The tenderer shall take care of emptying sludge plants on Nøtterøy, Tjøme, Brøtsø and Hvasser islands. Færder municipality has approx 1 600 sludge plants. The majority of these plants are ordinary interceptors for sludge. The contract also includes emptying mini-treatment plants, sealed tanks and grey water systems. The emptying frequency is either every year or every second year.