CS228403B1 - Method of concentration biologic,particularly activated sludge - Google Patents

Abstract

Activated sludge is biologically converted into a form in which it is readily concentrated by conventional means. The method of concentration comprises adding to the sludge oxygen-containing nitrogen compounds, most suitably nitrates or nitrites, in an amount of 50 to 1000 g/m<3> under anaerobic conditions so as to form sludge flakes with an altered physical structure, formed by enzyme activity, which are directly concentrated.

Description

It is an object of the present invention to provide a method of thickening biological, especially activated sludge, by altering the physical structure of the sludge that occurs in said process

These sludges are formed during waste water treatment, so-called biological filtration and biological activation. When. These purification processes are assisted in the waste water by a variety of microorganisms present here that utilize the dissolved impurities to produce biomass. (The waste water is thus freed from dissolved substances and the purified is discharged into streams. Separated microorganisms form biological sludge.

This sludge must either be disposed of or used for further processing.

To dispose of sludge it is used classical methods based on their use. It is mainly liquidation on so-called sludge fields and sludge lagoons, where water is soaked and evaporated and sludge is discharged under combined aerobic and anaerobic conditions. This method requires considerable areas and degrades the environment in the area. A better way to dispose of with respect to the environment is to shed off anaerobic rats.

This is, however, expensive to invest because it requires a pressurized closed pressure chamber. Here, deep destruction occurs, in which the sludge is almost mineralized and large losses and degradation of organic matter occur through the consistent development of gases such as methane, carbon dioxide, hydrogen, hydrogen sulphide, ammonia, nitrogen, etc. In both methods, the sludge can only be used for fertilization. However, it is possible to obtain energy in the form of flammable gases (methane, hydrogen sulphide, hydrogen).

Since the sludge biomass contains about 40% protein in the dry matter, there is an effort to use some kinds of sludge for feeding purposes. However, for this purpose the sludge biomass must be dried and this requires the sludge to be drained as much as possible before drying. However, the dewatering and thickening of biological sludge is a very difficult issue well known in the art. This is due to the fact that the activated sludge has an unsuitable physical structure manifested by attracting large amounts of hardly removable water, which is very voluminous.

The biological sludge obtained by sedimentation only has a dry matter content of only about 1%. For its concentration, the so-called pressure flotation is used, which consists in injecting finely dispersed compressed air into the sludge suspension whose bubbles carry the sludge flakes to the surface. The floated sludge thus reaches a maximum of 5% dry matter. Thickening is only due to a sharper separation of the liquid phase from the slurry, but the physical structure remains unchanged. This process requires considerable investment and energy costs associated with obtaining compressed air.

The biomass separated in this way is then further concentrated on decanter centrifuges, but the achieved concentration is up to 10% of dry matter relative to the unchanged physical structure. In order to increase the blasting effect, the physical structure of the treated sludge is improved by physicochemical methods such as the application of aluminum or iron salts, polyelectrolytes, etc., which change the electrical charge of the sludge micelle and the hydration coating, surface of sludge particles. The change in physical structure achieved in this way allows a good concentration to be achieved on a decanter centrifuge and is close to that achieved by centrifugation of unicellular microorganisms such as yeast.

This process also requires considerable costs, especially for chemicals - polyelectrolytes - the cost of which is constantly increasing. These disadvantages are overcome by the process according to the invention, in which the change in the physical structure of the sludge is achieved in an inexpensive manner by utilizing the enzymatic activity of the microorganisms found in the biological, particularly activated sludge.

The unsuitable physical structure of the sludge is due to the already mentioned hydration coating of microorganisms and extracellular water inside the sludge micelle also because a number of sludge-forming microorganisms form slimy capsules of polysecharide nature, which substances are present directly in the cell. The mucilages have a high water-binding capacity and are essentially the main cause of poor sludge drainage. The efforts made so far to improve the physical structure of the sludge did not take this into account, and the methods used were therefore not very effective.

The change of the physical structure of sludge by enzymatic processes is only attempted to be solved by Czechoslovakia. No. 133,046 A method of thickening organic sludge (Berta, Fechtner, Hanzlíček, Verner, Veselý) and the Czech patent no. No. 147,346 A method of reducing the liquid phase content of organic sludge (Berta, Dyr, Hanzlíček, Verner, Veselý). According to these methods, however, focused primarily on the so-called biological flotation, a significantly higher concentration of the flotated solid phase of the sludge suspension and energy savings compared to the so-called pressure flotation is achieved by controlled fermentation using pre-propagated Pure or sludge suspension of selected cultures. denitrifying bacteria and with or without the addition of nitrate ions.

These processes are considerably less expensive, but are time-consuming, two-stage handling required, and the volumes of the tanks in which the inoculum preparation and the biological flotation are performed.

The method of thickening the biological, particularly activated sludge according to the invention solves some of these drawbacks.

It is based on the fact that the oxygen-containing nitrogen compounds 8 are preferably added to the sludge, preferably nitrates and / or nitrites, in an amount of 50 to 2,000 g / πΡ at a temperature of 5 to 45 ° C at a pH of 5 to 8.5. up to 2 hours by enzymatic action The resulting sludge flakes with altered physical structure directly concentrate the centrifugation.

Unlike the cited Czechoslovak. patents process takes place without any additional microorganisms, so there is no long-term fermentation lasting several tens of hours, nor biological flotation, but only short-term intense enzymatic activity of already present microorganism cells in the sludge, due to the addition of relatively large amounts of oxygen compounds nitrogen.

Said process to obtain sludge flakes with altered physical structure allows direct thickening of the original sludge from 1 to 2% dry matter to 14 to 16% dry matter by means of a decanting centrifuge (without flotation).

It has been found that a very large variety of microorganisms present in the sludge is able to change the physical structure of the sludge to a desired degree in a very short time. Measuring the dissolved oxygen was found that in the layer of sludge suspension in the near zone of the water above it was a "fast reduce dissolved oxygen to form & RI anaerobic environment postačuuící for moderate activity in the sludge frequently represented denitrification bakkteií _e

Furthermore, it has been found that, with the intense activity of these nitrate reductants, their enzymatic equipment makes it possible to use as a carbon source which, in addition to the nitrate compounds, a condition of the aforementioned mucilaginous capsule and hydrolytically disrupts them.

In addition, part of these nitrate reductants, particularly Clootridiaceae, produce exogenous proteolytic enzymes disrupting the cell membrane of the sludge. The overall result of these enzymatic processes is an initial, very mild degree of decomposition, such as occurs in the decontamination process, sufficient to change the physical structure, but without any loss and degradation of the organic sludge matter.

The creation of optimal conditions for inducing spontaneous intense citrate-inducing activity to achieve the desired effect, which have been precisely determined, consists solely in ensuring sufficient addition of nitrates and adhering to anaerobic or at least aikioeroeroid conditions, temperature and pH.

_T as _the nitrate or nitrite compounds may suitably pouuít sodium nitrate, potassium and especially ammonium and calcium, which pouužvají the farmers as fertilizers seacoast and are inexpensive я highly soluble. · Depending on the nature and composition of the sludge, they are applied in an amount of 40 to 2,000 g of NO2 per 1 m · slurry as a 10 to 20% solution. The optimum pH is between 7.0 and 8.5. In terms of temperature, the process works well in the temperature range of 15 to 37 ° C and must not be lower than 5 ° C. Annarobic conditions are defined by the concentration of dissolved oxygen of max. 0.1 mg O2 per liter of slurry.

This greatly simplifies the entire process, reduces it enormously - in a matter of minutes - and greatly reduces investment and operational costs. The fact that the flotation effect is unnecessary in this process allows the process to be carried out by a continuous process in a relatively small volume. reactor. The amount of nitrate added that is necessary for the good running of the process depends on the nature, composition and properties of the biological sludge being treated. In general, the optimum and economical addition can be determined such that the NO content in the separated sludge water after the process is not greater than the original content in the liquid phase of the treated slurry.

The following is an example of a method for the thickening of biological sludge according to the invention.

Ex 1 and 'dl

1 ° К suspension ^{Pla b} y ^t he ^s ECCL ivovarrébo ^ and ^the aluminum containing ⁸⁰ kg sus ovanýc ^^ ^ ^ solutes are added 3000 g of technical calcium nitrate · in the form of a 20% solution. The mixture is centrifuged for 10 to 15 seconds and centrifuged after 15 minutes on a decanter centrifuge. 77 kg of slurry is obtained, which represents 96.25% of the original min. suspended solids, of a dry matter content of.

Example 2

The procedure is the same as in Example 1, but for 1 000 1 of sludge suspension containing 0.8% suspended suspended solids, 1 000 1 of treated sludge suspension is continuously admixed per hour with 1.5 1 of a 20% technical calcium nitrate solution. stirring at the inlet of the continuous reactor. The remaining compartment of the reactor is without stirring. From the reactor, 1,001.5 l of sludge with changed physical structure flows out per hour and is continuously centrifuged on a decanter centrifuge. 56 kg / h of a slurry concentrate with a dry matter content of 14% are obtained.

Claims (1)

A process for the concentration of biological active sludges, characterized in that oxygen-containing nitrogen compounds, preferably nitrates or nitrites, are added to the sludge in an amount of 50 to 2000 g / m @ 2 at a temperature of 5 to 45 ° C at a pH of 5 to 8.5. after 15 minutes to 2 hours, the resulting sludge flakes with altered physical structure directly concentrate by centrifugation.