The Removal Of Nickel, Sulphur And Nitrogen In Electroplating Wastewater By The Hypochlorite Oxidation + SRB Coupled With Denitrification Thiobacillus

Electroplating nickel-containing wastewater is a kind of recalcitrant industrial wastewater due to EDTA-Ni with a space hexahedral structure.Moreover,some electroplating wastewater contains a large amount of nitrate and sulfate but little carbon source,which is also animportant element of environmental pollution.Therefore,this paper took EDTA-Ni and nitrate as target pollutants,and coupled catalytic oxidation of hypochlorous acid by nickelhydroxyl with sulfate reducing bacteria?SRB?and Thiobacillus,to remove nickel,sulfur and nitrogen in electroplating nickel-containing wastewater,which not only realized the standard discharge of nitrate and nickel,but also achieved the recovery and utilization of nickel.The oxidation of EDTA-Ni by sodium hypochlorite catalyzed by hydroxyl nickel oxide was studied.It was found that the treatment process not only exhibited high catalytic efficiency?>95%nickel?by regenerating catalyst,but also recycled the nickle at the same time.Through SEM,IR,XRD,XPS and other characterization,it was demonstrated that the surface characteristics,group structure and valence state of catalyst elements of catalyst were basically unchanged after reaction.Moreover,the removal efficiency even increased by reusing catalyst.Therefore,it is believed that the regeneration process of nickel hydroxide and nickel hydroxide played an important role in catalytic oxidation of EDTA-Ni by hypochlorous acid,which celebrated the generation of free oxygen from hypochlorous acid to degrade EDTA-Ni.SRB was employed to reduce SO₄^2-and remove Ni simultaneously and the results of response surface methods?RSM?indicated that the optimal condition of Ni removal by SRB were pH of 6.9,C/S of 1.68 and MLVSS of 5.14 and the maximum Ni removal efficiency reached approximately 68%.Moreover,the effects of Fe²⁺and Fe³⁺on the performance of the reactor were also investigated and the results showed that Fe²⁺and Fe³⁺with low concentration could reduce the damage of TDS to microorganisms by consuming TDS to form FeS and further promote the sulfate reduction and Ni removal,while Fe²⁺and Fe³⁺with high concentration restrained the sulfate reduction and Ni removal,since excess FeS precipitation covered the cell surface and impeded mass transfer of microorganisms.The results of high-throughput sequencing RDA analysis revealed both Desulfomicrobium and Halothiobacillus had positive correlativity with the concentration of TDS and Ni,while Deslfobulbus and Desulfovibrio had positive correlativity with pH.Furthermore,Fe²⁺and Fe³⁺with low concentration could accelerate the growth of SRB and improve the removal efficiency of Ni.Thiobacillus denitrificans was employed for simultaneous sulfur oxidation and denitrificaiton and the results of response surface methods?RSM?indicated that the optimal condition of Ni removal by thiobacillus denitrificans were pH of 7015,C/N of 1.14 and S/N of 0.99,in which the residual NO₃^-and TDS were 17.03 mg-NO₃^--N/L and 61.56 mg-TDS/L,respectively.Moreover,the effects of Fe²⁺and Fe³⁺on the performance of the reactor were also investigated and the results showed that low concentration of Fe²⁺?1 mmol/L?could effectively promote the removal of TDS and NO₃^-,while high concentration of Fe²⁺?4mmol/L?could result in the decease of their removal efficiencies.The results of high-throughput sequencing RDA analysis revealed that Thauera,Sulfurospirillum and Thiobacillus were positively correlated with SO₄^2-concentration and NFL,while negatively correlated with TDS,NO₃^-and NFH,which further comfirmed that low concentrations Fe²⁺had a positive effect on the growth of microorganisms,while high concentrations Fe²⁺showed an inhibitory effect.The coupling of SRB and Thiobacillus denitrificans was used for the sulfate reduction,the Ni removal and the denitrification.The results indicated that the reduction of nitrate was more priority than sulfate with the increase of C/N ratio and the removal of nickel had positive correlativity with C/N.In addition,when S/N ratio was beyond 1.0,the removal of Ni was not increased continuously.Moreover,the effects of Fe²⁺and Fe³⁺on the performance of the reactor were also investigated and the results showed that low concentration of Fe²⁺?0²mmol/L?could not inhibit the reduction of sulfate,but caused the decreased TDS.On contrary,the low concentration of Fe²⁺promoted the sulfur oxidation and denitrification.Nevertheless,the removal of Ni also increased significantly as the concentration of Fe²⁺increased to 4 mmol/L.The analytic results of KEEG and OGE indicated that the introduction of Fe²⁺with low concentration enhanced the function of transcription,energy production and conversion,carbohydrate conversion and mechanism,the amino acid transport and metabolism and carbohydrate metabolism and thus promoted the the growth of microorganisms such as Sulfurospirillum,Thauera,Desulfomicrobium,Stenotrophomonas and Pseudomonas.However,the high concentration of Fe²⁺inhibited their growth due to the limitation of the substrate exchange between cells with the external environment.In order to illuminate the mechanism of sulfur cycle,two strains with the most excellent performance SRB1 and SOB1were purified and identified as Desulfovibrio and Sulfurospirillum,respectively.It was found that the addition of Fe²⁺and sodium lactate after24 hours of incubation could furthest promote the sulfur reduction,nickel removal and sulfur oxidation.Through the mechanism analysis,the SRB-SOB system constitutes a sulfur cycle system through sulfur reduction and sulfur oxidation process.Through the comparison calculation experiment of SO₄^2-concentration,it is confirmed that the denitrification process belongs to the chemical autotrophic process,and it is found that Fe²⁺does not participate in the redox process through the measurement of sulfur.In this paper,nickel cycle catalytic oxidation system and sulfur cycle system were successfully constructed to removal nickel and nitrate successfully.In the hypochlorous acid catalytic oxidation,nickel could be removal efficiently and reused through the cycle of Nickel oxyhydroxide and nickel hydroxide.In the sulfur cycle system,the nitrates and residual nickel in electroplating wastewater was deeply treated and removed completely,so that the electroplating wastewater could be fully discharged up to the standard.This paper provides the theoretical basis and experimental basis for a new method of advanced oxidation and microorganism combined treatment for electroplating wastewater.