In 1987, filamentous bacteria outbreaks in this northern pulp mill’s activated sludge basins were a problem. Anoxic conditions in sludge deposits between its diffuser heads, caused by a lack of mixing, encouraged the growth of Thiothrix . 'This filamentous organism results in classic bulking,' reported the manager. Chlorine was tried but didn’t correct the source of the problem. 'We needed to correct the problem immediately with minimal downtime. 'We run the mill 24 hours a day, 362 days per year.'
To eliminate the sludge buildup, they needed strong mixing capability to keep the 1.35 MG (5114 m 3) and 0.5 MG (1892.7 m 3) basins aerobic. Other criteria were: cost, fast delivery, and quick installation. AIRE-O2® aspirator aerators matched the mill’s needs. Four 50 hp (37 kW) units were installed and operational within six hours. 'Immediately after turning them on, we could see the improvements in the mixing. Anoxic conditions were eliminated and the treatment plant responded within 48 hours.'
' We have run solids tests and found we have no stratification in the 18 feet (5.5 m) deep basins,' reported the mill. Oxygen profiles on the AIRE-O2® system show good dissolved oxygen levels at both bottom and top levels. The units have been running continuously and have eliminated many of the maintenance headaches the mill had found in other aerator types.