Veolia (Australia)

Atrazine (ATZ) is one of the most widely used herbicides and is highly scrutinized due to its environmental impact. Given its extensive use, ATZ is likely to be exposed to high-temperature conditions such as those encountered during wildfires, incineration, or thermal desorption processes. However, there are limited experimental data on the thermal decomposition of ATZ. The present study investigates the decomposition of ATZ in a flow reactor constructed of α-alumina at temperatures between 400 and 800 °C. At temperatures above 400 °C, thermal decomposition was observed to occur and the formation of HCl and several hazardous chemicals, including hydrogen cyanide and cyanoacetylene were observed during the thermal decomposition of ATZ. Quantum chemical calculations were also performed to elucidate the decomposition pathways and determine the relevant reaction rates. These findings provide crucial insights into the risks associated with exposing ATZ to high temperatures and the potential release of harmful gases from its thermal decomposition.

ABSTRACT A mining operation uses mechanical vapor recompression to treat mine tailings water for discharge to the environment. To maintain the mine’s operations, the removal of an additional 1 MLD of water is required. The water has a high TDS, is supersaturated, and a low pH. A range of water treatment technologies were reviewed and assessed. It was determined that a membrane system was the best option to deploy, and an NF/RO system was recommended for further evaluation. However, because the tailings water pH is in the vicinity of most membrane isoelectric points (~3-4), electrostatic rejection would be greatly affected, allowing excessive ion transmission to the permeate. It was hypothesized that a membrane with an isoelectric point >4 would provide enhanced rejection. Two acid resistant NF polymeric membranes with isoelectric points at approximately pH 5 were tested at laboratory scale. The volume recovery was restricted due to supersaturation chemistry limitations, not osmotic pressure or the operating pressure of the selected membranes. An overall system recovery of ~50% was achievable. An integrated flowsheet was developed for a system that required significantly less capital and energy that an additional thermal evaporation process.

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In this study, a high-rate fibre filter was used as a pre-treatment to stormwater in conjunction with in-line flocculation. The effect of operating the fibre filter with different packing densities (105, 115 and 125 kg/m3) and filtration velocities (20, 40, 60 m/h) with and without in-line flocculation was investigated. In-line flocculation was provided using 5, 10 and 15 mg/L of ferric chloride (FeCl3·6H2O). The filter performance was studied in terms of pressure drop (ΔP), solids removal efficiency, heavy metals (total) removal efficiency and total organic carbon (TOC) removal efficiency. It is found that the use of in-line flocculation at a dose of 15 mg/L improved the performance of fibre filter as measured by turbidity removal (95%), total suspended solids reduction (98%), colour removal efficiency (99%), TOC removal (reduced by 30–40 %) and total coliform removal (93%). The modified fouling index reduced from 750–950 to 12 s/L2 proving that fibre filter can be an excellent pre-treatment to membrane filtration that may be consider as post-treatment. The removal efficiency of heavy metal was variable as their concentration in raw water was small. Even though the concentration of some of these metals such as iron, aluminium, copper and zinc were reduced, others like nickel, chromium and cadmium showed lower removal rates.