Drying Studies of Purple Non-Sulphur Bacterial Biomass and Application as a Single-Cell Protein Feed for Litopenaeus vannamei

Growing population, land loss and climate change have led to growing pressures on global food production and nutrition, water, and other such resources, leading researchers to seek opportunities for alternative food and feed sources. In this regard, single-cell protein (SCP) has emerged as an attractive opportunity due to its high productivity rate and lack of competition with arable land. Purple non-sulphur bacteria (PNSB) are one organism with a strong potential for single-cell protein. PNSB are anoxygenic bacteria that handle wastewater with elevated organic strength, producing biomass containing relatively high protein content and having proven probiotic characteristics with marine shrimps and different fish species. This research assessed the use of SCP biomass, produced from the integrated PNSB-based treatment of fuel synthesis process wastewater (FSW) in a circular economy approach, as feed for shrimp aquaculture. The fuel synthesis process is a major economic industry for Qatar and produces one of the largest industrial wastewater flows.

Firstly, the study examined the drying kinetics of the PNSB biomass produced from the treatment process, then tested the use of the same extracted mixed culture of PNSB as a feed for Litopenaeus vannamei. Given the complex nature of fuel synthesis process wastewater, a key goal of the research was to assess the efficacy and safety of PNSB biomass harvested from (FSW) as marine shrimp feed. Ten different drying kinetic models were trialed on the thin-film (2 mm, 3mm, and 4 mm) oven-drying data for temperatures varying between 60℃ and 120℃, and the best model was selected through statistical analysis. The Ameri model fitted the best in cases of 60℃ and 80℃ in all of the considered thickness of biomass, while the Midilli-Kucuk model performed better at 100℃ and 120℃ for the majority of the thicknesses (with the exception of Page model in case of 2 mm at 100℃ and 4 mm at 120℃) where temperature gradients across the biomass become more pronounced. The drying rate decreased with increasing thickness of the biomass film because more time and energy are required to remove moisture from the paste through the film to the surface. No significant differences existed in the proximate composition of the PNSB biomass dried at the different considered temperatures. After the drying study, the PNSB biomass was mixed at different ratios (0, 15, 30, 45, and 60%) with commercial feed (control). A 35-day trial was done to analyze the diets’ impact on shrimp growth and mortality.

The results indicated a comparable growth of shrimps with the control for 15 and 30% PNSB blends having a growth rate between 0.50±0.08% to 0.53±0.07% by the end of the trial while the control had 0.49±0.04%. However, the 45% and 60% PNSB blends showed significantly lower growth, with the latter achieving a ratio of only 0.21±0.09%. The shrimps fed with these diets did not experience any deaths, which were observed in some other conditions including the control. The results indicate the safety of using the PNSB biomass acquired from FSW in shrimp farming and encourage further research on the sustainable production of aquaculture feed by blending it with microbial protein obtained potentially from waste sources.