Effect of Agitation on Anaerobic Co-Digestion of Swine Manure and Food Waste

Abstract The synergism of food waste associated with swine manure can provide an increase in biogas production, besides promoting greater stability in the anaerobic co-digestion process. To verify this effect, co-digestion tests were performed in two reactors, one with agitation, and the other without agitation. In both systems, gasometers were used to measure biogas production in an experiment lasting two hydraulic retention times (HRT). On each feeding day, the temperatures of the ambient and of the effluent taken from the reactors were measured, and samples of the food waste and effluent were collected to perform analysis of pH, total solids (TS), volatile solids (VS), fixed solids (FS), volatile acidity (AV), and total alkalinity (TA). In addition, the chemical oxygen demand (COD) was determined every five days, and gas composition was determined at the beginning of the second HRT. As important results, in both reactors a decrease in pH was verified due to the weakening of the buffer effect of the medium. This was due to the low alkalinity found in the food waste, causing an increase in acidity in the contents of the reactors. The volume of biogas produced was higher in the reactor with agitation, which meant an increased efficiency of the process. Finally, a low methane content was verified through chromatographic analyses, indicating a reduction in the activity of the microorganisms present in the medium. Thus, it is concluded that agitation linked to anaerobic co-digestion of swine manure with food waste exerted a positive effect on biogas production.

Avaliação da dispersão de curvas força x elongação de segmentos de cólon descendente de ratos por meio do modelo sigmoidal de Boltzmann / Evaluation of the force x elongation curves dispersion of descending colon of rats using Boltzmann's sigmoidal model

OBJETIVO: avaliar a dispersão de curvas Força x Elongação (FE) representativas do comportamento mecânico de alça cólica íntegra de ratos. MATERIAIS E MÉTODOS: dez segmentos de cólon descendente de ratos machos Wistar foram submetidos ao teste biomecânico Energia Total de Ruptura. Cada curva gerada por esse ensaio foi ajustada ao modelo de Boltzmann, o qual correlaciona os valores de força e elongação por meio da combinação dos parâmetros A1, A2, x0 e d x. Nesse contexto, para cada parâmetro, foram calculadas as médias, os desvios padrão e correlações. Após, determinou-se a dispersão resultante da força em todo processo de deformação através de uma análise que considera as correlações entre as grandezas, com base na lei de propagação das incertezas. Para determinar um intervalo no qual estarão contidos 95% dos valores de força, a dispersão resultante foi multiplicada por um fator de abrangência considerando-se uma distribuição normal. RESULTADOS: os valores da média, do desvio padrão e das correlações foram determinados. A dispersão resultante dos valores de força foi expandida, delineando-se limites dentro dos quais estarão contidas as curvas FE para um intervalo de confiança de 95%. CONCLUSÃO: essa metodologia poderá auxiliar na avaliação de variáveis que interfiram no comportamento mecânico intestinal.

PURPOSE: to evaluate the dispersion of Force x Elongation curves (FE) that represents the mechanical behavior of rat's colon. MATERIALS AND METHODS: ten descending colon segments were submitted to the Total Energy of Rupture Test. Each curve generated by this test was fitted to Boltzmann model that correlates the values of force and elongation through the combination of the parameters A1, A2, x0 and d x. Then, for each parameter were calculated the mean, standard deviation and their correlations. Later, the resultant dispersion was determinated in the whole deformation process by an analysis that considers the correlations between the greatnesses based on the propagation of uncertainties law. The resultant dispersion was multiplied by a coverage factor, considering a normal distribution, to determinate an interval in which 95% of force values will be present. RESULTS: the mean, standard deviation and correlation were determined. The resultant dispersion of force values was expanded drawing limits inside which FE curves will be for a confidence interval of 95%. CONCLUSION: this methodology will be possibly used to evaluate variables that act on the intestinal mechanical behavior.