Study On The Reclamation Of Biotreated Textile Wastewater By The Hybrid Processes Based On Ozonation And Removal Behavior Of Organic Matter

In this study, several hybrid processes based on ozonation (O3) were designed for the reclamation of biotreated textile wastewater, according to removal and transformation behavior of effluent organic matter (EfOM) in the different steps. The quality of treated water was considered to satisfy the requirement of dyeing and printing in textile industry for process use.Firstly, with the color being represented by ADMI value (American Dye Manufactures Institute), EfOM characterization was conducted by XAD resin absorbents and Ultra filtration cut-off fractionation, and spectroscopy technologies. Results showed that dissolved organic matter (DOM) predominated in EfOM, being rich in tryptophan-like and humic-like compounds. The percent ratio between hydrophobic and hydrophilic fractions was around1.5～2.0:1in terms of DOC, while both UV254and ADMI value of raw sample were mostly contributed by hydrophobic one of apparent molecular weight (AMW) higher than10k Da.Secondly, effects of ozone dose, reaction temperature and intial pH on the ozonation efficacy of biotreated textile wastewater were evaluated, and the regular changes of EfOM biodegradability and adsorbability on activated carbon with the specific ozone consumption were also elucidated. The removal efficiencies of water quality parameters in ozonation were in the following order:ADMI value>UV254> COD> DOC. The critical time of EfOM removal rate could be indentified, based on ozone exposure in the aqueous phase. It was known from thermodynamics analysis that, the minerlization efficiency in ozonation was more sensitive to the change of reaction temperature than the removal of UV254and ADMI value. At original pH (around8.0), the ozonation efficacy was proved to be acceptable. In addition, the increase of specific ozone consumption improved EfOM biodegradability significantly, with hydrophilic organic matter as the predominate fraction of biodegradable DOC (BDOC) produced by O3. On the one hand, ozonation improved the adsorbability of some compounds by causing the decrease of average apparent molecular weight of EfOM, and on the other, resulted in the acculumation of non-adsorbable fraction by increasing its hydrophilicity. Idealy, the estimated removal efficiencies of DOC, UV254and ADMI value in biotreated textile wastewater by using ozonation followed by biological activated carbon could reach83.4%,95.9%and99.6%, respectively.The performance of coagulation with pre-ozonation made it obvious that, the ozone dose of0.6mg03·mg-1COD employed in pre-oxidation step, not only helped reducing samples UV254, ADMI value and fluorescence intensity, but also limited the formation of BDOC and the adverse effect on subsequent coagulation. Ozonatin in the presence of granular activated carbon (GAC/O3) presented a higher pre-oxidation efficacy, and improved the treatability of hydrophobic and high molecular weight fractions by aluminium coagulation. After the optimization design, a novel hybrid process including stepwise coagulation and intermediate GAC/O3oxidation was employed in the reclamation of biotreated textile wastewater. It made full use of each technology advantages and their beneficial interactions. Pre-coagulation using polyalumium chloride (PACl) at pH8.0did not result in an obvious decrease of samples pH, but the effective removal of hydrophobic compounds, which was in favor of maintaining a strong catalytic ozonation in GAC/O3, even under continuous operation lasting several hours, and enhanced the removal of hydrophilic fractions of AMW in1～10k Da via post-coagulation at pH5.5. When the PAC1dose of25mg·L-1as A1was used in both pre-and post-coagulation, and3.1mg03·mg-1COD and10g GAC·L-1were applied in GAC/O3, the highest removal efficiencies of water quality parameters like turbidity, colour, COD, DOC and UV254were95.8%,97.5%,88.1%,68.7%and90.5%, respectively. Under this condition, its operating cost was3.20yuan per ton wastewater, in which the percent of intermediate oxidation step was around80%.Following the effective removal of EfOM, the desalination of reclaimed water was conducted by the ion exchange resin train, including strong acid type HD-8cation one and weak base type D315anion one. With the exchange flow rate of4times resin bed volume (BV) per hour, the water yield in one turn was around40to46BV. Its quality, such as total dissolved solid (TDS) less than35mg·L-1and conductivity less than50μS·cm-1etc, was far superior to the requirements of reuse water quality standard in textile industry (FZ/T01107-2011). Additionally, ion exchange resin could be reused, after being regenerated sufficiently by HCl or NaOH solution.