AD MICROBIOLOGY 101 - Part I
Anaerobic digestion (AD) facilities consist of a complex arrangement of piping, electrical and mechanical systems. When you take all this equipment into consideration, in addition to the daily tasks of receiving feedstock and managing finished digestate, its easy to understand why the smallest part of the system, the bacteria, might get overlooked. Read on to understand how getting to know this microscopic component of AD may be the best way to guarantee success in biogas production.
The ultimate measure of a successful anaerobic digestion (AD) facility is the gas yield. The goal is for a high and consistent gas yield, but in reality, many operating facilities find this difficult to achieve. Since an AD facility integrates so many different components, getting to the root of the problem can be intimidating. Generally speaking though, large swings in production are often an indication of mechanical issues such as mixing failures, crust layers, clogged sensors, or problems relating to the CHP or gas clean-up. Biological problems, in contrast, do not show up overnight but tend to occur as small and steady daily decreases in gas production. Understanding how the bacteria in an AD system works can help facility owners and operators stay ahead of gas production problems and consistently produce high yields.
Electron micrograph of methanogenic bacteria.
Anaerobic digestion (AD) is a natural process where bacteria break down organic materials and produce methane (CH4). The key groups of bacteria that are active in the digestion process are acetate-forming, sulphur-reducing, and methane-forming. These bacteria break down organic materials into substrates using enzymes. The three main groups of substrates are:
carbohydrates
fats
proteins
and the two types of enzymes used to break them down are:
endo-enzymes
exo-enzymes.
High gas-yielding feedstocks contain high percentages of these three substrates, but enzymes and coenzymes are needed by bacteria to perform digestion and thus play a vital role in the AD process.
Micronutrients, also known as trace elements, keep the bacteria healthy and able to produce all the enzymes necessary for digestion. Just as the human digestive system requires varied nutrition to maintain bacterial diversity and promote good health, micronutrients help to support diversity and balance in the AD bacterial community. This leads to higher and more consistent methane production.
To determine whether your system needs supplemental feeding, two critical steps are involved.
Feedstock Analysis
Digestate Analysis
These inexpensive analyses are completed to rule out nutrient deficiencies and toxicity problems as well as to determine what micronutrients are already present. An experienced operations consultant like Fitec can use this information to create customized feeding solutions that will lead to an optimal environment for AD bacteria and optimized biological performance.
Feedstock and digestate analysis are necessary because each AD system is unique and has different requirements. Supplemental feeding programs are a simple and cost-effective way to ensure that the biological requirements of the system are met.
Biogas systems are quite complex and there are many points at which errors can accumulate. Keeping attuned to what is happening inside the digester is an important way to ensure successful operations. Fitec has over 20 years of experience in AD operations, with staff specializing in biological analysis. Contact us today to learn more about our custom trace element program and stay tuned for AD Microbiology – Part II to learn about other tools and resources for understanding your biological system and improving gas yields.
