| Recirculating aquaculture systems is getting attention and application in the world, and will become one of the main direction of aquaculture industry sustainable development. It has many characteristics, such as efficient, controllable, water-saving and land-saving, little environmental pullution. In this paper, as a core of bio-filter and constructed wetlands, the bio-film formation and efficiency of purifing water of bio-filter were studied; the changes of microbial community structure on bio-carrier of recirculating aquaculture systems during different periods were analysed by PCR-DEEG; simulated mariculture effluent and constructed indoor compound vertical flow constructed wetlands system, the influence factors of constructed wetlands purifying mariculture effluent were discussed, on this base, the optimal operating parameters of the systems were determined, and the systems were operated two months, the performance of treating water and preliminary mechanism were studyed. The main conclusions are as follows:1. Adding a certain amount of probiotics and nutrient in bio-filter, bio-carrier surface formed community structure relatively stable bio-film after a month of bio-film formation. Then devised productive experiment of breeding Cynoglossus semilaevis Günther using recirculating aquaculture systems. The system run stably, and the bio-filter could reduce the concentration of ammonia-nitrogen, nitrite-nitrogen, chemical oxygen demand and phosphate, which maintained the concentration of pollutants of systems in a reasonable level and Cynoglossus semilaevis Günther grew well.2. It presented a trend that the quantity of heterotrophic bacteria, ammonia oxidize bacteria and nitrite oxidize bacteria increased gradually to a top and then fallen slowly to a stable level. The number of heterotrophic bacteria was 1-2 orders of magnitude more then ammonium oxidation bacteria and nitrite oxidize. The composition of microbial community of the bio-carrier was very abundant in different periods, and Shannon index was 1.53, 1.44, 1.57, 1.08, 1.27 and 1.30, respectively. During different periods,there was a certain shift in the microbial community structure, which existed some unique species and common species. Beside A4 period and B1 period Cs value(similar index) was low, the Cs value in two adjacent periods was high,indicating the variation and succession of the microbial community was slow and regular, and ensured the stable effect of bio-film treating mariculture effluent. 3. The microbial community distributed widely in bio-filter. The 33 DGGE bands belonged to theα-Proteobacteria,β-Proteobacteria andγ-Proteobacteria of Proteobacteria (seventeen operational taxonomic units), the bacillus of Firmicutes (one operational taxonomic units) and the Flavobacteria of Bacteroidetes (fifteen operational taxonomic units), respectively. Proteobacteria and Flavobacteria were main communities. Several bacteria had an effect on removal of pollutants for farming water and the effluent water quality could meet the requirements of high-density culture. The Nitrosomonas and some other facultative anaerobic bacteria(Flavobacteriaceae bacterium)were identified,which indicated that there may be coexisted pathways of nitrification and denitrification in bio-filter. These functional bacteria played a very important role in operating systems.4. With the increase of salinity, the removal rate of chemical oxygen demand and ammonia-nitrogen didn't change significantly (P>0.05), the removal rate of phosphate was decreased gradually and changed significantly (P<0.05), but the reed showed a strong salt-tolerant ability, growing well under the condition when the salinity reached to 20. As the hydraulic load increasing, the removal rate of chemical oxygen demand, ammonia-nitrogen and phosphate also showed a fall tendency and changed greatly (P <0.05). While the pollution load increasing, the removal rate of chemical oxygen demand, ammonia-nitrogen and phosphate were showed a trend that increased first and then decreased gradually. When the pollution was chemical oxygen demand 10 mg﹒L-1, ammonia-nitrogen 2 mg﹒L-1, phosphate 0.5 mg﹒L-1, the efficiency of water treatment was highest, and the average removal rate was 75%, 62%, 49%, respectively. When the concentrations of dissolved oxygen increasing, the removal rate of chemical oxygen demand, ammonia-nitrogen and phosphate had no significant change (p>0.05).5. In the optimized conditions, the constructed wetlands operated two months. The average removal rate of total suspended solid was more than 90%, the average removal rate of ammonia-nitrogen and biochemical oxygen demand was more than 70%, the average removal rate of chemical oxygen demand was more than 60%, and the average removal rate of nitrite-nitrogen, nitrate-nitrogen, total nitrogen, phosphate, total phosphorous and total organic carbon was between 30% and 50%. The quality of effluent was well, which met the standard of water reuse.6. Bio-filter and constructed wetlands had a certain practical application value and advantage in purifying mariculture effluent. |
