Method for producing microalgae feed by using anaerobic biogas slurry of kitchen waste

Abstract

The present application relates to a kind of method for producing microalgae feed by using kitchen waste anaerobic biogas liquid, microalgae is used to treat kitchen waste anaerobic biogas liquid, and then the microalgae growing enrichment is harvested and used as feed.The present application utilizes microalgae resource treatment kitchen waste anaerobic biogas liquid, not only can improve kitchen biogas liquid water quality, substantially reduce the content of ammonia nitrogen total nitrogen, improve carbon-nitrogen ratio, reduce color, conducive to subsequent standard treatment, and the converted microalgae biomass is used as microalgae feed raw material, with economic and environmental advantages.Realize the coupling of biogas liquid purification and resource recycling technology, alleviate the problems of large carbon emission, high energy consumption and the like faced by current treatment process.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a method for improving the quality of anaerobic digestate from kitchen waste using microalgae and for producing feed using the microalgae enriched from it. Background Technology

[0002] In recent years, with the growth of the population and the improvement of people's living standards, the rapid development of the catering industry has led to a rapid increase in the amount of food waste generated and the discharge volume has been increasing year by year. After sorting, crushing, and impurity removal, solid-liquid separation, and oil-water separation systems, food waste undergoes anaerobic fermentation treatment. The resulting anaerobic digestate is characterized by high ammonia nitrogen and C / N imbalance, making it difficult to treat. The existing treatment process is the activated sludge process, but it suffers from problems such as poor nitrogen and phosphorus removal efficiency, long process flow, and high aeration energy consumption. Microalgae, due to their ability to photosynthesize and their extremely strong reproductive and survival capabilities, can absorb various inorganic elements and organic matter from wastewater. They can absorb and purify large amounts of nitrogen and phosphorus in wastewater, and the microalgae wastewater treatment process has received widespread attention in recent years.

[0003] In research on wastewater purification using microalgae, removing pollutants from the wastewater is only the first step. Even after purification, if the resulting microalgae cannot be recycled and are directly discharged into natural water bodies, they will still pollute the environment. Therefore, how to fully utilize the biomass energy of the algae is a crucial aspect of subsequent research. During wastewater purification, microalgae accumulate large amounts of lipids, proteins, and polysaccharides. Microalgae proteins can be used as additives for animals and humans, fibers can be used as pulp supplements, and oils can be converted into biodiesel. Therefore, microalgae can be used to extract and develop oils for biodiesel development, and to extract polyunsaturated fatty acids, proteins, and polysaccharides for the development and utilization of bio-nutritional products. However, since microalgae grow in wastewater, their bodies inevitably contain some pollutants from the wastewater. Therefore, current technology generally uses incineration for the final treatment of microalgae used in wastewater treatment. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for producing microalgae feed from anaerobic digestate of kitchen waste. This method utilizes microalgae to treat anaerobic digestate, which not only improves the quality of the digestate by significantly reducing ammonia and total nitrogen content, improving the carbon-to-nitrogen ratio, and lowering color, thus facilitating subsequent treatment to meet standards, but also provides the converted microalgae biomass that can be used as a feed ingredient, offering both economic and environmental advantages. This method couples digestate purification and resource recycling technologies, alleviating the problems of high carbon emissions and high energy consumption faced by current treatment processes.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for producing microalgae feed using anaerobic digestate from kitchen waste includes the following steps:

[0007] Step a) Domestication and expansion of microalgae: Add the selected microalgae to a diluted, lower concentration of anaerobic digestate from kitchen waste and allow them to grow freely under light conditions. Take out new microalgae and add them to a higher concentration of anaerobic digestate from kitchen waste, allowing them to grow freely. Repeat the above operation to continuously improve the pollution tolerance of the microalgae until the microalgae can grow and reproduce in the original anaerobic digestate from kitchen waste. Add the microalgae that can grow and reproduce in the original anaerobic digestate from kitchen waste to the culture medium for expansion.

[0008] Step b) Pretreatment of anaerobic digestate from kitchen waste: Pretreatment of anaerobic digestate from kitchen waste to appropriately reduce the concentration of ammonia nitrogen and total nitrogen in the digestate;

[0009] Step c) Microalgae treatment of anaerobic digestate from kitchen waste: Add well-grown microalgae to the pre-treated anaerobic digestate from kitchen waste to grow and reproduce, while absorbing nitrogen and phosphorus nutrients from the wastewater and consuming organic matter, thereby improving water quality;

[0010] Step d) Microalgae harvesting and algae powder preparation: Centrifuge the biogas slurry containing microalgae to separate algae from water, and dry the obtained precipitated concentrated algae slurry to obtain microalgae powder, which is microalgae feed.

[0011] Furthermore, in step a), the temperature for microalgae acclimatization is 25–35°C; the humidity for acclimatization is 50%–80%; and the light conditions are a light intensity of 8000–12000 Lx.

[0012] The culture medium is BG11 medium.

[0013] Among them, domesticated microalgae (see Figure 1 According to the identification, its composition is as follows: Chlorella accounts for 56%, Microcystis accounts for 20%, Nephroticosa and Scalybugs account for 20%, and others account for 4%. No molds, Salmonella and Microcystis were detected. It meets the microbiological indicators required by DB32 / T564-2010 standard. It has strong environmental adaptability and is heterotrophic, and can be used to treat anaerobic digestate from kitchen waste to improve water quality.

[0014] Furthermore, the pretreatment methods in step b) mainly consist of aerobic biological treatment and catalytic ozone oxidation treatment, and after pretreatment, high-throughput sequencing was performed to identify that the main species composition was Chlorella (see...). Figure 1 In the ozone pretreatment (B) group, Chlorella comprised 56% of the species composition, while in the aerobic pretreatment group, it comprised 57%. The pretreated wastewater also contained a small amount of microalgae.

[0015] Furthermore, the amount of domesticated microalgae added in step c) is 0.1-0.15 g / L dry weight; the wastewater indicators before and after microalgae treatment are measured to evaluate the overall effect of microalgae on biogas slurry purification.

[0016] The drying process is freeze-drying.

[0017] Furthermore, the freeze-drying time in step d) is 24 hours.

[0018] The microalgae powder was ground after freeze-drying to evaluate the feasibility of using the microalgae powder obtained after wastewater treatment as feed.

[0019] This invention provides a method for producing microalgae feed using anaerobic digestate from kitchen waste, which has the following beneficial effects:

[0020] This invention utilizes microalgae enriched from purified wastewater to prepare feed. The enriched microalgae include those added during wastewater treatment and those already present in the pre-treated wastewater. During the entire wastewater purification process, both types of microalgae grow and reproduce, absorbing nitrogen and phosphorus nutrients and consuming organic matter, thereby improving water quality. Using microalgae to treat anaerobic digestate from kitchen waste not only improves the digestate's quality, significantly reducing ammonia and total nitrogen content, improving the carbon-to-nitrogen ratio, and lowering color, facilitating subsequent treatment to meet standards, but also significantly reduces greenhouse gas emissions during the microalgae denitrification process, achieving low-carbon and green treatment. The harvested microalgae, identified as primarily Chlorella, are high in protein and rich in nutrients, with toxic substance content below feed standards, demonstrating their potential for feed production. This multi-benefit approach is environmentally friendly and aligns with sustainable development requirements. Therefore, this invention efficiently and cost-effectively improves the quality of anaerobic digestate from kitchen waste while fully utilizing its resource-available organic matter to obtain high-quality algal powder feed, demonstrating significant environmental and economic benefits.

[0021] Microalgae contain various vitamins, proteins, oils, polysaccharides, and carotenoids. Feeding them to livestock can reduce breeding costs and improve the nutritional content of the feed, offering multiple benefits. The microalgae powder obtained by this invention, after testing, meets the standards of DB32 / T 564-2010 for crude protein content and GB13078-2001 for feed hygiene. No harmful microorganisms were detected, making it a rare and high-quality feed. Attached Figure Description

[0022] Figure 1 This is a diagram showing the composition analysis of microalgae.

[0023] A represents the composition of microalgae domestication and screening; B represents the species composition analysis diagram of high-throughput sequencing after wastewater pretreatment.

[0024] Figure 2 Example 1: Comparison of water quality indicators before and after microalgae treatment of anaerobic digestate from kitchen waste.

[0025] A shows the change in total nitrogen over time; B shows the change in ammonia nitrogen over time; and C shows the change in microalgal biomass over time.

[0026] Figure 3 This is a comparison chart of the microalgae powder obtained after wastewater treatment in Example 1 and the nutrients in several major feeds.

[0027] A compares protein content, and B compares fat content. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the claims of the present invention.

[0029] Example 1 - Aerobic biological pretreatment

[0030] 1) Dilute the anaerobic digestate of kitchen waste with pure water at a volume ratio of 1:4. Inoculate the selected microalgae (taken from natural lake water) into the diluted digestate. When the microalgae grow to a better concentration, centrifuge them and then inoculate them into 50% digestate for further acclimatization and cultivation. Repeat this process to continuously improve the pollution tolerance of the microalgae until they can grow and reproduce in the original anaerobic digestate of kitchen waste.

[0031] 2) The obtained tolerant microalgae were added to BG11 medium and placed in a constant temperature room for cultivation. The cultivation temperature was 28℃, the humidity was 60%, the light intensity was 10000lx, and the light was provided all day for expansion cultivation to obtain a sufficient amount of algal solution. The solution was centrifuged at 8000r / min for 5min. During the centrifugation process, the microalgae were repeatedly rinsed with deionized water 3 times to obtain enriched microalgae.

[0032] 3) Using anaerobic digestate from kitchen waste as the treatment target, the supernatant was collected after settling for aerobic biological pretreatment: An SBR (Sequencing Bioreactor) model was adopted, with an effective reactor volume of 2L (sludge solubility of 8g / L) and a water exchange rate of 25%. The operating cycle was 24 hours, including 22.5 hours of aeration, 1 hour of settling, and 0.5 hours of inlet and outlet operation. After 14 days of continuous acclimatization, 400mL of anaerobic digestate from the kitchen waste was collected for later use starting from the 15th day.

[0033] 4) The acclimatized microalgae were inoculated into the anaerobic digestate of kitchen waste that had undergone aerobic biological pretreatment. The inoculation amount was 0.1 g / L, and the treatment conditions were as follows: temperature 28±1℃; light intensity 8000~12000Lx, with full-day illumination. During the treatment, the growth status of the microalgae and wastewater indicators (ammonia nitrogen, TN, and color) were monitored in real time to evaluate the wastewater purification effect.

[0034] 5) After treatment, the anaerobic digestate from the kitchen waste treated with microalgae was centrifuged and concentrated to harvest the algae liquid. It was then freeze-dried and ground to obtain microalgae powder. The protein, oil, and toxic substance content of the powder were determined to evaluate its feasibility as a microalgae feed.

[0035] Table 1. Changes in anaerobic digestate parameters from kitchen waste in Example 1

[0036]

[0037] Table 2. Changes in microalgal biomass in anaerobic digestate from kitchen waste treated with microalgae in Example 1.

[0038]

[0039] Table 3 Main nutrient components of microalgae powder in anaerobic digester for treating kitchen waste in Case 1

[0040]

[0041] Table 4. Toxic components of microalgae powder in anaerobic digester slurry from food waste treated in Example 1

[0042]

[0043] 6) As shown in Table 1, Table 2 and Figure 2 As shown, the changes in indicators before and after the treatment of anaerobic digestate from kitchen waste using microalgae are as follows: TOC content decreased from 450.5 mg / L before treatment to 218.4 mg / L after treatment; ammonia nitrogen decreased from 2205 mg / L before treatment to 2.57 mg / L after treatment; total nitrogen decreased from 2532.42 mg / L before treatment to 188.41 mg / L after treatment; color decreased from 60 times before treatment to 40 times after treatment; and biomass increased 10 times. These data indicate that the method of the present invention has a good treatment effect and effectively improves the effluent quality.

[0044] 7) As shown in Tables 3 and 4 and Figure 3As shown, the microalgae powder obtained after treating anaerobic digestate from kitchen waste has a crude protein content of up to 50.1%, and its moisture and ash content also meet the DB32 / T 564-2010 standard. Compared with some other plant, animal, and microbial feeds, it has significant advantages. The analysis results of lead, arsenic, mercury, and cadmium meet the GB13078-2001 feed hygiene standard, proving that the microalgae powder after treating anaerobic digestate from kitchen waste can be used as a high-quality feed.

[0045] Example 2 - Ozone Pretreatment

[0046] 8) The domestication and cultivation of microalgae, the treatment of pretreated anaerobic digestate from kitchen waste, and the process and steps for harvesting microalgae and preparing algal powder are the same as in Example 1. The difference is that the pretreatment of the anaerobic digestate from kitchen waste is catalytic ozone oxidation treatment: 200 ml of anaerobic digestate from kitchen waste is added to a 500 mL absorption bottle, which is filled with 2 / 3 volume of solid catalyst. An air source is used as the ozone source, and ozone at a concentration of 30 mg / L is introduced at a flow rate of 500 mL / min for 60 minutes, and then it is ready for use.

[0047] Table 5. Changes in anaerobic digestate parameters of kitchen waste in Example 2.

[0048]

[0049] Table 6. Changes in microalgal biomass in anaerobic digestate from kitchen waste treated with microalgae in Example 2.

[0050]

[0051] Table 7. Main nutrient components of microalgae powder in anaerobic digestate from food waste treated in Example 2.

[0052]

[0053] Table 8. Toxic components of microalgae powder in anaerobic digester slurry treated with kitchen waste, Example 2

[0054]

[0055] 9) As shown in Tables 5 and 6, the changes in indicators before and after the treatment of anaerobic digestate from kitchen waste using microalgae are as follows: TOC content decreased from 450.5 mg / L before treatment to 134.3 mg / L after treatment; ammonia nitrogen decreased from 2205 mg / L before treatment to 69.2 mg / L after treatment; total nitrogen decreased from 2532.42 mg / L before treatment to 90.18 mg / L after treatment; color decreased from 60 times before treatment to 20 times after treatment; and biomass increased by 5 times. These data indicate that the method of the present invention has a good treatment effect and effectively improves the effluent quality while microalgae grow.

[0056] 10) As shown in Tables 7 and 8, the microalgae powder obtained after treating anaerobic digestate from kitchen waste has a crude protein content of 52.1%, and the moisture and ash content also meet the DB32 / T 564-2010 standard; the analysis results of lead, arsenic, mercury and cadmium meet the GB13078-2001 feed hygiene standard, proving that the microalgae powder after treating anaerobic digestate from kitchen waste can be used as a high-quality feed.

[0057] 11) Microbial testing of microalgae feed, see Table 9.

[0058] Table 9. Microbiological Indicators of Microalgae Feed

[0059]

Claims

1. A method for producing microalgae feed using anaerobic digestate from kitchen waste, comprising the following steps: Step a) Domestication and expansion of microalgae: Add the selected microalgae to a diluted, lower concentration of anaerobic digestate from kitchen waste and allow them to grow freely under light conditions. Take out new microalgae and add them to a higher concentration of anaerobic digestate from kitchen waste, allowing them to grow freely. Repeat the above operation to continuously improve the pollution tolerance of the microalgae until the microalgae can grow and reproduce in the original anaerobic digestate from kitchen waste. Add the microalgae that can grow and reproduce in the original anaerobic digestate from kitchen waste to the culture medium for expansion. Step b) Pretreatment of anaerobic digestate from kitchen waste: Pretreatment of anaerobic digestate from kitchen waste to appropriately reduce the concentration of ammonia nitrogen and total nitrogen in the digestate; Step c) Microalgae treatment of anaerobic digestate from kitchen waste: Add well-grown microalgae to the pre-treated anaerobic digestate from kitchen waste to grow and reproduce, while absorbing nitrogen and phosphorus nutrients from the wastewater and consuming organic matter, thereby improving water quality; Step d) Microalgae harvesting and algae powder preparation: Centrifuge the biogas slurry containing microalgae to separate algae from water, and dry the obtained precipitated concentrated algae slurry to obtain microalgae powder, which is microalgae feed; In step a), the temperature for microalgae acclimatization is 25–35°C; the humidity for acclimatization is 50%–80%; and the light conditions are a light intensity of 8000–12000 Lx. The pretreatment methods in step b) are mainly aerobic biological treatment or catalytic ozone oxidation treatment; The selected microalgae were taken from natural lake water.

2. The method according to claim 1, wherein the culture medium in step a) is BG11 culture medium.

3. According to the method of claim 1, in step a), the amount of domesticated microalgae added to the biogas slurry in step c) is 0.1-0.15 g / L dry weight.

4. The method according to claim 1, wherein the drying in step d) is freeze drying.

5. According to the method of claim 4, the freeze-drying time in step d) is 24 hours.

6. The method according to claim 5, wherein the freeze-dried microalgae are ground into powder.

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