This study investigated the rheological behavior of raw physicochemical sludges and sludges that were digested at different organic loading rates (OLRs) (1, 5, 10 and 15 gVS L(-1) d(-1)) during methanogenesis suppression to produce hydrogen anaerobically. The Herschel-Bulkley model was used to describe the rheology of these sludges with specific properties. The results indicate that the Herschel-Bulkley model adequately described the rheology (τ0 ≠ 0) of this type of fluids (R(2) > 0.98). In addition, the raw physicochemical sludges and those that were digested at different OLRs had dilatant behaviors (n > 1), which increased with increasing OLR. These results identified the apparent viscosity, yield stress, pH and OLR conditions that allow for the production and suppression of methane, as well as the conditions that guarantee the production of hydrogen.
The influence of the increase of the organic loading rate (OLR) on methane production in a continuous stirred-tank reactor (CSTR) from physicochemical sludge generated in a poultry slaughterhouse was evaluated. Total solid (TS) to obtain OLR of 1, 5, 10 and 15 g VS L(-1) day(-1), with hydraulic retention times of 29, 6, 6 and 4, respectively, were conditioned. The results showed a decrease in pH levels and an increase in the theoretical volatile fatty acids (VFA). While the yield of methane production decreased from 0.48 to 0.10 LCH4/g VSremoved, respectively, the OLR-10 managed on average 38% removal of volatile solids (VS) and a yield biogas production of 0.81 Lbiogas g(-1) VSremoved and 1.35 L day(-1). This suggests that the OLR increases in an anaerobic system from physicochemical sludge only inhibits the methanogenic metabolism, because there is still substrate consumption and biogas production.
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