Lagoon Effluent Treatment Using Grass Filtration

The Western Treatment Plant (WTP) is one of the largest treatment plants in Australia treating more than 500 ML of sewage per day, discharging treated effluent to Port Phillip Bay in Victoria, Australia. The Port Phillip Bay Environmental Study (1992-1996) concluded that there was a need to reduce nitrogen loads from WTP to lower the risk of eutrophication, especially during winter when grass filtration was in operation. Therefore, in 1997, Melbourne Water initiated a pilot study to investigate the effectiveness of grass filtration for polishing wastewater that had received prior lagoon treatment. The study involved field monitoring of seven trial grass filtration bays at the WTP for hydraulic and water quality data from mid-May to early-October 1997. The results of the pilot study revealed that the removal rates of these nutrients were higher during the first half of the trials than during the second half. The results also showed that the removal rates of nutrients were inversely proportional to the hydraulic loading rates of the bays. A hydraulic loading rate of 40 mm/d was found to be optimal in this pilot study for achieving a balance between wastewater throughput and nutrient removal.