Research On Advanced Treatment Of Reverse Osmosis Concentrated Water From Printing And Dyeing Wastewater

The textile,printing and dyeing industry is one of the important industries supporting the economic development of our country,but in the process of production,there will be a large number of high pollution and difficult to degrade wastewater,and arbitrary discharge will seriously harm the safety of water ecosystem.In recent years,due to the combination of pretreatment（coagulation or physicochemical）-biochemical method-double membrane（microfiltration/reverse osmosis）technology used in the treatment of printing and dyeing wastewater,it provides a new way for its resource utilization and sustainable utilization.However,reverse osmosis（RO）can only convert about 75.0%of printing and dyeing wastewater into recycled water,and about 25.0%of the generated concentrated water（ROC）still needs immediate treatment.Generally,the ROC obtained from the treatment of printing and dyeing wastewater by biochemical and RO processes mostly contains dissolved organic matter（DOM）,mainly including various intermediates of dyes and auxiliaries,Soluble Microbial Products（SMPs）and inorganic salts.How to effectively meet the requirements of ROC treatment is one of the most challenging research directions.The main work and results of this study are as follows:1、Through the analysis of water quality characteristics,it can be seen that the aromatic degree of printing and dyeing ROC is relatively high,and the main organic compounds are mostly the intermediate products of dye biodegradation,such as benzene series,triazine,naphthalene and their products,which can be roughly classified as aromatic and SMPs.The DOM content with molecular weight less than 1k Da is the most,accounting for about 55.3%;the second is that the molecular weight of organic matter is between 3.5 and 5 k Da,accounting for about 17.8%.In addition,the hydrophobic substances account for 63.4%,the hydrophilic substances account for 24.9%,and the transitional substances between them account for 11.7%.This shows that the hydrophobic DOM of small molecules dominates the ROC of dyeing and printing;2、In the coagulation and sedimentation pretreatment unit,the best coagulant and coagulant aid are polyaluminium chloride（PAC）and chitosan（CTS）.When the p H of influent water was adjusted to 5.0,the dosage of PAC and CTS was 180 mg/L and 30 mg/L respectively,and the precipitation time was 60 min,the removal rates of UV₂₅₄and DOC in wastewater were 36.3%and 46.4%respectively.At this time,COD,DOC and chroma of the effluent decreased to 141.0 mg/L,83.4 mg/L and 74.0times respectively.In addition,the analysis of effluent water quality shows that the hydrophobic DOM with conjugated double bonds,aromatics and molecular weight between 3.5 and 5 k Da can be effectively removed after coagulation and sedimentation pretreatment3、In the Fe⁰/H₂O₂treatment process,when adjusting the p H of the coagulant sedimentation inlet water to 3.0,Fe⁰dosage to 1.34 g/L,H₂O₂dosage to 22.5 m M and reaction time to 60 min,the DOC of the outlet water decreased from 155.2 mg/L at the beginning to 23.0 mg/L（COD=42.0 mg/L）,the removal rate reached 72.4%,and the color is colorless and transparent,which realizes the first level A standard of industrial wastewater.And GC-MS analysis further proves that all kinds of organic substances are converted into lower molecular substances,such as alkanes,aliphatic groups and organic acids.