Study On Removal Of Organic Pollutants In Water By Bicarbonate Activated Hydrogen Peroxide System

In recent years,water is used for a variety of purposes by humanity while growing economic,increasing population developing urbanization and industrialization are completely demanded water resource.Also,environmental water is gradually becoming unsafely by discharging wastewater to water resources,so that the water is contaminated by containing organic pollutants and heavy metal.The source water pollutions are generated from various types of pollutants in wastewater effluent such as dyeing,battery,printing,mining,metal urgical engineering,electroplating,pigment,nuclear power operations,electric appliances manufacturing,semiconductor,cosmetics,and so on.For the reason that untreated or adequately treated textile wastewater can have adverse effects on the natural ecosystems and have long-term health effects.The absorption of water contaminated by dye can cause serious damage to human health and other organisms.A wide variety of dyes are ubiquitous in printing and dyeing wastewater,which are characterized as poor biodegradability,high chroma,and strong toxicity.Once dyes are absorbed by humans,they tend to accumulate in the liver,kidneys,bones,heart,and brain,and then some pathogenic effects would occur.If not properly treated,dyes are stable and can exist in the water environment for a long time,causing aquatic ecosystem damage and water pollution.Therefore,the effective and economical treatment of wastewater containing a variety of dyes has become an inevitable requirement for cleaner production technology in the textile industries.Therefore,it is necessary to explore other green and friendly advanced oxidation technologies based on hydrogen peroxide activation.The present study is to investigate the bicarbonate activated hydrogen peroxide system to remove organic pollutants in wastewater.In this study,Acid orange II?AO7?was used as the target dye in the treatment of dye wastewater by HCO₃^--H₂O₂ green activation method.AO7 removal performance and decomposition mechanisms were systematically explored.Preliminary results show bicarbonate activated hydrogen peroxide system can remove AO7 quickly and efficiently compared with a single H₂O₂ system.Then,all AO7 was removed within 30 min's processing,and its decomposition process in the HCO₃^--H₂O₂system was endothermic.The optimum conditions for degrading AO7 were as follows:initial concentration 10 mg/L,the temperature was 318 K,the quantity of Na HCO₃ was 0.005mol/L,the quantity of H₂O₂was 0.002 mol/L,p H 9.5,the AO7 removal efficiency after 60 min was 90%.The degree of contribution of the different active substances to the degradation of AO7 was investigated from the perspective of the inhibition by a radical scavenger.Based on the qualitative analysis of the active substances,using the COD,UV-vis,3DEEM,and GC-MS explored the degradation of AO7.Relatively higher reaction kinetic rate constant was obtained at a relatively lower AO7 initial concentration,appropriately larger H₂O₂,and HCO₃^-dosages,and weak alkaline conditions.O₂·^-was the main active substances for AO7 decomposition,and·OH and ¹O₂ also participated in the AO7 decomposition as analyzed by different scavenger tests.The attacks of these active substances to AO7 molecules resulted in the destruction of the benzene ring,naphthalene ring,and the azo groups.Finally,the removal of chemical oxygen demand reached 72%after 60min's oxidation treatment.The main degradation intermediates contained salicylic acid,phenol,1,4-benzendiol,and dibutyl phthalate;and the possible decomposition pathways of AO7 in this system were proposed.Classical chemical precipitation technology is inefficient for the removal of heavy metal-organic complexes from wastewater.In addition,a novel and green strategy of coupling bicarbonate-activated hydrogen peroxide?BHP?oxidation and alkaline precipitation were proposed for simultaneous decomplexation of Cu-ethylenediaminetetraacetic acid?Cu-EDTA?and Cu precipitation.The Cu-EDTA decomplexation efficiency reached 92.0%after 328 K and p H 9.3 within 60 min of the BHP treatment,and the decomplexation process was spontaneous and endothermic.Using HPLC,TOC,GC-MS,SEM,EDX,FTIR,XPS to investigate the reaction mechanism and analyze the degradation results.The study found that the HCO₃^--H₂O₂ oxidation system generated a large amount of reactive substances such as·O₂^-,·OH,and ¹O₂ were identified,and·O₂^-was predominant in the Cu-EDTA decomplexation.The weak alkaline environment provided by bicarbonate favored the generation of the reactive substances and subsequent Cu-EDTA decomplexation.Relatively higher H₂O₂ dosage favored Cu-EDTA decomplexation,while excessive bicarbonate dosage inhibited the reaction.TOC removal efficiency and Cu removal efficiency reached 78.4%and 68.3%after 60 min treatment,respectively.Under the oxidative degradation of the active substances,the stable structure of the complex heavy metal Cu-EDTA was destroyed which led to the breakage of the chemical bond between Cu²⁺and EDTA.Subsequently,the complex copper can be transferred into a free copper ion,and then the free copper ion can be removed by precipitation after alkali addition.EDTA will continue to break the chemical bond in the bicarbonate activated hydrogen peroxide system to complete the oxidative degradation reaction and be removed.The Cu–O and Cu–N bonds in Cu-EDTA were destroyed by the reactive substances,and a series of Cu-containing intermediates,small organic molecules such as ethanamine,ethylene glycol,butanediol,and NO₃^-were produced.The released Cu ions were precipitated as Cu₂?OH?₂CO₃,Cu CO₃,Cu?OH?₂,and Cu O.Possible pathways of Cu-EDTA decomplexation in the system were proposed.