MXPA97008196A - Fertilizer and procedure for the production of my - Google Patents

Abstract

The present invention relates to a process for producing a fertilizer from an organic waste material, the method comprising treating a waste having a water content of not more than 90% by weight and which has been alkalized, with dioxide nitrogen or a precursor thereof in sufficient quantity to reduce the pH by at least 2.0 pH units, the process produces an organic fertilizer in which the percentage by weight of nitrogen in the form of nitrogen oxide is greater than the percentage in Nitrogen weight in the form of ammonium ion

Description

FERTILIZER AND PROCEDURE PflRfl Lfl PRODUCTION OF THE SAME FIELD OF THE INVENTION The invention relates to a fertilizer and a process for the production of the same using an organic waste such as, for example, sewage sludge or other domestic, industrial or agricultural organic waste. The process of the invention produces an organic fertilizer that is stable, is not harmful to the environment and is enriched with nitrogen compared to the original waste. In addition, the microbial count in the physical product is well below the upper limit of safety established by the different regulatory authorities for such materials, and it is low enough that the nitrogen content of the fertilizer is not reduce by microbial metabolism before its application to its Lo. The fertilizer of the invention has proved to be as effective in improving crop yields as conventional inorganic fertilizers.

BACKGROUND OF THE INVENTION For many years now, inorganic chemical fertilizers have dominated the fertilizer market. However, it has recently been recognized that the exclusive use of inorganic fertilizers is detrimental to the natural capacity of the soil to replenish microbiological and plant nutrients. They do not contain organic materials to replace the loss of the superficial layer of soil by erosion and therefore, during their application they are easily percolated towards deposits, lakes and lakes causing pollution. In view of these disadvantages, the use of fertilizers based on organic material is becoming increasingly popular, as they can enrich the soil without substantial danger to the environment. Organic waste materials such as sewage sludge and other household, industrial and agricultural organic wastes are good candidates for organic fertilizers because they are available in huge quantities, and the disposal of these wastes is, by itself, , a problem for the environment. Several methods are known to convert organic waste materials into organic fertilizers. However, a production process that is commercially viable has not been achieved. Ideally, the procedure should set or enrich the nitrogen content of organic waste, hydrolyze organic components to increase their suitability to be metabolized by soil and plant microorganisms, and reduce the microbial population of organic waste. Different approaches have tried to achieve these objectives. For example, sterilization or disinfection of organic waste has been achieved by exposing the waste to high temperatures (pasteurization, drying) using an external heat source. This treatment, however, does not achieve any nutrient enrichment. Alternatively, the waste can be transformed into compost, but this takes weeks or months and produces a bulky material with a high water content that is inconvenient to use as a fertilizer. Procedures for enriching the nutrient content of the organic waste and effecting-hydrolysis of the organic components are also known. For example, US-FL-5125951 describes the conversion of ammonia to thermally stable compounds such as ammonium nitrate and diarnome phosphate by treatment of sewage sludge with nitric acid or phosphoric acid, respectively. Another known method, which causes the hydrolysis of the organic components and some disinfection of the waste, is to treat the organic waste material with acid to hydrolyze the organic components and reduce the pH. Then lcali, usually ammonia, is added to raise the pH to a value that is suitable for application in the soil. The addition of ammonia increases the nitrogen content, and aggressive pH changes reduce the microbial count. The processes using, for example, phosphoric acid or sulfuric acid to acidify the waste, are described in US-A-4743287, EP-A-0428014 and UO 91/16280. A similar procedure in which the acidifying agent is nitrogen dioxide is described in GB-4242B0. A common feature of all these prior art processes is that acidification of the waste is first carried out before the addition of alkali to restore the pH to approximately neutral. The inventors have now made the unexpected discovery that reaction times can be reduced and the efficiency of the process can be substantially increased if the pH of the crude residue is first raised by adding alkali, followed by acidification with nitrogen dioxide. These improvements in efficiency make commercially feasible the production of a fertilizer from waste materials, particularly because some wastes, such as cLoaca water sludge, are frequently treated with alkali for stabilization and disinfection purposes prior to transport. and elimination. In addition, this procedure achieves the dual objective of nitrogen enrichment and disinfection, while producing a stable and environmentally acceptable product that can have more than 50% of the total nitrogen content in the form of nitrites and nitrates. Thus, in accordance with a first aspect of the invention, there is provided a process for producing a fertilizer from an organic alkaline waste material having a water content of not more than 90% by weight and a pH of about 9.0 or higher, which comprises introducing nitrogen dioxide or a precursor thereof into said alkaline waste material in an amount sufficient to reduce the pH by at least 2.0 pH units. In a second aspect, the invention provides a method for producing a fertilizer from organic waste material that comprises no more than 90% by weight of water and is not previously alkalized, by first adding a different alkali of ammonia to the organic waste material. in sufficient quantity to increase the pH by at least 2.0 pH units, preferably raise it to approximately 10.0 or more, and subsequently introduce nitrogen dioxide (NO2) or a precursor thereof into the material, in an amount sufficient to reduce the pH in at least 2.0 pH units, preferably reduce it to 8.0 or less. These processes can produce a fertilizer in which the total nitrogen content is from about 5% to about 9% dry weight, which is sufficient for many applications. However, it can be suitably adapted to produce a fertilizer having a total nitrogen content of up to about 15% dry weight. The amount of added NO2 is usually sufficient to counteract the pH increase caused by the addition of the alkali, so that the pH is restored to that of the starting material. The correct stoichiometric amounts of alkali and NO2 required can be easily calculated by the expert. By increasing the amount of added alkali, NO2 must be added for neutralization, which has the effect of additionally enriching the waste in nitrogen. As an alternative, a higher total nitrogen content can be achieved by introducing the NO2 or precursor thereof in an amount greater than that required to re-establish the H from the waste to neutral, and thereby increase the level of acidification. Then you can restore neutrality by introducing ammonia. This final addition of ammonia further increases the total nitrogen content and is particularly advantageous for a high nitrogen content fertilizer, since the low molecular weight, in comparison with NO2, allows to increase the nitrogen content of the waste without substantially increasing the handle. . Nevertheless, due to the volatility of ammonia, it is preferable that the final pH of the product is slightly acidic since this compensates for the loss of much of the ammonia into the atmosphere. In the organic fermentatives produced according to the methods of the present invention, the weight percentage of nitrogen in the form of nitrogen oxides, such as nitrite and nitrates, is greater than the weight percentage of nitrogen in the Ammonium ion form This is very uniform in those embodiments of the invention where ammonia is added in the final stage, because most of the nitrogen enrichment is provided by NO2. If ammonia is not added, then a fertilizer is produced in which more than 50% by weight of the total nitrogen is in the form of nitrates and nitrites. This makes the fertilizer of the invention highly potent. These levels of nitrates and nitrites are not achieved by means of the known prior art processes for producing fertilizer from organic waste. For the production of a fertilizer suitable for application in the soil, and which is easily storable and transportable, the waste is usually dried following the various steps of the process described above, preferably to a water content of 20% by weight or less. It may undergo additional treatment as discussed below in greater detail. Any industrial, domestic or agricultural waste is suitable for conversion into a fertilizer in the process of the invention, provided that it has an organic component and does not include an excessive level of heavy metals or other toxins. Sewer water sludge is a particularly appropriate starting material, either untreated or alkalized to make it suitable for transportation and disposal. Preferably, the water content of the waste should be from about 50 to 90% by weight and the most suitable materials are those with a solids content of approximately 20 to 35% by weight. Of course, the water content of any organic waste material can be appropriately adjusted for use in the methods of the invention. The processes of the invention can be carried out in a batch reactor sealed at atmospheric pressure or, preferably, at increased pressure until the reaction cycle is complete. Then, the pressure can be reduced to vent the waste gases. Alternatively, the process can be one in which there is a continuous feed of the starting material and a continuous removal of final product, alkali, NO2 and any other additions introduced at appropriate insertion points along the route of the waste trajectory. organic. Again, an elevated pressure is preferred during the mixing and reaction stages with a reduction at atmospheric pressure or lower for the venting of waste gases in the collection stage. Preferably, the batch reactor or the continuous feed apparatus will be insulated against heat loss. As mentioned above, the inventors of the present have found that pre-alkalizing the waste prior to the addition of acid confers several advantages not present in the previously known processes. Initial alkalization should not be carried out with ammonia due to its volatility when added to waste that has not previously been acidified. However, the alkaline compounds suitable for addition are calcium oxide (lime, CaO), potassium hydroxide (KOH), sodium hydroxide (NaOH), calcium hydroxide (Ca (0H) 2) V calcium carbonate (CaC? 3). Calcium oxide is the lcali particularly preferred for use in the process of the invention. As mentioned above, sewage sludge can be treated with lime (CaO) in sewer water plants. In addition, CaO reacts with water to form Ca (0H) 2, thus having a drying effect on the waste. Calcium phosphate is also formed that becomes soluble in water when the pH becomes neutral with NO2, thus increasing the amount of phosphorus available to vegetables. The amount of added alkali should be-approximately equal, in base equivalents, to the amount of added NO2. When CaO is the only alkali, the amount should be approximately 60% of NO2 based on weight, giving 6-27% by weight of the final product. Appropriate quantities of other alkalis can be easily calculated considering their molecular weights, base equivalents and dissociation constants. The addition of an alkali as the first stage in the process of the invention has several effects. First, it causes alkaline hydrolysis of organic components in the waste, so that it can be metabolized more easily by plants and soil bacteria. Secondly, the chemical reaction causes an increase in the temperature of the waste which, depending on the ambient temperature at which the procedure is carried out, can have the effect of reducing the microbial population. Third, it increases the pH, which facilitates a high uptake of NO2 in the second stage of the process, and also has a bactericidal effect. The alkaline waste produced in the first stage of the process is stable and is partially disinfected. It can be transported and stored without odor or health problems. In addition, because the low pH is avoided, corrosion problems do not arise. In this way, the waste that is suitable for converting it into fertilizer can be stored in the alkalized state for some considerable time or it can be obtained pre-calibrated from a supplier. In all embodiments of the invention, nitrogen dioxide may be introduced into the organic waste material as a liquid or as a gas. Alternatively, a NO2 precursor such as tet or i or dimorgen or other nitrogen oxides or their salts can be used. The liquid NO2 can be obtained commercially in the raw state, but preferably NO2 gas is generated at the site of the waste treatment apparatus. This allows the heat released from the gaß generator to be used for the drying stage of fertilizer production, which has obvious economic advantages. In addition, using a NO2 generator that converts NH3 to NO2 provides a direct source of ammonia at the treatment site that can be used in the final stage of the process if a high nitrogen content fertilizer is required. When NO2 is added to the reactor, it reacts with water to produce nitric and nitrous acid, in accordance with 11 equation: 2N02 «H2O - > HNO3 + HNO2 The production of nitrous and nitric acids reduces the pH of the suspension to neutral or lower. The amount of added NO2 must be sufficient to bring the pH of the organic waste substantially back to the pH of the starting material or below the ism. As with the addition of lime, because the NO2 reacts with water, it has an additional drying effect on the waste. The precise quantity supplied depends on the required level of nitrogen enrichment and the initial constitution of the waste, and will also be determined by the amount of alkali that has been added. In a typical procedure operation, the addition of NO2 will be from about 10 to 45% of the final product's weight. The desired pH can be achieved by admitting NO2 in a reactor batch for a relatively short period of 15 to 20 minutes. However, the actual treatment time depends on the type of reactor, the applied pressure, the degree of mixing, the particle size of the suspension and the water content of the waste. In continuous reactors, it may well be that in the batch reactors, very short times of NO2 treatment may be sufficient, of a few rninutoß.

In addition, oxygen can be introduced into the reactor to improve the oxidative processes in the suspension, which causes the favored production of nitric acid on nitrous acid. Oxygen can be injected into the initial stream or into the final stream of O2, or injected in conjunction with the same. In addition to the procedures described above, the waste may optionally require other types of bonding at different points, either before or after treatment with alkali, NO2 or additional ammonia. For example, before the treatment begins, it may be advantageous to convert the waste into a suspension of uniform particle size by passing it through a chopper or mill. As long as it is desired to produce fertilizer that is well balanced in nutrients, the analysis of the nutrient content of the waste can also be carried out in order to supplement it, either the starting waste material or the fertilizer product when Nutrient levels are inadequate. Additional nutrients should be added at an appropriate point during treatment and before drying. For example, it may be convenient to add nitrogen, phosphorus, calcium, magnesium, sulfur, potassium or the salts thereof and / or other rnicronutrient.es. Tests may also be carried out to determine the presence of toxic materials in the waste. As mentioned above, however, the drying effects of CaO and NO2, the treated organic waste is further dried, preferably to a water content of 20% by weight or lower. Drying can be facilitated by using the heat evolved from a NO2 gas generating apparatus. The organic fertilizer can be applied to the soil after drying without any further treatment, but in practice it is better to form the fertilizer into pellets or granules that are easily transportable and practical for the user. The process of the invention produces a fertilizer based on organic waste which is well balanced, stable, easy to handle and with a high nitrogen content in comparison with the organic fertilizers of the prior art. In the fertilizer of the invention, the nitrogen content will be 5% by weight or greater, preferably between 5 and 15%. The fertilizer eßrich in cornpueßtoß containing soluble nitrogens in a form suitable for its uptake by vegetables. This gives the fertilizer a high potency, so that only small volumes per unit area of soil need to be added, and therefore the presence of heavy metals and toxins in the waste is less problematic. In particular, the nitrogen of NO2 as the main source of nitrogen means that a significant proportion of non-organic nitrogen is in the form of nitrite and nitrate, instead of the ammonium ion as with the prior art processes. Nitrites and nitrates give a much more immediate growth effect than ammonia. In addition, the fertilizer is of a neutral pH, which means that the user does not need to apply lime to the soil as is the case with the inorganic fertilizers rnáe acids conventionally used. As a result of changes in pH and / or temperature, the method of the invention is efficient in reducing the microbial population so that the fertilizer meets the requirements of the regulatory authorities. In a typical procedure, the count of bacteria coli formes terrnotolerantes (TCB) decreased from >; 2.40Q before treatment to < 100 after treatment. In Norway, the safety limit to be used in the disposal of sewage sludge in agriculture is 2,500 TCB per gram of dry matter. In this way, the process produces an organic fertilizer well within the safety limit. Field tests were carried out using the fertilizer of the invention. An increase in organic nitrogen availability of 10-30% at 50-70% was observed. Contrary to the use of general fertilizers, the pH of the soil remained stable. In addition, there were good effects of initial and prolonged growth and a lower percentage of embodied or flattened crops. Laes that are bent or broken can hinder the harvest and result in a lower grain quality. The invention will now be described with reference to the following examples.

EXAMPLE 1 1,600 g of sewage sludge was charged to a batch reactor to which 51.5 g of 85% KOH and 56 g of CaO were added. The mixture was stirred until reaching a pH of 11.4, followed by injection of 200 g of NO2 over a period of two hours with intermittent pulses of oxygen until the pH was again reduced to 6.3. During the treatment, the temperature of the waste material increased from 17 ° C to 50 ° C. The chemical analysis of the starting material and the final product gave the following results. (1) Total nitrogen increased from 2.3% to 12.1% by dry weight. (2) Nitrate in the nitrate form increased from 0.0021% to 10.3% dry weight. (3) The increased nitrate content represents 50g? 80% of the nitrogen injected. (4) The nitrogen in the ammonium ion range decreased from 0.75% to 0.20% by dry weight. (No ammonia was added and the loss was mainly due to high pH combined with atmospheric conditions in this test). (5) The material is increased from 19.5% to 26.2%.

EXAMPLE 2 2000g of sewage sludge comprising approximately 400g of dry matter was loaded into a batch reactor, and mixed with 78.5 g of CaO. The mixture was stirred until it reached a pH of 10.3. 130g of NO2 was injected into the reactor over a period of 15 to 20 minutes to reduce the pH to 6.3. During the treatment, the waste temperature increased from 3.5 to 8 ° C. This small increase in temperature compared to Example 1 is due to the very low ambient temperatures at which this experiment was carried out, and to the fact that the reactor vessel was not insulated against heat loss. The chemical analysis of the starting material and the final product gave the following results: (1) The total nitrogen increased from 2.5 to 8.5% in pebbels. (2) Nitrogen in the nitrate and nitrite range increased from 0.002% to 6.1% in dry pe. (3) The increased nitrate content represents 120g or 92% of the nitrogen injected in the NO2 form. (4) The nitrogen in the ammonium ion range decreased from 0.5 to 0.4% by weight εec. (5) Material ßeca increased from 20% to 26%.

EXAMPLE 3 2000g of sewage sludge comprising approximately 400g of dry matter in a batch reactor was charged, and mixed with 60g of CaO and 20g of KOH. The mixture was stirred until it reached a pH of 10.1. 105g of O2 was injected into the reactor for a period of 15 to 20 minutes until a final pH of 8.4 was reached. During the treatment, the waste temperature increased from 6.9 to 12 ° C. The small increase in temperature compared to Example 1 was due to the same reasons as described in Example 2. The chemical analysis of the starting material and the final product gave the following results: (1) The total nitrogen increased from 2.5 to 6.5. % by weight ßeco. (2) Nitrate in the form of nitrate and nitrite increased from 0.002 to 4.1% by dry weight. (3) The increased nitrate content represents 81g or 78% of the nitrogen injected in the NO2 form. (4) The nitrogen in the ammonium ion structure remained unchanged. (5) Dry material increased from 20% to 24%.

EXAMPLE 4 2000g of sewage sludge comprising approximately 400g of dry matter in a batch reactor was charged and mixed with 39.3 g of CaO until a pH of 9.9 was reached. Then 116g of NO2 was injected into the reactor over a period of 15 to 20 rnmutoß haßta reducing the pH to 4.2. Deßpuéß ße injected 30 g of NH3 into the reactor to produce a final pH of 7.5. During the treatment, the temperature of the dioxide increased from 0 to 10 ° C. The small increase was for the same reasons given in example 2. Chemical analysis of the starting material and the final product gave the following results: (1) The total nitrogen increased from 2.5 to 10% by dry weight. (2) The nitrogen in the nitrate and nitrite forms increased from 0.002 to 5.4% by dry weight. (3) The increased nitrate content represents 105g or 92% of the nitrogen in the NO2 range. (4) Nitrogen in the ammonium ion range increased from 0.5% to 3.3% in dry pe. (5) Dry material increased from 20% to 25%.

Microbiology A microbiological analysis was carried out on the starting material and the final product for each of the examples 1 to 4. In each case, the results were as follows: Bacteria coli formes terrnotolerantes (TCB) by grarno of material èseca diínrninuyeron de < 2,400 before treatment to < 100 (detection limit) after treatment.

The foregoing (Examples 1 to 4) exemplifies the process of the invention when carried out in an intermittent manner. In Figure L there is schematically shown a suitable apparatus for carrying out the process in a continuous form, in which 1 is a sewage sludge pump, 3 and 5 are first and second chemical injection pumps which can be used for the addition of alkali, O2 or NH3, 7 is a dryer and granulator- and 8 is receptacle for receiving the fertilizer particles errninatedß.

EXAMPLE 5 A field trial was carried out on an oat crop comprising a fertilizer made in accordance with the present invention and a mineral fertilizer 21-4-10 (NPK). The field contained 28 plots and the test contained 7 different treatments, each of which was repeated 4 times. The treatments comprised mineral fertilizer and the organic fertilizer of the invention at 6, 9 and 12 kg N / 1000 rn2, and a ßm fertilizer control was used. The results were as follows: TABLE I As is evident from Table I, the fertilizer of the invention produces a significant increase in crop yield that is only slightly lower than the yield with the known mineral fertilizer. However, the yield can be increased by using the fertilizer of the invention in larger amounts, since this is a relatively low cost option compared to the increase in the dosage of a mineral fertilizer. Furthermore, as can be seen, the incarnation or flattening of the harvest that is associated with the use of mineral fertilizers is significantly reduced, using the fertilizer of the invention.

EXAMPLE 6 A greenhouse test was carried out to compare the effects of the soil pH of the fertilizer of the invention and the fertilizer 21-4-10 (NPK). The results are as follows: The experiment confirms the stability in pH of the fertilizer of the invention, in comparison with the mineral fertilizer, where increasing quantities cause the ≤ soil to acidify.

Claims (31)

00 NOVELTY OF THE INVENTION CLAIMS

1. - A process for producing a fertilizer from an organic waste material having a water content of not more than 90% by weight and a pH of about 9.0 or greater, which comprises introducing nitrogen dioxide or? N precursor same in said waste material in sufficient quantity to reduce the pH in at least 2.0 pH units.

2. A process for producing a fertilizer from organic waste material, said material comprises not more than about 90% by weight of water; the method comprises the steps of: (a) adding an alkali to said organic waste material in an amount sufficient to increase the pH by at least 2.0 pH units and (b) introducing nitrogen dioxide (NO2) or a precursor thereof in the material produced in step (a) in sufficient quantity to reduce the pH by at least 2.0 pH units, with the proviso that the alkali used in step (a) is not ammonia (NH3).

3. A process according to claim 2, further characterized in that said alkali is aggravated in an amount sufficient to increase the pH to 10.0 or more and said NO2 or precursor thereof is added in sufficient quantity to reduce the pH to 8.0 or less.

4. A process according to claim 2 or claim 3, further characterized in that the NO2 or the precursor thereof adds in sufficient quantity in the sheet (b) to counteract the increase in pH caused by the alkali added in the cloth. (a), so that the pH ß restores ßubstancially to that of the starting material.

5. A process according to claim 2 or claim 3, wherein the aggregate amount of NO2 or precursor thereof in step (b) is greater than that required to restore the pH of the waste to that of the starting material, and the process comprises the additional step (c) of introducing ammonia (NH3) into said waste.

6. A process according to claim 1, further characterized in that the aggregate amount of NO2 or precursor thereof is greater than that required to restore the pH of said waste to neutrality, and the process comprises the additional step of introducing ammonia in said waste.

7. - A method according to claim 1 or claim 6, characterized in that after the addition of said NO2 or precursor thereof or ammonia, said waste material is εeca.

8. A method according to any of claims 2 4, further characterized in that the material produced in the cloth (b) is dried.

9. The process according to claim 5, further characterized in that the material produced in step (c) is dried.

10. A method according to any of the preceding claims, further characterized in that said organic waste material is agricultural, industrial or domestic waste, or sewage sludge.

11. A process according to any of the claims, precedents further characterized in that said organic waste material comprises between 50 and 90% by weight of water.

12. A method according to claim 11, further characterized in that said organic waste material has a solidoß content of between 20 and 35% by weight.

13. A method according to any of the preceding claims, further characterized in that before the fertilizer production process, said organic waste material is passed through a mill or chopper to create a suspension of uniform particle size.

14. A method according to any of the preceding claims, further characterized in that before the fertilizer production process, said organic waste material is analyzed to determine its content of plant nutrients., metals and toxins.

15. A process according to any of claims 2 5 and 7 to 14, further characterized in that the alkali added in step (a) is selected from CaO, KOH, NaOH, Ca (0H) 2 V CaCÜ3.

16. A process according to claim 15, further characterized in that the alkali added in the sheet (a) is CaO.

17. - A method according to any of the preceding claims, further characterized in that said O2 is introduced into the organic waste material in the form of a gas or a liquid.

18. A process according to claim 17, further characterized in that said NO2 is injected together with oxygen into said organic waste material.

19. A process according to claim 17, further characterized in that before or after the introduction of said NO2 or precursor thereof, oxygen is introduced into said decenecho material.

20. A process according to any of claims 1 to 19, further characterized in that said NO2 is introduced into the organic waste material or a precursor thereof, for example dimtrogen tetroxide.

21. A process according to any of the preceding claims, further characterized in that the amount of added NO2 is from about 10% to about 45% by weight of the final product.

22. A method according to any of claims 2 to 5 and 7 to 21, further characterized by adding additional nutrients before, during, or after the paßoe (a), (b) or (c). to the waste material orgam co.

23. A process according to claim 1 or claim 6, further characterized by adding additional nutrients to said organic waste stream.

24. A process according to claim 22 or claim 23, further characterized in that additional nutrients are selected from nitrogen, phosphorus, calcium, magnesium, sulfur, potassium and the ßaleß of loe mißrnoß.

25. A method according to any of the preceding claims, further characterized in that it is an intermittent process carried out in a sealed container.

26. A method according to any of the preceding claims, further characterized in that it is a continuous process.

27. A method according to any of claims 7 to 26, further characterized in that during the drying step the water content of said organic waste material is reduced to 20% by weight or less.

28. A method according to claim 27, further characterized in that the dried organic fertilizer is formed into particles. 29.- A fertilizer based on organic waste, character-raised because the percentage by weight of nitrogen in the form of nitrogen oxides is higher than the percentage by weight of nitrogen in the form of ammonium ion. 30. A fertilizer based on organic waste according to claim 29, further characterized in that more than 50% of the total nitrogen content of the same is in the form of nitrates and nitrites. 31. A fertilizer according to claim 29 or claim 30, characterized in that the number of thermotolerant coli forme bacteria per gram is less than 2500.