制革废水中含铬有机物的生物吸附-矿化协同去除机制

Synergistic Removal Mechanism of Chromium-Containing Organic Compounds in Tannery Wastewater by the Cooperation of Biosorption and Mineralization

制革含铬废水预处理后仍残留少量有机络合态铬,并以此形式进入生化处理,故活性污泥对有机络合态铬的吸附及破络行为值得关注。实际废水实验结果表明,好氧活性污泥在2 h内同步吸附化学需氧量(COD)和Cr(Ⅲ),Cr(Ⅲ)去除率达92.5%,但COD去除率不足15%。吸附前后活性污泥中有机络合态铬的分子粒径集中分布在2~3 nm和小于2 nm的区域,且吸附后仍残留少量有机络合态铬。随生化处理时间延长,Cr(Ⅲ)逐渐进入微生物内部,低浓度Cr(Ⅲ)促进微生物分泌胞外聚合物(EPS),高浓度Cr(Ⅲ)抑制EPS分泌。Cr(Ⅲ)较多分布在松散附着型EPS和紧密黏附型EPS中,EPS上的-OH、C-O-C、C-OH和-COOH为Cr(Ⅲ)提供吸附位点。该研究为制革废水铬排放总量控制及深度处理提供了理论依据。

A small amount of organic complexed chromium compounds remain and then enter into the bio-treatment system after the pretreatment of chromium-containing tannery wastewater.Thus,it is of great significance to study the adsorption and de-complexing behavior of organic complexed chromium compounds by activated sludge.The bio-treatment results of actual wastewater show that the aerobic activated sludge could simultaneously adsorb chemical oxygen demand(COD)and Cr(Ⅲ)within 2 h,and the removal rate of Cr(Ⅲ)reached 92.5%,while the removal rate of COD was less than 15%.Before and after adsorption,the molecular particle size of organic complexed chromium in activated sludge was concentrated in the region of 2-3 nm and less than 2 nm,and a small amount of organic complexed chromium remained after adsorption.With the prolongation of biochemical treatment period,Cr(Ⅲ)gradually entered to the interior of microorganisms.Cr(Ⅲ)at low concentration could promote the secretion of extracellular polymeric substances(EPS)in microorganisms,while high concentration of Cr(Ⅲ)could inhibit its secretion.Cr(Ⅲ)was mostly located in tightly bound EPS and loosely bound,and functional groups such as-OH,C-O-C,C-OH,and-COOH on EPS could provide advantageous adsorption sites for Cr(Ⅲ).This study provides a theoretical basis for the total control and advanced treatment of chromium-containing tannery wastewater.