In der Aquakultur sind Kreislaufanlagen ein umweltfreundliches und wassersparendes Produktionsverfahren. Hohe Besatzdichten und das Prinzip der Wasserführung im Kreislauf führen jedoch auch zu einem erhöhten Risiko von Infektionskrankheiten. In dem hier beschriebenen Projekt wurde untersucht, wie sich niederfrequenter Ultraschall (nf-US) in Kombination mit der in der Aquakultur bewährten UV-C Bestrahlung zur Kontrolle von Pathogenen einsetzen lässt. Es wurden vergleichende Untersuchungen zur Effizienz von nf-US, UV-C und deren Kombination gegen prokaryotische und eukaryotische Modellorganismen durchgeführt. Während sich UV-C als sehr effektiv gegen Bakterien erwies, konnte die Gesamtkeimzahl mit nf-US nicht reduziert werden. Eine Vorbehandlung des Wassers mit nf-US verringerte jedoch die mittlere Größe der im Wasser suspendierten Partikel und konnte so die Effektivität von UV-C zur Inaktivierung von Bakterien verbessern. Zur Abtötung eukaryotioscher Organismen wird eine deutlich höhere UV-Dosis als zur Kontrolle von Bakterien benötigt. Eine starke Erhöhung der UV-C Dosis ist jedoch durch die dann mögliche photo-induzierte Bildung von Nitrit aus Nitrat limitiert. Alternativ könnte nf-US zur Abtötung eukariotischer Parasiten verwendet werden. Unterschiedlichen Organismen unterscheiden sich stark in ihrer Empfindlichkeit gegenüber nf-US, wobei sich die dosisabhängige Abtötung sehr gut mit Funktionen einer exponentiellen Abnahme beschreiben lässt. Die toxikologische Untersuchung des mit UV-C und/oder nf-US behandelten Wassers mit dem Fischeitest und dem Leuchtbakterientest ergab keinen Hinweis auf die Bildung toxischer Nebenprodukte. Diese Studie zeigt, dass nf-US mit Dosen, die gegen eine Vielzahl an Parasiten wie Ciliaten, Nematoden und Crustaceen wirksam sind, sicher eingesetzt werden kann. Die Kombination von nf-US und UV-C könnte ein geeignetes Verfahren sein, um alle relevanten Pathogene in Kreislaufanlagen zu kontrollieren. / Recirculating aquaculture systems are well-known as environmentally friendly and high water-efficient production systems. The high stocking densities and low water exchange leads to an increased risk of infectious diseases. In this project the combination of low frequency ultrasound (LFUS) with ultraviolet-C (UV-C) light for the control of pathogens was studied. A comparative study about the efficiency of LFUS, UV-C and their combination against prokaryotic and eukaryotic model organisms was performed. Against bacteria, the application of UV-C was very effective, while the application of LFUS was not effective. However, a pretreatment of the water with LFUS decreased the average size of the suspended particles and improved the bactericidal effect of UV-C light. Compared to the low bactericidal dose of UV-C, a much higher UV-C dose was required for inactivation of eukaryotic model organisms. A significant increase of UV-C dose, however, can be limited by the possible photo-induced formation of nitrite from nitrate. Alternatively, LFUS can be used to kill eukaryotic parasites. However, the efficiency of LFUS differed greatly between species and can be well described by functions of an exponential decay. The evaluation of whole effluent toxicity by using the fish egg test and luminescent bacteria test revealed no evidence of toxic disinfection by-products formation during UV-C irradiation and/or LFUS sonication. This study shows that LFUS can be applied safely at energy densities that are effective against a wide range of eukaryotic parasites like ciliates, nematodes and crustaceans. The combination of LFUS and UV-C could provide an appropriate water treatment with respect to all relevant pathogens in recirculating aquaculture systems.

Det kommer ske en stor utbyggnad av elektrolys för produktion av vätgas i Sverigeoch övriga världen. För att sänka produktionskostnaden och därmed göra vätgasenbilligare analyserar denna rapport vilket behov av syrgas och värme som en landbaserad fiskodling har, samt hur mycket syrgas och värme fiskodlingen skulle behövaköpa från en elektrolysör. Analysen visar att de arter som används i studien - tilapia(Oreochromis, Oreochromis,. Alcolapia), regnbåge (Oncorhynchus mykiss) och lax(Salmo salar) - i en odling som producerar 40 ton fisk om året skulle förbruka cirka1,16 procent av syrgasen och cirka 0,35 procent av värmen från en 3 MW PEMelektrolysör. Försäljningsvärdet av syrgasen och värmen från en 3 MW elektrolysörberäknas till cirka 695 000 SEK/år för syrgasen och cirka 1 830 000 SEK/år för värmen. Den genomsnittliga kostnaden för syrgas och värme för arterna i studien i enodling på 40 ton/år beräknas till 8900 SEK/år för syrgasen och 6400 SEK/år förvärmen i en landbaserad fiskodling. / There will be a major expansion of electrolysis for production of hydrogen in Sweden and the rest of the world. To reduce production costs and thus make hydrogencheaper, this report analyzes how much oxygen and heat a fish farm consumes andtherefore would need to buy from an electrolyser. The analysis shows that the species used in the study - tilapia (Oreochromis, Oreochromis, Alcolapia), rainbow(Oncorhynchus mykiss) and salmon (Salmo salar) - in a farm that produces 40 tonsof fish per year would consume 1.16 percent of the oxygen and 0,35 percent of theheat produced from a 3 MW PEM electrolyzer. The value of the oxygen and theheat from a 3 MW electrolyser is calculated at SEK 694,939/year for the oxygenand SEK 1,829,813/year for the heat. The average cost for the species in the studyin a 40 tonne/year fish farm is calculated at SEK 8,900/year for the oxygen and SEK6,400/year for the heat in a land-based fish farm.

Population escalation in the developing world has been associated with increased poverty, food insecurity and environmental degradation. The situation in Rwanda, with 2.82% annual population increase is no exception. The objective of the present study was to investigate an innovative integrated system of sustainable production suitable for resource-poor rural farmers, the Integrated Rabbit–Fish–Rice (IRFR) system. The study was targeted towards contributing to Rwanda government’s goals of eradicating extreme poverty and hunger, enhancing food security as well as abating environmental degradation. Three experiments, were carried out between 2008 and 2010, and designed to fertilise pond water with rabbit droppings and boost phytoplankton production. We also used results from our previous study, conducted in 2005 in the same ponds and under similar experimental conditions, especially rabbit and fish species and age, fishpond dimensions, as well as the fertilisation mode. The fishpond effluent was re-used to irrigate rice fields rather than being discharged into the environment. This study advocated the potential adaptation of rabbits to wetland conditions and the role of rabbit droppings as organic fertilisers in providing a better environment for fish production. On-farm resources, including rabbit droppings, were the main source of nutrients in the system. The analysis of nutrient flow revealed that 27% N and 79% P of the total nitrogen and phosphorus in fertilizing input in fishponds were supplied by rabbit droppings only. Nile tilapia Oreochromis niloticus were able to recover 18.5–37.6% N and 16.9–34.3% P of the total nitrogen and phosphorus inputs, the rest being accumulated in the pond water and the sediment, making them useful for soil fertilisation. The re-use of nutrient-rich effluent in rice irrigation increased rice production, allowing a successful complete substitution of inorganic fertilisers. The irrigation also reduced environmental pollution as the water seeping through rice field was 31.8 and 83.3% less concentrated in total phosphorus and nitrite pollutants, respectively, than was the pond water. Economically, the IRFR generated up to 597% net return over that of the rice inorganically fertilised, thereby substantiating the sustainability of the system. Overall, it is concluded that the IRFR system works well, is readily applicable, and capable of high, diversified, and sustainable production on limited land. As such, the study demonstrates the potentialities of the IRFR system to contribute successfully to poverty reduction, and the enhancement of food security in rural areas. The system promises economic returns and is environmental friendly. The research recommends the optimal range of rabbit density, that is, 800–1200 rabbits per hectare of pond, and the best fish stocking density, that is, 3 fish.mˉ², for a sustainable IRFR culture system. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.