|Biogas Plants in Animal Husbandry (GTZ, 1989)|
|5. Biogas technique|
The purpose of conducting measurements on a biogas plant is to enable timely detection of developing problems, adjustment to optimum operating conditions, and gathering of practical 'data for comparison with those of other plants. The following variables can be measured quickly and easily:
- gas production via dry gas meter or by measuring the fill level
of the gasholder
- weight of inputs via a hand-held spring scale
- temperature via an ordinary stem thermometer or electronic temperature sensor
- total-solids content by drying a sample at 104 °C and weighing the residue on a precision balance
- H2S content of the gases via a gas test tube
- pH via litmus paper.
The contents of the substrate/slurry can only be determined by a special laboratory.
Various levels of precision are recommended, depending on the set objective and corresponding time, effort and equipment expenditure.
Observation by the user
- measuring the gas consumption through daily checking of the calibration marks on the gasholder
- measuring the daily input quantities via defined-volume vessels
- measuring the air/slurry temperature with a thermometer.
Daily notation of measured values.
Daily gas production as a function of substrate input and temperature.
Field testing by the extension officer
- installation and daily reading of a dry gas meter to determine the rate of gas production
- random sampling of the CO2 and H2S contents of the biogas
- determination of quantities added by weighing the moist mass and water on a spring scale
- random sampling to determine the total solids content of the substrate
- measuring the digester temperature with the aid of a remote electronic thermometer
- measuring the ambient temperature with a mini-max thermometer
- determining pH levels via litmus paper
- laboratory testing to determine the C/Nratio, volatile solids content and manurial quality of digested slurry.
Daily entry of measured values in a log book.
Interpretation of results
- time history of daily gas production as a function of temperature and substrate input
- time history of specific gas yield (Gy = m³ gas/kg TS) and of specific gas production (m³ gas/m³ Vd) as a function of temperature
- time history of pH
- time history of maximum and minimum ambient temperatures, i.e. mean monthly and annual temperatures, plus extremes.