Logical Waste offers a standard Bio Methane Potential assay which conforms to the Moller (2004) method using mesophilic digestate as inoculum. We could conform to the German VDI4360 method, however it is our experience that given the additional costs involved, the accuracy does not significantly differ from the Moller method.

Gas volume measurements are performed in simple liquid displacement modules, each fitted with a digital sensing mechanism allowing displacement of a specific volume of liquid to be recorded together with a timestamp. A single rig can assay 8 samples at once. Usually, one to two samples are inoculum (blind), therefor 6-7 samples can be performed every 20 – 40 days. Samples are usually done in duplicate or triplicate.

The rig can also be used to obtain methane concentration over time using a 2-step displacement arrangement and chemical absorption of CO2. It requires double the number of displacement modules, data acquisition and data handling.

The major advantage of the Logical Waste BMP assay is that gas flow measurement does not rely on human intervention, i.e. reading of displacement values from glass cylinders or syringes. The displacement modules (Proprietary GasCap modules) are individually calibrated and all values are normalised to NTP (Normal Temperature and Pressure). Mixing of samples is automated by a mechanism external to the sample flasks.

Logical Waste currently does not perform Total Nitrogen, Ammonia Nitrogen, Total Solids and Volatile Solids analysis. All samples received will be sent to an external laboratory in Cape Town for analysis prior to BMP assay start. We do however perform Alkalinity and Volatile Fatty Acid (VFA) analysis based on the 2-point FOS/TAC (Nordmann method) method used in the German biogas industry. Only initial and final digested samples may be analysed.

Logical Waste GasCap module

BMP sample provision procedure:

The following procedure to be adhered to for accurate, repeatable results:

    1. 2 litre sample to be sent fresh in tight sealing bottles (plastic)
      • A sample kit can be sent from Logical Waste for sample collection.
    2. Use insulating packaging to prevent pre-mature degradation (Samples may be frozen prior to courier).
    3. Courier samples overnight if possible.
    4. Samples received at the lab will immediately be dispatched to the external laboratory.
    5. Samples will be stored at < 4 °C until laboratory results are made available.
    6. Turnaround on a standard BMP assay is 40 consecutive days including lab analysis and reporting.

The report will contain as a minimum;

  1. Analysis result of feedstock samples
  2. CH4 flow in ml vs time graph for each sample
  3. Normalised CH4 potential in units of Nm3 CH4/kg VS
  4. CH4 content in units of vol % (If this option is selected)
  5. Kinetic constants (If this option is selected)
  6. Short summary of assay