Pré-tratamentos térmicos e alcalinos aplicados em lodo de flotador proveniente de abatedouro de frango visando melhorar o potencial bioquímico de metano

Abstract

Residues rich in proteins and lipids are generated daily in poultry slaughterhouses and can be used to generate energy through anaerobic digestion. However, these residues are poorly soluble and tend to form crusts inside the reactors, causing a reduction and delay in the production of biogas. In addition, they can generate operational difficulties due to obstruction of pipes. These disadvantages can be overcome through physical and chemical pretreatments. Thus, the objective of this study was to evaluate the effects of thermal, alkaline and thermoalkaline pre-treatments applied to chicken slaughterhouse flotation sludge (CSFS). In order to determine the type of pre-treatment with greater effectiveness in relation to solubilization, degradation and production of biogas and methane, when applied to CSFS, pre-treatments were tested in two phases. In the first phase, the thermal pretreatments (120 and 190 °C), alkaline (0.3 and 0.6 gNaOH/gVSsubstrate) and thermoalkaline (0.6 gNaOH/gVSsubstrate at 120 and 190 °C) were evaluated. In relation to the control (raw sludge), the heat pretreatment reduced the methane yield by 14.3% (at 120 °C) and 35.9% (at 190 °C). The alkaline pre-treatment resulted in the best anaerobic digestion performance, with 0.3 gNaOH/gVSsubstrate increasing sludge solubilization by 48.1% and methane yield by 20% when compared to the control. Increasing the NaOH concentration to 0.6 gNaOH/gVSsubstrate improved sludge solubilization by 52.1% and methane yield by 42.3%, however, it delayed the onset of organic matter degradation activity and the peak of biogas production in 21 days. The thermoalkaline pretreatment showed intermediate results between the thermal and alkaline pretreatments. After the greater effectiveness of alkaline pre-treatments was verified, in the second phase, pre-treatments with NaOH and KOH were evaluated at concentrations of 0.02, 0.05, 0.15, 0.25 and 0.5 g / gSVsubstrate. The pretreatments at concentrations of 0.02 and 0.05 g of NaOH and KOH / g SVsubstrate did not significantly improve the substrate characteristics and the anaerobic digestion performance, so much so that the similarity between them and the control ranged from 86 at 99%. Pre-treatments at concentrations of 0.15, 0.25 and 0.50 g of NaOH and KOH / g SVsubstrate resulted, when compared with the control, in improvements of 23 to 55% in sludge solubilization, increases between 8, 8 and 53.2% in the production of biogas and methane, as well as in higher efficiencies of removing proteins (from 61.7 to 68.1%) and lipids (from 89.7 to 93.4%). KOH pretreatments were less inhibitory when compared to NaOH pretreatments at higher concentrations (0.50 g base per g of sludge volatile solids).