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.

Correlation between heavy metal ions (copper, zinc, lead) concentrations and root length of Allium cepa L. in polluted river water

The present work was performed using the common onion (Allium cepa L.) as a bioindicator of toxicity of heavy metals in river water. The test waters were collected at two sampling sites: at the beginning and the end of the Toledo River. The bulbs of A. cepa L. were grown in test water with nine concentration levels of copper, zinc and lead from 0.1 to 50 ppm. In the laboratory, the influence of these test liquids on the root growth was examined during five days. For test liquids containing below 0.03-ppm dissolved Cu the root growth was reduced by 40 percent However, the same reduction occurred for 1-ppm dissolved Zn. For dissolved Pb, results reveal toxicity above 0.1 and 0.6 ppm at the beginning and the end of the Toledo river water, respectively.