KR-20260062704-A - Optimization Anaerobic Digestion of Waste Activated Sludge Through Combined Microwave Irradiation and Zero-Valent Iron Pretreatment

Abstract

The present invention relates to a method for optimizing the anaerobic digestion of waste activated sludge through combined pretreatment with microwave irradiation and zero-valent iron, and more specifically, to a method for optimizing the anaerobic digestion of waste activated sludge by improving the physical, chemical, and biological characteristics of waste activated sludge through combined pretreatment with microwave irradiation and zero-valent iron (ZVI), thereby increasing methane production and improving the anaerobic digestion performance of waste activated sludge.

Inventors

• 안종화
• 하승한

Assignees

• 강원대학교산학협력단

Dates

Publication Date

20260507

Application Date

20241029

Claims (10)

1. A pretreatment method for the anaerobic digestion of waste activated sludge comprising the steps of injecting zero-valent iron and irradiating with microwaves.
2. A pretreatment method for the anaerobic digestion of waste activated sludge according to claim 1, characterized in that the temperature of the microwave is 100 to 200℃.
3. A pretreatment method for the anaerobic digestion of waste activated sludge according to claim 1, characterized in that the zero-valent iron is in powder form.
4. A pretreatment method for the anaerobic digestion of waste activated sludge according to claim 1, characterized in that the injection amount of zero-valent iron is 1 to 5 g/L.
5. A pretreatment method for the anaerobic digestion of waste activated sludge according to claim 1, characterized in that the temperature of the microwave and the amount of zero-valent iron injected are determined through BMP testing, kinetic analysis, and microbial activity analysis.
6. In paragraph 5, the above BMP test is (a) a step of pre-culturing the inoculum; and (b) a step of producing biogas by reacting a pre-cultured inoculum with waste activated sludge, and Herein, a pretreatment method for the anaerobic digestion of waste activated sludge, characterized in that the pre-culture period is determined based on the working volume and daily biogas production of the reactor.
7. A pretreatment method for the anaerobic digestion of waste activated sludge according to claim 6, characterized in that the value obtained by dividing the daily biogas production by the effective volume of the reactor is 0.03 to 0.04 (unit: mL biogas / mL working volume / day).
8. A pretreatment method for the anaerobic digestion of waste activated sludge according to claim 6, characterized in that steps (a) and (b) are performed under the same conditions.
9. A pretreatment method for the anaerobic digestion of waste activated sludge according to claim 6, characterized in that the inoculum is collected from an anaerobic digester sludge, impurities are removed, and then refrigerated.
10. A pretreatment method for the anaerobic digestion of waste activated sludge according to claim 6, wherein step (a) creates an anaerobic state by purging nitrogen gas into the inoculum and then sealing it.

Description

Optimization of Anaerobic Digestion of Waste Activated Sludge Through Combined Microwave Irradiation and Zero-Valent Iron Pretreatment The present invention relates to a method for optimizing the anaerobic digestion of waste activated sludge through combined pretreatment with microwave irradiation and zero-valent iron, and more specifically, to a method for optimizing the anaerobic digestion of waste activated sludge by improving the physical, chemical, and biological characteristics of waste activated sludge through combined pretreatment with microwave irradiation and zero-valent iron (ZVI) to increase methane production and improve the anaerobic digestion performance of waste activated sludge. Biogas production utilizing anaerobic digestion to convert organic waste, including sewage sludge, into energy is one of the most feasible methods for achieving sustainable development. Anaerobic digestion is generally widely used for the treatment of industrial wastewater, livestock wastewater, and sewage sludge, and is an environmentally friendly technology for the treatment of various organic wastes (Gao et al., 2023). Anaerobic digestion is a biochemical treatment method that converts organic matter into methane through hydrolysis, acidogenesis, and methaneogenesis stages using microorganisms, including bacteria and archaea, under oxygen-free anaerobic conditions (Xu et al., 2018; Ye et al., 2024). Microorganisms involved in anaerobic digestion are classified into acid-producing bacteria, acetate-producing bacteria, and methanogens (Wang et al., 2018). Recently, research is underway to analyze the state of digesters through the microbial community by analyzing 16S rRNA gene data (Pei et al., 2022). The biochemical methane potential (BMP) test is a method to determine the methane potential and biodegradability of organic waste, such as sewage sludge, in an anaerobic digestion batch reactor. Additionally, pre-incubation is performed to improve the reproducibility of the BMP test by removing organic matter contained in the inoculum for a certain period (5-10 days) (Himanshu et al., 2017; Kabakci et al., 2024). The activated sludge process is widely used in wastewater treatment due to its low operating costs and excellent performance in biological phosphorus removal (Wang et al., 2023). Waste activated sludge (WAS) refers to the sludge settled during biological sewage treatment processes, excluding return sludge. It is estimated that approximately 103 million tons of waste activated sludge will be generated annually in sewage treatment plants worldwide by 2025 (Xu & Dai, 2021). Organic substances such as polysaccharides, proteins, and lipids account for 80% of the volatile solids in waste activated sludge, which is attracting significant interest in resource recovery through anaerobic digestion. However, conventional anaerobic digestion of waste activated sludge suffers from the problem of low hydrolysis efficiency. Because waste activated sludge is composed of cell walls, intracellular components, and extracellular fibrous structures (extracellular polymeric substance, EPS), the reaction period is long, and methane production is low. To improve these problems, a pretreatment process is required for the anaerobic digestion of waste activated sludge, and in order to properly pretreat waste activated sludge, it is important to accurately understand the structure of activated sludge flocs, which are clumps of microorganisms that are interlocked and connected to one another through fibrous structures (EPS) outside the microbial cells. To date, methods such as ultrasonic treatment, high-temperature heat treatment, ozone oxidation, cavitation treatment, alkali treatment, enzyme treatment, mechanical treatment, acid treatment, microbial treatment, wet oxidation process, and vacuum treatment have been tested and developed as pretreatment methods for waste activated sludge. In order to increase the overall efficiency of sewage sludge treatment, processes and devices are required that can effectively dismantle the structure of sludge flocs and also attack and destroy the cell walls of microorganisms, thereby allowing intracellular substances and internal water to be released to the outside. Accordingly, there is still a demand for sludge pretreatment processes that can further improve sludge reduction, dewatering capacity, and anaerobic digestion efficiency through a simpler process. Accordingly, the inventors of the present invention have made diligent efforts to solve the above problems and have confirmed that when microwaves and zero-valent iron (ZVI) powder are simultaneously applied to the pretreatment process of waste activated sludge and optimal conditions are sought to perform an anaerobic digestion process, the physical, chemical, and biological characteristics of the waste activated sludge are improved, thereby increasing methane production and improving the anaerobic digestion performance of the waste activated slu