An experimental and computational investigation of performance of a new stormwater quality improvement device: Green Gully

Developing methods to recycle and reuse stormwater and effluent/waste water has become an important and urgent issue. In order to manage water resources in a sustainable manner and to help reduce national water restrictions, treated stormwater can play a significant role. Before reusing, treatment is mandatory to remove the different types of pollutants from the stormwater. To reduce the extent of pollutants, stormwater quality improvement devices (SQIDs) are introduced that filter run-off before it enters the waterways. SQIDs are used to help protect the creeks, rivers and beaches by trapping or collecting rubbish and pollutants that end up in our stormwater drains. The Green Gully is one of the new concepts to remove gross pollutants from stormwater. The main purpose of the Green Gully is to remove pollutants from stormwater as quickly and effectively as possible and divert the water for reuse, especially for watering roadside plants and gardens. This study aims to determine the performance in terms of efficiency of the Green Gully using a laboratory model. To achieve the goal, an extensive literature review relevant to the research such as stormwater reuse, stormwater quality improvement devises, numerical simulation and water-quality for stormwater were done. The Green Gully was designed, developed and installed in the existing flume in Fluid Mechanics laboratory of CQUniversity. Efficiency, defined as the amount of water flow passed through the Gully screen with respect to the total inflow (in percentage), was determined for three types of gully screen (cross-diagonal, perpendicular and square screens) and for three different angles of flume base (0º-horizontal level, 1º and 2º- inclined). Each experiment was conducted using only water flow and water flow with mixed litter. Mixed litter consisted of leaves, cigarette-butts, bottle-caps, plastics and papers. It was found from the experimental results that the cross-diagonal screen at the flume base angle of 0º achieved the highest efficiency overall, while the perpendicular screen performed well when no litter was mixed with the water flow. A three dimensional Computational Fluid Dynamics (CFD) model was developed to validate the experimental measurement using CFD code FLUENT (6.3.26). Geometry creation and mesh generation was done using GAMBIT (2.3.16). Experimentally determined efficiency of the cross-diagonal screen at flume base angles of 0º, 1º and 2º (using only water flow) was compared with CFD simulated efficiency. It was found that the experimentally determined efficiencies are in good agreement (within 3% to 10% for flume base angle of 0º and 1% to 16% for flume base angle of 1º) with simulated efficiencies. For flume angle of 2º, simulated efficiency varies from 20% to 36%. Futhermore, stormwater road runoff quality parameters were tested in the laboratory to determine the level of treatment required for road runoff to reuse for watering roadside plants or gardens. American Public Health Association (APHA) standard methods for examination of the water and waste water were followed for water quality tests. Laboratory test results were compared with the results of other study available in the literature and with Australian and New Zealand Environment and Conservation Council (ANZECC) standards. Significantly different (higher or lower depending on the parameters) water quality data were found compared to that of the ANZECC standard. It is identified from the test results that a tertiary level of treatment arrangement should be added to the Green Gully facility for purifying and reusing stormwater. Simple laboratory chemical reactors, known as plug flow reactor (PFR) or continuous-flow stirred-tank reactors (CSTR) can be designed and installed for a tertiary level of treatment to attain stormwater quality suitable for roadside plants or gardens. This study contributed to the understanding of the new SQID 'Green Gully', its performance investigation and types of gully screen in relation to fresh water flow and water flow with mixed litter. This study developed a method to improve the resilience of Australian irrigation to drought and climate change -- Abstract.