A method of decontaminating wastewater sludge to a level that meets or exceeds USEPA Process to Further Reduce Pathogens standards, wherein lime or kiln dust and/or other alkaline materials are mixed with wastewater sludge in sufficient quantity to raise the pH of the mixture to 12 and above for a predetermined time and drying the resulting mixture.
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1. A method of treating wastewater sludge to provide a fertilizer for agricultural lands which can be applied directly to the lands which consists essentially of the following steps:
mixing said sludge with at least one alkaline material; wherein , the amount of added material mixed with said sludge being sufficient to raise the pH of said mixture to at least 12 and to hold the pH of greater than 12 for at least 7 days , ; and actively drying said mixture for at least 30 days and until a minimum solids concentration of 65% solids is reached, the amount of added material being also sufficient to maintain the pH above 12 until the sludge solids achieve at least 60% solids by weight, the amount of added material mixed with said sludge and the length of time of drying being sufficient to reduce significantly offensive odor of the sludge to a level that is tolerable ; , to reduce animal viruses therein to less than one plaque forming unit per 100 ml of said sludge; , to reduce pathogenic bacteria therein to less than three colony forming units per 100 ml of said sludge ; , to reduce parasites therein to less than one viable egg per 100 ml of said sludge ; , to reduce vector attraction to said sludge ; and to prevent significant regrowth of the pathogenic microorganisms, while being insufficient to eliminate all beneficial non-pathogenic microorganisms from the sludge.
5. A method of treating wastewater sludge to provide a fertilizer for agricultural lands which can be applied directly to the lands which consists essentially of the following steps:
mixing said sludge with at least one alkaline material; wherein , the amount of added material mixed with said sludge being sufficient to raise the pH of said mixture to at least 12 for at least 72 hours , ; concurrently with the high pH pH, heating the mixture to at least 50°C C., but not at a temperature sufficient to cause sterilization, the amount of heat being sufficient that the sludge stored in a static condition will be maintained at a temperature of at least 50°C C. for at least 12 hours , ; and actively drying said mixture until a minimum solids concentration of 50% solids is reached, the amount of added material mixed with said sludge, the heating, and the length of time of drying being sufficient to reduce significantly offensive odor of the sludge to a level that is tolerable ; , to reduce animal viruses therein to less than one plaque forming unit per 100 ml of said sludge ; , to reduce pathogenic bacteria therein to less than three colony forming units per 100 ml of said sludge ; , to reduce parasites therein to less than one viable egg per 100 ml of said sludge ; , to reduce vector attraction to said sludge ; and to prevent significant regrowth of the pathogenic microoganisms, while being insufficient to eliminate all beneficial non-pathogenic microorganisms from the sludge.
2. The method set forth in
3. The method set forth in
4. The method set forth in
6. The method set forth in
7. The method set forth in
8. The method set forth in
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Basically, the process of this invention comprises mechanically dewatering the sludge; chemical stabilizing of the wastewater sludge with quantities of lime, cement kiln dust or lime kiln dust or mixtures thereof sufficient to maintain a pH of 12 and above for at least two hours and preferably for days; and then actively drying the sludge by an aeration process such as a Brown Bear aerating device. To achieve PFRP pathogen reduction criteria, the treated sludge is aerated dried such that the sludge is at least eighty percent (80%) by weight solids and preferably ninety percent (90%) by weight solids. The product is allowed to air cure for about 10 days after the desired solids content is achieved. The drying and curing of the mixture may also be accomplished by a windrow method, turn-over-method, or other forced air methods. The curing time or aeration time is dependent on the type of storage facility (cover covered, enclosed, or open), aeration procedure, mix design, physical and chemical properties of the admixtures, quality of the mixing facilities, percent solids of dewatering cake, and type of sludge. The chemical stabilizing admixture can be added after mechanical dewatering, if desired. Lime, cement kiln dust and lime kiln dust are excellent flocculents and thus can be useful in conditioning prior to mechanical dewatering with most equipment.
The range of lime, cement kiln dust or lime kiln dust mixed with the sludge is about ten percent (10%) by weight to 200% by weight of the dry sludge depending on the variables listed above.
The addition of high reactant-heat generating materials or heating the sludge and materials may be used to reduce the total amount of admixture required and/or to reduce the drying and/or curing time required. Addition of anhydrous ammonia and either phosphoric acid or sulphuric acid to chemical stabilized sludge, having a pH of 12 and above, produces sufficient heat to help reduce pathogens to a level equivalent to PFRP processes and at the same time increases the nutritional value of the sludge while reducing curing time and natural active drying requirements. In addition to chemical generated heat, mechanical or electrical heat may be applied to dry and cure the mixture.
The solid waste generated by cement manufacture is primarily kiln dust. This dust contains a mixture of raw kiln feed, partly calcined material, finely divided cement clinker and alkaline and alkali carbonates and sulfates (usually sulfates). There is economic value in returning the dust to the kiln, but when the alkali content of the returned dust is too high for the product clinker to meet specifications, the dust must be discarded. Up to about 15% of the raw materials processed may be collected as dust and of this about half may be low enough in alkalis to be returned to the kiln. The rest usually stockpiled as a waste material which usually is discarded and may be a nuisance and possibly a hazard.
Typically, the major oxide found in a cement kiln dust are: SiO2, A12O3, Fe2O3, CaO, MgO, So3, Na2O and K2O.
The solid waste generated by lime manufacture is primarily lime stack dust. This dust contains a mixture of raw kiln feed, partly calcined material, and finely divided material. There is no value in returning the dust to the kiln, as it is too fine and passes directly through to the precipitator again. Up to about 15% of the raw materials processed may be collected as dust. It is usually stockpiled as a waste material which usually is discarded and may be a nuisance and possibly a hazard.
Typically, the major oxides found in line stack dust are: CaO, MgO, SO3, CO2 and Availabe Free Lime.
A combination of materials may be used to provide the most economical system such as using line, cement kiln dust or lime kiln dust or mixtures thereof to achieve chemical stabilization, and adding bulking material such as slag fines, fly ash, gypsum, fluidized bed residue, dry sulphur scrubber residue, calcium sulphate fines, and the like, to assist in dewatering. Lime, cement kiln dust or lime kiln dust alone cannot achieve the desired results of reducing pathogens to PFRP levels, but when used in combination with a drying process, the decontamination can achieve PFRP levels.
The process will drastically reduce the odor of the sludge, even though the pH may drop below 9 during the curing period and the use of admixtures as bulking agents reduces the volume of the sludge for disposal or utilization.
In a test, the use of cement kiln dust (CKD) and lime to stabilize and disinfect sludge from the Toledo municipal wastewater treatment plant was studied.
Specifically, tests were conducted to determine whether the processes embodying this invention met requirements to be classified as a Process to Significantly Reduce Pathogens (PSRP) and a Process to Further Reduce Pathogens (PFRP). As indicated above, for PSRP classification, the fecal and total coliform bacterial counts must be reduced by two logs and the animal virus count must be reduced by one log. For PFRP classification, animal viruses must be less than one (1) plaque forming unit (PFU) per 100 ml of sludge; pathogenic bacteria (Salmonella) must be less than three (3) colony forming units (CFU) per 100 ml of sludge; and parasites (helmonth eggs - Ascaris) must be less than one (1) viable egg per 100 ml of sludge, wherein 100 ml of sludge is equivalent to about five (5) gms of dry solids. (As indicated in EPA Memorandum of November 6, 1985).
As illustrated by
The principal bacterial indicator used by EPA in the setting of PFRP standards for agricultural use of sludge is the pathogen Salmonella enteritidis typhimurium.
The enterovirus, Poliovirus type I, was measured for survival by assaying for viable virus on tissue culture lawns of Vero cells. The virus viability was decreased by cement kiln dust and lime treatment to levels associated with PFRP processes in one day, i.e. less than one viable virus per five (5) gm dry weight sludge as illustrated in FIG. 7. Virus levels in the untreated sludge sample decreased almost two (2) logs in one day and the entire population died in one (1) week.
In other treatment processes for the stabilization of wastewater sludge the viability of the helminth ova has been the major difficulty encountered and certainly the most stringent of the EPA parameters to meet. The initial level of Ascaris eggs added to the sludge was 16000/5 gm dry weight sludge. Recovery following the procedure for measuring viability of these eggs ranged from about two percent (2%) in the digested sludge to about six percent (6%) in the combined sludge. The viability of these recovered eggs is shown in
The reduction of pathogens that occurred in the sludge as a result of cement kiln dust or lime addition appears to be due to the samples initially achieving a pH of 11.5 followed by a synergistic interaction of elevated pH and drying. This proposition is supported by the following facts: a) the samples without high pH but with significant drying did not experience a significant decline in microorganisms; b) the samples such as the twenty-five percent (25%) by weight cement kiln dust treated combined sludge exhibited an initial high pH but a subsequent lower pH plateau and showed a killing of the Ascaris eggs continued at nearly logarithmic rates; c) the longer the pH remained elevated above 9.5, as in the twenty-five percent (25%) by weight and thirty-five percent (35%) by weight cement kiln dust samples, the better the killing results with the Ascaris eggs; d) as shown in the curve for the five percent (5%) by weight lime samples, higher pH by itself, without elevated drying, showed a delay in the killing of the Ascaris eggs.
As illustrated by
It was also determined that the addition of cement kiln dust or lime to sludge had an effect on the material handling aspect of such sludge. The thirty-five percent (35%) by weight cement kiln dust treated sludge had an individual particle size averaging about two to five (2-5) mm in diameter and thus rendered the treated sludge easy to handle. In contrast, the lime treated and the fifteen percent (15%) and twenty-five percent (25%) by weight cement kiln dust treated samples all contained very large lumps averaging about three to eight (3-8) cm in diameter and rendered the treated sludge less easy to handle.
The following conclusions were reached regarding lime and kiln dust treated sludge processes:
1. Sludge treated with cement kiln dust or lime in all cases tested met PSRP classification requirements.
2. Cement kiln dust treated sludge enhanced the drying rate of sludges particularly in the first four (4) weeks of treatment.
3. Cement kiln dust treated sludge loses its pH value more rapidly than lime treated sludge.
4. Bacterial pathogens such as Salmonella are controlled to PFRP levels by five (5) weeks when such sludges are treated with twenty-five percent (25%) and thirty-five percent (35%) by weight cement kiln dust or ten percent (10%) by weight lime.
5. Enterovirus levels were controlled to PFRP levels within one day by both cement kiln dust and lime treated sludges.
6. Ascaris egg survival was reduced by more than three (3) logs by higher dosage treatments within four (4) weeks. The twenty-five percent (25%) CKD, thirty-five percent (35%) CKD and ten percent (10%) by weight lime treated sludges have been shown to reach PFRP (1 viable egg/5 gm dry wt sludge) levels by day forty-six (46). The sample containing fifteen percent (15%) CKD in the combined sludge did not reach PFRP standards, while the sample with fifteen percent (15%) CKD in digested sludge did.
7. Both CKD and lime treatments reduce sludge odor. Only thirty-five percent (35%) CKD by weight treatment reduced odor to mild levels.
8. Drying was not sufficient by itself to kill microorganisms in sludge.
9. Regrowth of pathogens (Salmonella) was effectively prevented over the eighty (80) days of the study.
10. All EPA PFRP standards were reached after six (6) weeks of incubation of the twenty-five percent (25%) CKD, the thirty-five percent (35%) CKD and the ten percent (10%) lime by weight treated sludges.
With regard to the three PFRP standards the following results were achieved by six plus (6+) weeks (46 days):
| STANDARD | |||||
| SLUDGE | TREATMENT | Salmonella | Virus | Ascaris | All |
| COMBINED | Control | No | No | No | No |
| 15% CKD | No | -- | No | No | |
| 25% CKD | Yes (35) | Yes (1) | Yes (46) | Yes | |
| 35% CKD | Yes (27) | -- | Yes (46) | Yes | |
| 5% Lime | Yes (46) | -- | Yes (46) | ? | |
| 10% Lime | Yes (27) | Yes (1) | Yes (46) | Yes | |
| DIGESTED | Control | No | No | No | No |
| 15% CKD | Yes (46) | -- | Yes (46) | ? | |
| 25% CKD | Yes (46) | -- | Yes (46) | Yes* | |
| 35% CKD | Yes (27) | -- | Yes (46) | Yes* | |
| 5% Lime | No | -- | Yes (46) | No | |
| 10% Lime | Yes (27) | -- | Yes (46) | Yes* | |
Tests were conducted on the following 12 treatment groups:
| Combined | Digested | |||
| 1. | Untreated | 7. | Untreated | |
| 2. | 15% CKD | 8. | 15% CKD | |
| 3. | 25% CKD | 9. | 25% CKD | |
| 4. | 35% CKD | 10. | 35% CKD | |
| 5. | 5% Lime | 11. | 5% Lime | |
| 6. | 10% Lime | 12. | 10% Lime | |
Each of these treatment groups (5000g sludge plus treatment) was contained in a 10 liter plastic tub. These were kept dry at 68F and were mixed twice weekly to facilitate drying. Samples were removed at 0, 1, 7, 13, 27, 46 and 80 days and processed to determine pathogen and microorganism survival. The parameters that were determined at each sampling are listed as follows:
percent solids
pH
volume
fecal coliforms
fecal streptocci
Salmonella enteritidis typhimurium
Ascaris suum eggs
Human enteric virus (Polio Type I-vaccine strain)
The data from which the above referenced results and
| TABLE I | |||||||||
| % | Volume/ | # FC/ | # FS | # Sal/ | # Virus/ | # V Ascaris Eggs | |||
| Tub # | Treatment | ph | Solids | 100 gS | 5 g DWS* | 5 g DWS | 5 g DWS | 5 g DWS | 5 g DWS |
| 1 | combined CONTROL | 6.8 | 92.7 | 76 | 1.7 × 106 | 6.5 × 105 | 7.5 × 105 | -- | -- |
| 2 | 15% CKD/COMB | 8.3 | 94.8 | -- | 1.7 × 105 | 3.4 × 107 | 12.5 | -- | -- |
| 3 | 25% CKD/COMB | 8.9 | 95.2 | 57.2 | 5 × 102 | 3.4 × 105 | 0.4 | -- | -- |
| 4 | 35% CKD/COMB | 9.3 | 93.3 | -- | 5 × 102 | 2.8 × 102 | 0.4 | -- | -- |
| 5 | 5% LIME/COMB | 8.4 | 91.2 | -- | 5.5 × 102 | 3.5 × 103 | 2.9 | -- | -- |
| 6 | 10% LIME/COMB | 11.7 | 92.2 | 74.0 | 5 × 102 | 6.5 × 100 | 2.9 | -- | -- |
| 7 | DIGEST CONTROL | 6.3 | 92.4 | 74.0 | 4.7 × 106 | 2.4 × 105 | 3.5 × 106 | -- | -- |
| 8 | 15% CKD/DIG | 8.4 | 93.9 | 6.5 × 103 | 1.1 × 105 | 0.4 | -- | -- | |
| 9 | 25% CKD/DIG | 9.2 | 93.6 | 56.0 | 5 × 102 | 6.5 × 102 | 0.4 | -- | -- |
| 10 | 35% CKD/DIG | 9.6 | 92.4 | 5 × 102 | 2.4 × 101 | 0.4 | -- | -- | |
| 11 | 5% LIME/DIG | 8.6 | 92.4 | 2.8 × 102 | 4.8 × 101 | 0.4 | -- | -- | |
| 12 | 10% LIME/DIG | 12.0 | 92.5 | 72.0 | 4.9 | 6.5 × 101 | 0.4 | -- | -- |
| TABLE II | |||||||||
| % | Volume/ | # FC/ | # FS | # Sal/ | # Virus/ | # V Ascaris Eggs | |||
| Tub # | Treatment | ph | Solids | 100 gS | 5 g DWS* | 5 g DWS | 5 g DWS | 5 g DWS | 5 g DWS |
| 1 | COMBINED CONTROL | 7.3 | 92.3 | 76.0 | 1.9 × 106 | 2.8 × 108 | 6.5 × 104 | -- | 80.8 |
| 2 | 15% CKD/COMB | 8.4 | 94.7 | 1.0 × 104 | 1.5 × 107 | 4.9 × 101 | -- | 2.8 | |
| 3 | 25% CKD/COMB | 8.4 | 94.2 | 68.0 | 4.9 × 100 | 2.6 × 104 | .4 | -- | 0 |
| 4 | 35% CKD/COMB | 10.1 | 91.9 | 0.4 | 6.5 × 101 | .4 | -- | 0 | |
| 5 | 5% LIME/COMB | 8.1 | 93.1 | 3.5 × 102 | 6.5 × 104 | .4 | -- | 0 | |
| 6 | 10% LIME/COMB | 12.5 | 89.7 | 82.0 | 6.7 | 1.1 × 103 | .4 | -- | 0 |
| 7 | DIGESTED CONTROL | 6.5 | 93.6 | 76.0 | 3.4 × 107 | 6.5 × 104 | 5.5 × 104 | -- | 37 |
| 8 | 15% CKD/DIG | 8.4 | 93.9 | 1.0 × 105 | 5 × 105 | .4 | -- | 0.3 | |
| 9 | 25% CKD/DIG | 8.2 | 95.2 | 62.0 | 4.9 | 1.1 × 104 | .4 | -- | 0 |
| 10 | 35% CKD/DIG | 10.3 | 92.5 | 4.9 | 2.4 × 102 | .4 | -- | 0 | |
| 11 | 5% LIME/DIG | 8.1 | 92.9 | 3.5 × 102 | 3.7 × 103 | 3.65 | -- | 0 | |
| 12 | 10% LIME/DIG | 12.7 | 92.4 | 88.0 | 4.9 | 3.7 × 103 | .4 | -- | 0 |
| TABLE III | |||||||||
| % | Volume/ | .# FC/ | # FS | # Sal/ | # Virus/ | # V Ascaris Eggs | |||
| Tub # | Treatment | ph | Solids | 100 gS | 5 g DWS* | 5 g DWS | 5 g DWS | 5 g DWS | 5 g DWS |
| 1 | COMBINED CONTROL | ||||||||
| 3 | 25% CKD/COMB | <0.5 | |||||||
| 4 | |||||||||
| 5 | 5% LIME/COMB | 3.2 | |||||||
| 6 | |||||||||
| 7 | |||||||||
| 8 | |||||||||
| 9 | |||||||||
| 10 | |||||||||
| 11 | 5% LIME/DIG | <0.5 | |||||||
| 12 | |||||||||
| TABLE IV | |||||||||
| % | Volume/ | # FC/ | # FS | # Sal/ | # Virus/ | # V Ascaris Eggs | |||
| Tub # | Treatment | ph | Solids | 100 gS | 5 g DWS* | 5 g DWS | 5 g DWS | 5 g DWS | .5 g DWS |
| 1 | COMBINED CONTROL | 8.28 | 50.6 | 82.0 | 2.8 × 106 | 6.5 × 108 | 6.5 × 106 | -- | 332 |
| 2 | 15% CKD/COMB | 8.2 | 94.4 | -- | 1.9 × 106 | 3.4 × 106 | 5 × 101 | -- | 8.5 |
| 3 | 25% CKD/COMB | 8.6 | 91.7 | 71.2 | 3.7 × 109 | 1.1 × 106 | 8.5 × 102 | -- | 5.8 |
| 4 | 35% CKD/COMB | 10.2 | 83.4 | -- | 1.2 × 101 | 1.9 × 103 | <.5 | -- | 1.9 |
| 5 | 5% LIME/COMB | 8.12 | 88.9 | -- | 2.0 × 102 | 4.9 × 104 | 2.7 × 103 | -- | 12.0 |
| 6 | 10% LIME/COMB | 12.4 | 82.0 | 79.2 | 1.0 | 3.9 × 103 | <.5 | -- | 6.5 |
| 7 | DIGEST CONTROL | 6.8 | 72.2 | 84.0 | 4.5 × 106 | 4.5 × 108 | 9.5 × 106 | -- | 156.6 |
| 8 | 15% CKD/DIG | 8.4 | 94.9 | -- | 4.7 × 103 | 4.9 × 102 | 1.1 × 102 | -- | 19.7 |
| 9 | 25% CKD/DIG | 8.4 | 92.9 | 68.0 | 4.8 | 1.1 × 104 | 4.3 | -- | 8.6 |
| 10 | 35% CKD/DIG | 10.4 | 82.1 | -- | 3.2 | 2.2 × 103 | <0.5 | -- | 0.8 |
| 11 | 5% LIME/DIG | 8.2 | 83.5 | -- | 4.1 | 1.2 × 104 | 5.5 × 102 | -- | 0.8 |
| 12 | 10% LIME/DIG | 12.4 | 80.1 | 74.0 | <.5 | 2.8 × 103 | <0.5 | -- | 1.7 |
| TABLE V | |||||||||
| % | Volume/ | # FC/ | # FS | # Sal/ | # Virus/ | # V Ascaris Eggs | |||
| Tub # | Treatment | ph | Solids | 100 gS | 5 g DWS* | 5 g DWS | 5 g DWS | 5 g DWS | .5 g DWS |
| 1 | COMBINED CONTROL | 8.9 | 41.6 | 86.4 | 2.4 × 107 | 4.4 × 108 | >7.5 × 106 | -- | 378 |
| 2 | 15% CKD/COMB | 8.3 | 74.7 | -- | 6.0 × 106 | 1.4 × 108 | >4.3 × 105 | -- | 74.9 |
| 3 | 25% CKD/COMB | 10.0 | 75.1 | 68.8 | 3.5 × 101 | 1.4 × 105 | >4.3 × 104 | -- | 35.5 |
| 4 | 35% CKD/COMB | 11.5 | 70.4 | -- | 3.2 × 102 | 2.6 × 102 | >7.0 × 102 | -- | 9.4 |
| 5 | 5% LIME/COMB | 12.4 | 50.8 | -- | 3.2 × 104 | 6.5 × 104 | >9.5 × 102 | -- | 55.7 |
| 6 | 10% LIME/COMB | 12.4 | 52.7 | 84 | 0.8 | 6.0 × 103 | >9.0 × 102 | -- | 20.3 |
| 7 | DIGEST CONTROL | 8.9 | 34.9 | 84 | 7 × 107 | 4.6 × 107 | >1.2 × 106 | -- | 351.9 |
| 8 | 15% CKD/DIG | 8.9 | 80.4 | -- | 2 × 103 | 4.0 × 105 | >8.5 × 104 | -- | 63.0 |
| 9 | 25% CKD/DIG | 9.9 | 76.1 | 67.2 | 0.6 | 4.2 × 104 | >1.1 × 103 | -- | 17.6 |
| 10 | 35% CKD/DIG | 12.3 | 72.8 | -- | 4.7 | 2.5 × 103 | >1.1 × 103 | -- | 9.2 |
| 11 | 5% LIME/DIG | 12.4 | 59.3 | -- | 8 | 1.2 × 104 | >2.0 × 102 | -- | 80.7 |
| 12 | 10% CIME/DIG | 12.4 | 59.5 | 80.8 | 8 | 5.5 × 103 | >2.0 × 102 | -- | 15.7 |
| TABLE VI | |||||||||
| % | Volume/ | # FC/ | # FS | # Sal/ | # Virus/ | # V Ascaris Eggs | |||
| Tub # | Treatment | ph | Solids | 100 gS | 5 g DWS* | 5 g DWS | 5 g DWS | 5 g DWS | .5 g DWS |
| 1 | COMBINED CONTROL | 8.8 | 29.9 | 88.0 | 5.5 × 107 | 1.3 × 108 | 1.3 × 106 | 0 | 445.6 |
| 2 | 15% CKD/COMB | 10.0 | 51.0 | 9.5 × 105 | 2.8 × 107 | 5.0 × 104 | -- | 201.4 | |
| 3 | 25% CKD/COMB | 11.3 | 54.4 | 70.0 | 0.6 | 5.0 × 103 | 7.5 × 102 | 0 | 107.8 |
| 4 | 35% CKD/COMB | 12.5 | 65.8 | 0.5 | 7.5 × 102 | 3.3 × 101 | -- | 27.8 | |
| 5 | 5% LIME/COMB | 12.3 | 46.8 | 0.7 | 8.5 × 102 | 0.7 | -- | 96.3 | |
| 6 | 10% LIME/COMB | 12.3 | 46.2 | 76.8 | 0.7 | 8.0 × 100 | 0.7 | 0 | 57.7 |
| 7 | DIGEST CONTROL | 8.6 | 36.1 | 87.2 | 4.1 × 107 | 2.3 × 106 | 1.1 × 106 | -- | 243.7 |
| 8 | 15% CKD/DIG | 10.2 | 49.7 | 6.5 × 101 | 1.0 × 104 | >5.5 × 102 | -- | 155.7 | |
| 9 | 25% CKD/DIG | 11.2 | 51.9 | 70.0 | 1.3 × 100 | 7.5 × 102 | 7.5 × 101 | -- | 16.2 |
| 10 | 35% CKD/DIG | 11.7 | 61.7 | 0.5 | 4.3 × 102 | 6.0 × 101 | -- | -- | |
| 11 | 5% LIME/DIG | 12.3 | 42.8 | 0.8 | 6.0 × 102 | 9.0 × 101 | -- | 130.5 | |
| 12 | 10% LIME/DIG | 12.4 | 42.8 | 76.0 | 0.8 | 5.0 × 102 | 9.0 × 101 | -- | 105.6 |
| TABLE VII | |||||||||
| % | Volume/ | # FC/ | # FS | # Sal/ | # Virus/ | # V Ascaris Eggs | |||
| Tub # | Treatment | ph | Solids | 100 gS | 5 g DWS* | 5 g DWS | 5 g DWS | 5 g DWS | .5 g DWS |
| 1 | COMBINED CONTROL | 7.3 | 31.61 | 78.0 | 6.5 × 108 | 1.3 × 107 | 4.0 × 105 | 3.3 × 104 | 520.5 |
| 2 | 15% CKD/COMB | 11.7 | 44.9 | 3.4 × 106 | 9.0 × 106 | 8.0 × 104 | -- | 130.5 | |
| 3 | 25% CKD/COMB | 12.7 | 51.3 | 80.0 | 1.2 × 102 | 1.5 × 102 | 7.0 × 101 | 0 | 99.6 |
| 4 | 35% CKD/COMB | 12.9 | 59.2 | 5.5 × 102 | 1.7 × 103 | 6.0 × 102 | -- | 448.5 | |
| 5 | 5% LIME/COMB | 12.4 | 36.7 | 2.1 × 101 | 1.1 × 104 | <1.2 | -- | 54.4 | |
| 6 | 10% LIME/COMB | 12.4 | 43.7 | 84.0 | 4.5 × 100 | 1.7 × 102 | <1.2 | 0 | 61.0 |
| 7 | DIGEST CONTROL | 7.6 | 34.8 | 90.0 | 2.2 × 107 | 2.2 × 106 | 6.5 × 104 | -- | 99.3 |
| 8 | 15% CKD/DIG | 11.7 | 44.4 | 2.8 × 102 | 1.4 × 104 | 1.3 × 101 | -- | -- | |
| 9 | 25% CKD/DIG | 12.5 | 55.1 | 74.0 | 1.1 × 102 | 1.4 × 103 | <0.9 | -- | 43.6 |
| 10 | 35% CKD/DIG | 13.0 | 60.5 | 1.0 × 101 | 2.7 × 103 | <0.9 | -- | 42.9 | |
| 11 | 5% LIME/DIG | 12.2 | 38.2 | 1.6 × 101 | 2.0 × 103 | <1.3 | -- | -- | |
| 12 | 10% LIME/DIG | 12.4 | 46.1 | 82.0 | 1.3 × 101 | 1.3 × 103 | <1.1 | -- | 58.6 |
| TABLE VIII | |||||||||
| % | Volume/ | # FC/ | # FS | # Sal/ | # Virus/ | # V Ascaris Eggs | |||
| Tub # | Treatment | ph | Solids | 100 gS | 5 g DWS* | 5 g DWS | 5 g DWS | 5 g DWS | .5 g DWS |
| 1 | COMBINED CONTROL | 8.28 | 50.6 | 82.0 | 2.8 × 106 | 6.5 × 108 | 6.5 × 106 | -- | 332 |
| 1 | COMBINED CONTROL | 5.9 | 30.9 | 92.0 ml | 9.7 × 106 | 7.8 × 105 | 1.5 × 104 | 2.0 × 106 | n = 582.4 |
| 2 | 15% CKD/COMB | 11.5 | 33.2 | -- | 9.7 × 106 | 7.8 × 105 | 1.5 × 104 | -- | -- |
| 3 | 25% CKD/COMB | 12.5 | 42.9 | 76.0 ml | 9.7 × 106 | 7.8 × 105 | 1.5 × 104 | -- | -- |
| 4 | 35% CKD/COMB | 12.8 | 45.3 | -- | 9.7 × 106 | 7.8 × 105 | 1.5 × 104 | -- | -- |
| 5 | 5% LIME/COMB | 12.3 | 49.4 | -- | 9.7 × 106 | 7.8 × 105 | 1.5 × 104 | -- | -- |
| 6 | 10% LIME/COMB | 12.4 | 49.4 | 74.0 ml | 9.7 × 106 | 7.8 × 105 | 1.5 × 104 | -- | -- |
| 7 | DIGEST CONTROL | 7.0 | 34.6 | 88.0 ml | 1.8 × 107 | 4.1 × 105 | 5.2 × 104 | -- | -- |
| 8 | 15% CKD/DIG | 11.7 | 35.5 | -- | 1.8 × 107 | 4.1 × 105 | 5.2 × 104 | -- | -- |
| 9 | 25% CKD/DIG | 12.4 | 37.0 | -- | 1.8 × 107 | 4.1 × 105 | 5.2 × 104 | -- | -- |
| 10 | 35% CKD/DIG | 12.7 | 39.1 | -- | 1.8 × 107 | 4.1 × 105 | 5.2 × 104 | -- | -- |
| 11 | 5% LIME/DIG | 12.4 | 40.2 | -- | 1.8 × 107 | 4.1 × 105 | 5.2 × 104 | -- | -- |
| 12 | 10% LIME/DIG | 12.4 | 46.9 | -- | 1.8 × 107 | 4.1 × 105 | 5.2 × 104 | -- | -- |
The above results are disclosed and claimed in U.S. patent application Ser. No. 019,888, filed Feb. 27, 1987, having a common assignee with the present invention.
In accordance with the present invention, it has been found that the method can be optimized to achieve optimum results. In accordance with the present invention, the method comprises advanced alkaline stabilization with subsequent accelerated drying.
Definitions:
1. Alkaline Materials. Cement kiln dust (CKD), lime kiln dust (LKD), quicklime fines, pulverized lime, or hydrated lime in the preferred forms disclosed in Appendix A. Alternative alkaline materials may be substituted in whole or in part if they meet performance criteria shown below. 2. Advanced Alkaline Stabilization with Subsequent Accelerated Drying.
Alternative #1: Sufficient addition of the alkaline materials described above to produce the following specifications:
The amount of alkaline materials added is sufficient to achieve a pH of greater than 12 and to hold the pH of greater than 12 for at least seven (7) days. Thorough mixing sufficient to achieve hydrolysis within the sludge cake is required. The advanced alkaline stabilized sludge is then dried, for example, as by aeration, for at least 30 days and until a minimum solids concentration of 65% solids is reached. The amount of alkaline materials is sufficient that the sludge solids will achieve at least 60% solids by weight before the pH drops below 12∅
Alternative #2: Sufficient addition of alkaline materials plus predetermined heat described above to produce the following specifications:
The amount of alkaline materials added is sufficient to achieve a pH of greater than 12 and to hold a pH of greater than 12 for at least 72 hours. Thorough mixing sufficient to achieve hydrolysis with the sludge cake is required. Concurrent with this high pH, the sludge is heated to a temperature of at least about 50°C C., but not a temperature sufficient to cause sterilization. Sufficient heat is added so that the sludge when stored in a static condition will be maintained at a temperature of at least 50°C C. for at least 12 hours. The temperature increase may be obtained using exothermic reactions from the alkaline materials or from other thermal processes. Stabilized sludge is then dried by aeration until a minimum solids concentration of 50% solids is achieved.
When mixed or blended with sludge, the fine alkaline materials described above not only provide uniform intimate contact with sludge to maintain an unfavorable biochemical environment but also have large specific surface area which can provide sorptive odor control and accelerated drying rates. The process will reduce vector attraction and reduce pathogens to below detectable limits. Specifically, the process, advanced alkaline stabilization with subsequent accelerated drying, will achieve a maximum of approximately 1 PFU (plaque forming unit) of animal viruses per 100 ml of sludge, 3 CFR (colony forming units) of pathogenic bacteria (salmonella) per 100 ml of sludge when sludge is equivalent to approximately 5 grams of dry solids per 100 ml.
The fine CKD, LKD, lime materials (as described in Appendix A) are uniformly mixed into either liquid sewage sludge or dewatered sewage sludge cake. Uniform and thorough additions are achieved utilizing either mechanical or aeration mixing (wet sludges), or mechanical mixing (dewatered sludges) to produce advanced alkaline stabilized treated sludge. If the resulting sludge is in cake form, the air active drying process described below is directly initiated. However, if the resulting sludge is in liquid form, it is dewatered while pH still exceeds 12 utilizing convention thickening/filtering process technology to an intermediate solids level to produce a handlable handleable cake material (appoximately 15-50% solids). The alkaline materials are added in sufficient quantity to ensure elevation of pH greater than 12 and mixing should be sufficiently thorough as to cause hydrolysis of the sludge.
Alternative #1: The advanced alkaline stabilized dewatered sludge cake is then air actively dried (while pH remains above 12 for at least seven days) through intermittent turning of windrows or other active drying processes at least thirty (30) days and until the solids level reach and maintain a minimum of 65% solids. The amount of alkaline materials is sufficient to maintain the pH above 12 until the solids level exceeds 60%.
Alternative #2: The advanced alkaline stabilized dewatered sludge cake is heated while the pH exceeds 12 using exothermic reactions from the alkaline materials or other thermal processes to achieve a temperature of at least about 50°C C. throughout the sludge; but not at a temperature sufficient to cause sterilization, and stored in static condition in such a manner as to maintain said temperature for at least 12 hours. The heat-treated advanced alkaline stabilized dewatered sludge cake is then air actively dried (while pH remains above 12 for at least three days) through intermittent turning of windrows or other active drying processes until the solids level reach and maintain a minimum of 50% solids.
The PFRP product resulting from the process as specified and described above can be ultimately utilized through marketing/distribution channels, land application programs,or as a landfill cover material.
Experiments have been conducted as follows:
In this experiment, 5000 g samples of Toledo sludge were mixed with 15%, 25% or 35% cement kiln dust or 5% or 10% lime. The mixture was kept at 72°C F. at approximately 20% humidity for over 60 days. The results showed that drying of the sludge was improved with the CKD and that PFRP criteria were met for each microbial standard with the 25% and 35% CKD and for the 10% lime. The pH of the sludge/CKD mixture stayed above 12 for three days. The odor control on the sludge treated with 35% CKD was better than any other treatment and was quite satisfactory. The microbial results can be summarized as follows: (Numbers represent viable counts per 5 gm of dry weight of sludge.) (No regrowth of pathogens occurred after the days listed.)
| Salmonella typhimurium | Fecal coliforms | |
| 0 days = 1.5 × 10 | 0 days = 9.7 × 10 | |
| 28 days = <1 | 13 days = 3.2 × 10 | |
| Poliovirus | Fecal streptococci | |
| 0 days = 2.0 × 10 | 0 days = 7.8 × 10 | |
| 1 day = <1 | 13 days = 2.6 × 10 | |
| 7 days = <1 | 46 days = 6.5 × 10 | |
| Ascaris suum eggs | ||
| 0 days = | ||
| 42 days = <1 | ||
This experiment compared lab and field treatments of Monroe, Michigan, sludge with 35% CKD. The field windrows were arranged 3 sets of 10 units of 7 tons each. The microbiology was conducted on the middle set of windrows that received mixing with a "Brown Bear" twice a week. The mean temperature was about 45°C F. and the humidity showed a mean of about 65%. Drying in the field was very poor with solids reaching 54% at 28 days and 72% only after 64 days. The pH of the windrows remained above 12 for over 28 days. At 64 days the pH had fallen to 10.6. The odor control was very good immediately following the CKD addition. The microbiology can be summarized as follows:
| Salmonella typhimurium | Fecal coliforms | |
| 0 days = 104 | 0 days = 8.9 × 10 | |
| 28 days = <0.3 | 1 day = 7.9 × 10 | |
| Poliovirus | 7 days = <0.3 | |
| 0 days = 0 | Fecal streptococci | |
| 1 day = 0 | 0 days = 2.4 × 10 | |
| Ascaris suum eggs | 1 day = 2.1 × 10 | |
| 0 days = <1 | 14 days = 2.8 × 10 | |
| 1 day = <1 | ||
| 7 days = <1 | ||
Sludges from three cities were separately tested as described below.
a. Des Moines, Iowa
Municipal sludge was mixed with 30% CKD. Drying at 7 days reached 65% solids while the pH remained above 12. Odor control with the CKD was excellent. The microbiology can be summarized as follows:
| Salmonella typhimurium | Fecal coliforms | |
| 0 days = <2 | 0 days = 2.4 × 10 | |
| 7 days = <2 | 7 days = 2 | |
| Poliovirus | Fecal streptococci | |
| 0 days = ND | 0 days = 2.4 × 10 | |
| 7 days = ND | 7 days = 2.3 × 10 | |
| Ascaris suum eggs | ||
| 0 days = 2.4 | ||
| 7 days = <1 | ||
b. Dupage County, Ill.
Municipal sludge was mixed with lime kiln dust at 35%. Drying was good reaching 63% in 2 weeks and 85% in 5 weeks. The pH had fallen to 9.0 at 2 weeks and 7.2 at 5 weeks. The odor control was good at 2 weeks and excellent at 5 weeks. The microbiology can be summarized as follows:
| Salmonella typhimurium | Fecal coliforms | |
| 0 days = ND | 0 days = 2.3 × 10 | |
| 14 days = ND | 14 days = 2 | |
| 35 days = ND | 35 days = 22 | |
| Poliovirus | Fecal streptococci | |
| ND | ND | |
| Ascaris suum eggs | ||
| ND | ||
c. Toledo sludge treated at Sylvania Township, Ohio
Approximately 550 tons of Toledo's municipal sludge was treated with 6% lime fines at the treatment plant following which it was trucked to the Sylvania site where it was mixed with 35% CKD and mixed in windrows (8' wide, 3.5' high, 200' long) on a 3 times a week basis with a "Brown Bear". The weather conditions were wet and summer temperatures averaged about 80°C F. The drying was good reaching 64% solids in 30 days and 69% in 60 days. The pH remained above 12 for over 60 days and only fell to 11.2 at 90 days. The odor control was good initially and very good after 30 days. The microbiology can be summarized as follows:
| Salmonella typhimurium | Fecal coliforms | |
| 0 days = 1.4 × 10 | 0 days = 1.1 × 10 | |
| 30 days = <2 | 30 days = 2 | |
| 60 days = <2 | 60 days = <2 | |
| Poliovirus | Fecal streptococci | |
| ND | 0 days = 3.0 × 10 | |
| Ascaris suum eggs | 30 days = <2 | |
| 0 days = 20 | 60 days = 20 | |
| 30 days = <1 | ||
| 60 days = <1 | ||
Municipal sludge from Toledo was brought to the Medical College for mixing (25000 g per cooler) with "bag house" quicklime and/or CKD in the following percentages:
1. Control 0%;
2. 35% CKD 3. 6% lime +35% CKD;
4. 10% lime +35% CKD
5. surface application of 35% CKD
6. 20% lime
The purpose of using these combinations was to measure temperatures achieved and determine if incubation times could be shortened in order for treated sludges to reach PFRP standards. Maximum temperatures recorded were as follows for each of the above: 1 (25°C C.); 2 (38°C C.); 3 (46°C C.); 4 (58°C C.); 5 (25°C C.); and 6(87°C C.). The maximal temperatures of the limed samples could have been higher given optimal mixing conditions since additional mixings soon after lime additions reduced temperatures. Drying was good reaching 52% in the CKD only treated samples in 14 days and exceeding 64% in all others. The pH remained above 12 for 24 hours in the CKD (#2) sample and remained above 12 for over 56 days in all others. Odor control was good in all treated samples. The microbiology can be summarized as follows:
| Salmonella typhimurium | Fecal coliforms | ||
| 0 days = 2.4 × 10 | 0 days = 4.8 × 10 | ||
| 3 days | 3 days | ||
| # 2 = 3.5 × 10 # 2 = 1.3 × 10 | |||
| # 3 = <1 | # 3 = <1 | ||
| # 4 = <1 | # 4 = <1 | ||
| # 6 = <1 | # 6 = <1 | ||
| Poliovirus | Fecal streptococci | ||
| ND | 0 days = 8.7 × 10 | ||
| 3 days | |||
| # 2 = 3.0 × 10 | |||
| # 3 = 2.3 × 10 | |||
| # 4 = 3.0 × 10 | |||
| # 6 = <1 | |||
| Ascaris suum eggs | |||
| 0 days = 145 | |||
| 1 day | 7 days | 28 days | |
| # 1 = 64 | # 1 = 88 | # 1 = 152 | |
| # 2 = 19 | # 2 = 13 | # 2 = <1 | |
| # 3 = <1 | # 3 = <1 | # 3 = < 1 | |
| # 4 = <1 | # 4 = <1 | # 4 = <1 | |
| # 6 = <1 | # 6 = <1 | # 6 = <1 | |
In this experiment, 6% or 8% "bag house" quicklime was added to Toledo municipal sludge at the treatment plant and then this mixture was incubated in storage bins for a minimum of 12 hours. Temperatures did not drop below 52°C C. with the 6% lime or 56°C C. with the 8% lime over the 12 hours. After this incubation, the limed sludge (approximately 50 tons) was trucked to the Toledo Port Authority site for mixing with 35% CKD and then mixed twice weekly with the "Brown Bear". The drying was good reaching 58% in 14 days and 60% in 28 days with the 6% lime treated mixture and 54% in 14 days and 63% in 28 days with the 8% lime treatment mixture. The pH of the 6% lime treated mixture was over 12 for 66 days and in the 8% lime mixture it was over 12 for the 28 days of the test. Odor control once the 35% CKD was mixed in was very good. In order to adequately test the killing power of the two-stage lime/CKD process, a cloth bag containing sludge and the correct treatment mixture (8% lime followed by 35% CKD) was seeded with Ascaris eggs and inserted directly into the incubation bin and subsequent windrow. The microbiology can be summarized as follows:
| Salmonella typhimurium | Fecal coliforms | |
| 6% L + 35% CKD | 6% L + 35% CKD | |
| 0 days = <1 | 0 days = 2.8 × 10 | |
| 1 day = <1 | 1 day = <1 | |
| 14 days = <1 | 14 days = <1 | |
| 8% L + 35% CKD | 8% L + 35% CKD | |
| 0 days = <1 | 0 days = 2.8 × 10 | |
| 1 day = <1 | 1 day = <1 | |
| Poliovirus | Fecal streptococci | |
| ND | 6% L + 35% CKD | |
| Ascaris suum eggs | 0 days = 8.9 × 10 | |
| 6% + 35% CKD | 1 day = <1 | |
| days = 2 | 14 days = <1 | |
| 1 day = <1 | 8% + 35% CKD | |
| 14 days = <1 | 0 days = 2.8 × 10 | |
| 8% L = 35% CKD | 1 day = <1 | |
| 0 days - 137 (seeded) | 14 days = <1 | |
| 1 day = <1 | ||
| 14 days = <1 | ||
The above results shows conclusively that the treatment process using CKD or lime/CKD in a two-stage process both cause the treated municipal sludges to meet the PFRP criteria. The specific treatment determines the processing time necessary for the sludge (when seeded with 1×10 Salmonella and 1×10 Ascaris eggs) to reach PFRP levels. The process and process times are as follows:
1. CKD only - always within 46 days
2. 6% lime +35% CKD, no heat - 30 days
3. 6% lime +35% CKD, with 46°C C./12 hrs - 3 days
4. 6% or 8% lime +35% CKD with 52°C C./12 hrs - 1 day
Further tests have shown that the method results in a stabilization of heavy metals.
Material Specifications
Quick Lime:
Shall meet specifications for quicklime as identified in ASTM C 911. At least 75% of the material shall pass a #100 sieve.
Hydrated Lime:
Shall meet specifications for hydrated lime as identified in ASTM C 911. At least 75% of the material shall pass a #200 sieve.
Kiln Dust:
Material collected in a rotary kiln producing portland cement or quicklime in accordance with ASTM C 150 and ASTM C 911, respectively.
In an oxide analysis the material must contain at least a total of 35% CAo and Mgo. The loss on ignition shall not exceed 30%. Reactive alkalines and alkalis (CAo +Mgo - [LOI×1.2]+K2o +Na2o) shall exceed 12%. Maximum allowable levels of trace elements:
cadmium (Cd): 25 mg/kg
copper (Cu): 500 mg/kg
lead (Pb) 900 mg/kg
nickel (Ni) 100 mg/kg
mercury (Hg) 5 mg/kg
zinc (ZN) 1500 mg/kg
At least 75% of the material shall pass the #100 sieve.
At least 50% of the material shall pass the #200 sieve.
Burnham, Jeffrey C., Nicholson, John P.
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