|Resource Efficiency and Production
|Technology and Treatment
While phosphorus (P) is vital to crop development, Australia’s old, extensively weathered soils are low in phosphorus and often need to be supplemented with fertilisers containing it (ca. $3-4/kg P). Phosphorus in wastewater is a nuisance; it can reduce the effectiveness of reverse osmosis membranes and is expensive to remove using additional chemicals.
WORK UNDERTAKEN AND OUTCOMES
|This project sought to recover phosphorus (P) from wastewater via adsorption to P-selective media that are easily separable from water, possess direct agronomic value, and are economically viable.The project attempted to shift P removal towards a routine recovery and reuse opportunity, yielding treated, recyclable water and a P-rich solid as a new, sustainable agricultural P source to be used as an additive to fertilisers.
Laboratory trials of the P-adsorbent media were conducted on a range of synthetic and real treated wastewater effluents to demonstrate the efficacy of the products for P recovery. Freshly calcined MgO absorbed > 100 g P/kg, however, did not generally remove P to concentrations below 2 mg/L. All synthetic hydrotalcites removed P to < 1 mg/L. Nanoclay hybrid materials were found to have rapid P uptake kinetics and were very effective in removing P from low strength wastewaters. MAR schemes using recycled water can be technically and economically feasible based on factors such as site selection, soil type, pre-treatment of recycled water, infiltration rates, management of vegetation, and operation and maintenance regimes. National case studies of recycled water MAR schemes, together with a consistent approach to economic analysis, will fill the knowledge gaps and will assist Australian water utilities to better design, invest and operate MAR with recycled water.
ADOPTION AND IMPACT
The potential ‘competitive edge’ of the P-absorbent technologies is their ability to be directly substituted to replace coagulants and enable productive use of P incorporated into a solid form. The project
evaluated the benefits and risks of the absorbents against existing wastewater treatment technologies, such as struvite crystallisation.
MgO required approximately 10 times the loading to achieve the same P removal as struvite precipitation. In addition, the higher chemical and material handling costs are not currently economically attractive as an additive by the fertiliser industry in Australia at this time. Nanoclay hybrid absorbents offer an alternative to the use of traditional coagulants. The competitive edge for the nanoclay material is their potential ability to reduce sludge handling costs and the improved potential for recovery as a saleable soil conditioner in regions with sandy soils with poor nutrient retention. While hydrotalcite offered enhanced performance in lowering P concentration compared to other absorbents, its high cost currently limits its practical application.