Digestão anaeróbia de dejetos de bovinos leiteiros: efeito da dieta e da adição de caldo de cana-de-açúcar

The aim was to evaluate the anaerobic digestion process of the manure fed of dairy cattle on different roughages in which sugar cane broth was added to some manure as an additive. The treatments evaluated in the digesters were substrates containing manure from cows fed on maize silage (substrate MS), or manure from cows fed on fresh sugar cane (substrate FS) or manure from cows fed on quicklime hydrolyzed sugar cane (substrate HS). Manure from animals fed on fresh sugar cane or quicklime hydrolyzed sugar cane were also evaluated with sugar cane broth and aforementioned substrates FSJ and HSJ, respectively. In the two last substrates, the added amount of sugar cane broth was 6  % on fresh matter basis (volume/volume). 15 batch process biodigesters and five semi-continuous biodigesters, all of them with a 10 L useful capacity, at 30±2  oC. The parameters evaluated were pH, partial alkalinity, volatile solids (VS) removal and CH4 yields. Alkalinity and pH values did not indicate risk of anaerobic digestion process failure. The VS removal was similar in the batch and semi-continuous digesters, 51 % for every substrate. In batch digesters, higher CH4 yields were obtained from substrates FSJ and HSJ, averaging 0,258 L CH4 g VS-1. In semi-continuous digesters, the highest CH4 yield was from substrate FSJ, 0,226 L CH4 g VS-1. Similar CH4 yield was obtained from substrates MS, FS, HS and HSJ in semi-continuous digesters, averaging 0,171 L CH4 g VS-1. Sugar cane broth added to substrates (6 %, volume/volume) incremented the CH4 yield up to 24 %.