In 2018, Bega Cheese Environmental Manager – Northern Victoria, Sean Trebley was given the task of upgrading the wastewater aeration system at the company’s Strathmerton plant.
The wastewater system consisted of a dissolved air flotation (DAF) unit, which flowed into an aerated lagoon, and after this the effluent was stored in two non-aerated lagoons during winter, before irrigation in summer.
Aerators are needed to keep the chemical oxygen demand (COD) down and reduce odours in both the aerated lagoon and the downstream non-aerated lagoons.
The company had an ageing system of surface aerators in the aerated lagoon, consisting of two 22kW units and six 8kW units. However, generally only one or two of these units were operated at any given time.
Over a number of years these surface aerators had progressively failed because of their age and repairing them meant deploying cranes and/or boats to access them.
This process was expensive and had resulted in damage to the dam liner. Eventually it became uneconomical to keep on repairing the aerators. So Bega Cheese decided to look for a solution that was safer for operators and easier to maintain.
Sean Trebley contacted Hydro Innovations to discuss the application of “bank-mounted” Venturi Aeration systems. These systems are mounted on the banks of lagoons and use a self-priming pump to draw water from the lagoon. The pump discharges it under pressure through the venturi aerator.
The unit draws in atmospheric air using the “venturi effect”, mixes it with the water being pumped, and discharges it back into the lagoon, charged with dissolved oxygen.
Trebley and his team liked the idea of bank-mounting because it gave operators easy access to equipment for monitoring and/or repair, making it much safer and more cost effective to maintain. Their only concern was whether the units were as efficient as the surface-mounted technologies.
Hydro Innovations was able to provide information indicating that with the use of the right pump, oxygen transfer efficiency for Venturi Aeration units can be as high or higher than 1.86kgO2/kWh, making them as at least as efficient as the surface (floating) technologies.
The aerated lagoon contained 45ML of effluent, with in-flows from 80 to 120ML per year. This required a 150mm Venturi Aeration unit and was paired with a Gorman-Rupp V6A60-B self-priming pump, with a hydraulic efficiency of 70%.
Bega Cheese installed the unit early in 2019.
Before installation: The condition of the lagoon after the previous system had been decommissioned several months before.
After installation: Two weeks on, and it can be seen that ripples from the aerator “radiate” to all parts of the lagoon, ensuring a good level of mixing.
Since installation, operators have seen a continued increase in the dissolved oxygen (DO) level, and have seen COD fall by 50% even though the higher level of mixing was resuspending settled solids, which became more “bioavailable” to the colony-forming units.
Sean Trebley and the Bega Cheese crew are happy with the ever-increasing levels of DO, the reduction in COD, and their odour-free lagoon. The wastewater and maintenance teams are also pleased that monitoring and maintenance can be done safely, and without the use of cranes, boats or winches.
More information about Venturi Aeration venturi aerators and Gorman-Rupp pumps can be obtained from Hydro Innovations.
02 9898 1800