A composite carbon source prepared from organic solid waste, a preparation method thereof and application thereof in denitrification

Abstract

This invention belongs to the field of wastewater treatment technology, specifically relating to a composite carbon source prepared from organic solid waste, its preparation method, and its application in denitrification. The invention uses a mixture of rice wine lees and rice flour water as raw materials, which is then mixed with inoculated sludge and subjected to anaerobic fermentation by microorganisms to obtain a fermentation broth. The supernatant is then separated to obtain the composite carbon source. The resulting composite carbon source increases the proportion of VFAs (volatile fatty acids) and the proportion of acetic acid within the VFAs, and contains easily biodegradable organic components such as lipids, proteins, and polysaccharides. Using this composite carbon source as a denitrification composite carbon source results in a higher denitrification rate than commonly used commercial carbon sources such as acetic acid, glucose, and methanol, while the residual COD after denitrification is lower than that of commonly used commercial carbon sources. It exhibits a high denitrification rate and good biodegradability. This invention uses a mixture of food processing industry solid waste and wastewater to prepare a supplementary carbon source for wastewater treatment plants. When providing the same COD concentration of supplementary carbon source, the cost of wastewater treatment using this composite carbon source is lower.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically, it relates to a composite carbon source prepared from organic solid waste, its preparation method, and its application in denitrification. Background Technology

[0002] Low carbon-to-nitrogen ratios are a common problem in urban and industrial wastewater treatment plants in my country, often requiring long-term supplemental carbon sources for denitrification to meet the total nitrogen emission requirements of biological denitrification processes. Commonly used commercial carbon sources include acetic acid (sodium acetate), methanol, and glucose, which are relatively expensive, significantly increasing wastewater treatment costs. Therefore, using suitable organic solid waste to produce acidic fermentation for denitrification carbon sources is a wastewater-solid waste co-treatment method that improves the resource utilization of solid waste while simultaneously enhancing wastewater denitrification efficiency. It can also reduce the cost of supplemental carbon sources at wastewater treatment plants, making it a research hotspot and development trend in recent years.

[0003] Currently, there are many studies on acid-producing fermentation of solid waste such as sewage sludge, kitchen waste, and crop straw from sewage treatment plants. However, how to increase the proportion of volatile fatty acids (VFA) in the fermentation broth, especially the proportion of acetic acid in VFA, while also including other nutrients that are beneficial to denitrifying microorganisms, so that the fermentation broth can have a good denitrification effect when used as a supplementary carbon source, and can replace commonly used commercial carbon sources, and reduce sewage treatment costs, is a current research challenge in the preparation of composite carbon sources. Summary of the Invention

[0004] In view of the above-mentioned problems existing in the prior art, the purpose of this invention is to provide a composite carbon source prepared from organic solid waste. Another purpose of this invention is to provide a method for preparing the composite carbon source. A further purpose of this invention is to provide the application of the composite carbon source in denitrification.

[0005] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a composite carbon source using organic solid waste includes the following steps:

[0007] S1: Mix the rice wine lees with rice flour water to obtain the fermentation substrate;

[0008] S2: The inoculated sludge is mixed with the fermentation substrate to obtain a mixture. The mixture is then subjected to anaerobic fermentation by microorganisms to obtain a fermentation broth. The supernatant is then separated to obtain the composite carbon source.

[0009] Furthermore, based on sCOD, the mixing ratio of the rice wine lees to the rice flour water is (9-11):1.

[0010] Furthermore, the COD equivalent of lipids in the fermentation substrate is 25% to 30%, and the COD equivalent of proteins and polysaccharides is 3% to 10%.

[0011] Furthermore, the concentration of the inoculated sludge is 20-25 g / L; by volume, the inoculated sludge accounts for 15%-25% of the mixture.

[0012] Furthermore, the mixture has a total TS of 9-11 g / L and a total sCOD of 6-9 g / L, and the sum of the COD equivalents of proteins, polysaccharides, and volatile fatty acids in the mixture accounts for 25%-40% of the total sCOD.

[0013] Furthermore, in S2, the fermentation conditions are as follows: the pH of the mixture is adjusted to 5.5~6.5, the oxidation-reduction potential is controlled at -100~-300mv at a temperature of 35℃±1℃, and the mixture is mechanically stirred at a speed of 150~300 rpm for 8-12 days, with the preferred fermentation time being 10 days.

[0014] The composite carbon source prepared by the aforementioned method.

[0015] Furthermore, in terms of COD, the volatile fatty acid COD equivalent of the organic components of the composite carbon source accounts for 30% to 50%, and the sum of the COD equivalents of lipids, proteins and polysaccharides accounts for 25% to 40%; the acetic acid mass concentration of the volatile fatty acid accounts for 40% to 60%.

[0016] The aforementioned composite carbon source is used in denitrification.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] This invention prepares a composite carbon source using a mixture of rice wine lees and rice flour water as raw materials. The resulting composite carbon source increases the proportion of volatile fatty acids (VFAs) and the proportion of acetic acid within the VFAs. The organic components (calculated as COD, mg / L) in the resulting composite carbon source have a volatile fatty acid content of 30%–50%, with acetic acid accounting for 40%–60% of the volatile fatty acids, and also contain easily biodegradable organic components such as lipids, proteins, and polysaccharides. Using this composite carbon source as a denitrification composite carbon source offers advantages such as high denitrification rate and good biodegradability. The denitrification rate is higher than that of commonly used commercial carbon sources such as acetic acid, glucose, and methanol, while the residual COD after denitrification is lower than that of commonly used commercial carbon sources. This invention also prepares a supplementary carbon source for wastewater treatment plants by mixing solid waste and wastewater from the food processing industry. When providing the same COD concentration of supplementary carbon source, the cost of wastewater treatment using this composite carbon source is lower than the cost of adding acetic acid, glucose, or methanol. Attached Figure Description

[0019] Figure 1This is a schematic diagram showing the statistical results of the proportion of volatile fatty acids (VFA) in the composite carbon source obtained at different fermentation times in the examples;

[0020] Figure 2 This is a schematic diagram showing the changes in COD composition of the composite carbon source obtained at different fermentation times in the example.

[0021] Figure 3 This is a schematic diagram showing the proportion of each component in the VFA of the composite carbon source obtained at different fermentation times in the examples.

[0022] Figure 4 This is a schematic diagram showing the changes in COD composition of the composite carbon source obtained at different fermentation times in Comparative Example 1.

[0023] Figure 5 This is a schematic diagram showing the proportion of each component in the VFA of the composite carbon source obtained at different fermentation times in Comparative Example 1.

[0024] Figure 6 This is a schematic diagram showing the changes in COD composition of the composite carbon source obtained at different fermentation times in Comparative Example 2.

[0025] Figure 7 This is a schematic diagram showing the proportion of each component in the VFA of the composite carbon source obtained at different fermentation times in Comparative Example 2.

[0026] Figure 8 A schematic diagram illustrating the denitrification effect of different carbon sources;

[0027] Figure 9 This is a schematic diagram showing the residual COD after 6 hours of denitrification treatment using different carbon sources. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments.

[0029] The sources or properties of each raw material are as follows:

[0030] Inoculation sludge: Secondary sedimentation tank sludge from urban wastewater treatment plants, TS=20~30 g / L;

[0031] Yellow wine lees: Waste lees from yellow wine brewing plants, TS=9~10 g / L, sCOD=120~150g / L;

[0032] Rice noodle water: Wastewater storage tank of the wastewater treatment plant of rice noodle manufacturing plant, TS=3~4 g / L, sCOD=20~25g / L;

[0033] Example

[0034] Sludge from the secondary sedimentation tank of a municipal wastewater treatment plant was used as inoculum sludge, with a concentration of 26.5 g / L. 20% of the effective volume of inoculum sludge was added to a constant-temperature anaerobic digester. A mixture of rice wine lees and rice flour water at a sCOD ratio of 10.4:1 was used as the acid-producing fermentation substrate. The lipid COD equivalent of the fermentation substrate was 28%, and the combined COD equivalent of proteins and polysaccharides was 10%. 80% of the effective volume of the fermentation substrate was added to the constant-temperature anaerobic digester and mixed thoroughly, maintaining the initial total saturation (TS) at 25.6 g / L and the sCOD at 64.4 g / L. The sum of the COD equivalents of proteins, polysaccharides, and vitamin A (VFA) accounted for 37% of the total total oxidative calcium (TCOD). The pH was adjusted to 5.5 using hydrochloric acid and sodium hydroxide, and the temperature was maintained at 35℃±1℃. The oxidation-reduction potential (ORP) was -200±50mv. The mechanical stirring speed reached 200 rpm. After fermentation for a period of time, the resulting fermentation broth was centrifuged, and the centrifuged liquid was taken as the composite carbon source.

[0035] The statistical results of the proportion of volatile fatty acids (VFA) in the complex carbon sources obtained at different fermentation times are shown in the figure. Figure 1 The compositional changes of the composite carbon source are shown in [reference needed]. Figure 2 Total volatile acids are denoted as TVFA. The percentage of acetic acid in TVFA is shown in the results below. Figure 3 The higher the TVFA (Total Volatile Acid) ratio, the better. Acid production reaches its peak after 10 days of fermentation, with TVFA reaching 41%. Acetic acid production is also highest after 10 days, reaching 44%. After 10 days, the total COD will decrease. Although the TVFA ratio increases at this point, the actual TVFA concentration has decreased somewhat. Therefore, the optimal fermentation time is 10 days.

[0036] Comparative Example 1

[0037] Sludge from the secondary sedimentation tank of a municipal wastewater treatment plant was used as inoculum sludge, with a concentration of 26.5 g / L. 20% of the effective volume of the inoculum sludge was added to a constant-temperature anaerobic fermenter. Rice wine lees and water were mixed at a sCOD ratio of 6.2:1 as the acid-producing fermentation substrate, with lipids, proteins, and polysaccharides accounting for 30% of the total COD equivalent. 80% of the effective volume of the fermentation substrate was added to the constant-temperature anaerobic fermenter and mixed thoroughly. The pH was adjusted to 5.5 using hydrochloric acid and sodium hydroxide. Under conditions of 35℃±1℃, an oxidation-reduction potential (ORP) of -200±50 mV, and a mechanical stirring speed of 200 rpm, fermentation was continued for a period of time. The resulting fermentation broth was centrifuged, and the centrifuged liquid was used as the composite carbon source.

[0038] The optimal fermentation time (i.e., the time when VFA reaches its peak) is 12 days. For example... Figure 4 and Figure 5 As shown, the total volatile fatty acids (TVFA) in the composite carbon source obtained at the optimal fermentation time accounted for 40%, and acetic acid accounted for 39% of the total volatile acids (TVFA).

[0039] Comparative Example 2

[0040] Sludge from the secondary sedimentation tank of a municipal wastewater treatment plant was used as inoculum sludge, with a concentration of 26.5 g / L. 20% of the effective volume of the inoculum sludge was added to a constant-temperature anaerobic fermenter. A mixture of rice wine lees and rice flour water at a sCOD ratio of 10.4:1 was used as the acid-producing fermentation substrate, with lipids, proteins, and polysaccharides accounting for 38% of the total COD equivalent. 80% of the effective volume of the fermentation substrate was added to the constant-temperature anaerobic fermenter and mixed thoroughly. The pH was adjusted to 7.5 using hydrochloric acid and sodium hydroxide. Under conditions of 35℃±1℃, an oxidation-reduction potential (ORP) of -200±50 mV, and a mechanical stirring speed of 200 rpm, fermentation was continued for a period of time. The resulting fermentation broth was centrifuged, and the centrifuged liquid was used as the composite carbon source.

[0041] like Figure 6 and Figure 7 As shown, the optimal fermentation time is 10 days. The optimal fermentation time is when the volatile fatty acid (VFA) content in the obtained complex carbon source is 29%, and the acetic acid content in the total volatile acid VFA is 41%.

[0042] Denitrification effect verification experiment:

[0043] In the example, the fermentation broth obtained after 10 days of fermentation was centrifuged, and the composite carbon source, analytical grade acetic acid, analytical grade glucose, and analytical grade methanol of the centrifuged broth were used for denitrification experiments for comparison.

[0044] Sludge from the secondary sedimentation tank of a municipal wastewater treatment plant was washed with deionized water. After adding deionized water and centrifuging, the supernatant was discarded. Deionized water was added again, the mixture was stirred thoroughly, and centrifuged again to remove the supernatant. This washing process was repeated three times. The washed sludge was used as sludge for the denitrification experiment. The denitrified sludge was added to an Erlenmeyer flask, and the sludge concentration (MLSS) was controlled at approximately 3000 mg / L. An appropriate amount of potassium nitrate was added to maintain the initial NO3 concentration. - -N was 20 mg / L. Appropriate amounts of composite carbon source, analytical grade acetic acid, analytical grade glucose, and analytical grade methanol were added respectively, and the mixture was diluted with ultrapure water to a final volume of 250 mL, keeping the initial COD of each experimental group at 50 mg / L.

[0045] The denitrification effect of different supplementary carbon sources was investigated using a 25℃ constant-temperature shaker experiment. Figure 8 It can be seen that the denitrification rates of the composite carbon source, acetic acid, glucose, and methanol after 6 hours were 3.31, 3.23, 3.11, and 2.98 mg / L·h, respectively, with the composite carbon source exhibiting the highest denitrification rate. The nitrate removal rates after 6 hours were 99.1%, 96.7%, 93.3%, and 89.4%, respectively, with the composite carbon source showing the highest nitrate removal rate. The residual CODs of the composite carbon source, acetic acid, glucose, and methanol after 6 hours of denitrification were 8, 9, 9, and 10 mg / L, respectively. Figure 9 The microbial availability of composite carbon sources is similar to that of analytically pure carbon sources and slightly better than that of other carbon sources.

[0046] Cost calculation for denitrification with different carbon sources:

[0047] The fermentation broth prepared in this invention needs to be centrifuged to remove solid components before being used as a composite carbon source for denitrification. Therefore, the yield of the composite carbon source is calculated as 90% of the fermentation broth volume. The main costs in the preparation of the composite carbon source are electricity consumption and reagent consumption, with the reagent consumption mainly consisting of NaOH and hydrochloric acid for pH adjustment. The preparation of the carbon source requires stirring for 8-10 days, with a stirring power of 10 W / m³. 3 Electricity costs are calculated at 1 yuan / kw·h. The preparation costs of each liquid carbon source are shown in Table 1.

[0048] Table 1. Increased cost per ton of water for denitrification processes using different carbon sources.

[0049]

[0050] As shown in Table 1, the cost of adding the composite carbon source of the present invention is only RMB 0.045 / t, which is lower than the cost of adding other commercial carbon sources (RMB 0.093~0.210 / t, which is only 21.4%~48.4% of the cost of adding other commercial carbon sources). Moreover, the denitrification rate is higher than that of commercial carbon sources, making it a high-quality carbon source with both excellent technical and economic indicators.

Claims

1. A method for preparing a composite carbon source using organic solid waste, characterized in that, Includes the following steps: S1: Mix the rice wine lees with rice flour water to obtain the fermentation substrate; S2: The inoculated sludge is mixed with the fermentation substrate to obtain a mixture. The mixture is then subjected to anaerobic fermentation by microorganisms to obtain a fermentation broth. The supernatant is then separated to obtain the composite carbon source. Based on sCOD (soluble COD), the mixing ratio of the rice wine lees to the rice flour water is (9-11):1; The fermentation substrate contains 25%–30% COD equivalent of lipids and 3%–10% COD equivalent of proteins and polysaccharides. The concentration of the inoculated sludge is 20-25 g / L; by volume, the inoculated sludge accounts for 15%-25% of the mixture; In S2, the fermentation conditions are as follows: adjust the pH of the mixture to 5.5~6.5, maintain the redox potential at 35℃±1℃, control the redox potential at -100~-300mv, and mechanically stir at 150~300 rpm for 8-12 days.

2. The method for preparing a composite carbon source from organic solid waste according to claim 1, characterized in that, The mixture has a total TS of 9-11 g / L and a total sCOD of 6-9 g / L. The sum of the COD equivalents of proteins, polysaccharides, and volatile fatty acids in the mixture accounts for 25%-40% of the total sCOD.

3. The method for preparing a composite carbon source from organic solid waste according to claim 1, characterized in that, The fermentation time is 10 days.

4. The composite carbon source prepared by the method according to any one of claims 1-3.

5. A composite carbon source according to claim 4, characterized in that, In terms of COD, the volatile fatty acid COD equivalent of the organic components of the composite carbon source accounts for 30% to 50%, and the sum of the COD equivalents of lipids, proteins and polysaccharides accounts for 25% to 40%; the mass concentration of acetic acid in the volatile fatty acids accounts for 40% to 60%.

6. The application of the composite carbon source as described in claim 4 in denitrification.

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