Nitrogen removal improvement in small wastewater treatment plants with hybrid and tertiary moving bed biofilm reactors

This paper focuses on two small wastewater treatment plants that have been upgraded with MBBRTM after a pilot-scale study. The first plant was built for 3000 p.e., the actual load was 5800 p.e. as nitrogen. In this plant each aerated tank was divided into two sectors: the first one was kept as an activated sludge tank, the second one was transformed into a hybrid MBBRTM; after biofilm growth, average pollutants concentrations were 484 mg/l COD and 79 mg/l TKN in the raw wastewater, 50 mg/l COD and 0.64 mg/l NH4-N in the final effluent. The second plant was built for 400 p.e., the actual load was 549 p.e. as nitrogen. In this plant a sludge thickener was transformed into a denitrification tank, an out-of-use tank was recovered as a tertiary nitrification MBBRTM; after biofilm growth average pollutants concentrations in the raw wastewater were 456 mg/l COD and 58.8 mg/l NH4+; activated sludge tanks removed 360 mg/l COD and 28.9 mg/l NH4+, tertiary MBBRTM removed 14 mg/l COD and 10.6 mg/l NH4+. These results prove that hybrid and tertiary MBBRTM are good solutions to upgrade small plants without building new tanks.