WO1993024418A1

WO1993024418A1 - Method for processing liquide manure

Info

Publication number: WO1993024418A1
Application number: PCT/NL1993/000108
Authority: WO
Inventors: Dirk Kuiper
Original assignee: Dirk Kuiper
Priority date: 1992-05-26
Filing date: 1993-05-26
Publication date: 1993-12-09
Also published as: NL9200930A

Abstract

The invention relates to a method for processing liquid manure comprising separating the manure into a fraction substantially consisting of liquid components of the manure and a solid part, supplying the liquid manure and diluting water to an algae pond which contains algae and/or bacteria as biomass, the amount of diluting water being sufficient for diluting the liquid fraction by a factor between 2 and 50, removing or largely removing the biomass from the effluent of the algae pond, and returning the volume which was added as diluting water and flush water, to the influent and/or the animal quarters for reuse.

Description

Title: Method for processing liquid manure

The invention relates to a method for processing liquid manure, such as pig manure, utilizing algae.

Pig manure consists of feces and urine (slurry) . The solid content of sow manure is approx. 5% and that of manure from fattening pigs is 10-12%. The manure is normally collected in its entirety in manure cellars, in most cases together with flush water from the animal quarters. At suitable times, the manure is pumped from the manure cellars into tankers and spread over pastures and agricultural land. The production of manure has witnessed a strong increase over the past decades, which has led to topdressing. More and more environmental objections are raised, mainly on account of the ammonia emission and the high phosphate discharge. On account of this surplus of manure, there exist plans everywhere for a number of large central manure processing plants. The surplus manure will be transported to these plants and be processed there, and the farmer bears the transportation and processing costs.

The greater part of these costs is caused by the liquid part of the manure. In terms of volume this is the larger part; it contains a large proportion of the total amount of ammonia and urea, but otherwise it is rather dilute. Accordingly, it seems to have important advantages to separate the manure at the farm into a "solid" part and a "liquid" part. The solid part can then be removed at relatively minor costs to a processing plant or to agricultural areas with a deficiency of manure. The liquid part would have to be processed in situ , but no satisfactory methods to that end have been found yet. The invention provides possibilities for processing the liquid manure utilizing algae and provides different embodiments to that end. In principle, this method may well be employed for a single farm, but also for a few neighboring farms and even for a central manure processing plant. The processing of manure with algae has already been investigated on a test plant scale in many places in the world. The application on a technical scale does occur, but not with the objective of purifying the manure to a specified degree where it can be discharged.

In this method the organic substances of the liquid manure are broken down by bacteria to form C0₂ and water, which may also give rise to the liberation of inorganic nutrients such as H₃, nitrate and phosphate. The bacteria use oxygen. Under the influence of light, the algae present take up the CC>₂ and inorganic nutrients again and form new algal biomass therewith. In this process oxygen is released, which is used by the bacteria again. Thus, the manure is completely broken down in aerobic manner and from the components new biomass is formed. No aeration is required; with "normal" aerobic purification, the costs of aeration account for approx. 60% of the total cost. Also, in the algal process no C0₂ is released and algal biomass is formed which has a certain value and can be put to good use. For the technical implementation of the process, generally an algae pond is used. In most cases, this is a closed, shallow lagoon, or carousel in which the water is kept moving by means of a paddle wheel. This is schematically depicted in Figure 1. The supply of the manure takes place continuously or periodically; the same applies to the discharge. Accordingly, the process is carried out continuously or semicontinuously. The influent stream and the effluent stream are substantially the same and losses through evaporation can be compensated by supplementary addition of water. The average retention time in the algae lagoon differs and is for instance between l day and 10 days. Experiments with a test plant have shown that the complete pig manure, i.e. solid and liquid together, cannot be treated in an algae pond. The algae do not grow, possibly because the particles of the solid manure absorb too much light. If exclusively liquid manure is added, the algae do grow, but it appears that after some time growth stagnates. This, too, could be explained inter alia by too high a light absorption.

It was found, however, that this stagnation of algal growth does not arise if the liquid manure is diluted with water. The necessary dilution depends on the separation of solid and liquid and the further previous history, but may vary between a few times and twenty to fifty times, drawn to the orgininal amount of manure. Good results were obtained with ten-fold and with twenty-fold dilution, calculated on undiluted manure, i.e. without flush water. As such, this dilution is not a problem. The amount of manure which is treated is not affected by it. It does require, however, that an amount of water be added which is ten to twenty times the amount of the manure to be processed. This may pose a problem in areas which depend on groundwater, certainly if the groundwater level is reduced as it is. Moreover, more water has to be discharged and if the concentration of certain substances, for instance total N, satisfies the requirements set, the total load still increases ten or twenty-fold as a result of the dilution.

The invention concerns a method wherein the biomass is removed or substantially removed from the effluent of the algae pond, whereafter the volume which was added as diluting water and flush water is returned again to the influent and/or to the animal quarters for reuse. The remaining part, i.e., the volume corresponding to the volume of the originally added manure, is discharged or used in another manner.

In the method described above, the algal biomass is removed from the water of the pond and this water is returned to the pond again. The separation of the algal biomass can be effected by a suitable sedimentation. In that case, the water flows between plates arranged in parallel. The algal biomass sinks and forms a layer on the plates. The water so stripped of algae can be returned directly to the algae pond. The layer of the algal biomass is periodically removed from the plates and collected as concentrated algal liquid. The removal of the algae from the plates is effected by circulating the liquid at an increased flow rate. In order to enhance this removal of the algae, air bubbles or solid particles or chemicals may be added to the liquid. A further aspect of the invention is that the algae are removed from the water of the pond by passing this water between parallel plates which are arranged horizontally or at a slant. The liquid flow rate is then less than 10 m per hour and the plates are spaced apart less than 3 cm. The algal biomass is removed from the plates by circulating the liquid to which additives, such as gases, solid particles or chemicals may or may not have been added.

The liquid manure is colored brown and the effluent, too, after removal of the biomass, is light brown. This is caused by humus-like substances, "Gelbstoffe". If this liquid is repeatedly recirculated, the color in the algae pond may increase too strongly, which may impede the growth of the algae. It is therefore of importance that the color is removed from the effluent before it is returned. Research has shown that this can be properly done with a slow filtration.

The invention further concerns a method wherein the effluent, after removal of the biomass, is treated for the removal of the color. This may be effected inter alia through a slow filtration over a filter bed of, for instance, sand, anthracite, or active carbon, optionally in combination with UV exposure and/or a treatment with hydrogen peroxide. This is schematically indicated in Figure 2.

In the applications and the development projects elsewhere, what was generally considered was the percentage by which certain components can be reduced, for instance, the total N content. Also considered was the amount of algal biomass that could be formed with manure as a source for nutrients. Little or no attention was paid to the quality of the water to be discharged, at any rate this was not a primary- concern, in our situation, on the other hand, this is precisely the case. The water to be discharged may for instance contain a maximum of 10 mg total N per liter (i.e., after filtration of the biomass) . This means that the water in the pond should not contain more than 10 mg of N per liter either (see Figure 1) . The influent contains much more and is strongly diluted in the pond. As long as the concentration in the pond is 10 mg/1, discharge may take place and approximately the same amount of influent (volume) is supplied. When the concentration in the pond exceeds the discharge limit set, the effluent, and therefore the influent, should be reduced. The retention time becomes longer and the concentration will decrease. This can be controlled automatically by measurement of the total N content or quantities derived therefrom. The same applies to other components which are subject to discharge limits, such as phosphate. The measurement of these concentrations which is automatically coupled to the effluent stream can also be automatically coupled to the influent stream.

A further aspect of the invention is that the effluent stream, and the influent stream coupled thereto, are controlled by measurement of relevant quantities such as the content of nitrate, ammonia or phosphate. It can thereby be accomplished that the effluent has a quality which always satisfies a value to be set, such as for instance the discharge standard. This control can be carried out continuously and automatically, but also semiautomatically or periodically-nonautomatically.

As stated, the urea in the liquid manure and also the organically bound nitrogen are converted by bacteria to ammonium ions and, to a lesser extent, to nitrate. The algae take up the ammonium and, to a lesser extent, the nitrate. At higher pH values, the ammonium ions are largely converted to ammonia. This can easily escape from the water into the air as gaseous ammonia. If this occurs, the nitrogen, it is true, is removed from the liquid manure, but is partly released into the air as gaseous ammonia, which is precisely the reverse of what is intended.

A further aspect of the invention is that the pH value in the algae pond does not exceed a maximum value of 8, which is achieved by adding some acid to the water or through the process control of the pond.

Of further relevance to the control of the process is the concentration of the algal biomass and, in conjunction therewith, the depth of the liquid in the pond. The concentration of the biomass can be measured by means of absorption of light of a suitable wavelength and on the basis of the measured value the depth of the liquid can be set by a (temporary) relative adjustment of the influent and effluent streams or by the addition of supplementary water. Suitable depths vary from 5 cm to 70 cm.

- The invention further relates to a method for the optimum setting of the depth of liquid in the pond and the algal biomass by measuring the absorption of light of a suitable wavelength and coupling this absorption to the influent and/or effluent stream or an additional supply of water. This control can be carried out automatically, semiauto atically or nonautαmatically.

The liquid manure may contain approx. 2,000 mg N/l. If this manure is diluted 20 times, for instance, then the concentration of the influent is 100 mg N/l. The effluent will be adjusted to the discharge requirement, for instance 10 mg N/l; the water in the pond, too, will then contain 10 mg N/l. The influent, therefore, is strongly diluted and it is possible that one or more of the nutrients present

(N, p, etc.) thereby become growth-limiting. In that event, algal growth will be less strong than is possible under the specified conditions, for instance at the specified light intensity. If the pond were not set at 10 mg N/l but, for instance, at 25 mg N/l, then the concentration of all nutrients can be sufficient to avoid any limitation of growth. The algal growth is much faster and the first 75% of the N input is rapidly converted to algal biomass. The effluent of this pond could subsequently be used as influent for a second pond which is set at 10 mg N/l. Accordingly, algal growth is slower here, but only little N needs to be converted. In this way two ponds can process significantly more than can one pond having the same surface area as the two together. In the second pond the growth is limited, so that the algae concentration will be lower than in the first pond. This can be compensated by making the pond deeper, but the algae concentration will be remain relatively low. Now the influent of the second pond is equal to the effluent of the first pond and accordingly has an algae concentration which is higher than that in the second pond. It is well known that adding to an algae reactor an additional amount of algae which are in the growth phase leads to the nutrients present being taken up at an accelerated rate. Such an effect will also occur in the two- algae ponds arranged in series, which is an additional advantage.

The invention also concerns a method in which, for the processing of the liquid manure, not just one algae bioreactor (algae pond) is used, but two or more ponds which are arranged in series and may differ in surface area and depth, and in which the effluent of a pond is used in whole or in part as influent for the next pond, optionally after some treatments. Different types of algae and cyanobacteria are suitable for use in the present invention. It is also possible to use mixtures. It is for instance possible to use a mixture of algae, one type exhibiting optimum growth at low teπφeratures and one type exhibiting optimum growth at high temperatures. Depending on the season, one type will have the upper hand, which is advantageous in that a good activity is always ensured.

It is possible that the liquid manure does not contain all nutrients necessary for optimum growth of the algae or does not contain them in the right proportion. For instance, it is possible that the N/P ratio is too high, in other words, there is a deficiency of phosphate. In this situation, it may be advantageous to add a minor additional amount of phosphate to the influent of the ponds or one of the ponds. In the case of phosphate, it is useful to add it as phosphoric acid because this moreover yields a reduction of the pH. A further aspect of the invention is that additional nutrients are added to the influent of the algae pond(s) , the nutrients in question being present in the liquid manure in a concentration so low that they are growth-limiting. In the case of phosphate, this can be added as phosphoric acid. It is possible that the amount of liquid manure to be processed is so large that the surface area of the algae pond would have to be larger than is desired, in this situation it is possible to remove a large proportion of the nitrogen, and also of the phosphorus, through a prepurification consisting of a nitrification/denitrification process. This process can be carried out continuously, semicontinuously or batchwise. It may moreover be carried out in two steps, i.e., denitrification and nitrification, but also in one step combining the two processes. The process can moreover be carried out efficiently by using a packing material in the reactor consisting of thin, loose fibers which are fixed at only one point: a system with so-called "soft fiber filling elements". The combination of this denitrification with an algae pond is highly efficient because the denitri ication need not be controlled with extreme accuracy since the final discharge quality requirement is achieved in the well- controlled algae pond. The phosphate content can be reduced in the denitrification as well, either biologically or chemically. A further aspect of the invention is that the nitrogen content and the phosphate content of the liquid manure are reduced in a pretreatment consisting of a denitrification/nitrification process which is carried out in conventional ways or with the aid of the so-called "soft fiber filling elements". This pretreatment may take place continuously, semicontinuously or batchwise, both as two separate processes and in one combined process. The algal biomass contains several substances which have a good effect on the health of humans and animals. These include vitamins, caratenoids and growth stimulators. The positive effect on the health of sows and piglets has been demonstrated with algae which had been cultured especially for that purpose and are dosed in amounts of approx. 10 g per day. From the liquid manure of a sow, per day approx. 50 g algal biomass can be cultured, i.e., amply sufficient for the above- mentioned effects. A further aspect of the invention is that the algal biomass which is formed in the purification of the liquid manure is used as feed for the animals to promote health and fertility.

The urine of pigs contains a relatively high concentration of chloride and this also applies to the purified liquid manure. In some areas, this is a bar to the discharge thereof into the surface water or to its use for raining. The pigs consume the chloride by way of the feed. The chloride is largely added to the feed by the cattle feed manufacturers. A part of the chloride is taken up by the sows and the piglets, another part remains in the solid part of the manure. Thus the liquid part of the manure contains an amount of chloride equivalent to 40% to 70% of the chloride in the feed. The purified liquid manure could therefore be used as drinking water for the pigs if the chloride content of the cattle feed is sufficiently reduced.

A further aspect of the invention is that purified liquid manure, purified utilizing algae or another method, optionally after sterilization, is used as drinking water for the animals, with the chloride content of the cattle feed or the content of other components in the cattle feed being adjusted to this situation.

A further aspect of the invention is that the effluent of the algae pond is fed directly to the animals, i.e., the liquid containing the biomass. This means, for instance, that the effluent of the algae pond is separated into a part which contains little or no biomass and which is used as flush water or for dilution and a smaller part which contains the greater part of the biomass and which is used as feed.

The effluent of the algae pond contains biomass which consists of algae and of bacterial biomass. Both are good food for daphnias and in same places in the world the effluent of the algae pond is accordingly supplied to "daphnias ponds". The daphnias in turn are fed to fish. It is also possible, however, to feed the daphnias in the chloride-containing water directly to the animals (pigs) . Daphnias are highly nutritive, they comprise approx. 60% proteins. This additional step may constitute a veterinary advantage because daphnias eat bacteria and also any pathogenic organisms that may be present.

A further aspect of the invention is that the effluent of the algae pond is directed to a daphnia pond and that the effluent of this pond, i.e., water with daphnias, is fed directly to the animals. It is also possible to filter the daphnias from the effluent and use them as feed.

The methods described hereinabove relate to the processing of liquid manure. The manure is first separated into solid manure and liquid manure, the idea being that the solid manure is removed to a central manure processing plant or to agricultural areas. It is also possible, however, for this solid manure to be processed in the same place as the liquid manure. This processing can be an anaerobic fermentation, but also, for instance, a drying process, a combustion or a wet oxidation. In these processes liquid streams and/or gas streams are released which contain undesired substances such as carbon dioxide, ammonia, odorous substances (stench) , ammonium salts, nitrates, and the like. These substances can also be processed in an algae pond. This may be the same algae pond that is used for the liquid manure or a separate one. The gaseous substances may be injected directly into the algae pond, but they may be also be first removed from the air stream in a gas scrubber and be added to the pond along with the scrubbing water. If the scrubbing water must be acid, for instance for binding ammonia, then phosphoric acid can be used for the acidification.

An aspect of the invention is that gaseous and liquid waste streams from plants for processing solid manure are purified by means of an algae pond, optionally after a pretreatment. The processing of solid and liquid manure is coupled to this. A further aspect is that if an ammonia- containing stream is treated by means of a gas scrubber with a view to removing ammonia, the scrubbing water can be acidified with phosphoric acid.

The processing of the solid manure may consist of a drying process. This requires heat, which can be obtained in whole or in part from solar energy by designing the drying plant as a solar collector. The plant consists of a closed space through which air is passed which may or may not have been preheated. On the side of the light, the space is closed witii a light-permeable heat-insulating material. The manure is spread out, either as such or in granular form.

The methods described hereinbefore relate to the processing of liquid manure. The invention can be used for processing pig manure but also for processing manure from other animals, such as cows, calves, chickens, geese, ducks, furred animals, and the like. The invention moreover relates to the processing of other waste streams which contain organic substances and, further, also nitrogen and phosphorus, where optionally additional phosphorus can be added. These are, for instance, waste streams of breweries, dairy factories, other foodstuff industries, and the like.

Claims

C AIMS

1. A method for processing liquid manure, comprising separating the manure into a fraction substantially consisting of liquid components of the manure and a solid part, supplying the liquid manure and diluting water to an algae pond which contains algae and/or bacteria as biomass, the amount of diluting water being sufficient for diluting the liquid fraction by a factor between 2 and 50, removing or largely removing the biomass from the effluent of the algae pond and returning the volume which was added as diluting water and flush water, to the influent and/or to the animal quarters for reuse.

2. A method according to claim 1, wherein the effluent water, after removal of the biomass, is decolored by a slow filter with sand, anthracite, active carbon or any other suitable material as filter material, optionally in combination with UV exposure and/or ozone and/or a treatment with hydrogen peroxide.

3. A method according to claim l or 2, wherein the quality of the effluent is adjusted and controlled by measurement of the concentration of ammonia, nitrate and phosphate, whereby the effluent stream is controlled and, coupled thereto, the influent as well, said adjustment and control taking place automatically, semiautαmatically or nonautomatically.

4. A method according to claims 1-3, wherein the depth of the liquid in the algae pond(s) and the concentration of the biomass are optimally adjusted to each other and controlled by measuring the concentration of the biomass through light absorption with light of an optimum wavelength, and by coupling this absorption to the influent and effluent streams or additional supply of water, which control can be carried out automatically, semiautomatically or nonautomatically.

5. A method according to claims 1-4, wherein two or more series-arranged algae ponds are used, which may differ from each other in surface area and in depth, the effluent of one pond being used in whole or in part, with or without a prior treatment, as influent for a next pond.

6. A method according to claims 1-5, wherein the biomass of the effluent stream is used as animal feed.

7. A method according to claims 1-6, wherein the purified effluent from which the biomass, or a part thereof, has been removed, is used as drinking water for the animals.

8. A method according to claims 1-7, wherein the effluent, optionally after concentration, is in its entirety fed to animals.

9. A method according to claims 1-8, wherein the effluent of the algae pond(ε) is passed into a daphnia pond and the cultured daphnias are separated from the effluent of this pond and are used as feed for animals.

10. A method according to claims 1-8, wherein the effluent of the algae pond(s) is passed to a daphnia pond and the effluent of this pond, i.e., liquid with daphnias, is fed to the animals.

11. A method according to claims 1-10, wherein the algae pond(s) are used for processing liquid manure and for processing gas streams and liquid streams originating from the processing of the solid manure, while these streams may undergo some pretreatment, such as gas scrubbing of the gas streams, with the scrubbing water being acidified, preferably with phosphoric acid.

12. A method according to claims l-ll, wherein the liquid, and, possibly, solid, manure to be processed comes from pigs, cows, calves, poultry, furred animals or consists of mixtures thereof.

13. A method according to claims 1-12, wherein the solid constituent of the manure is dried by means of solar energy in a closed insulated space with air being passed therethrough.

14. A method according to claims 1-13, wherein the dried manure is combusted and the heat released is used as additional heat for a drying plant of manure or other wet solid substances.

15. A method according to claims 1-14, wherein the liquid stream to be processed does not consist of liquid manure but consists of waste streams, for instance from breweries, dairy factories and other (foodstuff) industries.