| The wastewater from acrylic fiber production process presents significant harms to the enviroment because of its complex components and poor bio-degradation. Nowadays, it is a difficult problem in wastewater treatment field. Illustrated by the example of Fushun acrylic fiber factory of petrochemical company, the present wastewater treatment process could not satisfy the requirement of wastewater discharge standard. After secondary biotreatment process, the concentrations of COD and NH4+-N in effluent are still very high, and there is nearly no removal of TN due to the lack of available organic carbon source for denitrification. In order to meet the more stringent requirement of wastewater discharge standard, it is urgent for related enterprise to find an economical and effective advanced treatment process.In this study, complete water quality analysis of the important unit samples in present treatment process was carried out, in order to analyze the composition of refractory organic pollutants and investigate the transformation discipline of each kind of pollutant. After the anaerobic and aerobic biological treatment process, most of nitriles and phenols in dry-spun acrylic fiber wastewater (DAFW) could be biodegraded, and some nitrogenous organic compounds such as acrylonitrile degraded and formed ammonia which resulted in a high ammonium concentration in effluent. The composition of residual refractory organic compounds was alkanes and oligomers, which made the effluent COD concentration higher than the discharge standard. According to the characteristics of DAFW and comparison of the effects of several treatment processes, a new advanced treatment process was proposed which integrated nanofiltration, nitritation, anaerobic ammonia oxidation (anammox) and electro-heterogeneous catalytic oxidation. The feasibility of this process was investigated both in lab-scale and pilot-scaleExperimental results showed that refractory organic matter remained in biochemical effluent was retained effectively and the ammonia nitrogen was also removed by the charge balance in the nanofiltration process simultaneously. The effluent basically met the discharge standard. Furthermore the treatment quantity of the subsequent process was reduced significantly by nanofiltration concentration process. The permeate quality of nanofiltration process was affected by operational parameters such as temperature and Trans-Membrane Pressure (TMP). After two stage filtration, COD and ammonia nitrogen concentration of the permeate were32mg/L and17mg/L under TMP of0.45-0.6MPa and the temperature between30-35℃. The pilot test indicated that the SS concentration of the influent had a critical influence on the stable operation of nanofiltration device. After using the pretreatment device to remove SS of the influent, the TMP was always below0.75MPa though it increased slowly during continuous operation. The membrane fouling was lighter when nanofiltration process was sued for advanced treatment of DAFW. The membrane pollution and running resistance could be effectively reduced by cleaning and maintaining nanofiltration membrane with physical and chemical method.After the nanofiltration process, nitritation/anammox and electro-heterogeneous catalytic oxidation were chosen to remove carbon and nitrogen from the nanofiltration concentrated liquid. The membrane bioreactor was used to realize the nitratation process, for its efficient microbial entrapment effect and longer sludge retention time. Compared with lab experiments, results of pilot tests indicate that the nitritation process could start up quickly when seeding mature nitrifying bacteria. The NHLt+-N removal efficiency and the ratio of NO2--N/NOX--N were85%and0.8, respectively. The addition of KClO3could control NO3--N concentration of the MBR effluent effectively, which could be enhanced with the shorter HRT. The conversion of NO3--N was maintained at relatively low level and the concentration of NO3--N was basically below30mg/L under stable operation period.The batch and continuous test results of anammox process showed that anammox reaction rate decreased slightly when treating DAFW, but there was no acute toxicity and cumulative inhibition to the anammox bacteria. Fast start-up of anammox reactor with low inoculation sludge was achieved by seeding of high purity anammox bacteria and the utilization of non-woven fabric of cubic stereo shade structure as biofilm carrier. In the artificial culture stage, the removal efficiencies of NH4+-N and NO2--N were maintained at90%and95%, respectively. When treating actual wastewater, anammox bacteria were sensitive to temperature and SS. During the period of stable operation, the removal efficiencies of NH4+-N and TN decreased to85%and73%, respectively. The anammox bacteria genus has diversified, which transformed from single B. Anammoxidans sp. in inoculum to Kuenenia sp. as the predominate bacteria in reactor, which indicated that the condition of treating DAFW benefited the growth of the Kuenenia sp.The COD removal of nanofiltration concentrated water was achieved by electro-heterogeneous catalytic oxidation process. The COD concentration was decreased to85mg/L and the COD removal efficiency was83%under the operation condition of reaction time3h, voltage4V and H2O2dosage of3mL.Results of the pilot and lab tests showed that the refractory organic pollutants and NH4+-N in DAFW could be removed effectively by application of the advanced treatment process. Simple cost estimation showed that engineering construction total investment of this process was17.23million RMB and operation cost was4.56yuan/ton. |
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