The engineering context
What the assignment needs to resolve
Low saleable CBG output can originate in feed quality, biological conversion, gas capture, upgrading availability or delivery constraints. A troubleshooting assignment begins by locating the loss within that chain. Increasing feed without establishing the cause can make a biological or mechanical constraint worse.
The investigation combines a time-aligned operating record with site observations and targeted sampling. Useful evidence includes feed quantity and solids, gas flow and composition, holder level, equipment run hours, alarm history and laboratory trends. Missing or unreliable measurements are treated as findings in their own right.
Locate the loss before choosing the intervention
| Observed pattern | Possible areas to investigate | Evidence needed |
|---|---|---|
| Less raw gas per day | Feed reduction, lower organic input or biological disruption | Feed records, TS/VS, temperature and laboratory trends |
| Raw gas stable, CBG lower | Methane fraction, recovery, analyser error or upgrading stoppage | Inlet/product/off-gas balance and matched operating periods |
| High holder level and more flaring | Restricted downstream capacity or unavailable gas demand | Upgrader/compressor stops, dispatch timing and storage profile |
| Higher electricity per kg | Lower output denominator, inefficiency or changed duty | Submeter data, actual run hours and equipment loading |
| Unstable slurry transfer | Rheology, obstructions, suction conditions or wear | Duty data, pressure readings and authorised inspection |
Altpreneur scope
How we approach the work
Establish the baseline
Reconcile weighing, gas measurement, operating hours, downtime, utilities and laboratory records. Check whether instrumentation and reporting are comparable.
Biological assessment
Review feed changes, loading, retention, temperature, alkalinity, VFA trends, inhibition risks and digestate observations with the operating team.
Mechanical and gas-train assessment
Examine receiving, mixing, pumping, upgrading, compressor capacity, gas losses and controls to identify bottlenecks and reliability problems.
Improvement programme
Prioritise corrective actions by safety, production effect, cost and feasibility. Define measurements that can show whether each change worked.
Decisions worth getting right
Use a defined baseline
Compare equivalent feed and operating periods. A trial after changing several conditions at once rarely isolates the value of one intervention.
Prioritise by safety and production consequence
Restore reliable measurement and remove immediate hazards before chasing small energy savings. Corrective work follows approved isolation and operating procedures.
Verify the effect
Each action should have an expected result, a measurement method and a review date. Retain changes only when their effect is supported by operating evidence.
Assignment outputs
What you receive
- Baseline and root-cause assessment
- Prioritised corrective-action plan
- Monitoring and trial protocol
- Performance-review report
To begin
Useful starting information
- Recent production, feed and laboratory logs
- Equipment details and breakdown records
- Current operating constraints and target performance
Scope and responsibility
Emergency response remains with the site's authorised personnel. Recovery time and achievable output depend on the plant condition and cannot be promised before diagnosis.
Common questions
Does low gas production always mean the digester is undersized?
No. Material quality, loading, inhibition, mixing, measurement errors, gas loss and downstream downtime can all contribute.
Should we add chemicals before testing?
A change should follow an identified cause and an approved procedure. Uncontrolled dosing may mask a symptom or worsen process instability.
Evidence & further reading
Source material
- IEA Bioenergy Task 37: Process monitoring in biogas plants
- US EPA AgSTAR: Anaerobic Digester/Biogas System Operator Guidebook
- IEA: Key issues affecting biogas and biomethane projects
Technical references inform the discussion. Final design, operating limits and policy eligibility depend on the project and applicable current documents.