Magnesium hydroxide liquid for odour control

A catchment dosing approach

Mission Beach is a mixed residential and tourist area and is home to the iconic Cassowary. A sewerage scheme was commissioned by Cassowary Coast Regional Council in 2006 to collect the wastewater from three constituent communities and pumped by two major stations, at Wongaling and North Mission Beach, to the Main Transfer Pump Station (MTPS). The MTPS then pumps 23km to the Tully Sewerage Treatment Plant (STP).

This sewer main suffered significant corrosion due to “rotten egg gas” (H2S) release in the drained sections. The Tully plant is designed for phosphate removal with liquid alum dosing for phosphate trimming and powered lime dosing for alkalinity and pH correction.

A trial of Calix’s ACTI-Mag Magnesium Hydroxide Liquid (MHL) dosing commenced in December 2017 with the primary objective to control septicity, odour and corrosion issues. Calix proposed additional objectives including the control of Fat, Oil & Grease (FOG) build-up, elimination of lime dosing at the Tully plant and partial elimination of alum dosing for phosphate removal.

The trial eliminated odours by maintaining pH between 8.2 and 8.5. Pump station cleaning was substantially reduced due to decreased FOG accumulation. The lime dosing system was prone to blockage and breakdowns, however dosing of ACTI-Mag has allowed suspension of lime dosing. Also, the dose rate was reduced by more than 75 per cent whilst still meeting phosphate effluent discharge limits.