AbstractSince 1969, Incitec Ltd., one of Queensland's largest companies has operated the Gibson Island fertiliser manufacturing works site located in Brisbane, situated between the Brisbane River and Aquarium Passage. As is the case for other industries operating on the Brisbane River, the site is being placed under increasing pressures from regulators and the public to reduce environmental impacts on the Brisbane River and Moreton Bay. The rationale for this thesis was to investigate the use of a combination of passive chemical and biological treatment methods, and incorporate into the design the functional characteristics into a wastewater management system. The system would be required to treat plant wastewater, receiving wastewater from a nearby municipal sewage plant to reduce the level of nutrients (nitrogen, phosphorus), suspended solids (including algae counts) and heavy metals in water to be reused in the manufacturing processes. Two concurrent studies were undertaken to gain a greater understanding of expected inflow quality and existing removal mechanisms occurring within the site oxidation pond. The first study reviewed historical data from the oxidation pond, with the other being a study of the diurnal effects on removal of nutrients and metals. Results of these studies found that considerable removal of nutrients occurred as a result of denitrification processes because of anoxic conditions, as well as uptake by green algae. The effect of high levels of ammonia had a controlling impact on the oxidation of nitrogen species by destroying algal populations. The limiting factor in the proliferation of algal species in this case was phosphorus.
Another element of this thesis was a study on the use of bauxite residues in wetland treatment for the removal of nutrients, metals and faecal coliforms. It was found that over 99% removal of phosphorus and faecal coliforms was achieved in one of the three columns used in the study whilst operating with continuous-flow, ensuring the presence of oxygen in soil-solution. Simultaneously, up to 70% removal of metals was achieved for Cr, Zn, Al, Mg, Mn and Cu. In columns operating under anoxic conditions on account of static residence, extensive desorption of nutrients (in particular ammonia) and trace metals was observed. Sodium and sulfur were not reduced during the trial, giving rise to the inflow criterion that TDS tolerant aquatic species should be used in the anaerobic phase of the proposed system. A limitation to the study was that although saturation estimations were calculated, the saturation breakthrough of the red mud in the trial columns is still unknown. Research will continue at Gibson Island Works until this achieved.
Based on the results of the above studies, a three-stage wastewater management system was designed incorporating the removal characteristics determined during the studies. The proposed system incorporated 49,000m2, utilising existing containment facilities. The first two stages of the system were designed to remove phosphorus and trace metals via a series of vertical-upflow red mud cells. The third stage of the system incorporated the anaerobic processes required for denitrification and polishing of metals to occur. An investigation was undertaken on the existing quality of pond sediments. Based on results, it was apparent that the pond contains sediments laden with heavy metals of a potentially toxic nature, in particular Cr. The study found that Cr (VI) levels in the sediments were low, and met regulatory criteria for in-situ remediation. The encapsulation of pond sediments was incorporated into the wastewater management treatment system design.
The commissioning of the system would provide considerable savings resulting from reduction in water use and purchase of a more cost-effective source of water. The concept of environmental and financial sustainability were the fundamental driving factors for the motivation to undertake this research. The viability of the Gibson Island Works site is dependent on the implementation of future initiatives intended to save on non-renewable resources: a vision aligned with community expectations.
|Date of Award
|David Parry (Supervisor)