Aeration efficiency and oxygen consumption in the treatment of wastewater from coffee fruit processing using a cascade aeration system

ABSTRACT

This study aimed at assessing the efficiency of aeration and organic matter removal of a cascade aeration system treating wastewater derived from coffee fruit processing (CW). The system consisted of one 4.14-m cascade with 23 steps (height, width and length of 0.18, 0.32 and 0.60 m, respectively), one receiving tank to store CW for three hours and one distribution tank, from which it was recirculated through the system. The system remained operating for thirty days during which CW recirculated three times a day under a constant flow rate of 1 L s^-1 and being replaced every ten days. In each recirculation cycle, samples of effluent and affluent were collected and analyzed. The cascade aeration system incorporated an average of 0.2 mg L^-1 of oxygen every one meter of cascade steps. The aeration efficiency was 0.128 or 0.141 depending whether or not salt effect on CW was considered. The high concentration of organic material in CW hampered the detection of major changes in dissolved oxygen contents. We also found that 26 minutes was the ideal time to maintain CW in the receiving tank.

Aerobic treatment; Organic residue; Coffee fruit