KR19990028251A - Process for Treating Residual Activated Sludge - Google Patents

Abstract

The present invention relates to a process for the treatment of sediments formed during biological purification of municipal and industrial wastewater and can be used in various fields of industry, in particular in paper and pulp production. The pre-enriched residual activated sludge is treated with stirring as white mud obtained in the causticization of the green liquor during the sulphate-pulp production process. White mud is used at a ratio of 1: 5-10 to the ratio of remaining activated sludge. The sludge thus treated is preferably dehydrated by filtration at a temperature of 75-104 ° C. Dehydrated precipitates are dried and incinerated. In addition to the purified alkaline hydrolyzate, the ash residue obtained is used in the production process of sulphate-pulp production. This process for the treatment of residual activated sludge enhances the filtration process without the use of expensive chemical reagents, and makes full use of the product obtained in the treatment of sludge as well as the utilization of sulphate-pulp production waste, ie white mud, And to significantly reduce material costs while simplifying the technique.

Description

Process for Treating Residual Activated Sludge

It is known to treat residual activated sludge with a specific reagent and then separate it into concentrated additives and water by filtration or precipitation. In most cases, various ammonium salts (see US Pat. No. 4,240,904, international patent classification C02F 11/14, 1980) and organic compounds (see USSR inventor no. 827424, international patent classification C02F 11 / 14.1981), as well as second chloride An aqueous solution of iron and lime oil (see OIYakovleva et al., "Sewage Treatment", "Lesnaya Promyshlennost", Moscow, 1975, pp. 40-43) is used for this purpose.

Filtration and auxiliary filtration materials, for example inorganic compounds such as chalk, gypsum (see above-mentioned USSR inventories No. 827424), or copolymers of methacrylic acid derivatives with acrylamide (British patent specification No. 1466185, It is also known to process residual activated sludge by separating it into water and thick precipitates by using high molecular organic compounds (see International Patent Classification C02C 3 / 00,1977).

One of the major disadvantages of the above mentioned process is the use of expensive chemical reagents without any practical reproducibility.

The most recent known art describes a process for treating residual activated sludge, including presedimentation and subsequent filtration steps, without the step of treating the reagents. The precipitate formed as a result of dehydration of the residual activated sludge is treated on a filter cloth as an aqueous alkaline solution or a white sulphate liquid. In this case, a highly concentrated alkaline solution of the residual activated sludge described above is obtained, which is then vaporized and fed for incineration (see USSR inventor no. 1038287, International Patent Classification C02F 11/14, 1983).

The main disadvantage of this known process is the low efficiency and high duration of the dewatering process of the precipitate by filtration, which is due to the disadvantageous structure of the precipitate with high specific filtration resistance while retaining water tightly. Moreover, the process requires the use of expensive alkaline reagents (see Yu. N. Nelepin, "Sulfate Pulp Production", "Lesnaya Promyshlennost", Moscow, 1990, p. 531).

The present invention relates to a process for the treatment of sediments formed during biological purification of municipal and industrial wastewater and can be used in various fields of industry, in particular in paper and pulp production.

The present invention has been made to solve the above problems with the known art, and an object of the present invention is to enhance the process for dehydration of the precipitate by filtration, without the use of expensive chemical reagents, sulphate-pulp production wastes. In addition to utilizing at a minimum cost, it is to provide a new process for treating residual activated sludge that allows full utilization of the obtained products (purified alkaline hydrolysates and ash residues).

The above technical result according to the invention is that the white mud versus residual activation is obtained from the pre-enriched residual activated sludge, which is the white mud obtained in the causticization of the green liquor during the sulfate-pulp production process. The ratio of sludge is 1: 5-10, treated with stirring, and then achieved by incineration of dehydrated, dried and dehydrated precipitates by filtration.

This process consists of pre-dehydrated residual activated sludge, white mud obtained during the causticization of the green liquor during the sulphate-pulp production process. It sets it as 10 and differs from a well-known process at the point of processing, stirring.

The white mud used in the process according to the invention for the treatment of residual activated sludge is a sulfate-pulp production waste which is a black suspension having a density of 1.25-1.35 Kg / cyb.dm and having the following chemical composition (% by weight). :

CaCO ₃ - 38.50

NaOH-3.30

Na ₂ CO ₃ - 1.48

H ₂ O-51.85

Other Ingredients-3.02

By regenerating the waste black liquid during the sulfate-pulp process, it is known that the fusion cake (mineral portion of the waste black liquid) is formed with its main component sodium carbonate. Then, the fusion cake is dissolved and the green liquid formed with it is causticized by the addition of calcium oxide to give a dark white liquid and calcium carbonate precipitate, which is white mud. In general, the continued use of white mud requires repeated washings with fresh water using special chemical reagents (see USSR inventors 827424, C02F 11/14, 1981). The need to use fresh water and expensive organic compounds complicates the process considerably and increases costs.

The use of the white mud according to the invention solves two problems at once: on the one hand, the process is enhanced while lowering the cost of the treatment of the residual activated sludge, and on the other hand, the process for the utilization of the white mud. Lower costs and simplify the process.

The process of treating the thickened residual activated sludge during presedimentation of the sediment comprises the complete alkali of the bioorganic part (less than 83% by weight of the dry residue) of the sludge by white mud containing alkali residues. Subsequent to hydrolysis, salts, amino alcohols and many protein derivatives of amino acids are formed. Next, calcium carbonate, which constitutes the main content of the white mud, is present in an amount of 17% by weight on a dry weight basis and, upon vigorous stirring, is homogeneously distributed in the large fibers and solid particles dissolved in the remaining activated sludge. This leads to a change in the adverse structure of the residual activated sludge precipitates, which hold water strongly and have high specific filtration resistance under normal conditions (ie no special reagents are present). Thus, white mud, a sulfate-pulp production waste in the process according to the invention, on the one hand, replaces expensive alkali reagents and, on the other hand, performs the function of an auxiliary filtration material.

This process is carried out in the following manner.

The remaining activated sludge is pre-enriched in radial or vertical ponds. Most preferably, the thickening is carried out until the concentration of residual activated sludge is 13-40 g / l. Immediately after thickening, the remaining activated sludge is fed to the mixer where it is treated with white mud with stirring. White mud is used at a ratio of 1: 5 to 10 with respect to the remaining activated sludge to achieve the maximum efficiency of post-filtering. If the sludge is treated with less white mud than the amount mentioned above, the filtration rate is significantly reduced. It is not technically efficient to use white mud in amounts exceeding the above ratios. Most preferably, stirring is performed at a temperature of 75-104 ° C. It is also possible to use lower temperatures above room temperature, but in this case the treatment process is further delayed. The treatment is carried out until the bioorganic portion of the residual activated sludge is completely dissolved. The resulting mixture, which contains the alkali hydrolyzate, undissolved fibers and solid particles present in the remaining activated sludge, is then homogeneously distributed among the particles of the sludge precipitate together with calcium carbonate as a result of the agitation and vacuum filter Or supplied to a pressure filter to dewater. The purified alkaline hydrolyzate obtained by filtration can be used in the reagent regeneration step during the production cycle of sulfate-pulp production, without subsequent processing. The dehydrated precipitate formed at the filter surface is then heat dried in a drying drum and incinerated in the utilization plant furnace. Ash residues comprising calcium oxide are used in the stage of green liquid causticization during the production cycle of sulphate-pulp production.

After precipitation in the radial pond, 0.75 l of white mud suspension is added to 5 l of an aqueous suspension of residual activated sludge with a concentration of 30 g / l and stirred vigorously at 95 ° C. for 15 minutes. The resulting mixture is fed to a vacuum filter and the precipitate is dewatered. In this case, the filtration rate is set at 40 l / sq.m / min. Purified alkaline hydrolyzate is fed for use in the production cycle of sulphate-pulp production. Dehydrated precipitate formed on the filter surface is removed and heat dried at 850 ° C. and then incinerated. The ash residue obtained is fed to the stage of green liquid causticization.

This process for treating residual activated sludge enhances the filtration process without the use of expensive chemical reagents (using waste from sulphate-pulp production), and utilizes sulphate as well as the utilization of sulphate-pulp waste, ie white mud. Complete utilization of the product obtained in the treatment of water and purified alkaline hydrolyzate) and significantly reduces material costs while simplifying the production process. For comparison, the filtration rate according to the known process is 4 l / sq. m / min. On the other hand, the reduction of the dehydration process time, which is different in the present process, results in a reduction in the energy consumed in the execution.

Claims (3)

The residual activated sludge is pre-riched, dewatered by filtration, the dehydrated precipitate is dewatered and dried, and before the filtration step in the first place, the pre-riched residual activated sludge is green in the sulfate-pulp production process. A process for the treatment of residual activated sludge, which is carried out while stirring with the ratio of white mud to residual activated sludge being 1: 5-10 together with the white mud obtained in the causticization of liquor). The process according to claim 1, wherein the thickening is carried out until the concentration of residual activated sludge is 13-40 g / l. The process according to claim 1 or 2, wherein the white mud treatment is carried out at a temperature between 75-104 ° C.