An integrated study on the biological treatment of NO3-N Laden Aquaculture Wastewater

Abstract

Sustainable Aquaculture development in India warrants Environmentally Sustainable Recirculating aquaculture systems which can lower environmental impact and conserve water. However, such technologies are not popular since majority of brackishwater shrimp aquaculture is still practiced as   semi-intensive  enterprise.  An important challenge in biological aquaculture wastewater treatment in recirculating units is accumulation of nitrate nitrogen of upto 500 mg/L, which is reported to be  toxic  to  fish  at  levels  of  20  mg  of  NO3 -N/L.  Biological denitrification  using  attached  growth  is  a suitable method; but is in want of cheaper materials to be used as bacterial support medium.  The present study evaluated indigenously available coconut  coir  fibre  compared to commercially available synthetic Fujino spirals for denitrification of nitrate laden synthetic aquaculture wastewater in upflow  anaerobic  packed  bed  column  bioreactors. In  the  experiments,  maximum  nitrate  removal  (99%)  was  achieved using  coconut coir  fibre  as  the  bacterial  support  medium. The performance of coconut coir fibre was comparable to that of Fujino spirals. Physical and biochemical tests results further compounded  it’s  resilience , structural integrity. PCR analysis confirmed presence of Denitrifying genes. Subsequent application of support medium with coconut coir fibre anaerobic baffled reactor obtained maximum COD  removal  of  96  %  and  95  % . Post aeration using cascading method removed residual ammonia and restored  dissolved oxygen. A  conceptual  model  for  the  integration  of  anaerobic  and  aerobic  processes  in  the  treatment  of  nitrate  laden  aquaculture  wastewater  has  been developed based on the findings.