Anaerobic digestion of poultry litter was studied with reutilization of its effluent in the process by pumping into reactor feeding, contributing to the moisture content and making part of the feeding organic load: 0.5 and 1.0 kg VS/m3/day, at evaluations 1 and 2, respectively. The hydraulic residence time lasted 10 days for both evaluations and the useful volume of reactor was 35 m3, with a semi-continuous reactor feeding, under field conditions. The stability of anaerobic digestion was verified through Shewhart control chart. Average efficiency of biogas production was 0.0119 m3/(kg VSadded) at evaluation 1 and 0.0429 m3/(kg VSadded) at evaluation 2. In the second evaluation, the study revealed that biogas produced more energy as methane than spent with electric energy in reactor feeding. According to Lower Process Capability Index (Cpl), measure developed for convenience engineering to quantify the performance of a process, the anaerobic digestion in the second evaluation was capable in its energy operations.
Key words: Biogas, Lower Process Capability Index, operational energy viability index, Shewhart control chart, statistical process control.
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