How to Increase Biogas Production: 8 Practical Ways to Improve Digester Yield

Learning how to increase biogas production is not simply a matter of feeding more organic material into an anaerobic digester. Sustainable improvement comes from stabilising the biological process, selecting compatible feedstocks, maintaining effective mixing and using operating data to identify the true cause of lost methane yield.

This updated guide explains eight practical areas that anaerobic digestion plant operators should examine when biogas output is below expectations.

Anaerobic digestion relies on a complex community of microorganisms. These organisms break down biodegradable material through hydrolysis, acidogenesis, acetogenesis and methanogenesis.

Each stage depends on the preceding stages operating in reasonable balance. A change that accelerates acid production without allowing the methanogens to respond may reduce biogas production rather than increase it.

That is why there is no universal additive, mixer setting, feedstock or pretreatment method that will increase gas yield at every plant.

The correct approach is to establish a reliable operating baseline, identify the limiting factor and introduce controlled changes while monitoring the biological response.

Key Takeaways

Stability comes first. A stable digester normally offers a better foundation for optimisation than one being pushed close to biological failure.
More feed does not necessarily mean more gas. Excessive organic loading can cause volatile fatty acid accumulation and falling methane production.
Feed consistency matters. Sudden changes in feedstock composition can destabilise the microbial population.
Mixing must be effective, not merely intensive. Too little mixing creates dead zones, but excessive mixing can waste energy and may disrupt microbial associations.
Co-digestion can increase methane yield. However, the outcome depends on the feedstock mixture, loading rate, nutrient balance and presence of inhibitors.
Pretreatment must deliver a net benefit. Extra gas production should exceed the energy, maintenance and capital cost of the treatment process.
Monitoring should guide decisions. Gas flow alone usually does not reveal why production has changed.
Measure net exportable energy. A higher gross biogas yield has limited value if pumps, mixers, heating and pretreatment consume the gain.

First Establish What “Increasing Biogas Production” Means

Before modifying the process, decide which result is actually required.

The objective could be to:

increase total daily biogas volume;
increase methane concentration;
produce more methane per tonne of feedstock;
raise digester throughput without losing stability;
reduce unplanned downtime;
lower the digester’s internal energy demand;
or increase the amount of electricity, heat or biomethane available for sale.

These objectives are related, but they are not identical.

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For example, adding a wet, readily digestible feedstock may increase total gas production while reducing gas yield per tonne of material handled. Increasing mixing intensity might improve contact between microorganisms and substrate, but the additional electricity demand could reduce net exportable energy.

A meaningful optimisation programme should therefore track methane production and net useful energy, not just raw biogas volume.

1. Stabilise Feeding and Organic Loading

Consistent feeding is one of the most important requirements for stable anaerobic digestion.

Methanogenic microorganisms grow relatively slowly. They cannot always accommodate sudden increases in readily degradable organic material. If acid-forming organisms produce volatile fatty acids faster than the methanogens can convert them, alkalinity may be consumed and pH may eventually fall.

Even before a large pH change becomes visible, the plant may experience:

rising volatile fatty acid concentrations;
a worsening VFA-to-alkalinity or FOS/TAC ratio;
falling methane percentage;
increased carbon dioxide;
foaming;
odour changes;
and declining specific methane yield.

Practical actions

Feed smaller quantities at regular intervals rather than creating large shock loads.
Measure feedstock mass or volume rather than relying on loader-bucket estimates.
Track total solids, volatile solids and chemical oxygen demand where appropriate.
Calculate the organic loading rate rather than monitoring only daily tonnage.
Introduce new feedstocks gradually.
Do not raise loading merely because unused hydraulic capacity appears to exist.
Review hydraulic and solids retention times before increasing throughput.

A gradual loading increase supported by biological monitoring is normally safer than a large step change.

2. Improve Feedstock Selection and Consistency

Different feedstocks have very different biochemical methane potentials. Fats, oils and some food-processing residues can produce substantially more methane per kilogram of volatile solids than cattle slurry or dilute wastewater.

However, the material with the highest theoretical methane yield is not necessarily the best feedstock for a particular plant.

Operators must also consider:

moisture and total solids content;
the proportion of readily degradable material;
carbon-to-nitrogen balance;
sulphur content;
ammonia formation;
salinity;
trace elements;
packaging and physical contaminants;
pumping and mixing characteristics;
seasonal variation;
pasteurisation requirements;
digestate quality;
and the security and cost of supply.

A high-energy feedstock can cause acidification if it is added too quickly. Protein-rich materials may contribute to ammonia inhibition. Sulphur-rich materials can increase hydrogen sulphide production and gas-cleaning costs.

Create a feedstock acceptance procedure

Each incoming material should be characterised before routine acceptance. The procedure may include:

supplier information and provenance;
visual inspection;
pH;
dry matter and volatile solids;
chemical oxygen demand;
biochemical methane potential testing;
nitrogen and ammonia;
sulphur;
contamination levels;
and a controlled full-scale introduction plan.

Regular testing is particularly important where food manufacturing residues vary with production schedules or product changes.

3. Optimise Mixing Without Over-Mixing

Effective mixing helps distribute fresh feed, microorganisms, heat and alkalinity throughout a wet anaerobic digester.

It can also reduce:

settled solids;
floating layers;
temperature gradients;
localised overloading;
short-circuiting;
and inactive zones within the tank.

However, the presence of operating mixers does not prove that the effective digester volume is being mixed adequately.

Worn impellers, incorrect mixer angles, excessive viscosity, fibrous material and changes in feedstock rheology can all reduce performance.

Questions to investigate

Are solids accumulating on the tank floor?
Is a floating crust developing?
Are there significant temperature differences between sampling points?
Has the feedstock become more viscous since the plant was designed?
Are mixer current readings changing?
Is gas production affected when mixer operating periods change?
Are all mixers contributing effectively, or is one unit doing most of the work?

Continuous maximum-power mixing is not automatically optimal. Intermittent mixing may provide adequate homogenisation at lower energy cost in some systems.

Any trial should be controlled carefully. Mixer run times, electrical consumption, gas production, solids behaviour and biological indicators should be recorded before and after each change.

Safety warning: Digester mixing equipment must never be inspected or adjusted without following the plant’s isolation, confined-space, explosive-atmosphere and gas-safety procedures. Anaerobic digesters can contain methane, hydrogen sulphide and oxygen-deficient atmospheres.

4. Use Co-Digestion to Improve Feed Balance

Co-digestion means digesting two or more feedstocks together.

It can improve methane yield where the materials complement one another. For example, a carbon-rich crop residue may balance a nitrogen-rich manure, while a readily degradable food residue may increase the energy content of a dilute slurry.

Research reviews generally find that well-designed co-digestion can improve nutrient balance, dilute inhibitors and raise methane production compared with mono-digestion of some low-yield substrates.

But synergy should never be assumed. The result depends on:

the feedstock ratio;
organic loading rate;
retention time;
temperature;
ammonia and sulphur concentrations;
trace nutrient availability;
mixing;
and the acclimatisation of the microbial community.

A safe co-digestion approach

Obtain representative samples of the proposed feedstock.
Check its physical and chemical characteristics.
Conduct biochemical methane potential or laboratory digestion tests where the risk justifies them.
Assess permit, animal by-product and digestate-quality implications.
Introduce the material at a low proportion.
Hold the loading steady while monitoring the response.
Increase the proportion only when stable performance has been demonstrated.

A feedstock that produces more gas may still be commercially unattractive if it creates depackaging costs, grit accumulation, foaming, digestate contamination or a large increase in transport movements.

Need a More Detailed Guide to Biogas Optimisation?

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It covers feedstock selection, methane potential, carbon-to-nitrogen balance, pretreatment, digester configurations, co-digestion, process monitoring and biogas upgrading.

See What Is Included in the Practical Guide

5. Consider Pretreatment Where Hydrolysis Is Limiting

Pretreatment aims to make organic material more accessible to the microorganisms responsible for digestion.

Methods include:

screening and contaminant removal;
chopping or maceration;
extrusion;
thermal hydrolysis;
steam explosion;
ultrasonic treatment;
chemical treatment;
enzymatic treatment;
and biological pre-acidification.

Particle-size reduction can increase surface area and may accelerate hydrolysis for fibrous or structurally resistant materials. It may also improve pumping and reduce floating layers.

But reducing particle size does not always increase methane yield. The benefit depends on the substrate and whether particle size is actually the rate-limiting factor.

Over-processing can create disadvantages:

high electrical demand;
accelerated equipment wear;
greater grit and contaminant fragmentation;
microplastic formation from packaged food waste;
rapid acid release;
and increased maintenance costs.

Assess net energy, not gross gas gain

A pretreatment system is worthwhile only when the value of additional useful energy and operational benefits exceeds:

capital repayment;
electricity or heat consumption;
maintenance;
replacement parts;
labour;
and any additional digestate or reject-management costs.

Trials using representative material are preferable to relying solely on supplier claims.

6. Maintain Stable Temperature and Retention Time

Methanogens are sensitive to sudden temperature changes.

Mesophilic digesters commonly operate around the mid-30s °C, while thermophilic plants operate at higher temperatures. The correct operating point depends on the process design, feedstock and required treatment standard.

Consistency is usually more important than chasing a nominally ideal temperature.

Temperature instability can arise from:

cold feed additions;
failed heating equipment;
poor heat-exchanger performance;
inadequate insulation;
temperature-sensor error;
stratification caused by poor mixing;
and rapid seasonal changes in feedstock temperature.

Retention time must also be sufficient for the material being treated. Increasing throughput reduces hydraulic retention time unless additional digestion volume is provided.

Where slowly degradable solids leave the digester before sufficient conversion has occurred, methane potential is transferred into the digestate rather than captured in the gas system.

Operators should examine:

hydraulic retention time;
solids retention time;
volatile solids destruction;
residual methane potential;
and the performance of any secondary digester or covered digestate store.

7. Improve Process Monitoring and Respond Earlier

Daily gas volume is an important performance indicator, but it is a delayed and incomplete measure of digester health.

A useful monitoring programme may include:

feedstock mass and composition;
organic loading rate;
digester temperature;
pH;
alkalinity;
volatile fatty acids;
VFA-to-alkalinity or FOS/TAC ratio;
total ammonia nitrogen and free ammonia;
total and volatile solids;
biogas flow;
methane and carbon dioxide concentration;
hydrogen sulphide;
mixer and pump electrical demand;
foam and crust observations;
and digestate residual gas potential where appropriate.

The value lies not only in individual test results but in trends.

A single pH value may appear normal because the digester has sufficient buffering capacity, even while volatile fatty acids are accumulating. Combining gas composition, alkalinity and VFA trends can provide earlier warning.

Use a consistent operating dashboard

Record key variables at consistent intervals and compare them against:

the plant’s established stable baseline;
the previous week and month;
feedstock changes;
maintenance events;
and changes in mixer, pump or heating operation.

This makes it easier to distinguish biological deterioration from a faulty gas meter, blocked pipe, condensate problem or mechanical failure.

8. Identify and Control Biological Inhibition

Anaerobic digestion can be inhibited by compounds naturally released from feedstocks or introduced with incoming material.

Common concerns include:

free ammonia;
hydrogen sulphide and sulphide;
salts;
long-chain fatty acids;
cleaning chemicals;
antibiotics and disinfectants;
heavy metals;
and sudden high concentrations of volatile fatty acids.

The effect depends on concentration, pH, temperature, exposure time and the microbial community’s previous acclimatisation.

For example, the proportion of total ammonia present as more inhibitory free ammonia increases with pH and temperature. A thermophilic digester may therefore respond differently from a mesophilic plant receiving the same nitrogen loading.

Correct the cause, not only the symptom

Possible responses include:

reducing or temporarily stopping the problematic feedstock;
lowering the organic loading rate;
diluting a concentrated inhibitory material;
improving feedstock blending;
correcting trace-element deficiency only after appropriate analysis;
allowing time for microbial acclimatisation;
and obtaining specialist biological advice where instability is severe.

Additives should not be used as a substitute for identifying the underlying problem.

Enzymes, trace elements, adsorbents and microbial products may provide benefits under particular conditions, but their effects should be tested against a baseline and assessed after accounting for their continuing cost.

Do Not Ignore Mechanical and Gas-System Losses

A fall in recorded biogas output is not always caused by the biological process.

Before changing feed or adding chemicals, inspect the mechanical and gas-handling system for:

gas leaks;
failed or inaccurate flow meters;
condensate blockage;
pressure-control problems;
relief-valve releases;
flare operation;
leaking digester roofs or membrane holders;
blocked gas-cleaning media;
pump wear;
mixer failure;
and heat-exchanger fouling.

Gas leaks reduce revenue and can create serious fire, explosion, asphyxiation and climate risks. Inspection and leak detection must be carried out using appropriate equipment and safe systems of work.

Measure Specific Methane Yield and Net Energy

Operators should avoid judging performance solely by daily cubic metres of biogas.

Useful performance measures include:

cubic metres of methane per tonne of fresh feed;
cubic metres of methane per kilogram of volatile solids added;
volatile solids destruction;
plant availability;
combined heat and power electrical efficiency;
biomethane recovery;
methane slip;
and net exported energy after parasitic demand.

An apparent improvement in gas production may disappear when adjusted for:

increased feed quantity;
a more energy-rich feedstock;
lower methane concentration;
additional mixer power;
pretreatment electricity;
digester heating;
or greater upgrading losses.

Good optimisation is evidence-led. Establish the baseline, change one principal variable at a time where practicable, allow sufficient time for the biological response and compare the net result rather than relying on a short-lived increase in raw gas flow.

A Practical Biogas Optimisation Sequence

For an operating plant with disappointing output, the following sequence can help prevent random and potentially harmful interventions:

Confirm the measurement. Check gas meters, methane analysers, pressure, condensate removal and calibration.
Review mechanical availability. Confirm that pumps, mixers, heating systems and gas-cleaning equipment are operating correctly.
Establish the feed balance. Verify actual feed quantities, solids, volatile solids and recent compositional changes.
Review loading and retention time. Calculate organic loading rather than relying on nominal daily tonnage.
Examine biological trends. Review pH, alkalinity, volatile fatty acids, ammonia, gas composition and temperature.
Identify the likely limiting factor. Avoid treating several possible causes simultaneously.
Plan a controlled intervention. Define the proposed change, expected response, monitoring period and stop criteria.
Measure net benefit. Include energy use, downtime, chemicals, maintenance and feedstock costs.
Document the result. Retain successful settings and lessons in the site operating procedures.

How Much Can Biogas Production Be Increased?

There is no responsible universal percentage.

The potential improvement depends on how far the plant currently operates below its practical capability.

A well-designed, well-fed and closely controlled plant may have little scope for additional methane yield without capital modification. A poorly mixed or unstable plant may offer substantially more opportunity.

Results reported in laboratory studies should not be transferred directly to commercial plants. Laboratory reactors often use:

selected and prepared feedstocks;
small controlled batches;
stable temperatures;
long test periods;
and conditions that do not include full-scale pumping, contamination, downtime or parasitic energy demand.

For this reason, the best optimisation target is usually a reliable improvement against the plant’s own measured baseline.

Take the Next Step

Efficient Biogas Production Techniques & Methods is a concise 36-page PDF for operators, farmers, developers, engineers, consultants and students who want the principal optimisation factors collected in one place.

The guide expands on feedstock methane potential, carbon-to-nitrogen balance, pretreatment, digester design, co-digestion, monitoring and biogas upgrading.

See What Is Included in the Practical Guide

Frequently Asked Questions

What is the quickest way to increase biogas production?

There is no universally safe shortcut. Begin by checking gas measurement, mechanical equipment, feed consistency, organic loading and process-monitoring trends. Correcting an identifiable fault can produce a faster and more reliable result than adding a new feedstock or additive.

Does adding more feedstock always produce more biogas?

No. Additional feed can increase production only while the digester retains sufficient biological, hydraulic, mixing and heating capacity. Overloading may cause volatile fatty acid accumulation, falling methane concentration and process failure.

Can mixing increase methane yield?

Effective mixing can improve contact between substrate and microorganisms, distribute heat and reduce dead zones. However, excessive mixing can consume unnecessary energy and may not increase methane yield. Mixer operation should be optimised for the specific digester and feed rheology.

Does smaller feedstock particle size always produce more gas?

No. Particle-size reduction can help where hydrolysis of fibrous or structurally resistant material is limiting. Some studies have found little or no methane-yield improvement for particular substrates. Energy demand, equipment wear and contaminant fragmentation must also be considered.

What is the best carbon-to-nitrogen ratio for anaerobic digestion?

Published optimum ranges vary because feedstocks, reactor types and operating conditions differ. Carbon-to-nitrogen ratio should not be used as the only feed-selection criterion. Ammonia, sulphur, trace nutrients, degradability and loading rate are also important.

Can co-digestion increase biogas yield?

Yes. Compatible co-substrates may improve nutrient balance, dilute inhibitors and add readily degradable organic matter. The feedstocks must be tested and introduced gradually because some combinations can destabilise the process.

Which parameters should a biogas plant monitor?

Typical parameters include feed quantity and composition, organic loading rate, temperature, pH, alkalinity, volatile fatty acids, ammonia, solids, gas flow, methane concentration, hydrogen sulphide and plant energy use. The appropriate programme depends on plant design and feedstock.

How long does it take to see an improvement?

Mechanical corrections may affect recorded gas output immediately. Biological responses may take days or weeks, depending on retention time, feedstock and the nature of the change. Stable trends are more meaningful than a brief increase.

See What Is Included in the Practical Guide

Conclusion

Increasing biogas production requires more than selecting one promising technology or adding a high-energy feedstock.

The most reliable improvements normally come from combining:

consistent feeding;
appropriate organic loading;
compatible feedstocks;
effective mixing;
stable temperature;
sufficient retention time;
early detection of inhibition;
and disciplined process monitoring.

Optimisation should begin with a measured baseline and a clear definition of success. Changes should then be introduced methodically, with the result assessed in terms of specific methane yield, process stability and net exportable energy.

This approach may be less dramatic than claims of instant or universal yield increases, but it is far more likely to produce a safe, repeatable and commercially worthwhile improvement.

Sources and Further Reading

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Important: This article provides general educational information. Anaerobic digesters involve biological, mechanical, electrical, chemical, confined-space, fire and explosion hazards. Plant changes should be assessed and implemented by suitably qualified personnel in accordance with the site’s permits, operating procedures, equipment instructions and applicable safety requirements.

[Published in 2019. Rewritten June 2026.]

Comments

- Ahmed
- January 13, 2020
Awesome article. Loughborough Uni has made a breakthrough with a concept of centralized monitoring of decentralised biogas generation has been achieved, where monitoring is enabled in real time. Soon these little biogas generators will be making much more biogas.
- The FindleGook
- January 23, 2020
Such useful Post! Did you ever hear about steam explosion pre-treatment? You hold the biomass at a high temperature for a period of time, and then suddenly drop the pressure. It’s like a steam explosion and the cellular structures get well and truly busted open! Suggest adding it here.