Method for synchronously removing nitrate and sulfate in wastewater by utilizing polybutylene butyrate

Abstract

The invention discloses a method for synchronously removing nitrate and sulfate in wastewater by utilizing polybutyric acid butanediol ester. According to the method, an up-flow denitrification biological filter is adopted, PBS is filled in the up-flow denitrification biological filter to serve as a unique solid slow-release carbon source and a biofilm carrier, wastewater is pumped in from the bottom of a reactor and flows upwards through a PBS filler layer, and a denitrification reaction and a sulfate reduction reaction are conducted in different height intervals through a biofilm on the surface of filler respectively; the synchronous removal of nitrate and sulfate is realized. The stable slow release performance and carrier function of PBS are utilized, carbon source competition of denitrifying bacteria and sulfate reducing bacteria is effectively reduced through microbial function layering, and the method has the advantages of being low in operation cost, free of secondary pollution, good in effluent quality, simple in process and the like, and is suitable for deep treatment of wastewater containing nitrate and sulfate.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for simultaneously removing nitrates and sulfates from wastewater using polybutylene butyrate. Background Technology

[0002] With increasingly stringent water environment management standards, advanced denitrification of secondary effluent from urban wastewater treatment plants has become a crucial step in mitigating eutrophication. Since secondary effluent typically exhibits a low carbon-to-nitrogen ratio (C / N < 3), it cannot meet the needs of heterotrophic denitrifying bacteria, necessitating the addition of an additional carbon source as an electron donor to ensure denitrification efficiency.

[0003] Traditional external carbon source addition mainly uses small-molecule liquid organic compounds such as sodium acetate, methanol, or ethanol. Although these carbon sources have high utilization rates, they have many limitations in practical engineering applications: First, the dosage is difficult to precisely match with fluctuating water quality. Insufficient addition will lead to incomplete denitrification, while excessive addition will easily cause the effluent organic matter (COD / TOC) to exceed the standard, causing secondary pollution; Second, the storage and transportation equipment for liquid carbon sources is complex, with high operation and maintenance costs, and some carbon sources (such as methanol) are flammable and explosive, posing safety hazards.

[0004] In recent years, denitrification processes utilizing solid slow-release carbon sources instead of liquid carbon sources have attracted widespread attention. Existing solid carbon sources are mainly divided into natural biomass (such as corn cobs, straw, and sawdust) and biodegradable polymers (BDPs, such as PBS, PCL, and PLA). Although natural biomass is inexpensive, its composition is complex, and the rate of organic matter release is extremely unstable, often accompanied by severe discoloration and large amounts of soluble organic matter (DOC) release in the initial stages of operation. In contrast, synthetic polymers possess excellent biodegradability, mechanical strength, and stable slow-release carbon source performance, and can simultaneously serve as electron donors for microorganisms and biofilm carriers, simplifying process operation. Currently, direct filling is often used for wastewater treatment, for example, directly filling polycaprolactone (PCL) (Chinese patent application CN105800791A) or polybutylene succinate (PBS) (Chinese patent application CN109019870A) as both the solid carbon source and microbial growth carrier for denitrification under low carbon-to-nitrogen ratio conditions.

[0005] However, actual wastewater (especially industrial wastewater and some urban tailwater) often contains a certain concentration of sulfate. Under anoxic or anaerobic conditions, the denitrification process and the sulfate reduction process may interfere with each other due to competition for the same carbon source. The presence of sulfate may lead to incomplete denitrification, causing a significant accumulation of nitrite nitrogen and increasing the emission of the greenhouse gas nitrous oxide. Currently, there is limited research on the application of slow-release carbon sources to simultaneously remove nitrates and sulfates from wastewater. Summary of the Invention

[0006] This invention provides a method for simultaneously removing nitrates and sulfates from wastewater using polybutylene butyrate. This method achieves the goal of simultaneously removing nitrates and sulfates from wastewater by slowly releasing organic matter, avoiding secondary pollution that could cause COD to exceed the standard.

[0007] The technical solution of the present invention is as follows:

[0008] A method for simultaneously removing nitrates and sulfates from wastewater using polybutylene butyrate includes the following steps:

[0009] (1) Adjust the pH of the wastewater containing nitrates and sulfates to 7.5±0.2, and supplement phosphorus sources and trace elements to ensure normal microbial growth;

[0010] (2) Using an upflow biofilter reactor, the interior is filled with PBS as the only solid slow-release carbon source and biofilm carrier. The wastewater containing nitrate and sulfate prepared in step (1) is pumped into the bottom of the reactor. Under anaerobic conditions, it flows upward through the PBS packing layer. The biofilm on the surface of the packing simultaneously carries out denitrification and sulfate reduction reactions, thereby achieving the simultaneous removal of nitrate and sulfate.

[0011] Furthermore, in step (1), the nitrate nitrogen concentration in the wastewater containing nitrate and sulfate is 25 mg / L to 50 mg / L, and the sulfate concentration is 25 mg / L to 80 mg / L.

[0012] Furthermore, in step (1), the phosphorus source is selected from potassium dihydrogen phosphate, sodium dihydrogen phosphate, etc.

[0013] Furthermore, in step (2), the particle size of PBS is 3 mm.

[0014] Furthermore, in step (2), the hydraulic residence time (HRT) is 4 to 8 hours.

[0015] Furthermore, in step (2), the PBS filling height is 40 cm or more, preferably 60 cm or more.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] (1) Using PBS as a carbon source, its organic matter release is stable and will not produce secondary pollution. At the same time, the organic matter release concentration can be controlled by the response of nitrate and sulfate concentration in wastewater. In addition, it has the advantage of lower price compared with other polymer slow-release carbon sources such as PCL.

[0018] (2) PBS can also serve as a biofilm carrier, providing an important site for the growth and reproduction of microorganisms, and has the characteristic of large biomass loading. The results of sampling and detection along the process showed that the nitrate nitrogen concentration was below 0.2 mg / L at 20 cm, that is, denitrification and nitrogen removal could be completed before the filling height reached 20 cm, and then sulfate was removed by the sulfate reduction process of microorganisms. The average sulfate removal rate was 79.96% and 71.01% (at sulfate concentrations of 25 mg / L and 50 mg / L). This stratification of microbial functions can effectively reduce the competition for carbon sources between denitrifying bacteria and sulfate reducing bacteria, thereby better removing nitrates and sulfates in wastewater with low carbon-to-nitrogen ratios simultaneously, with an average total nitrogen removal rate of 98%.

[0019] (3) The process is simple and easy to implement, with low operating costs. There is no large accumulation of byproducts such as nitrite nitrogen and ammonia nitrogen. The total nitrogen concentration in the effluent is low. It is suitable for the deep treatment of wastewater containing nitrate and sulfate. The treated effluent is better than the national Class A discharge standard and has good application prospects. Attached Figure Description

[0020] Figure 1 The changes in the concentrations of nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen in the influent and effluent;

[0021] Figure 2 This shows the changes in sulfate concentration in the influent and effluent.

[0022] Figure 3 The total nitrogen concentration in the effluent;

[0023] Figure 4 The TOC concentration of the effluent;

[0024] Figure 5 This shows the variation of nitrate nitrogen concentration along the route;

[0025] Figure 6 This shows the change in sulfate concentration along the route. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0027] Example 1

[0028] A method for simultaneously removing nitrates and sulfates from wastewater using polybutylene butyrate includes the following steps:

[0029] (1) An upflow denitrification biofilter reactor with a volume of 2.1 L was constructed. The reactor was filled with PBS with a particle size of 3 mm as the only solid slow-release carbon source and biofilm carrier. The filling height of the packing was 60 cm, and the effective volume after filling was 0.8 L.

[0030] (2) The concentrations of nitrate nitrogen and sulfate in the simulated wastewater were both 25 mg / L. Potassium dihydrogen phosphate provided the phosphorus source, sodium bicarbonate adjusted the pH of the influent (7.5±0.2), and trace elements were added to ensure the normal growth of microorganisms.

[0031] (3) Simulated wastewater was pumped into the bottom of the reactor and flowed upward through the PBS packing layer. Under anaerobic conditions, the biofilm on the surface of the packing removed nitrate and sulfate simultaneously through denitrification and sulfate reduction. After treatment, the wastewater flowed out from the outlet. The hydraulic retention time was maintained at 6 hours. The reactor operated for 36 days.

[0032] The average removal rate of nitrate nitrogen was 99.32%, the average removal rate of sulfate was 71.01%, there was no accumulation of nitrite nitrogen in the effluent, the average concentration of ammonia nitrogen in the effluent was only 0.23 mg / L, the average concentration of total nitrogen in the effluent was only 0.60 mg / L, and the average concentration of TOC in the effluent was 20.25 mg / L.

[0033] Example 2

[0034] Based on Example 1, the influent sulfate concentration was increased to 50 mg / L, and the reactor continued to operate for 30 days. The average nitrate nitrogen removal rate was 99.46%, the average sulfate removal rate was 76.96%, there was no accumulation of nitrite nitrogen in the effluent, the average ammonia nitrogen concentration in the effluent was only 0.27 mg / L, the average total nitrogen concentration in the effluent was only 0.62 mg / L, and the average TOC concentration in the effluent was 10.25 mg / L.

[0035] Example 3

[0036] Based on Example 2, the influent sulfate concentration was increased to 80 mg / L, and the reactor continued to operate for 34 days. The average nitrate nitrogen removal rate was 99.45%, the average sulfate removal rate was 49.42%, there was no accumulation of nitrite nitrogen in the effluent, the average ammonia nitrogen concentration in the effluent was only 0.22 mg / L, the average total nitrogen concentration in the effluent was only 0.27 mg / L, and the average TOC concentration in the effluent was 5.50 mg / L. The reactors of Examples 1 to 3 operated continuously for a total of 100 days without changing the packing material.

[0037] Figure 1The data shows the concentration changes of nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen in the influent and effluent. The influent nitrate nitrogen concentration remained constant at approximately 25 mg / L. The reactor achieved a nitrate nitrogen removal rate of over 90% on the 8th day of operation. After stabilization, the average nitrate nitrogen removal rate in Stage I was 99.32% (36 days). Stage II lasted 30 days with an average nitrate nitrogen removal rate of 99.46%. Stage III lasted 34 days with an average nitrate nitrogen removal rate of 99.45%. No nitrite nitrogen accumulated throughout the entire operation cycle, and the effluent ammonia nitrogen concentration was below 1 mg / L.

[0038] Figure 2 The table shows the changes in sulfate concentration in the influent and effluent. In Stage I, the influent sulfate concentration was approximately 25 mg / L, and the reactor achieved a removal rate of over 50% on day 15 of operation, with an average removal rate of 71.01% after stabilization. In Stage II, the influent sulfate concentration was approximately 50 mg / L, and the average sulfate removal rate was 76.96%. In Stage III, the influent sulfate concentration was approximately 80 mg / L, and the average sulfate removal rate was 49.42%.

[0039] Figure 3 The total nitrogen (TN) concentration in the effluent is shown. The average TN concentrations in the effluent at each stage of the reactor were 0.60 mg / L, 0.62 mg / L, and 0.27 mg / L, respectively.

[0040] Figure 4 The TOC concentration in the effluent is shown. The average TOC concentrations in the effluent at each stage of the reactor were 20.25 mg / L, 10.25 mg / L, and 5.50 mg / L, respectively.

[0041] Figure 5 This shows the variation of nitrate nitrogen concentration along the reactor flow path. Nitrate nitrogen in each stage of the reactor process was essentially removed in the region with a packing height of 0–20 cm.

[0042] Figure 6 The table shows the variation of sulfate concentration along the reactor flow path. The sulfate concentration at each stage gradually decreased with increasing packing height. The average sulfate concentrations at each stage when the packing height was 20 cm were 15.97, 34.66, and 60.34 mg / L, respectively, while the average sulfate concentrations at each stage when the packing height was 60 cm were 6.63, 9.37, and 45.03 mg / L, respectively.

[0043] In summary, this reactor, utilizing polybutylene succinate as a slow-release carbon source and biofilm carrier, demonstrated excellent nitrate nitrogen removal performance during long-term operation. The average removal rate exceeded 99% across all three stages, with no accumulation of nitrite nitrogen in the effluent, and the effluent ammonia nitrogen concentration consistently below 1 mg / L. The average total nitrogen concentration in the effluent was also below 1 mg / L, indicating that the reactor achieved efficient and stable nitrogen removal. Analysis along the process showed that nitrate nitrogen was rapidly removed primarily within the packing height range of 0–20 cm. Sulfate removal rate was affected by the influent concentration; the average removal rates in stages I and II were 71.01% and 76.96%, respectively. In stage III, the removal rate decreased to 49.42% when the influent concentration increased to 80 mg / L, and the concentration gradually decreased along the process. The average TOC concentration in the effluent decreased from 20.25 mg / L to 5.50 mg / L with each stage of operation, indicating a gradual increase in the reactor's ability to remove organic matter. Overall, the reactor was highly effective in simultaneously removing nitrate and sulfate and exhibited good operational stability.

Claims

1. A method for simultaneously removing nitrates and sulfates from wastewater using polybutylene butyrate, characterized in that, Includes the following steps: (1) Adjust the pH of the wastewater containing nitrates and sulfates to 7.5±0.2, and supplement phosphorus sources and trace elements to ensure normal microbial growth; (2) Using an upflow biofilter reactor, the interior is filled with PBS as the only solid slow-release carbon source and biofilm carrier. The wastewater containing nitrate and sulfate prepared in step (1) is pumped into the bottom of the reactor. Under anaerobic conditions, it flows upward through the PBS packing layer. The biofilm on the surface of the packing simultaneously carries out denitrification and sulfate reduction reactions, thereby achieving the simultaneous removal of nitrate and sulfate.

2. The method according to claim 1, characterized in that, In step (1), the nitrate nitrogen concentration in the wastewater containing nitrate and sulfate is 25 mg / L to 50 mg / L, and the sulfate concentration is 25 mg / L to 80 mg / L.

3. The method according to claim 1, characterized in that, In step (1), the phosphorus source is selected from potassium dihydrogen phosphate or sodium dihydrogen phosphate.

4. The method according to claim 1, characterized in that, In step (2), the particle size of PBS is 3 mm.

5. The method according to claim 1, characterized in that, In step (2), the hydraulic residence time It takes 4 to 8 hours.

6. The method according to claim 1, characterized in that, In step (2), the PBS filling height is above 40 cm.

7. The method according to claim 1, characterized in that, In step (2), the PBS filling height is above 60 cm.

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