The Israeli Journal of Aquaculture - Bamidgeh 54(2), 2002
The Annual Dan Popper Symposium


SULFIDE OXIDATION IN A ZERO-DISCHARGE
MARINE RECIRCULATING SYSTEM


Iliya Gelfand¹, Eddie Cytryn¹,², Jaap van Rijn¹*

1 Department of Animal Sciences, The Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot 76100, Israel
2 Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization, The Volcani Center, Beit Dagan, Israel


Abstract

A unique treatment system allowing culture of marine fish without waste discharge has been operated for the past three years at our facilities in Rehovot. The system supports intensive culture of gilthead seabream (Sparus aurata) in a completely closed mode and comprises an aerobic and an anaerobic treatment stage. In the aerobic stage, ammonia is oxidized to nitrate by nitrifying bacteria situated in a trickling filter. In the anaerobic stage, consisting of a digestion basin and a fluidized bed reactor, organic waste from the fish tank is biologically degraded with a concomitant reduction of nitrate to nitrogen gas. Sulfide formation, from reduction of sulfate in the anaerobic treatment component, forms a potential threat to the successful cultivation of fish in this marine zero-discharge system.

In the present study, it was demonstrated that reduction of sulfate to sulfide takes place in organic-rich and nitrate-poor zones in the digestion basin. Sulfide concentrations in the effluent of the digestion basin were occasionally as high as 80 µM. However, due to rapid oxidation in the fluidized bed reactor situated between the digestion basin and the fish tank, the sulfide concentrations were lower than 0.2 µM in water leaving the anaerobic treatment stage. Laboratory incubations of crude cultures derived from the fluidized bed reactor demonstrated that sulfide oxidation coincided with a reduction of nitrate. Subsequent studies on denitrifying strains isolated from the fluidized bed reactor revealed the presence of heterotrophic as well as chemolithotrophic denitrifiers capable of reducing nitrate to nitrogen gas and oxidizing sulfide to elemental sulfur and sulfate. DGGE analysis of PCR-amplified 16S rDNA fragments showed a close affiliation between the microbial community of the fluidized bed and known marine sulfide-oxidizing denitrifiers.

*Corresponding author. Fax: 972-8-9465763; e-mail: vanrijn@agri.huji.ac.il

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