The Effect Of Biological Materials In Water Treatment Of The Marine Recirculation Aquaculture System(RAS)

Wastage treatment is the most important in the recirculating aquaculture system and removing inorganic inorganic-nitrogen is one of the targets. In order to find the materials and methods to remove the inorganic-nitrogen efficiently, this study measured the five biofilters (White glass ring、Volcanic rock、Red breathing loop、Coral sandstone、Bacterial ball) specific surface area, analysed the effects of mixing different dosages and ratios to remove and transform TAN、NO2--N and NO3--N. Moreover, this study investigated the absorption of Caulerpa sertularioides on TAN、NO2--N and NO3--N.The study showed that the highest specific surface area was in Bacterial ball, reaching34.876±3.405m2/g, while the lowest value of4.488±0.865m2/g was in Coral sandstone. White glass ring、Red breathing loop and Volcanic rock had the similar specific surface area, ranging from8.259to9.203m2/g.The highest efficiency of removing inorganic-nitrogen was in White glass ring, followed by Red breathing loop, Volcanic rock、Coral sandstone and Bacterial ball. During biofilm cultivation,the lowest of TAN in White glass ring was at17day and the rest biofilters were at23day. The efficiency of White glass ring and Red breathing loop to remove TAN were92.5,90.7%, respectively, while the rest biofilm was between85～88%. For removing NO2--N, the highest efficiency was in White glass ring, followed by Volcanic rock, Red breathing loop, Bacterial ball and Coral sandstone. There was no effect to remove NO3--N in these five biofilters and only at the accumulation. When treating higher concentration of TAN after biofilm cultivation, the lowest concentration of TAN (0.215mg/L) was shown at15day in White glass ring and Red breathing loop with95.5%removing efficiency; White glass ring had the highest efficiency to remove NO2--N and the highest value of5.943mg/L at7days, then the efficiency decreased quickly. Red breathing loop had the lower efficiency to remove NO2--N in comparison with White glass ring as the highest value was at9days. Volcanic roc、Coral sandstone and Bacterial ball had the lowest efficiency with the highest value at about11days. White glass ring, Red breathing loop, Volcanic rock, Coral sandstone and Bacterial ball showed an increasing trend to accumulate NO2--N. The concentration of NO3--N was still increasing.The concentration changes of TAN could be fitted as y=ae-bx formula with better goodness of fit (R2≥0.9218) after the recirculation aquaculture system was treated with5biofilters. The parameter b in the formula was biggest in White glass ring treatment and the lowest was in Bacterial ball treatment. The concentration changes of NO2--N and NO3--N could be fitted as y=1/(a+b/xlnx+c/x) formula with goodness of fit R2≥0.9218. Moreover, when the five biofilters were used to treat TAN, the concentration change was negatively correlated between TAN and NO2--N and NO3--N.The highest efficiency to remove TAN was in Red breathing loop and Coral sandstone treatments with the quality ratio of14and2%, respectively. The concentration of TAN was lowest at21days and removing rate was97.49(Red breathing loop) and97.23%(Coral sandstone). Regarding the removing efficiency of NO2--N, Red breathing loop treatment at quality ratio of10and14%was the best, the concentration of NO2--N started to increase at5days, peaked at11days and decreased to lowest at about25days. Coral sandstone treatment at quality ratio of2%had also good efficiency to remove NO2--N as the concentration started to increase at7days, peaked at17days and decreased to lowest at29days. The concentration change of TAN could be fitted as y=a/(1+becχ)+d with goodness of fit R2≥0.9851, while the concentration change of NO2--N and NO3--N could be fitted as y=xaeb/χ+cχ+d with goodness of fit R2≥0.9574.The higher efficiency to remove TAN and NO2--N was in treatment with the ratio of White glass ring、Red breathing loop and Coral sandstone at8:3:1. During the period of biofilm cultivation, the concentration of TAN decreased to lowest of0.025mg/L at10days with the removing rate at98.5%; The concentration of NO2--N started to increase at5day, peaked at10days and then decreased to the lowest of0.035mg/L; the concentration of NO3--N was still in the accumulation period. When the biofilm cultivation was mature, the concentration of TAN decreased to the lowest of0.036mg/L at4days, the concentration of NO2--N peaked at2days and decreased to lowest (0.02mg/L) at5days. The concentration of NO3--N was still in the accumulation period. The TAN concentration change could be fitted as y=a/(1+b*e(c*χ))+d with the goodness of fit R2≥0.9969before and after biofilm cultivation. The concentration of NO2--N and NO3--N could be fitted as y=xa*e(b/χ+c*χ)+d with the goodness of fit R2≥0.9117.The highest absorption of TAN and NO2--N by C. sertularioides was produced when the concentration at11～15g/L, the TAN concentration decreased to0.10mg/L at8h with the removing rate of80.9%, the NO2--N concentration decreased to0.02mg/L at30h with the removing rate of91.6%. There was no significant difference between each other. TAN concentration decreased to0.09mg/L at24h when the C. sertularioides at9g/L, and the concentration was then decreased to lowest of0.11mg/L at48h when the C. sertularioides at7g/L. No removing effects were found at48h when the C. sertularioides below5g/L. The concentration of NO2--N decreased to0.15mg/L at48h when the C. sertularioides below7g/L. The higher absorption rate of NO3--N was found when the C. sertularioides at17～19g/L with no significant difference. The concentration of NO3--N dropped to0.05mg/L at24h with removing rate of92.6%. When the C. sertularioides at9～11and7g/L, the concentration of NO3--N decreased to0.05and0.3mg/L respectively at48h.