Study On The Removal Of P-aminophenylarsonic Acid From Water By Iron Electrocoagulation

p-Aminophenylarsonic acid(p-ASA),also known as arsanilic acid,with the molecular formula C6H8AsNO3,is a common feed additive for livestock and poultry.The hazards of pASA include its own impact on the environment and its partial degradation to the more toxic trivalent and pentavalent arsenic after entering the environment.In normal natural water bodies,p-ASA molecules exist mainly in the form of anions.The current methods for removing p-ASA include coagulation,chemical precipitation,ion exchange methods,photodegradation and biological methods.Electrocoagulation(EC)is a commonly used electrochemical water treatment process with origins dating back more than 100 years,and the technology is widely used in the treatment of dyeing and textile wastewater,waste leachate wastewater,agricultural wastewater,and domestic wastewater in many fields,etc.EC is also an effective inorganic arsenic removal technology,and there are no relevant reports indicating that there have been studies on p-ASA removal In this study,iron electrocoagulation was used to remove p-ASA from water.In this study,we investigated the effects of different factors on the removal of p-ASA from water by EC including current density,plate spacing,background electrolyte and initial pH,and also investigated the mechanism of p-ASA removal from water by EC,including the study of the mechanism of the synergistic action of free radical oxidation,and analyzed the mechanism of oxidative degradation of p-ASA with the aid of DFT calculations,and finally used an in-house designed electrochemical.Finally,an in-house designed electrochemical reactor coupled with ceramic membrane was used to initially investigate the continuous flow effect of iron electrocoagulation process.The results of the study are as follows,four different sets of current densities(1.75 A/m2,5.0 A/m2,10.0 A/m2 and 20.0 A/m2)were set to obtain 100%removal of total arsenic within 60 min,but the increase in current density resulted in higher energy consumption,plate loss and sludge leading to an increase in total cost,which was 0.131,0.255,0.312 and 0.701 USD/m3 for the four sets of current densities.The costs for the four current densities were 0.131,0.255,0.312 and 0.701 USD/m3,respectively,and the pH increased more rapidly.Also higher current densities did not produce higher current efficiencies,with current efficiencies below 100%for the 10.0 A/m2 and 20.0 A/m2 conditions.Four different spacings of 0.45 cm,0.9 cm,1.8 cm,and 2.7 cm were used for the experiments,and 0.9 cm was used as the final spacing for the subsequent experiments.The removal effects of NaCl and Na2SO4 were compared as background electrolytes respectively,while the same concentration gradient was set for both background electrolytes to investigate the effect of different background electrolytes on the removal of p-ASA.Compared with the use of NaCl electrolyte,the removal rate was slower with the use of Na2SO4 electrolyte,and the final removal rate did not reach 100%with This was attributed to the competition between the negatively charged SO42-and the also negatively charged p-ASA molecules for the adsorption sites of the flocs produced by EC,which made the removal of total arsenic weaker.Four different initial pH values(4.0,6.5,8.5 and 10.0)were set to investigate the effect of different initial pH values on the removal of total arsenic,and the overall trend was that the removal rate of total arsenic decreased as the initial pH increased.The concentration of different arsenic forms during the removal of p-ASA by EC was analyzed with time using HPLC-ICP-MS,and a characteristic peak of As(Ⅲ)was found during the reaction.The intermediate products produced during the degradation of Fe EC were identified by UPLC-Q-TOF-MS.The intermediate products were p-nitrophenol and 4,4’(hydrazine-1,2-diyl)bisphenol,and the concentration of nitrate nitrogen was analyzed,which first increased slightly and then decreased slowly.The Gaussian software was used to perform a series of quantum chemical calculations on the p-ASA,and the reaction sites of the p-ASA molecule were investigated in depth mainly in the vicinity of N and As atoms,and the bondbreaking positions and oxidation mechanism of the p-ASA molecule were determined in combination with the intermediate products.The flocs produced at the end of p-ASA removal from water by EC were characterized at a current density of 5.0 A/m2,an initial pH of 6.5,a pole-plate spacing of 0.9 cm,0.01 mol/L NaCl,and p-ASA concentration of 10 mg As/L.The morphological characteristics,surface functional groups,and elemental valence of the produced floes were analyzed,in which the produced flocs were amorphous crystals,and the iron hydroxide removed most of the p-ASA from the water mainly in the form of electrostatic adsorption and double-ligand complexation.The removal of p-ASA from water using the coupled ferroelectric flocculation-ceramic membrane process can achieve 86%removal of p-ASA under continuous testing,and the effluent quality is stable after three hours of continuous operation,and the turbidity of the effluent can reach 0 NTU after passing through the ceramic membrane.