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Park, Y.; Khim, J.; Kim, J.D. Anaerobic Co-Digestion. Encyclopedia. Available online: https://encyclopedia.pub/entry/50766 (accessed on 08 May 2024).
Park Y, Khim J, Kim JD. Anaerobic Co-Digestion. Encyclopedia. Available at: https://encyclopedia.pub/entry/50766. Accessed May 08, 2024.
Park, Yongwoon, Jeehyeong Khim, Jong Doo Kim. "Anaerobic Co-Digestion" Encyclopedia, https://encyclopedia.pub/entry/50766 (accessed May 08, 2024).
Park, Y., Khim, J., & Kim, J.D. (2023, October 25). Anaerobic Co-Digestion. In Encyclopedia. https://encyclopedia.pub/entry/50766
Park, Yongwoon, et al. "Anaerobic Co-Digestion." Encyclopedia. Web. 25 October, 2023.
Anaerobic Co-Digestion
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This entry is adapted from the peer-reviewed paper 10.3390/pr11041294

The anaerobic mono-digestion treatment of organic waste can be challenging due to nutrient imbalances and a lack of microbial diversity. However, anaerobic co-digestion has been shown to effectively address both challenges without the need for additives.

organic waste anaerobic co-digestion bio-gasification

1. Anaerobic Co-Digestion

Anaerobic co-digestion has been shown to improve the efficiency of organic waste treatments with different properties and complementary characteristics and offers significant economic advantages. The anaerobic mono-digestion treatment of organic waste can be challenging due to nutrient imbalances and a lack of microbial diversity. However, anaerobic co-digestion has been shown to effectively address both challenges without the need for additives [1][2][3][4]. Anaerobic co-digestion has many essential factors, the most important of which are described below.
Substrate is a crucial factor for anaerobic digestion efficiency. It is converted into biogas through biochemical processes, such as hydrolysis, acidogenic fermentation, acetogenesis, and methanogenesis, that accompany anaerobic digestion [5]. The velocity and rate of conversion into methane gas vary with the substrate’s chemical composition. The substrate, largely composed of carbohydrates, proteins, and fats, is converted into simpler molecules through a biochemical process and finally into methane and other substances [6][7]. Protein-rich organic substrates, such as livestock manure, have a high energy content and produce relatively high volumes of methane. A high concentration of ammonia interferes with microorganism activity and increases the instability of anaerobic digestion, causing system failure. However, suitable co-substrate-like food waste can adjust the C/N ratio to its optimum value. Carbohydrate-rich organic substrates, such as food waste, contain considerable amounts of simple sugars and disaccharides that are easily decomposed by methanogenic microorganisms and can easily produce volatile fatty acids (VFAs). However, a decrease in pH because of VFA accumulation, a high carbon-to-nitrogen (C/N) ratio, and concentration of heavy metals and toxic substances can cause challenges in anaerobic digestion. Suitable co-substrate-like animal manure can adjust the VFA concentration. Additionally, fat-rich organic substrates can be easily decomposed and produce large volumes of biogas. However, challenges such as blocking, adsorption to biomass, and foaming may occur, where carbohydrate-rich co-substrate can be used to adjust the nutritional balance [8][9][10].
The optimal pH range for biogas production in an anaerobic digester is 6.8–7.2. Acidogenic microorganisms are less sensitive to pH and can tolerate a pH range of 4.0–8.5; the optimal pH for hydrolysis and acidogenesis is 5.5–6.5 [11][12]. In contrast, methanogenic microorganisms are highly sensitive to pH, and the appropriate pH is approximately 7. Therefore, a two-stage digester is sometimes used to divide the anaerobic digester into two parts with different pH ranges to maximize the efficiency of anaerobic digestion. Therefore, pH is an important factor in determining the health of anaerobic digesters. Methane production may not be successful if the pH is not maintained within the optimal range, such as when the pH drops as a result of excessive VFA during the anaerobic digestion of a single substrate, including high-concentration food waste [9][13]. Anaerobic co-digestion of food waste with a pH of <4 and livestock manure with a pH of >8 can lead to increased gas production compared to separate digestion provided that the feedstock mixture is adjusted to maintain an optimal pH of 6.5–7.5 throughout the process [14].
According to previous studies on biogas production through anaerobic digestion, the typical C/N ratio is 20–30 [11][15][16][17]. However, determining the optimal C/N ratio is challenging because it depends on the chemical composition and biodegradability of the substrate [18]. However, system instability can be reduced if the C/N ratio is maintained within the normal range [9]. The challenges that can occur when an appropriate C/N ratio is not maintained are as follows: a high C/N ratio may cause excessive VFA generation, and a low C/N ratio may lead to excessive generation of total ammonia nitrogen. These are intermediate products of the metabolic process that interfere with the production of methane [19]. Methane production can be increased by maintaining an appropriate C/N ratio in anaerobic co-digestion, such as swine manure, rice straw mix [19], cow manure, and energy crop mix [20].

2. Design of a Full Scale Anaerobic Co-Digester

Anaerobic digestion (AD) generally works well on a laboratory or intermediate scale, but problems may arise when scaling up to larger reactors [6]. Potential issues include unpredictable substance behavior in the mixture, leading to problems such as odor, fermentation cessation, or slowed fermentation rates; difficulty with solid waste processing, which can accumulate within the reactor and hinder the fermentation process; difficulties maintaining proper temperature control, which can lead to overheating in some areas and slow fermentation rates in others; and difficulty maintaining consistent flow rates, which can affect both the speed and stability of the fermentation process. To address these challenges, effective flow control and characterization of mixture properties are required in large-scale AD reactors. Additionally, appropriate technology and operational strategies must be adopted to ensure the stability and efficiency of large-scale anaerobic digestion.
In order to ensure the stable operation of large-scale anaerobic digesters, mixing is a crucial factor. Many mixing devices have been applied to anaerobic digestion; they can be classified largely as mechanical, hydraulic, and pneumatic mixing devices [21]. Most anaerobic digesters used in Korea are vertical-flow cylindrical digesters that use mechanical mixing. If not mixed properly, stratification occurs in the anaerobic digester, causing light materials to accumulate in the upper layer and heavy particles to sink to the lower layer. Subsequently, anaerobic digestion occurs only in the middle layer, resulting in a shorter retention time [22][23]. This phenomenon frequently occurs in anaerobic digesters installed in Korea, as reported in a Dongdaemun Environmental Resources Center case study, a food waste treatment facility in Seoul fitted with a dry anaerobic digestion system [24]. Mixing is crucial when treating food waste with high total solids (TS) rather than low TS [23]. Therefore, the shape of the anaerobic digester and the mixing of waste are important factors. A report has described the stable treatment of high-concentration food waste at 15 m3/day using effective mixing with a horizontal anaerobic digester [25]. Thus, a horizontal anaerobic digester equipped with large impellers can be a viable alternative to solve the existing mixing problems.
With the recent development of computer models and the complexity of mathematical expressions for the anaerobic digestion process, full-scale performance can be predicted to a relatively meaningful degree through batch experiments and kinetic models [26][27]. In Korea, the size design and methane production rate of anaerobic digesters for various substrates are predicted using biochemical methane potentials (BMPs), specific organic loading, and kinetic models.

References

  1. Karki, R.; Chuenchart, W.; Surendra, K.C.; Shrestha, S.; Raskin, L.; Sung, S.; Hashimoto, A.; Khanal, S.K. Anaerobic co-digestion: Current status and perspectives. Bioresour. Technol. 2021, 330, 125001.
  2. Liang, J.; Luo, L.; Li, D.; Varjani, S.; Xu, Y.; Wong, J.W.C. Promoting Anaerobic Co-digestion of Sewage Sludge and Food Waste with Different Types of Conductive Materials: Performance, Stability, and Underlying Mechanism. Bioresour. Technol. 2021, 337, 125384.
  3. Mata-Alvarez, J.; Macé, S.; Llabrés, P. Anaerobic Digestion of Organic Solid Wastes. An Overview of Research Achievements and Perspectives. Bioresour. Technol. 2000, 74, 3–16.
  4. Mata-Alvarez, J.; Dosta, J.; Romero-Güiza, M.S.; Fonoll, X.; Peces, M.; Astals, S. A Critical Review on Anaerobic Co-digestion Achievements between 2010 and 2013. Renew. Sustain. Energy Rev. 2014, 36, 412–427.
  5. Li, Y.; Chen, Y.; Wu, J. Enhancement of Methane Production in Anaerobic Digestion Process: A review. Appl. Energy 2019, 240, 120–137.
  6. Zhang, R.; El-Mashad, H.M.; Hartman, K.; Wang, F.; Liu, G.; Choate, C.; Gamble, P. Characterization of Food Waste as Feedstock for Anaerobic Digestion. Bioresour. Technol. 2007, 98, 929–935.
  7. Zhang, C.; Su, H.; Baeyens, J.; Tan, T. Reviewing the Anaerobic Digestion of Food Waste for Biogas Production. Renew. Sustain. Energy Rev. 2014, 38, 383–392.
  8. Chow, W.L.; Chong, S.; Lim, J.W.; Chan, Y.J.; Chong, M.F.; Tiong, T.J.; Chin, J.K.; Pan, G.-T. Anaerobic Co-Digestion of Wastewater Sludge: A Review of Potential Co-Substrates and Operating Factors for Improved Methane Yield. Processes 2020, 8, 39.
  9. Hagos, K.; Zong, J.; Li, D.; Liu, C.; Lu, X. Anaerobic Co-digestion Process for Biogas Production: Progress, Challenges and Perspectives. Renew. Sustain. Energy Rev. 2017, 76, 1485–1496.
  10. Rasapoora, M.; Young, B.; Brarb, R.; Sarmahc, A.; Zhuangc, W.-Q.; Baroutiana, S. Recognizing the Challenges of Anaerobic Digestion: Critical Steps Toward Improving Biogas Generation. Fuel 2020, 261, 116497.
  11. Rincon-Perez, J.; Celis, L.B.; Morales, M.; Alatriste-Mondragon, F.; Tapia-Rodríguez, A.; Razo-Flores, E. Improvement of Methane Production at Alkaline and Neutral pH from Anaerobic Co-digestion of Microalgal Biomass and Cheese Whey. Biochem. Eng. J. 2021, 169, 107972.
  12. Ward, A.J.; Hobbs, P.J.; Holliman, P.J.; Jones, D.L. Optimisation of the Anaerobic Digestion of Agricultural Resources. Bioresour. Technol. 2008, 99, 7928–7940.
  13. Kwietniewska, E.; Tys, J. Process Characteristics, Inhibition Factors and Methane Yields of Anaerobic Digestion Process, with Particular Focus on Microalgal Biomass Fermentation. Renew. Sustain. Energy Rev. 2014, 34, 491–500.
  14. Ministry of Environment, South Korea. The Policy Direction of Biogasification. 2022. Available online: https://me.go.kr/home/web/policy_data/read.do?pagerOffset=0&maxPageItems=10&maxIndexPages=10&searchKey=title&searchValue=%ED%8F%90%EC%9E%90%EC%9B%90&menuId=10259&orgCd=&condition.toInpYmd=null&condition.fromInpYmd=null&condition.deleteYn=N&condition.deptNm=null&seq=7923 (accessed on 20 December 2022).
  15. Su, L.; Sun, X.; Liu, C.; Ji, R.; Zhen, G.; Chen, M.; Zhang, L. Thermophilic Solid-State Anaerobic Digestion of Corn Straw, Cattle Manure, and Vegetable Waste: Effect of Temperature, Total Solid Content, and C/N Ratio. Archaea 2020, 2020, 8841490.
  16. Chen, X.; Yan, W.; Sheng, K.; Sanati, M. Comparison of High-Solids to Liquid Anaerobic Co-digestion of Food Waste and Green Waste. Bioresour. Technol. 2014, 154, 215–221.
  17. Parkin, G.F.; Owen, W.F. Fundamentals of Anaerobic Digestion of Wastewater sludges. J. Environ. Eng.-ASCE 1986, 112, 600–604.
  18. Li, Y.; Park, S.Y.; Zhu, J. Solid-state anaerobic digestion for methane production from organic waste. Renew. Sustain. Energy Rev. 2011, 15, 821–836.
  19. Riya, S.; Suzuki, K.; Terada, A.; Hosomi, M. Influence of C/N Ratio on Performance and Microbial Community Structure of Dry-Thermophilic Anaerobic Co-Digestion of Swine Manure and Rice Straw. Med. Bioeng. 2016, 5, 11–14.
  20. Comino, E.; Rosso, M.; Riggio, V. Investigation of Increasing Organic Loading Rate in the Co-digestion of Energy Crops and Cow Manure Mix. Bioresour. Technol. 2010, 101, 3013–3019.
  21. Deublein, D.; Steinhauser, A. Biogas from Waste and Renewable Resources; Wiley-VCH Verlag GmbH& Co. KGaA: Weinheim, Germany, 2008.
  22. El Ibrahimi, M.; Khay, I.; El Maakoul, A.; Bakhouya, M. Food waste treatment through Anaerobic Co-digestion: Effects of Mixing Intensity on the Thermohydraulic Performance and Methane Production of a Liquid Recirculation Digester. Process Saf. Environ. Prot. 2021, 147, 1171–1184.
  23. Lindmark, J.; Thorin, E.; Fdhila, R.B.; Dahlquist, E. Effects of Mixing on the Result of Anaerobic Digestion: Review. Renew. Sustain. Energy Rev. 2014, 40, 1030–1047.
  24. Choi, C.; Lee, C.-Y.; Song, C.-Y.; Yoon, Y. Plant (Dongdaemun Environment and Resources Center) Operation Case Study: Anaerobic Digestion of Food Waste. Korea Soc. Waste Manag. 2016, 33, 819–832.
  25. Lee, Y.; Park, H.; Yu, Y.; Yoo, H.; Yoo, S. Pilot-scale Study of Horizontal Anaerobic Digester for Biogas Production using Food Waste. World Acad. Sci. Eng. Technol. 2011, 59, 2531–2534.
  26. Koch, K.; Hafner, S.D.; Weinrich, S.; Astals, S.; Holliger, C. Power and Limitations of Biochemical Methane Potential (BMP) Tests. Front. Energy Res. 2020, 8, 63.
  27. Filer, J.; Ding, H.H.; Chang, S. Biochemical Methane Potential (BMP) Assay Method for Anaerobic Digestion Research. Water 2019, 11, 921.
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Subjects: Environmental Sciences
Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register :
Yongwoon Park
,
Jeehyeong Khim
,
Jong Doo Kim
View Times: 276
Entry Collection: Wastewater Treatment
Revisions: 2 times (View History)
Update Date: 27 Oct 2023
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