| Polyvinyl alcohol (PVA)-containing desizing wastewater containing high strength of recalcitrant organic matters and waste alkali are discharged from final textile wastewater. Due to its poor biodegradability, the desizing wastewaters require adequate and sufficient treatment before being allowed to be discharged into surface waters.An improved lab-scale hybrid anaerobic baffled reactor (HABR) was developed to treat desizing wastewater. The modification was achieved by increasing the height of HABR and application of proper effluent recycle, which enabled to increase the ability of entrapping microbe-rich small particles in the reactor and prompted the formation of granules. The reactor combined the advantages of EGSB and ABR simultaneously.This research came from crosswise tasks: "the project design for 2400 t/d textile wastewater treatment of Lanling dying and prting plant" (No. H20081208). And this work was also supported by the Innovation Foundation of Donghua University for Ph.D. candidates (No. BC200828) and and the Key Subject Construction Item of Shanghai city (No. B064).First, the paper studied the start-up of HABR and optimization of the operation parameters of HABR; The biodegradation characteristics of PVA 1799 were studied; The structures and micro-ecology characteristics of anaerobic granular sludge in each separation compartment of HABR were studied; The transformation of desizing wastewater in HABR was investigated; the performance of HABR under steady condition was examined and tracer studies were carried out in order to determine the hydrodynamics of HABR.The results indicated;(1) The wastewater was treated on mesophilic condition after anaerobic granular sludge was inoculated in the HABR, the pH of influent was 6.5～8.0 and alkalinity was suitable higher. Hydraulic retention time (HRT) was 168h and the influent concentration was increased from 1800 mg/L to 13520 mg/L gradually during the experiments. The experimental results indicated that the removal of CODCr was above 45% and the pH and alkalinity of effluent were relatively stable. At the same time sludge appeared obviously granulation, the start-up was successfully finished. HABR can be restarted-up in a short time and the activities of anaerobic granular sludge can be restored quickly.(2) Within 135 days of the orthogonal experiment for optimization of the operation parameters of HABR, the effect of three important factors including alkalinity of influent, effluent recycle ratio, HRT and each factor at three levels were studied using Taguchi's method. The results showed that the most important factor contributing to the COD and PVA removal efficiency was HRT followed by effluent recycle ratio and lastly, influent alkalinity. By comprehensively comparing experimental data and considering cost, the optimum condition was chosen as alkalinity of influent 500 mg/L, effluent recycle ratio of 94 times influent rate and HRT 5 d.(3) The biodegradability of PVA 1799 under anaerobic conditions was demonstrated using anaerobic granular sludge from HABR. The results showed that the microorganism composition and particle size of the granular sludge directly influenced the PVA removal rate. Alkalinity influenced degradation of PVA 1799, and high alkalinity suppressed PVA 1799 degradation. It was indicated the degradation of PVA 1799 was suppressed by high glucose concentration; when starch was taken as carbon source, starch molecule first adsorbed on sludge surface and degraded before PVA; It took longer time to degrade PVA 1799 when using soybean milk as carbon source; The inhibition test of PVA concentration on anaerobic granular sludge activity showed: the activity of anaerobic granular sludge was suppressed when PVA concentration between wastewater treated and wastewater for acclimated sludge had larger difference.(4) It was indicated the good removal of COD was achieved probably due to the formation of granular sludge. Hydrogen-utilizing methanogenic bacteria were predominant in interior of granular sludge in compartment 1. As for compartment 2, there were no absolutely predominant bacteria and there were multiple and complicated bacteria communities. In compartment 3, the predominant bacteria were Methanococcus and Methanobacterium. In compartment 4 of the reactor, the predominant bacteria were similar to Methanobrevibacter. The SMA of granular sludge in each compartment of HABR was different when the starch, acetate, propionate and butyrate were taken as substrate respectively. The result indicated the composition of microbe was different in each compartments, acidogenic bacteria were predominant in the front, while methanogenic bacteria were predominant in the rear.The content of coenzyme F420 in granular sludge of HABR varied along the reactor, which had no same tendency of variation of SMA, the result maybe due to content of methanogenic bacteria species was different, so it had poor correlation.(5) Judging from the FTIR and 'H NMR analysis of influent and effluent wastewater, it was indicated the molecule chain of PVA fractured in the process of anaerobic biodegradation by the microbes, some of PVA molecules could be facultatively broken down into simple intermediate products. Biodegradation of PVA certainly occurred in an anaerobic environment, which had the same degradation mechanism under anaerobic conditions as that under aerobic conditions, but a different biodegradation pathway might exist under anaerobic conditions due to different experimental conditions. Results of the product analyses confirmed the biodegradation of PVA occurred under anaerobic conditions, it also offered an effective desizing wastewater degradation craft.(6) Under optimum condition (alkalinity of influent 500 mg/L, effluent recycle ratio of 94 times influent rate and hydraulic retention time of 5 d), the system demonstrated a good performance of COD and PVA removal efficiencies (around 42.0% and 18.0% respectively) and the average concentration of alkalinity in the effluent was around 700 mg/L and pH value was above 6.8. Proper pH and alkalinity were of key importance for the stable operation of HABR. The system at the HRT 5 d had highest observed methane yield averaged at 0.30 L CH4 /g COD removed of HABR. Based on the tracer studies carried out at three different effluent recycle ratio, it was observed that the flow pattern within the HABR remain intermediate between plug and perfectly mixed flows (0.105 |
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