Ovivo system overcomes stringent trade waste limits

When the local council changed the criteria for discharge to local sewage treatment works, a New South Wales juice producer turned to Ovivo Australia to supply, construct and commission a new waste water treatment plant (WWTP) at its factory.

Specialising in shelf-stable juices, the prominent juice producer processes a variety of fruits and vegetables in its factory, removing the pulp to be sold as a by-product. The company found itself subject to stricter trade waste criteria when its waste - both wastewater and general waste - was found to have high loadings when discharged to the council sewage system.

Ovivo’s solution was a biological treatment plant designed specifically to reduce BOD5 and TSS levels to below council limits, maintain the discharge pH range and keep the discharge flow below a set value.

With the factory’s wastewater pH rising as high as 12 during cleans and instantaneous discharge up to four times the average flowrate, Ovivo had its work cut out for it. The treatment plant required a robust process design to overcome the feedwater variation.

Ovivo’s design consists of a twin sequential batch reactor (SBR) system, with flow buffering/storage upstream and downstream of the tanks, and a sludge dewatering system for excess waste activated sludge dewatering.

Neutralised effluent is transferred to the equalisation tank in the new WWTP. The tank provided temporary storage prior to the effluent entering either SBR. The equalisation tank is kept aerated to suppress odour, maintain mixing and remove a small amount of BOD5. Effluent is then transferred into one of the two SBR tanks, which are run out of sync so effluent is fed into one of the two tanks every three hours during a six-hour batch process.

Sludge removed from the SBR during the batch process is sent to the sludge tank for intermediate storage and thickening. The sludge is then dewatered in a Huber inclined sludge press (ISP) and deposited into a bin for off-site disposal. The Huber ISP is a unique system that Ovivo has now employed at several sites across Australia that offers low washwater requirements, low rotational speed and high performance.

The plant performs very well, with a 96% removal of BOD5 and a 90% removal of TSS. The range of the incoming pH to the equalisation tank is between 5 and 12, while the discharge pH has been maintained between 7.5 and 7.9, well within the allowable range of 7-10 pH set by the local council.

Commissioning of the plant was rapid, with discharge limits being met within several weeks of plant seeding.

Ovivo AeroStrip fine bubble diffusers were used due to their simple self-flushing design and high oxygen rates, typically 4-5 kg O₂ per kWh. This aeration strategy enables the most efficient use of the positive displacement blowers, reducing power demand while ensuring sufficient dissolved oxygen levels are maintained within the reactor.

The plant is controlled via a PLC and SCADA package, providing operators a modern and comprehensive control system to operate, maintain and optimise the treatment plant.

Since commissioning, the plant has operated with stability and consistent discharge quality.