| RAS (Recirculating aquaculture system) offers several advantages, such as saving water, less pollution, high density and more production, being freedom of area and climate, handing convenience. It is regarded as an effective and sustainable method to increase product quality without any pollution in mariculture industry.The waste water treatment and reusing is the most important thing in RAS, especially to the removing of TAN (total ammonia nitrogen). As the core unit of RAS, biological filter plays a key role on removing NH3-N and NO2-N, which are both toxic to fish even at a low concentrations.To the biofilter, there are many things we still don't known. For example, how to select and optimize the mediums to make the biofilter work more efficient, what's the dynamic of the microorganism community and the characteristics of the biofilm, how to control and management the system according to its nitrification kinetics, and so on. For the purpose of design and optimization of marine biofilter, the following work had been done: 1) the ammonium removal efficiency and the dynamic of the bacteria community in marine biofilter charged with bamboo substrate; 2) comparing the ammonium removal efficiency of four kinds of marine biofilters charged with different mediums; 3) impacts of organic carbon on TAN removal rate of the different marine BAF; 4) nitrification kinetics of marine biofilters charged with bamboo substrate.Firstly, ammonium removal efficiency and the dynamic of the bacteria community in marine biofilter charged with bamboo substrate during the start-up and steady-state period were examined. The hydraulic retention time, temperature, gas/water ratio and pH were 1 hour, 18～25℃, 3:1 and 8.05～8.53, respectively. Results showed that bamboo biofilter enable the nitrifying bacteria to grow rapidly with the influent TAN concentration of 0.08～0.15mg/L, and the number of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria is 4.5×105 CFU/mL, 1.5×105 CFU/mL (smooth) and 1.1×106 CFU/mL (crude) in steady-state period, respectively. The ammonia removal efficiency was high with TAN removal efficiency of 80%. The effluent TAN concentration of bamboo biofilters was below 0.06mg/L, which was much lower than the toxic level for almost all cultural species. Bamboo medium can meet the requirements of application in RAS. Secondly, the membrane-hanging process and comparison on ammonia removal efficiency among the four different mediums biofilters had been evaluated. Results indicate that when HRT is 30 min, temperature is controlled in the range of 14～18℃, salinity is 31, influent TAN concentration is 0.5 mg/L, it takes at least two months for biofilm to reach a steady-state with a high TAN removal efficiency. The relatively invariable inlet loading is good for membrane-hanging and steady-going. The effluent nitrite concentration from bamboo biofilter is low and less than 0.07mg/L, while, effluent nitrite concentration from maifan stone and ceramic pellet biofilters are much higher with maximum value of 0.28 and 0.13 mg/L, respectively. The TAN removal rate of bamboo, maifan stone, ceramic pellet, plastic biofilters are 331.38, 425.73, 310.38, 128.24 mg/ (m3·h). The ceramic pellet with the largest specific surface area is much better for biofilm to format and make the biofilter much easy to be control stable. According to TAN removal efficiency, cost and energy consumption, the bamboo medium has many advantages in mariculture wastewater treatment.Thirdly, the impact of organic carbon on TAN removal rate was investigated for four types of marine biofilters. The experimental results showed that high TAN removal rate was observed when COD/TAN was less than 10, however, when COD/TAN ratio increased from 10 to 30, it decreased about 70% for a substrate concentration of 0.5 mg/L. The relationship between COD/TAN ratios and TAN removal rates matches binomial function very well when using polynomial analyzing.Fourth, kinetic characteristic for mariculture wastewater treatment was studied in bamboo mediums biofilter. The experimental condition is DO>6 mg/L, COD <0.01mg/L, 25℃, salinity 31, with ammonia as a single limiting substrate. The experimental results indicated that the steady-state kinetics of substrate removal can be described by the Monod-type expression and kinetics parameters were evaluated by integral method: Vmax=1828.70mg/ (m3·h), ks=0.3916mg/L, R2=0.9752. It can be successful application in the kinetic model for prediction of TAN removal rate by validating. |
