HIGHLIGHTS:

The pretreated conditions at temperatures below 100 °C showed better energy balances.

The highest single-stage yield was 255.65 NmL CH₄∙gVS^-1, obtained by pretreatment at 120 °C for 24 min.

The highest two-stage yield was 277.57 NmL CH₄∙gVS^-1 when pretreated at 160 °C for 48 min.

ABSTRACT

Hydrothermal pretreatment (HPT) allows the solubilization of the hemicellulose, leading to increased biodegradability for microorganisms. This paper presents a study based on the evaluation of the variables time (12 to 60 min), temperature (80 to 200°C), and solid/liquid ratio (4 to 8 g mL^-1) for the HPT (autohydrolysis) of synthetic poultry litter (rice straw: poultry manure 1:5) using the Doehlert matrix. Twelve HPT conditions followed by anaerobic digestion were evaluated with a focus on methane production. Firstly, tests were conducted to evaluate biogas production in a single stage in a single reactor, where both the acidogenic and methanogenic phases occur. Subsequently, tests were conducted to evaluate biogas production in a two-stage, consisting of separating hydrogen and methane production phases. The best performance of the biochemical potential of methane was the conditions 6 (24 min, 120 °C, and solid-liquid ratio = 4) in a single stage and 3 (48 min, 160 °C, and SLR = 8) in a two-stage, producing 255.6 and 277.6 NmL CH₄gVS^-1, respectively. Using the desirability criteria, two hydrothermal pretreatment (HPT) conditions were evidenced/ condition 1 in two stages (12 min, 80 °C, and SLR = 4)- (D1-2S) and condition two in two stages (12 min, 98 °C, and SLR = 4) - (D2-2S) showed high methane production, 248.9 and 249.3NmL CH₄∙gVS^-1, respectively.

Key words:
chicken manure; autohydrolysis; anaerobic digestion