Food security, specifically in water-scarce regions, is a local and global aim which requires innovative solutions. Assimilation based recirculating aquaculture systems (AsRAS ) such as aquaponics, algaponics and bacterioponics can be such a sustainable solution. All AsRAS involve the integration of conventional recirculating aquaculture system (RAS) with assimilation based reactor in a symbiotic arrangement. In aquaponics for example, fish excretions are assimilated as a nutrient source for vegetable production (Zhu et al., 2022) , where in algaponics and bacterioponics it would be replaced by macro or micro algae and bacteria respectively. As a result, the assimilation of the fish waste by plants or bacteria treat the water, and enables its recirculation back to the fish tank. This practice allows for extremely high efficiency in the use of water and nutrients, greatly limits the discharge of pollutants and recovers or saves a lot of energy (Yogev and Gross, 2019) .
In recent years w e have developed three different AsRAS that are operated on fresh or brackishwater in multi-loops near-zero waste setups. The systems include separate loops for fish production (RAS) and for the assimilation organism growth which facilitate optimal conditions for each crop. In addition, in some systems two separate treatment loops are used to treat the solid waste (e.g. from fish and inedible plant bits) by anaerobic digestion, producing nutrient-rich supernatant which is good for plant growth and energy via biogas .
In all tested systems f ish stocking density reached up to 80 kg/m3 with typical density of approximately 50 kg/m3. Feed (45% protein content) was applied daily at 2% of body weight. Typical fish performance was observed with a survival rate >95 % and feed conversion ratio ranged between 1.1-1.4. Significant energy saving was demonstrated; from >80% in the aquaponics system and 50% in the bacterioponics/biobloc based RAS. C arbon sequestration was 1.4 higher than the feed carbon in the aquaponics system , which reduced the carbon footprint of typical RAS by 64% where similar or even higher reduction is expected for the algaponics -based AsRAS. Moreoven in all of the studied AsRAS significant reduction of nitrous oxide was recorded when compared to traditional RAS.
Th ese stud ies are among the first to demonstrate highly efficient AsRAS production with near-zero water and waste discharge and with significant energy recovery or savings. We postulate that AsRAS systems have a great potential to replace the traditional nitrification-denitrification based RAS.
Yogev, U., Gross, A., 2019. Reducing environmental impact of recirculating aquaculture systems by introducing a novel microaerophilic assimilation reactor : Modeling and proof of concept. J. Clean. Prod. 226, 1042–1050. https://doi.org/10.1016/j.jclepro.2019.04.003
Zhu, Z., Yogev, U., Goddek, S., Yang, F., Keesman, K. J., Gross, A. 2022. Carbon dynamics and energy recovery in a novel near-zero waste aquaponics system with onsite anaerobic treatment. Science of The Total Environment, 833, 155245. https://doi.org/10.1016/j.scitotenv.2022.155245