aquaculture waste water reuse

BY Leslie Ter Morshuizen

As the world population grows towards 8 billion people, natural resources are being stretched to provide adequate food, shelter and water for these masses.  Aquaculture provides high quality food products using a minimum of space, and in doing so is rightly being heralded as one of the industries that will enable us to feed our people.

The definition of aquaculture is the farming of fish and other aquatic organisms and the industry produces over 100 million tons of product each year.  In order to achieve these massive outputs we need to input certain components, including fish, feed, light, water, labour, power and a few others according to the infrastructure type and species being farmed.  The result is that we are then able to output the fish (or other organism being farmed) but in doing so also produce wastes in the form of faeces, carbon dioxide and mortalities.  In areas where the species that is desirable to farm does not match the climate we utilise recirculating systems inside insulated environments to maintain optimal growth conditions throughout the year.  These intensive systems enable us to produce huge tonnages off a relatively modest area of land; this in turn means that the inputs are confined to a small area resulting in more concentrated waste streams.
With freshwater as a resource at an all-time premium, aquaculture needs to be responsible in the way we use and discharge water for our farming processes.  The first step is to reduce usage through implementing water wise farming techniques to reduce the amount of water we require and that needs to be dealt with.  In years gone by the wastes from a fish farm were seen as a problem, and the management thereof involved disposal.  Now days we view the resources in the wastes as a secondary income stream, available to aid the farm in making attractive profits.

The 1st component of the wastes is the water itself which we wish to clean and reuse on the fish, or utilise for irrigating crops.  Solids carried out with the effluent water can be concentrated and used as fertiliser or possibly for the production of methane gas if the production volumes are high enough.  Dissolved organics such as nitrate and phosphate are primary fertilisers for plants and can be used in aquaponics to grow valuable vegetable crops, to grow algae for a range of uses or to grow duckweed which can be fed back to the fish (species dependant).

 August 26, 2017
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