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The Woodman Point Wastewater Treatment Plant (WWTP) at Western Australia has experienced two separate problems causing avoidable maintenance costs, the build-up of massive struvite (MgNH 4 PO 4 . 6H 2 O) scaling downstream of the anaerobic digester and the formation of hydrogen sulfide (H 2 S) levels in the digester gas to levels that compromised gas engine operation and caused high operating costs on the gas scrubber. As both problems hang together with a chemical imbalance in the anaerobic digester, we decided to investigate whether both problems could be (feasibly and economically) addressed by a common solution, (such as dosing of iron solutions to precipitate both sulfide and phosphate), or by using separate approaches.Laboratory results showed that, the hydrogen sulfide emission in digesters could be effectively and economically controlled by the addition of iron dosing. Slightly higher than the theoretical value of 1.5 mol of FeCl 3 was required to precipitate 1 mol of dissolved sulfide inside the digester.Due to the high concentration of PO 4 3-in the digested sludge liquor, significantly higher iron is required for struvite precipitation. Iron dosing did not appear an economic solution for struvite control via iron phosphate formation. By taking advantage of the natural tendency of struvite formation in the digester liquid, it is possible to reduce the risk of struvite precipitation in and around the sludge-dewatering centrifuge by increasing the pH to precipitate struvite out before passing through the centrifuge. However, as the Mg 2+ /PO 4 3-molar ratio in digested sludge was low, by increasing the pH alone (using NaOH) the precipitation of PO 4 3-was limited by the amount of cations (Ca 2+ and Mg 2+ ) available in the sludge. Although this would reduce struvite precipitation in the centrifuge, it could not significantly reduce PO 4 3-recycling back to the plant. For long-term operation, maximum PO 4 3-reduction should be the ultimate aim to minimise PO 4 3-accumulation in the plant. Magnesium hydroxide liquid (MHL) was found to be the most costeffective chemical to achieve this goal. It enhanced struvite precipitation from both, digested sludge and centrate to the point where more than 95% PO 4 3-reduction in the digested sludge was achieved.

The Water Corporation of Western Australia uses polymeric ultrafiltration (UF) membranes across a range of applications including surface waters with high natural organic matter (NOM), recycling of secondary treated wastewater and pre-treatment for seawater reverse osmosis (SWRO). These challenging raw water conditions require expensive chemical dosing and clean-in-place (CIP) regimes, high frequency of membrane replacement and reduced membrane life. The greater durability of ceramic membranes, with optimal ozone and coagulant dosing, offer a potential capital and operating advantage over polymeric UF membranes. The Water Corporation collaborated with PWN Technologies (PWNT) to establish a ceramic membrane pilot plant at the Beenyup Wastewater Treatment Plant (WWTP). Optimised performance of the pilot plant was established and compared with existing UF membranes treating secondary treated wastewater prior to reverse osmosis (RO) in an indirect potable wastewater recycling application. Findings show a sustainable flux rate of 150 L/m2/h is achievable with ceramic MF membranes while filtering secondary treated wastewater. Higher flux rates up to 250 L/m2/h have been tested and are possibly sustainable, however, other bottlenecks in the pilot plant (ozone generator capacity) prevented longer test runs at this flux. Comparable design flux rates for polymeric UF membranes are 50 L/m2/h.

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