WO2012115589A1

WO2012115589A1 - Method and system for sanitization of pathogen containing liquid waste in composting applications

Info

Publication number: WO2012115589A1
Application number: PCT/SE2012/050205
Authority: WO
Inventors: Gösta Andersson; Anna Calo; Annika C. Nordin
Original assignee: Telge Nät Ab
Priority date: 2011-02-25
Filing date: 2012-02-23
Publication date: 2012-08-30
Also published as: WO2012115587A1; EP2678295A1

Abstract

A method and system for sanitization of a liquid waste product comprising a first step of subjecting said waste to biological treatment under aerobic conditions resulting in a temperature increase producing a fermented and heated product, and a second step wherein the pH of said fermented and heated product is adjusted to an alkaline pH and incubated for a time sufficient to eliminate or reduce the concentration of pathogens in said waste.

Description

Title

Method and system for sanitization of pathogen containing liquid waste in composting applications

Technical field

[0001 ] The present invention relates to the field of waste water and effluent treatment, and in particular to a method and system for aerobic treatment and the subsequent sanitization of pathogen containing waste water and effluent streams.

Background

[0002] The excrements from humans and farm animals are not only a potential environmental and sanitary problem; they also represent a significant source of nutrients, which could be used for the production of biomass for the production of food and energy. In industrialized countries, the last decades have involved a shift from merely focusing on minimizing pollution and eutrophication of water bodies, to the development of systems for the reuse of the nutrients in human and animal excrements. As excrements, regardless of their human or animal origin, always contain pathogens, there is a risk of disease transmission.

[0003] Recirculation of human and animal excrements and using them, separately or in admixture, as fertilizers in the production of animal feed or human food also involves the risk of zoonoses, the transmission of diseases between animals and humans. Well-known examples of bacterial zoonoses include

Salmonella and enterohaemorrhagic E. coli (EHEC) and examples of parasitic zoonoses include tape worms (Taenia spp) and cryptosporidiosis.

[0004] In the industrialized countries, the infrastructure for collection and treatment of human excrements is generally well developed, and there is a growing interest in the reuse and recirculation of nutrients. In the developing countries however, there is an urgent need for both improving sanitary conditions and reducing environmental pollution. The possibility to recirculate the nutrients in waste flows, such as human and animal excrements, could add economic benefits, such as reducing the cost of importing fertilizers, in addition to

improvements in hygiene and environmental protection.

[0005] The challenge is to thus develop a sustainable sanitization system which prevents disease and promotes health, protects the environment, conserves water, and recycles recovered nutrients and organic matter.

[0006] Aerobic biological treatment, such as but not limited to composting, such as wet composting, is a practical approach to the treatment of waste water and effluents, also including human and animal excrements, as the conditions generally favor non-pathogen bacteria, and the temperature increase aids in reducing the number of pathogens. The end-product can then be used as fertilizer or soil conditioner, and applied for use in agriculture and/or landscaping.

[0007] Relying on aerobic biological treatment alone however requires long treatment times. In Sweden, the current requirement for sanitization of human and animal excrement is that the material must be subjected to at least 55°C for at least 10 hours (Recommendations for professional storage, digestion and composting of waste, issued by the Swedish Environmental Protection Agency, NFS 2003: 15, June 12, 2003).

[0008] Similar guidelines and requirements have been issued by international organizations, such as the World Health Organization (WHO). Within the

European Union (EU), there is currently an ongoing effort to update and amend the Directive 86/278/EEC on agricultural use of sewage sludge.

[0009] Further, successful biological treatment requires sufficiently energy content which frequently is related to a high dry solids or dry matter (DM) content in order to maintain the aerobic biological treatment, for example the composting. It is estimated that a DM content of at least 2.5 % is necessary. In practice, unless very long treatment times are used, an even higher DM content is preferred. With increasing DM content, the substrate becomes more viscous, which in turn is associated with problems of its own. There are however technologies suitable for this purpose, for example the method and device for the treatment of especially highly viscous substrates and for blending air into the substrate disclosed in WO 93/00302.

[0010] Sanitization using high pH is also well-known, and the addition of lime, caustic soda, ammonia, and urea has been practiced. The recommendation for high pH treatment of sewage products requires pH 12 for at least 3 months. When ammonia is present, lower pH and shorter treatment times may suffice. At the same time, the use of ammonia creates an environmental issue and constitutes an occupational hazard.

[001 1 ] One specific problem encountered in aerobic biological treatment of human excrement is that the DM content is very low, at least until low flushing toilets have been widely installed. Sewage having a DM content below 1 % (w/w) is generally held to be unsuitable for biological treatment, such as composting or wet composting. Another problem is that a combination of the current long treatment times and increasing sewage volumes requires very large installations to achieve a satisfactory throughput. The background art includes different approaches to address these problems:

[0012] DE 3622750 A1 relates to a process for the sanitization of sludge at a temperature of at least 60°C, involving at least two heating steps, wherein the first step is an aerobic, thermophilic process, and the second step involves external heating.

[0013] WO 96/28400 relates to composting processes for the production of a useful microbial product for either subsequent bioremediation processing of various substrates or direct application to soil as an agricultural fertilizer. The composting process has multiple steps including an early step of creating extremely high temperature and extremely high pH, by adding alkaline materials, followed by a second composting stage, where nutrients are added to the compost pile.

[0014] WO 03/072514 discloses a method for sanitization of organic waste, based on a drying step followed by an increase in pH and/or temperature. Said drying step can be a mechanical dewatering step, and the temperature increase can be achieved by solar heating. WO 03/072514 also teaches an aerobic treatment of the waste, for example in combination with the drying step.

[0015] It remains however to find a practical and robust solution, allowing greater flexibility in the choice of starting materials for aerobic biological treatment, and ensuring that the end product is safe to use. These problems, and others evident to a skilled person, are solved by the subject-matter of the independent claims. Preferred embodiments are set forth in the dependent claims

Summary

[0016] An object of the present invention is to make available a method and system for safe, effective and economical sanitization of liquid waste of different origin, including liquid waste having a low DM content. Another object is to make available a method and system for safe, effective and economical sanitization of liquid waste which is faster and requires a reduced input of energy and chemicals, compared to known methods and systems.

[0017] These objects and others are met by a method for sanitization of a liquid waste product comprising a first step of subjecting said waste to a biological treatment under aerobic conditions resulting in a temperature increase producing a biologically treated and heated product, and a second step wherein the pH of said treated and heated product is adjusted to an alkaline pH resulting in the formation of uncharged ammonia (NH₃) for a time sufficient to eliminate or reduce the concentration of pathogens in said waste.

[0018] In the method and corresponding system, the liquid waste product comprises at least one of sewage, sludge, human excrements, animal

excrements, greywater, and biowaste, or different mixtures thereof, such as for example the mixture of waste water/sewage/sludge normally encountered in septic tanks, sewage treatment plants of different sizes, and in traps or filters for sludge and phosphorous. [0019] The dry matter concentration of the liquid waste product is preferably in the interval of at least about 0.1 % (w/w), more preferably at least about 0.35 % (w/w), most preferably at least about 0.45 % (w/w). According to one embodiment of the method and corresponding system, the dry matter concentration of the liquid waste product is increased to about 1 % (w/w) by the addition of another substance with higher DM, such as manure, biowaste, ash, side-streams, byproducts and waste products from food production, agriculture, forestry, including saw mill waste, and waste from pulp and paper production. The substance to be added is chosen so, that an appropriate energy and/or nutrient content are/is achieved in the liquid waste product. For example can a waste product from food production be added in order to increase the energy content of the liquid waste, whereas for example ash will increase the pH.

[0020] One step in the method, or unit operation in the corresponding system, comprises the biological treatment of the liquid waste product under aerobic conditions until an increased temperature is achieved, for example a temperature of at least 30°C, preferably at least 35°C, more preferably at least 40°C, and most preferably at least 45°C is reached.

[0021 ] Another step in the method, or unit operation in the corresponding system, comprises sanitization of the treated and heated product, wherein the sanitization step involves the adjustment of the pH to at least pH 8, preferably to about pH 9, and most preferably to above pH 9, resulting in the formation of uncharged ammonia (NH₃).The pH adjustment may be performed through the addition of one of a base, urea, ammonia, lime or a combination thereof. Urea can be added to a concentration of about 0.1 to about 2.5 % (w/w) depending on the DM, temperature and composition of the product to be sanitized, as well as considering the intended end-use of the sanitized product. Preferably urea is added to a concentration of at least about 0.2 % (w/w), more preferably to a concentration of about 0.5 to 1 .0 % (w/w). Conceivably the amount of urea is in the interval of about 1.0 to about 2.0 % (w/w) in particular when the temperature is in the lower end of the above temperature interval. [0022] According to one embodiment of the method and system, the biological treatment step comprises an aerobic treatment such as composting, preferably wet composting.

[0023] According to one embodiment, freely combinable with other

embodiments, the ammonia sanitization step is performed in the same vessel or reactor as the initial aerobic treatment step, for example the wet composting step.

[0024] According to one embodiment of the method, or unit operation in the corresponding system, the sanitized end product is used for fertilization purposes, or for soil amelioration or soil improvement.

[0025] As apparent from the description, the disclosed method can be realized also as a system, plant or installation for the sanitization of a liquid waste product and the reuse of nutrients, comprising a reactor for performing a biological treatment under aerobic conditions, and a sanitization reactor, wherein the product is passed from the reactor into the sanitization reactor only when the temperature exceeds 30°C, preferably at least 35°C, more preferably at least 40°C, and most preferably at least 45°C, and where the pH in the sanitization reactor is adjusted to at least pH 8, preferably to about pH 9, and most preferably to above pH 9 or higher, resulting in the formation of uncharged ammonia (NH₃).

[0026] Said sanitization step is preferably an alkaline sanitization, most preferably an ammonia sanitization where the pH of the liquid waste product is increased by the addition of an alkaline agent, resulting in the formation of uncharged ammonia (NH₃). Examples of alkaline agents include urea, lime, ammonia, sodium or potassium hydroxide, ash, or the like. Most preferably said sanitization step is an ammonia sanitization step and the added alkaline agent is urea.

[0027] Preferably said sanitization reactor is insulated. According to one embodiment, said biological treatment step comprises composting, preferably wet composting. [0028] According to another embodiment, the reactor for performing a biological treatment under aerobic conditions has a dual function, and serves also as a sanitization reactor.

[0029] According to yet another embodiment, several reactors are provided in parallel.

[0030] Preferably said system comprises means for heat recovery, wherein heat is recovered downstream, e.g. in the product storage silos, and used for heating the incoming material as it is fed to the reactor, for maintaining an elevated temperature in the sanitization reactor, or for heating adjacent buildings and spaces, such as for example living quarters, office space, animal stables etc.

[0031 ] One particular embodiment is a sanitization reactor adapted for use in the present method and/or system.

Brief description of the drawings

[0032] The invention is now described, by way of example, with reference to the accompanying drawings, in which:

[0033] Fig. 1 schematically shows a system according to an embodiment where the reactor 30 serves both as the reactor for the aerobic treatment step, and as sanitization reactor;

[0034] Fig. 2 schematically shows a system according to an embodiment where the reactor for the aerobic treatment step is separated from the sanitization reactor;

[0035] Fig. 3 schematically shows a system according to an embodiment where several (here shown as two) reactors are provided in parallel.

[0036] Fig. 4 schematically shows a system according to an embodiment wherein one arrangement for the recovery of heat is illustrated; and [0037] Fig. 5 schematically shows a system according to an embodiment wherein another alternative or supplementary arrangement for the recovery of heat is illustrated.

Description of embodiments

[0038] Before the present invention is described, it is to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims and equivalents thereof.

[0039] It must be noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Also, the term "about" is used to indicate a deviation of at least +/- 2 % of the given value, preferably +/- 5 %, and most preferably +/- 10 % of the numeric values, where applicable. In addition to the above, the following terms will be used:

[0040] The term "sewage" is intended to encompass domestic, municipal and industrial liquid waste products, here with the exception of such industrial waste flows which are clearly unsuitable for biological and later use as fertilizer, for example because of their content of non-degradable toxic substance, such as but not limited to heavy metals.

[0041 ] The term "human and animal excrements" is intended to include both urine and feces, separately or in admixture, and in the case of animal excrements, also called manure, also a varying amount of bedding straw, peat, sawdust or the like.

[0042] The term "biological treatment" is intended to encompass any biological treatment capable of increasing the temperature of the liquid waste, as well as aiding in the reduction of the number of pathogenic microorganism therein. Currently preferred non-limiting examples of biological treatment include

composting, and in particular wet composting.

[0043] The term "eliminate" used in the context of pathogen counts means that the number of specific bacteria, virus or Ascaris is reduced to a level at which they no longer pose a problem considering the intended use of the digestate.

[0044] The term "significantly reduce" also used in the context of pathogen counts means at least a 3log10 reduction, i.e. that the number of specific bacteria, virus or Ascaris is reduced by a factor 1000.

[0045] The term "sanitization" means the reduction and/or elimination of pathogens. Current rules, e.g. EC 208/2006, the Commission Regulation of 7 February 2006 regarding processing standards for biogas and composting plants and requirements for manure sets a limit for E. coli and enterococcae in manure derived compost at max 5000/g, and requires that no Salmonella is detected in a set of 5 samples of 25 g each. It is expected that these limits will be reduced to less than 1000/g DM.

[0046] It is also expected that future requirements will include threshold values also for helminth eggs (Ascaris spp), and there is a tendency that the requirements for sanitization of human and animal excrements will be harmonized. For example, EC 1774/2002, the regulation laying down health rules concerning animal byproducts not intended for human consumption, which can be applied to manure treatment, already requires a 5log10 reduction of Enterococcus faecalis or

Salmonella senftenberg w775. The regulation also requires a 3log10 reduction of Ascaris in chemical processes and a 3log10 reduction for parvo virus or other thermo tolerant viruses, in products where they are identified as a relevant hazard.

[0047] In the present description, the term "sanitization" is applicable to the treatment of waste regardless of origin, and it is conceived that the sanitization of animal excrement is equally important as the sanitization of human excrements, in order to guarantee that the end product can be safely used also in food

production, for example as fertilizer on farm land used for growing edible crops. In some texts, the term "hygienization" is used instead of "sanitization" but for the purposes of this description, these terms are considered to have the same meaning.

[0048] The term "ammonia sanitization" means a sanitization where the toxic properties of uncharged ammonia (NH₃) contribute to the killing of microorganisms present in the waste. In solution, ammonia is in equilibrium with its conjugate acid (NH₄ ⁺):

NH₃ + H₂O ^ NH₄ ⁺ + OH^"

[0049] The formation of uncharged ammonia in the liquid waste is dependent on temperature, pH and the available ammonium ions (NH₄ ⁺). Increasing pH and temperature shifts the equilibrium towards uncharged ammonia. However, for ammonium sanitization the concentration of ammonia has been shown to be of higher importance than the pH achieved. Thus, the addition of ammonia, or preferably urea, which is degraded into carbon dioxide and ammonia, results in an effective sanitization, here called ammonia sanitization.

[0050] Thus, one embodiment makes available a method for sanitization of a liquid waste product comprising a first step of subjecting said waste to biological treatment under aerobic conditions resulting in a temperature increase producing a biologically treated and heated product, and a second step wherein the pH of said biologically treated and heated product is adjusted to an alkaline pH, to result in the formation of uncharged NH₃ for a time sufficient to eliminate or reduce the concentration of pathogens in said waste.

[0051 ] Preferably said second step follows directly on said first step, wherein the term directly means that the liquid waste after being subjected to the biological treatment and while remaining at an elevated temperature, is led directly to said sanitization step. Alternatively, both the biological treatment and the sanitization steps are performed in the same reactor. [0052] In the above method and in a corresponding system, the liquid waste product comprises at least one of sewage, sludge, human excrements, animal excrements, greywater, and biowaste, or different mixtures thereof.

[0053] The dry matter concentration of the liquid waste product is preferably at least about 0.1 % (w/w), more preferably at least about 0.35 % (w/w), most preferably at least about 0.45 % (w/w). According to one embodiment of the method and corresponding system, the dry matter concentration of the liquid waste product is adjusted to about 1 % (w/w) by the addition of manure and/or biowaste. An important advantage of the invention is that also dilute liquid waste can be treated, also liquid waste having initial DM below what would be required in known methods and systems.

[0054] One step in the method, or unit operation in the corresponding system, comprises the biological treatment of the liquid waste product under aerobic conditions until a temperature of at least 30°C, preferably at least 35°C, more preferably at least 40°C, and most preferably at least 45°C is reached.

[0055] Another step in the method, or unit operation in the corresponding system, comprises sanitization of the biologically treated and heated product, wherein the sanitization step involves the adjustment of the pH to at least pH 8, preferably to about pH 9, and most preferably to above pH 9. Importantly, the pH is adjusted to a level resulting in the formation of uncharged ammonia (NH₃). The pH adjustment may be performed through the addition of one of urea, ammonia, lime, sodium or potassium hydroxide, ash, or a combination thereof. Preferably urea is added to a concentration of at least about 0.2 % (w/w), more preferably to a concentration of about 0.5 % (w/w).

[0056] An advantage of using urea is that this is a source of nitrogen which is practical and safe to handle, easily available and which adds to the nutritional value of the fertilizer.

[0057] According to one embodiment of the method, the biological treatment step comprises a composting step, preferably a wet composting step. [0058] According to one embodiment of the method, or unit operation in the corresponding system, the sanitized end product is used for fertilization purpose, or for soil amelioration or soil improvement.

[0059] As apparent from the description, the disclosed method can be realized also as a system, plant or installation for the sanitization of a liquid waste product and the reuse of nutrients, comprising an aerobic reactor and a sanitization reactor, wherein the product is passed from the said reactor into the sanitization reactor only when the liquid waste has attained an increased temperature, preferably a temperature exceeding about 30°C, and where the pH in the sanitization reactor is adjusted to at least pH 8, preferably to about pH 9, and most preferably to above pH 9, resulting in the formation of uncharged ammonia (NH₃).

[0060] Preferably said sanitization step comprises an ammonia sanitization step. Preferably said sanitization reactor is insulated. According to one embodiment, said biological treatment step comprises a composting step, preferably wet composting.

[0061 ] According to another embodiment, the reactor for performing a biological treatment under aerobic conditions has a dual function, and serves also as a sanitization reactor. In such embodiments, said reactor is preferably insulated.

[0062] According to yet another embodiment, two or more reactors are provided in parallel, a set-up with many advantages. This makes it for example possible to optimize the aerobic biological treatment, as well as treating several batches in a parallel or semi-parallel fashion. This also makes it possible to recirculate part of the contents between reactors, for example to seed a new batch with aerobically treated material from another reactor. Seeding a batch with microorganisms that have been shown to thrive under the aerobic conditions in a previously performed biological treatment step may compensate for differences in the microbiological flora in the incoming material, and it will facilitate a fast start of the aerobic treatment, and aid in the selection of a microbial composition suitable for the biological treatment step. [0063] Preferably said system, as disclosed in any one of the above

embodiments, or combinations thereof, also comprises means for heat recovery, wherein heat is recovered downstream, e.g. in the product storage silos, and used for heating the incoming material as it is fed to the reactor, for maintaining an elevated temperature in the sanitization reactor, or for heating nearby installations, buildings such as living quarters, office space, animal stables, or warehouses.

[0064] One embodiment includes a sanitization reactor adapted for use in a method and/or system as described above. Said sanitization reactor can also be a separate component, suitable for incorporating in an existing waste management system, in order to modify such system to operate entirely or in part according to the present disclosure.

[0065] The method and system will now be disclosed in closer detail, with reference to the figures, for example Fig. 1 , where two receiving tanks 10 and 20 are schematically shown. While one receiving tank may suffice, it is advantageous to have two or more, for example to make it possible to receive sewage and waste of different origin and composition, for example human sewage, manure, biowaste, and to mix these in suitable proportions to ensure an even material feed to the reactor 30. Thus, two or more receiving tanks can be used e.g. for balancing the DM concentration or the nutritional content in the material feed to the reactor 30.

[0066] The receiving tank or tanks are preferably insulated, covered or closed tanks, which makes it possible to control temperature and eliminate potential problems with smell etc. A skilled person will be capable of choosing or designing receiving tanks of a suitable construction and size, depending on the nature of the waste product to be treated, as well as considering the desired throughput of the process.

[0067] For achieving an estimated capacity of about 3000 m³/a, the size of a receiving tank could suitably be 100 to 500 m³, preferably about 200 m³ It is currently held that two receiving tanks of about 200 m³ each would afford sufficient capacity and flexibility. Preferably each receiving tank is equipped with a biofilter for absorbing unwanted smells, e.g. a peat-filled filter through which air from the receiving tank or tanks is led.

[0068] From said receiving tank or tanks, the liquid waste or sewage is pumped or otherwise led into a reactor 30. On the way to the reactor 30, the sewage is preferably macerated, and it can also be preheated. There may also be sieves or similar means for trapping objects exceeding a certain size, in order to prevent downstream problems, such as clogging of lines, damage of pumps and valves etc.

[0069] Said reactor 30 is preferably a closed, insulated tank equipped with means for mixing 31 and means for aeration 32. The means for mixing can be a conventional propeller or turbine mixer, a circulation pump, or for example a device according to WO 93/00302. The means for aeration can be any

conventional means, for example a manifold for the injection of air. Alternatively, it can include a device according to WO 93/00302. Preferably the reactor is also equipped with anti-foaming means, for example means for detecting foam and for dosing anti-foaming agents into the reactor when needed.

[0070] When the reactor serves both as the reactor for the aerobic biological treatment, and for the sanitization step, it may include means 42 for feeding alkaline materials, preferably a nitrogen source, e.g. urea, operationally connected to the reactor. Said means can be for example a pump, a conveyor or a feeding screw or worm, depending on the properties of the alkaline materials. In the alternative, the addition of the alkaline material can also be performed manually or semi-manually.

[0071 ] The size of the reactor can be in the interval of 10 to 100m³, preferably about 25 to 50m³. For example, a reactor having a volume of about 32m³ can be constructed as a standing cylinder having a height of about 8m, and a diameter of about 3m. As mentioned above, the reactor is preferably insulated in order to minimize the influence of varying outdoor temperatures. The degree of insulation can be determined by a skilled person, and optimized for the volume, intended throughput and intended geographical location of the set-up.

[0072] It is conceived that two or more reactors are used in parallel, in order to increase the capacity of the installation, for making the method and system less vulnerable to disturbances, for allowing maintenance without interrupting the process etc.

[0073] The reactor can be emptied in its entirety or, preferably only partially, leaving for example about 10 %, about 15 %, about 20 %, or about 25 % or more of the volume to be mixed with new substrate. It is conceived that partial emptying will significantly shorten the time required for the biological treatment to reach the desired temperatures, as the microorganisms remaining in the reactor will multiply rapidly when new substrate is added. It is conceived that a certain selection of microorganisms will take place, leading to the development of a flora particularly suited for the biological treatment.

[0074] Alternatively, or in addition to the above, it is conceived that part of the contents of the reactor may be returned to the receiving tank or tanks in order to inoculate the liquid waste with the microorganisms necessary for the biological treatment.

[0075] Fig. 2 shows a system according to another embodiment, comprising two receiving tanks 10 and 20, a reactor 30 having means for mixing 31 and means for aeration 32, as disclosed in the context of Fig. 1 .

[0076] The biologically treated product is then led from the reactor 30 into a sanitization reactor 40. It is conceived that two or more sanitization reactors are used in parallel, for example to increase throughput and/or in order to make it possible to analyze the pathogen count in the product before releasing it into the storage tank or tanks 50 and 60.

[0077] The sanitization reactor preferably has a size of about 10 to about 50m³, depending on the desired capacity of the system. The sanitization reactor may be designed as a horizontal, insulated cylinder. Again, the degree of insulation can be determined by a skilled person, and optimized for the volume, intended throughput and intended geographical location of the set-up.

[0078] Means 42 for feeding alkaline materials, preferably a nitrogen source, e.g. urea, are operationally connected to the sanitization reactor 40 or reactors. Additionally, the sanitization reactor is preferably equipped with mixing means 41 . The mixing means can be a circulation pump, a propeller, a turbine, a paddle mixer or the like, present in the reactor, or means for mixing the alkaline materials, e.g. nitrogen source into the product when fed to the sanitization reactor, e.g. a motionless mixer (not shown) situated in the line feeding the product into the sanitization reactor 40.

[0079] The sanitization reactor (or reactors) may further be equipped with means for handling air vented from the reactor. Such means can be chosen from biofilters, carbon filters, ozon treatment, and various scrubber installations, depending on the quality of the vented air, e.g. problems with smell, ammonia etc. Preferably a biofilter is used, wherein the vented air is led through a filter containing particulate organic matter, e.g. peat, saw dust, straw, wood chips etc or a mixture thereof. After use, this organic matter, now enriched with volatile substances including ammonia, can be used for fertilization or soil amelioration.

[0080] When the sanitization has been completed, the reactor 40 is emptied, and the sanitized product may be used directly or stored in one or more storage tanks or ponds 50 and 60 before being used as fertilizer. Preferably said storage tank or tanks is/are covered, and preferably have means for mixing, as well as means for the collection and treatment of gases released from the product.

[0081 ] The size of a storage tank is normally in the interval of 1000 to 2000m³, but can be smaller or larger depending on the intended storage time and throughput of the process.

[0082] Fig. 3 illustrates an embodiment, where several (here shown as two) reactors are provided in parallel. The reactors and their means for mixing are denoted 30', 30", and 31 ', 31 ', respectively. The means for aeration 32, as well as the means 42 for feeding alkaline materials, are here schematically shown as being arranged between the reactors 30' and 30", but it is conceived that they could be individualized to each reactor.

[0083] As shown in Fig. 4, residual heat can be recovered from the storage tanks 50 and 60 and used for heating the sanitization reactor 40. Generic means are illustrated as item 70, shown in Fig. 4. Heat recovery can be achieved using conventional heat exchangers and a suitable medium, e.g. water, but can also include a vapor-compression refrigeration device normally referred to as a heat pump. Coils or the like can be placed in the storage tanks and in the sanitization reactor 40, here illustrated as 71 and 72 respectively.

[0084] Fig. 5 shows an embodiment where heat is recovered from the storage tanks 50 and 60 using means 80, e.g. one or more heat exchangers, and used to heat the reactor 30. Coils or the like can be placed in the storage tanks and in the reactor 30, here illustrated as 81 and 82 respectively.

[0085] Additionally, or alternatively, further heat exchanging systems could be applied to recover heat from the reactor, and use it to pre-heat the material entering the reactor, in order to ensure an even temperature in the reactor. It is also conceived that surplus heat generated by peripheral equipment, such as pumps, compressors (for aerating the reactor), fans, etc, could be used e.g. for heating the waste material before feeding it to the reactor, or for maintaining the temperature in the sanitization reactor, or for other heating or conditioning purposes.

[0086] An advantage of the method and system disclosed herein is that the heat that develops in the initial biological treatment process is used to amplify the effect of the sanitization step.

[0087] Compared to alkaline sanitization alone, the combined biological treatment and ammonia sanitization can be performed at a lower pH, requires less time, smaller addition of alkaline chemicals, and therefore affords a larger throughput. Similarly, compared to biological treatment alone, the combined biological treatment and ammonia sanitization guarantees proper sanitization, may allow shorter treatment times, and may allow a larger throughput. The method and system is also suitable for scale-up, either by adding parallel lines, by increasing the volume of the reactor and sanitization reactor, or both.

[0088] When a nitrogen containing material, for example urea, is used as the alkaline material, it affords the additional advantage of increasing the nutritional value of the sanitized end product. Similarly, the use of potassium hydroxide (KOH) increases the nutritional value of the end product.

[0089] Another advantage is that the method and system as disclosed can be applied to effluent streams having a low DM concentration. The initial biological treatment step does not have to be taken to the high temperatures required for sanitization by temperature alone, which reduces the treatment time and increases throughput.

[0090] Another advantage is the relatively low investment cost compared to installing municipal sewers in areas where this is not present, for example rural and sparsely inhabited areas.

[0091 ] The method and system is thus an alternative to expanding the municipal sewer network, and makes it possible to develop areas that are difficult to access, and where the sewage handling has been a limiting factor.

[0092] The following examples are intended to illustrate but not limit the invention.

Examples

Example 1. Laboratory scale urea sanitization at different temperatures

[0093] Urea sanitization was tested on sewage fractions (human faeces and urine) at different constant temperatures ranging from 4 - 34°C and using different concentrations of urea, ranging from 0.5 to 2 % (w/w). The sanitization effect was measured as the reduction of Salmonella, Enterococcus, E. coli, Ascaris eggs and three bacteriophages as viral models. The organisms were added to the material prior treatment.

[0094] For analysis of pH in samples with DM D 10 %, a dilution in de-ionized water (1 :9) was performed, whereas in liquid samples pH was analyzed without dilution, at room temperature, using an Inolab 720 pH meter (WTW, Weilheim, Germany).

Total ammonia nitrogen was analyzed using the indophenol blue method (Merck; Whitehouse Station, NJ) measuring absorbance on a Thermo Aquamate (Thermo Electron Ltd, Cambridge, UK). The concentration of uncharged ammonia, NH₃, in solution was calculated from the measured total ammonia, pH and temperature according to Emerson et al. (EMERSON, K., RUSSO, R., LUND, R. &

THURSTON, R., 1975, Aqueous ammonia equilibrium calculations: Effects of pH and temperature. Journal of the Fisheries Research Board of Canada, 32, 2379- 2383).

[0095] Microbial sampling was performed in an exponential time interval from days 1 , 2, 4 etc with the material mixed manually for approximately 1 min prior to each sampling. Ten (10) gram of material were mixed with 90ml of phosphate M15 pH 7.2 buffer (SVA, Uppsala, Sweden), to neutralize pH. From this, as 10-fold series was made with the first 1 ml dilute with phosphate buffer and the following steps with physiological saline solution, NaCI 0.85-0.90 % (SVA).

[0096] All bacteria were detected by the standard plate methods: Salmonella spp. was cultivated on xylose lysine desoxycholate agar (Oxoid, Sollentuna, Sweden) containing 0.15% sodium novobicin, and Enterococcus spp. on Slanetz- Bartley (SlaBa) agar (Oxoid) without differentiating between added E. faecalis and Enterococcus spp. The standard ISO10705-1 (1995) double-layer agar method was used to enumerate S. typhimurium bacteriophage 28B, enterobacteria phage MS2 and coliphage Phi X 174. The bacterial host strain S. typhimurium phage type 5, S. typhimurium WG 49 (ATCC 700730) and E. coli ATCC 1370 were used or enumeration of the respective bacteriophages.

[0097] The urea sanitization was shown to be functioning already at an addition of 0.5 % urea, but it was concluded that for fractions with DM D 10 % the initial pH and buffer capacity of the waste influenced the pH from such low urea additions, thus the NH₃ concentrations. The inactivation of pathogens could be positively correlated to NH₃ concentrations in combination with temperature. In relation to inactivation relying only on an alkaline pH the inactivation of Ascaris eggs were very efficient at temperatures of 20°C and above and a NH₃ concentration above 50 mM NH₃ which is one of the strengths of the sanitization method.

Example 2. Pilot scale urea sanitization at ambient temperature

[0098] Urea sanitization was tested in pilot scale experiments at a private farm where the end product was used for fertilization (Holo, Sweden). Liquid waste consisting mainly of human feces and urine together with water used for flushing was collected at a nearby camping, and from black water tanks at private homes. The DM of the liquid waste was on average less than 0.5 % as the waste was collected from installations having normal toilets. Total DM was determined by Oven Drying at 100°C for 24 hr according to standard laboratory procedure.

[0099] Microorganisms analyzed were originating from the liquid waste.

Microbiological and chemical analysis was performed at an accredited laboratory according to the methods given in brackets: Enterococci (SS EN ISO 7899-2); coliform bacteria (Colilert™); E.coli (Colilert™); Salmonella (NMKL 71 , 1999); pH (SS 028122-2); DM (SS 0281 13); total nitrogen (SS-EN ISO1 1905-1 ) and ammonia nitrogen (SS-EN 1 1732:2005).

[00100] Batches of 30 m³ were delivered to the pilot plant and subjected to treatment by 2% urea and stored at ambient temperature, in average 14°C. The addition of urea resulted in an increase from pH 7 to 9.2 measured three months after the addition of urea. The initial pH may have been higher, however long term storage of samples show that the pH remained at 9.15 after an additional two months. It was concluded that at this low DM the added urea resulted in a pH above 9 that was stable but due to the low temperature a very slow inactivation of microorganisms was measured despite the high urea addition. Since the tank was not optimized for urea treatment significant losses of ammonia was measured.

Example 3. Pilot scale serial wet composting and sanitization of sewage

[00101 ] Batches of 30 m3 sewage water exhibiting a dry matter (DM)

concentration ranging from 0.64 to 3.8 % (w/w) and a neutral pH was received at a pilot plant (Sorby Gard, Kvicksund, Sweden) operating according to the principles outlined in the description. The DM was determined by Oven Drying at 100°C for 24 hr according to standard laboratory procedure.

[00102] Ammonia and pH measurements as above, see Example 1 . The bacterial count was determined for Enterococcus, thermotolerant coliform bacteria (mainly E. coli) and when present, also Salmonella.

[00103] Following the initial biological treatment, here a wet composting step, temperatures of 33 to 45°C in combination with 0.45-0.5% (w/w) urea were tested.

[00104] The temperature increased 5-6°C per day for the examined DM and the pH increased during the composting phase from neutral to slightly basic. Adding 0.45-0.5% urea increased the pH to 8.9-9.0 and the pH was stable throughout the sanitization. The added urea decomposed into ammonia and no losses of ammonia was measured from the combined composting and sanitization reactor. The mixing of the material in the reactor enables the urea decomposition and homogeny for the treatment and very little variation were measured between samples.

[00105] The material was containing Salmonella which were eliminated in less than 5 days of treatment even at a temperature of 33°C. E. coli was reduced 5 Iog10 in 1 week to less than 1 day for the above described temperatures. For example, in the 43.5°C treatment the amount of thermotolerant coliform bacteria was reduced from 1x108/g DM to the detection level of 1x102/g DM, within two days. Within one week, also the Enterococcus count was down to below the detection limit of 1x103/g DM.

[00106] The viability of Ascaris eggs decreased with 80% in 9 days of treatment at 33°C which is promising for the combinations of higher temperatures and urea additions.

[00107] The following table shows the temperature development in a 30 m³ batch which had both a low DM, 0.64 % (w/w) and low temperature, 8°C when delivered to the pilot plant.

Table 1 . Temperature increase during biological treatment

[00108] When the temperature had reached 43.5°C on day 8, the biological treatment was interrupted, and urea was added to the warm, treated product. It is conceived that the urea sanitization step could be initiated earlier, for example at day 5, when the temperature already exceeds 30°C. The time distribution between the biological treatment step and the sanitization step depends inter alia on the DM concentration of the sewage. Sewage having a relatively high DM is likely to be able to reach a higher temperature in the biological treatment step, and a shorter urea sanitization will suffice. However, if the sewage has a relatively low DM, the biological treatment may possibly not result in temperatures higher than about 30 to 35°C, and then is conceived that a longer sanitization step, or a higher addition of urea, will be required.

[00109] The results in any case show that sewage water having a very low DM concentration can be successfully treated, and that the disclosed method and system can be applied in a large scale (30 m³). [001 10] The system described gives homogeny in treatment that ensures fully hygienized waste and the preservation of ammonia in the material until use as fertilizer prevents any re-growth of bacteria during storage.

[001 1 1 ] The results show that using the same reactor for the composting and sanitization is a feasible option.

[001 12] Although the invention has been described with regard to its preferred embodiments, which constitute the best mode presently known to the inventors, it should be understood that various changes and modifications as would be obvious to one having the ordinary skill in this art may be made without departing from the scope of the invention as set forth in the claims appended hereto.

Claims

1 . A method for sanitization of a waste product comprising a first step of subjecting said waste to biological treatment under aerobic conditions resulting in a temperature increase producing a treated and heated product, and a second step wherein the pH of said treated and heated product is adjusted to an alkaline pH and incubated for a time sufficient to eliminate or reduce the concentration of pathogens in said waste.

2. The method according to claim 1 , wherein the biological treatment step comprises a composting step, preferably a wet composting step.

3. The method according to claim 1 , wherein the waste product comprises at least one of human excrements, animal excrements, sludge, greywater, and biowaste.

4. The method according to claim 3, wherein the dry matter concentration of the waste product is at least about 0.1 % (w/w), preferably at least about 0.35 % (w/w), most preferably at least about 0.45 % (w/w).

5. The method according to claim 3, wherein the dry matter concentration of the waste product is adjusted to about 1 % (w/w) by the addition of one of manure, biowaste, and ash, or a combination thereof.

6. The method according to claim 1 , wherein during the first step, the waste product is subjected to biological treatment under aerobic conditions until a temperature of at least 30°C, preferably at least 35°C, more preferably at least 40°C, and most preferably at least 40°C is reached, before initiation of the second step.

7. The method according to claim 1 , wherein the second step involves the adjustment of the pH of the waste product to at least pH 8, preferably to about pH 9, and most preferably to above pH 9.

8. The method according to claim 1 , wherein the pH adjustment is performed through the addition of one of urea, ammonia, lime or a combination thereof.

9. The method according to claim 7, wherein the pH is adjusted to a level resulting in the formation of uncharged ammonia (NH₃) in the waste product.

10. The method according to claim 8, wherein urea is added to a

concentration of at least about 0.2 % (w/w), preferably to a concentration of about 0.5 % (w/w).

1 1 . The method according to any one of claims 1 - 10, wherein the first and second steps are performed consecutively, in the same container.

12. The method according to any one of claims 1 - 10, wherein the first and second steps are performed in separate containers.

13. The method according to any one of claims 1 - 12, wherein the end product is used for fertilization purposes.

14. A system for the sanitization of a waste product and the reuse of nutrients, comprising at least one aerobic reactor (30) and optionally a sanitization reactor (40), wherein the product is passed from said at least one reactor into the sanitization reactor only when the temperature exceeds 30°C, and wherein a sanitization step is performed in said sanitization reactor, by adjusting the pH in the sanitization reactor to at least pH 8, preferably to about pH 9, and most preferably to above pH 9.

15. The system according to claim 14, wherein said aerobic reactor (30) is a reactor for performing a composting step, preferably a wet composting step.

16. The system according to claim 14 or 15, wherein the adjustment of pH comprises an addition of one of urea, ammonia, lime or a combination thereof into the reactor.

17. The system according to claim 16, wherein the pH is adjusted to a level resulting in the formation of uncharged ammonia (NH₃) in the waste product.

18. The system according to claim 14, wherein said aerobic reactor (30) also functions as sanitization reactor (40).

19. A sanitization reactor (40) adapted for use in a system according to any one of claims 14 - 18.