RU2082700C1 - Method of reusing activated sludge - Google Patents

Abstract

FIELD: biological purification and manufacture of building materials. SUBSTANCE: invention relates to using activated sludge from biological purification station in manufacture of building materials. Activated sludge is stabilized , decontaminated, and set free of heavy metals by agency of cement. The latter is achieved by adding sludge as component into concrete mix in amount providing required fluidity of mix, which is then supplemented with 0.1-0.25% (based on concrete mix weight) of lime that corresponds to 3-7% based on dry sludge weight. Resultant mix is subjected to heat-wet treatment at 80-95 C. High alkalinity of mix (pH 11-12 and higher) provided by cement and elevated temperature of treatment result in reliable decontamination and complete stabilization of sludge. Such a disposal of activated sludge eliminates expenses on water separation and decontamination, on heavy metal neutralization, on transportation or power consumption in case of using activated sludge as fertilizer or when burned. EFFECT: simplified disposal of environmental harmful material. 2 tbl

Description

 The invention relates to methods for the disposal of activated sludge biological treatment plants and can be used to improve the ecological state of the environment and in the production of building materials and products.

 A known method of disposal of sewage sludge as fertilizers with pre-treatment, which provides for compaction, stabilization and dehydration. In this case, lime is added to the sediment, which improves the yield of sediment (Turovsky I.S. Treatment of sewage sludge. M. Stroyizdat, 1988, pp. 63-81, 208-220).

 However, this method requires significant capital and energy costs to remove water, does not neutralize toxic heavy metals, toxic and carcinogenic organic compounds, leads to the gradual accumulation of these and other harmful substances in the soil and their passage into the human body.

There is a method of disposal of sludge with its disinfection using lime, which is introduced in an amount that provides a pH of 11-12, and its dose at a sediment moisture of 70-80% is 15-20% (by CaO) of the mass of sludge. When this occurs, the temperature increases and the sediment is heated to 60 ^o C due to the exothermic reaction of slaking lime. (Pokrovskaya S.F. Kasatikov V.A. Use of urban sewage sludge in agriculture, M. VNIIGEIagroprom. 1987, p. 3-19).

 However, this method does not exclude the need to remove water and the associated energy costs, since for fertilizers the sediment is used in a loose solid state, in addition, the introduction of lime also does not neutralize toxic heavy materials.

The closest is the method of disposal of activated sludge by introducing it into the concrete mixture in an amount providing a water content in the mixture of 5-50% providing the required mobility mix, and adding lime in an amount of 1-15%
However, this method does not provide sufficient strength and destruction of sulfur-containing organic substances of activated sludge, which during prolonged storage in the open air pass into the gaseous phase with a sharp unpleasant odor (for example, carbon disulfide, hydrogen sulfide, etc.).

 The objective of the invention is the creation of a method for the disposal of activated sludge biological treatment plants with stabilization and disinfection or and neutralization of heavy metals using cement and heat treatment and improving the environmental condition of the environment.

The problem is achieved by the method of disposal of activated sludge, including the introduction of activated sludge into the concrete mixture in an amount providing its required mobility, and the addition of lime, so that lime is introduced in an amount of 0.1-0.25 wt. concrete mixture and carry out heat and humidity treatment at a temperature of 80-95 ^o C.

 The introduction of sludge as components in the concrete mixture in such an amount as to ensure its required mobility allows disinfection, stabilization of activated sludge and the binding of heavy metals through the use of cement in the concrete mixture, which ensures high alkalinity due to reaction with water (pH 11-12 and higher). This leads to stabilization and disinfection of activated sludge, as well as to detoxification of activated sludge by adsorption and chemical bonding of heavy metal cations by hydration products with a highly developed specific surface. The inventive method will allow to utilize activated sludge at minimal cost without the organization of special technology, as well as completely eliminate the unpleasant odor. In addition, this allows you to replace in the manufacture of concrete drinking or industrial water, which in modern conditions is becoming scarce, with water contained in activated sludge.

The introduction of lime into the concrete mixture in an amount of 0.1-0.25% by weight of the concrete mixture and the heat and moisture treatment of concrete with a temperature increase of up to 80-95 ^o C provide a more complete disinfection with complete deworming of the sludge. In addition, the introduction of lime in the specified amount eliminates the decrease in concrete strength observed when only activated sludge or lime is added to the concrete mixture in an amount beyond the specified values.

 Stabilization and disinfection of activated sludge and the binding of heavy metals improves the ecological state of the environment and eliminates the possibility of the gradual accumulation of toxic substances in the soil and their transition into the human body.

 The method is as follows.

Active sludge from the secondary settling tanks of biological treatment plants is introduced as components into the concrete mixture (mixing water and additives in the form of biological cells and inorganic impurities) containing crushed stone, sand and cement, which, when interacting with water, provide an alkalinity of pH 11-12 and higher, while activated sludge is taken in such an amount as to provide the required mobility of the concrete mixture. Lime is also introduced into the concrete mixture in an amount of 0.1-0.25 wt. concrete mixture, which corresponds to the amount of 3-7 wt. including dry residue or 3-7 wt. the precipitate at its moisture content of 99.0-99.5% is subjected to concrete mixture with sludge by heat and moisture treatment, raising the temperature to 80-95 ^o C, and continue processing taking into account the given modes.

 Example 1

A concrete mixture of the following composition is prepared per 1 m ³ : cement - 338 kg, sand 465 kg, crushed stone 1219 kg, water 225 l. Three concrete samples with dimensions of 10x10x10 cm (series 1) are made from this mixture. The samples are subjected to heat and humidity treatment according to the regime of (2) + 3 + 6 + 3, respectively, preliminary exposure, temperature rise to 80 ^o C, isometric heating at this temperature, cooling (in hours). Then after 12 hours, the samples were tested to determine the compressive strength.

Samples of series 2, consisting of 3 samples, are prepared from a concrete mixture with the same consumption of cement, sand and gravel. Instead of mixing water, activated sludge from the secondary settling tanks of the Bezlyudovsky biological treatment complex in Kharkov is used. In this case, the dry solids content of activated sludge is previously determined in a known manner by drying at a temperature of 105 ^o C to constant weight. The content of activated sludge was 0.35%. Active sludge was introduced into the concrete mixture in an amount of 226 kg / m ³ . The water content was 225.2 l / m ³ , which provides the same mobility of the concrete mixture as in series 1, and the solids content was 0.8 kg / m ³ .

Concrete samples are prepared with a size of 10x10x10 cm of series 3, 4, 5, 6, 7, 8 with the same composition for the consumption of cement, sand, gravel and activated sludge, as in series 2, and lime is added to this composition in an amount of 0.8 kg / m ³ , 2.4 kg / m ³ , 3.2 kg / m ³ , 4.8 kg / m ³ , 7.2 kg / m ³ , 10.4 kg / m ³ , which is respectively 1, 3 , 4, 6, 9 and 13 wt. hours from the dry residue of activated sludge. Steaming and testing of samples is carried out as in the previous series.

 The test results of concrete samples are shown in Table 1. According to the table, it is clear that series 2 samples containing activated sludge as components of the concrete mixture and not containing lime have an average compressive strength of 10.5 MPa lower than in control series 1 ( 13.4 MPa). This indicates that biological cells of activated sludge adversely affect the strength of concrete.

 Samples of series 5 containing lime in an amount of 4 wt. hours from the dry residue, have a maximum average strength of 15.2 MPa, which is 1.8 MPa higher than the strength of the control samples, i.e. 13% This composition is chosen as a worker.

 Multiple similar tests confirmed that the introduction of lime in the amount of 3-7 wt. hours from the dry residue active or always compensates for the negative effect of the latter on the strength of concrete.

 The test data for samples of heavy concrete series 1, 2 and 5 are given in the conclusion of the Institute of Colloid Chemistry and Water Chemistry named after A.V.Dumansky Academy of Sciences of Ukraine and the table to it.

Example 2. Prepare a concrete mixture of the following composition per 1 m ³ : cement 159 kg, sand 197 kg, expanded clay 868 kg (void P = 0.32), water 145 l. 3 concrete samples with dimensions of 10 x 10 x 10 cm are made from this mixture (series 1). The samples are subjected to heat and humidity treatment according to the regime of (2) + 3 + 6 + 3, respectively, preliminary exposure, temperature rise to 80 ^o C, isothermal heating at this temperature, cooling (in hours). Then after 12 hours, the samples were tested to determine the compressive strength.

Concrete samples of series 2, consisting of 3 samples, are prepared from a concrete mixture with the same cement, sand and expanded clay consumption as in series 1. Instead of mixing water, activated sludge is used from the secondary settling tanks of the Bezlyudovsky Biological Treatment Complex in Kharkov. In this case, the dry solids content of activated sludge is preliminarily determined as in Example 1. The content of activated sludge was 0.54%. Active sludge was introduced into the concrete mixture in an amount of 146 kg / m ³ . The water content was 145.4 l / m ³ , which provides the same mobility of the concrete mixture as in series 1, and the solids content was 0.6 kg / m ³ .

Concrete samples of 10 × 10 × 10 cm in size are prepared in series 3, 4, 5, 6, 7, 8, 9 with the same composition for the consumption of cement, sand, expanded clay and activated sludge, as in series 2, and lime is added to this composition in an amount 0.6 kg / m ³ , 1.2 kg / m ³ , 1.8 kg / m ³ , 2.7 kg / m ³ , 3.6 kg / m ³ , 4.5 kg / m ³ , 5, 4 kg / m ³ , which is respectively 1, 2, 3, 4, 5, 6, 7, 5 and 9 wt. hours from the dry residue of activated sludge. The pairing and testing of the samples is carried out in the same way as the previous series.

 The test results of expanded clay concrete samples are given in table. 2. According to the table. Figure 2 shows that series 2 samples containing activated sludge as components of the concrete mixture and not containing lime have an average compressive strength of 4.6 MPa lower than in control series 1 (5.2 MPa). Samples of a series of 7 containing lime in an amount of 6 wt. hours from the dry residue, have an average strength of 10.0 MPa, which significantly exceeds the strength of the control samples.

 The test data of light concrete samples of series 1, 2 and 7 are given in the conclusion of the Institute of Colloid Chemistry and Water Chemistry named after A.V.Dumansky Academy of Sciences of Ukraine (see table 1 and 2).

 Acid extracts were made from the samples of the series indicated in examples 1 and 2 and tested for the presence of heavy metals by the atomic absorption method (device AA-I).

 Thus, the proposed method allows you to utilize the activated sludge of biological treatment plants by introducing it into the concrete mixture as its component without compromising the strength of concrete. Compared with the prototype, complex stabilization, disinfection and detoxification of activated sludge occur, while the possibility of toxic substances entering the human body is completely eliminated. Environmental pollution is also completely eliminated. An additional effect is the replacement of drinking or industrial water in concrete mixtures, which in modern conditions is scarce and expensive, with wastewater sludge. Transport costs, fuel costs associated with the delivery of activated sludge to sludge cards or as fertilizer to agricultural fields are also reduced. The latter, as a rule, are removed over long distances, far exceeding the distance to the factories of reinforced concrete structures and concrete plants, usually located within the city.

Claims (1)

A method of utilizing activated sludge, including introducing activated sludge into the concrete mixture in an amount providing its required mobility, and adding lime, characterized in that lime is added in an amount of 0.1 - 0.25% of the total weight of the concrete mixture and heat and moisture treatment of the concrete is carried out at a temperature of 80 95 ^o C.

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