N/P absorption performance of Ulva lactuca and Eucheuma denticulatum in aquaculture wastewater

CHEN Yajing; MAO Yunxiang; WANG Zhendong; ZHANG Shuai; ZHOU Ziyang; TANG Lei

doi:10.13984/j.cnki.cn37-1141.2025.03.019

Abstract：Aquaculture wastewater is produced during the aquaculture process of maricultured animals,which may lead to eutrophication and pollution of seawater environment when discharged directly.Macroalgae,as the primary producers in marine ecosystem,can absorb nitrogen and phosphorus and reduce the eutrophication of seawater effectively.In this study,two economic macroalgae,Ulva lactuca and Eucheuma denticulatum,were choosed to absorb nitrogen and phosphorus in aquaculture wastewater.Orthogonal experiment was performed to explore the effect of four factors,combination of macroalgae,ratio of nitrogen phosphorus,type of nitrogen source and concentration of inorganic nitrogen.The optimal combination scheme for the treatment of aquacul-ture tail water was obtained and applied to the treatment of aquaculture tail water,and a certain economic sea-weed yield was obtained at the same time.The best combination of different nutrients was obtained by orthogo-nal experiment.For the absorption of NH3-N,the best combination was U.lactuca and E.denticulatum(layered)+ratio of nitrogen phosphorus 6∶1+NH3-N+concentration of inorganic nitrogen 200 μmol/L.For the absorption of NO3-N,the best combination was U.lactuca+ratio of nitrogen phosphorus 12∶1+NO3-N+concentration of inorganic nitrogen 150 μmol/L.For the PO4-P absorption rate index,the best com-bination is E.denticulatum+ratio of nitrogen phosphorus 3∶1+NH3-N∶NO3-N 1∶1+concentration of inorganic nitrogen 200 μmol/L.During absorbing N and P,the two economic seaweeds also maintained a high daily growth rate with U.lactuca up to 24.46±0.53％/d and E.denticulatum up to 8.11±0.15％/d.The optimal scheme was selected to treat the aquaculture wastewater produced in mariculture farm.According to the discharge requirement of aquaculture tailwater of Hainan Province,China(local standards DB46/T 475-2019),the first-level discharge standard of inorganic nitrogen should be less than 35.7 μmol/L,the secondary discharge standard of active phosphate should be less than 3.12 μmol/L.It was found that the inorganic nitro-gen concentration and PO4-P concentration can be reduced to below the provincial emission standard within 9 days by the selected two optimal combinations.Similar results can also be obtained after reducing the density of macroalgae from 1.0 g/L to 0.7 g/L.In this study,we established an efficient and ecological treatment for aq-uaculture wastewater with different types of nutrients and also proposed a new model for large-scale,high den-sity and mixed cultivation of U.lactuca and E.denticulatum.