Dolomitic limestone as an alkalizing agent for treating cassava starch wastewater in an anaerobic reactor

Resumo

Cassava starch has a low Volatile Acidity/Total Alkalinity ratio, low buffering capacity and quickly acidified. In this trial, dolomitic limestone was used as an alkalizing agent in an anaerobic reactor to treat cassava wastewater. The dolomitic limestone contained 27% CaO and 23% MgO and had grain sizes of 24.5 to 38.1 mm. The average Chemical Oxygen Demand of the wastewater was 13331.30 mgO₂L^-1, the volumetric organic loading rates ranged from 1.23 to 16.43 gCODL^-1d^-1 and the hydraulic retention times ranged from 10.00 to 0.80 days. The results showed that the calciumconcentrations increased in the reactor effluent and the magnesium concentrations decreased as the organic load increased. The Ca²⁺ and Mg²⁺ concentrations were approximately 5000 and 5.05 times greater in the sludge than in the inoculum, respectively. The average pH, Total alcalinity, Volatile Acidity and Volatile Acidity/ Total alcalinity values were 6.69, 882.54 mgCaCO₃L^-1, 221.55 mgCH₃COOHL^-1 and 0.22, respectively. 2.51% of the limestone was wasted. Finally, it was concluded that the limestone effectively controlled acidification through the alkalinity increased in the system.