Biological treatment of second cheese whey using marine microalgae/cyanobacteria-based systems

The biological treatment of second cheese whey (SCW) was investigated using two different marine cultures, the microalgae Picochlorum costavermella and the cyanobacterium Geitlerinema sp. SCW is produced as a by-product in the manufacture of whey cheese and is characterized by a high organic load (d-COD), an acidic pH and high salinity. Seawater from the coastal area of Rio, near Patras, was used for dilution of the SCW to achieve an initial concentration of about 2000 mg d-COD/L in both cases without any external addition of the inorganic nutrients N and P.

Lab-scale experiments were conducted in separate Duran flasks with a working volume of 1L, under non-sterilized conditions, at room temperature (24 ± 1 ◦C), under continuous stirring (150 rpm) and continuous illumination (2000 lux) and without mechanical aeration. Optical microscopy studies revealed the development of a mixed-microorganism culture, consisting of the dominant microalgae/cyanobacteria biomass and the indigenous bacteria of the SCW.

The growth of the mixed biomass over time was studied, as was the removal of NO₃^- - N, PO₄^3-, d-COD and sugars. The simultaneous accumulation of bioproducts, such as proteins, carbohydrates and lipids, was also evaluated. The final biomass concentration was similar for both cultures, 710 mg/L for Geitlerinema sp. and 800 mg/L for P.costavermella, and the d-COD removal was approximately 55% and 65%, respectively. High removal rates were also achieved for sugars, with values of up to 80% and 91%, respectively. The cyanobacteria-dominated culture achieved higher carbohydrate (25.4%) and similar protein contents (19.8%) but a lower lipid (5.0%) content on the last day (10^th day) of cultivation than the microalgae-dominated culture (10.7%, 21.3% and 11.1%, respectively).

The biological approach used in this study has demonstrated that marine microalgae/cyanobacteria-based systems can be used as post-treatment steps for the treatment of dairy wastewater, while producing biomass useful in the biotechnology industry at the same time.