Determination of the biogas potential of urine with solid-liquid separation in the fertilizer bed

In this study, an alternative manure collection method was developed to separate manure and urine in the manure bed of a dairy cattle barn under the climatic conditions of Van province. The urine obtained with this method, with its high nitrogen content, was added to mixtures with high cellulose content waste paper, which is abundant and easily available in Van and its vicinity, as a carbon source. Five different mixtures were prepared, each with two replicates. As inoculum, equal amounts of manure taken from manures transported to the manure depot by the traditional method were added to each reactor (inoculum-substrate ratio 1:1). Ten 1000-ml bioreactors were used for biogas production. The mixtures added to the bioreactors for biogas production were operated for a total of 66 days. Gas production in the SI10, SI20, and SI30 bioreactors ceased on the 38th day, and gas production in the SI0 bioreactor ceased on the 40th day. Gas production in the SI50 bioreactor continued throughout the operating period and was stopped on the 66th day due to insufficient economic production of gas. As a result of the research, SI50 was the most efficient bioreactor with a specific daily biogas yield of 203.38 ml/g TS, and SI30 was the least efficient bioreactor with a specific daily biogas yield of 68.58 ml/g TS. The highest cumulative specific methane yield was obtained from the SI50 bioreactor with a value of 135.85 ml/g TS. The lowest methane yield was observed in the SI30 bioreactor with a value of 33.55 ml/g TS. The removal efficiencies of total solids were determined to be 86%, 85%, 83%, 82%, and 81% for the SI50, SI30, SI20, SI10, and SI0 bioreactors, respectively. The removal efficiencies of volatile solids were determined to be 87%, 85%, 85%, 84%, and 84% for the SI50, SI30, SI20, SI10, and SI0 bioreactors, respectively. The highest total solids and volatile solids removal was achieved in the SI50 bioreactor. Due to the high soluble chemical oxygen demand (CODs) content that can be decomposed rapidly biologically, the SI50 bioreactor showed a higher biogas yield increase compared to other mixtures. This can be explained by the fact that the rate-limiting step in the other four mixtures is hydrolysis, but the rate of digestion is determined by methanogenic activity in the SI50 mixture.