Performance Of Nitrogen And Phosphorus Recovery From Aquaculture Wastewater Based On Struvite Crystallization Method And Modified Pig Manure Biochar And Its Application In Agricultur

In recent years,farming manure resource treatment technology has received wide attention due to serious pollution of farming manure.In this paper,pig manure,collected from a pig farm in Liuhe District,Nanjing City,Jiangsu Province,was used as a research object to recover nitrogen and phosphorus from farming wastewater based on a treatment method combination struvite crystallization method and adsorption method by pig manure biochar modified magnesium.In addition,the struvite and pig manure biochar was used to preparation of coated fertilizer,and its fertilizer efficiency was also evaluated.The main conclusions are shown as follows:（1）The removal rates of NH₄⁺-N and PO₄^3--P and the purity of struvite recovered from swine wastewater were obviously influenced by pH,Mg/P molar ratio and residence time（HRT）.The removal rates of NH₄⁺-N and PO₄^3--P and recovered struvite from swine wastewater were respectively 26.67%,74.57%and 88.45%by the fluidized reactor under optimal operation conditions factores,such as pH at 9.5,Mg/P of 1.3,HRT at 90 min.（2）The adsorptions process of NH₄⁺-N and PO₄^3--P by pig manure biochar（BC）,MgCl₂modified biochar（MgCl₂-BC）,Mg（OH）₂modified biochar（Mg（OH）₂-BC）,MgO modified biochar（MgO-BC）,and MgCl₂-6H₂O+Na OH modified biochar（MgCl₂-6H₂O+Na OH-BC）were in accordance with the Langmuir isothermal adsorption model.The maximum adsorption quantities of the five biochars for NH₄⁺-N and PO₄^3--P were followed the order:MgO-BC>MgCl₂+Na OH-BC>Mg（OH）₂-BC>MgCl₂-BC>BC,and the maximum adsorption quantites for NH₄⁺-N and PO₄^3--P by MgO-BC were respectively 122.01 mg/g and206.85 mg/g.（3）The characteristics of pig manure biochar were significantly influenced by MgO.The specific surface area of MgO-BC was 144.431 m²·g^-1.Compared to BC,specific surface area amd total pore volume of MgO-BC increased more than 8 times and 3 times,respectively.The optimum contiditon for NH₄⁺-N and PO₄^3--P adsorption by BC was the addition dosage of 0.8g/L,pH of 7 and 6 for inital solution.The adsorption of NH₄⁺-N and PO₄^3--P by BC was mainly a physical adsorption process.The optimum condition for adsorption NH₄⁺-N and PO₄^3--P by MgO-BC was 0.6 g/L and pH of 7 for inital solution.The adsorption of NH₄⁺-N and PO₄^3--P by MgO-BC was exothermic,and the adsorption process was more consistent with the Langmuir model and thepseudo-second-order kinetic mode.The main mechanism of NH₄⁺-N and PO₄^3--P adsorption by MgO-BC was the crystalline precipitation of guanoite.（4）Differend biochar,including original biochar,biochar after adsorption nitrogen and phosphorus,struvite,mixture of biochar and struvite,and mixture of biochar and struvite after adsorption nitrogen and phosphorus were respectively used as fertilizer cores to prepare encapsulated fertilizer C,encapsulated fertilizer C+NP,encapsulated fertilizer MAP,encapsulated fertilizer C+MAP and encapsulated fertilizer C+MAP+NP.Their compressive strength was respecively 16.21 N/granule,15.31 N/granule,12.94 N/granule,18.56 N/granule and 19.44 N/granule,which are greater than 12 N/granule and meet the requirements slow-release compound fertilizer of the national standard（GB/T23348-2009）.The residual weight ratios of C+MAP and C+MAP+NP were respectively 95.75%and 95.55%,and the water absorption multipliers were respectively 1.65 and 1.68.The performance of struvite compounded with biochar coated fertilizer was better than that of single struvite or biochar coated fertilizer in all aspects such as granule forming,compressive strength,abrasion resistance,water absorption and water resistance.（5）The the growth of peas was promoted after addition of struvite and biochar compound wrap fertilizer.Compared to the control treatment,total uptake of nitrogen by peas increased by 1.6 times,and total uptake of phosphorus increased by 4.8 times when struvite and biochar compound wrap fertilizer was added into soil.