Effects Of Several Environmental Factors On Nitrification And Nitrite Accumulation In Seawater Biofilter

As the largest aquaculture country in the world,the total output of china ranks first in the world.However,the rapidly development of mariculture in China has caused damage to the coastal water environment.The traditional marine aquaculture model of resource dependence and extensive management had no longer conform to the requirements of marine sustainable development.As a new industrial breeding technology,Recirculating Aquaculture System has the advantage of saving water resources,protecting environment,economy and high yield,it is one of the important directions in the development of modern aquaculture.The biofilter is the core water treatment unit of the recirculating aquaculture system,and its stable and efficient operation is the key to the recirculating aquaculture system.The operational process of biofilter may be affected by many environmental factors,resulting in instability of its water treatment capacity.In order to improve the nitrification performance of the biofilter,this paper evaluated the influences of temperature,pH and the concentration of TAN on the biofilters.The main results are as follows,?1?Under the condition of the influent ammonia nitrogen concentration is about 2.0mg/L,the water temperature is about 22,the salinity is 30 per thousand,and the dissolved oxygen?DO?is about 6mg/L,the study focusing on the start-up stage,which in different circumstances of pH?7.0,7.5,8.0,8.5?impact biofilter under natural biofilm condition.The results showed that with the change of time,the treatment of biofilter with TAN and NO₂^--N became more and more stable.And under the circumstance of p H=7.5⁸.0,biofilter could quickly establish and improve nitrification capacity and maintain stable operation in about50⁷0 days.Especially under the circumstance of pH=7.5,the start-up time of biofilter cost lowest.At 36d,the treatment efficiency of TAN reached more than 80%,and the accumulation of NO₂^--N began to disappear,and it could start successfully around 50d.?2?Under the condition of the influent ammonia nitrogen concentration is about 2 mg/L,the COD concentration is 4.0⁵.0 mg/L,the salinity is 30 per thousand,and the DO is about 6.0mg/L evaluated the influences of temperature and pH on the biofilters.The effect of TAN and NO₂^--N in biofilters were studied under different temperatures?10,15,20,25,30??and different p H values?7.0,7.5,7.7,8.0,8.5?.Under the experimental conditions?t=10³0,p H=7.0⁸.5?,nitrification is more sensitive to temperature than pH.In addition,the inhibition of temperature on the oxidation of nitrite is stronger than that of ammonia oxidation by pH.The results showed that the removal rate of TAN and NO₂^--N by biofilters increased with the increase of temperature from 10?to25?.The oxidation rate of TAN was the highest at 25?and pH 7.7,reaching to 0.7931 mgL^-1h^-1.The oxidation rate of NO₂^--N was higher than that of other treatment groups at 25?and pH7.5.In addition,it was found that the nitrite accumulation increased with the increase of temperature and pH value at t=10²5?and pH=7.0⁸.5,and the nitrite accumulation was most serious at t=25?and p H=8.5.And the nitrite accumulation was most serious at t=25?and p H=8.5.The nitrification function of biofilter is the result of nitrification bacteria,which is greatly affected by environmental factors.Therefore,the suitable temperature and pH are the guarantee of efficient and stable operation of biofilter.?3?Under the condition of average inlet temperature of 25,salinity of 30 and dissolved oxygen?DO?of about 6 mg/L,the effect of different ammonia nitrogen concentration?0⁹.0 mg/L?on nitrification performance of biofilter was studied.It is found that the biofilter has a certain buffering capacity for influent ammonia nitrogen concentration,and within a certain range of ammonia nitrogen concentration,the biofilter can adapt to the new influent condition at about20²5d?The higher the concentration of ammonia nitrogen in the biological filter,the stronger the nitrification ability of the biofilter,and the better the treatment effect of TAN and NO₂^--N.The ammonia nitrogen is 9.0mg/L,the degradation rate of ammonia nitrogen is 2.5714 mgl^-1h^-1;ammonia nitrogen is 6.0 mg/L,the degradation rate of ammonia nitrogen is 2.0 mgl^-1h^-1;ammonia nitrogen is 3.0 mg/L,the degradation rate of ammonia nitrogen is 1.7143mgl^-1h^-1;ammonia nitrogen is 1.5 mg/L,the degradation rate of ammonia nitrogen is 1.500 mgl^-1h^-1;ammonia nitrogen is 0.5 mg/L,the degradation rate of ammonia nitrogen for 1.500 mgl^-1h^-1.It is also found that the short-term accumulation of NO₂^--N occurs during the operation of the biofilter,and The higher the influent ammonia nitrogen concentration is,the higher the NO₂^--N concentration in the short period of the biofilter is.Water circulation in the breeding process,should be based on biological tolerance to TAN,adjust the biofilter HRT concentration of NO₂^--N,this guarantee does not affect the growth of aquaculture organisms under the condition of reducing the energy consumption of circulating water,reduce economic investment.