Wastewater treatment using grass filtration

Abstract

The Western Treatment Plant (WTP) is one of the largest treatment plants in Australia treating more than 550 MI of sewage per day. Three different biological treatment processes, namely lagoon treatment (all year around), land treatment (during summer) and grass filtration (during winter), are used to treat the raw sewage, which is finally discharged to the Port Phillip Bay. A recently commissioned project, identified the discharge of treated sewage from the WTP to the Port Phillip Bay, as a major contributor of nutrients, which pose a risk of algal blooms in the Bay. Therefore the efficiency of Italian Ryegrass filtration at the WTP for polishing effluent, to reduce the nutrient loads discharged to Port Phillip Bay was investigated in this project. The project aimed at evaluating an optimal hydraulic loading rate for Italian Ryegrass filtration. The results indicated that at hydraulic loading rate of 40 mm/d the grass filtration system produces sufficient waste treatment to comply with the WTP discharge license requirements for total nitrogen load, BOD, SS, Faecal Coliform and pH in winter. However, ammonia and total phosphorus concentrations and colour standards may be violated unless improvements to the supply system and clearing of the bays from dead organic matter are undertaken.