Foundenmental Study on Nitrification Process of Seawater Biofilter to Treat the Mariculture Wastewater
|School||Qingdao Technological University|
|Keywords||recirculting aquaculture system bamboo ring-packed biofilter marine quaculture wastewater accumulation of nitrite nitrogen nitrification kinetic|
The treatment and recycling of the wastewater are the core technologies in the marine RAS, in which the removal of ammonia nitrogen and nitrite nitrogen that are harmful to aquatic animals is the key to the successful operation of the technology. The starting point of the issue was service production, based on the basic experimental studies on the biofilter nitrification of marine fish culture scene. By constructing bamboo ring-packed biofilters that were used to deal with the practical fish wastewater, we systematically studied the nitrification process in biofilter that is the most important water treatment technology in RAS. Main conclusions were as follows:⑴Through the practical studies on the industrial RAS, we found that the RAS had well economic efficiency, little environmental pollution and an extensive application prospect. In the daily production management, feeding behavior on fish ponds significantly affected the ammonia nitrogen, COD and SS concentrations but little did the nitrite nitrogen concentrations. Arc filter screen and protein separator played major roles on the SS and COD removal respectively, the biofilter was irreplaceable to the ammonia nitrogen, nitrite nitrogen and COD degradation and it also had a certain effect on the rejection filter of the SS. At the same time we found that the two kinds of marine fish culture system, Epinephelus malabaricas and Cynoglossus semilaevis, had significant differences in water quality pollutant and the physical and chemical indicators.⑵The pollutant removal characteristics of bamboo ring-packed biofilter during the start-up period and steady-state period to wastewater in marine culture with the high salinity and low ammonia nitrogen loading we studied, and we also studied the differences on pollution removal rate between the experimental biofilters and the site-biofilters during the steady-state period, all results showed that when the influent ammonia nitrogen concentration was from 0.93 mg/L to 1.33 mg/L, nitrite nitrogen concentration was from 0.12 mg/L to 0.29 mg/L, dissolved oxygen was from 7 mg/L to 9 mg/L, pH was from 7.1 to 7.4, temperature was from 23℃to 24℃, salinity was from 29 to 30 and the HRT was 30 minutes, the development of the biofilm for experimental biofilter needed 45 days. During steady-stage period, ammonia nitrogen removal rate was from 30% to 39%, nitrite nitrogen also had a significant removal rate, the lowest effluent concentration was 0.06 mg/L for experimental biofilters. In the comparative experiments of experimental biofilters and site-biofilters, the experimental biofilters had distinct advantages in the removal of ammonia nitrogen, nitrite nitrogen and SS concentration. Its maximal removal of ammonia nitrogen was 52% and SS was 57%, and the lowest effluent nitrite nitrogen was 0.12 mg /L. The site-biofilter had a little higher COD removal rate with a maximum value of 14%, although the COD removal rates of the both types of biofilters had poor results.⑶The experiments studied the accumulation of nitrite nitrogen in experimental biofilters during the steady-state period. Through the researches of influence organic loading, ammonia loading, temperature, pH, dissolved oxygen and other operating conditions, we concluded that the low dissolved oxygen was the main factor for the nitrite nitrogen accumulation. At the same time, we analysised the possible factors in denitrification process that may lead to the nitrite nitrogen accumulation, and we thought denitrification promoted the nitrite nitrogen accumulation.⑷We researched the influence of different operating conditions on removal rate of ammonia nitrogen and COD, and the results showed some conclusions as follow:①When the influent SS concentration was from 1.55mg/L up to 3.49mg/L, the ammonia concentration was upward in the overall trend, and the maximal removal rate was 40% increased with the increasing of SS concentrations. The influent SS had no significant effect on the COD concentrations and the COD removal rate was steady at 14%.②When the influent pH was from 6.50 up to 8.28, the overall trend of ammonia nitrogen removal rate was firstly increasing slowly, stabilizing and followed by the sharp decline. The maximal removal rate reached 54% when pH was 7.34, and the removal rate decreased from the pH value of 7.70 but stabilized at 47%, and then it decreased rapidly to about 10% when pH was more than 8.24. At the same time, in the influent water pH ranges, COD removal rate of the overall trend was a slight increasing and stabilization. For example, when pH was from 6.72 up to 7.14, the removal rate was stable but less than 10%, and when pH was more than 7.31 the removal rate increased and eventually stabilized between 20% and 22%.③When the influent water temperature was from 11.0℃up to 25.9℃, the ammonia nitrogen removal rate reached maximal 45% at 23.3℃, COD removal rate was steady around at 20% when the temperature was higher than 25.4℃.④In the experimental study of four HRTs, when the HRT was 40min or 80min, the maximal removal rate of ammonia nitrogen was 49%, COD removal rate was up to 20% when the HRT was 40 min.⑤In the optimum HRT of experimental biofilters, when the packings height was from 20 cm to 40 cm, COD removal rate was better than other removal rates, and it reached the maximal value of 26% at the height of 40 cm, while the ammonia nitrogen removal was better than other removal rates when the packings height was from 60 cm to 80 cm, and the maximal removal rate was 51% with the packings height of 60 cm.⑸Supposing that the ammonia nitrogen was the only limiting factor in nitrification and at different influent flow (40,70 and 100L/h) under the conditions of the RAS, we studied the ammonia nitrogen concentration and nitrification rate dynamic equation.The results showed that when ammonia concentration was very low, the nitration reaction consistented with first order kinetic equation and nitrification reaction rate and ammonia concentration were proportional to substrate concentration. When the ammonia nitrogen concentration was very high, the nitration reaction consistented with zero order kinetic equation and nitrification reaction rate was nothing to do with the ammonia nitrogen concentration. Established by a large number of experimental datas about nitrification kinetic model under different influent water flows can be used to predict the effluent ammonia concentration in an actual fish wastewater.The dissertation studied the bamboo ring-packed biofilter in marine wastewater treatment, and the researches can provide some basis conclusions on marine wastewater treatment system for nitrification biofilter, it can also provide a reference to the removal of ammonia nitrogen and other pullutions in water treatment units in commericial aquaculture productions.