Characterization and Treatment of Incinerator Process Waters

Transcription

1 Characterization and Treatment of Incinerator Process Waters R. J. SCHOENBERGER and P. W. PURDOM Drexel University Philadelphia, Pennsylvania S. J. LEVY Department of Health, Education, and Welfare Cincinnati, Ohio H. I. HOLLANDER Roy E. Weston West Chester, Pennsylvania MISCELLANEOUS DISCUSSION Question by F. G. Andrews, Town of N. Hempstead: Why were there no coliform tests conducted? Answer: Some microbiological testing was done but at F very few coliforms would exist. Question by R. Kopita, Peabody Scrubber: Explain the 5800 gpm of water and isn't this excessive? Answer: This is not excessive and less could affect the data. Some losses to evaporation are okay. DISCUSSION by W. M. Harrington, Jr., Whitman, Requardt & Associates, Baltimore, Md. pended solids existing in one degree or another in most mixed process water effluents. While this is a costly arrangement, it is necessary to provide a conservati ve design if we are to prevent additional pollution from occurring. An apparent side benefit from larger lagoons is the temperature modification which assists in the ph correction, thus reducing the quantity of chemicals required for this purpose in the recycled process water. One very important point brought out in this paper is the need to perform some tests on the water samples as soon as possible after they are taken if meaningful results are to be realized. I can only hope that this worthwhile effort will continue to a point where improved design and operating efficiencies can be realized by the development of refined design criteria. A designer has only to be faced with the task of determining process water treatment criteria to recognize the lack of information available today. In fact, it is almost impossible to determine a retention time in a clarifier or lagoon system with any degree of removal efficiency being predicted from the operation. The problem becomes more significant where stream quality standards are being increased to a point where a high degree of process water treatment is required before it can be discharged to a surface water course. In fact, water that is suitable for discharge to surface streams is almost certainly suitable for reuse in the plant process water system. Most present designs consist of a mechanical clarifier to remove the larger suspended particles, followed by a lagoon, or lagoons, to provide the several days' detention time necessary to remove the very fine sus NOTE: See Err3ta, page 104. DISCUSSION by Robert K. Hampton, Hampton Equipment Co., Inc. The need for studying the handling and disposing of process water from incinerator plants is now even more urgently needed due to the emphasis on more sophisticated air pollution control devices. I read with interest this paper which endeavored to pull together the published data on this subject. It would have been more helpful to the industry if the authors had contacted the writers of the previous papers mentioned so that additional information or corrections could have been made a part of this paper. The pioneering effort made by Felix Matusky and myself was done without Federal Subsidy. The Consulting Engineers and Municipalities invol ved 66

2 gave freely of their information and time. As stated in the paper, we were not trying to establish a definitive design guide but to determine first, that there was a problem, and second suggest areas where further investigation was needed. Due to the stress on low capital cost construction and extremely competitive bidding, very few, if any, plants built have had the instrumentation installed that would have given the information on flow rates that would normally be expected by a research oriented individual. This is probably why the authors' Plant No.1 does not have this information available. While Plant No.2 does have these instruments, these were probably added after construction and possibly funded by the Federal Government, as could be assumed from the credits at the end of the paper. Due to the lack of knowledge on this subject, it would be well to qualify general statements, such as gallons of water required per ton of refuse even further than the broad range given, which, however, is an improvement over some of the single average numbers that have been accepted as fact by unknowledgeable people. An interesting observation is made concerning the possibility of batch quenching of residue, possibly using less water than in a residue conveyor system with a still water bath. As most batch plants use from 50 to 75 gpm per ash hopper and a reduced continuous flow of water between dumping of the grates, this assumption seems questionable. Here again the lack of meters at various testing points prevents a definite conclusion. With regard to the question of alkalinity, the majority of the samples were tested by the same independent testing laboratory. Another sample from the same point questioned in the authors' paper tested by the same aboratory indicated an alkalinity of 12 4 and a ph of Besides a combination of residue and fly ash laden water from secondary combustion chambers, floor drains and other plant drain ar eas are collected in the same wet well. This could possibly account for the seeming inconsistency. However, as pointed out in our original paper, this is why a series of tests conducted by people experienced in testing and laboratory procedures, as well as experienced in incinerator plant design and operation, is necessary to secure meaningful information. The type of information given for Plant No.2 is sorely needed in the industry and I am more than willing to have some of my income tax dollars as well as local real estate tax dollars support it. I strongly suggest that this type of research be continued, and where funding can be found, that future studies be coordinated with such efforts already in being, such as those of the ASME Power Test Code Committee which is developing a Code fo r Testing Large Municipal Incinerators and' the S'Ulb-Committee of the Design Committee of the ASME Inc1ne rator Division which is cooperating with the Bureau of Solid Wastes Management of the U.S. Public Health Service in pointing out additional areas of information requiring extensive field measurements. These are areas not needed for performance testing, but win enable designers and operators to do a' Detter job. DISCUSSION by J. W. Stephenson, Havens and Emerson, Ltd., New York, N.Y. This paper is a valuable contribution to the still limited knowledge of characteristics of incinerator process water. It comprises a report on studies funded in part by a research grant - an ideal situation which, at present, is too infrequently encounteted. Unfortunately, the securing of reliable, detailed data on incinerator water characteristics over a sufficiently long period of time is a costly undertaking for which it is unlikely that the facilities will be provided in the average municipal incinerator plant under the original construction program. For example, elimination of a 6-in. plant water meter and the associated val ves and piping resulted in a $10,000 saving when one recently completed plant was rebid in This was a single meter on the main plant water supply line and, since it would have metered recirculated water with sewage plant effluent makeup, it had been specified for service at elevated temperature with screened water containing small quantities of abrasive material (fly ash). The provision of additional facilities for metering individual water uses such as air pollution control equipment supply and effluent, siftings sluice, residue quench, clarifier detention time, etc., would have increased the total cost and, therefore, the saving resulting from its elimination, substantially above the $10,000 noted above. It is obvious that justification of such expense to the owner of an already costly proj ect may be quite difficult. In addition, personnel requirements for observations and samplings for a detailed survey and the necessary laboratory analyses represent costs which the average designer or owner may be unwilling or unable to assume. Until research funding is available to meet the high cost of detailed surveys as outlined above, it should be possible to accumulate valuable data at substantially less expense at many plants. This will require: 67

3 1. The use of design flow rates, detention times, etc. In general, actual operating rates should not vary from design rates sufficiently to introduce significant error in the results. 2. The use of a sewage or water treatment plant laboratory or other nearby laboratory for the analytical work. Many municipalities have such laboratories which are equipped to make the required analyses of incinerator water. 3. Sampling, observations, laboratory work, etc., by plant operators or other municipal personnel following a program established and generally supervised by the designer or other knowledgeable individual. It has been this reviewer's observation that incinerator plant operating personnel, as a group, are interested and most willing to assist in such a program, and that permission for their participation can usually be obtained, provided there is no serious interference with normal plant or laboratory operation. Further, the designer's familiarity with details of plant design, construction and operation should permit him to establish and initiate the program and provide the necessary supervision during routine visits and by telephone without requiring an inordinate amount of his time. On the above basis, the data in Table 1 are the result of a sampling and testing program at the Ansonia, Connecticut, incinerator May 6, 7, and 8, The plant has two continuous feed rocking grate furnaces, each with nominal capacity of 100 tons/24 hr but operating at a rate in excess of 150 tons/24 hr, over a total of approximately 16 hr during the test period. Plant water is recirculated air pollution control chamber effluent with primary water pollution control plant effluent for makeup. APC chamber effluent is plant water overflow from a Detrick-Jens scrubber combined with city water from the continuous bottom flush. Design flow rates are 400 gpm for the scrubber and 150 gpm botton flush. The clarifier is designed for 30 minutes detention of the APC chamber effluent at 600 gpm. Sampling points were as follows: Plant Water - Bottom of 6 in. main, approximately 25 ft downstream from pumps. Scrubber Tank Overflow - Top of tanks. APC Chamber Effluent - Outlet of submerged discharge pipe in sump adjacent to chamber. Clarifier Effluent - Weir trough discharge to sump. Temperatures were determined at the sample points coincident with the sampling. ph determinations were made at the end of each day's sampling. Solids determinations were made several days after sampling. Referring to Table 1, scrubber tank overflow data are available for only two days because of difficulty in establishing the sampling procedure. All other sources were sampled for three days. Plant water data are presented for both two days and three days to permit appropriate comparisons. There is no ready explanation for the higher solids content of the scrubber tank overflow than of the plant water. Plant water is used for the scrubber and there is no other water introduced to the system between the pumps and the scrubber. Samples were taken at top of scrubber tanks before the water was exposed to the gas stream, and all analyses were made by the same technician. Solids content of samples from these two sources would, therefore, be expected to be the same. Samples were taken at regular intervals throughout each day's operation, starting immediately after the furnaces were fired, to provide indication of the rate and extent of buildup of the various conditions. Inclusion of the early samples in Table 1 undoubtedly results in average figures less severe than would be the case if they were eliminated from consideration or if the plant operated over longer daily periods. Table 1 is an indication of the type of data that can be accumulated with relatively little expense. If available for a large number of plants it would provide valuable guidelines for designers. There is no question but that more complete data, such as that advocated by the authors of the subject paper, would be infinitely more valuable and is needed; however, until the necessary funds are available for complete surveys of a large number of plants, information such as that in Table 1 will be most helpful. Information on quench and sluice water, etc., can be added to such a program with little additional expense. The report of ASME's PTC committee will include recommendations for sampling and analytical procedures. In many, if not most, instances, procedures set forth in "Standard Methods" [1] will be recommended, and until and unless other procedures are found preferable for incinerator waste waters, those of "Standard Methods" should be followed. Reference [1] Am erican Public Heal th Association, "Standard Methods for the Examination of Water and Wastewater Including Bottom Sediments and Sludges." 68

4 Table 1 Characteristics of Incinerator Plant Water s Ansonia, Conn. May 6,7,8, 1969 Total mg/l Plant Water (3 days) Samples Average 415 Maximum 626 Minimum 278 Plant Water (2 days) Samples Average 379 Maximum 604 Minimum 278 Sol ids Susp. mg/l ettl eabl e mill 6 (a) (a) 1.2 Scrubber Tank Overflow (2 days) Samples (a) Average Maximum Minimum APC Chamber Effluent Samples Average Maximum Minimum Clarifier Effluent Samples Average Maximum Minimum (a) Composite Samples 7 (a) 16 7 (a) 1.5 ph (b) Temp F (b) Probably contaminated by caustic soda used (or ph correction. DISCUSSION by Charles O. Velzy, Charles R. Velzy Associates, Inc., White Plains, N.Y. The results of the investigation reported in this paper add a little more to the knowledge of this important aspect of incinerator design and operation. Two statements made in the Introduction require expansion for purposes of clarity. The concept of incineration as a means of waste reduction to produce a residue suitable for disposal in a landfill is a typical American concept. I think consideration should be given, especially in the heavily urbanized areas of this country, to achieving proper control of burn-out and residue quality and then processing the residue for beneficial use. In such a case incineration becomes a means of ultimate disposal and landfill area is only necessary as a means of standby disposal. In the last paragraph of the Introduction, treatment of incinerator process waters is presently mandatory in many areas to meet agency regulations, rather than being some possible future requirement as indicated in the paper. In the section on "Sampling and Analytical Procedure", the authors indicate that the rise in ph observed after a process water sample is collected is "generally acknowledged" to be a result of loss of carbon dioxide. I would appreciate it if the authors could ci te references or tests conducted by individuals or organizations that specifically demonstrate this to be fact. Even in this paper the role of CO, in depressing the ph of the process waters is inferred by conjecture rather than by analytical measurements. In the section entitled "Determinations and Analyses, Effluent-Water Quality", it is inferred that recirculation of process waters might be detrimental due to buildup of higher chloride levels. While chloride levels, no doubt, would build up in systems recirculating process waters, the total amounts of chlorides discharged to the environment in an uncontrolled manner would probably be significantly reduced. Such discharges might be eliminated entirely if a closed water loop were developed with treatment of a part of the process water flow to control solids buildup. A number of references in this paper are made to the role of CO, in depressing the ph in process waters, i.e. as cited above, in the section on "Water Stability Characteristics" immediately above Fig. 3, and in the "Conclusions". Yet, in Table 7 '. the ph is higher in the Spray Chamber, where the waters are hotter and are exposed to the CO,-laden flue gases, than they are in the Clarifier. It seems as if this does not fit the pattern of the CO, explanation. Perhaps the authors can clarify this apparent discrepancy. In the last paragraph of the "Conclusions" the authors point out the necessity for in-depth studies of incinerator wastewater characteristics and treatment requirements. The need for such studies has been recognized by the designers in this field for some years. We must find a way to commit money and manpower to a properly constituted investigative program to determine and correlate information in this area into adequate design and operation data. The time for brief, inadequate surface studies to determine if a problem exists is long past. DISCUSSION by leland E. Daniels, Bureau of Solid Waste Management, Cincinnati, Ohio The authors should be commended for their work in characterizing the process waters from two 69

5 incinerators. Their diligent effort in conducting the 'study and thorough analysis has produced some interesting data..as I looked at the mass of data contained in Tables 5, 7, and 8, two thoughts occurred to me: one was the variability of the data and the other was the question of what do all these data mean. The data from Plant No.1 are the only data where,we can readily see the variation, and naturally there are variations between the two different systems. As the authors concluded, "Incinerator water effluents vary considerably between the respecti ve sources of the water leaving the process and also between different incinerator plants. It is. apparent that 'the character of each system will have to be evaluated on an individual basis. " This is the logical and natural conclusion, but the question remains, "Why were there variations?" We know the pollutants were removed from the residue and flue gas and added to the process waters, but what exactly was the quality and quantity of these constituents to produce this waste water? If the authors had related the characteristics of the process to the residue and flue gas, the variation in the data could have been understood. The following comments pertain to the data presented in this paper: 1. The footnote at the bottom of Table 7 states that the initial raw water background was subtracted from the final ion concentration.. The total flow must be known and used when calculating the contribution of pollutants from a source. Table 8 does not have a footnote; was this also done for this table? 2. The authors state that "The high COD was corroborated by an independent test for volatile acids." I would like to know how the interferences were removed, how many tests were done on how many samples, and what the individual results were. 3. After determining the instability aspects of the process waters, I am interested in knowing how this was considered in their sampling program, analytical methods, and data presentation. 70