Nutrient recovery from reef-bound wastewater effluents (B3.9)

Task leader: Dr Phil Schneider, James Cook University.

Task associate: Ms Jo Johnson, Great Barrier Reef Marine Park Authority.

At present there are 35 sewage treatment plants located along the Queensland coastal zone, producing about 60,000 million litres of effluent annually. Significant quantities of nutrients (nitrogen and phosphorus) remain in this effluent, to the detriment of the surrounding coastal waterways and the Great Barrier Reef.

This task will investigate the simultaneous recovery of both phosphorus and nitrogen by a crystallization process. By adding a source of magnesium ions and adjusting the effluent pH, struvite crystals form, according to;

Magnesium + Ammonium + Phosphate = Struvite

Owing to its low solubility in pH-neutral solutions, struvite is an excellent slow-release fertiliser with no tendency to “burn” soils when over-applied, which occurs with traditional ammonium-phosphate fertilisers. This slow-release behaviour is ideal for coastal agriculture, since it reduces nutrient run-off and thus the impact on nitrification of coastal waters is lowered. This also leads to the more sustainable use of this nutrient resource.

Advanced tertiary wastewater treatment schemes, such as Biological Nitrogen Removal typically aim only to reduce levels of nitrogen, leaving behind significant amounts of phosphorus. Existing chemical methods for its removal ultimately lose phosphorus to the sludge exiting the plant. The main goal of this task is to develop a process that will generate and recover struvite crystals from municipal wastewater effluents.