Using Pcl As Solid Carbon Source For Treatment Of Recirculating Aquaculture System Water

The accumulation of nitrate in aquaculture has been a common problem and the best way to remove nitrate is biological denitrification. Biodegradable polymers has been wildly used as carbon source and carriers on denitrification,because of its biodegradability and slow releasing. The problem of denitrification using Polycaprolactone（PCL）as carbon source is excessive dissolved organic carbon in influent. To solve this problem, studied on using PCL as the carbon source and filtration medium to treat recirculating aquaculture system water.1. Addition of PCL as carbon source to treat nitrate in aquaculture wastewaterStudy on optimum PCL level for solid phase denitrification in recirculating aquaculture system wastewater treatment. With the same influent 0.1 Kg NO-3-N m-3·h-1, the higest average denitrification was group A, 2.24±1.32 Kg NO-3-N m-3·d-1. The amount of PCL in group D is 1 mg NO-3-N g-1·d-1,no accumulation of nitrire and ammonia in the effluent, and the removal effect is best. The concentration of DOC shows positive relationship with the amount of PCL. In 24 hours, the concentration of nitrate decrease with time increase, and DOC increase. The nitrire concentration of effluent in six groups were all below 0.1 mg/L. The concentration of DOC increased with the time.2. Treatment of RAS wastewater using PCL under different HRTThe effect of different HRT while using PCL as the carbon source and filtration medium were studied. The average denitrification rate of nitrate was 2.29±0.94、1.79±0.73、1.48±0.52、1.51±0.44 and 1.26±0.37 Kg NO-3-N m-3·d-1, respectively and group A hightest. Influent DOC were all lower than effluent DOC. Effluence DOC mostly remained below 20 mg/L. The concentration of DOC was increased with HRT decreased. Most of the time the nitrire concentration of effluent in all groups were below 1 mg/L. During the whole stage no obvious accumulation of ammonia was observed, and appropriate reduction of HRT facilitates the removal of TAN. The concentration of effluent alkalinity was higher than influent and increased with HRT decreased. The consumption rate of PCL was increased with HRT. Under different HRT conditions, the structure of PCL was not changed before and after use. Main phylum on biofilm is Proteobacteria, Bacteroidetes, Chlorobi and Gracilibacteria.3. Treatment of RAS wastewater using PCL under different influent nitrate concentrationThe effect of different influent nitrate concentration（Group A:100mg L,Group B:200mg/L）while using PCL as the carbon source and filtration medium were studied. The average denitrification rate of nitrate was 1.11±0.34 and 1.05±0.33 Kg NO-3-N m-3·d-1 when HRT is 0.71L/h. The removal rate of ammonia was 32.62% and 32.31%, respectively. Effluence DOC mostly remained below 20mg/L. The structure of PCL was not changed before and after use. Based on the phylum results, the dominate phylum is Proteobacteria and Bacteroidetes both in Group A and Group B. The dominate genera in Group A is Burkholderiales and in Group B is Burkholderiales and Bdellovibrio.4. Evaluation of PCL as a carbon source for recirculating aquaculture wastewater denitrificationEvaluation of PCL as a carbon source for recirculating aquaculture wastewater treatment for a long period. The average removal rate and denitrification rate of nitrate was 43.04% and 0.84±0.31 Kg NO-3-N m-3d-1. Effluence DOC mostly remained below 20mg/L. The concentration of effluent nitrire（below 1mg/L）was higher than influent. The concentration of effluent TAN was basically maintained below 1.5mg/L, and the change trend was consistent with influent. Solid-phase denitrifying biofilter using PCL as carbon source had no removal of total phosphorus（TP）. The structure of PCL was not changed before and after use. Main phylum on biofilm is Acidovorax、Bdellovibrio and env.OPS₁7_noran...