Study On The Petrochemical Wastewater Biodegradation In A Airlift Inner-loop Three-phase Fluidized Bed Bioreactor

Study on the biodegradation technology of petrochemical wastewater, improving the waste water purification and cycle utilization level are necessary for saving water resource and practicing the green concept.This paper adopted gas-lift inner-loop gas-liquid-solid three-phase fluidized bed reactor to continually biodegrade petrochemical wastewater with the microorganism UBD immobilized technology. After effectively biodegradation, the Chemical Oxygen Demand (COD) and Total Petroleum Hydrocarbons (TPH) of the petrochemical wastewater from Gaoqiao branch company (Sinopec) decreased from 624 mg/L to 93.6 mg/L and 48.7 mg/L to 2.4 mg/L respectively, the quality of the outlet water met the first grade emission standard of PRC (GB 8978-1996).The adaptability of microorganism UBD to wastewater was firstly investigated through batch experiment, the result showed the microorganism was not suitable for dealing with the wastewater including Cl- but the petrochemical wastewater. For coking wastewater, the removal rate of COD was between 40% and 60%, and that of TPH reached around 70%; for simulated petrochemical wastewater, the removal rate of COD could reach more than 85%, that of TPH could reach 83.7%. Under the optimized condition of microorganism concentration of 500μL/L(V/V), aeration and 25℃, the COD of actual petrochemical wastewater decreased from 1034mg/L to 293mg/L, the removal rate was 71.7%; the TPH decreased from 51.6mg/L to 3.3mg/L, the removal rate was 93.6%. This microorganism had fast and highly efficient ability to deal with the petrochemical wastewater and could reach good degradation effect in 48 hours compared with 72-240 hours of other types of microorganism. Microorganism UBD still had strong degradation ability toward the wastewater, which had B/C of 0.19 and was hard to degrade. The degradation of the UBD on the short chain n-paraffins was faster than long chain n-paraffins. pH of the system during the degradation process intended to fall mainly because of the organic acid generated from the petroleum compound by the effect of enzyme.Microorganism UBD was successfully immobilized by choosing PVA as gelata, sodium alginate, activated carbon and SiO2 as the coagulant aids, boracic acid and calcium chloride solvent as cross linker and sodium sulfate solvent as the solidification agent and adopting the gel entrapment technology to deal with the petrochemical wastewater. The most optimized mixture ratio was:mass fraction of PVA, SA, activated carbon and SiO2 was 4%,0.5%,1.5% and 1% respectively. The optimized cross linkage and solidification condition was:boracic acid solvent of 6wt% and calcium chloride solvent of 2wt% as the linkage agent and sodium sulfate solvent of 0.5wt% as the solidification agent; the solidification and infiltration time of sterilized water was both 24 hours. The effect of the microorganism on dealing with the wastewater was obviously improved with the immobilized microorganism and the removal rate of COD and TPH were increased compared with free microorganism. The immobilized microorganism pellet had better mechanical robustness, elastane and osmosis, could be utilized repeatedly and maintained good activity.The gas-lift inner-loop gas-liquid-solid three-phase fluidized bed reactor was self-designed and constructed. The factors of gas holdup, liquid cycle time, mixing time and volumetric oxygen transfer coefficient were considered from the point of fluid mechanics and the optimized operation conditions for the fluidized bed were:gas velocity of 180 L/h, solid holdup of 5%, under this condition, the fluidized bed had good fluid mechanics performance, which were gas holdup of 8.31%, liquid cycle time of 8s, mixing time of 35s and volumetric oxygen transfer coefficient of 20.67 min-1. The effect of immobilized microorganism UBD on dealing with the petrochemical wastewater in the fluidized bed was investigated and the optimized technological conditions were:solid particle filling rate of 5%, immobilized particle size of 3mm, gas velocity of 180L/h and hydraulic residence time of 15h. The gas-lift inner-loop gas-liquid-solid three-phase fluidized bed reactor had strong adaptability toward the variation of hydraulic and COD volume load, the volume load reached 2.56 kgCOD/(m3·d) which was 3-5 times higher than traditional activated sludge process.The kinetics for the degradation of microorganism UBD on the petroleum compounds was also investigated, the kinetic equation for Haldane substrate inhabiting biodegradation during the degradation of microorganism UBD on the TPH was: in which vmax=0.17b-1, Ks=25.87mg/L and the substrate inhibition constant Ki=672.77 mg/L. which indicated the petroleum compounds were not hard to be degraded for UBD microorganism.The enlarge culture for UBD microorganism was accomplished in this paper, therefore the supply of this microorganism to the petrochemical wastewater industry was guaranteed. The most suitable culture conditions for the microorganism UBD were:inoculum concentration of 3%, dissolved oxygen space of 80%, temperature of 30℃, speed of shaking incubator of 190rmp, the incubation media was peptone of 15 g/L, yeast powder of 5 g/L, NaCl of 10 g/L and the microorganism concentration of 13.75×107个/L. The UBD microorganism was Pusillimonas sp., Alcaligenaceae, Burkholderiales, Betaproteobacteria, Proteobacteria, Bacteria by using gram straining and 16SrDNAPCR sequencing.