Treatment Of Marine Culture Wastewater By IFAS-PNAD Process Based On Enteromorpha Ferment Liquor As Carbon Source

The discharge of Marine aquaculture wastewater increases with the increasing demand for Marine products,and the impact of Enteromorpha invasion in coastal areas every summer on the Marine environment,as well as the workload of Enteromorpha cleanup caused great trouble to people.In this paper,high salt,high ammonia Nitrogen（NH₄⁺-N）and partial nitrate nitrogen（NO₃^--N）and low Carbon Nitrogen ratio（C/N）in Marine culture wastewater were combined.Integrated Fixed-film Activated Sludge（IFAS）technology,Partial Nitrification（PN）technology,Anaerobic ammonia oxidation（Anammox）technology,Partial Denitrification（PD）technology,a novel Integrated Fixed-film Activated Sludge-Partial Nitrification,Partial Denitrification（IFAS-PNAD）process for the treatment of aquatic culture wastewater.The fermentation liquor was used as the carbon source in PD process.The optimal PD process conditions were determined based on response surface linear regression method.And through the determination of microbial activity,the damage degree of sludge cells,the change of the shape of sludge,the change of microbial community structure,the change of the content of related components in the fermentation process,the mechanism of efficient treatment of Marine culture wastewater by IFAS-PNAD process based on Enteromorpha ferment liquid as carbon source was revealed.It provided theoretical support for the practical application of IFAS-PNAD process in the future.The main conclusions are as follows:（1）In IFAS intermittent aeration system,activated sludge intermittent aeration system and activated sludge continuous aeration system,IFAS intermittent aeration system had the best PN effect and nitrogen removal stability.Under the conditions of10 g/L salinity,alternating deficiency/aerobic（aerobic 10 min,hypoxia 30 min）and aerobic stage,DO was controlled at 0.5±0.1 mg/L.IFAS intermittent aeration system could achieve about 90%Nitrite（NO₂^--N）transformation rate（NTR）,which was higher than 80%of activated sludge intermittent aeration system and 10%of activated sludge continuous aeration system.NO₂^--N/NH₄⁺-N at the end of the reaction was close to the theoretical value of Anammox（1.32）,which was conducive to providing a suitable substrate for the subsequent Anammox process.With the increase of salinity,the NTR of the system was significantly inhibited at 15 g/L salinity.In the process of acclimation from no salinity to 10 g/L salinity and 15 g/L salinity,the microbial community structure in the biofilm changed significantly.As a kind of Bacteroidota which could promote sludge granulation,the relative abundance of Bacteroidota changes from 11.4%to 62.5%and 39.7%.At the same time,OLB8 bacteria showed self-enrichment in 10 g/L and 15 g/L salt environments,and their relative abundance changed from 0%to 51.5%and 28.3%,respectively.The bacteria could reduce part of NO₃^--N generated by nitrification to NO₂^--N,providing more NO₂^--N for the system.To explain the mechanism that IFAS intermittent aeration system could get higher NTR at 10 g/L salinity than 15 g/L salinity.（2）The Nitrogen removal efficiency（NRE）of the Anammox system reached 78%at 10 g/L salinity after gradual acclimation.However,with the further increase of salinity,the nitrogen removal performance of Anammox system becomes unstable at12.5 g/L salinity,and the highest NRE could only reach 59%.However,at 15 g/L salinity,the nitrogen removal performance of Anammox system had become very unstable,and the highest NRE could only reach 51%.（3）The response surface linear regression method was used to establish 17batches of tests,in which the optimal PD salinity was 10 g/L.Combined with response surface linear regression method,to quantitatively describe the interaction between salinity,C/N and p H on Nitrate removal rate（NRR）,Nitrate nitrogen accumulation rate（NAR）,Nitrate nitrogen accumulation rate（NRR）,the influence of Chemical oxygen demand（COD）utilization rate（CUR）.Finally,the optimal PD process conditions of Enteromorpha ferment liquid as carbon source were obtained:when the salinity was 12.2 g/L,C/N was 4,p H was 8.5,the NAR,NRR,CUR could reach 77%,89%,51%.Combined with the predicted optimal conditions,90 days of experimental verification,by gradually increasing the influent NO₃^--N concentration,investigate the stability of Enteromorpha ferment liquid IFAS system,using sodium acetate as carbon source to form a contrast with Enteromorpha ferment liquid.The results showed that the calculation error between the actual value and the predicted value was less than 5%,indicating that the prediction model was reliable.The NAR of Enteromorpha ferment liquid system was significantly higher than that of sodium acetate system.The total chemical oxygen demand（TCOD）,Soluble chemical oxygen demand（SCOD）and humic acid content of Enteromorpha ferment liquid could be kept at a high level,and SCOD/TCOD could be kept at about 0.7.The results indicated that the proportion of soluble organic matter in Enteromorpha ferment liquid was high,which provided theoretical basis for Enteromorpha ferment liquid as carbon source.Thauera showed high adaptability to IFAS system with Enteromorpha ferment liquid as carbon source and to IFAS system with sodium acetate as carbon source.The relative abundance of Thauera changed from 0%to 35.6%and 33.3%,respectively.But compared with sodium acetate IFAS system,Enteromorpha ferment liquid IFAS system could effectively inhibit the growth of Proteobacteria and Azoarcus,and was more beneficial to the maintenance of Bacteroidetes.Bacteroidetes could ensure the full utilization of Enteromorpha ferment liquid and contribute to the formation of PD.