Coking Wastewater Treatment With Immobilized Activated Sludge And White Rot Fungi

Coking wastewater is a typical refractory wastewater which composed of toxic, highly concentrated contaminants. To date, many processes have been applied to coking wastewater treatment, such as A/O, A²/O, A²/O², SBR and MBR. Due to the instable removal effect of COD, NH₄⁺-N and color, most of these expensive and complex processes could not meet the need of emission and recycle. The process based on catalytic micro-electrolysis, immobilized activated sludge and immobilized white rot fungus were studied for coking wastewater treatment in this study. The field pilot scale test was also conducted to investigate the treatment effect.Fe-Cu catalytic micro-electrolysis by HD TMAB modified zeolite strengthening was applied for coking wastewater pretreatment. The optimal pH, HRT, material ratio (W/W) and aeration rate for catalytic micro-electrolysis were 4.0,45 min, 5(Fe):1.25(Cu):0.5(zeolite) and 15 L/(L min), respectively. The GC-MS analysis results indicated that,68.5 percent nitrogen-containing heterocyclic compounds were removed and sulfur-containing heterocyclic compounds were degraded completely. Fe-Cu catalytic micro-electrolysis had many advantages such as wider pH range in application, anti impulsion load, low running cost, not agglomerate and etc.The high efficient anaerobic activated sludge and aerobic activated sludge were selected and bred in SBR and UASB reactors, respectively. To prepare immobilized activated sludge, a method based on PVA-SA embedding technique was excogitated as follows:10% PVA (W/W),2% SA,0.5% CaCO₃,2% SiO₂,2% powdered activated carbon (PAC) and 50% concentrated aerobic activated sludge were mixed together. The mixture was dropped into cross-linking agent, which composed of saturated boric acid and 2% CaCl₂(w/v) solution, and kept for 4 h to form spherical beads, then transferring to 1 mol/L KH₂PO₄ solution and immersing for 1 h. For biodegradation of coking wastewater by immobilized activated sludge, pH ranging from 7.5 to 8.5, HRT ranging from 21 h to 27 h, aeration rate ranging from 7.5 L/(h L) to 10.0 L/(h L) and liquid-solid ratio ranging from 4:1 to 6:1 created suitable conditions, respectively. The results of GC/MS analysis indicated that the main organic contaminants were entirely degraded. The immobilized activated sludge gels formed in porous structure had good mechanical properties, intensity, elasticity, aeration endurance and a service life more than 2 years. The inhibitory effects of toxic compounds such as phenols, ammonia, free cyanide and thiocyanate, on coking wastewater biodegradation were reduced significantly by immobilization technology. The kinetic equation for organic compounds in coking wastewater biodegradation by immobilized activated sludge could be expressed as S=(2426+32.30113t)/(1+0.61873t). And the kinetic equation for SND could be expressed as [ln(S₀/S_e)]/S₀-S_e=0.12648·(t/S₀-S-e)+0.00192.The white rot fungus immobilized had a strong ability to degrade the refractory and toxic organic compounds in coking wastewater. The white rot fungus immobilized on coke was applied for coking wastewater advanced treatment in a BAF reactor. And pH ranging from 5.5 to 6.5, temperature ranging from 30℃to 40℃, and 24 h of HRT create suitable conditions, respectively. The removal rates of COD and phenol were about 70% and 98%, respectively. Parameters of the effluent could meet first class discharge standard of Integrated Wastewater Discharge Standard (GB8978-96). The white rot fungus immobilized in PVA+SA-(NH₄)₂SO₄+CaCl₂ gels had many advantages such as porous structure, high porosity, good mechanical properties, high biomass and good mass-transfer performance and etc. The effluent of this process could meet first class discharge standard of Integrated Wastewater Discharge Standard under the suitable condition as follows:pH ranging from 5.0 to 6.5, temperature ranging from 30℃to 40℃, and HRT ranging from 18 h to 24 h.Process composed of catalytic micro-electrolysis, immobilized activated sludge, white rot fungus MBR and RO was ideal treatment schemes for coking wastewater recycle. COD, NH4⁺-N and phenol in final effluent were 28 mg/L,0.12 mg/L and not detected (below 0.002 mg/L), respectively. The effluent could be recycled for industrial circulating cooling water, industrial boiler water and urban miscellaneous water.The field pilot scale test was conducted for coking wastewater treatment. The effluent of catalytic micro-electrolysis and immobilized activated sludge process could meet second class discharge standard of Integrated Wastewater Discharge Standard. And final concentrations in the effluent of 100～150 mg/L COD,< 5 mg/L NH₄⁺-N and <0.5 mg/L phenol were obtained.The effluent of catalytic micro-electrolysis, UASB and immobilized activated sludge process could meet first class discharge standard of Integrated Wastewater Discharge Standard. And final concentrations in the effluent of 80 mg/L COD,4 mg/L NH₄⁺-N and 0.2 mg/L phenol were obtained. These processes had many such as short flow, small floor area, easy operation, no sludge or wastewater return, impact load resistance, low construction and operating cost.