Promotion Effect Of Iron On The Nitrogen And Phosphorus Removal From Mariculture Wastewater

In recent years,intensive mariculture has developed rapidly in China.Although it has brought great economic benefits,it has also polluted the offshore environment.The tail wastewater of traditional mariculture was directly discharged into the sea after a physical separation of some bait residues and feces,which seriously damaged the ecological environment of the receiving water.Therefore,the potential pollution and harm of mariculture have been paid more and more attention,and the discharge standard of mariculture tail water has been upgraded.However,the biomass and growth rate of engineering microorganisms are limited by the high salinity and low pollutants of mariculture wastewater,which makes the application effect of many conventional biological denitrification and phosphorus removal technologies far lower than expected.As a cheap and readily available metal element,iron itself has a polyvalent transformation and is prone to redox reactions,which can provide or transfer electrons for microbial metabolism and promote microbial enrichment and denitrification and carbon removal;Iron can also be chemically flocculated and precipitated with active phosphate in water to enhance phosphorus removal.Therefore,in this study,Fe₃O₄-shell particles were prepared with Fe₃O₄ powder as raw material to enhance nitrogen and phosphorus removal in mariculture tail water.The physical characteristics,adsorption performance and removal effect of nitrogen and phosphorus of Fe₃O₄-shell particles were studied in order to provide theoretical basis for practical application.The research results are as follows:（1）Grind oyster shells into shell powder,add diatomite,PVP and Fe₃O₄ powder to mix and stir in proportion,and then put the oyster shells into the oven to dry,then the production of Fe₃O₄-shell particles can be completed.The surface of Fe₃O₄-shell particles is smooth,hard and not easy to break.The results of EDS scanning electron microscopy showed that Fe₃O₄and shell powder were interlaced in the particles,and the internal structure was relatively loose.There were large holes with biofilm attachment and material transfer to the particles.Iron is evenly distributed in the particles,which contributes to the slow release of iron.The experimental results show that the chemical adsorption capacity of Fe₃O₄-shell particles for phosphorus is 0.07 mg P/（g·d）.（2）The results showed that adding Fe₃O₄-shell particles（containing 10%Fe₃O₄）significantly promoted the systematic nitrogen removal,and the total nitrogen removal rate of Fe₃O₄-shell particles increased by 15.70%compared with the control group,while the total nitrogen removal rate of Fe₃O₄-shell particles increased by 2.62%;The removal rate of PO₄^3--P in the Fe₃O₄-shell particle reaction group was 58.07%,and the removal rate was increased by28.42%compared with the control group.The Fe₃O₄ powder reaction group had no obvious improvement effect.At the end of the reaction,the removal load of nitrogen and phosphorus by Fe₃O₄-shell particles was 0.17 mg N/（g·d）and 0.19 mg P/（g·d）.Compared with direct Fe₃O₄ powder,Fe₃O₄-shell particles have better promoting effect on systematic nitrogen and phosphorus removal.For Fe₃O₄-shell particles with smaller particle size,the effect of denitrification and phosphorus removal was more obvious.The reason is that the smaller the particle size,the larger the specific surface area,the greater the chance of microorganisms contacting the particle surface,and the more obvious the promotion effect on nitrogen and phosphorus removal.Microbial sequencing results showed that Fe₃O₄-shell particles could enrich the Marine nitrogen-functional bacteria,and reduce the occurrence of sulfur functional bacteria.（3）A denitrifying filter was constructed with Fe₃O₄-shell particles（containing 5%Fe₃O₄）.Results showed that the denitrification efficiency was greatly affected by COD/N.When the C/N=8,the COD removal rate was 84.73%,and the total inorganic nitrogen removal rate was the highest,reaching 99.03%.Fe₃O₄-shell particles had the highest removal load on nitrogen.0.08mg N/（g·d）;The removal rate of PO₄^3--P was 86.23%when the C/N=8.However,the removal load of Fe₃O₄-shell filter material to phosphorus was only 5.7 mg P/（kg·d）.Therefore,Fe₃O₄-shell particles can promote the removal of nitrogen and phosphorus in the tail water of mariculture.The material is environmentally friendly,easy to make and environmentally friendly.It is not easy to be broken in seawater and has a small iron loss rate.It can also play a role in anaerobic environment.Fe₃O₄-shell particles have high application potential and value in promoting nitrogen and phosphorus removal in mariculture tail water from both economic and environmental perspectives.