison of Productivity of Filters Under Different Modes of Operation Rate Type Operation gpm/ft Filter Run Length hrs. ApproximateProduction qpd/ft2 Declining rate 6-3 Constant rate 4 6 - 8 5 - 8 6,000 5,300 Declining rate 5-2 Constant rate 3 10 - 11 9 - 10 4,100 4,700 Prechlorination at 4 mg/1 was found to be an effective aid in color and taste and odor removal. When ozone was substituted for the chlorine, objectional taste was present in the filtered water, possibly due to re- action between ozone and the polymer used. Limited testing revealed that a cationic polymer may be effective in reducing the amount of alum required. Design of the plant will permit utilization of both alum and polymers. Floe volumes within a filter can be estimated by the procedure sug- gested by Hudson. The procedure is based on Kozeny-Fair-Hatch equation which relates hydraulic gradient or head loss to filter bed porosity. o Pt3 ^ = head loss at time t iQ = head loss at time zero pt = porosity of bed at time t K = constant III-7 ------- The constant K is evaluated from the known porosity of the bed at time zero. If the filtration rate is not constant a correction factor must be applied to the head loss, i^. This can be done by multiplying i^. by the ratio of the initial filter rate to the filter rate at time t. The decrease in apparent porosity of the bed with time can be assumed to be due to floe accumulation. This floe volume can in turn be related to the total water filtered and expressed as floe volume per unit quantity of treated water, usually volumes per million volumes. An obvious short- coming of this procedure is that the head loss through the filter is related to the apparent rather than actual porosity of the filter. Hence, if flow to certain channels in the filter is blocked at the channel entrance the head loss increase is the same as if the entire channel were filled with floe. This means that the actual floe volume contained in the filter is generally somewhat less than calculated by this procedure. In analyzing the pilot plant data it was found that floe volumes (vpm) calculated by this procedure generally decreased as the filter runs progressed. Average values for the filter runs, based on terminal head loss conditions, ranged from 1,500 to 2,500 vpm. This indicates that the actual floe volume in the filter bed is significantly more than what Camp indicated might be produced by high energy mixing. Several factors could explain this. First the floe density is being measured by two entirely different means, neither of which has been conclusively verified. Second, the floe may be small and dense as it enters the filter but may agglomerate as the filter run proceeds, and water may be entrapped in the process. III-8 ------- There was visual indication of floe agglomeration in that, as the filter runs progressed, floe grew from barely visible particles in the applied water to readily discernible size within the bed and on the filter bed surface. Also there were large floes in the filter backwash water. Let us assume that these figures are reasonably accurate and that the floe is considerably less dense in the filter bed than when it left the rapid mix or flocculators. The next question then is, what is the floe density after backwashing? Although careful measurements were not made on all runs, it was repeatedly observed that, in general, the floe in the backwash water settled to a volume of 1 gallon in 1 hour and to 0.5 gallons after standing overnight. Total water filtered per run ranged from less than 300 gallons on poor runs to about 450 gallons on the best run. Assuming 375 gallons filtered, a 0.5 gallon settled sludge volume would convert to 1,335 vpm. This figure is roughly the same as reported for settled sludge from upflow clarifiers and within the range of values reported for batch operated settling basins. Hence, although the direct filtration process using alum offers a number of advantages, the volume of sludge that must ultimately be disposed of is essentially the same as can be expected in a conventional plant. It should be noted that these results are based on work where alum doses in the order of 30 to 45 mg/1 were required in order to accomplish color removal. If a significant amount of this alum can be replaced with a polyelectrolyte, an increase in filter run length and a decrease in floe volume might occur. The problem to date has been that we have not found a polyelectrolyte that is really effective in removing color. III-9 ------- Acknowledgement The authors gratefully acknowledge the work and efforts of Mr. Alonso Gutierrez in operating the pilot plant. References 1. Camp, T. R., "Floe Volume Concentration", Jour. AWWA, 60:656 (June, 1968) 2. Camp, T. R. and Conklin, G. F., "Towards a Rational Jar Test for Coagu- lation", J. NEWWA, 84:325 (Sept. 1970) 3. Hudson, H. E., Jr., "Physical Aspects of Filtration", Jour. AWWA, 61:3 (Jan. 1969) 4. Neubauer, W. K., "Waste Alum Sludge Treatment"» Jour. AWWA, 60:819 5. Gates, C. D. and McDermott, R. F., "Characterization and Condition of Water Treatment Plant Sludge", Jour. AWWA, 60:331 (Mar. 1968) III-IO ------- REDUCING WATER PLANT SLUDGE BY DIRECT FILTRATION AND OXIDATION- Richard L. Woodward** Direct Filtration There has been a considerable increase in interest in direct filtration of water in recent years and it is likely to continue. A large number of surface water supplies now being used in this country are troubled by occasional quality problems due to turbidity, color or plankton growths and direct filtration may provide a more economical method of treatment than the conventional plant involving coagulation and sedimentation prior to filtration. In addition to providing a less expensive plant in first cost, it is frequently found that coagulant requirements may be lower than with conventional pre- treatment and that the handling of plant wastes is simplified. There are limitations to this process, of course. With highly turbid waters, it is more economical to remove the bulk of the turbidity by sedimentation than to place the entire load on the filters, A common guideline as to the upper limit of turbidity suitable for direct filtration is about 25 Jackson units but direct filtration plants are successfully treating waters with turbidity in the hundreds of units. On the other hand, there are plants where very short filter runs have been experienced even with low turbidity. The filter clog- ging problems associated with diatoms are well known and if these organisms are prevalent, it may not be economical to use direct filtration. The use of a coarse media (1.0-1. 5 mm) in a dual media *For presentation at AWWA Seminar May 13, 1973, Las Vegas, Nevada **Camp Dresser & McKee, Inc., Boston, Massachusetts rv-i ------- filter can help to overcome the tendency toward formation of a surface mat when diatoms are a problem. The use of chlorine or ozone prior to filtration may also help. Probably as important as the suspended solids in the raw water in determining the feasibility of direct filtration is the dosage of coagulant required to coagulate the suspended matter or color. The volume of material stored in a filter may be largely the highly hydrated alum or iron floe. Of course, when color is all that is being removed, the material clogging the filter is almost entirely floe. We have found in several instances that where the required alum dose for coagulation approached 30 mg/f it was necessary to 2 2 reduce filter rates from 5-7 gpm/ft to 3-4 gpm/ft in order to keep filter runs from dropping below about 10 hours. In such instances, it is doubtful whether direct filtration is truly economical. In some instances, the use of a cationic polyelectrolyte as the prime coagulant rather than a metal salt may make direct filtration more attractive. In some recent pilot plant tests we found the filter runs were about doubled when we switched from alum to a cationic polymer. It was necessary also to add a small amount of a poly- acrylamide as a filter aid immediately ahead of the filter. The costs of the coagulant chemicals were about equal as the ratio of polymer dose to alum dose was abo-ut 1:10 and the cost of the polymer was about 10 times the cost of alum. As a rule, the cationic polymers are not economically com- petitive with metal salts in coagulating true color but in some New England waters, they have been useful. At the Salem-Beverly, Mass. water treatment plant which is a soft, low turbidity water with a color generally below 50, it has been possible to reduce color by about two-thirds with only 1-2 ppm of Nalco 607 applied immediately IV-2 ------- ahead of the filters. However, there have been occasions when the polymer was not effective and it was necessary to use alum as a coagulant. The washwater from the filters settles well in sludge lagoons and the supernatant is returned to the raw water sources. Some of the cationic polymers are attacked by certain oxidizing agents. At Brockton, Mass. where Nalco 607 was tested, it proved ineffective probably because potassium permanganate is used there for oxidation of manganese. There appears to be little hard information on the dewatering properties of sludge from direct filtration plants. It is a common observation, however, that the solids from filter backwash water are readily settleable whereas the solids reaching the filter were those that had failed to settle in conventional pretreatment. The only quantitative information I have seen is from the Fylde Water Board in England where at their Stocks Plant a colored water is treated with alum and pressure filters. The plant treats about 26 mgd and the washwater (about 5 percent of throughput) contains some 300-400 mg/i of suspended solids. This washwater is settled in horizontal flow tanks after addition of 1 mg/l of polyacrylamlde. Without poly- acrylamide, the solids content of the sludge was about 1.7 percent. The settled sludge has a solids content of about 5 percent and the supernatant has a color of about 10 units and about 10 mg/l of suspended solids. This sludge is filter-pressed to about 25 percent solids without further chemical addition. ^ At the Fishmoor plant of the same Water Board, which also treats a colored water but with clarifiers prior to filtration, the solids content of the sludge drawn from the clarifiers is about 0.6 percent. Total sludge production IV-3 ------- from the two plants is not markedly different running around 18 kg per megaliter or about 150 pounds per million gallons. Oxidation In treating colored waters, the use of oxidants to bleach the color has considerable potential for reducing the amount of water plant waste. This has seldom been done very successfully as a sole method of treatment but has been effectively used along with other treatment processes. The various oxidants used in water treatment also serve other functions than decolorizing. Chlorine is the most widely used oxidizing agent in water treatment although its principal waterworks use is as a disinfectant. It is used widely to decolorize water. Riddick has described the use of chlorine at Ossining, New York,where chlorination to a free residual of 4 mg/l. This commonly reduced color from about 30-40 units to less than 10. It was necessary to use alum to keep the color at satisfactorily low levels about 10 percent of the time. Chlorine dosages were from 10-16 mg/f . Sulfur dioxide was used for (2) dechlorination after filtration. At Miami, Florida, chlorine is used to decolorize a hard groundwater after softening. Softening reduces the color from about 80 units to 25-30, A dosage of 12 mg/i of chlorine reduces the color to less than 10. Black and Christman studied the effect of three oxidants, chlorine, chlorine dioxide and ozone, on colored waters by bubbling the gases through samples of eight different colored waters until a constant color value was obtained. They determined color and C.O. D, on the samples before and after treatment. Their results are shown in Table 1. These show the IV-4 ------- TABLE 1. EFFECTS OF CHLORINE, CHLORINE DIOXIDE, AND OZONE ON COLOR REMOVAL AND CHEMICAL OXYGEN DEMAND (From Reference 3) Original Color Value after Oxidation COD of Sample Color Value Hi CIO, Concentrate (ppm) A 240 No data 8 0 2,800 B 352 98 u 0 \ ,394 C 156 72 10 0 996 D 108 30 3 0 1,316 £ 68 25 0 0 554 H 70 15 15 3 960 1 424 22 18 3 1,320 J 240 5 0 0 1,280 COD after Oxidation (ppm) Cl2 c\o2 O3 No data 750 615 1,060 80 220 318 40 152 408 120 129 0 0 82 780 751 794 830 652 742 616 514 810 ------- substantially different responses of the various waters to the three reagents. Under the conditions of this test, ozone was the most effective.! in reducing color- followed by chlorine dioxide and chlorine. However, there was no parallelism between color removal and reduction in C.O.D. Sample J, for instance, was completely decolorized by ozone but the C.O.D. was reduced by only about one-third whereas chlorine left a color of 5 units but removed more than 50 percent of the C.O.D. Chlorine dioxide has not been widely used in water treatment in the U.S. except for dealing with phenolic taste problems. It is an effective bleaching agent and is widely used for bleaching pulp but its cost is a major drawback to its wide use in water treatment. Ozone is widely used in Europe in water treatment and there are a number of ozone installations in Canadian water plants but only a few plants in the U.S. use ozone. O/.one is a powerful oxidizing agent and disinfectant. It decomposes to molecular oxygen and provides only short lived residuals in water. It is manufactured at the point of use by an electrical discharge in either dry air or oxygen. It does not react appreciably with ammonia as chlorine* does. (4 5 6) A number of plants in Great Britain and elsewhere ' * ' have used ozone and microstrainers for removal of color from water rather than using the more conventional coagulation and filtration. The microstrainer is used to remove algae and other particulate matter of comparable size and to reduce the amount of ozone required to decolorize and disinfect the water. Chlorine may be used prior to ozonation to remove some of the color and further reduce the ozone requirement. Some hazards are to be guarded against in using this approach. If iron or manganese is present as either an IV-6 ------- organic complex or in the soluble reduced state, it will be oxidized and form deposits in the distribution system. IVIanganese is typically oxidized rapidly by ozone to the permanganate form, even at near neutral pi I, but this is reduced by organic matter in the water to the insoluble manganese dioxide. In addition, the decolorizing action of ozone evidently results in the breakdown of the organic color mole- cules into simpler compounds which are more readily available as food lor bacteria than were the original compounds. Thus, although ozone may reduce the C.O. D. of the water, it may increase its B. O. D. This gives rise to biological growths in the distribution system with attendant customer complaints of dirty water and taste and odor problems. Maintenance of a chlorine residual in the distribution system can help to control the problem of biological growths but iron and manganese problems can best be handled by removing the offending materials with rapid sand filters. If the con- centrations are sufficiently low, it may bo possible to stabilize them by addition of sodium silicate to prevent their deposition in the (9) distribution system. Our firm has recently designed an emergency treatment plant for one of the water supply sources of Haverhill, Mass., which uses ozone for color removal and taste and odor control. Johnson's pond is one of four surface water sources which serve Haverhill and is essential for supplying the city's needs during summer peak demands. In the Fall and Winter of 1970 - 1971, it developed a heavy bloom of Aphanizomenon with 12, 000 - 20, 000 areal standard units per milli- liter of this blue green algae. The city was anxious to provide an emergency treatment plant which could be gotten into operation prior to the 1971 summer season. The water had been used with IV-7 ------- only chlorination. Pilot plant tests wore run in December, H)70 and January, lf)7 1, to determine what treatment would ho feasible. A microstrainor with 24 micron screen removed only about 20 percent of the Aphariizomenon and also showed poor removal, of odor. A dual media filter with one foot of 1.0 mm anthracite over 2. 0 feet of 0.4 mm sand was tested briefly at rates of 4 and 7 gpm per square feet. Although it generally was quite effective, at times there was serious penetration of the algae even at the 4 gpm rate. The area of filter needed was greater than was available in an exist- ing building, an old steam pumping station which had been converted to electricity leaving the space previously occupied by the boilers available for other use. It would not have been possible to provide a new building in time for the coming season. A diatomite filter was tested and showed generally complete removal of the algae cells although odor removal was relatively poor. In fact, at times the threshold odor number was higher in the filter effluent than in the influent. This treatment was recommended as the performance was adequate in algae removal and the needed equipment could be accommodated in the space available in the existing building. Ozone was provided following filtration to eliminate tastes and odors. It also reduces the color which ranges generally from 20 to 30 units to a range of 5 to 10 units. Since the plant has gone into operation, it has been found that filter runs and filter aid economy can be improved substantially by prechlorination and this is being done routinely. Post chlorination is practiced following ozonization as necessary to maintain a chlorine residual in the distribution system. IV-8 ------- This type of treatment has been satisfactory in solving Haverhill's problem although it is more expensive in operation than a conventional plant would have boon. SUMMARY Direct filtration and oxidation afford some opportunities for reduction in tin? amounts of waste from water treatment plants. Direct filtration is particularly attractive if cationic polyelectrolytes a re suitable- for treating the water. Oxidation alone is seldom adequate- for treatment but in combination with other processes, it may substantially reduce waste volumes. 11i:; i ;ni :\c• i:s 1 Hilson, !VI. A. Sludge Conditioning by Polyelectrolytes. J. Inst. Water Eng., 402-416 (1071). 2 Riddick, T. M. Controlling Taste, Odor and Color with Free Residual Chlorination. J'.A.W.W.A. 43, 545-552 (1951). ¦i B lack, A. P. and Ohristman, R. F. Chemical Characteristics of Fulvic Acids. J.A.W.W.A. 55, 897-912 (1963). 4 Campbell, R. M. and !Jescod, M. B. The Ozonization of Turret and other Scottish Waters. J. Inst. Water Eng. 19, 101-162 (1965). 5 O'Donavan, D. C. Treatment with Ozone. J.A.W.W.A. 57, 1167-1192 (1965). 6 Diaper, E. W. .1. Practical Aspects of Water and Waste Treatment by Ozone. In Ozone in Water and Wastewater Treatment. F. L. Evans III, Editor. Ann Arbor Science Publishers, Ann. Arbor, Michigan. (1972) 7 Van Haaren, F. W. J. Processes for the Removal of Organic Pollutants. Joint Symposium Society for Water Treatment and Examination and Water Research Assn. 113-122 (1970). 8 Hall, R. I. Discussion of Reference 7, Page 125. 9 Dart, F. J. and Foley, P. D. Silicate as Fe, Mn Deposition Preventative in Distribution Systems. J.A.W.W.A. 64, 244-249 (1972). IV-9 ------- MAGNttSUJM CARBONATE RECYCLING Riley N. Kinman, Ph.D., P. E. :;: Introduction Recycling is a new concept to most people engaged in water treatment, although it is not a new concept in other industries and it has been practiced by some people in water treatment. Consider the steel drum reconditioning industry, which has been reconditioning steel drums and re- cycling them for 40 years. An 18-gauge 55 gallon steel drum can be recycled up to 15 times. In 1968"'", 20*10^ new drums were manufactured and 45*10^ drums were recon- ditioned and recycled. This resulted in 1*10^ tons of steel used in recycle rather than the use of raw material. There were only two examples of true recycling in water treatment prior to the present concept of magnesium carbonate recycling. One of these, which is closely allied to the present chemical and indeed will be a part of the overall process, is the recovery and recycle of lime sludge as CaCO^ from which high purity CaO can be and has been reclaimed for many years at certain water softening plants. This process will be discussed in detail later. The second example of recycle in water treatment is in the disinfection of swimming pool water with iodine. In this process the I ion resulting from reaction of the active chemical species 1^ or HOI on an organism is recycled many times in a recirculating swimming pool before it is lost. This recycle permits economy of operation in swimming pool disinfection with iodine. Recycle of chemicals is a way of conserving chemicals and reducing the cost of treatment. ^Department of Civil and Environmental Engineering, University of Cincinnati, Cincinnati, Ohio v-1 ------- Alum has been the water coagulant of choice in this country since the early 1900's and has defied efforts to recover and recycle the alum. In recent years the iron salts have been successfully used by many water treatment plant operators, but again without recovery and recycle of the iron. Unfortunately perhaps, but maybe not, stringent anti-pollution measures now require that there be no dis- charge of waste sludges to receiving waters. The Federal 2 Water Pollution Control Act Amendments of 1972 set forth a national policy, 1. "It is the national goal that the discharge of pollutants into the navigable waters be eliminated by 1985;" and 2. "it is the national goal that wherever attainable, an interim goal of water quality which provides for the protection and propagation of fish, shellfish, and wildlife and provides for recreation in and on the water be achieved by July 1, 1983;." There are additional such statements of policy in the act. This means that all water treatment personnel must think seriously about recovery, reuse or recycle of all chemicals used in the treatment process and all chemicals removed from the water during the treatment process. Alum, the coagulant of choice in this country, cannot be recycled on a satisfactory basis, because of the economics of the recovery process and the acid sludges which are produced. The iron salts have resisted recovery 3 and recycle for about the same reasons. Black and co- workers have proposed magnesium carbonate, hydrolyzed with lime, as a prime candidate coagulant, which can be used, reclaimed and either be reused immediately or be recycled V~2 ------- at some future date. Magnesium Carbonate What is magnesium carbonate? The compound that is under consideration for use in water coagulation is the tri-hydrate form, MgCO^ • 3H2O. Other magnesium compounds could be used to provide the MgtOH^ floe in water, but each of the others has problems associated with its use of one kind or another. For example,some would add non carbonate hardness to the water, others would increase the total solids of the finished water and others have solu- bility problems associated with them. The desired reaction is as follows: MgC03 + Ca (OH) ^ »-Mg(0H)2 I + CaC03 ^ (1) The lime provides sufficient OH to exceed the solubility product constant for Mg(0H)2 an<^ solid Mg (OH) ^ floe is formed fa3t and settles fast conveying the impurities from the water to the sludge. [V+] [oh*] 2 = Ksp (2) 4 5 6 7 The magnesium hydroxide floe has been shown ' ' ' to be as effective as alum floe for removal of color, turbidity and other suspended matter from water. Both of the products in reaction (1) can be reclaimed from the sludge for recycle. The turbidity and other impurities removed from the water can be separated and placed in a landfill with no major difficulty. V-3 ------- Significance of Recycle to the Water Industry Let us forget for a moment that water treatment plant sludge can no longer be disposed of by sending it to the receiving water and consider just the savings in chemical when it is reclaimed and recycled. Let us assume that 10 mg/1 of any chemical is reclaimed and recycled. Table 1. Chemical Saved For 10 mg/1 Recycle Plant Size Daily Quantity Dosed Annual Tons Recycled (mgd) and Reclaimed # 1 83 15 5 417 76 10 834 153 20 1668 307 50 4170 763 100 8340 1525 Even a small plant of 1 mgd capacity would save over 15 tons of chemical yearly, A large 100 mgd plant could save 1525 tons of chemical on an annual basis. Just a small savings in chemical dosage, 10 mg/1, would result in tremendous savings of chemical as well as the prevention of pollution by discharge of the chemical. Recycle is something to be considered just from the standpoint of conservation of chemicals. Consider for a moment the data in Table 2, developed by Dr. Black^ and co-workers for the City of Dayton, Ohio. This table contains the values received for recovery and recycle of lime for the years 1958 to 1970 at their 100 mgd Ottawa Street Softening Plant. The totals V-4 ------- Year 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 Total Table 2 Production Figures and Value of Product Lime Recalcining Plant Dayton, Ohio 1958 - 1970 Lime Produced Value Lime Produced Value Total Lime Total Value Value of for Water for Sale to Produced of Lime Carbon Treatment Others Produced Dioxide Produced for Water Treatment 20,559 $382,397 4,712 $ 49,476 25,271 $431,873 $32,000 22,995 427,707 11,590 121,695 34,585 549,402 32,000 23,353 434,366 11,568 133,032 34,921 567 ,398 32,000 22,115 411,339 11,711 134,677 33,826 546,016 32,000 21,140 393 ,204 3 ,791 42 ,649 24 ,931 435 ,853 32,000 21,246 395,176 3 ,084 35 ,003 24,330 430 ,179 32,000 22,326 415,264 5,265 59,757 27,591 475 ,021 32,000 23,926 445,024 3 ,606 36 ,060 27,532 481 ,084 32,000 25,574 475,676 6 ,174 67 ,914 31,748 543 ,590 32 ,000 26,150 486,390 6,594 69,237 32 ,744 555 ,627 32,000 27,010 502,386 7 ,628 80,094 34 ,638 582 ,480 32,000 29,772 553,759 4 ,905 55,672 34 ,677 609,431 32 ,000 29 ,370 546,282 4 ,976 56,478 34 ,346 602,760 32,000 315,536 $5,868,970 85,604 $941,744 401,140 $6,810,714 $416,000 ------- represent considerable savings both in chemicals recycled and monies derived. For the 13 year period a total of 315,536 tons of lime were produced for water treatment at a value of $5,868,970. In addition 85,604 tons were pro- duced for sale at a value of $941,744. Also $416,000 of carbon dioxide were produced to make a grand total of $7,226,714 worth of products reclaimed and recycled. Lime Recovery for Recycle at Dayton, Ohio In lime-soda softening plants employing split treat- ment the calcium and magnesium removed from the water are precipitated and form two types of sludges. The first or primary sludge contains principally CaCO^ plus all of the magnesium as MgCOH^- Secondary sludge, produced by the reaction of excess lime in the settled primary effluent with calcium hardness in secondary raw water is practically pure CaCO^. Figure 1 is a schematic of the Dayton, Ohio Ottawa Street Water Softening Plant and lime recovery facility. Primary sludge is produced in basins 1 and 3 and secondary sludge is produced in basins 2 and 4. Secondary sludge is pumped to one of two sludge storage tanks designated "P" in the figure. Primary sludge is pumped to a sludge recarbonation basin designated "N" where it is mixed with scrubbed kiln gas containing about 20% C02< Most, but not all of the Mg(0H)2 is selectively dissolved from the calcium carbonate in the 50-mir»ute retention period provided. The recarbonated slury passes to a 130 foot diameter thickener from which the clear supernatant containing the magnesium, now in the form of soluble magnesium bicarbonate, overflows and is sent to a V-6 ------- —R Fig. 1. Ottawa Softening and Sludge-Processing Plant, Dayton, Ohio. Equipment for Recovery of Magnesium Carbonate Being Designed A—from well fields, B—plant bypass shaft, C—raw water junction, D~~double-decked south flume, E—slow-mix basin, F—settling basin, G—recarbonation basin, H—split- treatment bypass, I—filters, J—covered clear wells, K—wash water tank, L—wash- water reclaim lagoon, M—sludge pumps, N—sludge recarbonation, 0—sludge thick- ener, P—sludge-storage tanks, Q—feed-end building, R—rotary lime kiln, S—firing- end building, T—lime-storage bin, U—chemical unloading building, V—chemical- storage bins. V-7 ------- sewer. Thickened sludge, now mainly CaCO^ with some un- dissolved Mg(0H>2 and some insolubles, passes to a sludge storage tank from which it passes to three Bird centrifuges, these concentrate the slury to about 60% solids. This thick paste is then conveyed to the kiln where it is calcined into high quality CaO, The gases withdrawn from the kiln by induced draft fan are freed from particulate matter in four water fed scrubbers. Some of the scrubbed and cooled stack gas is then returned to the treatment plant by two compressors and used for water recarbonation. A major portion is transferred by two other compressors to the sludge recarbonation basin. The remainder exits from the stack. Hence two major products are produced in lime recovery according to the following reaction: CaCO, CaO + CO- (3) heat 1 The quality of the lime produced is excellent, CaO content ranges between 92 - 93%. The finished lime may contain as much as 4% MgO at the present time but an improved process will be employed so that essentially all of the Mg(OH)^ will be dissolved and recovered. Figure 2 is a schematic of the lime recovery process. Benefits From Lime Recovery 1. The cost of treating the water has been reduced. 2. Lime values present in the raw water are re- covered along with the lime used in treatment. 3. Calcium carbonate removed in the softening process is not discharged as a pollutant. 4. Considerable C02 is produced for use in carbon- ating the softened water. V-8 ------- FIGURE 2, RECOVERY OF CaO FROM CaC03 SLUDGE PRIMARY SLUDGE CaC03 + Mg(OH)2 + INSOLUBLES CARBONATION Mg(HCOt)9 TO SEWER THICKENING SECONDARY SLUDGE STORAGE CaCO? + INSOLUBLES CENTRIFUGATION REJECTS > t CALCINATION CaO STORAGE SELL OR REUSE CaO V-9 ------- 5. A continuous inplant supply of lime is available at all times. 6. Land is not required for storage of the lime sludge. Recovery of MgCO^ • 3H20 fronl M<3 (Q&) 2 Sludge 3 Black and co-workers presented the reactions involved in the pilot plant production of Magnesium carbonate in October of 1971 as follows: Mg (OH) 2 + 2C02 Mg (HC03) 2 (4) Mg (OH) 2 + C02 + 2H20 MgCQ3 ' 3H20 (5a) MgC03 • 3H20 + C02^=^ Mg(HC03>2 + 2H20 (5b) Mg (OH) 2 + Mg(HC03)2 + H20 >- 2MgC03 * 3H20 (6) Mg(HC03)2 + 2H20 —— ¦? V MgC03 3H20 + C02 (7) air Reaction (4) is the overall reaction by which the insoluble hydroxide is converted to the soluble bicarbonate. Re- actions (5a) and (5b) are consecutive and represent the two steps in the overall reaction. The concentration of bicarbonate steadily increases to an alkalinity of 16,500 ppm as CaC03. This is the equilibrium concentration for a kiln gas containing 20% C02. Reaction (6) shows that as carbonation proceeds there will be a tendency for the undissolved Mg(0H)2 to react with the dissolved Mg(HCO^)2 to form a precipitate of MgC03 * 3H2°" In Pract:i-ce the Mg (OH)2 could be fed at a rate no greater than the rate at which the Mg(OH)2 is dissolved by the C02- Reaction (7) takes place during product recovery. The clarified Mg(HC03)2 solution passes to a heat exchanger where it is warmed to 35°C to 45°C. It is then V-JO ------- aerated in a basin equipped with mechanical stirrers. Pre- cipitation of the tri-hydrate is essentially complete in 90 minutes. The white product MgCO^ • vacuum filtered, dried and bagged for shipment. The filtrate containing unprecipitated product will be recycled to the sludge storage tank. The underflow from the clarifier- thickener in which the carbonated sludge is clarified, is thickened CaCO^ sludge. This will be passed to a sludge storage tank for recovery of the CaCO^. When magnesium recovery is instituted at Dayton the following should occur: 1. Essentially all of the magnesium in the sludge will be recovered, 2. All of the water used to convey the sludge will be saved. 3. There should be no significant discharge of waste solids. 4. Lime production will be increased. 5. Lime quality will be improved. Figure 3 is a schematic of the Dayton, Ohio pilot plant for total recovery of softening sludge. The purity of the reclaimed magnesium exceeded 99.5 percent. Application of the Process to Treatment of Hard Turbid Waters Most of the large softening plants in this country are softening hard waters which contain clay turbidity. This turbidity has prevented the recalcination of the sludges for recovery of CaO, because the separation of the clay turbidity from the CaCO^ sludge could not be done in such a way as to prevent the buildup of insolubles in the finished lime. Black and co-workers have studied the V-ll ------- Waler Plant Settling Basm D ~ j Clear Water Overflow Can Be Returned to Plant Sludge SoVids Raw-Sludge Pump Ra-A Slodge V.ifer Plant Setting Ba^jn a» Van Speed Sludge Thickener Pump Lime Kiln Recarbonation Basin Stack Gas D Settlmg Tank Dewatered Soiids to Dryer J Compressed Air —* 3 Clear Water Return to ,, o , . Water Plant Magnesium Precipitator Magnesium Carbonate Dewatering Vessel Fig. 3. Total Recovery of Lime-Softening Sludge; Magnesium Carbonate Recovery Pilot Plant ------- separation of clay turbidity from the combined CaCO^, Mg(OH)^ and clay sludge by froth flotation. The mining industry has been using froth flotation for a long time to purify CaCO^ for use in applications involving a very pure white inert compound. They float the impurities off in large multi-unit cells with air and frothing agents. Thompson and Black^ presented a flow diagram for the appli- cation of MgCO^ in a turbidity removal plant in February of 1972. Figure 4 is a schematic of the basic steps involved in the recovery and recycle of lime and magnesium for such a plant. The sludge containing CaCO^, MgfOH^ and clay is first carbonated with kiln stack gas just as the process is con- ducted at Dayton. The Mg(OII)2 will be solubilized as a mixture of MgCO^ and MgCHCO^^* Separation of the mag- nesium from the calcium carbonate and clay is achieved by means of a vacuum filter. The filtrate containing the magnesium as MgCO^ and MgdlCO^^ is returned to the chemical feed point for reuse in the water treatment process. The filter cake containing CaCO^ and clay is con- veyed to a flotation unit for removal pf the clay from the CaCO-j by froth flotation. This froth containing mostly clay, but with some magnesium and calcium is sent to the landfill. Bench scale pilot plant tests conducted prior to this writing have shown that the magnesium remaining in the filter cake is less than 2%, or greater than 98% recovery of the magnesium is expected. Greater than 90% recovery of the CaCO^ is expected in such a process. A flotation unit will be used for separation of the clay V-l i ------- FIGURE 4, LIME AND MAGNESIUM RECOVERY WHEN SOFTENING A HARD TURBID WATER WATER STABILIZATION CARBONATION SLUDGE CaC03 + Mg(OH)2 + CLAY COo FROM KILN FILTRATE TO VACUUM FILTER CAKE MAY CONTAIN 1-2% MAGNESIUM CHEMICAL FEED (MgCO? + Mg(HOMo) CLAY TURBIDITY WITH FROTH TO LANDFILL CaCO CENTRIFUGE (THICKENING) CaCO KILN FLOTATION UNIT y (MIXER, ROUGHER, SEVERAL CLEANING CELLS CaO FOR CHEMICAL FEED AT PLANT AND SALE OF RECLAIMED MATERIAL V-14 ------- from the CaCO^ which contains a mixer for addition of frothing-agents, a roughing cell and probably two or three cleaning cells. The cleaned CaCO^ sludge will then be centrifuged to 60% solids and then sent to the kiln for pro- duction of CaO. By the time of this presentation larger scale pilot plant data should be available for this total recovery and recycle process. Advantages of Magnesium Carbonate-Lime Process for Hard, Turbid Water Treatment 1. Reduced cost of treatment. 2. Elimination of Alum sludge. 3. No discharge of pollutants. 4. Clay turbidity is the only material to be disposed of in a landfill. The key to the process is the complete or nearly complete separation of the three components of the sludge, namely calcium carbonate, magnesium and clay. If this separation cannot be achieved on a satisfactory basis, then the process will not be applicable to treatment of hard turbid waters. Large scale pilot testing should indicate the degree to which this can be accomplished. Summary A whole new technology has been proposed for water treatment involving the use of magnesium carbonate hydro- lyzed with lime to replace alum, with subsequent recovery and recycle of the magnesium and calcium. The process appears to offer a cheaper water and of the same or better quality as that produced by use of alum. Use of the process would eliminate the need for disposal of alum sludge and would provide for no discharge of pollutants by V—1 5 ------- the water utility. Use of the process would result in design changes in a water treatment plant. Key to the whole process is the ability to separate the components of the sludge for recovery and recycle. Work underway at the time of this writing should provide additional data on the separation process. Acknowledgements Appreciation is extended to Mrs. June Schuck for typing this manuscript. References 1. News Release, "Drum Reconditioning Industry Reduces Nation's Solid Waste Disposal Problems by Recycling One Million Tons of Steel Annually." National Barrel and Drum Assn., Inc. Wash., D.C. (1970). 2. "Federal Water Pollution Control Act-Amendments of 1972." 92nd Congress 2nd Session, U.S. House of Representatives, Report No. 92-1465, 1 (1972). 3. Black, A.P., Shuey, B.S., and Fleming, P.J., "Recovery of Calcium and Magnesium Values from Lime-Soda Softening Sludges." Jour. AWWA, 6_3, 616 (Oct.,1971). 4. Thompson, C.G., Singley, J.E., and Black, A.P., "Magnesium Carbonate - A Recycled Coagulant." Jour. AWWA, 64_, 93 (Feb., 1972). 5. Dept. of Public Utilities, Gainesville, Florida, "Magnesium Carbonate, A Recycled Coagulant for Water Treatment." Water Poll. Control Research Series 12120 ESW, U.S.P.A. Office of Research and Monitoring (June 1971). 6. Thompson, C.G., Singley, J.E., and Black, A.P., "Magnesium Carbonate - A Recycled Coagulant - II." Jour. AWWA, 64, 93 (Feb. 1972). 7. Kinman, R.N., "Magnesium Carbonate for Water Treatment" Presented at First Sanitary Engrg. Seminar, Central Ohio Section, A.S.C.E. (Mar. 1972). V-16 ------- DEMONSTRATION OF THE MAGNESIUM COAGULATION SYSTEM AT MONTGOMERY, ALABAMA C lilT G. Thompson ;! A. P. mack — Dr. Kinman, in the previous paper, discussed the theory unci chemistry involved in this new technology with particular emphasiK upon recovery of lime and magnesium values from the sludge. This presentation will, discuss the application of the process for the removal- of organic color and turbidity from the very soft water used by Montgomery, Alabama. Before discussing the Montgomery demonstration project, a brief review will be made of the processes encompassed by this new technology. There are three general processes involved: magnesium recycle, lime recovery, and the production of magnesium compounds. The decision as to which process should be used is determined by the characteristics of the raw water as well as the capacity of the water treatment plant. A series of seven schematic diagrams are pre- sented to allow better understanding of the processes involved and the relative positions of the equipment utilized. Figure 1 illustrates a typical alum water treatment plant with a sludge flow of approximately one to two percent soLids being returned to the river. Figure 2 shows the units required for magnesium recovery, recycle, and sludge dewatering. As discussed by Dr. Kinman, carbon dioxide is used to solubilize the magnesium as the bicarbonate with the thickener overflow recycled to the raw water. The underflow is dewatered using a vacuum filter and the filter cake land filled. Figure 3 is a schematic of the Montgomery Demon- *Co-Project Director and Consulting Engineer, Black Crow and Eidsnes.s, Gainesville, Florida **Co-Project Director, Consulting Chemical Engineer and Research Professor Emeritus VI.-1 ------- stration Plant but also shows the relative position of the magnesium recovery units. When lime recovery is practicable, generally when above 15 - 20 tons per day, the additional units shown in Figure 4 are required. The dewatered filter cake is reslurried, conditioned with the proper flotation reagents, and the calcium carbonate floated from the clay in a series of flotation coils. The calcium carbonate float is concentrated and burned in a kiln producting carbon dioxide and calcium oxide. As discussed, an excess over plant requirement, of both carbon dioxide and lime are produced. Figure 5 illustrates lime recovery with recycle of the magnesium carbonate. Those plants whose raw water is high in magnesium will be able to produce magnesium compounds from the recovered magnesium bicarbonate rather than recycle magnesium back to the raw water. Figure 6 illustrates two magnesium production processes. Boiling the clear magnesium bicarbonate liquor produces the basic carbonate while blowing air to strip the carbon dioxide produces magnesium carbonate tri-hydrate. Figure 7 illustrates a plant with magnesium and lime recovery as well as the capability of recycling magnesium when desired. The E. P. A. Demonstration Project 12120HMZ underway in Montgomery was a natural outgrowth of the laboratory research (1 2^ reported in the January and February issues of the Journal. ' Last June the results of approximately one year of pilot study were (3) presented at the A.W.W.A. Conference in Chicago, The project, funded by the American Water Works Association Research Foundation, the Environmental Protection Agency, and the Montgomery Water and Sanitary Sewer Board as shown in Table 1, is now in the full demonstration phase. VI-2 ------- TABLE 1 Funding for the Montgomery Demonstration Project June 1, 1971 - June 1, 1973. Environmental Protection Agency $99, 500 Montgomery Water and Sanitary Sewer Hoard 78, 500 American Water Works Association Research 24, 426 One half of the 20 mgd water treatment plant has been converted to utilize this new process for comparison of all phases of this new technology with the existing alum system. A partial analysis of Montgomery's raw water is shown in Table 2. TABLE 2 Typical range in raw water characteristics As CaC03 pll Alkalinity Hardness Magnesium Color Turbidity 6.6 - 7.0 10 - 22 10 - 22 0 - 5 5 - 60 2 - 300 Referring back to Figure 8, it can be seen that the Montgomery Plant, provides an excellent facility for such a demonstration as with only minor alterations two parallel plants with identical units results, Rapid mixing is not being provided for the alum treatment during this demonstration period. MAGNESIUM TREATMENT PROCESS - LAYOUT AND DISCISSION Rapid-Mix and Flocculation Figure 8 illustrates the recycle and chemical feed points using the two rapid mixers in series which provide a total detention time of four minutes at a five million gallon per day rate. Recycled magnesium bicarbonate is added to the raw water immediately prior to rapid mixing while uncarbonated recycled sludge and magnesium sulfate are added in rapid mixer number 1. Lime is added between rapid mixers number 1 and 2 adjusting the pH to the desired value. VI-3 ------- Lime Coed is controlled automatically using a pi I probe in rapid mixer number two, coupled to a pi I control ler and SC it controlled pump as shown in Figure 0. Flocculation is carried out using conventional rod type- variable speed floccuintors normally operated at the maximum speed. Recycled sludge has been provided for the following purposes: (1) Recycled calcium carbonate increases magnesium pre- cipitation kinetically as well as quantitatively as reported i i i ¦ . (4,5,6,7) by several early investigators. (2) A. portion of the magnesium hydroxide fraction of the sludge reacts with the recycled magnesium bicarbonate as well as the natural bicarbonate alkalinity and carbon dioxide in the raw water as: IV1 g (Oil)2 -t Mg (HCOs)9 - 2 Mg CO;) I 2]J,,t) This solubilif-ed magnesium carbonate is effective for coagulation when re-precipitated; however, some coagulated turbidity is also released. The overall effect is difficult to evaluate but is generally considered to be of some value. (3) The pre-formed calcium carbonate recycled, acts as a seed or nucleus for precipitation preventing a buildup on mechanical equipment. (4) The excess causticity in the sludge water, pl-1 11.40, reduces the lime requirements slightly. The pH in rapid mix number 1 is generally 10.0 or higher. The pre- cipitation reactions occur rapidly and produce small dense fLocculant particles. Even at maximum flocculation speeds the floe tends to settle from suspension. VI-4 ------- Settling - Carbonatioi) The Montgomery Plant utilizes conventional horizontal settling basins with mechanical sLuUgo removal in the first half. Approxi- mately two-thirds ol' the basin is used for settling with the1 remaining third used for two stage stabilization. Liquid carbon dioxide is metered manually into the settled water, dispersed through one inch PVC pipe1 drilled with small holes approximately two feet apart. Baffles of polyetheylene film were installed to prevent mixing back to the settling zone. The purpose of the two stage carbonation is to first convert the hydroxide to carbonate alkalinity, precipitating calcium carbonate. Very little of the calcium carbonate formed settles, however, the solid phase is relatively stable and does not redissolve upon final plf stabilization just prior to filtration. The carry over of calcium carbonate onto the filter does not shorten the length of filter runs and does not pass through the filter. !'roper adjustment of the settled water pll prevents calcium carbonate from precipitating on the sand in the filter. Precipitated calcium carbonate carried onto the filter is easily removed on back washing. Settled, stabilized waters from the alum and magnesium processes are separated and filtered in identical sand filters, generally at a rate of 1 - 2.5 gallons per square foot per minute. One of the four filters used on the magnesium process has been con- verted to a dual media filter, replacing three inches of sand with anthracite with an effective size of 1.2 mm. Magnesium Recovery and Sludge Handling Figure 10 illustrates the units comprising the sludge recovery system. Sludge is pumped at a controlled rate into the carbonation VT-5 ------- colls using a variable speed Moyno Pump. Four, ten cubic foot flo- tation cells a re used for sludge carbonation. Again pure carbon dioxide is used, however, the feed is automated as shown in Figure 11. Carbonate sludge is pumped into a ten foot diainter thickener with the overflow returned to the raw water- using an intermediate 1800 gallon storage tank. The recycled magnesium bicarbonate is pumped at a controlled rate to give the desired coagulant dosage. The thickener underflow is vacuum filtered pumping the filtrate to the magnesium bicarbonate storage tank and land filling the filter cake. There are .several reasons why pure carbon dioxide should be considered for use in the smaller plants not recovering lime. The rate which carbon dioxide solubilizes magnesium has been found to be first order- with respect to the partial pressure of the carbon dioxide. in addition pure carbon dioxide will dissolve approxi- mately 25, 000 mg/t of magnesium bicarbonate, considerably more than the lower percentage carbon dioxide produced from on site generation. The feed of liquid carbon dioxide is much simpler, more flexible, and easier to automate. Carbon dioxide feed is automatically controlled to achieve a carbonation pll of 7.3. Near 100 percent absorption efficiency is possible due to the very fine bubbles produced and the high driving force between the caustic sludge and the carbonic acid. At pll values below 7. 3 the reaction has gone to completion with the result being the loss of carbon dioxide to the atmosphere. The carbon dioxide bubbles cause foaming which is greatly accentuated by the slightly surface active organic color released from the sludge in carbonation. This foaming serves as a good indicator of excess carbonation and can be used for visual pH control of the process. VI-6 ------- Table .'•! gives a typical mass balance for the magnesium process in treating the soft water in Montgomery. It is important to note that the only caleiurn carbonate precipitated in coagulation is due to the recycled magnesium bicarbonate. The sludge produced will have an unusually high ratio of magnesium to calcium carbonate and low ratio of calcium carbonate to clay turbidity. The total sludge production on a dry weight basis is 1050 #'S/M.G. which is 66% calcium carbonate for this example. Project Limitation The conversion of the Montgomery Plant was done so on a temporary basis, limited by a very tight budget. All of the conversion was accomplished with water works personnel at a cost of less than twenty thousand dollars. As a result, the facility layout and mechanical equipment used was less than desirable in some instances. First stage stabilization of the finished water should be accom- plished with point source carbon dioxide addition using mechanical mixing and sludge recycle. As a result of adding carbon dioxide across the width of the basin an uneven distribution results causing the pH to vary depending upon gas flow. One side of the basin may have a pH of 9.6 while the other side, because of less gas flow, a pH of 10, 8 rather than a uniform pH of 10. 3. The result of this uneven pll distribution is a slightly higher finished water hardness, in the range of 65 to 85 mg/£ as calcium carbonate. Two stage carbonation has been used very successfully at many plants; therefore it was not of primary concern to this project. A carbonate hardness in the range of 35 - 50 mg/f is being obtained in plants operated and equipped properly. At the time this project was initiated, the city of Dayton, Ohio intended to supply magnesium carbonate produced from their VI-7 ------- TAP EE ;•! Typical Mass MaJance for Magnesium Process in Montgomery Raw Water' Characteristics Turbidity A ika Unity Carbon Dioxide Magnesium Total Hardness Flow 5 MOD fiO FTU4 0 nifj/i suspend solids IS nig/I as CaCO,, 6 mg/i '* 4 tn g/i as CaCO-.. 15 mg/f as CaCO,, Chemical Addition to Rapid iVlix Uecycled Magnesium iV'lagnesium Sulfate F -imt' - 50 mft/1 as CaCO-j - 5 nif;/f as CaCO-^ - 105 nift/1 as CaO Settled Sludge C ha r n c te r is tic s Turbidity (if/Day) Magnesium Hydroxide (///Day) Calcium Carbonate (///Day) 1667 100 3500 646 7 % of Total 25TB 20. 1 54. 1 Stabilization Point 1 Calcium Carbonate - Produced (///Day) Carbon Dioxide Required (///Day) - 1650 - 156 0 (ASSUMING 95% ABSORPTION EFFICIENCY) Stabilization Point 2 Carbon Dioxide Required (#/Day) - 390 (ASSUME 05% ABSORPTION EFFICIENCY) Carbonated Sludge Flow - 11. 5 G PiVl Magnesium Bicarbonate (As CaCO,,) 17, 000 mg/i Suspended Solids ' = 4.9% Carbon Dioxide Required (ft/Day) - 2050 (ASSUMING 98% ABSORPTION EFFICIENCY) VI-8 ------- Cont'd Tlibit.? :-i Thickener Over-flow - 17, 000 mg/1 Magnesium as CaCO,, Flow - 10.3 Gallons Per Minute Underflow - 40% Total Solids Flow - 1.2 Gallons Per Minute Vacuum Kilter Cake (60% Solids) - 8,769 ///Day 0/ Composition Water (///Day) - 3500 40.0 Calcium Carbonate (///Day) 3500 - 40.0 Turbidity - (///Day) - 1667 19.0 Magnesium (///Day as CaCO.,) - 102 1.0 Summary of Chemical feed Lime (///Day) - 4350 Carbon Dioxide (///Day) - 3900 Magnesium Sulfate (///Day) - 5215 Finished Water Analysis pll -8.5 Total Hardness - 75 (All as CaCO J CaLcium Hardness - 71 Total Alkalinity - 70 Magnesium Hardness - 4 Vl-9 ------- softening sludge, Knough product was produced and used in the pilot scale phase, however', Dayton's full scale production plant con- struction was delayed making it necessary to use magnesium sulfate as the make-up magnesium source. As pointed out in the previous paper, magnesium sulfate adds nonearbonate hardness in direct proportion to the make-up dosage. This increased hardness is of little concern to the Montgomery project considering the small make- up dosage required and the fact that the water is blended with the extremely soft alum treated water following filtration. The physical layout of the vacuum filter was less than desirable. The filter could not be operated during cold weather due to freezing of the filtrate under near vacuum conditions. The filter bed was manually filled requiring considerable operator attention. The more desirable and more costly layout would elevate the filter with the sludge1 pumped from the thickener to the filter bed, the cake discharged directly into a truck, and the overflow returned to the thickener. Results and Discussion Plant Operation and System Control These first four months of operation have found the magnesium coagulation system to be much more stable than the alum system particularly in the coagulation process. Under certain raw water conditions, the alum coagulation pll must be maintained within ± . 1 of a pH unit in order to treat the water satisfactorily. Slight variance from the optimum pll results in greatly decreased coagulation efficiency. The low alkalinity water used by Montgomery has a very poor buffer capacity, particularly after the addition of alum when the alkalinity is seldom above 1 mg/l as CaCO^. Slight changes in either pre-lime or alum feed can affect the coagulation pH to a large Vl-1.0 ------- degree. Automation of the lime feed and carbon dioxide feed for sludge carbonation has proven to be very satisfactory. Control of both feeds are such that less than 0. 1 pH from the desired pll occurs. Recovery of magnesium as the bicarbonate is routinely carried out at a constant rate sufficient to provide the average coagulation requirements. When raw water conditions are such that additional magnesium feed is required, make-up magnesium sulfate is used which increases the concentration of recovered magnesium after a period of approximately 24 hoars, excluding the mechanical defi- ciencies of the temporary installation, the magnesium system has performed well with a minimum of operator attention. Included in the appendix is a summary process control points and a brief discussion as to which tests are performed at the various sampling locations. Typical results of these tests are also included. Pilot vs Actual Results Excellent correlation has been found between pilot and full scale results. Magnesium solubility in the finished water agrees closely with the results reported last year in Chicago^ with similar tur- bidity removals and filter performance. Leaf filter tests as well as thickening tests on the carbonated sludge agree closely with results now being obtained. Economics (2 3) In the January and February issues of the 1972 Journal, *' a series of curves were presented which could be used to approximate chemical costs and economically optimum, operating conditions for any water. To illustrate the simplicity of the use of this approach for a single water the cost curves for Montgomery have been prepared. VI-11 ------- Figure 12 illustrates the effect of coagulation pH on magnesium replacement costs for both magnesium sulfate and magnesium carbonate tri-hydrate. An average of 4 mg/I ol' magnesium is normally present in the raw water. As a result primarily of the high magnesium content of the cake moisture, 3 0 pounds per day of magnesium, as C'aCO^, in the vacuum filter cake, is lost each day. As the coagulation pH increases less magnesium remains in the finished water therefore less make-up is required, decreasing the cost per million gallons for magnesium expressed as calcium carbonate. Figure 13 illustrates the effect of increased coaguLation pj 1 on carbon dioxide and lime costs. Fifty mg/i of magnesium as calcium carbonate were assumed in the recycle with the chemical costs as noted. Figure 14 is a summation of Figures 11 and 12 and represent the total cost for magnesium, carbon dioxide, and linn: as a function of coagulation pll. An optimum pH of 11.2 was found for the situation where magnesium carbonate tri-hydrate was used as the magnesium source with a total chemical cost of approximately $19.00 per million gallons. Using magnesium sulfate, an optimum pll slightly higher than 11.3 is found with a chemical cost slightly higher than $25. 00 per1 million gallons. Figure 15 illustrates the reduced costs and slightly higher optimum coagulation pll if a souce of carbon dioxide were available at the plant site. A cost of approximately $11.00 per million gallons at a pH of 11. 3 is indicated. If dolomitic lime will serve as a suitable magnesium source Figure 12 can be used to calculate chemical costs. The only restraints on coagulation pll in this case is to keep the magnesium Vl-12 ------- content in the finished water below some maximum level for hardness considerations; generally requiring the coagulation p IJ to be kept above 11.0 which would result in a chemical cost of only $10.00 per million gallons. The results thus f'ar would indicate that the cost estimates published in the earlier papers were conservative. A predicted cost for Montgomery's water of $18.23 was based on a purchase price for carbon dioxide of $20/ton rather than the $30/ton now being paid. From this brief discussion the importance of carbon dioxide is clearly indicated. Lime recovery becomes attractive even at the lower tonnages than would have been considered previously. Other sources such as stack or engine exhaust should be sought. The production of electrical power at the plant site with the use of exhaust gases in water treatment is a possibility which should be explored. When considering the economics of this process not only should chemical costs be compared but all water production costs which include costs for sludge treatment should be considered. The additional advantages which Dr. Kinman has presented should be included in process decision making. These advantages arc summarized and included in the appendix. Sludge Handling In previous papers on laboratory studies the release of organic color on sludge carbonation has been noted. These studies ¦were usually carried out for a single cycle of coagulation and carbonation of the resulting sludge. There has been concern that this released organic color will tend to build-up in the recycle system after several cycles and cause problems. VI-13 ------- Jn the past four months, many hundreds of cycles of carbonation- eoagulation have taken place with no problems resulting from organic color increase. A ratio is made of the magnesium solubilized to the color released and recorded every two hours of plant operation. This ratio has varied from 5 to 10 dependent upon the amount of organic color present in the raw water. There has been no upward or downward trend established. As the turbidity in the raw water changes, the ratio of calcium carbonate to turbidity is affected. The higher the percentage calcium carbonate the better the thickener performs. The thickener underflow ranges from 30 to 45 percent total solids dependent upon this ratio. Carbon dioxide, released from the super saturated carbonated sludge has caused some difficulties in thickening. Some solids carry over results, but lias caused no difficulties except in excessive wear of the recycle pump. The vacuum filter rates range from three lbs. per square foot per hour to twenty lbs. per square foot per hour with the higher rates reported for the higher calcium carbonate. Several daily filter reports are included in the appendix. A polymer dosage of approximately .25 pounds per tons of dry solids is added to the carbonated sludge to aid in thickening. High molecular weight anionic polymers have been found best suited for conditioning of the carbonated sludge. The costs are low, approxi- mately $1.00 per day, and the results extremely good. A typical jar test for sludge conditioning is included in the appendix. The rate of carbonation using the flotations cells and pure carbon dioxide, is extremely rapid. On occasions, as much as 175 pounds of magnesium per hour, as CaCO^, has been recovered, enough to feed 25 mg/i to a plant flow of 20 mgd. VI-14 ------- Filtration of Stabilized Waters Filtered water turbidity is recorded on one of the four filters treating alum processed water and three of the four magnesium filters. Filters are normally backwashed after one hundred hours operation or seven Feet of head-loss whichever comes first. The months of February and March were selected as representative of normal operation and the records indicated that the alum filter had an average filter run of 82.2 hours and an average head-loss of 6.4 feet at the time of washing. During this same time period the magnesium filters averaged 97.8 hours with a head-loss of only 3. 3 feet. The filter capped with anthracite processing the magnesium treated water averaged over 100 hours filter run with only 1.8 feet of head-loss between washing. There was no noticeable difference in filtered water turbidities comparing the sand filter processing magnesium treated waters with the anthracite capped filter. During this time period an average of 7 FTU of calcium carbonate turbidity were being placed on the filters. Ideally, some 15 to 20 FTU of turbidity resulting from calcium carbonate pre- cipitation will be normal with better carbon dioxide addition. Based on the experience in Montgomery and the experience of hundreds of softening plants, problems with shortened filter runs are not expected. Filtered turbidities have been generally lower on the magnesium processed water, however, as with the alum process, coagulation efficiency generally determines the filter efficiency. The stabi- lization of th'e settled water and resulting calcium carbonate pre- cipitation assists filtration in two ways. Unsettled turbidity serves as a nucleus for precipitation increasing the particle size for VI-15 ------- removal on tin? filter and the precipitated calcium carbonate con- ditions the filter surface for more1 efficient operation. No calcium carbonate penetration through the filter has been found. Flotation Studies Flotation separation of the calcium carbonate and the clay prior to lime recovery has been accomplished only on a laboratory scale to date. While the Montgomery Plant will not be considering lime recovery, it is important that this process be demonstrated on a sizeable scale for the many plants utilizing sufficient lime to consider recovery. A flotation system utilizing a string of six cells* has been constructed by the Wetnco Division of the PJnvirotech Corporation and will be loaned to the project from April 15 through June 1. The raw water turbidity changes will be reflected in the calcium carbonate to turbidity ratio of the sludge. A wide spectrum of con- ditions will be studied with product purity and recovery efficiency evaluated. Additional Magnesium Sources As discussed, dolomitic lime will be investigated as a supple- mental source of magnesium. A special blend of high calcium and dolomitic lime is being produced in Birmingham for the steel industry. This product would appear ideal for this application, however, it was not available until these last months of the project, Dayton, Ohio will soon be producing sufficient quantities of magnesium carbonate tri-hydrate as well as the basic carbonate for use in Montgomery. If the basic carbonate serves as a suitable '"Schematic flow diagram included in Appendix VI-16 ------- source of magnesium, production of magnesium from water plant sludges will he simplified. This of course affects those cities treating high magnesium content waters which find it profitable to produce magnesium compounds from their sludge. Summary The Montgomery Demonstration Project has accomplished the objectives undertaken at its origin. The magnesium process has been found to compare favorably with conventional water treatment methods in both overall operation and in the water quality produced. As would be expected, slightly increased labor and maintenance costs could be expected, however, these can be greatly offset by automation which is quite ameanable to this process. The magnesium process does more than treat water; it treats the sludge produced as an integral part of the system. Considering process economics, one must include chemical costs, capital costs, operating and main- tenance costs, as well as the various treatment considerations which includes sludge treatment in many cases. The various advantages of this new technology must also be factored into the decision making. Table 4 summarizes the comparisons between the two systems for soft waters such as found in Montgomery. The acceptance of this new technology will probably come first with those cities faced with sludge disposal problems, extremely high chemical costs for water treatment, or in those cities where lime and magnesium recovery is economically feasible. I invite those present, who may be faced with one or more of these situations, to seriously consider this new technology. There now exists, for many waters, an acceptable alternative to the age old alum or iron salts treatment process. VI-17 ------- TABLE 4 COMPARISON OF THE MAGNESIUM AND ALUM TREATMENT PROCESSES AT MONTGOMERY PARAMETER MAGNESIUM ALUM CHEMICAL DOSAGES AND COAGULATION pH FLOC CHARACTERISTICS SETTLING CHARACTER- ISTICS SLUDGE CHARACTER- ISTICS FILTRATION CHARACT- ISTICS FINISHED WATER CHARACTERISTICS CHEMICAL AND OPERATIONS ECONOMICS 1 Dependent upon water Conditions 875 %/M.G. CaC, 800#/M.G. Co2, and 100 #/W.c. of MgsOe, pH 11.z, highly buffered Precipitation products, dense, granual. Form very rapidly and not as kinetically dependent upon water temperature. Rapid, maximum clarifier loading ra- between lower rate for alum and high rate for softening plant. High pH disinfects. Carbonated sludge thickens to 40% solid plus. Approximately 1000 #/m.g. produced but all solids are dewatered as an integral part of the process. All sludge water recovered Generally lower filtered water tur- bidity, calcium carbonate loading will not shorten filter runs. SIightly increased hardness and alkalinity; 40 - 50 mg/1 as CaCOj, allows pH adjustment for corrosion control. Less favorable for low alkalinity waters, increased chemical cost unless COj source becomes available or dolomitic lime proves successful 250 # / M, G. of alum, 206 P/m.g. of Ca (cH) 2 pH from 6,0 - 6.4 more difficult tc main- tain. Hydrolysis products, flocculant, much longer in size , form slowly with gentle mixing much slower at colder temperatures. leGer.erally less than .75 gal/ft^/min loading rate, sensitive to velocity gradients in settli r.g basin . Gelatinous sludge normally less than 1% solids which can be thickened only to about 6% solids. Less pounds per million gals, produced, approximately 400'. kpprox- .imately 1% of total water treated lost due to sludge discharge. Filter runs dependent upon amount of floe carry over. Very low alkalinity and hardness, generals more red water, corrosion problems. Lower chemical cost and less operating and maintenance expense when alum sludge is not treated for disposal. 2 Assuming more effi- cient first stage carbonation ------- PRE-CHL0R1NE RAW WATER POST LIME SETTLING SLUDGE TO WASTE SETTLING ALUM TYPICAL ALUM WATER TREATMENT PLANT FIGURE 1 ------- TO RAW WATER C02 FROM STORAGE OR OTHER SOURCE MgiHCO,)- STORAGE F I LTRATE SOL IDS 30 40 SOLIDS TO IANOFILL THICKENER MAGNESIUM RECYCLE AND RECOVERY UNITS MAGNES IUM PROCESS FLOW DIAGRAM FIGURE 2 ------- C02 STORAGE F 1 LIT 1 E ! ft I 1 1 s! i KJ STABILIZATION KglHCOa )2 )¦¦ RAW WATER RECYCLE PUMP SETTl/ING MAGNPSIUM CARBONATI ON FILTH SETTLING ALUM SLUDGE TO WASTE MgtHCCh); STORAGE THICKENER SLUDGE UNDERFLO* i^Oi \CAKE TO LANDFILL VACUUM FILTER MAGNESIUM RECYCLE HAGNESIUM PROCESS FLOW DIAGRAM FIGURE 3 ------- DEWATERED CARBONATED SLUDGE REPULP CaO FOR REUSE OR SALE CaCO FLOTATION KILN (FLOAT) VACUUM F ILTER (UNDERFLOW) TURBIDITY FOR DISPOSAL LIME RECOVERY WITH USE OF CARBON DIOXIDE PRODUCED FOR SLUDGE CARBONATI ON AND SETTLED WATER STABILIZATION MAGNES IUM PROCESS FLOW DIAGRAM FICUP.E 4 ------- I fo U3 F 1 L T E R S STABILIZATION RAW WATER M«m°u ST0R*GE SETT ulNG MAGNUS I UM — C4RB0NATI ON S E T T L/l N G THICKENER VACtlU# FILTER REPULP KILN FLOTATION VACUUM FILTER TURBIDITY LIME RECOVERY MAGNESIUM PROCESS FLOW DIAGRAM FIGURE b ------- HEAT EXCHANGER \ to ¦fr- AERAT ION CELLS BASIC CARBONATE KETTLE 35 PRODUCTiON OF MAGNESIUM CARBONATE TRl-HYDRATE OR BASIC CARBONATE FROM WATER PLANT SLUDGE MAGNESIUM PROCESS FLOW DIAGRAM FIGURE 6 ------- F 1 L!T i . s STABILIZATION I to Ul RAW WATER AERATION CELLS HEAT EXCHANGER o Vc &- STGRAG£ SETTUING MAGNPS i {IM CARBQNATI ON THICKENER SETT Li! NG VACUUM FILTER -±C> CaCOi FLOTATION PRODUCT 0EWATER1NG REPULP VACUUM FILTER MeC03»3H20 TURBIDITY Li ME AND MAGNESIUM RECOVERY MAGNESIUM PROCESS FLOW DIAGRAM C L t. l, 7 ------- Raw Water L'reatec! Water tt///// /V)rrrr V///////YJ/////////-T7 Lime 1'LAN VIEW zzzzz Treated ''ater htpf// // ////////////// ///////////////// / // R, SECTION VIEW RAPID MIX AND CHEMICAL ADDITION POINTS FIGURE 8 VI-26 ------- 10-50 mA SIGNAL oo pH METER RECORDER CONTROLLER RAPID MIX LIME FEED PUMP LIME SLAKER < I FLOCCULATION pH CONTROL SYSTEM ------- SETTLED SLUDGE MgC03 to RAW WATER CARBONATED SLUDGE FILTRATE ELECTRICAL PANEL SUPERNATANT THICKENER UNDER FLOW DEWATERED CAKE | STORAGE H MONTGOMERY WTP SOLIDS HANDLING FACILITIES Figure 10 ------- Legend for Figure 10 Units Comprising Solids Handling System (See Diagram) 0-15 GPM Variable Speed Moyno Pump 2 dual ccl.1, 2' X 2' each, flotation cells with a total detention time of 45 minutes with a sludge flow rate of 7 GPM 30 GP1VI submersible pump to the thickener 10 foot diameter reactor-clarifier used as thickener Vacuum filter station 1) 3' >' 3' vacuum filter 2) Vacuum pump 3) Filtrate pump 4) Filtrate receiver 1800 gallon magnesium bicarbonate storage tank Recycle pumping system, 0-15 GPM Sludge drying beds, 8' / 8', 6" of gravel and four inches of sand VT.-29 ------- f PH 10-50 mA SIGNAL METER CURRENT TO AIR TRANSDUCER CONTROLLER RECORDER SLUDGE SLUDGE CARBONATER O oo SLUDGE CARBONATION pH CONTROL SYSTEM AIR VALVE :C02 Figure- 11 ------- $ 20.00- Mg = 4mg/I in raw water 30#/D LOSS IN FILTER CAKE (Mg as CaC03> $ 15.00- $/mg $ 10.00 < $ 5.00 I • ¦ « i » 11.0 11.2 11.4 11.6 pH MAKE-UP MAGNESIUM COST AS A FUNCTION OF COAGULATION pH Figure 12 ------- 50 Mg/I MgCo3 RECYCLE CaO @ $.01/ # C02 @ $.015/ # ^ $ 40.00- $ 30.00- $ 20.00- $ 10.00- 11.0 11.2 11.4 11.6 11.8 PH LIME AND C02 COSTS AS A FUNCTION OF COAGULATION pH Figure 13 ------- 50mg/f MgC03 RECYCLE CaO (5) $.01/# C02 @ $.015/# 30.00- $/mg 20.00- 10.00- 11.0 11.1 11.2 11.3 11.4 11.5 11.6 PH LIME, C02, and MAGNESIUM TOTAL COST AS A FUNCTION OF COAGULATION pH Figure 14 ------- RECYCLE $ 20.00- $ 15.00- $/mg $ 10.00 H 50 mg/l MgC03 RECYCLE CaO <§) $.01/ # M g C O 3 < Z $ 5.00 i I 1 1 1 1 1 11.0 11.1 11.2 11.3 11.4 11.5 11.6 pH LIME AND MAGNESIUM COSTS AS A FUNCTION OF COAGULATION pH Figure 15 ------- I u> PUMPER CELL PUMPER CELL .. _ PUMPER CELL Reagents nV T DEWATERED CAKE CaC03 ) a CLAYS CONDITIONING AND RESLURRY CELL ^ ft Pi TAILINGS I"O LANDFILL CLEANER #2 CONCENTRATE CLEANER #1 CONCENTRATE ROUGHER CONCENTRATE CLAYS, INERTS, LO-CaCO^ FINAL CONCENTRATE f Hl-CaCO-, ) TO DEWATERING. I LO-INERTS > £ LIME KILN & CLAY MAGNESIUM CARBONATE PROCESS FLOTATION CIRCUIT Figure 11 ------- REFERENCES Thompson, C. G., Singley, J. E., and Black, A. P. "Magnesium Carbonate — A Recycled Coagulant," Journal AWWA, 64:1:11 {January, 1972). Thompson, C. G., Singley, J. E,, and Black, A, P. "Magnesium Carbonate — A Recycled Coagulant Part II, " Journal AWWA, 64:1:94 (February, 1.972). Thompson, C. G. and Black, A. P. "Progress Report of the Magnesium Carbonate Project, Montgomery, Alabama," presented to 92nd Annual AWWA Conference, June, 1972. Sperry, W. A, "The Lime Softening of Water and the Use of th Sludge as an Aid Thereto," Journal AWWA, 6:215 (June, 1919). Hartung, H. O. "Experience With Up-Flow Type Basins," Water and Sewer Works, 1:91 (January, 1944). McCauley, R. F., and Eliassen, R. "Accelerating Calcium Carbonate Precipitation in Softening Plants, " Journal AWWA, 47:487 (May, 1955). Tuepker, J. L.f and Hartung, H. O. "Effect of Accumulated Lime-Softening Slurry on Magnesium Reduction, " Journal AWWA, 52:106 (January, 1960), Lawrence, R. W. "Equilibrium and Kinetics for the Carbonation of Magnesium Hydroxide Slurries, " Research and Development Progress Report No. 754, U.S. Department of Interior, (December, 1971). VI-36 ------- APPENDIX VI-37 ------- CONTROL SYSTEMS AND SAMPLING LOCATION A) Rapid Mixer number 1. Total and calcium hardness are determined on a filtered sample from which the magnesium feed can be determined. B) Rapid mixer number 2. Automatic pi I control of lime feed. C) Carbonation point 1. pH measurement and manual control of COg rotameter to maintain a pH of 10. 3. When the pH is too low or too high, the water is clear indicating that calcium carbonate precipitation is not taking place. D) Settled magnesium water flume. pH, turbidity, total hardness, calcium hardness, alkalinities, and acid turbidity are determined on a routine basis. E) Filtered magnesium treated water - continuous turbidity monitoring along with alkalinities, pH, and hardness deter- mined on a routine basis. F) Carbonated Sludge - Automatic pIT control of the carbon dioxide flow along with alkalinity titrations on a routine basis. G) Recycled magnesium control system - alkalinities measurement and flow control. H) Vacuum filter - filter rates, solids inflow, filtrate alkalinities, filter cake solids, and filter cake composition are determined on a routine basis. Suggested Automatic Control Systems I) Total hardness recorder at point A. This would relate directly to the magnesium concentration and could be used to automate the magnesium recycle. 2) pH Control system at points C and D to record and control the stabilization pH. VI-38 ------- C02 STORAGE RAW WATER U2(HC03); storage STABILIZATION CARBONATldN SETTLING ALUM ATE -SLUDGE TO WASTE SLUDGE UNDERFLOW \CARE TO LANDFILL VACUUM FILTER MAGNESIUM RECYCLE MAGNESIUM PROCESS FLOW DIAGRAM ------- TYPICAL CONTROL TESTS M agnesium Rapid mix number 1 pH 10.3 Total Hardness 100 Calcium Hardness 25 Magnesium Hardness 75 Rapid mix number 2 pi J 11.60 Magnesium Stabilized Water . g ^ Q T o t a! II a r d n e s s 70 Calcium Hardness 65 Total Alkalinity 65 (Non-carbonate hardness i.s equal to the mg/i of magnesium sulfate feed) Turbidity 7.0 FTU Aeid Turbidity 1.5 FTU Carbonated Sludge pi I 7.3 Total Alkalinity 14, 000 mg/i Color 7 00 Ft. -Co. units Alum l'Toccu la to r pit 5.9 Total Alkalinity 2.0 Settled Stabilized (lime) Water pH 9.0 Total Alkalinity 20.0 Total Hardness 28. 0 Turbidity 6.0 VI-A0 ------- Advantages oJ' the Magnesium Carbonate Process Soft Turbid and jar Colored Waters 1. Provides an economical and practical solution to the problem of the disposal of water treatment plant sludges. 2. Provides For the first time a coagulant which can he recycled and reused, 3. Increase settling rate of the floe produced should allow higher clarifier loading rates, 4. Produces a treated water which is noncorrosive since it can be stabilized by pU control. 5. Coagulates water in the pll range 11.2 - 11.5 which inactivates most viruses and destroys bacteria. 6. Should in most cases eliminate prechlorination where used. 7. In many cases, reduces chemical treatment costs. 8. Requires no important changes in treatment plant. 9. Simple to operate and may be automated. 10. Removes both iron and manganese where present. 11. Improves filterability of settled water. Additional Advantages t'or Hard Water 1. Makes it possible to reduce lime costs by about 50% by recalcining with excess lime to be sold for some waters. 2. Recovers the magnesium values from the sludge which may be sold. 3. Substantially reduces present chemical treatment costs, in some cases by $200, 000 - $700, 000 per year. VI-41 ------- MAGNESIUM CARBONATE PROCESS SLUDGE HANDLING DATA DATEFRIDAY, FEBRUARY 23, 1973 TIME SIudge Solids (X) Filtrate Alkali nity Solids g/ft2 Drum Speed ft/ft^/hr. Co Ca ke Anal t, 3s caco Mg iszs f. - % Moisture 3:15 Started 9 AM 43 .4 -- 303 .0 .88 3 .9109 -- _ 36 . 796 10 AM — -- .88 — -- - 11 AM TS 36 8 ¦ CH 300 7 ,400 307 .2 .88 3,9648 344 34 37 .408 12 N MH 6 8 — .88 — -- - — 1:30 39 . 9 — 353 .4 .88 4.5614 -- - 36.393 2 PM -- -- -- .88 — -- - — 3 PM -- — -- .88 -- __ - -- 4 PM 24.2 169.S . 88 2.2857 (This s low d e to a low J evei Ul 1 Closed rn ¦ ni trer sen 6 PM REMARKS: LEAF FILTER TEST 4:15 Form Wet 58.8 5:30 Dry Pry 37.0 21.8 % Moist = 37.07% 370 g/f+2 «¦ 4.74 #/f+2/hr ------- NAGKBSIl'tl CARSON ATE PROCESS SLVDGE HANDLING DATA DATE MONDAY, MARCH 5, 1973 TIKE SIudge Solids (%,) Fi1trate A1 kalini t u Solids q/ft2 (fpm} Prom Speed #/f t2/hi- Cake Analysis (as daCO-%} Bel t Setting Ca Mq % Moisture 8 AH 49.5 -- 450.6 1,666 ll . 02 66 38 .08 1 . 0 9 AM 10 AM 11 AM 48 . 8 529 . 2 1 . 25 9.7094 37.84 . 5 12 W 1 PM TTI 570 jo 5 Cii 530 MM 40 9,000 409 . 2 1 .66 6 10.0134 524 35 39.05 1 . 0 2 PM 43 . 9 367 ,2 J .666 8.9857 40 .29 1 .0 3 PM 4 PM 5 PM 6 PM REMARKS: LEAF FILTER TESTS Cake # Tine(Sec) Wei gilt (Grams) Cake % Moist Filtrate Eqaiv. Belt Filter Fate Sludg & Form Dry Wet Dry M.I. Setting (*/f+z/hr) Solids 1 25 5 330 97 .5 57.7 40 . 82 ?&.0 i> ! .44 48 . U% 2 160 230 77.2 45.8 40 .67 64 . 0 . 5 8.40 48 . 8% 3 115 170 65,2 38.7 40.64 59.0 1 .0 9 .47 45.3% ------- .Jar Test iJ(.)I ,Y:VI!¦]K CONDITIONING OF CARBONATED SLFDGE Polymer - Dow A2'5 To determine1 the optimum polymer dosage for sludge con- ditioning, a jar test is run each day. A.s the sludge solids change in character and concentration, so does the required polymer dosage. Following .settling, the jars are rapidly mixed, and the time to filter 100 mi of the mixed sludge determined for each polymer dosage. The results from a typical jar test is a.s follows: Polymer - Dow A23 ¦Jar No. 1 2 3 4 5 6 Polymer Dosage (Mg/i) 013579 Sludge Level After 10 IVIin. Settling (inches) 43/8 4 3/8 4 1/8 2 1/4 2 2 Time for filtration of 100 mi (Sec) 327 265 279 189 192 185 At the present polymer feed levels of 4-7 mg/1 , a cost of less than 30 cents per million gallons of water treated results. The polymer acts to produce a clearer supernatent, increase the solids concentration to the vacuum filter, and increase the filterability of the1 sludge. VI-44 ------- FiIter Cake -Flotation Reagents Condi tioner Rougher Rougher Concentrate Rougher Tails First Cleaner 1st Cleaner Concentrate 1st Cleaner Tails "V/ Second Cleaner 2nd Cleaner Concentrate (Product) 2nd Cleaner Tails SCHEMATIC DIAGRAM OF FLOTATION CIRCUIT USED AT MONTGOMERY, ALABAMA VI-45 ------- NOTES ------- NOTES ------- NOTES ------- NOTES ------- |