Elaine Groom

Optimizing the thermophilic hydrolysis of grass silage in a two-phase anaerobic digestion system

Thermophilic hydrolysis of grass silage (GS) at 55 °C with organic loading rates (OLRs) of 6.5, 5, 2.5 and 1.0 kg VS m(-3) days(-1) and hydraulic retention times (HRT) of 10, 6, 4 and 2 days were evaluated in 12 glass bioreactors side by side. The hydrolytic process was measured by variation in pH, volatile solids (VS), VS destruction, soluble chemical oxygen demand (sCOD), hydrolysis and acidification yields. Biological methane potential (BMP) assays were carried out to measure the upper limit for methane production of grass silage with different hydrolytic pretreatments at mesophilic temperature (37 °C). The optimum methane yield of 368 LN CH4 kg(-1) VS was obtained at an OLR of 1 kg VS m(-3)days(-1) and a HRT of 4 days, showing an increase of 30% in the methane potential in comparison to non-hydrolysed GS.

Batch and continuous biogas production from grass silage liquor

Herein batch and continuous mesophilic anaerobic digestion of grass silage liquor was studied. The continuous process was carried out in Armfield digesters with an OLR ranging from 0.851 to 1.77 kg COD m(-3) day(-1). The effect of recirculation of effluent from the digester was investigated using different OLRs of grass silage liquor feed. These results showed that as the OLR increased, the methane yield decreased for the reactor with no recycle and increased for the reactor with recycle. However, the COD removal for both digesters was nearly the same at the same OLR. Overall these studies show that grass silage liquor can produce a high quality methane steam between 70% and 80% and achieve methane yields of 0.385 m3 kg(-1) COD.

Evaluation of a pretreatment process for improved methane production from grass silage.pdf

Hydrolysis is a limiting step an anaerobic digestion. Hydrolytic pre-treatment of grass silage was evaluated at thermophilic temperature (55 °C), and the effect of organic loading rates (OLR) and hydraulic retention time (HRT) was studied. Two lab scale stainless steel continuously stirred reactors (10 L) and 12 glass reactors (2 L) were used. OLRs of 6.5, 5, 2.5 Kg VS m -3 d -1 and 10, 6, 4, 2 days HRT were evaluated. The parameters assessed as indicators for the level of hydrolysis were volatile solids destruction (VSD), volatile fatty acids (VFA) produced and soluble chemical oxygen demand (sCOD). Biological methane potential tests at mesophilic temperature (38 °C) were carried out for the evaluation of the effect of hydrolysis on the methanogenesis step.