Dolomitic limestone as an alkalizing agent for treating cassava starch wastewater in an anaerobic reactor¹

Calcário dolomítico como agente alcalinizante para tratamento de água residuária de fecularia em reator anaeróbio

ABSTRACT

Cassava processing wastewater has a low Volatile Acidity/Total Alkalinity ratio, low buffering capacity and became quickly acidified. In this trial, dolomitic limestone was used as an alkalizing agent in an anaerobic reactor to treat cassava starch wastewater. The dolomitic limestone contained 27% CaO and 23% MgO and granulometry between 24.5 and 38.1 mm. The average Chemical Oxygen Demand of the wastewater was 13331.30 mgO₂ L^-1, the organic loading rates (OLR) ranged from 1.23 to 16.43 gCOD L^-1 d^-1 and the hydraulic retention times ranged from 10.00 to 0.80 days. The results showed that the calcium concentrations increased in the reactor effluent and the magnesium concentrations decreased as the organic loading rates increased. Ca²⁺ and Mg²⁺ concentrations were approximately 5,000 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 mgCaCO₃ L^-1, 221.55 mgCH₃COOH L^-1 and 0.22, respectively. The loss of limestone mass corresponded to only 2.51% of the initial mass, after 134 days of anaerobic reactor operation. Finally, it was concluded that the limestone effectively controlled acidification through the alkalinity increased in the system.

Keywords:
acidity; alkalinity; calcium; magnesium