Efficiency of a Small Scale Hydroponics Wastewater Treatment

As a consequence of eutrophication in lakes and coastal areas requirements for reduction of nitrogen and phosphorus from wastewater introduced in Sweden in early 1990s. To meet these requirements, many wastewater treatment plants have been upgraded for biological nitrogen and phosphorus removal. A small-scale hydroponics system has been designed in Stockholm for domestic wastewater treatment and also removal of nitrogen and phosphorus. The treatment plant is built for research purposes and presently treats 0.6 m3 of domestic wastewater from surrounding area per day. The system uses anoxic pre-denitrification followed by aerobic tanks for nitrification and plant growth. A microalgal step further reduces phosphorus, and a final sand filter polishes the water. In this study the treatment capacity of this system was evaluated with respect to removal of organic matter, phosphorus and nitrogen. 90% COD removal was observed in the system. Nitrification and denitrification were well performed with total nitrogen reduction of 72%. Phosphorus was removed by 47% in the process. However, higher phosphorus removal values are expected, as the microalgal step will be further developed. The results show that acceptable treatment can be achieved using this kind of system. Further optimization of the system will lead to clean water as valuable plants to be harvested from the nutrient rich wastewater.