Study On Treating Antibiotic Wastewater By Hydrolysis Acidification-suspended Carrier Hybrid MBR

The quality of antibiotic wastewater is very complicated and hard to treat, which contains fermentation residue substrates and nutrients, microbial mycelium, intermediate metabolites, raffinate of solvent extraction process, distiller raffinate, fermentation filtrate and so on, leading to the wastewater characteristic of high concentrations of organic matter, large pH variations, strong biological inhibition, etc. In addition, with the promulgation and implementation of more stringent pharmaceutical industry water pollutants discharge standards (GB21903-2008.Discharge standards of water pollutants for pharmaceutical industry), how to make the pharmaceutical wastewater, especially the antibiotic wastewater, achieve the discharge standards becomes not only a hotspot for water treatment industry at home and abroad, but also a nodus for the pharmaceutical industry to be solved urgently. Consequently, it is necessary to investigate a feasible technology in technology and economy for the treatment of antibiotic wastewater. Depending on the characteristic of antibiotics wastewater and new discharge standards, the hydrolytic acidification-suspended carrier hybrid MBR technology was proposed. The results of hydrolytic acidification showed that the effluent quality was relatively stable under a large fluctuation influent quality (COD was 1670⁴200mg/L; SS was 270⁷30mg/L). HRT and temperature as the main operation parameters of hydrolytic acidification were investigated, results showed that the performance of hydrolytic acidification was better under the condition of HRT was 10h and the temperature was controlled at 20℃³0℃(acidifying degrees was around 50%, the effluent VFA was above 1500mg/L). The long-term operation results of acid hydrolysis acidification indicated that the biodegradability of wastewater was improved greatly, BOD5/COD increased from 0.29 to 0.49, SCOD/COD improved from 0.67 to 0.92. The effluent of hydrolytic acidification using suspended carrier hybrid MBR to treat the antibiotic wastewater showed that the COD removal rate was 91%⁹4% and the effluent COD was less than 200mg/L when the HRT was 12¹8h. When the HRT was more than 24h, COD removal rate stabilized around 95% and the effluent COD was less than 100mg/L, the quality met the related water pollutants emission limit (Discharge standards of water pollutants for pharmaceutical industry, Fermentation products categegory). Compared the suspended carrier hybrid MBR with the common MBR in the treatment efficiency after the pretreatment of antibiotics wastewater using hydrolytic acidification, under the same operating conditions, COD, ammonia nitrogen and TN removal efficiencies of suspended carrier hybrid MBR were better than those of common MBR, the removal rate increased by 4.8%, 8.2% and 8.3%.On the basis of the activated sludge and biofilm coexistence system dynamics analysis, the MBR organic matter degradation kinetic equation of activated sludge and biofilm coexistence suspended carrier hybrid MBR was built for the practical application and establishing the theoretical foundation through the material balance of organic matter. Under the experimental conditions, the COD half-saturation constant ( K_s,COD,sp) of carrier biofilm was 114.36 mg/L, the largest COD consumption rate ( q|^_{m ,COD,sp}) of carrier biofilm was 3.04mg/(number·d) , the maximum specific substrate degradation rate constant (V_max) was 0.62d^-1, substrate saturation constant (K_s) was 147.65mg/L. Organic matter degradation rate constant (K = V_max/Ks) was 0.004. The effluent COD was simulated by the model. Comparing with the experimental data, the result was in accordance with the practical operation. By numerically solved of suspended carrier hybrid MBR sludge yield coefficient Y and attenuation coefficient Kd, the conclusion was Y = 0.09, K_d = 0.0144, which were less than those in common MBR (Y=0.1327,K_d=0.0177) under the condition of SRT = 100d, HRT = 24h, MLSS = 12¹5g/L.The central composite design and response surface method were used to confirm the main operation parameters on affecting membrane flux. Experimental results showed that the critical flux decreased as the mix liquid suspended sludge concentration decreased. The critical flux was first increased and then decreased as the aeration intensity increased, while the aeration intensity was 0.05⁰.15m³/h, the maximum critical flux was obtained when the aeration intensity was 0.1m³/h. The critical flux was first increased and then decreased as the carrier filling amount increased, when the carrier filling amount was 5% to 15%, the maximum critical flux was obtained when the filling amount was 10%. Based on Response Surface Method, the effect of the sludge concentration, aeration intensity and carrier filling amount on critical flux was analyzed using two-factor interaction effect. The result showed that the mixed liquid suspended sludge concentration, aeration rate and carrier filling amount were main factors of impacting the membrane critical flux in suspended carrier hybrid MBR. The effect of the mixed liquid suspended sludge concentration, aeration intensity and carrier filling amount on membrane critical flux was in sequence that sludge concentration > aeration rate > carrier filling amount. The mathematical model of membrane critical flux was built, and the maximum relative error of the predictive value and experimental value was 6.58%, which indicated that the model prediction had a good effect and had a certain extrapolated prediction for the membrane critical flux. The optimal operating conditions for the critical flux were the mixed liquid suspended sludge filling amount was 10.85%. Under the constant flux continuous operation, adding carrier extended running time to achieve the critical TMP conditions 30kPa, suspended carrier hybrid MBR needed 89h, and it was 2.6 times than common MBR. The TMP average rising rate in suspended carrier hybrid MBR process was (dP/dt) 0.33 kPa/h, which was 37.5% in the common MBR process.SEM and confocal microscopy analysis on the surface of polluted membrane, combined with an analysis of ISA3d software on the micro-structural parameters of filter cake layer, revealed the main mechanism of suspended carrier on membrane fouling delay rate. Results showed that the suspended carrier on membrane fouling delay rate was mainly manifested by increasing cake porosity and decreasing filter cake layer weight under the same operation time (34h). The filter cake volume and thickness of suspended carrier hybrid MBR membrane surface were 3.2×105μm³ and 9.45μm, respectively, which were less than common MBR membrane surface 5.4×105μm³ and 12.6μm, and the cake surface specific resistance of the common MBR was only 25%. To achieve the same TMP (30kPa) conditions, the filter cake volume, average cake thickness and porosity of suspended carrier hybrid MBR were larger than those of common MBR. The increased cake porosity offseted the negative impact of membrane resistance, which was increased by cake weight and enhanced the performance of the membrane filtration.