WO2002051772A1

WO2002051772A1 - Process for compost of biomass and industrial sludge, including products produced by said process

Info

Publication number: WO2002051772A1
Application number: PCT/NO2001/000474
Authority: WO
Inventors: Jan Petter Hammer; Pål SMITS
Original assignee: LINDUM RESSURS OG GJENVINNING
Current assignee: LINDUM RESSURS OG GJENVINNING
Priority date: 2000-12-01
Filing date: 2001-11-28
Publication date: 2002-07-04
Anticipated expiration: 2003-06-01
Also published as: NO20006143L; NO20006143D0

Abstract

It is described a method for the compost formation of biomass and industrial sludge. The method is characterised in that the mass is pre treated by hygienic treatment, comprising milling and mixing with an additive which causes increase of the pH-value of the mixture, thereafter is new micro organisms of other strains added, by the means of addition of one or more structure forming agents, whereby the mass is mixed and pre compost formed in a reactor plant, or is spread for tendril compost formation.

Description

Process for compost of biomass and industrial sludge, including products-produced by said process

The present application concerns a method for forming compost of biomass and industrial sludge.

A prohibition against deposing wet organic disposal on the local waste disposal sites in Norway, came into force in 1999. This prohibition was reasoned with the environmental disadvantages, which these deposits entail. As a consequence an increased attention has been drawn to biological handling methods. The disposal contains important nutrients and represents therefore a considerable exploitable resource, both within the agriculture and also in other sectors.

Several Norwegian waste disposal site plants now compost wet organic disposal, aerobic and anaerobic. It is a well known problem that sites of this type often represent a considerable burden regarding to smell. Responsible for this smell burden is among others the content of organic acids, which are formed in the waste. These acids are formed by bacteria, by pre fermentation of organic material without the use of oxygen. The most important microbes responsible for forming the compost, are bacteria and fungi. A successful compost formation is dependent of how good a system can meet the fundamental needs of the microbial environment. These needs are first and foremost access to moisture, oxygen, balancing of nutrients and temperature control. With these needs met, the development of the microbial environment follows a roughly predictable pattern. The temperature is an important factor in compost formation. All micro organisms have a characteristically optimal growth temperature, where they reproduces and grow most rapidly. Micro organisms also have a minimal growth temperature under which they become metabolically inactive. Temperature is the basic factor, which influences the reaction rate in chemical and biochemical reactions. In general the enzymatic activity of the micro organisms doubles for every 10 °C - increase in temperature, up to a limit where the enzyme becomes inactive.

A well-organised compost formation system is heated to 40-50 °C, on two to three days. Most of the large scale compost formation systems use three to five days to be heated to 60-70 °C. Several tests have shown that the microbial activity diminishes when the temperature exceeds 60 °C. It is natural that the heat production decreases, when easily degradable compounds become less accessible, in well isolated compost formation systems, high temperatures would nevertheless could be maintained for a longer period of time.

Compost formation is defined as aerobic degradation of organic material, and can be disclosed by the following reaction :

Organic material + O₂ ^" -> Stable organic material + CO₂ + H₂O + heat In a compost formation plant the aeration of the plant functions as oxygen supply, so that oxygen is not becoming a limiting factor. Compost formation is namely strongly reduced by lack of oxygen. It has been shown that heat generation is reduced with a factor of 100 by compost formation with limited oxygen supply. If the compost formation is becoming anaerobic, organic acids, H₂S, nitrogen compounds and other compounds are produced, which can create considerable smell problems, in addition to be toxic for plant seeds. It is however, almost impossible to form compost of heterogeneous organic disposal wholly aerobic. It will always exist anaerobic pockets. Adequate oxygen supply, as well as good turn over does therefore not exclude the formation of organic acids and other compounds, which give strong smell. The most common factors, which lead to anaerobic conditions are :

- Too high content of water

- Too low porosity

- Rapidly degradable substrate

- Too big mass - Particle size

All these factors make it difficult for oxygen to penetrate through the mass.

In common compost formation plants the disposal, which arrives has often been subject to anaerobic conditions for 2-3 weeks. Thereby the waste has started a partially anaerobic degradation, with the consequence that the waste has increased occurrence of organic acids, and that colonies of anaerobic micro organisms are in majority in the waste.

This involves that it is difficult to turn the degradation to an aerobic degradation by mixing with structural agents and by air supply. It often takes a long time to establish aerobic conditions, including achieving temperature increase in the process. The occurrence of organic acids also involves the formation of undesired smell, which is a big problem with aerobic processes. Further many organic acids will act as toxins against desirable micro organisms. Finally the content of considerable amounts of acid together with high temperature and high moisture content involve great corrosion problems in many plants. pH when starting the compost formation will depend on the starting material. Theoretically material with pH 3-11 can be subject to compost formation, but the optimal range is between pH 5.5 and 8. Acidic conditions favour growth of fungi, whereas bacteria flourish at neutral conditions.

The compost formation process does comprise several aerobic and anaerobic processes, which go on at the same time. Shortlived lack of oxygen in compost finds place in both macro and micro pores, and this does involve temporarily production of short-chained fatty acids. These organic acids have a strong smell, but simultaneously they are easily degradable and function as a high energy source for aerobic micro organisms.

US Patent No. 5,252,116 describes a process for treatment of disposal sludge (sewage sludge), wherein it is used lime, fly ash, cement kiln dust and surfactants. This patent distinguishes, however from the present invention in several aspects. Firstly the end product, which is achieved according to this patent is a dry granulate without any biological activity. Further also the starting materials, which are treated are very different.

The present invention provides a solution to the above mentioned problems. The process, according to the present invention involves that the compost formation process is speeded up, is relatively free of smell, is economic and reduces the corrosion problems in the plants.

Closer defined the present invention comprises a method for compost formation of wet organic disposal and industrial sludge, which is characterised in that the mass is pre treated by hygienic treatment, comprising milling and mixing with an additive, which cause the pH-value to be brought to the range 8-14, and thereafter is added (inoculated) new micro organisms of other strains by the means of addition of the structure forming agent bark, whereby the mass is mixed and pre compost formed in a reactor plant, or is spread for tendril compost formation.

According to a preferred embodiment the additive, which causes that the pH

-value is brought to the range 8-14 is an oxide or carbonate of an alkaline or alkaline earth metal.

According to a further preferred embodiment the additive is lime, CaO or

Ca(OH)₂.

According to another embodiment of the invention the pH-value in the pre treatment is in the range 10-12. Preferably it is about 12. Another further preferred embodiment of the invention comprises that the. addition of the oxide or the carbonate of the alkaline- or alkaline earth metal is carried out in a simple closed pre treatment plant.

According to a further advantageous embodiment of the present invention it is used a slightly acidic bark as the^* structure forming agent. The present invention further achieves a mass for the use in the above mentioned method, which is characterised in the following composition :

Wet organic disposal or industrial sludge : 38-60%

Lime, CaO or Ca(OH)₂ : 2-10%

Structure forming material, bark : 38-60% Another aspect of the present invention comprises a product, characterised in that it is produced by means of a method as it is defined in the patent claims. It has been known since the Roman time that lime can be used to kill bacteria. Further lime has in centuries been used in connection with burial of bodies. It would therefore be obvious to suppose that addition of lime to a compost forming mass would kill necessary bacteria and with that counteract the compost forming process. Use of lime has either not, hitherto known, existed in compost forming plants for hygienic treatment of biological waste products. In the present invention it is essential that the mass is hygienic treated or stabilised by addition of an additive, such as lime, on an early stage, so that the formation of for example acids is effectively prevented or strongly reduced.

Thereafter it is mixed in a structure forming material, preferably bark

(cortex), and it is carried out an aerobic biological degradation with an exoterm temperature increase to 50-70 °C in 10-40 days and nights. By the method according to the invention the compost formation is rapid. With an industrial sludge it is for example achieved a rat degree 4 during 10 days and nights. The rat degree is a designation on a method, which is used in order to judge the stability of the compost. The principle of this method is to measure the temperature increase in samples, which are standardised with regard to moisture and porosity when the sample is placed in a thermos flask. The short compost formation time involves that the capacity can be doubled in a plant, which uses biomass/-structure in the ratio 1.1.

The process produces organic acids, as mentioned, to a very little extent. Instead it produces some NH₃-vapour. Thereby the corrosion problems are essentially reduced, at the same time the decomposition of concrete constructions are greatly diminished. In addition the bio filter will function better, partly due to fertilisation with NH₃, and partly due to that the bio filter mass get elevated pH in the absence of organic acids and supply of NH₃. Test carried out by the applicant has shown that the reduction of the smell problems, which is achieved with the use of lime is greatly significant. In the test it was chosen to measure ammonia (NH₃) and volatile organic compounds (VOC). The advantages by carrying out analyses of VOC, is that one can mirror the qualitative composition of the air. The VOC-measurements were carried out by the use of so called Tenax tubes, these are tubes which have adsorption layers on the inside. The gas to be measured can either be sucked through the tube (active measurement), with a manual pump which states exactly volume, or the gas can diffuse passively into the tube. It was chosen active measurement and the samples were analysed by NILU (Norwegian Institute for Air Research).

The results, which were achieved support with all desired clarity that the method according to the invention achieves a greatly reduction of both smell problems and corrosion.

In the process air from compost formation without lime, TVOC (total content of volatile organic compounds) before scrubber, were 38.792 and 25.375 μg toluene equivalents/m³ on two measurement days, respectively. This gives a mean of 32.084 μg/m³. Compared with the process air from compost formation with lime, measured on another date of only 3.036,6 μg/m³, TVOC was reduced with as much as 90,5% by addition of lime in the compost composition. Corresponding measurements for ammonia show a great increase of 380% from 267 μg NH₃/rn³ to 1041 μg/m³. The percentage reduction in TVOC after lime addition for measurement after scrubber was 82,1%, whereas the in the measurement after the bio filter was an increase of 169%. For ammonia there was a corresponding increase in the amount when lime was used of 2148% for measuring after scrubber and 1840,5% for measurement after the bio filter.

It was further carried out experiments in order to establish whether the above-mentioned method was useful for compost formation of problematic special disposal, such as waste containing antibiotics. This is waste, which cannot be deposited and which is too expensive to burn. The experiment was carried out in a closed compost plant. Dewatered antibiotic-containing sludge with a solid matter of 32-35% was mixed with bark. In one of the boxes lime corresponding to 20% solid matter of the sludge, was added. The compost formation went on for 25 days. Mixing in of sludge and running in of compost composition were not connected with any problems. The liquid consistency of the sludge, involved that it was necessary to use large amounts of bark, in average two times the weight of the sludge.

The process started rapidly in both boxes, the temperature progress almost followed a classical compost formation and entered the maturation phase with temperatures under 45 °C, after about two weeks. The gas measurements and measurements of solid matter and organic content show partly very high activity the first weeks. It was no unusual malodours from the process.

The content of antibiotics rapidly decreased in both boxes, most rapidly in the box with lime. Already by the mixing in with lime the content of antibiotics was reduced by about 90%. After 7 days compost formation at high temperatures the activity from antibiotics was not longer measureable. The same was the case after 13 days in the compost without addition of lime.

The end product showed relatively high stability (rat degree 4) after 13 and 25 days. Relative plant tolerance was good for the lime compost already after 25 days, but not for the compost without lime. It is not certain how long compost without addition of lime will have to be composted afterwards, before it fulfils the desired quality. On the basis of these results it is clear that the compost formation of sludge containing antibiotics is completely possible with the mentioned technology. The introduction of lime has a pronounced positive influence on the degradation of antibiotics and on the quality of the end product with regard to plant tolerance. These are results which are very surprising, in light of the present prior art.

Claims

Patent claims

1. Method for compost formation of wet organic disposal and industrial sludge, characterized in that the mass is pre treated by hygienic treatment, comprising milling and mixing with an additive which causes the pH-value to be brought to the range 8-14, thereafter is added (inoculated) new micro organisms of other strains by the means of addition of the structure forming material bark, whereby the mass is mixed and pre compost formed in a reactor plant, or is spread for tendril compost formation.

2. Method according to claim ^characterized in that the additive which causes the pH-value to be brought to the range 8-14 is an oxide or carbonate of an alkaline or alkaline earth metal.

3. Method according to any of the preceding claims, characterized in that the additive is lime, CaO or Ca(OH)₂.

4. Method according to any of the preceding claims, characterized in that the pH-value in the pre treatment is within the range 10-12.

5. Method according to claim 4, characterized in that the pH-value in the pre treatment is about 12.

6. Method according to any of the preceding claims, characterized in that the addition of the oxide or the carbonate of alkaline or alkaline earth metal, is carried out in a closed pre treatment plant.

7. Method according to claim 6, characterized in that it as structure forming material is used weakly acidic bark.

8. Mass for the use in the method according to claim ^characterized in that it has the following composition :

Wet organic disposal or industrial sludge : 38-60%

Lime, CaO or Ca(OH)₂ : 2-10% Structure forming material, bark : 38-60%.

9. Product, characterized in that it is produced by the method according to the claims 1-7.