Comparative Study Of Biofilters With Four Different Substrates To Simulated Mariculture Wastewater

Biofilter is the hard core of recirculating aquaculture system (RAS), and substrate is vital to the performance of biofilter. Bamboo Ring, Maifan Stone, Ceramic Pellet and Plastic Ball (PE) substrates were packed into different biofilters. And physical chemistry characters of substrates, COD removal rate and ammonia nitrogen removal rate were investigated and evaluated by simulated mariculture wastewater under different C: N ratio, COD and ammonium nitrogen removal mechanism and principle was analyzed and discussed. The results were showed as followed,(1) The specific gravity of Bamboo Ring substrate was near to sea water and the most comfortable for aquaculture production. The specific surface area of Ceramic Pellet substrate was the largest. The granule diameter of Maifan Stone substrate was the minimum, with the most possible total specific surface area. Specific surface area measured by BET principle reflected the largest possible surface area, but unfit for reflecting the surface area usable for absorption of biofilm bacteria.(2) COD removal rate and ammonium nitrogen removal rate of Maifan Stone substrate were the fastest because of adsorption effect, least granule diameter and possible total largest specific surface area,with the highest rate of 850g/m~3·d and 20g/m~3·d respectively. Secondly was the Bamboo Ring substrate, with the highest rate of 750g/m~3·d and 18g/m~3·d respectively in a similar C: N ratio to aquaculture water. Ceramic Pellet was just after the Bamboo Ring, with the highest rate of 750g/m~3·d and 15g/m~3·d respectively. Plastic Ball was the slowest, with the highest rate of 650g/m~3·d and 10g/m~3·d respectively. As carbon sources concentration improving, the TAN removal rate decrease and COD removal rate increase. If C: N ratio was higher than 12, it could destroy the biofilm structure and nitrification function.(3)The percentage of ammonium nitrogen removal for different substrates diversified significantly under different C: N ratio. The percentage of ammonium nitrogen removal for Maifan Stone,Ceramic Pellet and Plastic Ball ascend exponentially upward with time changing, respectively with fitting functions: y = 0.334Ln(x) - 0.173(R2 = 0.81),y = 0.195Ln(x) + 0.015(R2 = 0.75),y = 0.069Ln(x) - 0.039(R2 = 0.49); and Bamboo Ring ascending linearly upward with time changing, with fitting functions: y = 0.0251x(R2 = 0.91)。(4) Nitrobacteria number is lower than heterotrophic bacteria. Bamboo Ring's AOB number was the highest, amounting to 4.47×106 MPN/g. Under running condition of 15-22℃and HRT 0.5 h, different substrates'nitrobacteria number reached a plateau and matured in 40-50d,Bamboo Ring with 50d, others with 40d.(5) Choosing different substrate can impact the running stability of biofilter. Choosing substrate closely relates with biofilm maturation time and nitrification process, and affects obviously nitrifying efficiency.(6)Biofilters remove ammonium nitrogen periodically and cause fluctuation of ammonium nitrogen in biofilter outflow water, because of inflow fluctuation and changing of biofilm bacteria.