PERIPHYTON- BASED BIOFILTER FOR MARICULTURE EFFLUENT TREATMENT, POTENTIAL FOR SUSTAINABLE LAND- BASED MARICULTURE
Effluent treatment and high-protein feed incur much of land-based aquaculture's operation cost, and influence their sustainability. Periphyton is a plant- dominant community of aquatic micro and macro organisms that develops as natural film on different wet surfaces when exposed to elevated nutrient stream and light. Periphyton has been well demonstrated to serve as natural food source in aquaculture systems, while keeping water quality at high level. Marine periphyton, however, is insufficiently understood for commercial implementation in mariculture.
In the current study we examined the performances of a novel periphyton- based biofilter fed with effluents from mariculture system. Growth rates and yields and nutrient uptake rates were examined during two seasons. Metagenomics analyses, supported with microscopy and chlorophyll profiling, were performed to study the effect of seasonal changes, as well as other factors, on the community composition and dynamics in periphyton.
Periphyton showed to grow successfully with daily yields of 1.8 - 2.4 grams ash free dry weight per m2 of provided substrate. Multi comparison analyses confirmed correlation between the growth of periphyton biomass and the uptake of ammonia and phosphorus with uptake rates of 0.13 - 0.44 g TAN h-1 m-2 per one gram (afdw) of gained biomass (figure 1). The produced periphyton consisted 30-40% of protein, suggesting it potential for fish nutrition. Community composition in periphyton consisted diatoms; cyanobacteria as well as other bacteria; flagellate; nematode; and ciliate. Microalgae, mostly cyanobacteria in the summer and diatoms in the autumn, were dominated young periphyton. Silica enrichment of the effluent increased the diatoms abundance and diversity in the periphyton but also increased lipids content up to 9% of total biomass. Such chemical manipulation was also valuable postponing the appearance of macroalgae for at least 35 days.
Results from the study support the potential of marine periphyton as cheap, sustainable biofilter in mariculture. The required surface area for production of periphyton that will support commercial diet for growth of marine fingerlings can be calculated from results of current study.