Granulation of sludge under different loads of a glycerol fraction from biodiesel production

The aim of the research was to evaluate the possibility of using the crude glycerol fraction from biodiesel manufacturing processes for granular sludge production. The experiment was carried out simultaneously in four sequencing batch reactors (SBRs) at different carbon loads: 0.2 ± 0.08, 0.6 ± 0.16, 1.1 ± 0.27, and 1.3 ± 0.35 g COD/g TSS per cycle (COD – chemical oxygen demand, TSS – total suspended solids). Granulation did not occur in the reactor with the lowest organic carbon load. In the remaining reactors small granules began to appear after 25 cycles of reactor operation. In all reactors the efficiency of carbon removal remained at ca. 80%. The highest granular sludge production per cycle was 0.31 ± 0.28 g TSS/L; it was obtained at an organic load of 1.1 ± 0.27 g COD/g TSS per cycle. Most of the introduced COD was removed in the reactors during the first 5 h of aeration; the COD removal rate was correlated with the organic load and varied from 123.12 to 472.76 mg COD per litre and hour. Practical applications: With the increasing production of biodiesel fuel a problem arises with the utilization of glycerol that is a by‐product of the process. By‐product glycerol fraction from small agricultural installations is usually contaminated. Its composition varies depending on parameters of the transesterification process and it is unprofitable to purify it. In the present research we investigated one possible way of dealing with the by‐product. The glycerol fraction was successfully used as a carbon source for the production of aerobic granular sludge. The granules obtained can be used as a seed sludge in granule‐based reactors, or can be cofired with coal or directly combusted. Since aerobic granular sludge is one of the most promising technologies investigated during the last few years it appears to possess high utility.