Comparative assessment of olive oil mill effluents from three-phase and two-phase systems, treated for hydrogen production.

By-products of a two-phase and a three-phase olive oil mill process treated in an anaerobic fermentation system for hydrogen production, were evaluated by three bioassays: the zebrafish Danio rerio embryo test and two microbiotests, Thamnotoxkit F and Daphtoxkit F™ pulex. Samples from both processes were classified as "very toxic" with LC(50) values ranging from 1.52% (T. platyurus 24 h test) to 4.48% (D. pulex 48 h-LC₅₀). Toxicity values were differently correlated to physicochemical parameters showing different degree of influence. The treated effluents of both process systems remained very toxic showing the necessity for further treatment, aiming to environmentally safe discharges.