METHOD OF PREPARING SOIL CONDITIONER, AND APPARATUS USED IN THE METHOD

Abstract: The invention relates to a method of preparing a soil conditioner by supplying air to a substantially sealed space containing a mixture of undecomposed plant-originating or animal-originating organic substance and peat, the temperature in the space rising to between 70 and 75 DEG C. The supply of air to the mixture is continued so as to keep the temperature above 70 DEG C for about 24 hours, whereupon the mixture is dried by lowering the pressure above it. The invention also relates to an apparatus usable in the method, comprising one or more reactors, one or more fans, one or more exhausters, and means for measuring temperature and air pressure and for adjusting airflow, wherein a reactor base comprises punched ventilating pipes embedded in a floor 1 to 5 mm above a casting surface.

Description: METHOD OF PREPARING SOIL CONDITIONER, AND APPARATUS USED IN THE METHOD BACKGROUND OF THE INVENTION The invention relates to a method of preparing a soil conditioner by supplying air into a substantially sealed space containing a mixture of plant- originating or animal-originating organic substance and peat, the mixture having about 70% moisture, the temperature in the space rising to between 70 and 75°C. The invention also relates to an apparatus usable in the method. The 1990's witnessed an increasing need for a more natural pro- duction of plants, including improvement of the soil. Fields have typically been spread with chemical fertilizers, liquid manure and composted waste. However, the problem in fertilizing agricultural land with conventional chemical fertilizers or liquid manure is the usability of nutrients and their leakage from the soil to waterways, where they cause eutrophication. Known composting methods and apparatuses usually provide an initial compost within some days or weeks, after which a post-composting step of the duration of weeks or even months is still needed to obtain a product fulfilling quality requirements. Finnish Patent Application 962 431 , for example, discloses a weight-hopper composting device comprising composting modules arranged on a supporting base. Air is supplied to the composting device through the material to be composted having a diminished air pressure. The composting temperature is between 55 and 60°C. Odours (ammonia) are eliminated from the exhaust gas by means of a bio filter. The initial 10 to 14- day composting is succeeded by an about 3-month post-composting in heaps. EP-A 633 235 teaches a sealed reactor container having an air- permeable bottom, under which ventilating pipes are arranged. The composting apparatus has a sealed gas circulation and oxygen is added to the gas to be applied to the mass. The water evaporating from the mass is compressed and cooled by means of condensation in a heat exchanger, and the exhaust air containing carbon monoxide is returned to the reactor. When the sealed apparatus is opened, the gas therein is purified before emission to the atmosphere. DE 38 30 289 discloses an apparatus and method for composting mainly liquid material. The reactor vessel is a lying cylinder having a double wall structure. The composting reaction takes place at ambient temperature. The device is closed air-tightly and the pressure of the compost is lowered below the partial pressure of the water therein in order to dry the product. Detrimental microbes are also destroyed by means of vacuum, not heat. Dis- chargeable gases are filtered with a bio filter and disinfected by UV radiation. DE-A 195 13 701 teaches a sealed aerating reactor having a screen base. The essential idea of the method described in the publication is the alternation of overpressure and underpressure at intervals by alternating between gas supply and gas discharge. Known composting methods require a complex and expensive equipment. The progress and conditions of the reaction have to be followed, requiring either an expensive apparatus or human labour. The gas discharged from the reactions needs purification. BRIEF DESCRIPTION OF THE INVENTION The object of the invention is to provide a method of preparing a soil conditioner by means of biological decomposition, and an apparatus to be used in the method so as to offer an environmentally friendly and fast composting method and apparatus that require little human labour and whose material costs and operating costs are low, and the obtained product well pre- servable, easily usable, effective and easy to store/transport. An inexpensive price and adjustable capacity allow small waste treatment plants to be grounded close to the origin of the waste. The product obtained is easy to store and transport to the place of use, which may located far away. The invention thus relates to a method of preparing a soil conditioner by supplying air to a substantially sealed space containing a mixture of an undecomposed plant-originating or animal-originating substance and peat, the mixture having about 70% moisture, the temperature in the space rising to between 70 and 75°C. The method of the invention is characterized by continuing the supply of air to the mixture to keep the temperature above 70°C for about 24 hours, and lowering the pressure above the mixture by at least about 10 to 500 Pa until the moisture of the mixture is at most 50% by weight. The invention also relates to an apparatus usable in the method and comprising one or more reactor composting devices, one or more fans, one or more exhausters, and means for measuring temperature and air pres- sure and for adjusting airflow. The apparatus of the invention is characterized in that a reactor base comprises punched ventilating pipes embedded in a floor, the distance between holes being between 50 and 300 mm, 1 to 5 mm above a casting surface. The invention also relates to a soil conditioner prepared by the in- vention and the use thereof. A presentable product refers to a soil conditioner containing active mycocelial filaments. Its moisture is preferably below about 50% (bulk product) or even below 10% (bagged, briquette-form product). In a dry product, the mycocelial filaments are in a state of dormancy. Under long-term storage, a low humidity contributes to the retention of nitrogen in the mass. In this context, active mycocelial filaments refer to filaments (myce- lia) that decompose organic substances and promote the dissolution of nutrients and, consequently, their transfer to the use of the plants, under the decomposition. In this context, a substantially sealed reactor means that the reactor is sufficiently tight to generate overpressure, but, however, vent gas (air) 'leaks' to an extent enabling continuous supply of clean air. Should composting not proceed rapidly, a considerable amount of moisture and nitrogen would evaporate together with the vent gas, thus further slowing down the reaction. The invention is thus based on the fact that blowing air in the mixture to be composted and the aerobic decomposition initiated by the natural microbes (fungi) in peat generate an overpressure and a temperature rise to 70°C. Heat, pressure and continuous even aeration ensure a rapid, even and odourless aerobic decomposition process that can be interrupted by drying with vacuum suction, the content of organic undecomposed substance being for example 50%, calculated from the dry solids, after about 1 to 2 days after the rise in temperature. The aeration is continued non-stop also during the drying step. Hereby the temperature destroys harmful microbes and seeds of weeds, and the mycocelial filaments enter in a state of dormancy. On the other hand, the product contains sufficiently undecomposed organic substance, providing the mycocelial filaments with a good culture medium after activation. The advantage provided by the method and system of the invention is considerable speed. A mass composted for only about 1 to 2 days is ready for use as a fertilizer after an aerobic drying step without post-composting. For storage or transport, the mass is preferably further dried and briquetted. The workload required by the method is negligible. Owing to rapid decomposition, the moisture does need to be controlled during the reaction. The starting material can be prepared and the reactor batched by the use of conventional agricultural machinery and a screen bucket, for example. Composting waste reduces the load on the environment by return- ing organic material to the ecological cycle. No harmful or malodorous gases are generated in an aerobic decomposition process. BRIEF DESCRIPTION OF THE FIGURE Figure 1 shows the general structure of the apparatus. Figure 1 b is the floor plan of a composting apparatus comprising four reactor chambers (a, b, c, d). Each end of a reactor chamber comprises a pressure-tight door (e). In this solution, a machine room (f), in which fans (h), an exhauster and a monitoring system for measuring equipment are placed, is at the rear of the composting device. Figure 1 b is a floor plan of the outermost reactor chamber (a) of the composting device of Figure 1a. Figure 1c is a cross-section of a reactor chamber. For the sake of clarity, Figures 1 b and 1 c only show three parallel longitudinal aeration ducts (g). DETAILED DESCRIPTION OF THE INVENTION In the method of the invention, a soil conditioner is prepared by de- composing a mixture of peat and an animal-originating or plant-originating material under aerobic conditions so that the biological decomposition raises the temperature of the mixture to above +70°C. Peat is one of the main components of the material to be composted. The peat may be any peat containing vigorous flora. The peat is pref- erably dried peat, in which the natural flora is in a state of dormancy. Suitable animal-originating starting materials include bovine manure, poultry manure, sludge from a sewage disposal plan or piggery, or urine absorbed into peat. Owing to its high nutrient content, fur animal manure is particularly advantageous. When sludge is used as the starting material, the amount of the support material, i.e. peat, has to be increased so that the humidity of the starting mass is about 70% by weight. In a preferred embodiment, screened peat and animal-originating or plant-originating material are mixed applying the sandwich principle, and air is led to the obtained mixture. The temperature hereby rises as a result of the biological decomposition initiated by the natural flora in the material to be- tween 70 and 75°C and the pressure rises about/at least 5 to 10 Pa. Air is continuously led to the mixture so that the temperature remains above +70°C for about 24 hours. In the sandwich method, a 10 to 20-cm layer of dry peat (= stabiliz- ing material) and 10 to 20 cm of the material to be composted are screened several layers on top of each other. Air supply is initiated, whereupon the reactor is batched starting from the rear by screening a mixture taken from the sandwich bed to the final filling height. This way an even and loose compost mass not containing oxygen-free spots is obtained. The upper limit of the pressure is not critical. The pressure may be 0.05 bar, even higher. It is essential that the pressure is sufficient to achieve, together with the raised temperature, even moisture in the reactor vessel. A slight overpressure is sufficient to achieve this. The reaction is stopped by lowering the pressure above the mass with a discharge exhauster by at least/about 100 to 500 Pa during 1 to 2 days, i.e. until the moisture of the mass is about 50% by weight, even below that. Aeration is continued without interruptions. Alternatively, the pressure may be lowered at intervals of 4 to 12 hours for 1 to 10 minutes during 2 to 6 days, until the desired moisture content is obtained in the mass. The underpressure may be even 0.5 bar. In underpressure, it is essential to reach a pressure distinctly below the ambient pressure. At its fastest, the entire composting process only takes three days. The initiation step usually takes about 1 to 3 days. The actual composting reaction takes 1 to 2 days; usually one day is sufficient. The drying/stopping re- action also takes 1 to 2 days. Cold and/or moist air outdoors may lengthen the reaction times with more than 24 hours. In cold weather, the drying/reaction stopping time of the mass can be shortened by heating the air to be supplied to the reactor in a heat exchanger with discharge air. The method of the invention provides in a few days a soil conditioner that fulfils the quality requirements. Post-composting is not needed. The soil conditioner preferably contains at least 50% by weight of undecomposed organic material calculated from the dry solids. The soil conditioner is usable as such. To facilitate storage and transport, the moisture of the soil conditioner can be further lowered by applying a longer drying time and/or continuing the drying in a hot drying drum up to about 10% by weight of moisture. The soil conditioner can be further dried, pelletized with a compressor to briquettes, and packaged for storage and transport. When desired, the nitrogen content of the product can be raised by the addition of nitrogen-containing organic liquid or vacuolar fluid from plants to the mixture; suitable substances include urine and vacuolar fluid from potatoes, for example. Urea may also be used. The apparatus used in the method of the invention comprises one or more composting reactors, one or more fans, one or more exhausters, and means for measuring temperature and air pressure and for adjusting airflow. Optionally, the apparatus may also comprise a heat exchanger. The wall structures of the composting device are preferably concrete elements and the floor is preferably of casting concrete. At least one wall comprises one or more openable pressure-tight doors. Punched ventilating pipes are embedded in the floor and are pref- erably of an acid-proof quadratic steel pipe and so placed that the holes project from the casting surface. The distance between the holes in the pipes is preferably between 50 and 300 mm, becoming smaller towards that end of the pipe where the pressure is lower. The pipes are preferably placed about 0.5 metres apart. The placement and punching of the pipes are arranged so as to ensure an even aeration of the mass during the reaction. Air is blown to the reactor with one or more low-power fans. The amount of air is separately adjusted for each reactor, should several reactors be involved. The power of the exhauster is also low so as to preferably lower the pressure above the mass in the reactor by about 100 to 500 Pa in 1 to 10 minutes. The external energy required by the reaction is limited to low- powered supply and discharge fans, of which only a 3-kW supply fan, for example, is continuously switched on. The operating costs of the apparatus are about FIM 0.07 per one kilo of fur animal manure. The manufacturing costs of the apparatus are also significantly low, and the apparatus is suitable for use without extra insulation or heat even at a temperature of -25°C. The product obtained in accordance with the invention possesses a plurality of good characteristics. Stopping the composting process maintains the soil-conditioning effect of the composted mass in the soil owing to the decomposition caused by the organic substance and mycocelial filaments in the mass. Stopping the composting reaction by removing moisture, the mycocelial filaments in the mass enter in a state of dormancy, and are activated again when moisture increases. The soil conditioner of the invention thus promotes the formation of mycocelial filaments in the soil. Fungoid growth retains nutri- ents in the soil thus reducing the load on leachates and the amount of fertilizers required. Furthermore, mycocelial filaments release nutrients from organic materials so that they are more easily accessible to plants. The mass contains abundantly undecomposed organic substance, and nutrients are gradually released to the use of plants. The high temperature has destroyed any harmful microbes and seeds of weeds. Owing to its effectiveness, the product obtained is also ecological and suitable for natural production. Used in field cultivation experiments on oats and potato in an amount corresponding to a chemical fertilizer in respect of nitrogen, the fertilizer prepared according to the invention yielded a crop of oats and potato that corresponded to at least that of a chemically fertilized experimental plot. The size of feed clover fertilized with the product prepared in accordance with the invention (1 ,000 kg/ha) was almost double in respect of chemically fertilized feed clover. Biological fertilization favoured feed clover. The nutrient value of the feed turned out to be exceptionally good. Use in a home garden in growing sunflowers showed that the length of plants fertilized with the product prepared by the method of the invention was up to three times that of others. The stems of the flowers were so strong that they needed no support at all. The colour of the flowers was deeper, and the number of earthworms increased in the soil. Example 1 Composting reactor The reactor used comprised a quadratic 4 metres high space made of concrete elements and having a volume of 150 m 3 . One wall comprised a 3.8 m high and 4 m wide pressure-tight door (Figures 1 b and 1 c). The dimen- sions were so chosen that the reactor is easy to fill and empty mechanically. The floor was of casting concrete, with quadratic acid-proof steel ventilating pipes having an internal cross section of 20 cm 2 embedded therein. The pipes were placed at intervals of 0.5 metres 1 to 5 mm above the casting surface, and they were punched with 1-mm holes, first, close to the fan, more sparsely (distance between holes 300 mm), and at the end more densely (the last holes at 50-mm intervals). The device also comprised one fan (power 3 kW), a heat exchanger for heating incoming air during the drying step with the discharge air of a second reactor that was in the drying step, and an exhauster (power 5 kW) for removal of moisture and final drying. For monitoring the composting process, the device was provided with a thermometer, and the device also comprised means for adjusting airflow and clock control means. Example 2 Composting steps Peat and fur animal manure were screened to a particle size below 50 mm in volumetric ratios 1 :1 (corresponding to weight ratio 1 :3) to several about 15-cm layers on top of each other. Air supply was started at a 60-m 3 /h speed using the reactor of Example 1. Starting from the rear, the reactor was batched to a height of 1.5 metres with a screen bucket with a mixture extracted from the sandwich bed. The volumetric efficiency was between 40 and 60%. The reactor was sealed, whereby a clear overpressure (5 to 10 Pa) was generated in the compost. During 24 hours, the temperature rose to above 70°C because of decomposition initiated by aerobic microbes, particularly fungi, present naturally in the mass to be composted. Air supply was continued so that the temperature remained above 70°C during 24 hours. Owing to the pressure, the temperature and the even supply of air, the mixture and gas in the reactor were saturated evenly with aqueous steam. Owing to the rapid decomposition, the moisture in the reactor remained sufficient without any need to moisten the supply air. During the decomposition, a slight amount of quite odourless gas 'leaks' from the overpressurized reactor to the environment. The ventilating equipment according to Example 1 and the pressure continuously kept the mass uniformly oxidized without any need for mixing. Since the mass contained no anaerobic spots, no formation of malodorous ammonia gas was observed at any time. Example 2b As Example 2a, except that air was supplied at 50 m 3 /h. Example 3a Stopping the composting and drying the mixture The reduction in the moisture of the mixture was initiated by switching on a vacuum fan (suction effect 4 m 3 /min) at intervals of four hours for about 10 minutes, the underpressure being about 100 to 125 Pa. The air sup- plied was heated with a heat exchanger using process energy. The experiment was carried out in winter conditions. Moist air was removed for 2 days, i.e. until the moisture of the mixture was about 50% by weight. The pH value of the product was 7.8, and it smelled like a decomposing substance. The assay of the product was as follows: Dry solids g/kg 448 Ash content g/kg 223 Total phosphorus g/kg 14.3 Total nitrogen g/kg 11.9 Potassium g/kg 7.9 Calcium g/kg 120 Magnesium g/kg 4.7 All contents are calculated on the fresh weight. Example 3b Stopping the composting and drying the mixture The reduction in the moisture of the mixture was initiated by switch- ing on a vacuum fan (suction effect 4 rrrVmin), the underpressure being about 100 to 125 Pa. The suction was continued non-stop until the moisture of the mixture was about 50% by weight, i.e. about 24 hours. The properties of the product obtained corresponded to those of the product in example 3a. Example 3c Stopping the composting and drying the mixture The process was carried out as in example 3a, but the air supplied was not heated. The experiment took place in winter conditions. It took about 2 to 3 days until the moisture reached 50% per weight. The properties of the product obtained corresponded to those of the product in example 3a. Example 3d Stopping the composting and drying the mixture The process was carried out as in example 3a, but the air supplied was not heated. It took about 48 hours until the moisture reached 50% per weight. The properties of the product obtained corresponded to those of the product in example 3a. Example 4e Composting dried sewage sludge The apparatus used was the reactor according to example 1 and the method according to examples 2b and 3b. The starting material used was dried sewage sludge that had a dry solids content of about 20%, and peat. However, the amount of the peat, used as a support material, was increased (about +30% compared with example 2) so that the starting moisture of the mixture was about 70% by weight. The appearance and odour of the product obtained corresponded to those of the product in example 3a. Example 4f Composting piggery sludge The apparatus used was the reactor according to example 1. The composting was carried out as in examples 2b and 3b. The starting material used was piggery sludge having a dry solids content of about 12 to 15%. However, the amount of the peat, used as a support material, was increased (about +50% compared with example 2) so that the starting moisture of the mixture was about 70% by weight. The appearance and odour of the product obtained corresponded to those of the product in example 3a. Example 4g Composting manure concentrated with urine The apparatus used was the reactor according to example 1. The composting was carried out as in examples 2b and 3b. The starting material used was 30% by weight of manure, 20% by weight of urine, and 50% by weight of peat. The appearance and odour of the product obtained corresponded to those of the product in example 3a. Example 5 Composting at -25°C without a heat exchanger The experiment was carried out in the winter, the average temperature being below -20°C. The composting apparatus described in example 1 was used. The reactor was batched with a mixture of peat and fur animal ma- nure as described in example 2. At the beginning, the starting material and the reactor were at ambient temperature. During the entire process, the air supplied was outdoor air that was not heated. The reaction started after about two weeks, but after the temperature started to rise, it quickly reached 70°C. The composting process was continued for 48 hours, and the drying/stopping reac- tion took less than 3 days. The appearance and odour of the product obtained corresponded to those of the product in example 3a. Example 6 Drying and briquetting Ready-made compost was applied to a tipping pocket from which it was transferred to a drying drum. After a rock pocket at the end of the drying drum, the product was blown into the main cyclone and from there to a ham- mer mill. After the hammer mill, the product was circulated via an intermediate cyclone to a mixing worm. After the mixing, the mass was pelletized with a compressor. The hot pellets were moved to a cooling ventilator, after which the pellets were screened and the finest particles were blown back to the main cyclone. The ready briquettes were packed in bags and stored. Example 7a The product obtained in accordance with example 3d was dried and briquetted in accordance with example 6. The nutrient contents of the product obtained were Nitrogen (N) 2.2% (soluble nitrogen 0.7%) Phosphorus (P) 2.6% (soluble phosphorus 0.2%) Potassium (K) 0.5% (soluble phosphorus 0.2%) Magnesium (Mg) 0.4% Calcium (Ca) 4.2% Sodium (Na) 0.3% Moisture 7.6% Example 7b The product obtained in accordance with example 4g, concentrated with urea, was dried and briquetted in accordance with example 6. The nutrient contents of the product obtained were Nitrogen (N) 7.5% (soluble nitrogen 5.7%) Phosphorus (P) 2.3% (soluble phosphorus 0.15%) Potassium (K) 0.37% (soluble phosphorus 0.18%) Magnesium (Mg) 0.29% Calcium (Ca) 3.7% Sodium (Na) 0.24% Boron (B) 0.0004% Copper (Cu) 0.0018% Manganese (Mn) 0.0062% Zinc (Zn) 0.033% Moisture 14.8% It is obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in a variety of ways. Thus the invention and its embodiments are not limited to the above examples but may vary within the scope of the claims.

Claims: CLAIMS 1. A method of preparing a soil conditioner by supplying air into a substantially sealed space containing a mixture of undecomposed plant-originating or animal-originating organic substance and peat, the mixture having about 70% moisture, the temperature in the space rising to between 70 and 75°C, and continuing to supply air to the mixture so as to keep the temperature over 70°C for about 24 hours, after which the pressure above the mixture is reduced by at least about 100 to 500 Pa, and air is continuously supplied until the moisture of the mixture is at most about 50% by weight. 2. A method as claimed in claim 1, characterized by sieving the components in the mixture to be composted in layers as a sandwich bed and filling the reactor from the read by screening material from the sandwich bed up to the final filling height. 3. A method as claimed in claim 1 or 2, characterized in that the moisture of the composted mass after the reaction is stopped is below 50%, and even below 10%. 4. A method as claimed in any one of claims 1 to 3, characterized in that the soil conditioner obtained contains at least 50% by weight of the dry solids of undecomposed organic substance, and nutrients, micronutrients and mycocelial filaments. 5. An apparatus usable in a method as claimed in claim 1, 2 or 3, comprising one or more reactors, one or more fans, one or more exhausters, and means for measuring temperature and air pressure and for adjusting airflow, characterized in that a reactor base comprises punched ventilat- ing pipes embedded in a floor 1 to 5 mm above a casting surface. 6. An apparatus as claimed in claim 5, characterized in that the distance between the pipes is about 0.5 metres. 7. An apparatus as claimed in claim 5, characterized in that the ventilating pipes are quadratic. 8. An apparatus as claimed in claim 5, characterized in that the ventilating pipes are acid-proof. 9. An apparatus as claimed in claim 5, characterized in that the distance between the holes in the ventilating pipes is between 50 and 300 mm, becoming sparser towards that end of the pipe where the pressure is lower.

Inventors: VERTANEN PAEIVIOE, VERTANEN, PAEIVIOE
Applicants: ECOSPEC LTD OY, VERTANEN PAEIVIOE, OY ECOSPEC LTD, VERTANEN, PAEIVIOE
Application year: 2000
Main classification: C05F17
IPC codes: C05F9, C05F17