Study On Advanced Treatment Of Sintering Flue Gas Desulfurization Wastewater By CaO₂ Enhanced Fenton-MAP Combined Process

This study takes the sintering flue gas desulfurization wastewater of a steel company in Guangdong Province as the research object,its chemical requirements?COD?and ammonia nitrogen?NH₄⁺-N?still high and cannot meet the indirect emission standards in the GB13456-2012“Electrical Industry Water Pollutant Emission Standards”after chemical precipitation treatment,which need to be treated in depth for reuse or discharge to the total wastewater treatment center.Because of few domestic mature technologies for the removal of COD and NH₄⁺-N in the flue gas desulfurization wastewater of the steel industry,and the research work commissioned by a steel company in Guangdong Province.was carried out.Based on the preliminary study on the treatment method of sintering flue gas desulfurization wastewater,is used including small-scale research,scale-up study and CaO₂ enhanced Fenton-MAP combined process to remove COD and NH₄⁺-N from simulated wastewater and actual wastewater,and the main results are as follows:?1?The preliminary research results show that the removal rates of COD and NH₄⁺-N in the flue gas desulfurization wastewater are between 14%-86%and4.5%-15.8%,respectively.Among them,the removal rate of COD by CaO₂ enhanced Fenton method is 86%.The secondary treatment of NH₄⁺-N by the chlorination method,the stripping method and the magnesium ammonium phosphate precipitation method?MAP method?showed that the removal rate of NH₄⁺-N are between 16% and 90%,and the MAP method was for NH₄⁺-N removal rate is 90%.Herein,the CaO₂enhanced Fenton-MAP combination process is used to deeply treat COD and NH₄⁺-N in the flue gas desulfurization wastewater of Steel Plant.?2?The results of the pilot study indicate:The optimal process conditions for the CaO₂ enhanced Fenton method are:pH:3.0?3.5,Fe²⁺dosage:1.6mg/L,CaO₂dosage:2.0mg/L,[H₂O₂]/[Fe²⁺]=1.0,reaction time:30 min;the optimum process conditions for the MAP method:pH:9.0,temperature less than 40?,Mg:N:P=1.5:1:2.2,precipitation time:20 min.Under these conditions,the removal rates of COD and NH₄⁺-N could reach to 91.20% and 92.07%,respectively.And the COD and NH₄⁺-N concentrations were 177.8 mg/L and 19.03 mg/L,respectively,COD residual concentration below the indirect emission standards in the GB13456-2012 "Water Pollution Standards for the Iron and Steel Industry".?3?The results of amplification experiments show that CaO₂ enhanced Fenton-MAP combined process has good removal effect on COD and NH₄⁺-N in desulfurization wastewater,and the removal rates are stable at 79.98%?82.4% and 90.28%?92.75%,respectively.The concentrations of COD and NH₄⁺-N are160.5mg/L?199mg/L and 9.4mg/L?19.3mg/L,COD residual concentration lower than GB13456-2012“Water Pollution Standards for the Steel Industry”.?4?The mechanism of remove COD by CaO₂ enhanced Fenton process:?1?The total organic?TOC?of the original desulfurization wastewater?the effluent from the flue gas desulfurization wastewater of Steel Plant after chemical precipitation treatment?shows that the chemical oxygen demand caused by organic matter accounts for 10.16% of the total consumption.The results of GC-MS,high performance liquid chromatography,ion absorption and FT-IR showed that the main mainly sulfite,polycyclic aromatic hydrocarbons and organic/inorganic pollutants containing silicon-oxygen bonds,unsaturated Si-O-Si bonds and O-Si-Me bonds and desulfurization.?2?Unsaturated Si-O-Si bond and O-Si-Me bond in the pollutant adsorbed F^-and anion group(SO₃^2-etc.)in the raw wastewater,which made the COD in the desulfurization wastewater difficult to degrade,and the CaO₂ enhanced Fenton process to treat the raw wastewater.When the·OH can oxidize and degrade the polycyclic aromatic hydrocarbons in the wastewater,break the silicon-oxygen bonds,and open the ring-shaped siloxane,the silicon-oxygen bond breaks the ring to desorb the adsorbed anions and anions,mainly sulfite,polycyclic aromatic hydrocarbons and organic/inorganic pollutants containing silicon-oxygen bonds,unsaturated Si-O-Si bonds and O-Si-Me bonds and desulfurization.