NO20220305A1

NO20220305A1 - Method and device for biogas production as source for energy and algae key nutrinets; C, N and P

Info

Publication number: NO20220305A1
Application number: NO20220305A
Authority: NO
Inventors: Arne Råheim
Original assignee: Raaheims Energy Consulting
Priority date: 2022-03-10
Filing date: 2022-03-10
Publication date: 2023-09-11
Also published as: WO2023172146A1; NO348192B1

Description

Method and device for biogas production as source for energy and algae key nutrients; C, N and P.

The present invention relates to a method for anaerobic fermentation of different organic waste types as indicated by the preamble of claim 1,. According to another aspect, the invention provides an device for performing said method.

Background.

Biogas can be produced in a digestor by anaerobic digestion (AD) or fermentation of biodegradable materials, such as domestic waste, animal or agricultural waste, waste from fish farms, sewage sludge and other organic wastes. Biogas, made by AD in a digestor, consist mainly of methane (CH4; 60 to 70%), carbon dioxide (CO2; 30 to 40%) and small amounts of hydrogen sulfide (H2S), moisture and siloxanes, depending on the type of organic matter (OM).

If the anaerobic produced biogas is to be used for power (electricity) generation or transportation fuel (vehicle grade), it first must be upgraded by removing impurities to increase the calorific value (heating value). This upgrading includes drying, desulfurization and CO2 removal.

The CO2 separation is normally carried out by water scrubbing, physical or chemical absorption using organic solvents, pressure swing adsorption, or by permeation using membranes, depending on location and size of the system.

Phosphorous is a finite (limited) resource (peak phosphorous, Wikipedia). According to some researchers, earth’s commercial and affordable phosphorous resources are expected to be depleted in 50-100 years and peak phosphorous to be reached in 2030. Others suggest that the supplies will last for several hundred years. As with the timing of peak oil, the question is not settled, and the researchers in different fields regularly publish estimates of the rock phosphate reserves.

However, the limited mineable phosphate resources will eventually be a very challenging and costly problem, which will lead to a serious phosphorous crisis, unless the phosphorous from the different types of organic wastes is recycled and used, in an efficient, cost effective and sustainable manner. The phosphorous content is high in all organic waste forms, it is in this connection interesting to note that animal and human excrete almost 100% of the phosphorous they consume in food.

According to recent research, all organic waste benefits from being subjected to AD in a digestor if phosphorous together with other important nutrients, particularly nitrogen and other available nutrients, are to be used as fertilizer (Bachmann N.2015).

While the phosphorous from minerals can be regarded as a finite or very limited resource, this is not the case with nitrogen. The amount of nitrogen in the air and the supply of water for production of hydrogen, the two elements necessary for making ammonia NH3, would not be limited. It is still important to take care of the nitrogen nutrients in organic wastes in a sustainable and environmental manner by utilizing methods which takes this problem into account. For example, most of the nitrogen nutrients is lost when the organic matter is subjected to composting treatment (Möller et. al., 2016)

Application of microalgae for wastewater treatment is generally carried out in open raceway ponds (Campos et al.,2019; Shoener et al., 2014; Shilton et. al., 2012).

Moreover, microalgae can be used to upgrade the quality of biogas (reduction of CO2 in the biogas) generated during the anaerobic process inside the digestor (Meier et al., 2015).

However, the combined external (outside the digestor) use of the CO2 separated from the “raw biogas” (CH4 and CO2, sulfur components removed) made by an AD process in a digestor, with nitrogen (N) and phosphorus (P) (and other available/suitable nutrients) present in the liquid and solid digesatrates from the digestor for efficient and sustainable use in an algae production plant, has to the knowledge of the present inventor, so far not been shown/revealed.

While existing methods for anaerobic fermentation mainly focus on energy production, the process also involves components that are useful for other purposes or in other connections and which to little extent are taken care of.

Objectives

It is therefore an objective of the present invention to provide a sustainable and costefficient method for anaerobic fermentation that is more sophisticated than existing processes in the sense that it takes care of and make available more of the valuable components involved in the process.

A further objective is to provide such a method in which the raw material comprises biodegradable materials such as domestic waste, animal or agricultural waste, waste from fish farms, sewage sludge and other organic wastes.

It is a derived object to provide a method that is sustainable also in the sense that it it does not generate climate gases that are released to the atmosphere.

The present invention

The above mentioned objects are fulfilled by the method of the present invention as defined by claim 1.

Preferred embodiments of the invention are disclosed by the dependent claims.

The present invention provides a method for anaerobic digestion of organic waste materials providing energy in a sustainable manner. At the same time, the process preserves components that can act as valuable nutrients in a plurality of biological processes, such as processes for the production of food and fodder for human and animal consumption, hereunder in algae aquaculture farms.

The anaerobic digestion process thus provides, not only carbon as the most important nutrient from the digestor gas (biogas), but the anaerobic digestion process will also, from the liquid and solid digestrates, provide the other key nutrients N and P, and other necessary nutrients, a.o. useful for algae production.

A particularly useful embodiment of the present invention combines sustainable energy production with production and isolation of nutrients useful in algae production plants.

The use of liquid and solid digestrates, when applied in fertilizers in land-based farming, involves costly post digestor treatment, such as drying (use of energy). However, nutrient concentration and chemical precipitation to enhance the availability/use and transport of important nutrients, such as for example phosphorous (P) and nitrogen (N) in struvite (MgNH4PO46H2O) is still important (Daneshgar et. al., 2018)

The liquid and solid digestrates from the biogas digestor production contain important nutrients such as N and P, which in addition to Carbon from the CO2 gas in the biogas represents the key nutrients C, N, and P in algae production, with an approximate relationship 90:9:1.

It is important to note that the CO2 does not have to be “pure” to be utilized in an algae production plant. Thus, CO2 present in the water from the water scrubbing process would be directly available, with no further separation.

The sulfur removed from the biogas may also be a source for sulfur nutrient in the algae production, if the commercially available method used to remove the sulfur components of the biogas makes this convenient and cost effective.

Phosphorous is an element that is necessary for all life (incl. algae). Phosphorous is present in DNA, and ATP which is a molecule that carries energy within all cells.

When the digestrate nutrients are used in algae photobioreactors (Cuello and Ley, 2009) in an algae production plant, they are introduced to the algae production farm in a liquid state, this will limit the use of costly energy for drying. Any chemical treatment of the digestrates is also simpler and less costly and can even be entirely avoided.

While not limited thereto, the present invention may serve to provide key nutrients and components such as carbon, nitrogen, and phosphorous for use in algae production plants

The method according to the present invention is also useful for providing nutrients in the form of K, Na, Mg and others (Moller et. al., 2015).

The method according to the present invention is also useful in a total energy system based on biogas for heat (burning of raw biogas, sulphur components removed), power (separated methane for electricity and heat, combined heat and power, Bachmann, 2015) and transportation (methane of vehicle quality).

Detailed description of the invention.

Different non-limiting embodiments of the invention are illustrated below with reference to the enclosed drawings, where:

Figure 1 is a schematic view of the first more general embodiment of the present invention, in order to highlight the key features involved in the supply of key nutrients for algae production based on biogas and digestrates from anaerobic digestion in a digestor.

Figure 2 is a schematic view of another embodiment of the present invention, where more optional features are included in addition to an application where algae is used related to fish farms.

Attention is drawn to fig.1. An anaerobic digestor 50 for biogas production is charged with a charge material 11 based on different (or mixed) organic waste forms 10: domestic waste, animal or agricultural waste, waste from fish farms, sewage sludge or other organic wastes. The produced raw biogas 12 is desulfurized 60, and the desulfurized biogas 13 is charged to a CO2 separator 70 (selected among different commercially available types). A substantially pure methane (CH4) gas 15 leaves the CO2 separating unit 70 to a storage unit 100 and subsequent use for fuel and/ or for transportation.

While the step of desulfurization 60 is a step commonly used in such processes and not inventive as such, it is a step which for practical chemical purposes will rarely or never be omitted. However, depending on the method used for the desulfurization process, the separated sulfur may be utilized as sulfur nutrient if practically and/or economically feasible (not shown in fig.).

The CO214 leaving the CO2 separator 70 as gas or dissolved in liquid (water) depending on the separation method used, is adjusted to the optimum concentration level in a nutrient preparation unit 140, for introduction to an algae production plant 80.

The solid and liquid digestrates 16 leaving the digestor 50 are treated for extraction of the nutrients nitrogen (N) and phosphorous (P) and optionally other available nutrients in a nutrient extraction plant 90. In this process, the liquid and the solid digestrates are typically treated separately in order to obtain a convenient chemical form of the nutrients N and P and optionally other available nutrients 17. The nutrients are thereafter typically mixed with the CO2 in a nutrient preparation unit 140 for further introduction through gate 18 to the algae production plant 80, consisting of algae photobioreactors (Cuello and Ley, 2009). Additional nutrients 140a may be added through gate17a, and/or the concentration of the existing nutrients may be adjusted to the optimum concentration level for the algae type used in the algae production plant 80.

The algae 19 leaving the algae production plant 80 may be utilized in different facilities for making different algae-based products 110. The algae biomass rest/waste 120 contains most of the nutrients originally introduced to the algae production plant and can be transported by means of a conveyor 20 for use as valuable organic fertilizer 130, or the algae-based rest/waste can be transported back though a transportation system for algae biomass rest 21 to a storage system for organic waste forms 10 and optionally mixed with other organic waste forms, before introduction to the digestor 50 for production of biogas and reuse of nutrients. Optionally the algae biomass rest could be directly transferred to the digestor 50.

If the need for CO2 in a specific algae production plant is less than the CO2 in the biogas normally produced by anaerobic digestion (30 to 40%), the CO2 content of the biogas may be reduced up to 20% by introduction of hydrogen into the digestor (Andresen et. al., 2016). The same or similar reduction can be achieved by introduction of suitable algae (Meier et. al., 2015).

Attention is now directed to fig.2. The main components given in the general description of the invention in fig.1, are the same as in figure 2 and are numbered equally. In addition, fig.2 describes an embodiment, which contains additional components (particularly related to the handling of CO2 and energy issues) and a relation to fish farms for use of algae biomass and the organic waste form in this connection.

One of the reasons for the choice of fish farms is the need for more environmentally friendly treatments in the fish farm industry. Particularly phosphorous, which is an essential nutrient for every organism and plant on earth, is also yet a potential pollutant (from agriculture, fish plants), which may cause eutrophication of water bodies, where the fish farms often are placed. Another reason for the choice of fish farms is the enormous expansion expected in this industry, resulting in a very large increase in the amount of organic wastes, caused by fish excrements and food waste, combined.

Considering the expected large volume, this waste must/needs to be taken care of, particularly in relation to the phosphorous problem, where all the phosphorous from all the organic waste needs to be taken care of in order to prevent a future phosphorous crisis. Production of biogas and digestrates in a digestor, based on fish farm waste and/or other organic wastes is in addition recommended by researchers (Bachman N.2015, Möller et. al., 2016) for better access to, and no or minimal loss of essential nutrients from the digestrates.

In fig.2 an anaerobic digestor 50 for biogas production is charged with a charge material 11, based on waste from fish farms 10. The produced raw biogas 12 is desulfurized in a desulfurizer 60, and the main part of the desulfurized biogas 13a is charged to a CO2 separating device 70 (can be different types). A substantially pure methane (CH4) gas 15 leaves the CO2 separating unit 70 to a storage unit 100 and subsequent use in power generation and/or for transport fuel.

The desulfurization 60 is performed in the same manner and with the same options as in fig. 1.

The desulfurized biogas 13b may optionally be charged to a burner 150 to provide heat 23 if or when it is necessary to the total biogas-algae production-fish farm industry plant. Air is added to the burner 150 through inlet 24.

With “facility” as used herein is understood a unit or a plurality of units working in cooperation to perform a certain task.

The CO214a leaving the CO2 separator 70 enters a CO2 storage facility 75. The CO2 may optionally be mixed with the CO2 rich gas 14b from the burner, where the desulfurized biogas 13b is directly used as fuel with the original high CO2 content (30 to 40%).

Depending on the CO2 content of the exhaust 14c from the electricity and heat facility (f. ex. Combined heat and power)105, this off gas may also be mixed in 75. Note that the CO2 in the storage facility 75 does not have to be pure for being applied as nutrient in an algae production farm. The gas 14 from the CO2 storage facility 75 is further optimized in a nutrient preparation device 140 and brought in a form and concentration suitable for introduction though gate 18 into the algae production plant 80.

The solid and liquid digestrates 16 leaving the digestor 50 are treated by extraction to obtain as much as possible of the nutrients nitrogen (N) and phosphorous (P) and other available nutrients in a nutrient extraction plant 90. In this process, the liquid and the solid digestrates may be treated separately in order to obtain a convenient chemical form of the nutrients N and P and other available nutrients 17, for mixing with the CO2 containing liquid in the nutrient preparation unit 140 before being introduced through gate 18 to the algae production plant 80. Additional nutrients from a nutrient supply 140a may be added or the concentration of the existing nutrients may be adjusted, through gate 17a, to satisfy the nutrient need in the algae production plant 80.

The algae 25 leaving the algae production plant 80 may be directly used as fish feed in the fish farm 160. Alternatively, the algae 25a may be delivered to a fish feed plant 180 in order to provide a “tailor made” algae-based fish feed 25b to be used in the fish farm 160. In the latter case, some of this fish feed may be sold on the open market.

The algae 19 leaving the algae production plant 80 may optionally be utilized in different facilities for making different algae-based products 110 The algae biomass rest/waste 120 contains most of the nutrients originally introduced to the algae production plant and can thus be used as valuable organic fertilizer 130. It is also an option to transport the algae-based biomass rest/waste 120 back to the digestor 50 or to mix it in with the other organic waste 10 for production of more biogas and reuse of nutrients. This option is not shown in fig.2.

The fish waste 170 and food waste 27 from the fish farm 160 are collected and transported as flow 28 to the organic waste storage 10 and introduced to the digestor 50 through inlet 11.

If there is a need to reduce the CO2 content in the biogas this can be performed in the same manner as suggested in fig.1.

The burner 150 provides heat (if needed) to the total biogas-fish farm pant. This heat, if required, comes in addition to the electricity and heat 26 produced from methane 105, which could act as the main power and heat provider for the total industry plant. Note that the need for power (el. and heat) for clarity reasons, in fig.2, is not shown to be directed to all the facilities in the total industry plant, where there is an obvious need.

Further embodiments

While the step of desulfurization 60 is a step commonly used in such processes and not inventive as such, it is a step, which for practical chemical purposes will rarely or never be omitted. However, the sulfur removed from the biogas may also be a source for sulfur nutrient in the algae production, if the commercially available method used to remove the sulfur components of the biogas, makes this convenient and cost effective.

As explained in relation to fig.2 a partial flow of desulfurized biogas 13a is subjected to treatment in a CO2 separation unit 70, while another part of the desulfurized biogas 13b may be charged as fuel with high CO2 content to a burner 150.

The CO2 separation unit 70 is typically one using a principle for separation selected among water scrubbing, physical or chemical absorption using organic solvents, pressure swing adsorption and permeation using membranes.

The usage of fish farm related organic waste in the embodiment presented in fig.2, exemplifies very similar embodiments based on other organic waste forms 10, such as domestic waste, animal or agricultural waste, sewage sludge and other organic wastes and mixes thereof.

A common feature of the present embodiments and other similar embodiments based on other waste forms, is the application of anaerobic digestion of organic waste in a digestor 50 for production of biogas 12 and liquid and solid digestrates 16.

List of reference numbers in the drawings.

10 storage system for organic waste forms

11 inlet to the digestor 50 for organic waste

12 raw biogas from digestor to desulfurizer 60

13 desulfurized biogas (CH4+CO2) from desulfurizer to CO2 separator 70 (fig 1) 13a desulfurized biogas (CH4+CO2) from desulfurizer to CO2 separator 70

13b desulfurized biogas (CH4+CO2) from desulfurizer to burner 150

14 CO2 from the CO2 separator 70 in fig.1 and CO2 from the CO2 storage unit 75 in fig. 2

14a CO2 or CO2 rich gas to storage 75 for CO2 rich gas

14b CO2 rich gas to storage 75 for CO2 rich gas

14c CO2 containing exhaust from an energy plant 105

15 methane, CH4 , from the CO2 separating unit to methane storage facility 100. 15a methane to a heat and power facility 105

16 liquid and solid digestrates leaving the digestor for nutrient extraction N, P, and other nutrients 90

17 N, P and other nutrients for mixing with CO2 for mixing in the nutrient preparation unit 140

17a transfer gate from a nutrient supply 140a

18 transfer gate between the nutrient preparation unit 140 and the algae production plant 80

19 algae for production of different algae products 110

20 algae biomass rest from 120 to be used as organic fertilizer 130

21 transportation system for algae biomass rest, to storage system for organic waste forms 10

22 introduction of hydrogen or algae for reduction of CO2 and increase of CH4 in the biogas

23 transport of heat where needed in the total industry plant.

24 air inlet to the burner 150

25 algae for direct use in a fish farm 160

25a algae to fish feed plant

25b fish feed to fish farm 160

26 electricity and heat from the power plant 100

27 fish excrement and food waste from fish farm 160

28 waste from fish farm to organic waste 10 for production of biogas in the digestor 50

50 digestor

60 desulfurizer

70 CO2 separation unit

75 storage facility for CO2 rich gas

80 algae production plant

90 extraction facility for key nutrients (N+P) and other important nutrients from solid and liquid digestrates

100 methane, CH4, storage facility.

105 gas turbine or other el. producing device, facility for combined heat and power, CHP

110 production of algae products

120 algae biomass rest

130 organic fertilizer

140 nutrient preparation device

140a additional nutrients supply, if needed

150 burner of CO2 rich gas

160 fish farm

170 fish farm waste

180 fish feed plant

References Cited:

Andresen et. al.2016. Method and device for upgrading of biogas and hydrogen production from anaerobic fermentation of biological material. Norwegian patent 344851 B1.

Bachmann N.2015. Sustainable biogas production in municipal wastewater treatment plants. IEA Bioenergy

Campos et. al 2019. Nitrogen and Phosphorous Recovery From Anaerobically Pretreated Agro-Food Wastes: A Review. Frontiers in Sustainable Food Systems. Volume 2, Article 91

Cuello and Ley.2009. Accordion Bioreactor, WO 2011/063129 A2

Daneshgar et. al 2018. The potential Phosphorous Crises: Resource Conservation and possible Escape Technologies: A Review. MDPI Resources, 7,37.

Meier et. al 2015. Photosynthetic CO2 uptake by microalgae: An attractive tool for biogas upgrading. Biomass & Bioenergy 73: 102-109.

Möller et. al 2016. Compost and Digestrates from Urban Organic Wastes. Fact Sheet project IMPROVE-P.

Shilton et. al 2012. Plant based phosphorous recovery from wastewater via algae and macrophytes. Current Opinion in Biotechnology, 23: 884-889.

Shoener et. al 2014. Energy positive domestic wastewater treatment: the role of anaerobic and phototrophic technologies. Environmental Science: Processes and Impacts 16. 1204-1222.

Claims

Claims.

1. Method and device for production of biogas in an anaerobic digestor (50) with inherent separation of CO2 or CO2 rich gas (14) from the methane (15) produced, characterized in that

a digestrate (16) discharged from the digestor (50) is directed to an extraction facility (90) in which at least the nutrients nitrogen and phosphorus are extracted and directed to a nutrient preparation unit (140) in a flow (17)

while the raw biogas (12) from the digestor is subjected to desulphurization (60) and subsequent CO2 separation in a separation unit (70) from which CO2 is directed to the nutrient preparation unit (140) for combination with the nitrogen and phosphorous to a nutrition base flow (18) for subsequent use as nutrition.

2. Method as claimed in claim 1, wherein the anaerobic digestor (50) is charged with organic matters comprising organic waste selected among one or more of domestic waste, animal or agricultural waste, waste from fish farms, sewage sludge and other organic waste.

3. Method as claimed in claim 1 or 2, wherein the CO2 separation unit (70) is using a principle for separation selected among water scrubbing, physical or chemical adsorption using organic solvents, pressure swing adsorption, and permeation using membranes.

4. Method as claimed in any one of the preceding claims, wherein the methane (15) separated from the CO2 in the separation unit (70) is discharged to a storage (100) for methane for subsequent use as fuel for at least one of energy production and transportation.

5. Method as claimed in any one of the preceding claims, wherein the nutrition base flow (18) is charged to an algae production facility (80).

6. Method as claimed in any one of the preceding claims, wherein waste for the algae production facility (80) and/ or the algae products (110) are recycled (21) to become part of the biomass (11) being charged to the digestor (50).

7. Method as claimed in any one of the preceding claims, wherein the sulphur removed in the desulphurization unit (60) is used as nutrient in the algae production facility.

8. Method as claimed in any one of the preceding claims, wherein a partial flow of desulfurized biogas (13,13a) is subjected to treatment in a CO2 separation unit (70) thereby providing one discharge flow of methane (15) and one discharge flow of CO2 (14,14a), while optionally another part of the desulfurized biogas (13b) is charged to a burner (150) providing energy as heat and a discharge of CO2 rich gas (14b) for inmix with the discharge flow of CO2, or CO2 rich gas from the CO2 separation unit (70) in to the CO2 rich storage unit (75) and further use as the carbon (C) nutrient (14) in the algae production plant (80).

9. Method as claimed in any of the preceding claims, wherein the storage unit (75) is used for the CO2 rich gases (14a,14b,14c), from different sources of CO2 before entering the nutrient preparation unit (140), though gate (14) for inmix with other necessary nutrients before introduction to the algae production pant (80).

10. Method as claimed in any one of the preceding claims, wherein additional nutrients (140a) are added through gate(17a), and/or the concentration of the existing nutrients is adjusted to a desired concentration level for the algae type used in the algae production plant (80)

11. Method as claimed in claim 10, wherein additional nutrients are selected among any combination of K, Na and Mg.

12. Method as claimed in any one of the preceding claims, wherein algae biomass rest (120) is transported (21) to the storage for organic waste forms (10) for use or reuse in the digestor (50).

13. Device for production of energy rich biogas, CH4 and CO2 and nutrients by anaerobic digestion of organic waste forms, comprising a digestor (50), further comprising a facility (90) for extraction of at least phosphorous P and nitrogen N from the liquid and solid digestrates (16) produced in the digestor (50), a desulfurizer (60) arranged to remove sulfur from the energy rich biogas (12) leaving the digestor (50), a CO2 separator (70) arranged to separate CO2 from the desulfurized biogas (13) leaving the desulfurizer (60), forming a separate flow of methane (15) and a separate flow of CO2 (14), characterized in that the extracted P and N nutrients (17) leaving the extraction facility (90) is combined with the CO2 (14) in a nutrient preparation unit (140) for combination to a nutrition base flow (18) for subsequent use as nutrition.