Environmentally friendly RAS, which conform to strict environmental
legislation, are needed for small-scale, urban aquaculture.
For these purposes, the most important water quality
parameters are ammonia, nitrite and nitrate. While aerobic
nitrification of ammonia and nitrite has become a general standard
in such systems, the resulting nitrate accumulation has not
received the necessary attention. To address this oversight, we
have designed and tested an innovative denitrification bioreactor
system based on solid cotton wool as the primary carbon source
and a unique degassing device, which further increases the
biofilter’s efficiency and effectiveness. This design concept and the
above-described sludge management practice resulted in a very
high recovery of water and a negligible amount of waste for
disposal. Our results show that the process offers a number of
advantages: it provides highly efficient and controlled denitrification,
it uses a cheap and renewable carbon source, and it has a low
maintenance, compact configuration.