| Coking wastewater(CWW) is a typical high-load, high pollution, toxic/refractory industrial wastewater. Biological treatment, in which carbon and nitrogen removal is the core of treatment, is considered to be the most economical treatment method. However, multi-fraction mixed CWW(high organic content, a variety of toxic and hazardous pollutants) results in toxic and inert inhibition on microorganism. Moreover, pollutants exhibit antagonism in biological treatment. Such reasons result in low biodegradability of CWW and make it difficult to be degraded under anaerobic condition. Therefore, identifying the strong inhibitory component in CWW is of crucial significance for efficient carbon removal and even achieving anaerobic degradation in biological treatment.As the responses of microbial cells receptor to contaminant molecules in biological treatment are similar to chemical adsorption, adsorption and biodegradation process should have some correlation in pollutant removal. The polarity(hydrophilicity) and molecular size of the adsorbed species are the main factors to determine adsorption effect of pollutants. Polarity and molecular weight of contaminants in wastewater solution may be strongly associated with biodegradability of wastewater.DAX-8 macroporous resin was used to separate hydrophobic acids(HOA), hydrophobic bases(HOB), hydrophobic neutrals(HON) and hydrophilic substances(HIS) from CWW. Then the organic content distribution, UV absorption spectra, three-dimensional fluorescence excitation-emission matrix(3D EEMs) of each polar fraction were analyzed and their biodegradability were evaluated. The results showed that HOA was the main organic component, accounting for 55.9% and 56.8% of the total COD and TOC, respectively. HOA was also a major constituent of aromatic and fluorescent substance, but HON had the highest degree of aromatic structure and proportion of humic-like substance P(Ⅲ+Ⅴ). The BOD5/COD values and the dehydrogenase activity inhibition of different polar fractions showed that the order of refractory degree was HON > HOB > HIS > raw water > HOA. It was found that HON was the most refractory component for biodegradation inhibition in CWW, whose BOD5/COD value was only 0.21±0.02 and the inhibition degree of dehydrogenase activity reached 38.5%. Four UF membranes with different molecular weight cutoffs(MWCO) were employed in separating different molecular weight fracions from CWW, namely <1 k Da, 1~ 3 k Da, 3~ 10 k Da, 10~ 30 k Da and >30 k Da fracions. Small molecules(<1 k Da) are the main organics of CWW, whose COD and DOC account for more than 90%. They were also the main aromatic and fluorescent compounds, but 1~ 3 k Da fraction had the highest degree of aromatic structure. The BOD5/COD values and the dehydrogenase activity inhibition of different molecular weight fractions showed that 3~ 10 k Da and >30 k Da fracions are refractory components, especially the >30 k Da fraction has the strongest inhibition. Analysis of SUVA and biodegradability showed not all refractory substances in CWW were aromatic compounds. Humic-like substance(Ⅲ+Ⅴ) can indicate refractory substances in different polar fractions, but couldnot apply in different molecular weight fractions in CWW.Although the spectral characteristics of different polar and molecular weight fractions in CWW has been analyzed, but changes of spectral characteristics of coking wastewater during biological treatment,especially in full scale coking wastewater treatment plants(CWWTPs), had not been fully explored and were lack of attentions. Biological treatment process is the core part of the whole CWWTP, involving a variety of biological, chemical and physical processes. UV-visible absorption spectra and fluorescence excitation-emission matrix combined with parallel factor analysis(EEM-PARAFAC) could not only reflect removal behaviors of organic matter in the biological treatment process from the spectral perspectives, but also could be used as a method for rapid detection to provide an effective and feasible monitoring mean for CWWTPs.Taking Shaogang CWWTP as a case study aimed to characterize removal behaviors of dissolved organic matter by UV spectra and EEM-PARAFAC, and investigated the correlations between spectroscopic indices and water quality parameters. Efficient removal of carbon and nitrogen was achieved after the bio-treatment(removal rate of COD, DOC and TN: 91.3%, 87.3% and 69.1%). UV270 was found out to be a stable UV absorption peak of coking wastewater that could reflect the mixture of phenols, heterocyclics, polynuclear aromatic hydrocarbons and their derivatives. Molecular weight and aromaticity showed an increasing trend and the content of polar functional groups were greatly reduced after bio-treatment. Three fluorescent components were identified by PARAFAC: C1(tyrosine-like), C2(tryptophan-like), C3(humic-like). The removal rate of protein-like was higher than that of humic-like and C1 was identified as biodegradable substances in CWW. Correlation analysis showed UV270 had an excellent correlation with COD(r=0.921, n=60, p<0.01) and DOC(r=0.959, n=60, p<0.01) and significant correlations(r =0.875, n=60, p<0.01) were also found between C2 and TN. Therefore, UV270 and C2 could be used to trace organics content and TN in coking wastewater bio-treatment, respectively. |
