Anaerobic co-digestion of sugar beet tops silage and dairy cow manure under thermophilic condition

The effects of co-digesting different proportions of sugar beet tops (SBT) silage (40, 60, 80 and, 100 %, wet weight basis) with cow manure and duration of storage of two types of SBT silage (silage I: storage time of 120 days and silage II: storage time of 210 days) on digester performance in terms of biogas production and volatile solids (VS) reduction were investigated. The highest methane (CH4) yields were obtained at the 40 % proportion treatments and were 0.422 and 0.377 l/g VS for silage I and II, respectively. The digestion systems failed at 80 and 100 % proportions of silage I and 100 % proportion of silage II. Furthermore, 40 % proportion treatments presented highest VS reductions among manure-silage mixtures (57.0 % for silage I and 57.4 % for silage II) while the control treatment (manure only) had the highest VS reduction (65.0 %) among all the treatments. Based on the results, the 40 % proportion of SBT silage was most efficient for methane production. Comparison of digester performance at 40 and 60 % proportions showed that no remarkable differences were observed between silage I and II, indicating that duration of storage of SBT did not have any appreciable effect on digester performance.