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

ABSTRACT

The chemical character of process waters is examined with respect to sampling and possible treatability. Differences are noted between waters used for quenching and those used in scrubbers for air-pollution control. High chloride concentrations were found in both sources of process waters. Waters requiring biological treatment are probably limited to the quench waters.

INTRODUCTION

As suitable sites for long-term landfill become increasingly distant from the urban centers and with regulatory agencies now more critical of their opera­tion, there is a refocus toward incineration as the method of waste reduction of low-volume, non put res­cible residue to simplify and extend landfill opera­tions and maximize future site utilization. The poss­ible employment of broader financial and manpower resources through regionalized solid-waste manage­ment systems has prompted planners to include in­cinerators as a vital part of their regional master plans for solid-waste management. The increasing sensitivity of the public to environmental degrada­tion has stimulated re-examination of incinerator plant operations to eliminate or materially reduce, where possible, all aspects of pollution.

Most designers of new plants are cognizant of these needs and objectives, but, in some areas, the

204

H. I. HOLLANDER Roy E. Weston

West Chester, Pennsylvania

lack of definitive information hampers the develop­ment of responsi ve designs.

The ASME Nat�onal incinerator Conferences of 1964, 1966, and 1968 reported on current investi­gation and research as well as problem areas where the incineration systems for both municipal and industrial solid wastes could be improved. How­ever, a review of the published conference proceed­ings and discussions reveals a minimum of reported data on the magnitude, characterization, and treat­ability of incinerator process waters. Incinerator pro­cess wastewater flow rates may be low relative to the discharges from sewage treatment plants and some industries. However, there is increasing concern with regard to these wastewater discharges because of the more critical requirements of all discharges to our rivers and streams in addition to the effects on reliable operation and life of the incinerator wet-air­pollution-control devices and all equipment contain­ing or handling these waters when recycling is em­ployed.

At the 1966 conference, Stephenson and Carifero [1] came to the following conclusion after surveying almost 300 municipal incinerators: "To date there has been relatively little work done on characteristics and treatment of incinerator process waters-continu­ing studies are needed to permit designers to make proper provisions for wastewater disposal." Since then; the amount of research done on incinerator pro­cess water has not been significant. This paper will attempt to include pertinent data from what has been published and to correlate it with the information

and data obtained at two incinerator plants investi­gated in 1968. It is hoped this presentation will bring emphasis to the problem and illustrate the crit­ical need for in-depth investigations. The scope of the available data is obviously inadequate for secure design purposes, but it does point out the complexi­ities of the problem.

Incinerator process waters can be classed as com­plex industrial wastewaters, and much research needs to be devoted to their investigation and to solution of their treatment problems. As governmental control agencies tighten regulations on allowable stream and sewer discharges, suitable treatment may become mandatory. Even discharges to a sanitary sewer sys­tem and municipal treatment plant may have to be given pretreatment. Few incinerators now in opera­tion provide treatment other than simple clarifica­tion or at most clarification and pH adjustment. In the future, it seems that more sophisticated treatment will be required.

DESCRIPTION OF COMMON INCINERATION

WATER PROCESSES

Process waters in an incinerator facility may come from several sources. Air-pollution -control systems may be made up of several banks of water sprays, wetted baffle walls, wetted target piers, flooded chamber floors or water sprays in a gas conditioning (cooling) chamber ahead of mechanical or electrostatic collectors or high-energy flow-energy wet scrubbers. Depending on the particular system, substantial quantities of water may be needed. The collected water will not only trap fly ash but also absorb constituents from the flue gas. Another major source of water effluent may be from the residue quench and handling system.

This discussion will be limited to the two main sources of incinerator process waters: those result­ing from air-pollution-control systems, and wastewater from residue quenching and handling systems.

The general characteri zation of an incinerator wastewater will be influenced by a large number of factors including the type of incineration process, method of operation, type of refuse, type of air­pollution-control, quenching system, and the original source of the raw water. Individual variations en­countered in day-to-day operations such as moisture content of the refuse, instantaneous charging rate, furnace temperatures, and process waterflow rate and contact time will result in a wide range of analytical results. Characterization and treatment of process

205

waters is complicated and often unpredictable be­cause of these many variables.

Wastewater from an air-pollution-control device will vary in both character and quantity depending on the type of system. Water consumption may vary from 0.25 gal/lb refuse to more than 5 gal/lb of refuse depending on the water quantity recycled.

Incinerator residue-quenching systems use con­siderably less water than the gas-cooling and/or air­pollution-control systems. The water loss in the resi­due-quenching operation is from evaporation and that Significant portion absorbed or entrained by the resi­due and removed from the plant. There are two basic residue-quenching techniques: spray quenching or submerged tanks. One of these systems was at each of the two incinerator plants investigated and will be described subsequently along with the character of the raw water into and wastewaters discharged from the plants.

NEED FOR TREATMENT

The types of pollutants found in incinerator pro­cess waters affect the character of water in a variety of ways. Waters that are to be recirculated especial­ly through air-pollution-control equipment must be noncorrosive and nonerosive. Also, suspended par­ticles, which might possibly clog spray nozzles, must be minimized, or continual shutdowns will be required to keep the nozzles open and effective. Evaporative losses will cause a buildup of dis-sol ved solids in the process water. Erosiveness may be less important in water used for residue quench­ing. The evaporative losses in quench tanks are considerably less than in the air-pollution-control systems, but the carry-over of water in the residue results in an appreciable loss of water. Since the water is lost in the liquid state, the concentration of dis­sol ved solids in quench water will approach a stable maximum concentration. The concentration of solids should be controlled at a predetermined maximum value in order to protect pumping equipment as well as prevent corrosion and excessive erosion of the drag-out conveyors. The concentration can be con­trolled by bleeding water from the system and add­ing make-up water.

When the combustion of the refuse is incomplete, unburned organic matter may dissolve in the quench water. Under some conditions this organic matter undergoes biological decomposition and may produce slight odors. More often, the high-metallic concen­tration and temperature of quench water provides an

unfavorable environment for biological growth; hence, decomposition is minimized.

Waters that are wasted without reuse may also require pretreatment before discharge. Even waters discharged to a sanitary sewer system should re­ceive a minimum degree of treatment, unless the flow of such wastewater is small in relation to the capacity of the municipal sewage-treatment plant. Municipal biological-treatment plants are subject to upset by shock loads of inorganic wastes.

Discharge to a river or stream should also be ac­companied by some form of pretreatment. A signifi­cant heat-pollution load or high dissol ved-solids load can be imposed on the receiving stream. Sim­ilarly, settleable solids may blanket the stream bottom and adversely affect benthic organisms.

PREV IOUS STUD I ES

A review of the data reported in several studies that have been undertaken in the past several years provided a beginning point for this study. Cross and Ross [2] report the partial analysis of several scrubber waters from municipal incinerators in Florida. The Broward County (Florida) incinerator is a 300-ton/day plant having ram-feed charging and reciprocating grate furnaces. Air-pollution control consists of wet-bottom spray chambers equipped with wetted baffles. The water drains into a quench

T able I. Scru bber Water Chem i ca I Characteri sti c s*

Quality Raw Scrubber Constituent Standardt Water Effluent

Iron (Fe) 0.3 0.35 1.65

Cyanide (Cn) 0 0.21 5.19

Total chromium (Cr) 1.0 0.0 0.13

Lead (Pb) 0.50 0.0 1.30

Phenols 0.005 0.005 1. 721

Copper (Cu) 0.05 0.08 0.10

Zinc (Zn) 1.0 0.0 2.4

Manganese (Mn) 0.0 0.30

Aluminum (AI) 0.18 20.6

Barium (Ba) 0.0 5.0

* Adapted from Cross and Ross [2]. tState of Florida quality standard for incinerator effluents.

Data from Broward County, Florida incinerator. All values are expressed in mg/1.

tank and then flows through a rotating screen and pressure filter before being recirculated back through the plant. The results of analyses are pre­sented in Table 1. It should be pointed out that these results reflect the low-energy type of air­pollution-control device.

Cross and Ross also reported data from the McCoy Street incinerator in] acksonville, Florida. These data are given in Table 2. In this incinerator, the scrubber water is recirculated following simple sedimentation in a tank providing IS-min retention time.

Table 2. Scrubber-Water Chemical Characteristics*

Canstituent Concentration (mg/I)

Total solids 5,351.0

Calcium (Ca) 842.0

Magnesium (Mg) 129.0

Sulfates (S04) 791.0

Chlorides (Cl) 1,489.0

Total hardness (CaC03) 2,630.0

Free carbon dioxide (CO2) 114.0

pH 4.2

*Adapted from Cross and Ross L2]. Data from Jacksonville, Florida, McCoy Street inciner­ator.

Table 3. Chemical Analysis of Process Waters from Five Incinerators*

Sample Source pH

Plant A: Quench Water

Fly Ash Flushing Water 7.2

Plant B: Quench Water 11.6

Plant C: Quench Water 4.6

Plant D: Quench Water

Plant E: Quench Water 6A

Alkalinity

50

424

330

410

Total Solids

1,327

11,846

1,830

6,302

Suspended Solids

69

11

236

56

45

14

* Adopted from Matusky and Hampton [3]. All values are ex­pressed in mg/! except pH.

206

The data presented by Matusky and Hampton [3] are included in Table 3 so as to prevent a more complete review of the published information on the analyses of incinerator wastewaters. However, these authors did not describe the source of the samples, and the lack of information concerning the flow rates, retention times, quantities, patterns of treatment or recirculation, etc. limits the useful­ness of the data. An alkalinity of 330 mg/l (Plant C) seems highly unlikely in view of the low pH of the samples.

SAMPLING AND ANALYTICAL PROCEDURE

Uniform characterization of incinerator-process water is hampered by the lack of standardized ap­proaches for the collection, preservation, and analyses of samples. The complex nature of the waste and the high levels of ion concentration en­countered result in rapid changes within the sample and in complex interferences with normal analytical procedures. An investigator should be aware of several analytical considerations.

First, as the sample temperature drops to am­bient temperature after collection, the pH is obser­ved to rise. This is generally acknowledged to be a result of the loss of carbon dioxide, which is re­moved from flue gases with wet scrubbers.

Secondly, colorimetric and turbidimetric analyses are hindered by the deep color of quench water and by the large amounts of suspended material present in both scrubber water and quanch water. Suspended matter can be removed by filtration prior to anal­ysis, but color interference can be minimized only by dilution if the ion concentration allows dilution. Filtration through acti vated carbon may also be helpful in reducing color.

Finally, the presence of interfering ions in most "wet chemicals" tests represents a serious hind­rance to accurate analysis. Complexation is almost impossible to predict, and large analytical errors can result from the formation of many interfering complexes.

PROCES�WATER INVESTGATIONS

The plants for this investigation were selected hopefully to provide representative samples of some typical incinerator wastewaters. In view of the monetary constraints, it was not possible to sample all types of incinerators, and it is recognized that

207

each plant, even each furnace system, may have its individual differences in design parameters and mode of operation.

Residue Quench Waters

There are currently two widely used methods to quench the residue, which is one of the two major sources of process waters. The first method ulitizes a series of spray nozzles to quench the residue after it drops from the combustion grate. Excess runoff can be intercepted as it drains from the col­lection container or discharge hopper. This form of quenching may use less water than the second method to be described.

The second method commonly employs a water­filled quanch tank into which the residue drops from the grate. There are several plants that also sluice undergrate siftings into the residue quench tank to facilitate their handling and removal. A drag con­veyor moves from the bottom of the tank, up an incline (which permits dewatering), and into a con­tainer or truck for conveyance to the final disposal site.

Flue-Gas Conditioning Waters

The second major process-water source results from air-pollution control. Water is used in a number of different types of gas-expansion chambers, spray-cooling chambers, wetted baffles, low-and high-energy scrubbers, and spray cyclones. Water may be used to sluice fly ash from the collection hoppers of dry-collection systems.

Raw Water Supplies

Supplies for process water can include portable municipal sources, untreated ground or surface water, sewage treatment plant effluent, or some combina­tion of these sources. In some areas, special indus­trial sources or even saline waters have been used.

INC IN ERATOR PLANTS SUPPLI ED

The process waters from two incinerators in southeastern Pennsylvania were sampled and anal­yzed.

Incinerator No.1

At Incinerator No. L the source of water is the public supply (Table 4) and the process water is not recycled.

Incinerator No. 1 (Fig. 1) was constructed in 1960 and has two furnaces with a combined capacity of 600 tons/day. Both furnances have continuous-feed traveling grates in two sections- an inclined drying grate and a horizontal burning grate. The furnace size and configuration negate the need for a conven­tional secondary- combustion chamber. The flue gases leaving the furnace pass through a series of water sprays into the large hopper-bottom cooling-expan­sion chamber and impinge on a hung wet-baffle wall. Air is added through jets for turbulence to insure gas cooling. The water sprays do remove some of the coarser, suspended particulate matter. The cool­ed flue gases then pass into large-diameter centri­fugal dust collectors and exit via an induced-draft fan through a short, glass-lined stack. Furnace underfire and overfire combustion air are provided.

Depending on the condition of the nozzles, con­siderable spray water can collect at the bottom of the spray cooling chamber. The cooling-chamber catch as well as the material trapped in the dust

Table 4.

Analyses of Public Water Supplies

Incinerator Incinerator Determination No. 1 No. 2

Calcium (Ca) 35.0 84.0 Magnesium (Mg) 12.0 7.0 Sodium (Na) 32.0 20.7(Na+K) Potassium (K) 4.0

Chloride (Cl) 44.0 9.0 Sulphate (S04) 81.0 23.3 Nitrate (N03) 3.0 9.9

Ortho-phosphate (P04 ) 0.05 0.03 Poly-phosphate (P04) 0.06 0.66 ABS 0.13 0.03 Silica (Si02) 8.3 4.8 Bicarbonates (CaC03) 43.0 198.0 Carbon Dioxide (CO2) 6.0 1 5.0( calculated) pH 7.0 7.4 Color units 0.0 1.0 Free chlorine (Cl) 1.1 0.35 Iron (Fe) 0.02 0.01 Manganese (Mn) 0.00 0.00 Aluminum (Al) 0.02 0.02 Coporide (F) 0.95 0.06 Copper (Cu) 0.00

Notes: All determinations in ppm except pH and color. Incinerator 1: Queen Lane filtered water average for March

1968 (treated Schuylkill River water). Incinerator II: Philadelphia Suburban Water Company average

for June 1968. Source is Cedar Grove Well, 600 ft deep, gravel packed.

208

collector is carried to a small clarifier below. The clarifier solids are drained as they are mechanically conveyed to the main residue-dumpster container.

The clarifier supernatant is discharged to the sewer. Residue drops off the end of the grate into a hopper where water sprays are used for quenching.

The residue collects in the hopper, and at approxi­mately 5-min intervals is discharged into an open­top, steel dumpster container. There is an air-seal skirt between the hopper bottom and the dumpster container. The container has provisions to permit the quench water to drain directly into the sewer culvert. When the furnace is operating at design capacity, the container is filled with residue in approximately 30 min. The undergrate siftings are collected and removed in a dry state. Each of the two furnace systems at this plant is independent with the exception of the clarifier. An additional clarifier seems to be needed.

The plant receives municipally collected com­bined refuse and a small quantity of commercial re­fuse.

Incinerator No.2

At Incinerator No. 2 the municipal water supply (Table 4) was used for make-up water during this test, but the plant now uses effluent from the sew­age-treatment plant located adjacent to the incinera­tor.

Incinerator No.2 (Fig. 2) is a 300-tons/day sin­gle-furnace plant also of continuous-feed design, but with rocking grates. Residue drops off the combus­tion grate into a large quench tank equipped with a drag-out residue conveyor. Undergrate siftings "lre also sluiced into this tank. The furnace gas is directed downward as it leaves the combustion cham ber, passing through conditioning (cooling) water sprays and then up into the bottom of a Pea­body medium-energy scrubber for cleaning of the flue gas. The scrubber water mixes with the residue­quenching water and gas-conditioning spray water in the large siftings-residue-fly-ash receiving (holding) tank below. The flue gases flow up through the scrubber and, by means of induced-draft fans, are ejected out of two short, parallel stacks. The Peabody scrubber consists of a series of flooded, perforated plates, separated by upward-and downward-directed sprays. The flue gas is forced to flow up through the perforations and through the spray zones. Im­pinement plates are used to aid in the removal of particulate matter.

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The Peabody scrubber requires an appreciable water flow (4 gal/lb of refuse). The scrubber water drains directly into the quench tank, which serves as the flue-gas seal. From there, the combined water flows into a clarifier, which provides 10-min reten­tion time. The supernatant flows into two parallel lagoons where an additional 90-min retention is pro­vided before recirculation through self-cleaning Kinney strainers to the conditioning sprays and scrubber.

The community is basically an upper-middle class residential suburb of Philadelphia and receives prin­cipally combined municipal refuse as well as some commercial and industrial refuse. The plant receives refuse throughout the week, but burning is done only 3 or 4 days a week for 8 to 1 1 h/day.

DETERMINAT IONS AND ANALYSES

Effluent-Water Quality

All analyses were in accordance with procedures outlined in Ref. [7].

Table 5 shows the results of four grab samples of process water from the spray cooling-expansion chamber of Incinerator No. I. The apparent general trends indicate the water to be slightly acidic when steady-state operation has been achieved. Because of the acidic nature of the water, the free alkalinity

Table 5 Chemical Quality of Cooling-Expansion Chamber Water

Discharge at Incinerator No. 1

Constituent Test 1 Test 2 Test 3 Test 4

pH 7.9 5.5 3.5 6.2

Alkalinity (CaC03) 35.0 9.0 0 10.0

Nitrate {l\T03) 1.5 1.90 2.00 2.00

Phosphate (P04) 0.2 0.61 0.39 0.17

Chloride (CI) 582.0 453.0 567.0 422.0

Fluoride (F) 4.5 6.40 4.40 7.80

Calcium (Ca) 330.0 220.0 255.0 250.0

Sulfate (S04) 338.0 238.0 188.0 300.0

Sodium (Na) 85.0 63.0 73.0 60.0

Potassium (K) 27.0 14.8 16.7 14.0

Iron (Fe) 1.6 0.93 5.77 0.50

ABS (ABS) 1.91 0.1 0.19 0.21

All values are expressed in mg/l except pH.

2 1 1

is either quite small or entirely absent. Nitrate and phosphate concentrations are not high enough to be of concern; however, the fluoride constituent (4.5 to 7.8 mg/l) could be of concern if discharged to small streams used as public water supplies. The USPHS 1962 drinking-water standards [8] set a maximum fluoride concentration in public water at 1. 0 mg/l for temperate climates. Based upon this value, a dilu­tion in excess of four parts of stream water per single unit of effluent volume is needed.

The most troublesome constituents, however, are chloride and sulfate. The relatively high chloride and low pH contribute to corrosion in pumps, piping, spray chamber, or quench tanks. Chloride is also an ion that is difficult to remove by commonly used water-treatment processes. Electrodialysis, ion ex­change, or reverse osmosis would have to be used to remove chlorides. It should be emphasized that the data in Table 5 are for a once-through system, and recirculation of the process waters could result in even higher buildup of chloride levels than those shown.

Water Stability Characteristics

Both the quench water and scrubber water are normally well above ambient temperature and can include Significant quantities of dissolved gases such as carbon dioxide, carbon monoxide, sulfur dioxide, N02, HCl, and unburne d hydrocarbons. Ta­ble 6 lists data from a series of tests to determine the stability of the samples collected. In one test, the sample was maintained at the collection temper­ature ( 138"F). The sample was open to the atmos­phere, and the dissolved gases were allowed to es­cape.

The pH and temperature of each sample were measured for a period of 50 to 80 h. These data are plotted in Figs. 3 and 4. Data were obtained from two samples. Sample No. 1 was held to a tempera­ture of 138"F for 80 h during which the pH was re­corded. It can be observed that the pH rose over 1 pH unit in 20 h.

The second sample was allowed to cool to room temperature at its own rate. The pH and temperature was recorded for 50 h. Again a rise in pH was ob­served while the temperature was allowed to drop.

Analyses to determine the major constituents listed in Table 6 were made twice during each run, once when the sample was received and again after the pH had stabilized.

I Q.

The presence of CO2 in the water may be an ex­planation for the low pH of the scrubber water. There are several points that corroborate this poss­ibility. Several conclusions may be drawn by refer­ring to Fig. 4, which is typical of repeated plot­tings. The pH of the sample is seen to drop initial­ly, which can be accounted for by a difference in the partial pressure of CO2 between the flue gas and the atmosphere. Flue gas contains from 2 to 3 per­cent CO2 by volume., while atmospheric CO2 is only a small fraction of 1 percent. Also, the solubility of C02 decreases with a rise in temperature.

Changes in the process-water test-sample pH and alkalinity (acidity) can cause a vexing problem in attempting to arrive at a valid reproducible anal­ysis. Fairly rapid changes in alkalinity can cause fluctuations in the apparent organic content as well as in the buffering capacity of the water.

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212

If the process waters are supersaturated with gases other than CO 2, which tends to diffuse from the system and change the equilibrium, more accu­rate data on the system could then be obtained by using head-gas analyses.

To obtain meaningful data, a quantitative analysis should be performed soon after the sample is taken in the field, rather than accumulating the samples for subsequent analyses en masse at some later time or place. However, it would still be desirable to have the analyses data from accumulated samples, since this would be indicative of any changes occurring in these process water characteristics as influenced by time, temperature, churning, etc.

CORRELATION OF RESULTS

Table 7 lists the data from the three sources of

process waters from Incinerator No. 1. The three sources are the spray cooling-expansion chamber water, residue-quench water, and the effluent from the clarifier, which is simply settled spray-chamber water. As was previously established, the pH of the spray-cham ber water is slightly acidic. However, the pH of the quench water is highly alkaline. One source of alkalinity is the ash (freed during the combustion of the refuse) , solubilized in the quench water.

Of particular significance is the high concentra­tion of COD in the quench water. The high COD was corroborated by an independent test for volatile acids. High COD and volatile acid values indicate that the residue from these particular plants contain high concentrations of organic matter. However, the

Table 6 Effect of Sample Cooling on Chemical Quality*

for Incinerator No.1

Sample 1 t Sample 2tt Constituent Start End Start End

pH 3.32 6.96 3.50 5.59

Acidity to 4.5 135 76 to 8.3 140 54 107 97 Total 275 54 183 97

Chloride 535 605 375 310 Sulfate 206 210 182 188

* All values are expressed in mg/l except pH. tTemperature held constant at collection temperature (138°F). ttSample allowed to cool to ambient temperature.

exact nature of the organic matter had not been deter­mined. During combustion, many intermediate com­pounds are formed by pyrolysis, and incomplete burn­out of residue would partially control the organic content.

COMPARISON BETWEEN INCINERATOR PLANTS

The process water system of Incinerator No. 1 is different from that of Incinerator No 2. The primary difference is that the process water from Incinerator No. 2 is settled and recycled, whereas that from In­cinerator No. 1 is discharged after a single pass.

One expected consequence of the system in Incin­erato r No. 2 is the buildup of solids in the recycled water. Furthermore, it would be expected that the pH of the recycled water could drop to the point where corrosion problems mi"'''t become serious. Compari­sons were made to determine whether significant dif­ferences did exist between the two plant systems at equilibrium.

Table 7 Comparison of Incinerator No. Process Waters*

Sources Constituentt Spray Chamber Clarifier Quench

pH 5.3 4.8 11.3

Phosphates (P04) 3.67 3.19 4.78

Sulfate (S04) 212.0 228.0 210.0

Chloride (Cl) 133.0 202.0 416.0

Fluoride (F) 1.47 1.91 1.10

Total nitrogen (N) 0.53 0.24 4.70

Sodium (Na) 44.0 52.0 3.36

Hardness (CaC03) 386.0 477.0 647.0

Calcium (CaC03) 309.0 356.0 610.0

Magnesium (MgC°3) 77.0 121.0 37.0

Iron (Fe) 0.0 0.0 0.43

C.O.D. 60.8 28.6 2,190.0

Organic acids 24.0 12.0 682.0

Solids

Suspended 2,184.0 116.0 218.0

Percent volatile suspended 13.0 15.0 64.0

Total dissolved 710.0 860.0 2,450.0

* All data except pH in mg/l. tInitial raw water background substracted from final ion con­

centration.

2 13

Samples used in this study were 8-h composites made up of three or four individual grab samples. In-cinerator No. 1 was on its fourth day of continious operation, while Incinerator No. 2 was on its third day

Table 8 Incinerator Process Water Comparison

Plant Plant Plant No. 2 No. 1 No. 1

Constituent Combined Chamber Quench

Total solids 3,507 mg/l 2,134 mg/l 4,401 mg/l

Dissolved solids 3,370 mg/l 1,570 mg/l 4,070 mg/!

Suspended solids 137 mg/l 564 mg/l 331 mg/l

Settleable solids (Imhoff) 4.5 mg/l 21.5 mg/l 1.3 mg/l

Colloidal Solids 106 mg/l 8 mg/l 114 mg/l

pH 6.39 mg/l 4.55 11.44

Total alkalinity (as CaC03) 35.7 mg/l 5.2 mg/l 835 mg/l

Bicarb alkalinity (as CaC03) 35.7 mg/l 5.2 mg/l 0

Carbonate alkalinity (as CaC03) 0 0 788 mg/l

Hydroxide alkalinity (as CaC03) 0 0 57 mg/l

Total acidity (as CaC03) 34.2 mg/l 74.1 mg/l 0

Free CO2 30.1 mg/l 65.2 mg/l 0

Total CO2 61.5 mg/l 69.7 mg/l 342 mg/l

Sodium (as Na) 112 mg/! 77 mg/l 372 mg/l

Potassium (as K) 127 mg/l 33 mg/l 265 mg/l

Total Hardness (as CaC03) 958 mg/l 526 mg/l 1070 mg/l

Calcium Hardness (as CaC03) 405 mg/l

Magnesium hardness (as CaC03) 121 mg/l

Free chloride (Cl) 770 mg/l 290 mg/l 1,960 mg/l

Total chloride (Cl) 1,020 mg/l 340 mg/l 1,920 mg/l

Free Fluoride (F) 5.2 mg/! 5.5 mg/l negative

Total fluoride (F) 7.9 mg/l 6.0 mg/l 1.8 mg/!

Sulfate (S04) 380 mg/l 235 mg/l 390 mg/!

Volatile acids negative negative 315 mg/!

C.O.D. 425 mg/l 353 mg/l 2,512 mg/l

Iron (Fe) 0.2 ppm 0.3 mg/l 0.24 mg/l

Copper (Cu) 0 0.2 mg/l 0.1 mg/!

of single-shift operation. The Incinerator No.2 sam­ple was collected during the last 2.5 h of full opera­tion in order to give the furnace time to achieve the maximum operating temperature and to allow the pro­cess water to reach equilibrium temperature.

Incinerator No. 1's spray-chamber sample consist­ed of a composite of four grab samples taken at ap­proximately 1-h intervals between 11: 30 a.m. and 4:30 p.m. Samples were collected from the bottom of the spray chamber at a point where the process water flows from the chamber, just ahead of the clarifier.

The flow rate was measured over a 90° V -notch weir constructed at the spray-chamber water-discharge basin. The flow rate of 190 gal/min remained con­stant throughout the sampling period. Each grab sam­ple consisted of about 11 so that the total sample was approximately one gal. The pH of each sample (determined by using pH sensitive tape) was 5, 6, 6, and 6, respectively. The temperature of the four samples were 7 1OC, 69OC, noc, and 67OC, res­pectively. All samples were stored in capped con­tainers and refrigerated at SOC, during the time re­quired for the analyses. The results of the analyses are given in Table 8.

Comparison of the results between incinerator plants shows that the character of the combined water from Incinerator No.2 was Significantly dif­f�rent than the sum of the flows from Incinerator No. 1. A comparison of the flow rates showed that a flow of 1660 gal/min resulted from Incinerator No.2, whereas the spray-chamber flow rate from Incinerator No.1 was 190 gal/min and the quench water excess only 13 to 27 gal/min.

As would be expected, the pH of the combined process waters at Incinerator No.2 was only slightly acidic (6.39 pH) , whereas the spray chamber water from Incinerator No.2 was more acidic (4.55 pH). The Incinerator No. 1 quench water was alkaline ( 11.44 pH).

Of considerable importance from the standpoint of treatment is the high chloride concentration in the combined sample from Incinerator No.2 and the quench water from Incinerator No. 1. The high chlor­ide concentration could provide a dilute electrolyte solution for corrosion. In addition, discharge of these waters to surface streams would be in excess of the allowable chloride concentration for most stream criteria since drinking water criteria generally limit chlorides to 250 mg/!. To achieve this stream standard (assuming negligible chloride in the stream), the streamflow would have to be three to four times the incinerator-plant effluent flow. However, for the

2 14

two incinerators covered in this study, the dry-weath­er streamflow is many times greater than this dilution requirement.

Of almost equal importance is the potential retar­dation of biological treatment by the high concentra­tion of chloride. The retardation would be noticeable in the treatment of quench water where the COD level was measured at over 2500 mg/!. Biological or chemical treatment of these wastewaters is nec­essary prior to discharge to a surface stream to re­duce the oxygen demand. High chloride concentra­tions may inhibit such treatment by biological means.

CONCLUSIONS

Incinerator water effluents vary considerably be­tween the respective 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 evalutaed on an individual basis. A com­parison of the analytical results between the two in­cinerator plants tested in this study points to this conclusion.

The character of process waters resulting from quenching is different from that of gas-scrubber waters, especially in pH values. The higher vola­tile organic acid content of the quench water re­sults in a higher oxygen demand. The oxygen demand of the scrubber waters is decreased probably because of the greater dilution anti also because of the min­imal amount of unburned organic matter in the flue gas. There was no readily detectable biological de­gradation in the samples taken.

When sampling gas-scrubber waters, the pH is ap­parently depressed by the COz in the flue gas. Mech­nical handling of the water thereafter tends to re­lease the CO2 and thereby raise the pH. Extreme care during and after sampling would be necessary to maintain the sample temperature and maximize reten­tion of dissolved COz. Failure to follow these pre­cautions could yield erroneous alkalinity and pH data. If precise information is required, it would be preferable to measure pH by utilizing a pH meter at the time and place of sampling. Other sampling data do not appear to be affected by the release of COz or cooling. Cross and Ross reported similar results in that they also found an odd correlation between tem­perature and pH. Although there may be some valid­ity to the relationship, it is doubtful that the same relationship will apply to all incinerator systems.

The changes of water characteristics with time

after sampling affect the buffering capacity and the

overall resulting data when using conventional sam­

pling and analytical techniques.

Further studies on the characterization of incin­

erator process wastewaters will be required to deter­

mine realistic water treatment and recirculation rates.

The published data of the limited investigations on

incinerator wastewaters reveal the complexity and

magnitude of the problem and, therefore, the need for

in-depth studies to provide adequate information and

predictable data useful to the systems designer and

plant operator.

ACKNOWLEDGEMEIH

Portions of this study were funded by the Bureau

of Solid Waste Management, United States Depart­

ment of Health, Education, and Welfare under Re­

search Grant SW-OOOOs.

215

REFERENCES

[1] J. W. Stephenson and A. Cafiero, "Municipal Incin­

erator Design FTactices and Trends," Proceedings of 1966 National Incinerator Conference, ASME New York, N. Y.,

1966. [2] F. L. Cross, Jr. and R. W. Ross, ",Effluent Water

from Incinerator Flue Gas Scrubbers," Proceedings of 1968 Incinerator Conference, ASME, New York, N. Y., 1968.

[3] F. E. Matusky and R. K. Hampton, "Incinerator

Waste Water," FToceedings of 1968 National Incinerator

Conference, ASMC, New York, N. Y., 1968. [4] R. Schafish, "Characterization and Treatment of

Waste Water from a Municipal Incinerator," unpublished

paper, Drexel Institute of Technology, Philadelphia, Pa., March 21, 1969.

[5] W. Jen's and F. Rehms, "Municipal Incineration and

Air Pollution Control," Proceedings of 1966 National Incin­

erator Conference, ASME, New York, N. Y., 1966. [6] s. J. Levy, "Chloride Determinations Using the

Orion Specific Ion Electrode," unpublished report, Drexel

Institute of Technology, Htiladelphia, Pa., May 15, 1969. [7] American Public Health Association, Standard

Methods for the Examination of Water and Wastewater,

Includin� Bottom Sediments and Slud�es, 12th ed., New York

N. Y., 1965. [8] United States Department of Health, Education and

Welfare, Public Health Service, 1962 Drinkin� Water Stand­

ards for Public Water Supplies, Government Printing Office,

Washington, D. C., 1962.