The different methods for sludge disposal
April 23, 2026The different methods for sludge disposal
April 23, 2026Are Trace Element Deficiencies Quietly Costing You Biogas Yield?
Why Trace Elements Are Non-Negotiable for Methane Production
Anaerobic digestion is a multi-stage biological process. It is the final stage, methanogenesis, where microorganisms convert intermediates into methane, that is most sensitive to trace element deficiency and most directly responsible for biogas yield.
The microorganisms that produce methane are highly specialised and nutritionally demanding. Unlike the broader microbial community handling the earlier breakdown of organic matter, methane-producing organisms depend on specific trace elements to drive their core metabolic functions. Nickel, cobalt, and selenium are not optional. They are built into the enzymes these organisms rely on to do their job [1,2]. Without adequate supplies in a form they can use, methane production is throttled at the source, regardless of how much organic material is being fed into the system.
What makes this particularly difficult to catch is that the symptoms look like almost everything else. Inconsistent gas output, rising organic acids, and process instability are the same warning signs you would see from overloading, temperature swings, or inhibitory compounds [1]. Without specific testing, trace element deficiency can persist undetected for months, and the lost yield never announces itself.
Which Elements Most Commonly Limit Performance
Not all micronutrients carry equal risk of deficiency, and feedstock composition is the single biggest determinant of which elements are likely to be limiting. Plants running maize silage or energy crop mono-digestion are consistently the most vulnerable, as these feedstocks are inherently low in cobalt, nickel, and selenium [3,4]. Food waste systems present a similar challenge [5]. Manure-based systems are generally better buffered, but selenium can still fall short, particularly in regions where soils are naturally selenium-poor. The table below outlines the elements most relevant to anaerobic digestion, their biological role, deficiency indicators, and the feedstock scenarios where limitation is most likely.
| Element | Key biological role | Signs of deficiency | Risk | Most at-risk feedstocks |
| Nickel (Ni) | Core component of coenzyme F430; methyl-CoM reductase and hydrogenase function | H₂ accumulation, acetate build-up, declining CH₄ fraction | High | Maize silage, food waste, energy crop mono-digestion |
| Cobalt (Co) | Vitamin B12 synthesis; corrinoid enzymes for acetate and methanol conversion | Acetate accumulation, imbalanced microbial populations, reduced yield | High | Plant-based feedstocks, food waste, industrial organics |
| Selenium (Se) | Selenocysteine in formate dehydrogenase and hydrogenase; interspecies H₂ transfer | Formate accumulation, poor syntrophic activity, hydrogen imbalance | High | All systems in Se-deficient regions; plant-based mono-digestion |
| Iron (Fe) | Ferredoxins, cytochromes, hydrogenases; electron transfer across all digestion stages | Sluggish digestion, poor H₂ transfer, elevated H₂S | High | All systems — partially addressed by FeCl₃ dosing |
| Molybdenum (Mo) | Formate dehydrogenase (mesophilic systems); nitrogen cycling enzymes | Reduced nitrogen metabolism, slower microbial growth | Medium | Plant-based feedstocks; low-Mo agricultural regions |
| Tungsten (W) | Preferred cofactor for formate dehydrogenase in thermophilic archaea | Inefficient formate metabolism at elevated temperatures | Medium | Thermophilic digesters operating above 50°C |
| Zinc (Zn) | Enzyme cofactor across multiple digestion stages, including coenzyme M methyltransferase in methanogenesis and proteases in hydrolysis | Impaired hydrolysis, slower upstream digestion | Low-Med | Food waste; some industrial organic streams |
| Manganese (Mn) | Enzyme activation; oxidative stress management in microbial cells | Increased sensitivity to process disturbance; rarely a primary limiter | Low | Rarely limiting; most feedstocks provide adequate levels |
Nickel, cobalt, and selenium are the most universally limiting, particularly in plant-based and food waste systems [3,4,5]. Even when nominally present in the feedstock, nickel and cobalt are rapidly stripped from biological availability inside the digester by precipitation as insoluble metal sulphides. A system can appear adequately supplied on paper while the microbially available fraction of these elements is critically low, a distinction that feedstock analysis alone will not reveal.
Ferric Chloride as a Carrier for Micronutrient Dosing
Addressing trace element deficiency does not require a separate chemical programme. Ferric chloride, a widely used iron salt already dosed in most commercial biogas plants for hydrogen sulphide control, provides a ready-made vehicle for delivering the full micronutrient suite alongside its primary function. The acidic nature of FeCl₃ solutions keeps trace elements such as nickel, cobalt, and selenium in dissolved, bioavailable form, preventing them from precipitating in dosing lines before they reach the digester [5]. The result is a single dosing operation that delivers both H₂S control and micronutrient support simultaneously no additional tanks, no secondary pumps, no changes to existing infrastructure.
Dosing rates should be established through digestate analysis rather than generic targets, as requirements shift with feedstock composition and organic loading. Alkalinity should be monitored when adjusting FeCl₃ rates, as higher additions can affect pH buffering if not managed carefully.
Putting It into Practice
The starting point is always the same: test before you dose. A targeted digestate analysis measuring nickel, cobalt, selenium, and iron gives a clear picture of where deficiencies exist and at what level supplementation is needed. From there, dosing can be introduced gradually and adjusted based on performance response, methane yield, organic acid levels, and process stability are all reliable indicators of whether the microbial community is responding.
For many plants, the return is significant. Supplementation in deficient systems has consistently shown methane methane yield improvements ranging from 15–20% at full scale [6] to 23–39% in controlled studies [4,5], often with noticeable gains, often with noticeable gains in process stability within weeks, a meaningful outcome for a marginal addition to an existing chemical programme.
Our team at Aquasan is available to support third party digestate analysis, supplementation strategy through our dedicated biogas focused product line, and ongoing process optimisation for anaerobic digestion systems of all scales and feedstock types.
References
[1] Šafarič L, Shakeri Yekta S, Svensson BH, Schnürer A, Bastviken D, Björn A. (2020). Effect of Cobalt, Nickel, and Selenium/Tungsten Deficiency on Mesophilic Anaerobic Digestion of Chemically Defined Soluble Organic Compounds. Microorganisms, 8(4), 598. https://doi.org/10.3390/microorganisms8040598
[2] Thauer RK, Friedmann HC. (1990). Structure and function of the nickel porphinoid, coenzyme F430, and of its enzyme, methyl coenzyme M reductase. FEMS Microbiology Reviews, 7(3–4), 339–348. https://doi.org/10.1111/j.1574-6968.1990.tb04930.x
[3] Lebuhn M, Baur F, Munk B, Gronauer A. (2008). Biogas production from mono-digestion of maize silage — long-term process stability and requirements. Water Science & Technology, 58(8), 1645–1651. https://doi.org/10.2166/wst.2008.495
[4] Pobeheim H, Munk B, Johansson J, Guebitz GM. (2011). Impact of nickel and cobalt on biogas production and process stability during semi-continuous anaerobic fermentation of a model substrate for maize silage. Water Research, 45(2), 781–787. https://doi.org/10.1016/j.watres.2010.08.037
[5] Jiang Y, Dennehy C, Lawlor PG, Hu Z, McCarthy G, Gardiner GE, Zhan X. (2016). Enhanced Anaerobic Digestion of Food Waste by Supplementing Trace Elements: Role of Selenium (VI) and Iron (II). Frontiers in Environmental Science, 4, 8. https://doi.org/10.3389/fenvs.2016.00008
