Abstract
The Brazil's Biodiesel Production and Use Program introduces biodiesel in the Brazilian energy matrix, bringing along the perspective of a growth of the glycerin offer, co-product generated in the proportion of 10 kg for each 100 L of biodiesel. The aim of this study was to evaluate the addition of crude glycerin in the anaerobic digestion of cassava starch industry effluent (cassava wastewater), in a horizontal semi-continuous flow reactor of one phase in laboratory scale. It was used a reactor with a 8.77 L of useful volume, a medium support for corrugated conduit of polyvinyl chloride (PVC), temperature of 261 ºC, fed with cassava wastewater and glycerin, with hydraulic detention times of 4 and 5 days and increasing volumetric organic load of 3.05; 9.32; 14.83 and 13.59 g COD L-1 d-1, obtained with the addition of glycerin at 0; 2; 3 and 2% (v/v), respectively. The average removal efficiencies of TS and TVS were decreasing from the addition of glycerin to the cassava wastewater, averaging 81.19 to 55.58% for TS and 90.21 to 61.45% for TVS. The addition of glycerin at 2% increased the biogas production compared to the control treatment, reaching 1.979 L L-1 d-1. The biogas production as a function of the consumed COD was higher for the control treatment than for the treatments with addition of glycerin, which indicates lower conversion of organic matter into biogas.
Highlights
All vegetable oils can be processed into biodiesel (SUAREZ et al, 2007)
The crude glycerin had alkaline pH, which can be explained by the presence of residual NaOH, used as catalyst in the production of biodiesel
It was observed that the glycerin used showed great amounts of organic matter, 1,900 g O2 L-1 of Chemical oxygen demand (COD)
Summary
All vegetable oils can be processed into biodiesel (SUAREZ et al, 2007). The main routes for obtaining biofuels from fats and oils are the transesterification, in which one triglyceride reacts with alcohol in the presence of catalysts and the cracking, which consists in breaking of molecules by high temperatures in the presence or absence of catalysts. The transesterification of vegetable oils consists in the reaction of triglycerides with a short-chain alcohol (ethanol or methanol) in the presence of an acid or basic catalyst, generating as products a mixture of alkyl esters (biodiesel), fatty acid and glycerin (FERRARI et al, 2005; ROBRA, 2006). The glycerin obtained by the transesterification of vegetable oils (biodiesel production) has impurities such as water, alkali catalyst, unreacted alcohol and fatty acids, and other compounds. As the purification of glycerin is quite expensive, it is interesting to use the glycerin in processes that do not depend on high-purity level (MOTA & PESTANA, 2011)
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