| With the rapid development of economy,water pollution incidents become more and more serious in China.Especially for the enterprises that produce heavy metal containing wastewater,once their effluents fail to meet the discharge standards,it will result irreversible adverse effects on the surface waters.Based on the investigation of the existing arsenic-containing wastewater treatment system,the treatment process of arsenic-containing wastewater was investigated in this study,in the hope that the production wastewater can be discharged stably up to standard.First,the production process of the enterprise was analyzed to identify the main nodes that producing wastewater.It was found that the main sources of arseniccontaining wastewater were polycrystalline cleaning wastewater(W1),single crystal cleaning wastewater(W2),crystal processing wastewater(W3),wafer guide angle wastewater(W4),surface grinder and inner circular saw wastewater(W5),polishing and cleaning wastewater(W6)and acid fog cleaning wastewater(W7).The total output of the wastewater was 17 t/h.Then,the now used wastewater treatment system was systematically analyzed to found the existing problems.The removal principle and removal efficiency of main pollutants by each construction unit are also analyzed.It was found that the pretreatment tank had a weak treatment efficiency for the mill wastewater,the effluent total arsenic concentration exceeded 50 mg/L frequently.This led the influent total arsenic concentration of the wastewater treatment system exceeding its processing capacity.And it would further induce the effluent of the wastewater treatment system exceeding the discharge standard(up to 5 times).In order to make the arsenic-containing wastewater meet the discharge standard normally,two upgrading schemes are proposed,scheme 1 is "multi-reagents multidosing for arsenic removal + filter / reverse osmosis system for desalination" and scheme 2 is "grinding wastewater pretreatment + existing wastewater treatment system upgrading ".Under the same water volume and coagulant dosage,scheme 2can get better arsenic removal efficiency with fewer arsenic removal reagents.The effluent arsenic concentration reached to 0.04 mg/L.Scheme 2 had the characteristics of excellent arsenic removal efficiency,less sludge production,effective use of existing facilities,less invest and easy to operate and manage.Through exploring the operation conditions,it could be concluded that the initial total arsenic concentration had a great influence on the effluent quality.The lower the initial arsenic concentration in the raw wastewater,the lower arsenic concentration in the effluent.The pretreatment ofgrinding wastewater is a key factor affecting the stability of of the wastewater treatment system.The multi-dosing effect of arsenic removal reagent is better than that of one time dosing and the best reaction time is 30 min.Considering the persistent harm of heavy metals to surface waters,this study proposed an advanced treatment scheme based on adding "arsenic special adsorption treatment device" to the existing treatment system,and the whole scheme of reusing the wastewater after adding "MVR evaporation and concentration device" to the existing treatment system.The system used precipitator 403 as arsenic remover,and used arsenic special adsorption device to continue to remove arsenic in the wastewater.When the arsenic concentration reached 0.01 mg/L,the wastewater was discharged into the advanced and reused treatment system for reverse osmosis treatment.All the effluent entered the pure water system as supplementary water for production.After the follow-up advanced treatment,the COD and arsenic concentration in the effluent reached to 10 mg/L and almost zero,the total removal efficiency is more than 99.99%,respectively.Through the project benefit analysis,it was obvious that the project could achieve the unification from the aspects of economy,society and environment,and it provided contributions to the arsenic source control. |
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