Industrial Paper Mill

Surface aeration and liquid oxygen

The client, a large pulp and paper mill in South Africa, produces fine paper from bagasse. The mill uses an aeration lagoon to treat the wastewater before discharging into the local river. Before Mapal's installation, the plant was using a combination of surface aerators, aspirators, and liquid O2 in order to reduce the COD as required.

Challenge

To improve the dissolved oxygen concentration in the SBR, to improve the nitrogen removal and the setiling characteristics of the MLSS and to reduce the O&M complications and costs.

Solution

Mapal’s engineers calculated that replacing the liquid oxygen injectors would be the most economical solution as the operation and maintenance costs of the system were extremely high and provided the most room for savings.
An FFBA™ system was installed comprising of 4 floating aerators, 1 blower, air feeding pipes and manifold. In order to provide the fine bubble membranes most suited to the mill’s aggressive wastewater, Mapal undertook preliminary tests on a selection of materials. Four types of membranes were tested (EPDM, Polyurethane, Silicone and PTFE) over a period of 3 months. Upon completion of the tests and based on laboratory results, the decision was made to use Polyurethane membranes for the project.

Results

Having installed the Mapal aerators the mill operators were able to inject less liquid oxygen into the wastewater and therefore reduced their operational costs. Mapal’s floating aeration system was installed within 3 days without draining the lagoon or disabling the existing aeration equipment. Mapal achieved a Standard Aeration Efficiency (SAE) of more than 3kg oxygen/kW.