Factors that Influence the Biochemical Methane Potential (BMP) Test : Steps towards the Standardisation of BMP Test

Sammanfattning: Anaerobic digestion (AD) has gained increasing attention nowadays as an approach for both waste treatment and renewable energy generation. Currently, many different types of materials can be used as feedstock for biogas production via AD process, but their biodegradability (based on methane yield, BDCH4) and potential to produce biogas might vary significantly, and these properties are key parameters that should be taken into consideration for economy, design and operation of a full-scale biogas plant during the selection of potential feedstock.The BDCH4 and methane potential of a material are commonly determined using the Biochemical Methane Potential (BMP) test. However, a number of factors, e.g., temperature, pH, inoculum preparation, inoculum to substrate ratio (ISR), substrate concentration, mixing, etc. can affect the BMP test results. Moreover, the experimental setups, data analysis and presentation vary in different laboratories, and therefore, the results from different studies are not comparable. To improve the reliability and reproducibility of the BMP test and ensure that the results are more comparable, this PhD study evaluated the influences of various factors on the methane potential and degradation rate of a standard substrate (i.e., cellulose) and certain other types of materials. For example, mixing plays an important role in the BMP test because it aids in the distribution of microorganisms, substrates and nutrients; release of produced gases; and equalisation of the temperature in the digester, thereby enhancing the digestion process. In Paper IV, different mixing strategies were applied to evaluate the influences of mixing on the BMP test. The results showed that the methane potential of blank (inoculum only) was increased approximately 77% and 220% by automated continuous mixing at low intensity (10 rpm) and high intensity (160 rpm), respectively, compared with the methane production obtained from the manually shake system. For the most viscous substrate investigated, i.e., dewatered sludge (DWS), automated continuous mixing significantly improved the methane production. However, for a fine-powdered substrate cellulose and much diluted substrate 8'DWS (i.e., DWS diluted by a factor of 8), mixing is not necessary or the manual shaking once per day is sufficient during the BMP test. Furthermore, certain other important factors, such as experimental setup, inoculum preparation and substrate concentration, were also evaluated and displayed a significant impact on the BMP test.Finally, as an application of the BMP test, a case study was performed to evaluate the effects of different pre-treatments on lignocellulosic biomass (Miscanthus) for improved methane production. Miscanthus has been proven as one of the highest energy biomasses in recent years; however, its conversion to biogas/methane is limited due to its recalcitrant structure. The study showed that methane production of Miscanthus was significantly improved after size reduction, steam explosion (SE) and alkali pre-treatment.