Background

This 2.86ha aerated lagoon receives industrial waste from a number of food processing industries and municipal waste from Eltham – a town of just over 800 dwellings with a population of approximately 2000.

Cheese making factories and other processors contribute relatively high strength waste to the Eltham pond. Effluent flows from here to the Beach Rd wastewater plant in Hawera for final treatment. The pond has a good amount of mechanical aeration for its size.

• Depth: Relatively consistent varying between 1.1m and 2.0m with an average depth of 1.65m.
• Total sludge volume before treatment: 12,500m³ equating to 33% of the total pond volume.

The Eltham pond started receiving AMD (Advanced Microbial Digestion) treatment from Parklink’s dosing system in November 2014.

The Results

A sludge survey in February 2016 revealed a sludge volume of approximately 7,760m³. This equated to 4,800m³ of wet sludge volume removed over fifteen months.

Any remaining sludge has been thinned out and is now much lighter in density. Taking into account the stratification in sludge density relative to depth this equates to the removal of approximately 273 m³ of dry solids down from 865m³ in the original survey. The dry solids mass is what would remain of the sludge with the total absence of water or moisture.

To mechanically dredge the same amount of sludge and dewater to 20% solids it would equate to approximately 3,000 tonnes of material to be disposed of.