Water Quality Modelling of the Cedar Grove Constructed Wetland

Abstract

Maintaining high-quality discharge from wastewater treatment process is very important to ensure the health of the receiving water bodies. This is more so when a watershed is also shared with the drinking water supply. To ensure the safety of the environment, monitoring programs are implemented. Monitoring data can inform decision-makers and operators of any potential risks and breaches of operation environmental conditions. They can also inform stakeholders and the public about the water quality and the safety of the environment. However, communicating the water quality to the public can be challenging. The concept of the water quality index is attractive because it can simplify the otherwise technical parameters to a single descriptor or number which is easy to understand by non-technical stakeholders. This paper reports on the monitoring program of Cedar Grove constructed wetlands in Logan City, Queensland. The constructed wetlands were commissioned in August 2020. It is composed of eight cells arranged in three treatment series. The wetland is subject to strict environmental criteria. A monitoring program commenced in November 2020; weekly water samples were collected and analysed for key water quality parameters (pH, DO, BOD, TP, TN, NOx, NH3, TSS, TVS..etc). The Canadian Council of Environment Ministers Water Quality Index (CCEM WQI) was used to assess water quality. The wetland performed very well in removing NOx and NH3 (92-100%) and had 61% of TN. Phosphorus removal has negative removal of phosphorus. This is attributed to the fact that the incoming phosphorus concentrations are extremely low and likely below the wetland threshold level. The excess phosphorus source is likely to be the unaccounted loads from precipitation and wildlife activity. Nevertheless, the water quality was assessed as ‘Good’ and it has met all long-term environmental criteria defined in the operation license.