On-line monitoring of anaerobic-aerobic biotreatment of a simulated textile effluent for selection of control parameters

Parameters monitored on-line in a laboratory biological wastewater plant treating simulated textile effluent were examined for use in a control strategy. The plant, an anaerobic (UASB) reactor with an aerobic stage and overall HRT 1.8 days, was operated at steady-state and transient conditions with varying ratios of azo dye and starch. Gas flow rate, %CO2, biogas hydrogen levels and effluent bicarbonate alkalinity were assessed on-line in the anaerobic stage, together with on-line measurements of effluent total oxygen demand (TOD), colour, pH, and dissolved oxygen. Their ability to indicate process instability and efficiency, the reliability/maintenance of the instrumentation and delay in response were evaluated. On-line TOD measurement failed due to the wastewater's mineral content; biogas hydrogen content varied unpredictably. It is recommended that the other measurements be used together in a control system for textile effluent biotreatment, providing complementary information and redundancy.