Alkalinity indices for control of anaerobic treatment of readily acidifiable wastewaters

Abstract

The efficiency of an anaerobic treatment is determined by several environmental factors, among which pH and alkalinity are of great mportance. The startup of a full-scale anaerobic filter, used for the treatment of wastewaters from a cassava-starch extraction process, showed the importance of the alkalinity indices (buffer index, AI / AP index, and ) for the control of the process. The startup strategy, which comprised five stages, consisted in the decrease of the hydraulic retention time as the reactor responded in a favorable way in terms of COD removal efficiency and the behavior of the alkalinity indices. Due to the acidity of wastewaters, their prior conditioning with sodium bicarbonate was necessary. We found that, in stable conditions, the buffer index varied in the range from 0.20 to 0.35, the AI / AP index varied in the range from 0.40 to 0.55, and the α index was above 0.65. Moreover, we noted that the COD removal efficiency was closely related to the variation of the indices. Because of the simplicity associated with the calculation of the indices, we recommend their use for the control of the anaerobic process, by checking the applicability range of the indices for each wastewater type.