TWI876669B - Waste treating and by-product manufacturing method/equipment for reducing carbon emission and recycling organic waste - Google Patents

Abstract

The present invention relates to a method and apparatus for treating waste and producing byproducts for reducing carbon emissions and recycling organic waste. In particular, the present invention relates to a process and apparatus capable of reasonably separating and recycling wastewater containing high concentrations of methane, which is produced in the process of purifying polyhydroxyalkanoate (PHA), a biodegradable plastic material produced by microbial fermentation, and is used alone or mixed with various organic wastes or other types of biodegradable plastics, thereby producing various byproducts (RNG, Bio-Char, etc.) for resource utilization through anaerobic digestion.

Description

Waste treatment and by-product production method and device for reducing carbon emissions and recycling organic waste

The present invention relates to a method and apparatus for treating waste and producing byproducts for reducing carbon emissions and recycling organic waste. In particular, the present invention relates to a process and apparatus for rationally separating and recycling wastewater containing high concentrations of methane, which is produced in the process of purifying biodegradable plastic materials produced by microbial fermentation, namely polyhydroxyalkanoate (PHA), and is used alone or mixed with various organic wastes or other types of biodegradable plastics, so as to produce various recycling byproducts (biogas, RNG, hydrogen ( _H2 ), carbon dioxide ( _CO2 ), biosulfur, digestate, liquid fertilizer (liquid fertilizer), digestate, Bio-Char, manure, etc.) through anaerobic digestion.

Biodegradable plastics or bioplastics are a general term for plastics that can be degraded by bacteria or organisms, as well as polymer plastics based on biomass. Based on the raw materials or production/degradation mechanisms, biodegradable plastics are divided into natural polymer systems using natural compounds as raw materials, biosynthetic polymer systems produced by microorganisms, and chemically synthesized polymer systems synthesized using biomass produced by microorganisms as raw materials.

Among them, biosynthetic polymer substances, also called microbially produced polymers, are substances that use biopolymers produced by microorganisms to produce materials with properties such as plastics. Representative examples include polyhydroxyalkanoates composed of aliphatic esters, which can be collectively referred to as "PHA".

PHA is a polyester produced naturally through numerous microbial-based processes such as bacterial fermentation of sugars or lipids. It is biodegradable and exhibits thermoplastic or elastomeric properties with a melting point of 40-180°C.

As mentioned above, as a biodegradable plastic, although PHA itself has high environmental protection characteristics, it still needs some improvement when conducting environmental impact assessment (Life cycle assessment, LCA) on the entire process including raw material processing, production, use and disposal.

Specifically, in the case of amino acid fermentation, although amino acids and bacteria are included, they are easily separated and therefore easily recycled as feed and fertilizer. However, in the case of wastewater generated in the production process of PHA, a biodegradable plastic material based on fermentation, the bacteria are in a fragmented form that is difficult to use as feed or fertilizer, so a solution for utilizing this wastewater is needed.

Problem that the invention aims to solve

The present invention is proposed to solve the above-mentioned problems, and its purpose is to provide a method and apparatus for treating waste and producing by-products for reducing carbon emissions and recycling organic wastes, which can utilize high-carbon wastewater produced in the process of producing PHA in microorganisms after purification and fermentation, and produce useful by-products (renewable natural gas (RNG), biochar (Bio-Char) etc.) at a high yield through anaerobic digestion, and when the mixed recovery of wastewater containing high concentration of organic carbon and the produced PHA product is used for anaerobic digestion, it can actually be completely recovered 100% based on carbon, thereby greatly improving LCA and reducing manufacturing costs.

The technical problems to be solved by the present invention are not limited to the technical problems mentioned above. As for other technical problems not mentioned yet, a person with ordinary knowledge in the relevant technical field can obtain a clearer understanding through the following description.

Methods used to solve problems

The present invention provides a method for producing a by-product, which includes the following processes: a process for purifying PHA produced by microbial fermentation; a process for separating and recovering wastewater having a methane yield (CH ₄ yield) of 250 mL/g VS or more in the purification process; and a process for producing a by-product by anaerobic digestion using the separated and recovered wastewater.

At this time, the PHA may be a monopolymer or copolymer including one or more repeating units selected from the following group, the group consisting of 3-hydroxybutyric acid (3-HB), 3-hydroxypropionic acid (3-HP), 3-hydroxyvaleric acid (3-HV), 3-hydroxyhexanoic acid (3-HH), 4-hydroxybutyric acid (4-HB), 4-hydroxyvaleric acid (4-HV), 4-hydroxyhexanoic acid (4-HH), 5-hydroxyvaleric acid (5-HV) and 6-hydroxyhexanoic acid (6-HH).

The PHA may be a copolymer including 1 to 60 wt% of 4-hydroxybutyric acid (4-HB) repeating units, a copolymer including 1 to 30 wt% of 4-hydroxybutyric acid (4-HB) repeating units, or a copolymer including 30 to 60 wt% of 4-hydroxybutyric acid (4-HB) repeating units, based on the total weight, but is not limited thereto. The PHA may be poly(3-hydroxybutyric acid-co-4-hydroxybutyric acid).

Preferably, the methane yield (CH ₄ yield, mL/g VS) of the wastewater can be 300 mL/g VS or more. Depending on process conditions or the form and conditions of feed stock, the methane yield (CH ₄ yield, mL/g VS) of the wastewater can also be 350 mL/g VS or more.

In addition, in the process of manufacturing by-products, in order to increase the production of methane, various organic wastes that are difficult to treat can be used together with the wastewater. The organic wastes can be PHA that needs to be discarded due to low commercial value due to failure to meet quality standards, products made from PHA, food waste (food garbage), sewage sludge, livestock feces, disposable livestock products made of biodegradable materials, cups, plastic bags, straws and other disposable products made of biodegradable materials because they are difficult to recycle, or any one or a mixture of two or more of them.

Products made from the PHA as a raw material may be in the form of biodegradable containers made from or containing various types of PHA, or garbage bags for recycling waste, food waste bags, various disposable items for livestock, cups, plastic bags, straws, etc.

By utilizing recycled waste containing PHA, anaerobic digestion systems can be effectively applied to waste that is difficult to recycle and landfill, and methane generation can be maximized by mixing organic waste with PHA products.

At this time, the by-product can be biogas, digestate (fluid) or digestate (solid), specifically, it can be biogas, RNG, hydrogen (H2) or carbon dioxide (CO2) of processed biogas, it can also be liquid fertilizer (liquid fertilizer) of digestate or processed digestate, it can also be biochar, biosulfur or accumulated manure of digestate or processed digestate.

In the case of collecting carbon dioxide (CO2), it can also be commonly applied to collecting carbon sources emitted as CO2 during the fermentation process involved in the carbon rate described below.

In addition, FIG1 is a flow chart of the entire process according to a preferred embodiment of the present invention.

In the process of refining PHA, low-concentration wastewater can be reused in the refining process through a bypass, while high-concentration wastewater with a methane yield higher than at least one preset benchmark value can be directly fed into the anaerobic digestion tank, or can be fed into the anaerobic digestion tank in the form of wastewater sludge after pretreatment, i.e., a water treatment process.

Whether the wastewater has a high concentration higher than the reference value can be determined by a biochemical methane potential (BMP) test conducted at a pH of 7.5 to 7.8 and a temperature of 37 to 39°C.

Low-concentration wastewater (defined as wastewater with a methane yield (CH ₄ yield) less than 250 mL/g VS, or less than 300 or 350 mL/g VS as required) can be reused as process water for PHA purification process, etc. through membrane filtration and purification.

In addition, the low-concentration wastewater is concentrated to become high-concentration wastewater higher than the reference value, and then recovered together with the high-concentration wastewater, so that it can be directly put into the anaerobic digester, or put into the anaerobic digester through a water treatment process.

Referring to FIG. 2 , the unit processes of the purification process may generally include: ① a cell separation process, which removes impurities in the fermentation broth through a solid-liquid separation process and recovers cells containing PHA; ② a PHA extraction process, which dissolves cell components other than PHA through physical and chemical methods to recover Crude PHA; ③ an impurity separation and cleaning process, which separates the impurities dissolved by the solid-liquid separation process from the Crude PHA and cleans the Crude PHA; ④ an additional purification process, which removes impurities (lipids, proteins, etc.) contained in the extracted Crude PHA; ⑤ a product recovery process, which recovers the purified PHA through a solid-liquid separation process.

In the above-mentioned unit processes, waste water (filtrate) is discharged in ① cell separation process, ③ impurity separation and cleaning process, and ⑤ product recovery process, and can be divided into the first filter liquid, the second filter liquid, and the third filter liquid in this order.

The process wastewater generated in the PHA purification process has a high methane potential, especially in the case of a single first filtrate or a mixed filtrate in which the first filtrate is mixed with any one of the second filtrate and the third filtrate, showing a high BMP (Biochemical Methane Potential).

Therefore, compared with other organic biomass, a higher methane yield can be obtained when using PHA process wastewater. In the case of mixed filtrate, it is better to mix the first filtrate, the second filtrate and the third filtrate, and it is more preferable to mix them in a volume ratio of 1.5~2.5:1.5~2.5:0.5~1.5. Needless to say, the reasonable mixing ratio can vary according to the process conditions such as purification, anaerobic digestion, or the form and conditions of feed stock.

This wastewater (filtrate) with high methane potential can optionally be fed into the anaerobic digestion process via a water treatment unit.

At this time, at the process control level, based on the measured values of various parameters such as the water quality properties or flow rate of various wastewaters generated in the purification process, the solid content, the organic matter content, the type/morphology or content of mycelium, it is possible to determine whether the wastewater is mixed, whether it is reused (recycled), whether it has passed through a wastewater pretreatment process, whether it has been pretreated before being put into an anaerobic digester, etc., and based on this, the flow of wastewater can be controlled in real time.

Wastewater treated in anaerobic digesters is discharged in the form of gas, liquid, and solid phases. Gas phase flow refers to byproducts in the form of biogas, which can be obtained or resourced in the form of renewable natural gas (RNG) through carbon dioxide separation and collection processes. At this time, the collected carbon dioxide is also a byproduct discharged through the process, which can be processed or used as an additional carbon source. Liquid phase flow refers to the form of wastewater with reduced COD through anaerobic digestion, which can be used as industrial water or liquid fertilizer through additional processes such as wastewater treatment. In addition, byproducts of solid phase flow can be obtained in the form of renewable carbon or biochar, biosulfur, or compost through pyrolysis and other processes.

In addition to the aforementioned high-concentration wastewater (filtrate), other wastes can be mixed with wastewater and fed into the anaerobic digester. Specifically, plastic-related products using used PHA, various foods or sewage and wastes contained in these plastic products or combined with them in various ways, animal manure, etc. can be selectively mixed with wastewater and fed into the digester in view of the use, form, and composition of the final byproducts.

This can be considered as a resource recycling system involving the entire ecosystem related to biodegradable plastic materials, namely PHA products, and also a resource recycling system through comprehensive utilization of waste by-products.

The type and amount of waste materials other than wastewater fed into the anaerobic digester can be determined based on the WQ of the wastewater (filtrate) and the purpose, form, and composition of the target by-products to be produced, and the process can be used accordingly.

Invention effect

According to the present invention as described above, wastewater containing high concentration of organic carbon generated in the process of purifying PHA produced in microorganisms after fermentation is utilized, and useful by-products (renewable natural gas (RNG), biochar, etc.) are produced at high yields through anaerobic digestion.

The effects of the present invention are not limited to the effects mentioned above, but also include other effects that are clearly understood by those skilled in the art from the overall description of the specification but are not explicitly mentioned.

Below, the preferred embodiments of the present invention are described in detail with reference to the drawings. With reference to the drawings and the detailed embodiments described below, the advantages, features and methods of achieving ...

If there is no other explanation, all terms (including technical terms and scientific terms) used in this specification can be used as meanings that are generally understood by people of ordinary knowledge in the relevant technical fields. If there is no special definition in this specification for terms that have been defined in general dictionaries, they should not be interpreted with idealized or overly formalized meanings. The purpose of using terms in this specification is only to illustrate the embodiments, not to limit the present invention. In this specification, the expression of the singular should be understood to include the meaning of the plural, unless there is a clear explanation in the context.

The terms “comprises” and/or “comprises” mentioned in this specification should be understood as meaning that the elements, steps, operations and/or components involved do not exclude the possibility of the existence or additional possibility of one or more other elements, steps, operations and/or components.

Example 1. General properties analysis of PHA production process wastewater and evaluation of the feasibility of anaerobic digestion treatment

In the present invention, the water quality (WQ) of high-concentration carbon wastewater generated in the process of purifying PHA (specifically, P3HB-co-4HB, a polymer of 3-hydroxybutyrate, i.e., a copolymer of poly(hydroxybutyrate); P3HB and 4-hydroxybutyrate (4HB)) was analyzed by various parameters, and it was experimentally confirmed that it contains 2 to 4 times more methane than other biomass (wheat straw, etc.).

Table 1 Parameter First filter Second filter The third filter VS, g/L 3.2±0.4 4.1±0.4 4.8±0.1 tCOD, g/L 7.8±1.4 11.8±0.8 6.9±1.2 sCOD, g/L 4.9±0.6 6.2±0.9 3.2±0.8 tVFA, g/L 1.7±1.1 2.5±0.8 0.6±0.3 TOC, g/L 3.0±0.1 3.3±0.1 2.9±0.1 DOC, g/L 2.2±0.1 2.7±0.1 2.1±0.1 TP, mg/L 211±30 455±41 586±8 TAN, mg/L 274±21 700±34 309±11 pH 5.3±0.2 6.8±0.1 7.0±0.1

PHA production wastewater is a waste product of biological processes, and anaerobic digestion (AD) is a process that treats this wastewater and produces biogas as a by-product, so it can be considered the best choice.

Anaerobic digestion refers to the process of treating organic waste and producing biogas that can be used for energy production and organic fertilizer. It is widely used in the treatment of high-concentration biomass (agricultural waste, food waste, livestock and poultry feces, thick sludge, etc.).

Table 1 shows the water quality properties (WQ) of the first filtrate, the second filtrate and the third filtrate in the high-concentration carbon wastewater generated in the PHA purification process, measured by the following parameters, namely, volatile solids ignition loss (VS), total chemical oxygen demand (tCOD), soluble chemical oxygen demand (sCOD), total volatile fatty acid (tVFA), total organic carbon (TOC), dissolved organic carbon (DOC), total phosphorus (TP), total ammonia nitrogen (TAN) and pH.

Example 2. Biochemical Methane Production Potential (BMP) Test

All water quality (WQ) parameters (TS, VS, tVFA, tCOD, sCOD, TKN, TAN, TP, TOC, DOC, VSS) were analyzed according to standard methods (APHA, 2005). In addition, biogas composition analysis using gas chromatography was used.

The purpose of the biochemical methanogenic potential and biological methanogenic potential (BMP) test is to evaluate the possibility of a specific substance being used as a substrate for producing methane gas. The test was conducted at a medium temperature condition (38°C) with an initial pH of 7.55 for all samples. The overall concept diagram of the BMP test and the equipment used are shown in Figure 3. This embodiment sets the BMP value of the mixture (Mix) of the three substrates and the mixture mixed at a ratio of the first filtrate: the second filtrate: the third filtrate = 2:2:1 as the target.

Table 2 Sample Inoculum (mL) Substrate (mL) Water+Media (mL) VS _in (g/L) tCOD _in （g/L） tVFA _in (g/L) TOC _in (g/L) Blank (control group) 100 0 300 1.07 1.48 0.05 0.21 First filter 100 50 250 1.53 2.70 0.11 0.58 Second filter 100 50 250 1.78 3.00 0.09 0.63 The third filter 100 50 250 1.63 2.55 0.12 0.58 Mix 50ml 100 50 250 1.60 2.60 0.09 0.57 Mix 100ml 100 100 200 2.26 3.88 0.19 0.93 Mix 150ml 100 150 150 2.57 5.00 0.22 1.34

Table 3 Sample Total CH ₄ (mL) VS _in (g/L) _VSfin (g/L) COD _in (g/L) tCOD _fin （g/L） TOC _in (g/L) TOC _fin （g/L） pH _in pH _fin Blank 130 1.07 0.82 1.48 1.15 0.21 0.19 7.55 7.55 First filter 247 1.53 1.11 2.70 1.55 0.58 0.19 7.55 7.64 Second filter 212 1.78 1.25 3.00 1.5 0.63 0.23 7.55 7.38 The third filter 223 1.63 1.10 2.55 1.5 0.58 0.21 7.55 7.42 Mix 50ml 254 1.60 1.25 2.60 1.25 0.57 0.21 7.55 7.51 Mix 100ml 313 2.26 1.39 3.88 2.15 0.93 0.32 7.55 7.31 Mix 150ml 374 2.57 1.79 5.00 2.35 1.34 0.49 7.55 7.49

Table 2 shows the setting values and initial water quality (WQ) parameter measurements of various samples tested by BMP according to this embodiment, and Table 3 shows the final water quality (WQ) parameter measurements after the BMP test.

Figure 4 is a graph comparing the methane gas production by sample and date according to the BMP test. Referring to Figure 4, it is not difficult to find that compared with the control group (blank), all substrates (samples, substrates) showed significant methane (CH ₄ ) productivity.

When the substrate was the second filtrate and the third filtrate, compared with the first filtrate substrate or the mixed substrate (first filtrate: second filtrate: third filtrate = 2:2:1), it showed lower methane productivity. In particular, when it was the second filtrate, it showed the phenomenon of inhibiting the anaerobic digestion (AD) process in the first 7 days of the test.

The mixed substrates showed higher BMP performance compared to the single substrates, but even though the first filtrate substrate was a single substrate, it also showed results quite similar to the mixed substrates.

Example 3. Evaluation of methane yield according to substrate (filtrate) type Table 4 Sample Total CH ₄ (mL) VS _red (g) CH ₄ (ml)/VS _red (g) tCOD _red （g） CH ₄ (ml)/tCOD _red (g) TOC _red (g) CH ₄ (ml)/TOC _red (g) Blank 130 0.1 - 0.13 - 0.01 - First filter 247 0.17 1455 0.46 537 0.15 1600 Second filter 212 0.21 996 0.60 353 0.16 1313 The third filter 223 0.21 1062 0.42 531 0.15 1483 Mix 50ml 254 0.14 1784 0.54 470 0.14 1766

Anaerobic digestion (AD) of the first filtrate substrate was similar to that of the mixed substrate, showing very stable results. The mixed substrate showed the highest methanogenesis based on reduced VS and TOC.

In contrast, the second filtrate substrate showed a relatively low methanogenesis compared to the other substrates, even though the organic matter content was greatly reduced. This means that most of the organic matter was not converted into methane (CH ₄ ) but into carbon dioxide (CO ₂ ).

Example 4. Evaluation of methane yield according to loading variation

FIG. 5 is a graph comparing methane gas production by sample and by date for evaluating methane production rate according to loading.

For samples with higher organic loadings, additional pretreatment steps or longer processing times may be required due to the instability of _CH4 production, depending on the longer degradation/adaptation required.

Table 5 Sample Total CH ₄ (mL) VS _in (g/L) VS _fin (g/L) tCOD _in （g/L） tCOD _fin （g/L） TOC _in (g/L) TOC _fin （g/L） pH _in pH _fin Blank 130 1.07 0.82 1.48 1.15 0.21 0.19 7.55 7.55 Mix 50ml 254 1.60 1.25 2.60 1.25 0.57 0.21 7.55 7.51 Mix 100ml 313 2.26 1.39 3.88 2.15 0.93 0.32 7.55 7.31 Mix 150ml 374 2.57 1.79 5.00 2.35 1.34 0.49 7.55 7.49

Table 6 Sample Total CH ₄ (mL) VS _red (g) CH ₄ (ml)/VS _red (g) tCOD _red （g） CH ₄ (ml)/tCOD _red (g) TOC _red (g) CH ₄ (ml)/TOC _red (g) Blank 130 0.10 - 0.13 - 0.01 - Mix 50ml 254 0.14 1784 0.54 470 0.14 1766 Mix 100ml 313 0.35 901 0.69 454 0.24 1300 Mix 150ml 374 0.31 1188 1.06 353 0.34 1096

Referring to Tables 5 and 6, substrates with higher organic loadings showed higher total _CH4 production overall, but in the case of 50 mL of mixed substrates, showed higher efficiency for methane production based on the removed organic matter. Therefore, it can be seen that higher organic loading rates provide an inhibitory effect on the activity of methanogens.

Example 5. Evaluation of methane yield according to waste/wastewater type

Table 7 Biomass CH ₄ yield (mL/g VS) Wheat straw 200 Maize straw 219 Corn stover 225 Barley straw 91 Oat straw 246 Tomato residue 50 Paddy straw 73~202

Table 8 BMP Sample Total CH ₄ (mL) VS _in (g) CH ₄ yield (mL/g VS) Blank 130 1.07 - First filter 247 1.53 404 Second filter 212 1.78 298 The third filter 223 1.63 342 Mix 50ml 254 1.60 397 Mix 100ml 313 2.26 346 Mix 150ml 374 2.57 364

Referring to Tables 7 and 8, compared with organic waste (biomass) usually treated by anaerobic digestion process, the biomethane yield in the case of PHA production wastewater was significantly higher (~2-4 times) based on the original VS.

In addition, this result indicates suitability for anaerobic degradation and no specific toxicity or inhibitory response to methanogenic archaea.

In summary, it has been confirmed that the organic matter (carbon source) contained in the wastewater generated in the PHA production process (specifically the purification process) has a high potential for methanogenesis. Even compared with other organic biomass, the methane yield of PHA process wastewater is relatively high.

Therefore, it can be concluded that the anaerobic digestion treatment process that can effectively remove organic matter from the target wastewater and obtain by-products such as biogas is suitable as a PHA wastewater treatment process.

Example 6. Laboratory-scale anaerobic digestion reactor

FIG6 is a lab-scale anaerobic digestion reactor design concept diagram according to the present embodiment. It is a two-stage anaerobic digestion tank (two-stage AD process) consisting of an acidogenic reactor (ACR) and a methane generating reactor or a methanogenic reactor (MTR), which operates under mesophilic conditions and prepares and supplies 1L of mixed substrate every day. The total hydraulic retention time (HRT) is 28 days, consisting of 3 days for ACR and 25 days for MTR.

Before the PHA production wastewater was supplied to the anaerobic digestion reactor, dry food waste (FW) was supplied. Then, until the 39th day, a mixed substrate of the first filtrate: the second filtrate = 1:4 was supplied to the reactor, and then until the 62nd day, the mixed ratio was changed to the first: the second = 4:1 and supplied to the reactor, and from the 63rd day, a mixed substrate of the first filtrate: the second filtrate: the third filtrate = 2:2:1 ratio was supplied. The above-mentioned changes in the supply substrate and the resulting results are shown in Figure 7.

Since dry FW was supplied before PHA production wastewater was supplied, there were great changes in biogas and methanogenesis from the 1st day to the 40th day due to substrate changes, degradation of food waste residue particles, and adaptation of methanogens. There was a stabilization period from the 40th day to the 80th day, and the pH in the acidogenic reactor was stabilized at ~5.3±0.2. The result curves divided by adaptation, change period, stabilization period, and stable period as described above are shown in Figure 8.

After 80 days (nearly 3 HRT), the reactor showed stable biogas and methane production. The average biogas production after 80 days was about 4.85 L/day. The _CH4 concentration of the biogas remained stable, with _CH4 being about 70% of the total biogas volume and _CO2 being about 29% of the total biogas volume. The average _CH4 production was about 3.4 L/day. The result curve diagram, which is divided into the intervals before and after 80 days as described above and is shown in Figure 9.

The average VS of the mixed substrate was maintained at about 3.3 g/L and tCOD was maintained at about 8.8 g/L. Due to the presence of biomass and the inherently low VS concentration of the substrate, the VS reduction was maintained at a very low level. The VSS of the MTR, which represents the biomass concentration, ranged from about 2 g/L to about 2.5 g/L, which is equivalent to about 75% of the digested wastewater VS. It was confirmed that most of the organic matter present in the PHA production process wastewater in a dissolved state produces biogas, so the measured VS reduction efficiency is low and the dissolved organic matter (sCOD) is removed by more than 80%. A graph illustrating the above results is shown in Figure 10.

However, the tCOD measurement results showed a reduction rate of 70% (tCOD of anaerobic digested wastewater < 3g/L). The soluble COD (sCOD) of the digested wastewater was maintained at about 1g/L, and the measured sCOD reduction level was about 80%. The organic reduction level calculated based on TOC and DOC values has steadily shown a level of about 80%. The result curve of the tCOD and sCOD reduction levels as described above is shown in Figure 11.

In addition, referring to Table 9 below, in terms of methane production efficiency, the methane production is about 0.84L/g tCODrem, 0.72L/g sCODrem, 1.62L/g TOCrem and 1.6L/g DOCrem. It is reported that the level of anaerobic digestion of food target wastewater (food dry powder) is about 0.18L/g tCODrem, so a higher methane conversion rate is expected in the high-soluble organic matter of the target process wastewater. Figure 12 shows the methane production potential (left) of the comparison object, i.e., food or food target wastewater (food wastewater), and the methane production and organic matter removal rate (right) levels of the treatment facilities.

Table 9 CH ₄ (L/day) VS _sub (g) tCOD _sub （g） CH ₄ yield (L/g VS) _CH4 (L/L MTR) CH ₄ (L/g tCOD _rem ) Dried FW 14.2 31.2 52.7 0.46 0.57 0.18 PHA wastewater 3.4 3.3 8.3 1.03 0.14 0.84

Compared to the BMP test mentioned above, in the laboratory-scale reactor, the methane production showed a level of about 0.84L/g tCODrem and about 1.62L/g TOCrem. The methane potential based on TOC reduction was similar to that in the laboratory-scale reactor and BMP test, while the methane production based on tCOD removal was about 40% higher than that in the BMP test. It is speculated that this may be related to substrate instability, undefined organic compounds, mixing of the set-up and continuous system, and differences in operation.

Table 10 BMP Sample L CH ₄ /g VS _rem L CH ₄ /g tCOD _rem L CH ₄ /g TOC _rem First filter 1.46 0.54 1.60 Second filter 1.00 0.35 1.31 The third filter 1.06 0.53 1.48 Mix 50ml 1.78 0.47 1.77 Mix 100ml 0.90 0.45 1.30 Mix 150ml 1.19 0.35 1.10

Example 7. VFA accumulation according to target wastewater retention time

*92 Referring to Figure 13, PHA wastewater was placed in a 20L plastic container and stored in a refrigerator at 4°C. This substrate consumption takes about 2 months, and it can be observed that the tVFA concentration and composition change over time.

In addition, in terms of BMP testing, the efficiency evaluation of acidic/methane production processes under medium/high temperature conditions, the evaluation of target wastewater pretreatment conditions and methane yield under high temperature conditions, and the biodegradability evaluation of anaerobic digestion supernatant will become important factors. It is predicted that in terms of laboratory-scale reactor experiments, the export of parameters for large-scale and processes, and the evaluation of the degradation possibility of bioplastics (PHA) under anaerobic digestion conditions will become important factors.

In addition, high incubation methods for anaerobic digestion by-products (sludge, biogas), evaluation of the impact of effluents or by-products on environmental exposure may also become major considerations.

The embodiments of the present invention are described above with reference to the drawings, but it should be understood that those skilled in the art can implement these embodiments in other specific ways without changing the technical concept or essential features of the present invention. Therefore, it should be understood that the embodiments described above are only exemplary in all aspects and are not restrictive.

without

FIG. 1 is a flow chart of the entire process according to a preferred embodiment of the present invention.

FIG2 is a flow chart showing the specific unit processes of the PHA purification process and the wastewater (filtrate) generated.

Figure 3 shows a conceptual diagram of the BMP test (left) and a photograph of the fully automated BMP test system (AMPTSⅡ) (right).

FIG4 is a graph comparing methane gas production by sample and by date based on the BMP test.

FIG. 5 is a graph comparing the methane gas production by sample and by date, used to evaluate the methane production rate according to the loading.

FIG6 is a conceptual diagram of a lab-scale anaerobic digestion reactor design according to a preferred embodiment of the present invention.

FIG. 7 is a graph showing the substrate changes and performance of a lab-scale anaerobic digestion reactor according to a preferred embodiment of the present invention at different stages.

FIG8 is a graph showing the state changes of a lab-scale anaerobic digestion reactor at different periods of time in accordance with a preferred embodiment of the present invention in intervals.

FIG. 9 is a graph showing the state changes of a lab-scale anaerobic digestion reactor before and after 80 days according to a preferred embodiment of the present invention.

FIG. 10 is a graph showing the organic matter removal performance of a lab-scale anaerobic digestion reactor according to a preferred embodiment of the present invention.

FIG. 11 is a graph showing the tCOD and sCOD reduction results for a lab-scale anaerobic digestion reactor according to a preferred embodiment of the present invention.

FIG. 12 is a graph showing the potential for methane generation from food or food target wastewater (food wastewater) (left) and the level of methane generation and organic matter removal efficiency (right) in a treatment facility.

FIG. 13 is a graph showing the VFA accumulation efficiency of PHA wastewater during the refrigerated storage period.

without

Claims (14)

A method for producing a by-product, wherein the by-product is a resource-recyclable by-product produced from wastewater produced in a process of purifying polyhydroxyalkanoate (PHA), and the method for producing the by-product comprises the following processes: a process of purifying PHA produced by microbial fermentation; separating and recovering wastewater having a methane yield ( _CH4 yield) higher than at least one preset benchmark value (mL/g VS) in the purification process based on a biochemical methane potential (BMP) test conducted at a pH of 7.5 to 7.8 and a temperature of 37 to 39°C; and a process of using the separated and recovered wastewater for anaerobic digestion to produce gas-phase, liquid-phase, and solid-phase by-products. The method for producing a byproduct according to claim 1, wherein the PHA comprises a monomer or copolymer derived from one or more repeating units selected from the following group, the group consisting of 3-hydroxybutyric acid (3-HB), 3-hydroxypropionic acid (3-HP), 3-hydroxyvaleric acid (3-HV), 3-hydroxyhexanoic acid (3-HH), 4-hydroxybutyric acid (4-HB), 4-hydroxyvaleric acid (4-HV), 4-hydroxyhexanoic acid (4-HH), 5-hydroxyvaleric acid (5-HV) and 6-hydroxyhexanoic acid (6-HH). The method for producing a by-product according to claim 1, wherein the reference value is 250 mL/g VS. The method for producing a by-product according to claim 1, wherein the reference value is 350 mL/g VS. According to the method for producing a by-product as described in claim 1, in the process of producing the by-product, organic waste is used together with the wastewater. The method for producing by-products according to claim 5, wherein the organic waste includes any one of PHA, products produced using PHA as raw materials, food waste, sewage sludge and livestock feces, or a mixture of two or more thereof. According to the method for producing by-products described in claim 1, after the process of separating and recycling wastewater, it further includes: a process of pre-treating the separated and recycled wastewater in the form of wastewater sludge. The method for producing by-products according to claim 1, wherein the process for separating and recovering wastewater is the following process: separating and recovering wastewater with a methane yield ( _CH4 yield) higher than 250 mL/g VS; and separating wastewater with a methane yield ( _CH4 yield) lower than 250 mL/g VS so as to re-introduce it into the process for purifying PHA. The method for producing by-products according to claim 8, wherein the re-input process is the following process: separating wastewater with a methane yield (CH ₄ yield) lower than 250 mL/g VS; and purifying it through a water treatment process so as to be input into the process of purifying PHA. The method for producing by-products according to claim 1, wherein the process for separating and recovering wastewater is the following process: separating and recovering wastewater with a methane yield ( _CH4 yield) higher than 250 mL/g VS; and the process for concentrating low-concentration wastewater is to, after separating wastewater with a methane yield ( _CH4 yield) lower than 250 mL/g VS, concentrate the wastewater to a _methane yield of 250 mL/g VS or higher, thereby recovering the wastewater together with the wastewater with a methane yield ( _CH4 yield) higher than 250 mL/g VS. The method for producing by-products according to claim 1, wherein the process for separating and recovering wastewater is the following process: separating and recovering wastewater with a methane yield ( _CH4 yield) higher than 250 mL/g VS; partially separating wastewater with a methane yield ( _CH4 yield) lower than 250 mL/g VS so as to re-introduce it into the process for purifying PHA; and a process for concentrating low-concentration wastewater, which is to concentrate the wastewater with a methane yield ( _CH4 yield) lower than 250 mL/g VS to achieve a methane yield (CH4 yield) of 250 mL/g VS or higher after partially separating the wastewater with a methane yield ( _CH4 yield) lower than 250 mL/g VS, so as to recover it together with the wastewater with a methane yield ( _CH4 yield) higher than 250 mL/g VS. According to the method for producing by-products as described in claim 1, the process for purifying PHA is the following process: a cell separation process, which removes impurities in the fermentation liquid through a solid-liquid separation process and recovers cells containing the PHA; a PHA extraction process, which dissolves components other than the PHA in the recovered cells by physical and chemical methods to recover Crude PHA; an impurity separation and cleaning process, which separates the impurities dissolved by the solid-liquid separation process from the Crude PHA and cleans the Crude PHA; an additional purification process, which removes impurities contained in the Crude PHA; and a product recovery process, which recovers additional purified PHA through a solid-liquid separation process. According to the method for producing by-products as described in claim 12, the process of separating and recycling wastewater includes the following process: separating and recycling any one or a mixed filter liquid of two or more of the first filter liquid discharged in the cell separation process in the process of purifying PHA, the second filter liquid discharged in the process of separating and washing impurities, and the third filter liquid discharged in the product recovery process. According to the method for producing by-products as described in claim 13, the process of separating and recycling wastewater includes the following process: separating and recycling the mixed filter liquid of the first filter liquid, the second filter liquid and the third filter liquid, Based on the volume, the mixing ratio of the first filter liquid, the second filter liquid and the third filter liquid is 1.5~2.5:1.5~2.5:0.5~1.5.