Study On Absorption Rule And Contribution Rate Of Dissolved Nitrogen By Microalgae-bacteria Consortia

With the shrimp farming becoming mature gradually,to pursuit of the biggest economic benefits,the farming workers often adopt the high density cultivation,during which a large amount of nitrogen source flows into the pond environment in the forms of feed,dead shrimp bodies and excretions.It has a great adverse impact on the aquaculture ecological environment and global warming,so that how to solve the problem of ecological environmental protection becomes very urgent.At present,the use of bacteria and microalgae to regulate water quality has become the main ecological treatment,which has high efficient and economical advantages compared with chemical products in large scale of aquaculture ponds.Therefore,it has great value of applications to select bacteria and microalgae to construct microalgae-bacteria consortia for ecological environmental protection and reduce the nitrogen pollution in breeding environment.In this study,the effects of temperature,salinity and light intensity on the absorption of ammonia,nitrite and urea nitrogen by Oocystis borgei-Rhodopseudomonas palustris consortia were studied at different gradients.Orthogonal experiment was established to further determine the optimum environmental conditions for absorption of ammonia nitrogen,nitrite nitrogen and urea nitrogen by microalgae-bacteria consortia.The experimental results are as follows:（1）Effects of temperature,salinity and light intensity on ammonia nitrogen uptake in microalgae-bacteria consortia Temperature,salinity and light intensity had significant effects on the absorption of ammonia nitrogen by the microalgae-bacteria consortia（P<0.05）.With the gradual increase of environmental conditions,the absorption of ammonia nitrogen showed an upward trend and then decrease.At a temperature of 30℃,a light of 3500lx and a salinity of 15,the ammonia nitrogen absorption rate of microalgae-bacteria consortia reached the maximum,which was 3.367μg·g^-1·h^-1,3.367μg·g^-1·h^-1and 4.098μg·g^-1·h^-1,respectively.The orthogonal experiment showed that the optimal environmental conditions for absorbing ammonia nitrogen were at temperature 30℃,salinity 15 and light 3500 lx.In the microalgae-bacteria consortia,the average contribution rates of Rhodopseudomonas palustris and Oocystis borgei to ammonia nitrogen absorption were 38.2%and 61.8%in the temperature gradient,42.0%and58.0%in the salinity gradient,29.8%and 70.2%in the light intensity gradient, respectively.Oocystis borgei is the main contributor to the absorption of ammonia nitrogen in the microalgae-bacteria consortia.（2）Effects of temperature,salinity and light intensity on nitrite nitrogen uptake in microalgae-bacteria consortiaTemperature,salinity and illumination had significant effects on nitrite nitrogen uptake rate（P<0.05）.When the temperature was 30℃,the highest absorption rate of nitrite nitrogen was 2.086μg·g^-1·h^-1.The maximum absorption rate reaches 3.058 μg·g^-1·h^-1at salinity 5.The absorption rate of nitrite nitrogen increased first and then decreased with the increase of illumination,and the maximum absorption rate reached2.319μg·g^-1·h^-1at 3500 lx.The orthogonal experiment showed that the optimal environmental conditions for absorbing nitrite nitrogen were at temperature 30℃,salinity 5 and light 3500 lx.In the microalgae-bacteria system,the average contribution rates of Rhodopseudomonas palustris and Oocystis borgei to nitrite nitrogen uptake were 67.2%and 32.8%in the temperature gradient range,74.4%and 25.6%in the salinity gradient range,and 68.8%and 31.2%in the light intensity gradient,respectively.Rhodopseudomonas palustris is the main contributor to the absorption of nitrite nitrogen in the microalgae-bacteria consortia.（3）The effects of temperature,salinity and light intensity on urea nitrogen uptake in microalgae-bacteria consortiaTemperature,salinity and light intensity had significant effects on the absorption of urea nitrogen by the microalgae-bacteria consortia（P<0.05）.With the gradual increase of environmental conditions,the absorption of urea nitrogen showed an upward trend and then decrease.At a temperature of 30℃,a light of 3500 lx and a salinity of 25,the urea nitrogen absorption rate of microalgae-bacteria consortia reached the maximum,which was 0.986μg·g^-1·h^-1,1.012μg·g^-1·h^-1and 1.284μg·g^-1·h^-1,respectively.The orthogonal experiment showed that the optimal environmental conditions for absorbing urea nitrogen were at temperature 30℃,salinity 25 and light 3500 lx.In the microalgae-bacteria consortia,the average contribution rates of Rhodopseudomonas palustris and Oocystis borgei to urea nitrogen absorption were 25.6%and 74.4%in the temperature gradient,23.1%and76.9%in the salinity gradient,23.3%and 76.7%in the light intensity gradient,respectively.Oocystis borgei is the main contributor to the absorption of urea nitrogen in the microalgae-bacteria consortia.In conclusion,the Rhodopseudomonas palustris and Oocystis borgei consortia can absorb and remove ammonia,nitrite and urea nitrogen in a complex and variable environment,and can be applied to the whole process of shrimp culture.Therefore,the microalgae-bacteria consortia can be applied to the water quality regulation of shrimp culture pond,with very important application potential.