Influence of organic volumetric loading rate, nutrient balance and alkalinity: COD ratio on the anaerobic sludge granulation of an UASB reactor treating sugar cane molasses

Using sugar cane molasses (a byproduct of the sugar industry) as substrate an experimental work was carried out with the aim to obtain a granulated anaerobic sludge at controlled conditions of alkalinity and micronutrients. The experiment was carried out in a laboratory-scale-upflow anaerobic sludge blanket (UASB) reactor of 16.51 capacity. The substrate concentration was adjusted at a COD value of 3750 mgl−1 by addition of tap water. The ratios of Alkalinity:COD, N:COD and P:COD were maintained at 1.06, 0.018 and 0.0028 respectively. Under such conditions the production of spherical granules was observed after thirty days of operation. The average diameter of the granules grew progressively with the increase of the organic volumetric loading (Bv) achieving a maximum average value of 3.1 mm at the 90th day of operation and remained constant furtherly in spite of the increase of Bv. It was found that after the granules formation the addition of nutrients could be suspended while the Alkalinity: COD ratio could be reduced to 0.4 without changes on the process performance.