. (2013) Modelling and dynamic simulation of struvite precipitation from source-separated urine.Water Science & Technology, 67 (12 AbstractA model of a mixed-mode nutrient recovery reactor is developed for a urine feed, incorporating complex solution thermodynamics, dynamic conservation relations and a power-law kinetic expression for crystal growth from seed crystals. Simulations at nominal operating conditions predict phosphorus recoveries greater than 99%, based on existing process kinetic parameters and operating conditions employed in previously published studies. The overall rate of nutrient recovery depends on Saturation Index of the precipitating solid, the available surface area for mass transfer and the feed rate of the limiting constituent ion. Under the conditions considered, the nutrient feed rate appears to be the limiting factor for precipitation. Simulations demonstrate that diurnal feed flow variations of have a small effect on the rate of nutrient recovery. Overall, the study shows that valuable insights are gained in relation to process performance predictions, which should lead to more confident process design, operation and control.

Abstract:Conventional water treatment processes use aluminium sulphate (alum) as a coagulant in the production of potable water. While alum is an inexpensive and reliable means of treating water, the process generates waste water containing dissolved Al. This waste water is primarily dealt with via on-site retention. In this study we investigate the cultivation of the freshwater macroalga Oedogonium as a means to sequester dissolved Al from waste water from a conventional water treatment plant. Furthermore, we examine the use of CO 2 to manipulate the pH of cultivation as a means of enhancing the sequestration of Al by either increasing the productivity of Oedogonium or increasing the bioavailability of Al in the waste water. The relative bioavailability of Al under conditions of CO 2 and no-CO 2 provision was contrasted by comparing Al uptake by Diffusive Gradients in Thin Films (DGTs). Oedogonium was able to grow rapidly in the waste water (12 g dry weight m −2 day −1 ) while consistently sequestering Al. The Oedogonium-treated waste water had a sufficiently low Al concentration that it could be used in unrestricted irrigation in the surrounding region. When CO 2 was added to the waste water containing concentrations of Al up to 8 mg L −1 , there was a slight increase (~10%) in the rate of sequestration of Al by Oedogonium relative to waste water not receiving CO 2 . This was due to two concurrent processes. The provision of CO 2 increased the productivity of Oedogonium by 15% and the bioavailability of Al by up to 200%, as measured by the DGTs. Despite this strong effect of CO 2 on Al bioavailability, the increase in Al sequestration by Oedogonium when CO 2 was provided was modest (~10%). Al was sequestered by Oedogonium to concentrations below permissible limits for discharge without the need for the addition CO 2 . The cultivation of Oedogonium in waste water from conventional treatments plants can simultaneously treat waste water for re-use and provide a biomass source for value-added applications.