GB1582017A - Purification of liquid manure - Google Patents

Description

(54) PURIFICATION OF LIQUID MANURE (71) We, TATABANYAI SZEN BANYAK, a Hungarian body corporate of Tatabanya, Hungary do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a process for purifying liquid manure with a high content or organic substances which accrues when keeping cattle in large stables.

Straw is either not used at all or very seldom in modern large stables for keeping cattle. The accruing excrements and the urine together with other irrigation water and the water used for cleaning are collected in manure channels beneath the stables. The concentration of the liquid manure obtained in this manner will in the first instance depend on the volume of water used to remove the manure, but will, however exceed 2% in a large number of stables. The degree of pollution of this liquid manure is 50-100 times as high as in municipal sewage.

Such concentrated liquid manure has hitherto been utilised mainly as water for irrigation in farming; however, this goes hand in hand with a large number of problems, and for that reason the cleaning of the liquid manure accruing in cattle breeding stations has also become more prominent in recent years.

US Patent 3 745 113 describes a biological purification process for purifying liquid manure with more than 1% content of organic substances. In this process the minimum temperature of 42"C necessary for the mesophile thermophilic microorganisms will set in simultaneously after the appropriate waiting period. The process is only suitable in the case of a multi-stage biological purification process for the production of water of a given quality. The sludge is separated by precipitation from the partially purified water between individually aerated basins for biological purification.

Methods for treating the accrued liquid manure resulting from keeping livestock have been summarised in WATER POL LUTION CONTROL (1971/4).

Among the various methods of reconditioning, reference is also made to the aerobic reconditioning of the liquid manure washed out of stables into aerated activated sludge basins, pools or oxidation pits. The drained water is used for irrigating tilled land.

According to the variants described in the said publication the water which is intermittently extracted from the anaerobic basin is subjected to an aerobic after-treatment. In certain cases the canal system running underneath the stables is designed in the form of oxidation pits. The system operates as an overflow system without phase separation. The necessary dwell period can be several months.

US Patent 3 773 659 describes a biological method of purification for purifying sewage with a high content of organic substances, in which enzymes of bacteriological origin are introduced into the biological stage of the purification system in measured quantities in a special system operating under controlled conditions. The enzymes produced in a separate process are separated out of the fermented liquor after the addition of chemical coagulants. The reaction proceeds over a large surface area in the film phase, thereby requiring a suitable installation.

US Patent 3 763 038 proposes a combined chemical-biological purification process for purifying sewage containing organic substances. Salts of trivalent iron or salts of divalent iron together with an oxidising agent are used as the coagulating chemicals in the first stage, followed, if necessary, by ammonium sulphate and lime, with the sludge being removed from the water by precipitation after the coagulation. Part of the sludge is recirculated where necessary. The purified water is then fed into a biological purification plant with activated sludge, clarification agents again being added at the same time. The clarification agents used in this stage are iron salts, which are combined with an oxidising agent if necessary. The purified water is separated by precipitating the sludge.

Disadvantages of the processes described can be summarised as follows: 1. The pollution of the biologically purified water is still always high and the degree of purification is not sufficient, i.e. the quality of the purified water does not satisfy the stipulations laid down in the relevant water board specifications. Sufficiently pure water can only be achieved by multi-stage biological purification. The addition of enzyme manufactured under sterile conditions only complicates the issue even more with a process operating with a biological purification stage, which in addition causes the costs of the process to rise significantly.

2. The biological degradation proceeds slowly as the quantity of solid organic substances is high, and this means that such purification systems require a long dwell period, so that the investment and operating costs increase sharply.

3. The complex chemical-biological processes are only suitable for the purification of liquid manure with a relatively low content of dry substance.

The object of the present invention is to provide a new process in order to eliminate the shortcomings of the known processes, which can be used in different systems for large-scale cattle breeding and which is based on the use of only a small amount of flushing water to remove manure from the stables in mondern units.

The process according to the invention has been successfully proved in practice to be independent of the degree of pollution of the accruing liquid manure, and its efficiency is already very significant when the liquid manure discharged from the stable has a dry substance content of approximately 1.8%.

The invention thus provides a process for purifying liquid manure with a high content or organic materials which accumulates when keeping livestock in large stables, in which the liquid manure is homogenised under aerobic conditions without phase separation in a first stage, the homogenised liquid manure is then treated with chemical coagulants, the liquid and solid phases are separated on a pressure belt filter, the liquid phase is purified in a biological active sludge purification plant, the biologically purified filter water is subjected to a chemical postpurification with limc after removal of the activated sludge, the precipitated organic materials are separated from the purified water in a settling tank, and the purified water is then neutralised with carbon dioxide or by storage and the resulting precipitate separated therefrom in a settling tank.

An example of the process of the invention will now be described in further detail with reference to the drawing.

The liquid manure arriving at the pumping station (1) is conveyed to a homogeniser tank (2) by means of a reduction pump, where the liquid manure is aerated, held in suspension and homogenised. Aluminium sulphate and an anion active polyelectrolyte are then added as coagulating agents.

The crystalline aluminium sulphate is dissolved in a separate solvent vessel and the solution from the metering vessel (3) added by means of a metering pump. The anion active polyelectrolyte is dissolved in tap water at a pressure of 3 atm by means of a water jet pump, the solution then being added from the metering vessel (4) to the liquid manure leaving the homogeniser tank.

The dry substance content of liquid manure originating in stables amounts to 1.8-8%.

0.4-1.0 Kg aluminium sulphate and 25-50 g polyelectrolyte are added per cubic metre of the liquid manure passing to the filter.

The liquid manure leaving the homogeniser tank (2) is drained on the pressure belt filter (5) after the addition of the chemicals.

The filter material of the pressure belt filter is continuously washed with water at a pressure of 3-4 atm.

The filter water coming from the pressure belt filter (5) is purified in an aerated active sludge tank (6). The introduction of the air and continuous stirring is effected by means of a rotor with a vertical axis. The necessary dwell time is 20 - 30 hours, depending on the constitution of the filter water, an active sludge concentration of 6 - 10 g/l being used, with the sludge recirculated at 150 - 300%.

The activated sludge is separated in the gravity settling tank (7) and a part of the sludge is recirculated to the tank (6) by means of a pump.

The chemical post-purification of the biological purified filter water is provided from the dosage vessel (8) by supplying as much calcium hydroxide in the form of lime solution that the pH value of the clarified water is between 10 and 11.5. The lime is mixed with the biologically cleaned water in the chemical mixing vessel (9), while the organic materials and their aggregates precipitate in the flocculator (10). Precipitated organic materials are separated from the purified water in the settling tank (11).

The pH value of the settled water is between 10 and 11.5. This high pH value is neutralised in the neutralising unit (12) by the introduction of CO2 or by storing for 2-4 days.

The sludge which separates on neutralisation is removed from the drained water in the settling tank (13).

The sludge separated by biological purification and the sludges produced by the chemical post-treatment and by the neutralisation are fed back to the pumping station (1).

The process according to the invention is based on the following concepts: 1. In most cases, the disposal of the accrued liquid manure resulting from keeping livestock is a problem for the farming industry.

This has resulted in more and more methods of disposal of manure being adopted in recent years, with the object of the reduction in the quantity of liquid manure. Hence, the concentration of the liquid manure will increase of necessity.

In the processes for treating liquid manure known hitherto, it has only been possible for the mechanical biological treatment of liquid manure of such high concentration to be successful with exceptionally long dwell periods, and furthermore, the water discharged from the plant still has a high concentration of impurities.

Aluminium sulphate and anion active polyelectrolyte were added as conditioning chemicals before separating the sold and liquid phases. Research has shown that, contrary to expectation, when using the above chemical combination the amount of chemicals necessary for the conditioning does not increase proportionally to the dry content in the liquid manure, but the volume of chemicals necessary and the water content of the compressed sludge are reduced considerably due to the fibrous content of the liquid manure. Hence, these fibrous materials are not separated at the start of the purification process according to the invention, although it is very simple to remove them mechanically.

2. The dissolved and colloidal organic substance content is also very high after the biological purification. As a result of the digestive system of the animals and the feedstock supplied, a significant part of the organic compounds content will be nitrogenous, proteinaceous materials. The water emerging from the biological purification stage also still contains biologically nondegradable metabolic products of the microorganisms which are produced during the biological purification of the sewage.

The simplest method of removing these impurities is by coagulating the protein followed by adsorption. This double objective can be achieved by the addition of lime, if a minimum flocculation period of 25 minutes is observed after mixing in the lime to coagulate the protein.

As the usability of the discharged water after purification will not only be determined by the impurities, which can be measured by chemical methods, but also to a large extent on the basis of its bacteria content, a considerably higher pH value is maintained than that (10-11.5) necessary for coagulating the protein during the post-purification with lime, and the above-mentioned dwell period ensures that the total germ index of the discharged water lies between 102 and 103 germs/ml. This discharging water, from the veterinary hygiene point of view, will also be suitable for feeding back to the animal stables as flushing water, so that a considerable amount of clean water is saved. Furthermore, the small content of microorganisms makes it possible for the purified water to be utilised for irrigation or arable farm land after neutralisation without any diluting water, or if necessary to be discharged directly in the drains.

The most important advantageous of the process according to the invention can be summarised as follows: 1. Using the process according to the invention for purifying liquid manure it is possible to remove the solids at low cost in terms of energy and chemicals and to reduce the water content of the solid material to such a low level that the natural composting process of the material willl start by itself when stored in piles to produce a fermented manure for farming comparable with natural stable manure.

Because of the relatively small amount of pollution accruing in the liquid phase during the phase separation, it is possible to produce a liquid phase containing only a small amount of microorganisms in the purification steps, and which can be used for irrigating arable farm land without the addition of diluting water or which can be discharged into drains.

2. Compared with the processes known hitherto, the process according to the invention has the distinct advantage that the liquid manure from the stables with a minimum amount of water, and whose content in organic materials is high (1.8 - 8 O/o), produces a quality of water which satisfies the exceptionally stringent requirements to which it is subjected at present. Furthermore, it is possible to construct the purification equipment used in the process from the same components as those used in municipal water purification plants, i.e. it is not be necessary to manufacture equipment which differs from that conventionally used.

3. The high content of organic materials in the liquid manure is reduced to approximately 2-5 % of the original proportion after the biological purification; however, the remaining chemical oxygen requirement is still always very high. The organic material content is reduced still further by chemical post-purification before the water is discharged into the drains, while the removal of germs in the liquid phase is carried out simultaneously at this stage without any extra cost.

4. In the process according to the inven tion, it is possible to feed the sludge accruing during the post-purification of the liquid phase, after removing the solid phase, back to the start of the process, which means that the process will only produce two end products in this way: the purified water and the compressed sludge.

The process according to the invention will be illustrated with reference to the following specific examples.

When cleaning 100 parts of liquid livestock manure (25-30 g/l KOI, 12-15 g/l BOI5, dry substance content 25-30 g/l), 20-25 parts of sludge resulting from the following steps recycled. This quantity of sludge is continuously added to the 100 parts of liquid manure, followed by the addition of 0.4 - 1.0 kg Al2 (SO4)3 and 25-50 g of anion active polyelectrolyte per m3. The liquid manure conditioned in this manner is drained on a pressure belt filter. This produces 20-25 parts of compressed sludge with a dry substance content of 14-15%. The approximately 100 parts of filtered water accumulating after the pressing process will have the following parameters: KOI = 3.5-4 g/l, BOI5 = 1.6-2 g/l, suspended matter 1.5-2 g/l.

Approximately 15-17 parts of biological sludge dry substance content: 9-11 g/l) from the settling tank for biologically purifying active sludge is fed back into the liquid manure. The water accumulating after biological purification has a suspended matter content of 0.3 - 0.5 g/l, its volume amounts to 83-85 parts;KOI = 0.7-0.9g/l,BOI5 = 0.15-0.25 g/l.

This water is mixed with 0.8-1.5 kg of Ca(OH)2 per m3. After separation of the sludge formed in a phase separator, 5-7 parts of sludge with a dry substance content of 30-50 g/l and 78-80 parts of water is obtained with the following characteristics: KOI = 0.3 - 0.4 g/l, BOI5 = 0.04-0.06 g/l, suspensded matter content 0.05-0.1 g/l, pH = 11-11.5. The sludge is continuously recirculated into the automatically supplied liquid manure and the discharging water neutralised by injecting 0.15-0.2 kg/m3 of CO2 up to a pH value of 8. The resulting accumulation of 0.5-1 parts of sludge is separated in a gravity separation plant and fed back to the liquid manure. The output of purified water has the following characteristics: KOI = 0.3 - 0.4 g/l, BOI5 = 0.04 - 0.06 g/l, suspended matter 0.05 - 0.1 g/l, pH = 7.5-8, total germ index 102-103 germs/ml.

The water can be used for irrigation without any restriction or if necessary discharged directly into the'drains.

KOI = chemical oxygen requirement BOl5 = biological oxygen requirement at 50C WHAT WE CLAIM IS: 1. A process for purifying liquid manure with a high content or organic materials which accumulates when keeping livestock in large stables, in which the liquid manure is homogenised under aerobic conditions without phase separation in a first stage, the homogenised liquid manure is then treated with chemical coagulants, the liquid and solid phases are separated on a pressure belt filter, the liquid phase is purified in a biological active sludge purification plant, the biologically purified filter water is subjected to a chemical post-purification with lime after removal of the activated sludge, the precipitated organic materials are separated from the purified water in a settling tank, and the purified water is then neutralised with carbon dioxide or by storage and the resulting precipitate separated therefrom in a settling tank.

2. A process as claimed in claim 1 in which aluminium sulphate and an anion active electrolyte is added as coagulating agent before the filtration.

3. A process as claimed in claim 2 in which 0.4-1.0 kg of aluminium sulphate and 25-50 g of anion active electrolyte are used per m3 of liquid manure reaching the filter.

4. A process as claimed in any one of the preceding claims in which the lime is added so as to bring the pH of the filtered water to 10-11.5.

5. A process as claimed in claim 4 in which the pH value of 10-11.5 is sustained for minimum of 25 minutes.

6. A process as claimed in any one of the preceding claims in which the water discharged from the chemical post-purification is neutralised by the introduction of CO2.

7. A process as claimed in any one of claims 1 to 5 in which the water is discharged from the chemical post-purification is neutralised by storage for 2-4 days.

8. A process for the purification of liquid manure substantially as herein described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. tion, it is possible to feed the sludge accruing during the post-purification of the liquid phase, after removing the solid phase, back to the start of the process, which means that the process will only produce two end products in this way: the purified water and the compressed sludge. The process according to the invention will be illustrated with reference to the following specific examples. When cleaning 100 parts of liquid livestock manure (25-30 g/l KOI, 12-15 g/l BOI5, dry substance content 25-30 g/l), 20-25 parts of sludge resulting from the following steps recycled. This quantity of sludge is continuously added to the 100 parts of liquid manure, followed by the addition of 0.4 - 1.0 kg Al2 (SO4)3 and 25-50 g of anion active polyelectrolyte per m3. The liquid manure conditioned in this manner is drained on a pressure belt filter. This produces 20-25 parts of compressed sludge with a dry substance content of 14-15%. The approximately 100 parts of filtered water accumulating after the pressing process will have the following parameters: KOI = 3.5-4 g/l, BOI5 = 1.6-2 g/l, suspended matter 1.5-2 g/l. Approximately 15-17 parts of biological sludge dry substance content: 9-11 g/l) from the settling tank for biologically purifying active sludge is fed back into the liquid manure. The water accumulating after biological purification has a suspended matter content of 0.3 - 0.5 g/l, its volume amounts to 83-85 parts;KOI = 0.7-0.9g/l,BOI5 = 0.15-0.25 g/l. This water is mixed with 0.8-1.5 kg of Ca(OH)2 per m3. After separation of the sludge formed in a phase separator, 5-7 parts of sludge with a dry substance content of 30-50 g/l and 78-80 parts of water is obtained with the following characteristics: KOI = 0.3 - 0.4 g/l, BOI5 = 0.04-0.06 g/l, suspensded matter content 0.05-0.1 g/l, pH = 11-11.5. The sludge is continuously recirculated into the automatically supplied liquid manure and the discharging water neutralised by injecting 0.15-0.2 kg/m3 of CO2 up to a pH value of 8. The resulting accumulation of 0.5-1 parts of sludge is separated in a gravity separation plant and fed back to the liquid manure. The output of purified water has the following characteristics: KOI = 0.3 - 0.4 g/l, BOI5 = 0.04 - 0.06 g/l, suspended matter 0.05 - 0.1 g/l, pH = 7.5-8, total germ index 102-103 germs/ml. The water can be used for irrigation without any restriction or if necessary discharged directly into the'drains. KOI = chemical oxygen requirement BOl5 = biological oxygen requirement at 50C WHAT WE CLAIM IS:

1. A process for purifying liquid manure with a high content or organic materials which accumulates when keeping livestock in large stables, in which the liquid manure is homogenised under aerobic conditions without phase separation in a first stage, the homogenised liquid manure is then treated with chemical coagulants, the liquid and solid phases are separated on a pressure belt filter, the liquid phase is purified in a biological active sludge purification plant, the biologically purified filter water is subjected to a chemical post-purification with lime after removal of the activated sludge, the precipitated organic materials are separated from the purified water in a settling tank, and the purified water is then neutralised with carbon dioxide or by storage and the resulting precipitate separated therefrom in a settling tank.

2. A process as claimed in claim 1 in which aluminium sulphate and an anion active electrolyte is added as coagulating agent before the filtration.

3. A process as claimed in claim 2 in which 0.4-1.0 kg of aluminium sulphate and 25-50 g of anion active electrolyte are used per m3 of liquid manure reaching the filter.

4. A process as claimed in any one of the preceding claims in which the lime is added so as to bring the pH of the filtered water to 10-11.5.

5. A process as claimed in claim 4 in which the pH value of 10-11.5 is sustained for minimum of 25 minutes.

6. A process as claimed in any one of the preceding claims in which the water discharged from the chemical post-purification is neutralised by the introduction of CO2.

7. A process as claimed in any one of claims 1 to 5 in which the water is discharged from the chemical post-purification is neutralised by storage for 2-4 days.

8. A process for the purification of liquid manure substantially as herein described with reference to the accompanying drawing.