There are three big families of biological additives for biogas: micronutrients or trace elements (Ni, Co, Fe, Se, Mo), enzymes and bioaugmentation (adding microorganisms). A fourth, more recent route is added to them: conductive nanoparticles. They are not magic solutions, but they are not smoke either: each one solves a specific problem and only helps if that problem exists. Micronutrients have the most solid evidence (especially cobalt in maize mono-digestion); enzymes help with fibrous substrates; bioaugmentation gives uneven results; and conductive nanoparticles (such as Smallops OPS) do not add microorganisms, but multiply the efficiency of the ones you already have by enhancing DIET, and are compatible with the previous ones. The key is diagnosis: they are complementary to good operation, never a substitute for it.
When a digester underperforms, the temptation of the additive always appears: a product that, added to the reactor, promises more methane or more stability. The market is full of them, and not all of them deliver.
But dismissing them wholesale is as simplistic as believing they fix everything. Some biological additives do work, in the right problem and with judgement. No additive is by itself the philosopher’s stone, but together they can help to improve production considerably.
This article separates the wheat from the chaff among the three families (micronutrients, enzymes and bioaugmentation) —and, more recently, conductive nanoparticles—: what each one does, when it helps and when it doesn’t. It is the natural continuation of additives for biogas (the myth of the magic solution).
The types of biological additives (and an emerging fourth route)
It is worth not putting them all in the same bag. They are different things, with different mechanisms and evidence:
- Micronutrients or trace elements: trace metals that microbial enzymes need as cofactors (Ni, Co, Fe, Se, Mo).
- Enzymes: catalysts that accelerate a specific phase, above all hydrolysis.
- Bioaugmentation: adding living microorganisms (bacteria or archaea) to reinforce a function of the consortium.
- Conductive materials and nanoparticles: catalysts (biochar, magnetite, iron nanoparticles) that enhance electron transfer (DIET) and multiply the efficiency of the existing consortium, without adding new organisms.
Micronutrients and trace elements (Ni, Co, Fe): when they are lacking
Trace elements are the family with the most solid evidence regarding its effect. The methanogenic archaea need them as cofactors of their enzymes: without enough cobalt, nickel or iron, their activity drops even if there is plenty of substrate. Although some in excess are toxic, such as Ni.
The classic case is the mono-digestion of energy crops (maize), poor in trace elements: it is where supplementation most clearly works. On the other hand, a plant that co-digests slurry and varied waste usually has the micronutrients covered, and adding them changes nothing.
The lesson: micronutrients help when they are lacking, and that is only known through analysis. Balanced co-digestion is, in fact, the cheapest way to provide them.
Enzymes: help for hydrolysis
Enzymes (cellulases, proteases, lipases) act above all on hydrolysis, the phase that breaks down macromolecules. They make sense when that phase is the bottleneck: fibrous or lignocellulosic substrates (straw, solid manure, plant residues) that are digested poorly.
The evidence is more uneven than with trace elements: some tests show clear improvements, others none, and the cost of the enzyme can eat up the benefit. In already easily degradable substrates (fats, sugars), where hydrolysis does not limit, adding enzymes is of no use.
Bioaugmentation: adding microorganisms
Bioaugmentation consists of inoculating selected microorganisms to reinforce a specific function: degrading a toxic, tolerating more ammonia or accelerating start-up. It is the family with the most uneven evidence.
The problem is competition: the added microorganisms must establish themselves in an already occupied ecosystem, and often they do not manage to. It works better in specific situations (reactor start-up, recovery after a failure, adaptation to a very specific substrate) than as a routine supplement. To understand why, it helps to know the microbiology of the digester.
Conductive nanoparticles: boosting the microorganisms you already have
To the previous routes a more recent one with a different approach is added: conductive materials (biochar, magnetite and, above all, nanoparticles). They do not add a microorganism or a missing nutrient: they act as catalysts that multiply the efficiency of the consortium already in the digester.
The mechanism is DIET (direct interspecies electron transfer). In classic syntrophy, bacteria and archaea exchange electrons through hydrogen, a slow and fragile process. A conductive material allows that exchange to be direct, cell to cell: faster, more stable and less sensitive to disturbances.
This is where Smallops OPS nanoparticles fit: iron encapsulated in carbon. The difference with bioaugmentation is fundamental. Microbial additives try to compensate for a biological deficiency by adding new strains; OPS do not add organisms, but multiply the performance of the ones you already have, like a smart catalyst. In addition, the iron provides the micronutrient effect (cofactor of the methanogens) and the carbon matrix the conductive effect: two mechanisms in synergy within a single material.
Its great practical advantage is compatibility: conductive nanoparticles are fully compatible with the rest of the routes (trace elements, enzymes, bioaugmentation) and with a well-designed diet. They do not compete with them, they enhance them. In a real case of a 170 t/day plant with grid injection, this technology raised methane by 19 %, reduced H₂S from 200 to 5 ppm (−98 %) and allowed the fraction of olive cake in the diet to be increased, with more than 2,500 hours of stable operation.
When YES and when NO: the criterion
The right question is not «does this additive work?», but «does my digester have the problem this additive solves?». With that approach:
- It does make sense to consider trace elements in poor mono-digestion, enzymes in very fibrous substrates, bioaugmentation in a start-up or a recovery, or conductive nanoparticles to enhance DIET and gain methane and stability over the existing consortium.
- It does not make sense to add anything «just in case», without analysis, or to cover up an operational problem (a badly calculated OLR, poor control).
An additive never corrects poor operation; at best, it optimises good operation. That is the difference between spending and investing, as explained in the additives decision protocol.
Complementary, not substitutes for good operation
The central idea is this: biological additives are complementary. On a well-designed and well-operated process, a missing micronutrient or an enzyme in the right substrate, or some conductive nanoparticles, can add a real margin of production.
But on an overloaded, poorly fed or unstable digester, no additive works miracles: first you fix the operation, and only then do you assess whether a complement adds anything.
Frequently asked questions about biological additives in biogas
Do micronutrients improve biogas production?
Yes, but only when they are lacking. The methanogenic archaea need trace elements (nickel, cobalt, iron, selenium, molybdenum) as enzymatic cofactors; if the substrate is poor in them (typically maize mono-digestion), supplementing them clearly improves performance. In a plant that co-digests slurry and varied waste, the micronutrients are usually covered and adding them adds nothing. Only an analysis tells you if there is a deficiency.
Are enzymes useful for biogas?
They make sense when hydrolysis is the bottleneck, that is, in fibrous or lignocellulosic substrates (straw, solid manure) that are digested poorly. In those cases, cellulases or proteases can accelerate degradation. In easily degradable substrates (fats, sugars), where hydrolysis does not limit, they add nothing. The evidence is uneven and you have to assess whether the benefit compensates for the cost.
What is bioaugmentation in anaerobic digestion?
It is adding selected microorganisms (bacteria or archaea) to the digester to reinforce a specific function: degrading a toxic, tolerating more ammonia or accelerating start-up. Its effectiveness is uneven, because the added microorganisms must compete and establish themselves in an already-established ecosystem. It works better in start-ups or recoveries than as a routine supplement.
What are conductive nanoparticles and how do they differ from bioaugmentation?
They are materials, such as iron nanoparticles encapsulated in carbon (the Smallops OPS), that facilitate direct interspecies electron transfer (DIET) between the bacteria and the archaea of the digester. The difference with bioaugmentation is key: microbial additives add new microorganisms to compensate for a deficiency; conductive nanoparticles do not add organisms, but multiply the efficiency of the ones already there, like a catalyst. In addition, they are compatible with the other routes (trace elements, enzymes, diet), which they enhance, and translate into more methane, less H₂S and a more stable process.
Is it worth using additives in biogas?
It depends on whether your digester has the problem the additive solves. A missing trace element, an enzyme in a fibrous substrate, a bioaugmentation in a start-up or some conductive nanoparticles to boost the consortium can help. But adding additives «just in case», without diagnosis, or to cover up poor operation, is throwing money away. They are complementary to good operation, never a substitute: first you fix the process and then you assess the complement.
Smallops and judgement on additives
Before spending on an additive, it is worth knowing whether your digester really needs it and whether it will improve performance. At Smallops we analyse your process and your substrates to tell you which complement really adds value (and which does not) —including our OPS nanoparticles, iron encapsulated in carbon— with an Operational Excellence Diagnosis.
Does your digester really need an additive?
Request a Smallops Operational Excellence Diagnosis: we analyse your substrates and your process to know whether you are missing a micronutrient, whether an enzyme helps, whether OPS nanoparticles would boost your consortium or whether the problem is operational, before you spend on consumables.
References and standards
Schmidt, T. et al. (2014). Trace element supplementation in the biogas process. Bioresource Technology, 168, 20-27.
Romero-Güiza, M.S. et al. (2016). The role of additives on anaerobic digestion: a review. Renewable and Sustainable Energy Reviews, 58, 1486-1499. → doi.org/10.1016/j.rser.2015.12.094
Liu, F. et al. (2012). Promoting direct interspecies electron transfer with activated carbon. Energy & Environmental Science, 5 (10), 8982-8989. → doi.org/10.1039/C2EE22459C
Nkuna, R. et al. (2022). Insights into the role of bioaugmentation in anaerobic digestion. Fermentation, 8 (12), 707. → doi.org/10.3390/fermentation8120707
Choong, Y.Y. et al. (2016). Impacts of trace element supplementation on anaerobic digestion. Bioresource Technology, 209, 369-379.