MXPA00004158A - Stabilized liquid lime dispersion for sewage treatment - Google Patents

Abstract

A stabilized lime slurry for treatment of biological solids in sewage. The composition preferably includes 30-36%calcium hydroxide, 10-16%potassium hydroxide, 2-4%potassium chloride, 2-4%magnesium hydroxide, all on a dry basis, and the balance in water. This composition raises the pH rapidly for destroying pathogens, is sufficiently concentrated for economically feasible transportation, and reduces the cost, difficulties and dangers of treating sewage with a lime based composition while providing a resulting product from the sewage treatment process which can be spread upon agricultural soil in a manner which improves soil fertility without introducing undesirable or contaminating materials into the soil.

Description

LIQUID DISPERSION OF CAL, STABILIZED, FOR TREATMENT OF CLOCAL WATERS BACKGROUND OF THE INVENTION Field of the Invention The present invention relates generally to waste treatment, and more particularly relates to a composition for the treatment of sewage water containing biological solids. The composition reduces the difficulties and dangers of handling the treatment material, becomes highly active faster, thereby improving the capacity of the treatment facility and provides a solid liquid product resulting from the treatment process which is suitable for being applied to the solubilized for agricultural purposes.

Description of the Related Art The prior art describes an abundance of materials and processes for treating waste, such as sewage and sewage. Alkaline materials, including lime, have been used for the treatment of biological solids in municipal and industrial wastewater treatment plants. Such treatments are shown, for example, in U.S. Pat. 5,186,840 and 4,415,467. High alkalinity destroys potentially dangerous pathogenic microorganisms by raising the pH of the host material to a level at which microorganisms can not survive. Federal regulations require that biosolids be brought to and maintained at a pH level of 12 for at least 2 hours and at a pH level of 11 for an additional period of at least 22 hours to ensure the destruction of pathogens. Although the prior art teaches the treatment of wastewater with lime, there are problems associated with the methods and compositions of the prior art used for such treatments. The problems are a combination of: (1) the difficulty of mixing the lime in the sewage and the cost of the equipment to help the mixing; (2) the dangers to health and human properties due to the uses of dry particulate lime; (3) the low rate of activation of the lime to raise the pH and destroy the pathogens after being applied, which results in a retardation of the treatment process and therefore reduces the capacity of the treatment facility; and (4) the inclusion of materials in treated solid biological products from the sewage treatment process that are not suitable to be applied to the soil used for agricultural purposes. Conventionally, dry lime, CaO, or hydrated lime, Ca (OH) 2, well known as slaked lime, is added to a waste treatment plant in bulk or in bags, or similar containers. The lime is discharged into the biosolids treatment tanks, which results in a large proportion of the lime being submerged to the bottom as a mass that tends to clump together and is difficult to break. Attempts to break this are difficult and consume time with the dispersion of lime being inhomogeneous and incomplete. Due to the difficulty of dispersing lime under such conditions, the total capacity of the sewage treatment plant is reduced. One method to solve this problem is to install new additional equipment to increase the rate of dispersion of the lime and to initiate more quickly the activity of the lime. This, however, requires a greater capital investment. An example is found in U.S. Pat. 4,110,211. As a result, it is expensive to achieve the higher pH levels required by federal regulations.

Additionally, dry lime is a caustic material and disperses rapidly into the air, making it dirty and making it dangerous to handle and irritating to workers. Workers can breathe the lime or retain it on their skin, in their eyes or on their clothes, creating a potential that causes discomfort, injury or illness. In windy weather conditions, lime particles can also be brought to neighboring areas, creating a potential for damage to properties and the environment. The prior art has recognized that it would be desirable to supply lime to a sewage treatment plant by means of a cistern, in the form of an aqueous slurry (slurry) to make lime easier and safer to handle and to apply to the process. treatment. However, the lime that is mixed in the water sediments and agglomerates as deposits in the bottom of the container, and therefore • requires continuous or periodic agitation to stay suspended and dispersed. This requires an investment in additional equipment to maintain the suspension during storage and transport, although it eliminates the need for an investment in equipment in the treatment facility. Such a lime distribution system based on an aqueous suspension also requires that the suspension contain a sufficiently high proportion of lime to make the transportation of the suspension economical. Otherwise, this technique carries the cost of transporting excessive amounts of water. However, it is also believed desirable to be able to apply the treated biological particles resulting from the treatment of sewage to agricultural soils because doing so would make available a cheap source of organic materials, while providing cheap, non-polluting disposal of the products. solids from the sewage treatment plant. Unfortunately, however, previous lime suspensions contain materials that are added to keep the lime in suspension, but which are hazardous or are not beneficial for soil agronomy. Such undesirable materials include metals, such as sodium or other organic materials that form dangerous inorganic salts, and also organic compounds that have unknown consequences to plant and animal life. Such material is described in U.S. Pat. 4,849,128. Therefore, the object and purpose of the present invention is to provide a material that not only provides a stable lime slurry that is handled, stored and applied easily and conveniently to the sewage treatment process, but also be economic and, more importantly, as a result a product that is agriculturally and environmentally friendly when applied or dispersed over agricultural land as a fertilizer. It is an object and feature of the invention to use materials in the lime treatment composition that are effective in maintaining a sufficiently stable lime suspension concentrated to be economically feasible, which in turn also contributes to the nutritional condition of the soil, so that the application of the products of the sewage treatment plant to the soil for agricultural purposes becomes safe, legally permissible and desirable. A further object and feature of the invention is that it provides a material, which eliminates the need to invest in the installation of additional equipment in the sewage treatment facilities, by providing a lime suspension composition, which requires only that it be simply pumped into the lagoons of sewage treatment resistant and mixed with modest gitation.

BRIEF DESCRIPTION OF THE INVENTION The composition of the present invention is a stabilized suspension formed by a colloidal dispersion of lime in a solution of water and potassium hydroxide. Preferably, the suspension also includes potassium chloride to improve the flowability and magnesium hydroxide to maintain the balance of solids. This composition remains suspended indefinitely without the need for agitation or mixing, it can be sufficiently concentrated, so that it can be transported in effective quantities at a reasonable cost and can be handled efficiently and effectively without leaving deposits in the transport tanks. or storage or cause injury or discomfort to workers in the sewage treatment facility. This material also allows the biological products of sewage treatment to be applied to the fields and makes a beneficial contribution to soil agronomy. The preferred composition is hydrated lime in an amount substantially in the range of 20% -40% on a dry weight basis, potassium hydroxide in an amount substantially in the range of 5% -18% on a dry weight basis and % to 75% by weight of water. The preferred composition also includes potassium chloride in an amount substantially in the range of 0% -10% on a dry weight basis and magnesium hydroxide in an amount substantially in the range of 0% -10% on a dry weight basis. .

BRIEF DESCRIPTION OF THE DRAWINGS Figures 1, 2 and 3 are graphs that illustrate the cost and performance of the different combinations of potassium hydroxide and calcium hydroxide. Figure 4 is a graph illustrating the effects of the relative portions of water and solids. Figure 5 illustrates the ratio of alkalinity in milequivalents per gram to the percentage of calcium hydroxide in the composition. In the description of the preferred embodiment of the invention, specific terminology will be used in order to be clearer. However, the invention is not intended to be limited to the specific terms thus selected and it should be understood that each specific term includes all technical equivalents that operate in a similar manner to achieve a similar purpose.

DESCRIPTION OF THE PREFERRED MODALITY The main component of the present invention is hydrated lime (off) in a range of 20% -40% on a dry weight basis of the entire composition. The lime can be introduced into the water in its hydrated form or, alternatively, quicklime, CaO, can be added to the water and hydrated in the mixture during agitation. An additional portion of water is needed to quench the quicklime in situ to the hydrated calcium hydroxide form. The lime is highly alkaline and therefore provides a substantial amount of OH ions for antipathogenic activity.Preferably common commercial lime, which has a density of 20-30 pounds / cubic foot (0.32-0.48 g / cm3), is used. ), with particles having a size, of which 98% pass through a 200 mesh screen and 92% pass through a 325 mesh screen. The complete composition should include hydrated lime in an amount substantially in the range of 20% -40% on a dry weight basis It has been found that less than this range is not effective enough and that it is very expensive in economic terms to transport in effective amounts due to the cost of transporting an excess of water. It has been found that amounts exceeding this range deteriorate the flowability of the product and cause sedimentation of the dispersion.Preferably, the hydrated lime constitutes 30% -36% of the composition, and so It s preferably 32% -34% of the composition. Hydrated lime not only provides OH ions "to raise the alkalinity of treated sewage to destroy microorganisms, but additionally the calcium that remains in the treated sewage water provides a solid nutrient when applied to agricultural fields. The second important component of the composition of the present invention is potassium hydroxide, KOH, in an amount substantially in the range of 5% -18% on a dry weight basis. Although it is preferred to introduce KOH as a 45% aqueous solution when formulating the composition of the present invention, the proportions in the composition are described on a dry or solid basis for purposes of consistency and quality. in the KOH solution it becomes a portion of the aqueous component of the stabilized lime suspension of the invention. The amount of KOH used is considerably greater than the amount of alkali metal hydroxide used in the material of the prior art. KOH serves three purposes simultaneously: (1) it helps to disperse lime and keep the colloidal dispersion at a higher concentration; (2) it is a strong alkalizing agent that is very soluble in water and therefore provides a bacterial killer that acts quickly, which immediately attacks the bacteria in the sewage sludge; and (3) it supplies a significant amount of potash to the soil, which is an important agricultural fertilizer component. Potassium hydroxide provides a higher density material to help support heavy lime particles, not dissolved in suspension, which helps keep the colloidal dispersion at a high concentration, thus preventing agglomeration, and at the same time contributing to the alkalinity and consequent bacterial action. The potassium hydroxide is included in the composition in an amount substantially in the range of 5% -18% on a weight basis, and preferably in an amount of 10% -l-6%, and more preferably in the an amount of 12% -14%. A minimum of at least 5% is necessary for the previous activity to be significant. Quantities exceeding this range are excessively expensive since the product becomes economically unfeasible or practical. The water should constitute up to 40% to 75% by weight of the composition. The amounts of water that exceed this interval do not provide additional utility and only increase the cost of transportation and distribution of the product. The amounts below this range cause the composition to become very thick and viscous, and therefore very difficult and impractical to handle and pump. Preferably, the water constitutes 48% to 56% of the composition, and more preferably 48% to 52%. An additional important ingredient is potassium chloride, KCl, in an amount exceeding 0% and substantially in the range of 0% -10% on a dry weight basis. Preferably, the KCl is substantially in the range of 2% -4%, and more preferably it is used in an amount of 2%. KCl reduces the viscosity of the composition of the suspension of the invention to counteract the increase in viscosity resulting from the hydration of lime and the introduction of other particulate materials into the composition. The viscosity is reduced to maintain the ability of the composition to be mixed and to flow through the pumping equipment. If the composition reaches an excessive viscosity, problems arise in the manufacture of the composition, particularly in the mixing, and additionally the product becomes difficult to pump to and from the transport and storage tanks and to the treatment tanks. KCl helps maintain a higher concentration of lime and also reduces or eliminates the accumulation of deposits on the transport and storage tanks. The use of amounts that substantially exceed 10% of the composition does not provide an additional increase in their effectiveness, thus unnecessarily increasing costs. It has also been found that it is desirable to include magnesium hydroxide, Mg (OH2), in an amount substantially in the range of 0% -10% on a dry weight basis. Preferably, the magnesium hydroxide is included in the composition in an amount substantially in the range of 2% -4%, and most preferably in an amount of 2%. Magnesium hydroxide is preferably prepared by mixing magnesium oxide MgO, in water, but the formulations are given in terms on a weight basis of magnesium hydroxide for consistency purposes. Accordingly, it is preferable to provide some additional water for the hydration of the MgO in situ, as described above for the lime. Magnesium hydroxide is not very soluble in water and therefore does not contribute much to the alkalinity of the composition. Its main purpose is to help maintain the proper balance of magnesium and calcium soil for good agronomic practice. In a soil, it is desirable to have a magnesium to calcium ratio of the order of 1: 5 to 1: 7. Thus, the amount of magnesium hydroxide included in the composition depends somewhat on the magnesium content of the soil in the soil where the product of the treated sewage, completed, is expected to be dispersed. Since most soils have sufficient magnesium, it is desirable to apply just enough magnesium to maintain the proper balance. Some solids are high in magnesium and, for such solids, it is preferable to include less magnesium hydroxide and maintain a magnesium to calcium ratio in the composition of the stabilized lime slurry of the invention in the order of 1:10. Polyvinyl alcohol has also been added in an amount of the order of 1% to the composition to improve the suspension by increasing the density of the liquid to better support suspended particles. A polyelectrolyte can also be added for a similar purpose. In general, neither is necessary unless the water content exceeds 58%. Experimentation has shown that the preparation of a stabilized lime suspension composition according to the present invention is facilitated by first combining all the water and the potassium hydroxide in a receptacle to form an aqueous solution. The calcium hydroxide, potassium chloride and magnesium hydroxide are then introduced into this solution in a plurality of separate caps, which are separated by a stirring time interval. There must be at least two stages, preferably three, and four such stages are also useful. The number of stages depends on the amount, type and effectiveness of the agitation that is available to effect the homogeneous mixing. Less effective agitation requires more stages. At each stage a portion of each of these three constituents is inserted with the potassium chloride being added to the mixture, not initially, but simultaneously with the calcium hydroxide and preferably after it. In this way, the effect of potassium chloride on reducing the viscosity to counteract the increase in viscosity resulting from the introduction of lime is better done, to facilitate the ongoing stirring of the mixture and to aid in the dispersion of the lime. Calcium hydroxide, potassium chloride and magnesium hydroxide can be introduced in equal amounts in each stage, although variations of this are equally effective. Experience has also indicated that, preferably, agitation between the stages in which those three constituents are aggregated occurs at intervals of at least about 10 minutes. For example, a composition according to the present invention was manufactured using the components of the following Table 1.

TABLE 1 Material Weight in Percent Pounds (Kg) of Total Calcium Hydroxide 378 (171.6) 32.30 Potassium hydroxide (solution 371 (168.4) 31.70 to 45%) Water 363 (164.8) 31.0 Magnesium Oxide 23.4 (10.6) 2.0 Chloride 'of Potassium 23.4 (10.6) 2.0 Polyvinyl Alcohol 11.7 (5.3) 1.0 170. 5 (77.4; 100% Potassium hydroxide was a 45% solution, and therefore 55% of that solution represents water, in addition to the water added separately and shown in the Table. All the water, followed by all the potassium hydroxide solution, was added to the reactor vessel and mixed thoroughly by means of agitation. Then 68.0 pounds (30.9 Kg) of lime (18% of the total lime) was slowly added to the previous solution at a uniform flow rate and mixing was continued until the lime dispersed well. Then 7.8 pounds (3.5 Kg) of potassium chloride (33% of the total potassium chloride) was added by mixing with stirring and mixed thoroughly for about 10 minutes. Then 5.8 pounds (2.6 kg) of magnesium oxide (25% of the total magnesium oxide) was introduced under stirring and mixed thoroughly for about 10 minutes. Then an additional 86.9 pounds (39.5 Kg) (23% of the total lime) was added to the mixture, slowly, at a uniform flow rate and while dispersing. Then 5.85 pounds (2.7 Kg) of magnesium oxide (25% of the total magnesium oxide) was added under stirring and mixed thoroughly. Then 128.5 pounds (58.3 pounds) were added Kg) of lime (34% of the total lime) to the mixture, under agitation, and dispersed well. Then 7.8 pounds (3.5 Kg) of potassium chloride (33% of the total potassium chloride) was added to the above mixture and mixed for about 10 minutes. Then 5.85 (2.7 Kg) of magnesium oxide (25% of the total magnesium oxide) was added to the mixture and stirred for about 10 minutes. Then 94.5 pounds (42.9 Kg) of lime (25% of the total lime) was added slowly at a uniform flow rate and mixed until well dispersed. Then, 7.8 pounds were added (3.5 Kg) of potassium chloride (33% of the total potassium chloride) to the mixture and mixed for about 10 minutes. Then they added . 85 (2.7 Kg) of magnesium oxide (25% of the total magnesium oxide) to the mixture and mixing and stirring continued until the whole product was thoroughly mixed "and completely and the lime dispersed well. 11.7 pounds (5.3 Kg) of polyvinyl alcohol (100% of the total) to the mixture while mixing and stirring continued for at least 15 minutes. The product was then visually inspected to determine the dispersion, the specific gravity, the pH and the calcium content were measured, and a pour point test was conducted to ensure the suitability of the specification.

The resulting composition had finely divided particles of lime dispersed homogeneously and the composition, although relatively thick and viscous, nevertheless flowed easily. It was found that the material remained dispersed indefinitely when kept at a temperature of 0 ° or higher. The above measurements revealed that the composition had a pH at 68 ° F (5.77 ° C) in the range of 13.5 to 14.0. It was found that a 5% solution of the composition at temperature had a pH of 13.0. The material had a specific gravity of 1,403 grams per milliliter or 11.7 pounds per gallon U.S. The measurement of the pour point (fluidity) of the material at 0 ° F (-32 ° C) revealed a fluidity exceeding 90%. The fluency test was conducted by placing 400 milliliters of the composition in a 500 milliliter beaker, which was cooled to 0 ° F (-32 ° C) in a domestic refrigerator. During the cooling period it was stirred every hour until this temperature was reached. The contents of the beaker were then poured into the second beaker by inverting the first beaker for 10 seconds. The content of the second beaker at the end of those 10 seconds was then measured to determine the proportion of material that flowed into the second beaker.

Both of the small-scale laboratory tests and the large-scale field tests involving 140,000 gallons (529,900 liters) of biosolids were made in a composition incorporating the present invention. The composition was pumped into the biosolids treatment tank and found to disperse rapidly and completely. No lumps or masses of lime formed on the bottom of the holding tank. The pH of the biosolids rose rapidly and within 30 minutes it reached 12.3 and then it stabilized. 24 hours later, the pH was also higher than 12. Laboratory tests show that the destruction of pathogens was effective and that, as a result, the biosolids materials qualified as Class A sludge, as defined in regulations 503 of the EPA In all these tests, the minimum standards for the Class B sludge were achieved and additionally, in several cases, it reached the minimum for Class A. In the field tests, the composition was handled in a closed system comprised of tanks. sealed storage, pumps, valves, tubes and meters that allow handling or fully mechanized handling of the composition without requiring it to be touched or exposed to human skin. Such a closed system minimizes the risk of injury to workers and damage to property and the environment. Three additional experiments were performed to test the effectiveness of the different proportional combinations of the components of the stabilized lime suspension according to the present invention. The tests carried out and their results are as follows: TABLE 2 EXPERIMENT 1. To Test the Proper Composition Interval for Liquid Lime Suspensions. Composition in% Sample No. 1 2 3 4 5 6 Water 52 50 48.5 47 45 43 K0H, db 18 16 13.5 11 9 7 Ca (0H) 2 20 25 30 35 40 45 MgO 10 8 6 4 2 0 KCl 0 1 2 3 4 5 Six samples of 300 g were prepared according to the previous percent compositions.

Water and dissolved KOH were first placed in the mixing vessel. Lime, magnesium oxide and KCl were added in four increments, ie 1/4 lime, 1/4 MgO and 1/4 KCl were added and vigorously agitated followed by a second, third and fourth additions followed each time by vigorous agitation. The final agitation was for 30 minutes at moderate speed. The samples were transferred to 8 oz bottles. (226.8 ml) and were allowed to stand for 48 hours after which they were evaluated. Five response factors were observed and determined for the 6 samples of Experiment 1.

TABLE 3 - Results of EXPERIMENT 1 Sample No. 1 2 3 Sedimentation Sedimentation Slightly no no no Suspension (15%) sedimented Fluency Good Good Good Good Bad Bad Dispersion * Good Good Good Good Bad Bad PH adjustment * Good Good Good Good Bad Bad Titling of 12.0 12.2 12.5 12.8 13.1 13.3 Alkalinity, meq / g ** * 100 ml of 0.4% phosphoric acid solution was treated with liquid lime and observed.

** Titration of the alkalinity of the liquid lime with HCl IN Results of EXPERIMENT 1 of the six samples show that samples 5 and 6 were somewhat thicker to be manageable, while sample 1 and perhaps sample 2 were a both thin for storage and efficient operation.

TABLE 4 EXPERIMENT 2. To Test the Suitable KOH Concentration Interval to Produce Liquid Lime Suspensions Composition in% Sample No. 1 2 3 4 5 Water 42 44 46.5 49 51 KOH 18 16 13.5 11 9 Ca (OH) 2 32 32 32 32 32 MgO 6 6 6 6 6 KCl 2 2 2 2 2 These samples were prepared in a manner similar to those of EXPERIMENT 1 except that the lime, MgO and KCl were added in 3 increments by shaking after each of the three additions with final agitation for 30 minutes. The samples were tested after resting 48 hours.

TABLE 5 - Results of Experiment 2 Sample No. 1 2 3 4 5 Fluide z Very poor Poor Good Good Good Alkalinity, 12. 0 11. 9 11. 7 11. 5 11. 3 meq / g.

The suspension was good for all samples and the dispersion was good for samples 2-5. These results indicate that the water content is preferably 44% or higher leaving the% KOH at 16% or less when the lime, MgO and KCl combined are at 40%.

TABLE 6 EXPERIMENT 3. To Test the Effect of Potassium Chloride (KCl) Concentration on Liquid Lime Suspensions Composition in% Sample No. 1 2 3 Water 52 51 50 KOH 14 13.7 13.4 Ca (OH) 2 32 31.3 30.6 MgO 2 2 2 KCl 0 2 4 The samples were prepared in a similar manner to EXPERIMENT 2, with the amount of KCl being the main variable (from 0 to 4%). The concentration of KOH; Ca (OH) 2 and MgO in the water were selected from previous trials, which would make a good suspension. Three samples were evaluated mainly by a fluency test. The relative fluidity test used here was to place a heavy amount of liquid lime sample (450 - 260 gms) in a beaker at room temperature (25 ° C). The beaker was inverted at a high flow angle for 10 seconds. The amount of sample remaining in the beaker was calculated as one percent of the total sample.

TABLE 7 - Results of EXPERIMENT 3 Sample of% Remaining of the Experiment% of KCl Fluency Test 1 1 8.2 2 2 3.9 3 4 3.1 This test indicates that 2% KCl was effective in increasing the fluidity or transfer of the product by a significant amount. The 4% KCl was not much better than 2%. It was also noted that without KCl, the liquid lime was adhered to the sides of a polyethylene or polyvinyl chloride container while Samples 2 and 3 containing KCl were perfectly released.

TABLE 8 EXPERIMENT 4 - POTASSIUM HYDROXIDE AGAINST CALCIUM HYDROXIDE Composition in% Sample No.

Water 52 54 58 55 52 52 52 KOH, d.d. 4 1.7 3.7 8 10 Ca (OH) 2 42 40 36 3.7 38 36 34 Mg (OH) 2 2 1.7 1.

KCl 2 1.7 1.

These samples were made and evaluated in a similar way to Experiment 1, and the results observed were the following: TABLE 9 - Results of EXPERIMENT 4 Sample No. 1 2 3 4 5 6 7 Fluency very very poor good good good good Good poor (thick) (paste) Setting the very slow slow fast Fast pH * (minutes) slow (3) (2) (<1) (<1) (6) Alkalinity, 10.8 11.4 12.0 11.8 11.6 meq / g cost (a) cc / gal 29 36 44 49 54 (c / liter) (7.66) (9.5) (11.6) (12.9) (14.3) (b) a / eq. 0.51 0.60 0.70 0.79 0.88 ^ Starting with 200 ml of water adjusted to pH 2.2 with phosphoric acid to, impart, simulate the use of sewage sludge.

Table 9 shows the results of making several samples of lime suspensions in which KOH and Ca (OH) 2 varied mainly. Samples 1 and 2 were very thick, so they were diluted with water to produce samples 3 and 4 respectively. The low KOH levels did not give an immediate response in the pH adjustment test using a very dilute phosphoric acid solution, and adjusting the solution to a pH of 12.0. This and other observations led to the observation that KOH is necessary at least 5% or a ratio of at least a part of KOH to 8 parts of Ca (OH) 2. More KOH gives an even faster adjustment to the pH of 12.0. The soluble KOH looks for and destroys bacteria while the pH is adjusted uniformly to 12, better and more perfectly than with the Ca (OH) 2 in suspension alone. The more KOH used, the more direct and quick the pH adjustment of 12.0. However, KOH is considerably more expensive than lime. Therefore, the use of at least a part of Ca (OH) 2 with a part of KOH keeps the costs reasonable. A ratio of 2 to 1 is better. The soluble KOH produces a denser solution, thus giving more support to the maintenance of lime in the suspension. The result is that the KOH should be present in the composition at least in an amount that provides a ratio of KOH: Ca (OH) 2 of 1: 8 to provide a sufficiently rapid adjustment of the treated sewage a pH of 12.0, but should not exceed a ratio of 1: 1 and preferably 1: 2 to maintain a sufficiently low cost. Figures 1, 2 and 3 show the effects of cost and operation of the use of various combinations of KOH and Ca (OH) 2 - Figures 2 and 3 show a higher cost for higher levels of KOH in the mixture. The opposite is true for Ca (OH) 2. It is thought that a range of 0.7 s 1.2cz_ / eq covers the preferred cost / performance area. A lower cost level gives a poor performance. Figure 1 summarizes the range of effects, including the amount of water. In general, a water use of less than 42-46% is very thick to handle. Samples that contain more than 58% water are too thin, not very viscous. A use of more water is effective if a thickener is used to stabilize the suspension. However, even with a thickener, a level of approximately 75% water would be approximately the maximum for economical transportation and storage. Figure 4 also shows the effect of water against solids, including extra additives Mg (OH) 2 and KCl. The dotted line describes an interval of 47 to 54% of water, although 46 to 56% of water can be the preferred range, this can be extended to 75% if thickener is used. Polyvinyl alcohol or a polyelectrolyte can be used as a thickener to improve the suspension. Figure 5 shows the alkalinity (milliequivalents per gram -meq / g) against% of Ca (OH) 2. In general, alkalinity increases with an increase in Ca (0H) 2- However, Mg (OH) 2 and water have an influence on this parameter. Most prepared samples fall in the range of 10.5 to 12.5 meq / g, but diluted samples can be as low as 7 meq / g. The range of composition extracted from the graphs was previously established. The preferred interval produces products with good capacity to be worked. The wide range covers diluted compositions and thick ones that have marginal handling qualities. When the suspension is very diluted with water, some sedimentation occurs during storage and handling. Although certain preferred embodiments of the present invention have been described in detail, it should be understood that various modifications may be made without departing from the spirit of the invention or the scope of the following claims. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (21)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A stabilized lime suspension composition for the treatment of waste including biosolids, the composition is characterized in that it comprises: (a) hydrated lime; (b) potassium hydroxide; and (c) water.

2. The composition according to claim 1, characterized in that it also comprises potassium chloride.

3. The composition according to claim 2, characterized in that it also comprises magnesium hydroxide.

4. The composition according to claim 1, characterized in that it also comprises magnesium hydroxide.

5. A stabilized lime suspension composition for the treatment of waste including biosolids, the composition is characterized in that it comprises: (a) hydrated lime in an amount substantially in the range of 20% to 40% on a dry weight basis; (b) potassium hydroxide in an amount substantially in the range of 5% to 18% on a dry weight basis; and (c) water in an amount substantially in the range of 42% to 75% by weight.

The composition according to claim 5, characterized in that it also comprises potassium chloride in an amount substantially in the range of 0% to 10% on a dry weight basis.

The composition according to claim 6, characterized in that the potassium chloride is substantially in the range of 2% to 4%.

8. The composition according to claim 6, characterized. because it also comprises magnesium hydroxide in an amount substantially in the range of 0% to 10% on a dry weight basis.

9. The composition according to claim 8, characterized in that the magnesium hydroxide is substantially in the range of 2% to 4%.

10. The composition according to claim 9, characterized in that the potassium chloride is substantially in the range of 2% to 4%.

The composition according to claim 6 or 7 or 8 or 9 or 10, characterized in that the potassium hydroxide is substantially in the range of 10% to 16%.

The composition according to claim 8 or 9 or 10, characterized in that the calcium hydroxide is substantially in the range of 30% to 36%.

The composition according to claim 5 or 6 or 7 or 8 or 9 or 10, characterized in that the water is substantially in the range of 48% to 56% by weight.

The composition according to claim 5 or 6 or 7 or 8 or 9 or 10, characterized in that the ratio of potassium hydroxide to calcium hydroxide is at least substantially 1: 8.

15. The composition according to claim 14, characterized in that the ratio of potassium hydroxide to calcium hydroxide is substantially less than 1: 1.

16. A method for preparing a stabilized lime slurry mixture, the method is characterized in that it comprises: (a) combining water and potassium hydroxide to form an aqueous solution of potassium hydroxide, the amount of potassium is sufficient to provide a constituent of potassium hydroxide in the stabilized lime slurry mixture of 5% to 18% on a dry weight basis; (b) in at least 2 separate stages a certain time, separated by a stirring interval, mix in the solution and stir the calcium hydroxide, potassium chloride and magnesium hydroxide, the total amount of calcium hydroxide for all stages it is sufficient to provide a calcium hydroxide constituent in the lime slurry stabilized substantially in the range of 20% to 40% on a dry weight basis, the total amount of potassium chloride and magnesium hydroxide for all stages being sufficient to provide a constituent of potassium chloride and magnesium hydroxide in the stabilized lime slurry not greater than 0% and not to substantially exceed 10% on a dry weight basis, a portion of each of the calcium hydroxide, potassium and magnesium hydroxide is mixed in the solution in each stage, the potassium chloride in each stage is mixed not at the beginning, but simultaneously with the hydroxide of calcium in each stage.

17. The method according to claim 16, characterized in that there are at least 3 of such stages.

18. The method according to claim 17, characterized in that there are at least 4 of such stages. The method according to claim 16 or 17 or 18, characterized in that the agitation between the steps is carried out for at least substantially 10 minutes. The method according to claim 16 or 17 or 18, characterized in that the calcium hydroxide, potassium chloride or magnesium hydroxide are mixed in the solution in substantially equal amounts in each step. The method according to claim 20, characterized in that the stirring between the steps is carried out at least substantially for 10 minutes.