Biogas plant monitoring plays an important role in understanding biogas plant operations. It acts as a guideline for successful plant start-ups, restarts, and ongoing operations. Monitoring provides valuable insights into the operation of a biogas plant, helps in maintaining a stable process, mitigating the risks associated with inhibition or potential plant crashes.
One of the main benefits of continuous monitoring is gaining the ability to make timely and informed decisions. Biogas operations are complex and accidents can have costly consequences. Real-time monitoring enables you to identify and track changes that could serve as an early warning indicator for impending instabilities. Here are 5 common reasons for process instability that can be detected through continuous real-time monitoring.
Sudden changes in feedstock composition and nutrients can disrupt the microbial community and lead to process imbalances. If the feedstock supply changes, it can cause large variations in the recipe used in the biogas plant. This can increase the variability of the gas production rate and even lead to a decrease in biogas production. This highlights the potential direct impact of feed changes on process stability and biogas yield. Moreover, the mixture of different feedstock should be selected in a way that the carbon to nitrogen (C/N) ratio stays near the optimal range between 20 to 30 and possibly closer to 25.
Usually, the higher the organic loading rate a system can effectively treat, the better the cost-effectiveness of the process. However, exceeding the digester’s capacity to degrade organic matter can cause an accumulation of volatile fatty acids (VFAs) and other inhibitory compounds, leading to process instability. An organic overload occurs when the amount of organic matter fed to the biogas plant exceeds the total degradation capacity of the microbial community to produce biogas. This imbalance in the degradation process results in incomplete degradation, with the organic matter being partially converted to VFAs, which then accumulate in the reactor. For example, the typical range organic loading for continuous stirred tank reactor (CSTR) digesters is 1-4 kg VS/m3/day depending on the design of the digester, operational parameters and type of feedstock.
Maintaining stable process temperatures is crucial for the optimal performance of microbial activity and biogas production in biogas plants. Fluctuations in temperature may happen and they can significantly impact the composition and activity of the microbial community, therefore affecting the overall efficiency of the biogas process. For example, in thermophilic biogas processes, it is recommended to keep daily temperature variations at a minimum and even below 0.5°C, while for mesophilic processes, temperature variations less than 1°C are acceptable after the process is stable.
Ammonia inhibition is a common challenge in biogas operations, as high levels of ammonia can negatively impact the microbial population responsible for biogas production. Ammonia is released during the degradation of nitrogen-rich organic materials, such as animal manure and protein-rich feedstocks. Real-time monitoring of ammonia levels is crucial for early detection and intervention to mitigate ammonia inhibition. By continuously monitoring ammonia concentrations, operators can implement timely actions to maintain optimal conditions for microbial activity and biogas production. The specific range for ammonia concentration depends upon feedstock type, digester type and operational condition but typically ammonia inhibition can start at the concentration of 1.5 to 3 g NH4-N/L. Higher concentration of ammonia can increase the pH, cause inhibition in the methanogenesis step and eventually lead to process imbalance. Proper feedstock management mentioned above and adjusting the C/N ratio are key strategies to ensure an optimal process.
The presence of inhibitory substances in any feedstock poses a significant challenge to the anaerobic digestion process. These substances, which can include heavy metals, antibiotics, pesticides, and other toxic chemicals, have the potential to inhibit microbial activity and disrupt the overall efficiency of biogas production. Even at low concentrations, the heavy metals can inhibit the activity of microorganisms, leading to reduced biogas production and process instability. For example, inhibitory concentrations for lead and cadmium can start from 67 and 36 mg/L, respectively.
anessa specializes in developing software solutions for the biogas industry, encompassing different stages in a project’s lifetime from the initial evaluation to proactive operational feedstock planning and real-time monitoring. Our primary objective is to facilitate your growth by making each stage of the project lifetime approachable, easier to communicate, and manageable to report on. Our online solutions provide secure and robust simulations & dynamically visualized dashboards, empowering operators, developers, off-takers, and other entities within the biogas market to explore their potential with confidence.
We’d like to give a special thank to Dr. Farough Motasemi, Ph.D., CTO at anessa, and Dr. Farid Sayedin, Ph.D. Senior Process Manager at anessa, who wrote this article.
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