Method for fast start-up of sludge anaerobic fermentation

Abstract

This invention belongs to the field of waste sludge resource utilization technology, specifically involving a method for rapidly starting anaerobic fermentation of sludge. It includes the following stages: (1) inoculating rumen waste into low-concentration fermented sludge for mesophilic batch anaerobic fermentation, followed by heat shock treatment after fermentation; (2) adding high-concentration fermented sludge and continuing mesophilic batch anaerobic fermentation; (3) daily, after discharging the mixed fermented material from the system after stage 2 fermentation, adding high-concentration fermented sludge for mesophilic semi-continuous anaerobic fermentation. After the start-up period, a certain amount of organic load can be added daily for mesophilic continuous anaerobic fermentation. This invention adopts a batch-to-semi-continuous fermentation mode, utilizing rumen waste for inoculation and heat shock treatment, gradually improving the fermentation activity of microorganisms; it shortens the start-up time, ensures the entire fermentation system has stronger selectivity and stability, and greatly enhances the acid production efficiency of subsequent fermentation processes.

Description

Technical Field

[0001] This invention belongs to the field of waste sludge resource utilization technology, specifically relating to a method for rapidly starting anaerobic fermentation of sludge. Background Technology

[0002] With the rapid advancement of urbanization and the continuous development of the wastewater treatment industry, the output of residual sludge from urban wastewater treatment plants has been increasing year by year. As a typical solid waste, residual sludge has a complex composition, containing not only large amounts of organic matter, nitrogen, phosphorus, and other nutrients, but also potentially accumulating heavy metals, pathogens, and other harmful pollutants. Improper treatment and disposal can easily cause secondary pollution of soil, water bodies, and the atmosphere, threatening ecological security and human health. Therefore, achieving the scientific treatment, disposal, and resource utilization of residual sludge can not only effectively solve the sludge pollution problem, but also tap into the potential resource value of sludge, achieving the environmental protection goals of "reduction, harmlessness, and resource recovery," which has significant practical and strategic value for promoting ecological environmental protection and resource recycling.

[0003] Among the numerous technological pathways for the resource utilization of waste sludge, anaerobic fermentation acid production technology demonstrates broad application prospects due to its unique advantages. This technology uses waste sludge as raw material, and through the metabolic action of microorganisms in an anaerobic environment, degrades the organic matter in the sludge into volatile fatty acids. Volatile fatty acids, as important chemical raw materials and bioenergy precursors, can be widely used in fields such as biological nitrogen and phosphorus removal, bioplastics synthesis, and anaerobic digestion for methanogenesis, achieving efficient conversion and high-value utilization of sludge resources. Compared with traditional sludge treatment technologies (such as landfill and incineration), anaerobic fermentation acid production technology not only has lower energy consumption and cost but also effectively reduces sludge volume while simultaneously removing pollutants. It is a sludge resource utilization technology that combines environmental, economic, and social benefits.

[0004] However, in practical engineering applications, the anaerobic fermentation of sludge for acid production still faces many technical bottlenecks, among which the long start-up period, low fermentation efficiency, and unstable reaction process are the most prominent problems. Because the waste sludge contains a large number of macromolecular organic components and has a dense floc structure, microorganisms have difficulty quickly contacting and degrading the substrate, resulting in a long fermentation start-up period, typically requiring tens of days to reach a stable acid production level. Simultaneously, the complex microbial community structure within the fermentation system leads to low activity, insufficient numbers, and slow growth of acid-producing microorganisms, resulting in low acid production efficiency and insufficient volatile fatty acid yield to meet practical application requirements. Furthermore, problems such as acidification inhibition and ammonia nitrogen inhibition easily occur during fermentation, leading to poor stability of the fermentation system and severely restricting the large-scale promotion and application of anaerobic fermentation technology for acid production.

[0005] In response to the technical difficulties in the anaerobic fermentation and acid production process of sludge, this invention aims to overcome the limitations of existing technologies by adopting a batch-to-semi-continuous fermentation mode, utilizing rumen waste for inoculation and fermentation, and performing heat shock treatment to achieve rapid start-up of anaerobic fermentation of sludge and enhance acid production. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and design a method for rapidly starting anaerobic fermentation of sludge.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for rapidly starting anaerobic fermentation of sludge, the method comprising the following stages: Stage 1: Inoculate rumen waste into low-concentration fermentation sludge and carry out batch anaerobic fermentation at 35-40℃ for 3 days. After fermentation, perform heat shock treatment and then cool down to 35-40℃. Phase 2: Add high-concentration fermented sludge to the system treated in Phase 1, and continue batch anaerobic fermentation at 35-40℃ for 3 days; Phase 3: After discharging a portion of the mixed fermented material from the system after Phase 2 fermentation each day, add an equal amount of high-concentration fermented sludge and carry out semi-continuous anaerobic fermentation at 35-40℃ for 4 days.

[0008] The above three stages together constitute a 10-day start-up period. After the start-up period, an organic load of 8-10 g / L (based on total solids concentration) is added daily, and continuous anaerobic fermentation is carried out at a temperature of 35-40°C. The organic load is the ratio of the total solids (TS) content in the fermentation sludge entering the reactor daily to the effective volume of the reactor.

[0009] Furthermore, the concentration of the low-concentration fermented sludge is 10-15 g / L in terms of total solids concentration; the concentration of the high-concentration fermented sludge is 35-40 g / L in terms of total solids concentration.

[0010] Furthermore, the inoculation amount of rumen waste described in Stage 1 is 10% to 15% of the volume of low-concentration fermented sludge.

[0011] Furthermore, the amount of high-concentration fermented sludge added in stage 2 is 30% to 40% of the fermentation volume in stage 1, wherein the fermentation volume in stage 1 is the sum of the volumes of low-concentration fermented sludge and rumen waste.

[0012] Furthermore, the discharge amount of the mixed fermentation product and the addition amount of high-concentration fermented sludge in stage 3 are both 20-30% of the fermentation volume in stage 2, wherein the fermentation volume in stage 2 is the sum of the fermentation volume after the end of stage 1 fermentation and the volume of high-concentration fermented sludge.

[0013] Furthermore, the discharge volume of the mixed fermentation product and the addition volume of the high-concentration fermented sludge in stage 3 are both 25% of the fermentation volume in stage 2.

[0014] Furthermore, the rumen waste mentioned in Stage 1 is bovine rumen fluid from a slaughterhouse, which is filtered and stored in an anaerobic environment at 39°C.

[0015] Furthermore, the specific operation of the heat shock treatment described in stage 1 is as follows: heat up to 65-70°C and hold for 15-20 minutes.

[0016] Furthermore, the specific operation of cooling down to 35-40°C after the heat shock treatment in Stage 1 is as follows: after the heat shock treatment, the hot water heated to 65-70°C is quickly discharged, water is added for cooling, and the reactor is stirred at 90-110 r / min, and the temperature inside the reactor is monitored in real time; when the temperature drops to 35-40°C, the fermentation operation in Stage 2 is immediately started, and the water bath temperature is maintained at 35-40°C.

[0017] Compared with the prior art, the positive and beneficial effects achieved by the present invention are as follows: (1) After a 10-day three-stage start-up period, the sludge anaerobic fermentation system of the present invention is switched to continuous anaerobic fermentation mode. The production of volatile fatty acids (VFA) in this fermentation system can be rapidly increased and stabilized at about 3000 mg COD / L. However, the sludge anaerobic fermentation system that directly carries out continuous anaerobic fermentation mode without a start-up period only reaches about 800 mg COD / L on the 20th day, and the distribution of each VFA is relatively scattered and fluctuates greatly. This shows that the batch-to-semi-continuous fermentation start-up mode of the present invention can effectively shorten the start-up time and make the acid production efficiency of the entire fermentation system stable and efficient.

[0018] (2) This invention relies on three-stage tiered load operation to gradually improve the fermentation activity of microorganisms; by utilizing the excellent fermentation capacity of bovine rumen fluid, it can domesticate and enrich highly efficient acid-producing bacteria, while inhibiting the activity of methanogens through heat shock treatment; these processes not only shorten the start-up time, but also ensure that the entire fermentation system has stronger selectivity and stability, while greatly enhancing the acid production efficiency of subsequent fermentation processes, providing a practical and feasible technical solution for the engineering application of sludge anaerobic fermentation acid production technology. Attached Figure Description

[0019] Figure 1 The acid production data for each stage of the start-up period of Example 1 and the first 30 days of the subsequent continuous fermentation process, as well as the acid production data for Comparative Examples 1 and 2, are presented. Detailed Implementation

[0020] The present invention will be further described below through specific embodiments. These embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0021] The fermented sludge described in this invention is taken from the sludge thickening tank of a sewage treatment plant in Beijing. Through dilution or concentration, the concentration of low-concentration fermented sludge is controlled to be 10-15 g / L in terms of total solids (TS), and the concentration of high-concentration fermented sludge is controlled to be 35-40 g / L in terms of TS. The rumen waste is collected from bovine rumen fluid from a slaughterhouse in Beijing. It is filtered through four layers of gauze and then immediately placed in an anaerobic environment at 39°C for subsequent use. Example 1

[0022] A method for rapidly initiating anaerobic fermentation of sludge, the method comprising the following stages: Phase 1: Bovine rumen fluid is inoculated into low-concentration fermented sludge, with the inoculation volume being 10% of the volume of the low-concentration fermented sludge. Batch anaerobic fermentation is carried out at 35°C for 3 days. After fermentation, the temperature is raised to 70°C and held for 15 minutes for heat shock treatment. After heat shock treatment, the hot water heated to 70°C is quickly discharged, and water is added for cooling. At the same time, the reactor is stirred at 100 r / min, and the temperature inside the reactor is monitored in real time. When the temperature drops to 35°C, the fermentation operation of Phase 2 is immediately started, and the water bath temperature is maintained at 35°C. Phase 2: Add high-concentration fermented sludge to the system treated in Phase 1, wherein the amount of high-concentration fermented sludge added is 35% of the fermentation volume in Phase 1, and continue batch anaerobic fermentation at 35°C for 3 days. Phase 3: Discharge the mixed fermentation material from the system after Phase 2 fermentation daily. The amount of mixed fermentation material discharged is 25% of the fermentation volume of Phase 2. Add an equal amount of high-concentration fermented sludge and continue semi-continuous anaerobic fermentation at 35°C for 4 days.

[0023] The above three stages together constitute a 10-day start-up period. After the start-up period, an organic load of 10 g / L based on the total solids concentration is added daily, and continuous anaerobic fermentation is carried out at 35°C.

[0024] Comparative Example 1 Before the start-up period, an organic load of 10 g / L (based on total solids concentration) was added daily, and continuous anaerobic fermentation was carried out at 35°C.

[0025] Comparative Example 2 Only the fermentation process of stage 1 in Example 1 was carried out. After heat shock treatment, the temperature was lowered to 35°C, and an organic load of 10 g / L based on the total solids concentration was added daily. Continuous anaerobic fermentation was carried out at 35°C.

[0026] The acid production of Example 1 was measured at each stage of the start-up period and during the first 30 days of the subsequent continuous fermentation process, with Comparative Example 1 used as a control. The results are as follows: Figure 1 As shown, where Figure 1 (a) is the dissolved chemical oxygen demand of Comparative Example 1, which is the ratio of total dissolved organic matter (SCOD) and volatile fatty acids (VFA) in total dissolved organic matter (VFA / SCOD). Figure 1 (b) shows the distribution of VFA components in Comparative Example 1; Figure 1 (c) SCOD and VFA / SCOD for Comparative Example 2; Figure 1 (d) shows the distribution of the VFA components in Comparative Example 2; Figure 1 (e) SCOD and VFA / SCOD of Example 1; Figure 1 (f) shows the distribution of the VFA components in Example 1.

[0027] Using the method of this invention, the sludge anaerobic fermentation system, after a 10-day three-stage start-up period, transitions to continuous anaerobic fermentation mode. Its VFA production rapidly increases and stabilizes at around 3000 mg COD / L, with the VFA / SCOD ratio remaining stable above 50%. In contrast, Comparative Example 1 only reached approximately 800 mg COD / L by day 20, with a VFA / SCOD ratio of only around 30%. Comparative Example 2, which only underwent stage 1 fermentation, showed a slow increase in VFA production, stabilizing at around 2000 mg COD / L. This indicates that stage 1 fermentation alone cannot rapidly initiate acid production, and its acid production efficiency is not as high as in Example 1. Furthermore, the VFA / SCOD ratio shows that the subsequent acid production process in Comparative Example 2 is unstable compared to Example 1. Regarding the composition of acid production, in Example 1, the VFA composition was mainly acetic acid, followed by propionic acid, accounting for approximately 35% and 20% respectively, with other acids accounting for approximately 45% in total. In Comparative Example 1, the distribution of each VFA was more dispersed and fluctuated significantly. Although acetic acid was still the main component, its proportion was extremely unstable and showed no clear pattern. Therefore, the experimental results show that the three-stage anaerobic fermentation start-up method for sludge in the batch-to-semi-continuous mode adopted in this invention can effectively shorten the fermentation start-up time, quickly achieve high fermentation efficiency, and maintain stable and efficient acid production efficiency during subsequent continuous fermentation.

[0028] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the scope of protection of the present invention.

Claims

1. A method for rapidly initiating anaerobic fermentation of sludge, characterized in that, The method Includes the following stages: Stage 1: Inoculate rumen waste into low-concentration fermentation sludge and carry out batch anaerobic fermentation at 35-40℃ for 3 days. After fermentation, perform heat shock treatment and then cool down to 35-40℃. Phase 2: Add high-concentration fermented sludge to the system treated in Phase 1, and continue batch anaerobic fermentation at 35-40℃ for 3 days; Phase 3: After discharging a portion of the mixed fermented material from the system after Phase 2 fermentation each day, add an equal amount of high-concentration fermented sludge and carry out semi-continuous anaerobic fermentation at 35-40℃ for 4 days. The above three stages together constitute a 10-day start-up period. After the start-up period, an organic load of 8-10 g / L based on the total solids concentration is added daily and continuous anaerobic fermentation is carried out at a temperature of 35-40℃.

2. The method according to claim 1, characterized in that, The concentration of the low-concentration fermented sludge is 10-15 g / L based on total solids concentration; the concentration of the high-concentration fermented sludge is 35-40 g / L based on total solids concentration.

3. The method according to claim 2, characterized in that, The inoculation amount of rumen waste described in Stage 1 is 10% to 15% of the volume of low-concentration fermented sludge.

4. The method according to claim 2, characterized in that, The amount of high-concentration fermented sludge added in Stage 2 is 30% to 40% of the fermentation volume in Stage 1.

5. The method according to claim 1, characterized in that, The discharge volume of the mixed fermentation product and the addition volume of high-concentration fermented sludge in Stage 3 are both 20-30% of the fermentation volume in Stage 2.

6. The method according to claim 1, characterized in that, The rumen waste mentioned in Phase 1 is bovine rumen fluid from slaughterhouses, which is filtered and stored in an anaerobic environment at 39°C.

7. The method according to claim 1, characterized in that, The specific operation of the heat shock treatment described in Stage 1 is as follows: heat up to 65-70℃ and hold for 15-20 minutes.

Images