Bioremediation means the use of organisms to clean contaminated water or soil. In his dissertation at the University of Jyväskylä, Čedomir Stevčić studied the combined cultivation of microalgae and water fleas in wastewater from recirculating aquaculture system (RAS) in boreal climate (ca. 17 °C) can be used to trap the dissolved nutrients.
Water Fleas are small planktonic crustaceans that filter microalgae and microbes from water for food, and are themselves natural food for many fish. Careful selection of microalgal species can improve the efficiency of bioremediation systems. In current studies green microalgae proved to be best suited for the development of this bioremediation system, which can prevent loss of valuable dissolved nutrients into the surrounding aquatic ecosystems by reusing them. The results of the thesis thus support the concept of circular economy and sustainable wastewater management.
The needs to increase fish production and to decrease waste discharges and environmental impacts have directed the aquaculture industry towards more intensive production, which could lead to environmental problems (e.g. eutrophication). Consequently, this has stimulated the development ofRASnot only because they reduce water use but also for providing opportunities for waste management and the use of released nutrients.
Reusing of the system’s by-products via integrated multi-trophic aquaculture (IMTA) approach is among the main ongoing developments in RAS. In IMTA, two or more compatible organisms from different trophic levels are simultaneously cultivated in a single system, where wastes from the production of the fed organism are recycled to become inputs for secondary/tertiary organisms. Due to the optimized use of available natural resources and diversification of revenue-based activities, IMTA significantly increases the sustainability of RAS and aquaculture in general.
Presently, there is almost no recycling of the dissolved nutrients released from RAS, except for aquaponics (aquaculture combined with cultivation of plants without soil,i.e. hydroponics). Microalgae are among the best organisms for IMTA due to a dual application that they provide for the aquaculture as they treat wastewater by assimilating organic/inorganic nutrients while incorporating them into a biomass that can be later used as animal feed.
Biological harvesting by filter-feeding organisms (e.g. zooplankton) offers an alternative for the expensive mechanical and chemical harvesting of microalgae with possibilities for further utilization of the produced biomass. Daphnia water fleas, small planktonic crustaceans (Cladocera), are non-selective filter-feeders that feed on microalgae with high digestion efficiency.In particular, Daphnia magna is one of the most well-known live feed organisms that can be used for both juvenile and mature fish.
The wastewater from RAS sustained the growth and nutrient removal of green microalgae equally well as when using a reference algal medium. Additionally, the growth of Daphnia feeding on microalgae did not differ between microalgae cultivated in RAS wastewater or in the reference algal medium. The wastewater from RAS suits this IMTA system even without costly filtration of RAS wastewater, as microalgae had similar growth, nutrient removal, and nutritional quality in both unfiltered and filtered RAS wastewater.
M.Sc. Čedomir Stevčić defends his doctoral dissertation in Aquatic Sciences “The use of biological traps for water treatment in recirculating aquaculture systems” on Friday 12th of February 2021 ONLINE at 12.00 o’clock. Opponent is Professor Emeritus Lauri Arvola from University of Helsinki and Custos is Senior Lecturer Katja Pulkkinen from University of Jyväskylä. The doctoral dissertation is held in English.
The audience can follow the dissertation online.
Link to the online event: https://r.jyu.fi/dissertation-stevcic-120221
For further information:
Čedomir Stevčić, cedomir.stevcic@jyu.fi, tel. +358 46 969 0542
Reference (open access):
Stevčić C. “The use of biological traps for water treatment in recirculating aquaculture systems“, JYU Dissertations, number 353, Jyväskylä, 2021.
Source: University of Jyväskylä
