Method for comprehensively evaluating and screening carbon sources for sewage treatment

Abstract

The invention relates to the technical field of sewage treatment, in particular to a method for comprehensively evaluating and screening a carbon source for sewage treatment. In the method disclosed by the invention, the carbon source evaluation indexes are subjected to priority grading according to the importance degree of the indexes and the difficulty degree in actual detection in the process, so that the screening efficiency can be effectively improved while the main evaluation indexes of the carbon source are monitored; in the method, qualified carbon sources are subjected to secondary grading, the secondary grading is based on primary grading, an absolute value of a difference value between an index measured value and an index standard value is defined as a deviation factor, and the deviation factors in each priority are added and multiplied by the weight of each priority, so that the secondary grading can be realized. Denitrification efficiency, an economic index and a safety index are taken as main screening indexes in secondary grading, so that an economical and reasonable high-quality carbon source with good performance can be rapidly and efficiently screened out, and convenience is brought to carbon source screening work.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment, and in particular to a method for comprehensive evaluation and screening of carbon sources for sewage treatment. Background Art

[0002] Sewage refers to various polluted water such as urban domestic sewage, industrial wastewater from industries and industrial parks (agglomeration areas). In order to recycle water resources and protect the environment, sewage needs to be treated. By treating sewage, pollutants in the water body are removed and discharged after meeting certain standards, which is of great significance to the recycling of water resources and environmental protection.

[0003] At present, most municipal sewage treatment plants have insufficient carbon sources and need to add additional carbon sources for denitrification and denitrification. Carbon sources are classified into single carbon sources, composite carbon sources and waste source carbon sources according to their effective ingredients, and solid carbon sources and liquid carbon sources according to their forms. Carbon sources can provide carbon-containing compounds that provide nutrients for the growth and metabolism of microorganisms in the biochemical treatment system of sewage (waste) water. By adding carbon sources, the production and metabolism needs of microorganisms can be guaranteed, thereby ensuring the effect of sewage treatment.

[0004] The current carbon source market is overly one-sided in its pursuit of COD equivalent, resulting in uneven quality of reagents. Moreover, sewage treatment plants only focus on the nitrogen and phosphorus removal effects and prices when selecting carbon source reagents, and do not fully consider the N and P content, chromaticity, pH, and safety indicators in the carbon source reagents. Irrational use of reagents may lead to environmental unfriendliness or even the collapse of the sewage treatment system, so it is necessary to conduct a comprehensive evaluation and screening of the carbon sources used. However, since the existing carbon sources are mainly composite carbon sources, there are many types and many indicators that need to be monitored. In actual carbon source screening, experimenters often need to spend a lot of time and energy to screen out suitable high-quality carbon sources. The process is labor-intensive and the screening efficiency is low. Therefore, how to evaluate and screen carbon sources more efficiently and comprehensively is a problem that needs to be solved now. Summary of the invention

[0005] The purpose of the present invention is to provide a method for comprehensive evaluation and screening of carbon sources for sewage treatment, so as to solve the problems of insufficient screening indicators, high labor intensity of screening work and low screening efficiency when screening carbon sources.

[0006] To achieve the above object, the present invention adopts the following technical scheme: a method for comprehensive evaluation and screening of carbon sources for sewage treatment, comprising the following steps:

[0007] S1. Classifying the performance evaluation indicators of carbon sources to obtain performance evaluation indicators of different priorities;

[0008] S2. According to the priority set in S1, the performance evaluation index of the carbon source sample to be tested is measured according to the priority, and according to the set standard value of the performance evaluation index, the carbon source whose measured value of the performance evaluation index does not meet the standard is eliminated, and the carbon source whose measured value of the performance evaluation index meets the standard is retained;

[0009] S3, define the difference between the actual value of the performance evaluation index and the standard value of the performance evaluation index as the "deviation factor", add the deviation factors within each priority level and multiply them by the weight of each priority level, and perform secondary classification on the carbon sources that meet the actual value of the performance evaluation index of S2;

[0010] S4. Based on the results of the secondary classification in S3, the carbon sources with better quality are measured, the effluent indicators are tested, and the high-quality carbon sources that meet the actual production requirements are screened out.

[0011] Furthermore, in S1, the carbon source performance evaluation index is divided into levels one to five; the first level performance evaluation index includes COD Cr , TN and TP; the second-level performance evaluation index is the denitrification efficiency index; the third-level performance evaluation index is the economic index; the fourth-level performance evaluation index includes BOD5 / COD Cr , pH value, chromaticity, density, mass fraction of water-insoluble matter, chloride content, sulfate content and freezing point; the five-level performance evaluation indicators are safety indicators.

[0012] Furthermore, the safety indicators include flash point, metal corrosion rate, heavy metal content and biological toxicity; flash point ≥70.0℃; metal corrosion rate ≤6.25mm / a; mercury ≤0.00002%; cadmium ≤0.0002%, chromium ≤0.0005%; arsenic ≤0.0005%; lead ≤0.0005%; using rats as experimental subjects, biological toxicity LD 50 >2g / kg; For safety indicators, if the carbon source manufacturer holds a test report from a third-party authoritative organization, the safety indicator will be the first test indicator in the actual carbon source screening, and other indicators will be ranked in order. If the carbon source manufacturer does not hold a test report from a third-party authoritative organization, the safety indicator will be the fifth priority test indicator.

[0013] Furthermore, in S2, for the primary performance evaluation index, the COD of the composite carbon source Cr ≥2.5×10 5 mg / L; mass fraction of TN ≤0.03%; mass fraction of TP ≤0.006%.

[0014] Furthermore, in S2, for the secondary performance evaluation index, the denitrification efficiency index includes the denitrification rate and the effective utilization rate of the carbon source. The denitrification rate is the amount of NO3 removed per unit mass of MLVSS per unit time. --N mass, denitrification rate ≥ 1.5mgNO3 - -N / (gMLVSS·h); The effective utilization rate of carbon source is the ratio of carbon source consumption in the denitrification stage to the total added carbon source, and the effective utilization rate of carbon source is ≥60%.

[0015] Furthermore, in S2, for the three-level performance evaluation index, the economic index is the cost of removing 1 kg of nitrogen, and the value of the cost is ≤35 yuan / kg N.

[0016] Furthermore, in the above S2, for the four-level performance evaluation index, BOD5 / COD Cr The ratio is ≥0.55; the pH value is 3-9, and the pH value after the addition reaction is 6-9; the color after the addition reaction is ≤30; the density at 20℃ is 0.9-1.26g / cm 3 ; The mass fraction of water-insoluble matter is ≤0.2%; the chloride content is ≤0.4%; the sulfate content is ≤0.1%; the freezing point is negotiated between the supply and demand parties based on the actual application area to ensure that there is no ice in winter.

[0017] Furthermore, in the above S3, the weights of levels 1 to 5 are 5%, 40%, 35%, 5% and 15% respectively; when calculating the deviation factor, the value is the percentage or the value in front of the unit symbol, COD Cr The value is the numerical part of scientific notation, and the deviation factors of pH value, density and freezing point are recorded as 0; when COD Cr When it is greater than the minimum critical value, the actual COD Cr Converted to COD Cr The mass fractions of TN, TP, chloride, sulfate, mercury, cadmium, chromium, arsenic and lead were calculated from the ratio of the minimum critical values.

[0018] Furthermore, in the S3, the evaluation results of the secondary classification are expressed as excellent, good, medium and poor; when the evaluation result ≥17, the evaluation result is excellent; when 14≤evaluation result<17, the evaluation result is good; when 10≤evaluation result<14, the evaluation result is medium; when the evaluation result<10, the evaluation result is poor.

[0019] Furthermore, in the S4, carbon sources with excellent and good evaluation results are selected, and carbon sources with medium and poor evaluation results are discarded; the excellent and good carbon sources are measured, and during the measurement, when the effluent is stably up to the standard, the carbon source is a high-quality carbon source that meets the actual process.

[0020] Beneficial effects of the present invention:

[0021] 1. Comprehensive COD of the method of the present invention Cr , TN, TP, denitrification efficiency index, economic index, BOD5 / CODCr , pH value, chromaticity, density, mass fraction of water-insoluble matter, chloride content, sulfate content, freezing point and safety index, to conduct a comprehensive and comprehensive evaluation of the carbon source performance, which is more scientific and reasonable;

[0022] 2. Prioritize each performance indicator according to its importance and the difficulty in the actual detection process. While ensuring the detection of the main technical indicators, it can also greatly improve the detection efficiency and the screening efficiency of carbon sources;

[0023] 3. Carry out secondary classification of qualified carbon sources, improve the weight of denitrification performance, economic indicators and safety in the process, so as to screen out high-quality carbon sources that are both economical and safe and can meet production needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the carbon source evaluation process of the method of the present invention. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0026] like Figure 1 As shown, in the method of the present invention, the indicators related to the carbon source performance evaluation are graded according to priority, and the chemical oxygen demand (COD Cr ), total nitrogen (TN) and total phosphorus (TP) are used as the primary performance evaluation indicators. Chemical oxygen demand is the number of milligrams of oxygen required after all the carbon sources per unit volume or unit mass are oxidized. Total nitrogen is the total content of nitrogen in the carbon source sample, and total phosphorus is the total content of phosphorus in the carbon source sample.

[0027] The denitrification efficiency index is used as the secondary performance evaluation index. The denitrification efficiency index includes the denitrification rate and the effective utilization rate of carbon source. The denitrification rate is the NO3 removed per unit mass volatile sludge concentration (MLVSS) per unit time. - -N mass, and the effective utilization rate of carbon source is the ratio of carbon source consumption in the denitrification stage to the total added carbon source.

[0028] The economic index is used as the third-level performance evaluation index, and the economic index is the cost of removing 1 kg of nitrogen.

[0029] BOD5 / COD Cr , pH value, chromaticity, density, mass fraction of water-insoluble matter, chloride, sulfate and freezing point are used as the four-level performance evaluation indicators, among which BOD5 / COD CrIt represents the biodegradability index. The pH value includes the pH value of the carbon source sample itself and the pH value of the solution after the reaction in the denitrification efficiency index analysis. The chromaticity represents the chromaticity of the solution after the reaction in the denitrification efficiency index analysis. The density is the density of the carbon source sample. The mass fraction of water-insoluble matter is the content of insoluble matter in the carbon source sample. The chloride is the content of chloride in the carbon source sample. The sulfate is the content of sulfate in the carbon source sample. The condensation point is the temperature at which the carbon source sample reaches condensation.

[0030] Safety indicators are used as five-level performance evaluation indicators, among which safety indicators include flash point, metal corrosion rate, heavy metal content and biological toxicity; heavy metals include mercury, cadmium, chromium, arsenic and lead, and biological toxicity is measured using rats as experimental subjects.

[0031] In the method of the present invention, except for the denitrification efficiency index and the economic evaluation index, the determination of other indexes has corresponding determination standards, which can be measured according to the corresponding determination standards, and will not be described in detail here.

[0032] The determination of denitrification efficiency index specifically includes the following steps:

[0033] S1. Take a sample of the muddy water mixture at the end of a normally operating aerobic biological pool, and place the sample at 20°C until the dissolved oxygen level is below 0.5 mg / L;

[0034] S2. Determination of COD and NO3 in mud-water mixture - -N, MLSS and MLVSS content, take 8L of muddy water mixed sample into the reactor, add nitrate nitrogen to 50mg / L, and run in the simulated anoxic section of the biological pool under stirring conditions;

[0035] S3, adding different types of carbon sources into the reactor, all of which were added quickly according to a C / N ratio of 5, and setting a blank control;

[0036] S4. Under stirring conditions, ensure that the muddy water sample is fully mixed without stratification and the dissolved oxygen is below 0.5 mg / L. Take samples immediately after the initial mixing (within 30 seconds) and at 1, 5, 10, 15, 20, 25, 30, 40, 50, 60, 90, 120, 150 and 180 minutes respectively to determine NO3 - -N, NO2 - -N, COD content;

[0037] S5. After denitrification is completed, an aeration experiment is immediately carried out. After 8 hours of aeration, the residual COD content in the water is measured and the COD residual rate of the overexposure experiment is calculated.

[0038] S6. Calculate the denitrification rate and carbon source utilization rate.

[0039] The denitrification rate is the amount of NO3 removed per unit mass of volatile sludge concentration (MLVSS) per unit time. - -N mass, in mgNO3 - -N / (gMLVSS·h).

[0040] The effective utilization rate of carbon source is the ratio of carbon source consumption in the denitrification stage to the total added carbon source.

[0041] After the above calculations are completed, the economic index is the product of the amount of carbon source added and the carbon source cost during the denitrification efficiency index analysis process, and then divided by the mass of nitrogen removed during the denitrification efficiency index analysis process.

[0042] By setting standard values ​​for the above-mentioned performance evaluation indicators at all levels, it is possible to screen out carbon sources that meet the standards from a variety of composite carbon sources, which is more efficient; but it should be noted that in actual sewage treatment, if the COD equivalent of the carbon source is high, the actual dosage will be reduced. At this time, the requirements for the total nitrogen, total phosphorus, chloride, sulfate and heavy metal content in the carbon source will also be increased accordingly. When COD Cr When it is greater than the minimum critical value, the actual COD Cr Converted to COD Cr The mass fractions of TN, TP, chloride, sulfate and heavy metals are calculated based on the ratio of the minimum critical values. In addition, it is not easy to screen out a cost-effective carbon source in the actual screening process. Therefore, in the method of the present invention, the screened carbon sources are subjected to secondary classification. The secondary classification increases the weights of denitrification efficiency, economic indicators and safety indicators by weight, thereby screening out high-quality carbon sources with good economic safety and that can meet production needs.

[0043] Example 1

[0044] In a carbon source screening work, 16 composite carbon source samples need to be evaluated and screened to select high-quality carbon sources suitable for actual production operations.

[0045] In traditional screening work, the indicators of composite carbon sources are not measured comprehensively. In actual screening work, an average of 2 working days are required for one carbon source. If the manufacturer does not provide a third-party authoritative test report, in actual screening, one carbon source will take nearly 3 to 4 working days. The work intensity and time cost are very high, and the quality of the screened carbon sources is judged only by experience.

[0046] In this carbon source screening work, the method of the present invention was used for screening.

[0047] Among the 16 carbon source samples, 13 manufacturers provided test reports issued by a third-party authoritative organization, and the remaining 3 samples did not have relevant test reports.

[0048] According to the screening criteria of the safety index set in the method of the present invention, that is, flash point ≥70.0°C; metal corrosion rate ≤6.25mm / a; mercury ≤0.00002%; cadmium ≤0.0002%, chromium ≤0.0005%; arsenic ≤0.0005%; lead ≤0.0005%; rats were used as experimental subjects, and the biological toxicity LD 50 >2g / kg; 16 samples were compared, during which 3 samples were discarded, leaving 13 samples, of which 3 samples needed to be analyzed for safety indicators in subsequent tests and were further analyzed using the method of the present invention.

[0049] First, the COD of the carbon source sample Cr , TN and TP are measured, and COD is set during the process Cr ≥2.5×10 5 mg / L; mass fraction of TN ≤0.03%; mass fraction of TP ≤0.006%.

[0050] During the first-level testing process, 6 carbon source samples were discarded, including 2 samples without test reports issued by a third-party authoritative organization. The entire testing process took about 1 working day. After this step, there were 7 samples left, including 1 sample without a test report issued by a third-party authoritative organization.

[0051] The remaining samples were analyzed for denitrification efficiency and economic performance, and the denitrification rate was set to ≥1.5mgNO3. - -N / (gMLVSS·h); effective utilization rate of carbon source ≥60%; cost ≤35 yuan / kgN.

[0052] During this process, three carbon source samples were discarded, including one sample that did not have a test report issued by a third-party authoritative organization. At this point, only four carbon source samples remained. This step took about two working days.

[0053] The four samples were subjected to BOD5 / COD Cr , pH, chromaticity, density, mass fraction of water-insoluble matter, chloride, sulfate and freezing point; set BOD5 / COD Cr The ratio is ≥0.55; the pH value is 3-9 before addition and 6-9 after reaction; the color is ≤30 after reaction; the density is 0.9-1.26g / cm at 20℃ 3 ; Mass fraction of water-insoluble matter ≤0.2%; Chloride content ≤0.4%; Sulfate content ≤0.1%; Condensation point ≤-10℃; This process took about 5 working days, and 1 sample was discarded in the process. At this point, only 3 samples were left.

[0054] The remaining three samples were graded for the second time, and the weights of the indicators from level one to level five were 5%, 40%, 35%, 5% and 15% respectively. When the evaluation result was ≥17, the evaluation result was excellent; when 14≤evaluation result<17, the evaluation result was good; when 10≤evaluation result<14, the evaluation result was medium; when the evaluation result<10, the evaluation result was poor.

[0055] Among them, one high-quality carbon source, one good-quality carbon source, and one medium-quality carbon source sample were obtained. The medium-quality carbon source was discarded, and the time of this step can be ignored. The remaining two high-quality carbon sources were tested in production (the time of the actual measurement was not considered).

[0056] During the actual measurement process, the carbon source dosage was accurate and the appropriate carbon source addition site was selected. During the actual measurement process, both samples performed well, and the effluent water quality was up to standard and stable, which was a high-quality carbon source that met the production standards. In actual production, the use of high-quality carbon sources can well meet the usage requirements, and high-quality carbon sources can be used as emergency carbon sources in sewage treatment plants.

[0057] The above process took about 8 working days in total. Compared with the past, the screening was more comprehensive and the efficiency was significantly improved. At the same time, the economic cost of the carbon source screened was in line with expectations, which enabled the production cost to be effectively controlled.

[0058] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present invention.

Claims

1. A method for comprehensive evaluation and screening of carbon sources for sewage treatment, characterized in that: The following steps are involved: S1. Classifying the performance evaluation indicators of carbon sources to obtain performance evaluation indicators of different priorities; S2. According to the priority set in S1, the performance evaluation index of the carbon source sample to be tested is measured according to the priority, and according to the set standard value of the performance evaluation index, the carbon source whose measured value of the performance evaluation index does not meet the standard is eliminated, and the carbon source whose measured value of the performance evaluation index meets the standard is retained; S3, define the difference between the actual value of the performance evaluation index and the standard value of the performance evaluation index as the "deviation factor", add the deviation factors within each priority level and multiply them by the weight of each priority level, and perform secondary classification on the carbon sources that meet the actual value of the performance evaluation index of S2; S4. Based on the results of the secondary classification in S3, the carbon sources with better quality are measured, the effluent indicators are tested, and the high-quality carbon sources that meet the actual production requirements are screened out.

2. The method for comprehensive evaluation and screening of carbon sources for sewage treatment according to claim 1, characterized in that: In the above S1, the carbon source performance evaluation index is divided into levels one to five; The first-level performance evaluation indicators include COD Cr , TN and TP; The second-level performance evaluation index is the denitrification efficiency index; the third-level performance evaluation index is the economic index; the fourth-level performance evaluation index includes BOD5 / COD Cr , pH value, chromaticity, density, mass fraction of water-insoluble matter, chloride content, sulfate content and freezing point; the five-level performance evaluation indicators are safety indicators.

3. The method for comprehensive evaluation and screening of carbon sources for sewage treatment according to claim 2, characterized in that: The safety indicators include flash point, metal corrosion rate, heavy metal content and biological toxicity; flash point ≥70.0℃; metal corrosion rate ≤6.25mm / a; mercury ≤0.00002%; cadmium ≤0.0002%, chromium ≤0.0005%; arsenic ≤0.0005%; lead ≤0.0005%; using rats as experimental subjects, biological toxicity LD 50 >2g / kg; For safety indicators, if the carbon source manufacturer holds a test report from a third-party authoritative organization, the safety indicator will be the first test indicator in the actual carbon source screening, and other indicators will be ranked in order. If the carbon source manufacturer does not hold a test report from a third-party authoritative organization, the safety indicator will be the fifth priority test indicator.

4. The method for comprehensive evaluation and screening of carbon sources for sewage treatment according to claim 2, characterized in that: In S2, for the primary performance evaluation index, the COD of the composite carbon source Cr ≥2.5×10 5 mg / L; mass fraction of TN ≤0.03%; mass fraction of TP ≤0.006%.

5. The method for comprehensive evaluation and screening of carbon sources for sewage treatment according to claim 2, characterized in that: In S2, for the secondary performance evaluation index, the denitrification efficiency index includes the denitrification rate and the effective utilization rate of the carbon source. The denitrification rate is the amount of NO3 removed per unit mass of MLVSS per unit time. - -N mass, denitrification rate ≥ 1.5mgNO3 - -N / (gMLVSS·h); The effective utilization rate of carbon source is the ratio of carbon source consumption in the denitrification stage to the total added carbon source, and the effective utilization rate of carbon source is ≥60%.

6. The method for comprehensive evaluation and screening of carbon sources for sewage treatment according to claim 2, characterized in that: In S2, for the three-level performance evaluation index, the economic index is the cost of removing 1 kg of nitrogen, and the value of the cost is ≤35 yuan / kg N.

7. The method for comprehensive evaluation and screening of carbon sources for sewage treatment according to claim 2, characterized in that: In S2, for the four-level performance evaluation index, BOD5 / COD Cr The ratio is ≥0.55; the pH value is 3-9, and the pH value after the addition reaction is 6-9; the color after the addition reaction is ≤30; the density at 20℃ is 0.9-1.26g / cm 3 ; The mass fraction of water-insoluble matter is ≤0.2%; the chloride content is ≤0.4%; the sulfate content is ≤0.1%; the freezing point is negotiated between the supply and demand parties based on the actual application area to ensure that there is no ice in winter.

8. A method for comprehensive evaluation and screening of carbon sources for sewage treatment according to any one of claims 2 to 7, characterized in that: In the above S3, the weights of the indicators of level 1 to level 5 are 5%, 40%, 35%, 5% and 15% respectively; when calculating the deviation factor, the value is the percentage or the value in front of the unit symbol, COD Cr The value is the numerical part of scientific notation, and the deviation factors of pH value, density and freezing point are recorded as 0; when COD Cr When it is greater than the minimum critical value, the actual COD Cr Converted to COD Cr The mass fractions of TN, TP, chloride, sulfate, mercury, cadmium, chromium, arsenic and lead were calculated from the ratio of the minimum critical values.

9. The method for comprehensive evaluation and screening of carbon sources for sewage treatment according to claim 8, characterized in that: In the above S3, the evaluation results of the secondary classification are expressed as excellent, good, medium and poor; when the evaluation result ≥17, the evaluation result is excellent; when 14≤evaluation result<17, the evaluation result is good; when 10≤evaluation result<14, the evaluation result is medium; when the evaluation result<10, the evaluation result is poor.

10. The method for comprehensive evaluation and screening of carbon sources for sewage treatment according to claim 9, characterized in that: In the above-mentioned S4, carbon sources with excellent and good evaluation results are selected, and carbon sources with medium and poor evaluation results are discarded; the excellent and good carbon sources are measured, and during the measurement, when the effluent is stably up to the standard, the carbon source is a high-quality carbon source that meets the actual process.

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