Application of optical monitor to evaluate the coagulation of pulp wastewater

Coagulation/flocculation process is an important part of the solid/liquid separation in a wastewater treatment plant. However, conventional methods to determine coagulant dosage have led to poor results in real-time dosing control for the highly changeable quality of influent. In this study, we employ the photometric dispersion analyzer (PDA) to assess the feasibility of monitoring pulp suspended solids coagulation in pulp wastewater by batch trials. The use of PDA in the batch system to monitor the coagulation of filamentous microorganisms is also included. Batch test results indicate that PDA monitoring is an effective technique to reflect the state of aggregation of filament- and fiber-type solids and, therefore, can provide as a reliable index for determining the optimal dosage. In addition, in our coagulant dosing control system, the monitoring point of PDA should be set at the effluent of the rapid mixing unit. We also assess the feasibility using PDA monitoring in a continuous system simulating the wastewater treatment processes. Results demonstrate that stable PDA output can accurately reflect the changes of influent turbidity and coagulant dosage.