טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentBen Asher Raz
SubjectDevelopment of a Physicochemical Approach for Operation of
Seawater Recirculating Aquaculture Systems (RAS)
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Ori Lahav
Full Thesis textFull thesis text - English Version


Abstract

There is an unmet need for a new generation of recirculated aquaculture systems (RAS), which may improve economic aspects, fish welfare and environmental aspects, in addition to being a reliable technique for growing fish. This work focused on investigating the development of a new physicochemical approach for operation of seawater recirculating aquaculture systems (RAS). The concept is based on indirect ammonia electrooxidation for removal of nitrogen species, which are excreted by the fish in aquaculture systems, along with simultaneous disinfection of the water, for improving both water quality and fish welfare. A feasibility test for the physicochemical seawater RAS concept was demonstrated. Both fish performance and economic perspectives were proven beneficial. The process was shown to achieve up to 95% nitrogen removal while the rearing water was simultaneously disinfected. THM (as a case study for chlorination by products) were formed at relatively low concentrations during the electrolysis step due to the development of organic matter that showed low availability for reactions with bromine-chlorine species. The factors leading to reduced highly-brominated THM formation were revealed, and the removal of THM using aeration was quantified. The highly brominated THM content in the fish tissue was examined, and the bio concentration factor of bromoform and dibromochloromethane was found to be 1.35 and 0.23 l/kg, respectively, in muscle tissues at the system's conditions. The meaning of this finding is that the fish grown in the proposed process are edible with regard to the EPA regulations for bromoform and dibromochloromethane. A comparative experiment between a physicochemical and a bio-treated RAS was performed for evaluating the proposed inherent disinfection effect upon exposure to the nervous necrosis virus (NNV). Very low immune response was detected in the physicochemical RAS (relative to a control, biological-based treatment system), suggesting that the disinfection action substantially reduced the viral presence in the rearing water.