NL2026407B1

NL2026407B1 - Integrated livestock facility and manure processing system

Info

Publication number: NL2026407B1
Application number: NL2026407A
Authority: NL
Inventors: Don Douglas De Groot Erwin; Albertus Venantia Van Hooft Petrus; Hendrikus Johannes Meijer Andreas
Original assignee: Dutch Farmer Solutions Global B V
Priority date: 2020-09-03
Filing date: 2020-09-03
Publication date: 2022-05-04

Abstract

The invention relates to an integrated livestock facility and manure processing system, comprising a space configured for holding livestock (1a) and a manure vault (1b) underneath said space; a vessel for holding manure slurry (2); a separator section (3, 4) configured for separating manure slurry; a denitrification/nitrification section (5,6); a solids removal unit (7) configured to reduce the solids content of a fluid obtained in the denitrification/nitrification section and a further purification section (8a, 8b, 8c, 9). The invention further relates to a method for processing manure slurry.

Description

P128100NL00 Title: Integrated livestock facility and manure processing system The invention relates to a method for processing a manure slurry. The invention further relates to an integrated livestock facility and manure processing system.

INTRODUCTION In principle, manure from livestock is a useful product, because it is rich in nutrients. However, in view of an ongoing need of reducing emissions of greenhouse gasses, like methane (CH), and nitrogen-compounds, such as ammonia (NH3) and nitrous oxide (N20), there is ongoing need to improve the processing of agricultural waste-products, such as manure, from livestock, to reduce the unwanted emission of such components from manure into the atmosphere or in areas, e.g. nature parcs or urban areas, nearby places wherein the livestock are held. In many livestock operations, livestock (such as dairy-cattle or pigs) are held for a substantial amount of their lifetime in stables. The floors of the stables typically contain openings, such as a grid, through which urine and faeces produced by the livestock can pass. The urine and faeces (forming the manure slurry) are typically collected and stored in manure vaults underneath the floors. The manure vaults are emptied at intervals, e.g., about once per month. For legal or practical reasons, the manure collected from the vaults is not always immediately put to further use, e.g., to spreading manure over farmland or to be further processed (e.g., to produce dry manure). In many countries there are restrictions with respect to spreading out manure on land. E.g., in The Netherlands during a period of about five months per year (between about 1 September and about 1 February) it is not allowed to spread out manure. Therefore, manure taken from manure vaults is often stored in a manure container, such a silo, until further use.

Installations and methods have been described in the art to process livestock waste streams, e.g. to reduce the content of organic and nitrogen-rich matter.

For instance, ES2371612 relates to an installation for purifying slurry generated in livestock farms, comprising a homogenization tank, several biological reactors and a decanter. In use, a mixture of manganese, calcium carbonate, potassium chloride and citric acid is added, which are said to be nutrients to allow for a better unification of the liquid phase and the solid phase in the manure. Once the mixture is unified, it passes to the first biological reactor in which air is injected. The object of treatment of this bioreactor is to micronize organic matter until it is liquified. Only thereafter, the mixture is passed to a reactor downstream of the first bioreactor, wherein nitrate is removed (a denitrification tank) from the slurry. Downstream of the denitrification tank, a further biological reactor is provided, of which the outlet is connected to a decanter (for removing solid) equipped with an outlet for purified water and a recirculation circuit to the homogenization tank. EP3456408 relates to a similar system; it is stated to have several improvement for increasing performance and/or reducing costs in the purification of livestock waste. The specific problem of the formation of ammonia is not mentioned in either of these publications.

However, ammonia formation in manure (or manure slurry) is a serious problem. Ammonia is a volatile substance, which is harmful to livestock and humans. Further, ammonia - which may be converted to nitrate in the environment, is a contributor to nitrogen-compound deposition in areas surrounding the livestock facility, if emitted therefrom. The present invention in particular aims to provide a method for processing manure, respectively a system for the reduction in the emission of undesired nitrogen compounds, more in particular ammonia, from livestock facilities.

SUMMARY OF THE INVENTION The inventors realized that there are several contributors to ammonia formation in manure or manure slurry. Ammonia production already takes place inside the gastro-intestinal tract of livestock. The inventors further realized that that ammonia in manure (slurry) is not only ammonia formed in the gastro- intestinal tract. Ammonia is also formed by a reaction between faeces and urine. Furthermore, ammonia can be formed in nitrification reactors, wherein ammonia content is supposed to be oxidized by conversion into nitrate. However, in practice manure also contains substantial amounts of nitrogen-containing organic compounds, like amino acids or peptides. These can be degraded under aerobic conditions in nitrification reactors, thereby also forming nitrate. The inventors also realized that reducing the content of organic nitrogen-containing compounds upstream of a nitrification treatment is useful to achieve improved efficiency and/or effectivity of nitrogen-compound removal.

Starting from these insights the inventors developed an alternative method and an integrated livestock facility and manure processing system, which method and system can serve as an alternative for known methods and systems to treat manure slurry comprising a solid phase and a liquid aqueous phase. Herein, emission of undesired nitrogen compounds, in particular ammonia, nitrous oxide and/or nitrate, into the environment is advantageously reduced in a more effective and/or more efficient manner.

In particular the inventors found it advantageous to remove the manure on a daily basis, hereby reducing the formation of ammonia. The daily production of manure is separated into a thick fraction, having an increased solids content, which, optionally after drying, may be used as nutrients in agriculture (as a natural fertilizer) and a thin fraction, having a reduced solids content and subject the thin fraction to a nitrification and denitrification treatment as well as a series of further downstream treatments to obtain a purified aqueous liquid, with a sufficient quality to be used e.g. for irrigation purposes and/or to clean livestock facilities to facilitate the daily removal of manure. By removing a substantial part of the solids, which typically include nitrogen-containing organic compound from the material to be subjected to nitrification, the overall efficacy of the nitrification process is increased.

Accordingly, the present invention relates to a method for processing a manure slurry comprising a solid phase and a liquid aqueous phase, wherein - (a) the manure slurry is separated into a fraction having an increased solids content (thick fraction) — which typically is a wet fraction - and an aqueous fraction having a reduced solids content. (thin fraction), compared to the manure slurry; - (b) the thin fraction (obtained in step (a)) is subjected to a microbiological denitrification treatment and to a microbiological nitrification treatment thereby obtaining an aqueous fluid having a reduced nitrogen compound (e.g. organic nitrogen, ammonia, nitrite, nitrate) content, compared to the thin fraction; - (e)the aqueous fluid having a reduced nitrogen content (obtained in step (b)) is subjected to a solid removal treatment to obtain an aqueous liquid having a reduced solids content compared to the aqueous fluid having a reduced nitrogen content; and - (dd), the aqueous liquid (obtained in step (c))is subjected to a further purification to remove micro-organisms and dissolved salts thereby obtaining a purified aqueous liquid.

Further, the invention relates to an integrated livestock facility and manure processing system (suitable for carrying out a method according to the invention), comprising - a space configured for holding livestock (1a), preferably a roofed space, and a manure vault (1b) underneath said space; a vessel for holding manure slurry (2); a separator section (3, 4) configured for separating manure slurry into a thin fraction and a thick fraction; a denitrification/nitrification section (5,6) configured subjecting the thin fraction to nitrification and denitrification; a solids removal unit (7) configured to reduce the solids content of a fluid comprising solids and a purification section (8a, 8b, 8¢,9) configured to reduce the content of solids, micro-organisms and/or dissolved salts from a fluid; - a passage way (101) for passing manure slurry from the vault (1b) to the vessel for holding manure slurry (2); - a passage way (102) for passing manure slurry from the vessel for holding the manure slurry (2) to the separator section (3, 4); - a passage way (104) for feeding thin fraction from the separator section (3,4) to the denitrification/nitrification section (5,6);

- a passage way (106) for feeding thin fraction that has been treated in the denitrification/nitrification section (5,6) to the solids removal unit (7); - apassage way (107, 107a, 107b) for feeding the aqueous liquid having reduced solids content to the purification section (8a,8b,8¢,9). 5 Specific embodiments are concisely presented in claims 2-11 and 13-17, and further described in detail below.

The present invention provides an effective way to obtain both a nutrient-rich fraction (the thick fraction) suitable to produce compost for use in agriculture, forestry or gardening and water that can be re-used on the farm or discharged to surface water while being compliant to environmental regulations . In particular, it is possible to realise a reduction of 90 wt.% or more of the nitrogen compounds content (calculated as N) in the purified aqueous liquid (water) obtained in accordance with the invention, compared to the manure slurry. In a preferred embodiment, ammonia emission is reduced by about 97 % or more, compared to the manure slurry.

Further, it is possible to remove substantially all phosphorous compound from the aqueous phase of the manure slurry, to obtain aqueous liquid (water) with a strongly reduced phosphorous compound content. A reduction of 97 % or more (calculated as P) in thin fraction, compared to the manure slurry prior to the separation into the thick and thin fraction, is feasible.

The present invention also can provide a contribution to reducing emissions of one or more of the following components, wherein reductions are compared to reference values as applicable in the Netherlands per 1 September 2020, as provided by the Dutch Government (see : https: # rwsenvironment.euf or https:/www.infomil.nl/onderwerpen/landbouw/emissiearme- stalsystemen/emissiefactoren-per/).

A carbon dioxide equivalent emissions, possibly with 90 % or more, or even with 95 % or more, is feasible. E.g., methane emission reduction may be about 90 % or more. Nitrous oxide (N20) emission reduction may be about 75 % or more.

A reduction of fine particles into the atmosphere, is feasible. For secondary fine particles, a reduction of about 97 % or more is feasible.

The present invention can further contribute to a reduction of odour nuisance, due to a reduced emission of odorous components. For instance, odour emission may be reduced by about 50 % or more, in particular about 60 % or more.

Features, aspects, and advantages of the system and method of the present invention will become better understood from the following description, appended claims, and accompanying Figure 1, which schematically shows a preferred integrated livestock facility and manure processing system according to the invention.

Terminology used for describing particular embodiments is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term “or” includes any and all combinations of one or more of the associated listed items, and is thus broadly to be interpreted as “and/or”, unless the context clearly indicates otherwise. It will be understood that the terms "comprises" and/or "comprising" specify the presence of stated features but do not preclude the presence or addition of one or more other features. It will be further understood that when a particular step of a method is referred to as subsequent to another step, it can directly follow said other step or one or more intermediate steps may be carried out before carrying out the particular step, unless specified otherwise. Likewise, it will be understood that when a connection between structures or components is described, this connection may be established directly or through intermediate structures or components unless specified otherwise.

As used herein, nitrogen compounds are chemical compounds comprising at least one nitrogen and at least one other atom, i.e. compounds other than nitrogen gas (Nz). Nitrogen compounds present in manure slurry or formed during processing in accordance with the invention comprise in particular nitrogen compounds selected from the group consisting of organic nitrogen compounds (e.g. amino acids, peptides, proteins), ammonia and inorganic compounds composed nitrogen and oxygen (such as nitrate, nitrite). When referred herein to a nitrogen content’ or ‘nitrogen emission’, this is short-hand for ‘nitrogen-compound content’ respectively ‘nitrogen-compound emission’.

The term “(at least) substantial(ly)” or “(at least) essential(ly) “is generally used herein to indicate that it has the general character or function of that which is specified. When referring to a quantifiable feature, this term is in particular used to indicate that it is at least 50 %, more in particular more than 75 %, even more in particular more than 90 % of the maximum that feature. The term “essentially free” is generally used herein to indicate that a substance is not present (below the detection limit achievable with analytical technology as available on the effective filing date) or present in such a low amount that it does not significantly affect the property of the product that is essentially free of said substance.

In the context of this application, the term "about" means generally to include at least a deviation of 20 % or less from the given value, in particular a deviation of 10% or less, more in particular a deviation of 5% or less.

Suitable passage ways include typically conduits or other channels allowing the passage of a process stream, such as the slurry, thin fraction, aqueous fluid or liquid, a gas etc from a first processing unit to a second processing unit.

The invention is described more fully hereinafter with reference to the accompanying figure, in which embodiments of the invention are shown. In the figure, the absolute and relative sizes of systems, components, layers, and regions may be exaggerated for clarity. Embodiments may be described with reference to schematic and/or cross-section illustrations of possibly idealized embodiments and intermediate structures of the invention. In the description and drawings, like numbers refer to like elements throughout. Relative terms as well as derivatives thereof should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the system be constructed or operated in a particular orientation unless stated otherwise.

For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described.

DETAILED DESCRIPTION The manure slurry to be processed in accordance with the invention generally originates from a livestock facility (1) where livestock is held, preferably cattle or pigs. However, the method respectively system according to the invention may also be used for treatment of manure from other farm animals, in particular from poultry, sheep, goat or horses. Particularly good results are obtained with manure from pigs.

Preferably, the manure slurry is a mixture of urine and faeces, optionally comprising further organic matter, e.g. straw. Good results are in particular achieved with a liquid manure known in Dutch as “drijfmest! or “gier”.

Optionally, zeolites are added as dietary supplement to the livestock feed to suppress ammonia production in the gastrointestinal tract, usually in amount of about 0.5- 4 wt.%, in particular about 2 wt.%. Suitable supplements are known in the art, e.g. from Clays as dietary supplements for swine: A review, Subramaniam and Kim, Journal of Animal Science and Biotechnology (2015) 638.; The role of natural and synthetic zeolites as feed additives on the prevention and/or the treatment of certain farm animal diseases: A review, D. Papaioannou et al., Microporous and Mesoporous Materials 84 (2005) 161-170; Zeolites in poultry and swine production, Schneider et al., Ciëncia Rural, Santa Maria (2017), v.47: 08, e20160344; Effects of dietary inclusion of a zeolite (clinoptilolite ) on performance and protein metabolism of young growing pigs, H.D. Poulsen, N. Oksbjerg, Animal Feed Science and Technology 53 (1995) 297-303. Clinoptilolite is in particular preferred. As a result of including zeolite in the feed the average daily gain and/or feed conversion is improved, hereby significantly reducing the total content of nitrogen compounds (such as ammonia) in urine , in particular by up to about 20 %.

Usually, the manure slurry to be treated is a mixture of faeces and urine. The faeces and urine (forming the manure slurry) are typically collected in a manure vault (1b) underneath a space (1a) wherein the livestock is held, usually a roofed space, in particular a roofed space with side-walls (a stable). Stables for livestock are advantageously provided with an air circulation system. Air taken from the space wherein the livestock is held is preferably treated to remove odorous/potentially harmful components, such as ammonia, and/or dust particles. This can be done in a manner known per se, such as by making use of an air scrubber (10). Herein the air from the space wherein livestock is held, is e.g. passed through an acidic aqueous liquid, such as a sulphuric acid solution (pH, e.g., about 1 to about 2). It is also possible to use biological air scrubbers. These are advantageous for use in accordance with the present invention, since they do not need to be operated under strongly acidic condition; the used scrubber liquid (to be treated in the denitrification/denitrification section contains thereby no or less components that may be harmful to the micro-organisms for (denitrification.

Biological air scrubbers are generally known in the art and make use of bacteria converting ammonia into nitrate and/or nitrite.

The used scrubbing liquid (comprising ammonia, and — at least in case of biological scrubbers nitrite and nitrate), can also be subjected to denitrification and nitrification. Advantageously, the used scrubbing liquid is combined with the thin fraction in the denitrification reactor (in Figure 1: fed via conduit 110 to denitrification unit 5).

Considering that ammonia is in particular formed as a reaction between faeces and urine, it is preferred that the processing of the manure slurry starts relatively shortly after its formation, to avoid excessive formation of ammonia and subsequent evaporation into the livestock facility. Accordingly, the manure slurry is usually fed at least once a week, preferably at least 3 times per week, in particular at least about 7 times a week to a separation section (3,4) wherein it is separated into the thick fraction and the thin fraction, or at least fed to a, preferably air-tight, vessel for holding manure slurry (2), e.g. a closed basin or silo.

The manure slurry may be fed directly from the livestock facility to the separation section. Preferably, the manure slurry is first fed into a vessel for holding manure slurry (2), preferably via a conduit 101 between the vault 1b and vessel 2. The vessel 2, generally serves to provide buffer capacity, in particular when maintenance is carried out downstream in the installation for treating the manure slurry or parts thereof. Further, the manure slurry may be pre-treated in the vessel (2): e.g. nutrients for micro-organisms may be added; the manure may subjected to a microbiological treatment wherein carbon-containing compounds are converted to biogas, etc. Such treatment can be based on methodology generally known in the art per se. Further, in particular during start-up of the method/system of the invention manure slurry may be stored for a sufficient time to allow the growth of biomass, e.g. for allowing a microbiological treatment in the vessel or downstream thereof at a desired rate. In general, at least after a start-up phase, during normal operation, the average residence time in the vessel 2 can be relatively short, typically in the same order of magnitude as the average interval between supply step of the manure slurry from the livestock facility to the vessel, thus advantageously at least about once a week, more preferably at least about 3 times a week, in particular at least about once per day. The vessel 2 for holding the manure slurry is preferably provided with means for agitating the manure, such as a stirring device, which allows maintaining a homogeneous fluid.

In order to facilitate frequent removal of the manure from the livestock facility, in particular to allow efficient removal several times a week, such as about daily, the manure is preferably diluted with water or an aqueous liquid, as may be obtained from the further purification (d) in a method according to the invention. Advantageously, filtrate (109a, 109b) is used, obtained after subjecting the aqueous effluent with reduced solids content (107) from the solids removal unit (7) to hydrofiltration, ultrafiltration and/or nanofiltration (units 7, 8a and 8b in figure 1), wherein the nitrified and denitrified thin fraction has been treated. Such filtrate has been found to have sufficient microbiological and chemical quality to be used as cleaning liquid for the livestock facility (via conduit 109d), respectively dilution medium for the manure slurry via conduit 109¢. Alternatively or in addition a further purified aqueous liquid can be used, such as the permeate of a reverse osmosis (RO) which is preferably provided downstream of a filtration unit in the purification section of a system according to the invention (unit 9, fed from unit 8 via conduit 108 in figure 1). Frequent cleaning/diluting not only reduces average residence time of the manure in the livestock facility (1), it also contributes to a significant source directed decrease of ammonia and optionally other harmful components (e.g. manure gases, such as HzS, CH), whereby also air quality in the livestock facility is improved, and accordingly well-being and safety of animals in the livestock facility.

The manure slurry is separated into a thin fraction, with reduced solids content and a thick fraction, which has an increased solids content. The thick fraction generally still contains some water.

It generally has a pasty, semi-solid consistency.

The thick fraction is rich in nutrients and may be used directly or after further processing as a nutrient for plants, e.g. in agricultural production of plants, in forestry or in gardening.

Examples of further processing include drying, mixing it one or more other nutrient rich waste-products or adding other nutrients, or composting.

In principle the thin fraction may be obtained in a single separation step, in particular by making use of a press, such as a screw-press or a sieve-strap press.

However, the inventors found that efficiency is improved by subjecting the fraction with reduced solids content obtained from the first separation step is subjected to a further step wherein the solid content is further reduced.

In particular for improved efficiency, it is preferred that in the first step relatively large particles are removed to obtain an intermediate fraction with reduced solids content and that in a further separation step also relatively small particles are removed to obtain the thin fraction to be treated by nitrification and denitrification.

Advantageously, in a first step a device configured to remove relatively coarse particles from the fluid phase is used.

Such devices can in particular be selected from devices suitable to dewater sludges.

Preferably, a screw press or a sieve-strap press is provided as a first separator unit to remove relatively coarse particles.

In figure 1 the first separator unit is shown as unit 3,

which is connected to conduit 102 with the outlet for manure from vessel 2. The first separator unit (3) usually has a cut-off (such as pore-size) at 100 um or more, preferably at least 200 um or more, in particular at about 250 um.

The cut-off of the first separator unit (3) usually is about 800 um or less, preferably 700 um or less, in particular about 600 um or less The further separator unit preferably is a centrifuge.

In figure 1 this is shown as unit 4, which is conneeted via conduit 103 with the outlet for the intermediate fraction from separator unit 3. The further separator unit (4), downstream of the first separator unit (3) usually has a cut-off (such as pore-size) at 1 um or more, preferably at least 5 um or more, in particular at about 10 um.

The cut-off of the further separator unit (4) usually is less than 100 um, preferably 50 um or less, in particular about 20 um or less.

The fraction that is retained by the further separator unit (increased solids content compared to the intermediate fraction) can be combined with the fraction enriched in solids obtained in the first separator.

It has been found that a lower cut-off is advantageous for directing the majority of nutrients (preferably including the majority of phosphates) and carbon-containing compounds into the fraction(s) enriched in solids, whereby these are particularly useful for growing plants (e.g. as compost), and whereby the thin fraction has a relatively low content of nutrients and carbon compounds, which is advantageous for the subsequent nitrification and denitrification treatment. The resulting thin fraction is then subjected to nitrification and denitrification (in figure 1: fed into denitrification reactor 5 via conduit 104). In principle, the nitrification and denitrification conditions can be based on conditions known in the art, using nitrifying bacteria and denitrifying bacteria under conditions known in the art, e.g. as described in Development of a second- generation environmentally superior technology for treatment of swine manure in the USA, M.B. Vanotti et al., Bioresour. Technol. 100 (2009), 5406-5416, in Mestverwerking varkenshouderij systeem Biovink, Evink te Oosterwolde (Gld), R.W. Melse et al., Wageningen UR, 2002 or in Nitrification and denitrification in the activated sludge process, M.H. Gerardi, ISBN-13: 978-0:171065081.

In principle, the treatment of the thin fraction in the nitrification/denitrification section can be done in a single reactor, wherein the thin fraction is alternatingly subjected to nitrification and denitrification, by alternating between aerobic and anaerobic. Generally, use is made of separate reactors though, because this facilitates controlling the process conditions, and improving efficacy and/or efficiency of the removal of nitrogen compounds, such as ammonia and nitrate from the thin fraction.

The nitrification/denitrification chemical reactions can overall be described as a two-step process. Nitrification is the conversion of ammonia (dissolved in aqueous solution and protonated to form ammonium, NH4*) into nitrate (NOy), using oxygen. The overall chemical process can be described by the following formula: NH4 +2 Og ---> NOx + 2 Ht + H20 The nitrification process is catalysed by nitrifying bacteria, under aerobic conditions, and may -in practice — be a two-step process, wherein ammonium is first converted into nitrite (NO2) and subsequently into nitrate.

Reaction conditions, such as pH and temperature, can be chosen dependent on the nitrifying bacteria. Generally, Nitrosomas and Nitrocbacter bacteria can be used, preferably at a pH in the range of about 7 about 8.5 pH can e.g. be maintained by adding a buffer such as sodium bicarbonate. Temperature can be about ambient; temperature is preferably in the range of about 20 to about 30 °C. If desired, the temperature is actively maintained within this range. Advantageously, temperature of the air introduced in the nitrification reactor is controlled within a range at which the nitrification reaction proceeds fast, in order to maintain at least a reaction zone in the nitrification reactor having a temperature in this range, at which the nitrification reaction accomplished. Much preferred is a temperature of the aeration air in the range of about 25 to about 30 °C. Nitrifying bacteria are generally UV-sensitive. Accordingly, the nitrification reaction is usually carried out in the absence of UV-VIS light, preferably in the dark. During nitrification the reactor is actively aerated.

The denitrification process is responsible for converting nitrate into nitrogen gas (Nz). The needed energy is generated by oxidation of a carbon source, e.g.

24 NO: + 24 H* + 5 CsH1204 ---> 12 N2 + 30 CO: + 42 H20 Examples of carbon sources are saccharides, e.g. a monosaccharide (as illustrated in the above reaction formula) or a disaccharide. The saccharide, or part thereof, may be from a different (waste) stream, such as molasse; however, it is also possible to use solely or in addition carbon sources originating from the manure slurry abundant in the thin fraction.

The denitrification is catalysed by denitrifying bacteria. Besides nitrogen gas, in practice nitrous oxide is also usually formed (not shown in the reaction). It is considered that formation of nitrous oxygen can be reduced in accordance with the invention, for instance due to one or measures that contribute to less fluctuations in the process conditions, such as a (more) regular/frequent removal of the manure slurry from the livestock facility or the reduced content of solids (which solids content may be heterogenous in composition over time in the manure slurry) before the denitrification, by the separation into the thick fraction and thin fraction, preferably by a pressing step, preferably making use of a screw-

press or a sieve-strap press, followed by a centrifugation step; such separation is particularly suitable to reduce fluctuations in solids characteristics, qualitatively or quantitatively. In particular, good results are achieved with screw-pressing, followed by centrifugation.

The denitrification process usually takes place under anaerobic or near anaerobic conditions. Thus, generally, the dissolved oxygen content during denitrification is kept below about 1.5 mg/l, preferentially below 1.0 mg/l to essentially avoid the switching of facultative anaerobic denitrifying bacteria, which may be present, to aerobic nitrification. The pH during denitrification is preferably in the range of about 7 to 7.5. Denitrification temperature can usually be ambient; in particular the temperature can be as low as 0 °C or less, e.g. as low as about -3 °C. Denitrification temperature preferably is up to about 35 °C, in particular about 30 °C or less.

Thus, from both reactions, it is apparent that one would generally first carry out the step of nitrification to convert ammonia, and thereafter the step of denitrification to convert nitrate into the harmless nitrogen gas; however, organic substances in the thin fraction may also be degraded aerobically during the nitrification. These organic substances usually include organic substances containing nitrogen, such as amino acids and/or peptides. The degradation thereof proceeds much quicker than the degradation of ammonia by nitrifiers. Therefore, organotrophs (that degrade carbon material) can reproduce more quickly (order of magnitude: within 15-30 min) than nitrifying bacteria (order of magnitude: within 48-72 hrs) that convert ammonia in nitrite and nitrate. Because it is an object of the method to remove ammonia from (the thin fraction of) the manure slurry, the content of carbon-containing organic substances in the nitrification reaction is preferably kept relatively low, in particular at about 60 mg/l carbonaceous biological oxygen demand (cBOD), more in particular at about 40 mg/l or less ¢BOD. In order for nitrogen related biological oxygen demand (BOD) to be reduced, carbon BOD first must be reduced to a relatively low concentration (<40 mg/l) to ensure that adequate degradation of those soluble and simplistic forms of ¢BOD that inhibit the activity of nitrifying bacteria occurs. The inventors realised that it is possible to improve efficiency and/or efficacy of reducing ammonia content in the thin fraction by reversing the order of nitrification and denitrification, i.e.

to first subject the thin fraction to denitrification conditions (in denitrification reactor 5) and thereafter to nitrification conditions (in nitrification reactor 6). Subsequently, at least a part of the thin fraction having been subjected to the nitrification conditions is subjected again to denitrification. In principle this can be done in a further denitrification reactor down-stream of the nitrification reactor. However, it is preferred to recycle at least part of the thin fraction that has been subjected to nitrification to the denitrification (in figure 1: thin fraction from separator unit 4 enters the denitrification reactor 5 via conduit 104, is then fed to nitrification reactor 6, where it is aerated, and at least part is recycled to denitrification reactor 5 via recycle conduit 111). Preferably the ratio of influx via conduit 104 and 111 is between 4:1 and 2:1 respectively, more preferably about 3:1. In practice, the denitrification reactor and the nitrification reaction are first filled and recirculation between nitrification reactor and denitrification reaction is carried out for a number of times. Once the desired concentration of bacteria is reached for carrying out the respective reactions, the reactors have sufficient capacity to process the (daily) production of manure and the effluent from the nitrification and denitrification treatment can be fed to the next processing step (usually after the reduction in concentration(s) of nitrogen compounds to the calculated or measured maximum target concentration(s)).

The effluent from the nitrification and denitrification treatment is an aqueous fluid having a reduced nitrogen-compound content compared to the thin fraction upstream nitrification and denitrification treatment. It generally contains non-dissolved matter, such as biomass (micro-organisms such as bacteria), and optionally residual organic substances and/or non-dissolved inorganic substance.

Accordingly, downstream processing is needed to obtain an aqueous liquid that is suitable for being used in e.g. cleaning the livestock facility or for irrigation of agricultural land, or that is sufficiently clean to be discarded into the environment. Typically, the effluent from the nitrification/denitrification treatment is fed to a solids removal unit, such as a settler, in particular a decanter or clarifier (in figure 1: effluent from nitrification reactor 6 is fed into solids removal unit 7 via conduit 106). In the solid removal unit 7 a sludge is formed, enriched in solids and aqueous liquid having a reduced solids content compared to the nitrified and denitrified thin fraction that has been fed in to the unit 7. Sludge (containing biomass) is usually recycled to the nitrification or denitrification treatment, preferably to the denitrification reactor 5. Alternatively or in addition sludge may be recycled to vessel 2 for holding the manure. In figure 1, these recycles are shown as conduits 112, 112a and 112b respectively.

The aqueous effluent having a reduced solids content from the solids removal unit 7 is subjected to a further purification treatment. The effluent generally contains micro-organisms (such as denitrifying bacteria an nitrifying bacteria) and/or microparticles, e.g. of inorganic material and/or non-degraded organic substances. These can be removed using one or more further purification units (8 and 9 in figure 1). Preferably, the effluent is subjected to filtration, in particular using at least one technique selected from the group of hydrofiltration, micro-filtration, ultrafiltration and nanofiltration. It is thus possible to obtain a filtrate that can be used to dilute manure (slurry) in the livestock facility (1), e.g. by using it as cleaning water in the livestock facility to clean the space where livestock if held or the vault underneath the space, or to dilute manure slurry in the vessel (2) for holding manure slurry. This saves water and furthermore its combination with the manure slurry increases volume, contributing to a reduction of the average residence time of the manure slurry in the livestock facility (in the vault 1b) or the vessel 2 for holding manure slurry, from a usual one month or more, to about week or less, in particular about 1 day or less, more in particular about 12 hours or less.

Good results are achieved with hydro filtration (8a), and in particular with a filtration using a (paper) belt filter. Usually, the cut-off of this filtration is in the range of about 1 to about 30 um For this filtration, preferably a filter is used with a cut-off of about 20 um or less, in particular about 10 um or less. Usually, the filtrate is then further treated by a further filtration (end-filtration; units 8b and 8c in figure 1, fed via conduit 107a), using one or more filters with a lower cut-off than the previous (hydro) filtration. The end-filtration usually comprises an ultrafiltration (UF, 8b) and further a nanofiltration (NF, 80) after the UF. The cut- off of the UF-filter (unit 8b) generally is 10 nm or more; generally the cut-off of the UF filter (unit 8b) is 100 nm or less. The cut-off of the filter of the NF unit (8c) generally is 1 nm or more. The cut-off of the filter of the NF unit (8c) generally is 50 nm or less. Advantageously, the filtrate (109a, 109b) may be reused as cleaning liquid for the livestock facility (via conduit 109a and 109b to 1) or as dilution medium for the manure slurry silo 2 (via conduit 109 ¢). Further, UF/NF can be used to remove residual micro-organisms or potentially present pathogens, such as viruses and antibiotics. The effluent from the filtration system (8a, 8b, 8c, conduit 108 in figure 1) may further be subjected to reverse osmosis (RO, unit 9 in figure 1); usually, the effluent from solid removal unit 7 is first subjected to a filtration step (in units 8a 8b, 8c) and at least part of the filtrate thereof is subjected to RO. Particular good results are obtained with RO to remove relatively small substances dissolved in aqueous liquids, such as dissolved monovalent salts. The end-filtration making use of UF, NF and subsequent RO is an effective way to obtain water with a sufficient quality to allow the permeate to be released to surface water.

LEGEND TO FIGURE Livestock facility 1: livestock facility la space for holding livestock 1b manure vault Manure container 2 vessel for manure slurry Separator section 3 separator for removal of coarse solids (preferably a screw press or sieve-strap press) 4 separator for removal fine solids (centrifuge) Nitrification/denitrification section 5 denitrification reactor 6 nitrification reactor Solids removal 7: solids removal unit (settler/decanter)

Purification section 8a: hydrofiltration unit (belt filtration unit) 8b: ultrafiltration unit (UF) 8c: nanofiltration unit (NF) 9: Reverse osmosis unit (RO) Miscellaneous 10: air scrubber

Passage ways (conduits/channels) 101: passage way for feeding manure slurry from livestock facility (vault 1b) to vessel 2 102: passage way for feeding manure slurry from vessel 2 to separator section (to unit 3) 103: passage way for feeding intermediate fraction from separator 3 to separator 4 104: passage way for feeding thin fraction from separator 4 to nitrification/denitrification section (to denitrification reactor 5) 105: passage way for feeding thin fraction from denitrification reactor 5 to nitrification reactor 6 106: passage way for feeding nitrified&denitrified thin fraction to solids removal unit (settler/decanter 7) 107: passage way for feeding aqueous effluent from unit 7 to purification section (to hydrofiltration unit 8a) 107a: passage way for feeding aqueous effluent from hydrofiltration unit 8a to ultrafiltration unit 8b 107b: passage way for feeding aqueous effluent from ultrafiltration unit 8b to nanofiltration unit 8e 108: passage way for feeding filtrate of unit 8e to RO (9) 109: recycle for filtrate from purification section to vessel 2 or livestock facility 1: 109a: from ultrafiltration unit 8b 109b: from ultrafiltration unit 8e 109ec: to vessel 2

109d: to livestock facility 1 110: passage way for feeding used scrubbing liquid from scrubber 10 to nitrification/denitrification section (to denitrification reactor 5) 111: recycle for thin fraction from nitrification reactor 6 to denitrification reactor 5

112: recycle for sludge from unit 7 1124: to the nitrification&denitrification section 112b: to vessel 2

Claims

Conclusions

A method for processing a manure slurry comprising a solid phase and a liquid aqueous phase, wherein - (a) the manure slurry is separated into a wet fraction with an increased solid content (thick fraction) and an aqueous fraction with a reduced solids content (thin fraction), compared to the manure slurry; - (b) the thin fraction is subjected to a microbiological denitrification treatment and to a microbiological nitrification treatment, whereby an aqueous liquid having a reduced content of nitrogenous compounds (e.g. organic nitrogen, ammonia, nitrite, nitrate) compared to said thin fraction is obtained; - (c) the aqueous liquid having a reduced content of nitrogen compounds is subjected to a particulate removal treatment to obtain an aqueous liquid having a reduced solids content relative to the aqueous liquid having a reduced content of nitrogenous compounds; and - (d) the reduced solids aqueous liquid is subjected to further purification to remove microorganisms and dissolved salts, thereby obtaining a purified aqueous liquid.

A method according to claim 1, wherein the separation (a) comprises a pressing step, preferably using a screw press, to obtain said thick fraction and an intermediate aqueous liquid with reduced solids content and subjecting the intermediate aqueous liquid to a centrifugation step to removal of solid particles from the intermediate fluid phase to obtain said thin fraction.

3. Process according to claim 1 or 2, in which for carrying out the (b) nitrification and denitrification: the thin fraction obtained in step (a) is first fed to a denitrification reactor - without having undergone a nitrification step - in which the thin fraction is subjected to denitrification conditions (bl); The liquid fraction is fed from the denitrification reactor into a nitrification reactor in which the liquid fraction is subjected to nitrification conditions (b2), and then a first part of the liquid fraction which has been subjected to nitrification conditions is returned to the denitrification reactor and a second part of the liquid fraction is returned to the denitrification reactor. fraction subjected to nitrification conditions is subjected to (c¢) the solids removal treatment, which solids removal treatment preferably comprises a settling step.

A method according to at least one of claims 1 to 3, wherein further a used washing liquid - preferably a used washing liquid from a biological scrubber comprising ammonia, nitrite and nitrate - is fed from a livestock facility (in particular a barn), where the wash liquor has been used to remove ammonia from air from the livestock facility, and the spent wash liquor is subjected to nitrification conditions and to denitrification conditions along with the thin fraction.

A method according to at least one of the preceding claims, wherein particulate matter removed from the aqueous liquid having a reduced nitrogen content is recycled into the particulate removal treatment (c) and combined with the manure slurry upstream of the separation (a) or with the thin fraction to be subjected to denitrification and nitrification.

A method according to at least one of the preceding claims, wherein particulate matter removed from the nitrogen-reduced aqueous liquid in the particulate removal treatment (c) is subjected to a filtration in which microorganisms are removed from the liquid, whereby a filtrate is obtained and a portion of the filtrate is used to clean an area in which livestock is kept and the filtrate used for cleaning is combined with the manure slurry for processing.

A method according to at least one of the preceding claims, wherein aqueous liquid obtained in the solids removal treatment (¢) is subjected to (d1) a filtration to remove residual solids, thereby obtaining a filtrate and subjecting of all or part of the filtrate to (d2) a further purification, which further purification comprises reverse osmosis, where the purified aqueous liquid is obtained as a permeate.

A method according to any one of the preceding claims, wherein prior to the separation (a) of the manure slurry, the manure slurry is stored in a closed container (2) for holding manure slurry.

A method according to claim 8, wherein the manure slurry at least once a week, preferably at least 3 times a week, in particular about 7 times a week from a manure chamber (1b), below a space (1a) where livestock is kept, extracted and stored in the closed container (2) for holding the manure slurry until further processing.

A method according to at least one of the preceding claims, wherein the manure slurry is a mixture of faeces and urine, optionally comprising further organic material.

Method according to at least one of the preceding claims, wherein the manure slurry is a cattle or pig manure slurry.

An integrated livestock husbandry and manure processing system comprising a space configured for holding livestock (1a), preferably a space with a roof, and a manure cellar (1b) said space below, a closed container for holding manure slurry (2 ); a separator section (3,4) configured for separating manure slurry into a thin fraction and a thick fraction; a denitrification/nitrification section (5, 6) configured to subject the thin fraction to nitrification and denitrification; a solids removal unit (7) configured to reduce the solids content of a liquid comprising solids and a purification section (8a, 8b, 8e, 9) configured to reduce the content of solids, microorganisms and/or dissolved salts of a reduce fluid; a passageway (101) for feeding manure slurry from the manure pit (1b) to the manure slurry holding container (2); a passage (102) for feeding manure slurry from the manure slurry holding container (2) to the separator section (3,4); a passage (104) for feeding thin fraction from the separator section (3,4) to the denitrification/nitrification section (5.6); a passage (106) for feeding thin fraction treated in the denitrification/nitrification section (5,6) to the solid particle removal unit (7); a passage (107, 1074, 107b) for feeding aqueous liquid with reduced solids content to the purification section (8a,8b,8c,9).

An integrated livestock and manure processing system according to claim 12, wherein the separator section comprises a press, preferably a screw press, having an inlet in communication with the passage (102) such as to allow liquid supply from the container for holding manure slurry (2), the press (3) being configured to separate the manure slurry into a solid fraction, having an increased solids content and an intermediate fraction having a reduced solids content, said press having an outlet for the solids fraction and a separate outlet for the intermediate fraction, the outlet for the intermediate fraction communicating with a centrifuge inlet (4) via passageway (108) such that liquid can flow therethrough, the centrifuge being configured to further reduce the solids content in the intermediate fraction to obtain the thin fraction, which centrifuge has an outlet for the thin fraction passing through (104) connected in such a way that liquid can be supplied.

An integrated livestock farming and manure processing system according to claim 12 or 13, wherein the denitrification/nitrification section (5,6) comprises a denitrification reactor

(5) and a separate denitrification reactor (6), wherein the denitrification reactor (5) is positioned upstream of the denitrification reactor (6) and the denitrification reactor (5) has a liquid fraction inlet in communication with the liquid fraction outlet from the separator section (3,4) through the passage (104) for feeding thin fraction of the separator system (3,4) to the denitrification/nitrification section (5,6), and in which a recycle line (111) is provided for recycling thin fraction from the nitrification reactor (6) to the denitrification reactor (5).

An integrated livestock and manure processing system according to claim 12, 13 or 14, comprising a recycle (112, 1124, 112b) for returning sludge (enriched in solids) from the solids removal unit (7) to the denitrification/nitrification section (5, 6) or to the manure slurry container (2).

An integrated livestock and manure processing system according to at least one of the claims 12-15, wherein the livestock facility is provided with an air scrubber (10) - configured to remove odorous components, such as ammonia, and/or dust particles from air of the livestock facility under using an aqueous scrubbing liquid — the air scrubber being provided with an outlet which is fluidly connected to a channel (110) for feeding spent scrubbing liquid to the denitrification/nitrification section (5,6).

An integrated livestock farming and manure processing system according to at least one of claims 12-16, wherein the purification section comprises a hydrofiltration unit (8a), an ultrafiltration unit (8b) and a nanofiltration unit (8c), the ultrafiltration unit being positioned downstream of the hydrofiltration unit. and configured to receive filtrate from the hydrofiltration unit as a feed, the nanofiltration unit being positioned downstream of the ultrafiltration unit and configured to receive filtrate from the ultrafiltration unit as a feed, the purification section having an inlet communicating with an outlet for liquid from which solids have been removed in the solids removal unit (7) such that liquid can be passed through a passageway (107), the separation section further comprising a passageway (108) for feeding filtrate from the nanofiltration unit (8c) to an inlet of a reverse osmosis unit (9) for separating filtrate into a concentrate and a permeate, the separation section further comprising a recycle configured to return filtrate (109, 1094, 109b) from the ultrafiltration unit (8b) and/or the nanofiltration unit (8c) to the livestock room (1a through 109d), the manure pit (1b) or the manure slurry container (2 through 1090).

Use of an integrated livestock farming and manure processing system according to at least one of the claims 12-17 for keeping livestock and reducing the emission of one or more nitrogen compounds, preferably a nitrogen compound selected from the group consisting of ammonia, nitrate and nitrogen dioxide.

Use, optionally according to claim 18, of an integrated livestock farming and manure processing system according to at least one of claims 12-17 for keeping livestock and reducing the emission of one or more greenhouse gases.