engleski

Use of mussel production mesh stockings as a settling media, and wort as a carbon source in a marine denitrification bioreactor

Recirculating aquaculture systems (RAS) provide for the control of water quality under intensive feeding conditions using various unit processes to recycle and reuse culture water. Biological filtration is recognized as one of the most important and challenging segments of the system. While aerobic nitrification of ammonia and nitrite has become fundamental to such systems, the removal of the resulting nitrate accumulation has not received the necessary attention. The aim of this research was to investigate and quantify the potential benefit of the application of mesh stockings for mussel production, providing significant surface area per volume as a medium for bacterial settlement. The use of wort (raw material for beer production) was also examined for it's efficacy as the required carbon source for the bacterial growth. This study was carried out at the Business Innovation Centre for Mariculture of the University of Dubrovnik to qualify various components integral to the design of a marine RAS. The system consisted of two 1.5 mᵌ round tanks, a 1 HP pump for water distribution, a bead filter for mechanical filtration, rotating biological contactors providing the required nitrification and partial CO₂ sparging, and a UV-reactor for sterilization. Two plastic cylinders, 0.1 mᵌ each were included in the system to house the denitrification media. The nylon net stockings which were used as a settlement media for mussel production, were comprised of ellipsoid knots that connect the rectangular filaments. The number of knots and filaments were counted over one meter of the stockings length, using the recorded dimensions to calculate the surface area. Then, 400 m of stockings net was submerged into a denitrification reactor chamber, wort and nitrate were added, and a chemical oxygen demand and nitrogen ratio of 2.5/1 was maintained. In the described marine denitrification reactor, a stable nitrate removal rate of 40 mgL-1 per day was established using wort as a carbon source and net stockings for mussel production as a settling media. Nylon mesh proved to be a good media for the settling of denitrifying bacteria and its application in biological filters can be recommended. One meter of the material used in this research occupied a surface of 0, 083m2 and a volume of 2 x 10-5m3. It's specific surface area was calculated to be 4000 m2m-3. New settling material was used and achieved satisfactory biofiltration efficiency, even though biofilters containing a brand new media are usually more difficult to start. Stabile denitrification was achieved with carbon sources from wort, a raw material for beer production, consisting mostly of different carbohydrates that can be utilized by yeast. Further, wort has a very high chemical oxygen demand value so the added volume is almost negligible compared to the volume of the denitrification reactor. Since this is the first record of wort usage as a carbon source for denitrification, further research both in marine and freshwater conditions, is needed.

denitrification bioreactor ; mussel mesh stockings ; wort

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