Lenntech Water treatment & purification Lenntech Water treatment & purification

Ozone Application

Fish pond water treatment applying ozone for the Tivoli Park Copenhagen, Denmark.

Present Situation

Copenhagen's main and oldest tourist attraction, the Tivoli Park, has been a showcase for Denmark for the last 150 years. One of its dominant features is a vast artificial lake (12 million litres) stretched out over the main part of the park's surface. In this pond 500 gold fish, 400 carps and 50 Japanese carps swim. Through the intensive use of the pond, it's lack of water recirculation or refreshment, and excessive nutrients in the water from visitors throwing in food, the pond has no biological equilibrium. This results in excessive algae bloom, low oxygen level in the water and anaerobic rotting of the bottom layer of sludge.


The present situation results in a murky, untransparent pond water quality whereby the colorful fish cannot be seen by the visitors and guardians. Furthermore hydrogen sulfide escaping from the anaerobic rotting process of the ground sludge creates an unpleasant odour and poisons the fish. Lake flowers cannot live in such an environment and as fish need an oxygen rich environment.


The management of the Tivoli Park requested Ozone Alliance to install a self-operating pilot unit that could treat a limited but representative amount of pond water in an aquarium parallel to an equally sized non treated aquarium. In these aquaria living fish should be kept throughout the whole demonstration period. The demonstration system should apply a technology that could be scaled up to the full lake amount. Furthermore in the real set-up there would be no room for bulky treatment systems such as sand filters or protein skimmers.


As can be clearly seen in the above photo the results show a dramatic improvement in the water clarity, whilst keeping the fish active in an oxygen enriched environment. This has been done applying high concentration ozone through a venturi into the aquarium water. As a result Ozone Alliance has been requested to propose a full scale ozonisation system for the total 12 million litres of the Tivoli pond to operational before the park re-opens in May 1999.

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