FI123886B - Method for disinfecting sludge - Google Patents

Abstract

The invention relates to a method for disinfecting sludge, in which method burnt lime CaO is added to the sludge, the sludge mixture is agitated until the pH of the mixture exceeds 11, and peroxide such as peroxyacid, hydrogen peroxide or their mixture is added to the mixture to bind ammonia formed in the agitation step. The invention further relates to a soil amendment and a fertilizer produced by the method.

Description

METHOD FOR DISINFECTING THE LIQUID FIELD OF THE INVENTION

The invention relates to a method for disinfecting slurry and to a soil improvement agent and a fertilizer prepared by the method.

BACKGROUND OF THE INVENTION

Sludge treatment is one of the most expensive wastewater treatment steps. The amount of sludge is 10 large and harmful to health due to the presence of pathogenic microbes. The recycling of nutrients contained in sludges, eg in agriculture, has been possible only for limited technical, economic and hygienic reasons.

When EC legislation came into force, the use of sludge in agriculture virtually ceased in Finland. The rise in fertilizer prices in recent years has restored farmers' interest in 20 sludges as soil improvers, but high hygiene standards have led to the fact that sludges have been mainly landfilled and a small proportion of the sludge has been used in biogas reactors for biogas production.

25 Some installations use the so-called. lime stabilization method for sludge hygiene. In the lime stabilization, either slaked lime (Ca 6) or slaked lime, i.e., calcium carbonate (Ca (OH 2)), is added to the slurry. The pH of the slurry should rise to about 30 to at least 12 and the temperature to 55 ° C for two hours. Lime stabilization is a considerable investment-x £ and expensive.

cd The cost of the process is increased by the degassing required to eliminate ammonia generated during stabilization to avoid odor nuisance.

^ Anaerobic digestion of sludge to produce biogas (CH4) has become more common in medium and large wastewater plants. The cost of this method is also high, although the gas produced is a valuable source of energy for the wastewater plant. However, the plant's sludge must still be hygienized before it can be used 5.

Other treatment methods include aerobic composting and landfilling.

The above methods are expensive, have odor and other environmental hazards, and recovery of sludge is often not possible.

PURPOSE OF THE INVENTION

The object of the invention is to provide a new type of microbiologically efficient and economically advantageous method for disinfecting slurry. In particular, it is an object of the invention to alleviate the above problems.

It is a further object of the invention to provide a soil conditioner and a fertilizer meeting hygiene requirements.

SUMMARY OF THE INVENTION

The process for purifying sludge according to the invention is characterized in what is set forth in claim 1.

The soil conditioner according to the invention is characterized in what is set forth in claim 12. The fertilizer according to the invention is characterized in that set out in claim 13.

The invention is based on research carried out to improve the efficiency of

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A dosage of K 35 of organic peroxy acid such as peracetic acid in combination with non-slaked lime is excellent for hygienizing the sludge and binding the liberated ammonia in the purification of sludge from waste water treatment.

In the application, sludge means sewage sludge from sewage treatment plants, such as activated sludge from plant sludge and from biogas plants, such as digestate residues, and sludges from industrial processes such as the paper industry and the food industry.

In one embodiment of the invention, the dry weight of the slurry 10 is from about 20 to about 40% by weight, usually from about 25 to about 35% by weight. The slurry is mechanically dried, for example, by centrifugation, a screw, a drainage or chamber press, or another suitable mechanical dryer for slurry drying. The slurry is preferably dried by lin-15 coextraction.

The method of the invention disinfects pathogenic microbes such as E.coli and Salmonella from slurry so that the treated slurry meets regulatory requirements. The method also binds a portion of the ammonia released from the treatment to a water soluble nitrogen compound that remains in the treated slurry and thereby improves the nutrient properties of the slurry.

In the process of the invention, slaked lime CaO is added to the slurry and the slurry is stirred until the pH of the slurry mixture is above 11.

Non-slaked lime CaO reacts sensitively with sludge water to form calcium hydroxide.

i-slide: o ™ CaO + H 2 O - Ca (OH) 2 O) 30 This raises the pH of the slurry and the

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the effect is due in part to this increase in pH, since pathogens are unable to live or regulate Lito at high (> 10) pH levels. The reaction is exothermic, which further raises the temperature of the slurry. Increased temperature improves sludge hygiene-

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^ thia. Adding non-slaked lime releases 4 slurries of ammonia as the pH and slurry temperature increase.

Peroxy acid is then added to the slurry to bind the ammonia formed during the mixing step.

The chemical formula of peroxy acid is RCO3H, where R is an organic radical such as saturated or unsaturated, straight chain, branched or cyclic hydrocarbon. Peroxy acid binds ammonia 10 by forming water-soluble ammonium salts with it. Water-soluble ammonium salts of peroxyacids are well suited to plants as a nitrogen source. Peroxy acids are furthermore antibacterial agents. The most common peroxy acids are peracetic acid and peroxynuclear-15 malic acid.

In one embodiment of the invention, peracetic acid is added to the slurry mixture to bind the ammonia formed during the mixing step.

Peracetic acid binds ammonia to form water-soluble ammonium acetate salts with it. Peracetic acid also oxidizes coliforms as well as many other bacteria and unwanted microorganisms such as Salmonella and Legionella and Giardia parasites.

25 Peroxy acid such as peracetic acid also reduces the potential odor of the treated slurry.

The slaked lime is added to the slurry with vigorous stirring. Non-slaked lime is added as a powder. Any 6) cp 30 known mixer used in industrial mixing processes can be used for mixing.

Peroxic acid is added to the slurry mixture in a solution.

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as. The process of the invention can be used

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^ any strength of peroxy acid.

In one embodiment of the invention, 2 to 15% by weight of peracetic acid, preferably 12% by weight of commercial peracetic acid is used.

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The addition of peroxy acid is carried out in such a way that the mixing is as immediate and effective as possible. The addition may be effected, for example, by melting or spraying and onto the surface of the entire slurry mixture. Dosing can be enhanced by mixing.

In one embodiment of the invention, the mixing of CaO and slurry is continued until its pH is above 12.

The temperature of the slurry to be treated at the beginning of the process is usually from 20 to 37 ° C, depending on the origin of the slurry 10. The temperature of the biogas plant effluent sludge, the digestion residue, is about 37 ° C and the temperature of the activated sludge of the water treatment plant is about 20-25 ° C.

In one embodiment of the invention, stirring of the slurry mixture is continued until the temperature has increased from 10 to 30 ° C, preferably from 15 to 20 ° C and most preferably about 15 ° C.

In one embodiment of the invention, the slurry is stirred before the addition of non-slaked lime CaO.

In one embodiment of the invention, the slurry is stirred during and / or after the addition of peroxy acid.

Non-slaked lime CaO is added to the slurry at about 5-20% by weight of the slurry dry matter, preferably about 7-13% by weight, and most preferably about 10% by weight of the dry matter. The amount of non-slaked lime may also be greater or less than 25 depending on the characteristics of the slurry being treated.

Peroxy acid such as peracetic acid is added to a g of slurry of about 0.1 to 0.3% by weight of slurry solids, preferably about 0.15 to 0.2% by weight, and preferably about 0.18 to about 30 ppm. % of dry matter. The amount of peroxy acid may also be greater or less than this depending on the properties of the slurry to be treated.

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In the process of the invention, the pH is maintained at at least 11 until the amount of pathogenic microorganisms is below the maximum levels of regulatory authority. In one embodiment of the method of the invention, the pH is maintained at at least 11 for about 6 to about 1-2 hours. In another embodiment of the invention, the pH is maintained at at least 12 for about 1-2 hours.

In one embodiment of the method, the slurry, such as the dried sewage sludge from the water plant, is passed from a silo to a mixing device, where soda lime and peroxy acid are discharged from their feed tanks. The mixing tank measures pH and temperature with pH and temperature sensors and adjusts 10 slurry purification methods based on measurement results.

In the process of the invention, the addition and mixing of non-slaked lime and peroxy acid takes place either as a continuous process or as a batch process in a mixing tank. The mixing capacity of the mixing tank is sufficient to ensure uniform mixing of non-quenched lime, peracetic acid and slurry to ensure the desired end result.

In the process of the invention, the dosage amounts and the order of delivery of the non-quenched lime and peroxyacetic acid may be varied depending on the plant process and the quality of the slurry being treated.

In one embodiment of the invention, slaked lime and peroxyacid are mixed with the slurry 25 in a stepwise mixing device.

In one embodiment of the invention, peracetic acid is added to the slurry and non-slaked lime powder.

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£ they are fed into peracetic acid treated slurry.

The method of the invention is microbiologically effective. The process according to the invention significantly accelerates and enhances the treatment of sludge in plants. Immediate discharge of sludge from the plant

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saves logistics costs in the area as no intermediate storage is needed. The method-purified sludge does not

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cvj 35 contains harmful microbes and has economic value as a soil conditioner and fertilizer, e.g. because of the soluble nitrogen it contains. Equipment costs 7 are low and monitoring of the hygienization process is easy.

The system according to the method according to the invention is a simple to install, inexpensive and lightweight solution which can be easily installed in a water purification plant either as a continuously operating part.

Further, the process of the invention simultaneously increases the basicity of the slurry, binds part of the untreated slurry to the treated slurry and removes the harmful organic compounds from the slurry.

The soil improver according to the invention is prepared by a slurry purification process according to the invention. The soil improver is prepared by a method of adding non-slaked lime CaO to the slurry, mixing the slurry mixture until the pH of the mixture is above 11, preferably above 12; and adding peroxyacid, preferably peretic acid 20, to the mixture to bind the ammonia formed during the mixing step.

In one embodiment of the invention, stirring of the slurry mixture is continued until the temperature has increased to 10-30 ° C, preferably 15-20 ° C, and most preferably 25 ° C.

The fertilizer according to the invention is prepared by a slurry purification method according to the invention. The linen $ 2 ointment is prepared by a method of adding slaked lime CaO to the slurry, mixing the slurry mixture until the pH of the mixture is greater than 11, preferably greater than 12; and x is added to the mixture peroxy acid, preferably peroxy-

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acid to bind ammonia formed during the mixing step.

(¾ 35) In one embodiment of the invention, stirring of the slurry mixture is continued until the temperature has risen from 8 to 30 ° C, preferably from 15 to 20 ° C, and most preferably about 15 ° C.

The method produces disinfected sludge with microbial concentrations below the maximum levels authorized by the authorities.

The solids content of the slurry increases by about 10% in the treatment, which improves the handling of the slurry as a soil conditioner and fertilizer. After disinfection, the slurry can be taken directly to the field for spreading, or it can be at a time when the slurry is not allowed to be spread on the field, or to be field-coated.

Further, the method of the invention provides a soil improver and a fertilizer which has improved water retention and increases humus. The soil conditioner and fertilizer of the invention increase the pH of the fields, liming the fields and acting as a nitrogen source.

LIST OF FIGURES

Figure 1 shows a flow chart of a method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION Example 1

A method according to an embodiment of the invention is shown in Fig. 1 having a mixing tank (1), a slaked lime dosing tank (2) and a peroxyacid

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dosing tank (3), of which non-slaked lime and dehydrated peracetic acid are metered into the mixing tank by a suitable dosing means such as a pump. A pH sensor and a temperature-x £ temperature sensor are installed in the mixing tank. The sludge cd is fed to the mixing tank from the silo (5). The purified slurry is drained away from the mixing tank

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^ 35 slurry channels (4). The mixing tank (1) provided with an efficient mixer suitable for mixing the slurry may be movable or fixed.

Example 1 tests the purification efficiency of the process of the invention.

5 The sludge used is activated sludge from waste water treatment. The initial slurry temperature is about 25 ° C and the amount is about 10 tons. The sewage sludge may contain a pathogenic microbe e.g. E.coli from about 100,000 to 4,000,000 cfu / kg.

10 The sludge is added to the mixing tank (1) from the silo (5). The sludge is centrifuged to a dry solids content of about 30 wt% before being added to the mixing tank. Non-slaked lime is evenly added to the mixing tank from its dosing tank (2) as a powder while mixing is in progress. Add 300 kg of lime-free lime. The method measures the pH of the slurry mixture using any pH meter suitable for measuring pH. The method further measures the temperature of the slurry mixture by any sensor suitable for measuring the temperature. pH and temperature measurements can be made continuously or at desired intervals. According to the embodiment of the example, measurements were made at one-minute intervals.

The slurry mixture is stirred until the pH of the mixture is above 12 and for about one hour. The temperature of the slurry mixture increased during stirring to about 15 ° C. Thereafter, 200 kg of about 3% by weight of peracetic acid solution from the dosing tank (3) are uniformly injected into the mixing tank on the surface of the slurry to be treated, using separate nozzles σ> cp 30 m.

In an alternative method, the solution of peracetic acid is in a mixing tank.

cc Q_ The slurry mixture is then stirred further

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^ about an hour. The solution and powder volumes are continuously monitored (¾ 35 images) using a balance in the mixing tank.

In the method, the slurry is stirred for a total of about 1-2 hours at a rate of about 10 tons of slurry being treated. The treated slurry is then led directly from the duct (4) to the transport vehicle for removal.

Purified sludge tea according to Example 1 was analyzed for pathogens and other microorganisms as well as nitrogen, phosphorus and heavy metal concentrations for each of the components to be determined by an accredited method. The results are shown in Table 1.

10 __ concentrations in the sample in mg / kg k.a.

Salmonella E.coli <10 cfu / g

Nitrogen, water soluble 3.5 g / kg b.w.

Nitrogen, total weight__ 15 g / kg b.w.

Phosphorus, water soluble 160 mg / kg b.w.

Phosphorus, total length. 2.4 g / kg bw.

Arsenic <5.0 mg / kg b.w.

Cadmium 0.56 mg / kg b.w.

Chromium 20 mg / kg b.w.

Copper__17 mg / kg b.w.

Mercury <0.07 mg / kg b.w.

Nickel 13 mg / kg b.w.

Lead 4.5 mg / kg bw.

Zinc 200 mg / kg b.w.

m annealing loss __74.8% k.a._ δ pH 12

Cvj l_h-- O) o ^ The table shows that the microorganism and heavy metal concentrations do not exceed the limit values for soil and fertilizers set at> 15.

The solids content of the slurry increased by 10%.

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The results clearly show that the quality of the disinfected slurry is excellent and that the method of the invention is effective.

The invention is not limited to the above-described embodiment examples only, but many modifications are possible within the scope of the inventive idea defined by the claims.

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Claims (13)

A method for disinfecting sludge characterized by the addition of slaked lime CaO to the sludge; The slurry mixture is mixed until the pH of the mixture exceeds 11; and peroxyacid is added to the mixture to bind the ammonia that arises in the mixing stage. A process according to claim 1, characterized in that the sludge is sewage sludge from wastewater treatment plants or sewage sludge from biogas plants. Process according to Claim 1 or 2, characterized in that the dry weight of the sludge is 20 - 40 wt%, preferably 25 - 35 wt%. 15 Process according to any one of claims 1 to 3, characterized in that the peroxyacid is peracetic acid. Process according to any one of claims 14, characterized in that the sludge mixture 20 is mixed until the pH of the mixture exceeds 12. Process according to any one of claims 15, characterized in that the sludge mixture is mixed until the temperature of the mixture has risen 10 - 30 ° C, preferably 15 - 20 ° C, most preferably about 15 ° C. 25 Process according to any of claims 1-6, characterized in that the sludge is mixed into unleached lime CaO. O Process according to any of claims 1 to 7, characterized in that the sludge mixture is mixed in conjunction with the administration of peroxyacid and / or after the application. x A process according to any one of claims 1 cd -8, characterized in that unleached lime CaO is supplied 5-20 wt%, preferably 7-13 wt%, most preferably about 10 wt% of the sludge. dry substance. 00 Process according to any one of claims 1 to 9, characterized in that peracetic acid is applied to 0.1 - 0.3 wt%, preferably 0.15 - 0.2 wt%, most preferably about 0.18 wt. % of the sludge dry matter. Process according to any one of claims 1 to 10, characterized in that unleached lime and peroxyacid are mixed stepwise with the sludge. 12. Soil improvement agents prepared by a method according to any of claims 1-11. Fertilizer, prepared by a method according to any of claims 1-11. 10 co δ c \ j σ> cp CD X X Q. CD LO C \ J δ CNJ