This research mainly focused on the exploration of the possibility to utilize the liquid by-products (the circulating alkaline fluid of a bio-trickling reactor, containing NO3-, 7.0 ? pH ?7.5) as a fertilizer, with reduced environmental impact and economic benefits. The composition of the exhausted bio-trickling liquid (TL) was analysed in accordance with Dlgs. 75, 2010 of Italian Republic, which recognizes the CE Rules n.2003/2003 and n.834/2007. In particular, the TL discharged from a bio-trickling filter can be recognized into the category of nitrogen mineral organo-fluid fertilizers.