Test batch fermentation techniques, biogas measurement methods and methane concentration determination methods

C H Pham, T T T Cu, M T Jin and S G Sommer

NIAS, Hanoi, Vietnam
bachcuong03@yahoo.com

Abstract

Greenhouse gas emission is one of the biggest issues in over the world. Therefore, producing methane from anaerobic digestion of livestock waste production in biogas plant not only provides a recycle energy, but also reduces greenhouse gases emission. In Vietnam, thousands of biogas plants have been constructed on poor and remote livestock farms, the purpose of which has been to produce energy and to reduce the impact on the environment caused by animal production. However, understanding of how to optimize the biogas process or the efficiency of methane production is still very poor in Vietnam (Vu, et al. (2007)) and technologies for measuring biogas production has not been available at Vietnamese laboratories.

Three batch fermentation techniques namely Moller, et al., (2004) (Moller), Hansen, et at., (2004) (Hansen) and VDI 4630 (2006) (VDI); three biogas production measurement methods like syringe, water replacement system (WRS) and water replacement system continuously connected to digester bottles (CWRS); and two methane concentration measurement methods such as GC and CO₂ determination were investigated in Experiments 1, 2 and 3 respectively. Biomass used in all Experiments were fattening pig manure (FPM) (3.16% DM, 71.14% VS) and dairy cow manure (DCM) (7.87% DM, 83.61% VS).

In Experiment 1, the substrate (S): inoculum(I) ratio was 1:1 (based on VS), 50 ml:200 ml (fresh), and ≤ 0.5 (based on VS) for Moller, Hansen and VDI respectively. The results in three batch fermentation techniques showed that there was a not significant difference in both ultimate methane and biogas production between Moller and VDI while ultimate methane and biogas production were higher for Hansen than for either Moller or VDI in biomasses apart from FPM.

In Experiment 2, the substrate (S): inoculum (I) ratio (based on VS) was less than or equal 0.5 (VDI method) for three biogas production measurement methods. Ultimate methane production of syringe was lower than that of WRS and CWRS, but not significant difference between WRS and CWRS in both FPM and DCM. Nevertheless, there was a greater in ultimate biogas production for WRS than for CWRS and syringe, but not difference between syringe and CWRS in either FPM or DCM.

In Experiment 3, VDI method with 1 (S): 1 (I) ratio was also used for methane concentration measurement methods. The results indicated that methane concentration measured by CO₂ determination was greater than that of GC in both biomass, but these differences from 2.12 to 6.62% were not much so it could be acceptable to apply CO₂ determination if we do not have GC instrument.

It was concluded that VDI method with CRWS and methane concentration measured by CO₂ determination could be used in Vietnamese laboratories.

Table 3.1.1. Ultimate methane potential (L/kg VS, Mean±SD) of inoculum, fattening pig manure, dairy cow manure and cellulose powder with different batch fermentation techniques.

^a,b,c Means in the same column for each biomass with different superscripts are significantly different

^a,b,c Means of biomass or method in the same row or column respectively with different superscript are significantly different

Table 3.2.1. Ultimate methane potential (L/kg VS, Mean±SD) of inoculum, fattening pig manure, dairy cow manure and cellulose powder with different biogas measurement methods.

^a,b,c Means in the same column for each biomass with different superscripts are significantly different

^a,b,c,d Means of biomass or method in the same row or column respectively with different superscript are significantly different

Table 3.3.1. Methane concentration (Mean ±SD) measured by either GC or CO₂ determination methods

^{a, b} Means in the same row with different superscripts for each biomass are significantly different