Removal Characteristics of Sulfamethazine in Sequencing Batch Reactor

在畜禽养殖业中，抗生素被广泛地用来治疗动物疾病和促进动物生长，但是大多数使用的抗生素都未经机体代谢就直接通过粪便和尿液排泄出来，使畜禽废水成为环境中抗生素污染的重要来源。目前对于抗生素在以活性污泥法为主体工艺的污水处理厂中的去除效果已有不少报道，但结果多为进出水浓度检测，活性污泥对抗生素的去除研究还较少见。<br />序批式活性污泥反应器（Sequencing Batch Reactor，SBR）应用于畜禽废水的处理已被证实获得比较理想的污染物去除率。本文以解析抗生素在畜禽废水的SBR 处理工艺中的去除特性为研究目标，开展了以下工作：<br />首先，以集约化养殖场中较常用的磺胺类抗生素为研究对象，选择检测频率和平均检出浓度较高的磺胺二甲嘧啶（Sulfamethazine，SMN）为代表，研究了其在活性污泥上的吸附行为。考查了吸附时间、污泥浓度（MLSS）、pH 以及温度对SMN 吸附的影响。结果发现，活性污泥对SMN 的吸附过程很快，30 min 吸附量已达到平衡吸附量的80%，24 h 后已达到完全平衡。MLSS 浓度对SMN 的吸附去除有较大的影响，随着MLSS 浓度的增加，吸附去除率增加但是单位污泥吸附量下降。pH 值影响活性污泥的表面性质和SMN 的存在形态，对吸附量有较大影响。在10-30 &deg;C 范围内SMN 的线性分配系数随温度升高而减小。通过吸附热力学的研究可以推断，SMN 在活性污泥上的吸附过程是放热过程，以物理吸附为主，其中静电效应起主要的作用。<br />其次，探明了SMN 在活性污泥工艺中的去除过程。SMN 先是快速吸附到活性污泥的表面，然后进行生物降解。反应120 h 之后，SMN 的总去除率将近达到100%，其中99%归功于生物降解作用。虽然吸附贯穿整个反应过程，但生物降解是SMN 的主要去除机制。考察了SMN 的生物降解动力学以及MLSS 浓度、温度和初始COD 浓度等因素的影响。结果表明，SMN 的总去除率随MLSS 浓度的增加和温度的升高而提高，而单位污泥的去除率则随MLSS 浓度增加而降低，初始COD 浓度则对SMN 降解的影响不大。<br />最后，考察了SBR 对SMN 的去除效果以及SMN 的存在对SBR 运行效率的影响。结果表明，运行初期SMN 的去除效率相对不高且呈现出下降的趋势，而运行中期去除效率显著升高，运行后期去除效率趋于稳定。经过一个月的运行，SBR 对三个添加浓度（100、500 和2500 &mu;g/L）下的SMN 均有较好的去除效果，其中对低浓度SMN 的去除率相对更高。SBR 反应器进水中添加SMN 对出水的COD 和氨氮没有影响，但会使出水的硝酸盐氮和总磷的浓度略微升高，SMN 的存在可能对SBR 中的反硝化菌和除磷菌产生抑制作用。Antibiotics have been widely used to treat animal diseases and promote animal growth.However, the majority of applied antibiotics are excreted in feces and urine without metabolism in animal bodies, which makes swine wastewater an important source of antibiotics pollution in environment. To date, many studies have been reported on antibiotics removal in sewage treatment plants (STP) with activated sludge processes. However, most studies have just focused on the concentration detection of antibiotics in the influent and effluent, few about their removal characteristics.<br />Sequencing batch reactor (SBR) shows ideal treatment effect on the removal of<br />contaminants in the wastewater. Sulfonamides are one class of the most widely used and frequently detected veterinary antibiotics. The aim of this study was to investigate the removal characteristics of antibiotics in activated sludge processes.<br />Firstly, sulfamethazine (SMN) was chosen to investigate the adsorption behavior in<br />activated sludge process because of its high detection frequency and average concentration. The effect of adsorption time, mixed liquor suspended solids (MLSS) concentration, pH and temperature were investigated. The results showed that the adsorption of SMN onto activated sludge was a quick process. The adsorption amount had already achieved 80% of equilibrium adsorption amount within 30 min and reached complete equilibrium after 24 h. MLSS concentration had a significant effect on the adsorption behavior. The total adsorption amount increased with the increase of MLSS concentration, while the adsorption amount per unit MLSS decreased. As pH influenced the surface property of activated sludge and the<br />speciation of antibiotics, pH had an obvious effect on the adsorption amount. In the range of 10&ndash;30 &deg;C, the linear adsorption coefficient decreased with the increase of temperature. The adsorption of SMN onto activated sludge was an exothermic process due to adsorption thermodynamics and it was mainly a physical process, in which electrostatic effect played an predominant role.<br />Secondly, the removal process of SMN in activated sludge processes was investigated,which was characterized by rapid adsorption onto activated sludge and subsequent biodegradation. After 120 h, nearly 100% of SMN was removed, of which 99% was attributed to biodegradation. Though the adsorption processes existed during the whole reaction process, biodegradation played the predominant role while adsorption was insignificant. The biodegradation kinetics and several effects including MLSS concentration, temperature and initial COD concentration were investigated. The results showed that the total removal of SMN increased as the MLSS concentration and temperature increased. However, the removal<br />efficiency of per unit MLSS decreased as MLSS concentration increased. The effect of initial COD concentration was insignificant.<br />Finally, the removal efficiency of SMN in SBR and the influence of SMN in influent on<br />the operation of SBR were investigated. The results showed that the removal efficiency of SMN was relatively low and showed a decreasing trend in early operation, then increased obviously in the middle of operation and remained steady in late operation. After one month&rsquo;s operation, the removal efficiency of SMN with low concentration in influent was the highest.<br />However, the removal efficiencies of three different SMN concentrations (100, 500 and 2500 &mu;g/L) in influent were all relatively high, which implied that the SMN concentrations ranged from 100 &mu;g/L to 2500 &mu;g/L in influent showed no apparent inhibitive effect on microorganism in SBR. Biodegradation was the predominant role during the removal of SMN in SBR because the adsorption of SMN on activated sludge was small while the overall removal efficiency of SMN was high. The existence of SMN in influent increased the effluent concentrations of NO3--N and TP while showed no obvious effect on the removal efficiencies of COD and NH3-N. The existence of SMN probably showed inhibitive effect on denitrifying bacteria and phosphorus removal organisms