摘要
本研究采用臭氧—生物活性炭(O_3—BAC)工艺在西安市北石桥污水净化中心进行了以污水再生回用为目的的城市污水深度处理中试试验。试验以二沉池出水为原水，臭氧投量1.0～1.5mg／L，接触时间16min，原水经臭氧氧化反应后，导入生物活性炭滤柱。活性炭层高度为1.6m，滤速为3～6m／h。
工艺具有良好的深度处理效果：色度去除率为92.3％，浊度去除率为80.5％；反映有机物总量的指标UV_(254)、TOC、COD_(Cr)的去除率分别为78.5％，47.0％和64.0％；滤后水无异味，浊度小于0.6NTU,色度在4c.u.以下，TOC与COD_(Cr)分别在4.9mg／L和8mg／L左右。水质优良，可满足各种回用要求。
在低浓度臭氧化条件下，臭氧的除色效果显著，但不能有效去除有机物，主要是将大分子有机物转化为小分子有机物，并大幅度提高水中有机物的生化降解性。臭氧化前后有机物分子量测定结果和UV／TOC比值的变化充分证明了这一效果。
BAC可以进一步有效去除水的色度、浊度及水中有机物；同时对NH_3—N有较高的去除(平均去除率为53％)，但去除效果受原水NH_3—N浓度影响较大；有机物NH_3—N的去除主要在BAC上层40cm内完成。
BAC各层的生物量测定结果表明，生物量沿炭层深度呈递减关系，在生物膜成熟期，炭柱上层的生物量可以达315.9nmol Lipid-P/g活性炭；而最下层仅为35.9nmol Lipid-P/g活性炭。上层充足的溶解氧和底物供应为生物膜成长提供了有利条件。活性炭柱上层10cm生物量随时间呈S型趋势增长，其增长过程与悬浮微生物的增长过程相似，主要经历适应期、对数增长期、稳定期等阶段。
通过生化反应动力学分析建立了BAC去除有机物的三段拟一级反应动力学模型。由于生物量沿炭层深度递减，一级反应速率常数也沿炭层深度相应递减
Tertiary treatment of domestic wastewater is conducted for water reclamation at Beishiqiao wastewater Purification Center, Xi'an Municipality, with a process of low-concentration-ozonation followed by biological activated caibon (O3-BAC) filter in pilot scale. The secondary effluent was introduced into a vertical flow ozone reactor with an average contact time of 16 min at an ozone dose of 1-1.5 mg/L, and then led into a 1.6-meter-high BAC filter at a rate of 3-6 m/h.
The process achieved a remarkable effect of tertiary treatment of domestic wastewater. It removed 92.3% of color and 80.5% of turbidity. The average removals of organic substances in terms of UV254, TOC and CODcr were up to 78.5%, 47.0% and 64.0% respectively. The filtered water was completely free from offensive odor with turbidity lower than 0.6 NTU, color below 4 c.u., TOC and CODcr about 4.9mg/L and 8mg/L respectively. Quality of the treated water is good enough to meet the needs of water reuse for various purposes.
In spite of the low concentration of ozone applied, a remarkable color removal was achieveed Ozonation couldn't result in a substantial removal of organic substances, but according to the change of the molecular weight distribution and UV/TOC ratio before and after ozonation, it was found that organic matters with larger molecules were broken into smaller molecules, which improved the biochemical degradability of organic substances in the water.
Color, turbidity and organic substances were further removed after the ozonated water flowed through the BAC filter. Meanwhile, 53.9% of NH3-N was removed but the removal effect was not steady under the influenced of NH3-N concentration of the raw water. The organic substances and NH3-N were removed mainly in the upper 40cm of the BAC filter.
The biomass was found to decrease along the depth of the BAC filter. After the biofilm was
mathurated, the biomass in the upper 10cm was 315.9 nmolLipid-P/g activated carbon, but only 35.9 nmolLipid-P/g activated carbon in the lowest part. In the upper 10cm the measured biomass growth curve showed an S shape with time, which is similar to the growth process of suspended microorganism, characterized by an acclimatization period, a logarithmic growth period and finally a steady period.
Based on the analysis of bioreaction kinetics, a three-stage kinetic model was proposed to characterize TOC removal in the BAC filter. Because the biomass decreases with the depth of the BAC filter, the rate coefficient of the first-order reaction decreases with the filter depth as well.
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