摘要
在用活性污泥法处理城市污水和工业废水时往往会产生大量的剩余污泥,这些污泥的体积庞大,成分复杂,处理费用也较高,其处理与处置已成为污水处理过程中的难题之一。剩余污泥的含水量高达95%-99.5%,因此,脱水成为了污泥减量中的关键一环。污泥中胞外聚合物(EPS)的大量存在给污泥脱水造成了一定的困难。EPS是细菌细胞壁外膜周围保护细胞并阻止其脱水的水合胶囊或粘液的聚合体,它决定污泥的理化性质及生物特性。EPS的质量(包括其结合水)约占到污泥固体质量的近80%,主要由有亲水性与粘性的多聚糖、蛋白质、核酸、脂质和DNA等高分子物质组成。
当今应用最多的减小污泥体积的方法是机械脱水。而化学调理法则广泛应用于改善剩余污泥的机械脱水性能。
本研究利用Fenton试剂氧化破解剩余污泥,通过污泥过滤比阻(SRF)和毛细吸水时间(CST)表征污泥脱水性能的变化,重点考察pH、反应时间、H202和Fe2+的投加量等条件对污泥脱水性能的影响,旨在找出Fenton试剂氧化污泥提高其脱水性能的适宜条件,在此基础上回调污泥pH值,考察SRF、CST和污泥沉降体积(SV30)等指标,研究污泥脱水性能的变化。结果表明,Fenton试剂处理污泥改善其脱水性能的效能明显优于酸处理。pH为2.5、反应时间为60min、H2O2和Fe2+投加量分别为6g/L和4g/L为Fenton适宜反应条件。该条件,SRF和CST分别由1.34x1010s2/g和69.6s下降至1.31×109s2/g和20.6s,污泥脱水性能的到明显改善。Fenton反应氧化剩余污泥后,回调pH能明显改善污泥的脱水性能,但是对污泥沉降性能的改善不明显。
利用紫外光-Fenton(光Fenton)氧化处理剩余污泥,通过上清液的SCOD、多聚糖以及蛋白质浓度表征胞外聚合物(EPS)的破解情况,SRF和滤饼含水率表征污泥脱水性能的变化。结果表明,光Fenton反应破解污泥EPS和改善污泥脱水性能的效能明显优于Fenton反应和单独紫外光照射处理。pH为3,反应时间为2 h,H202投加量为4 g/L和Fe2+投加量为0.6 mg/L是处理试验污泥的适宜条件。在适宜反应条件下,污泥上清液中的SCOD、多聚糖和蛋白质浓度分别由67.46 mg/L、12.53 mg/L和8.62 mg/L增加到568.12 mg/L、448.62 mg/L和292.94 mg/L; SRF和滤饼含水率分别由2.4x109 s2/g和88.52%下降至5.26×108 s2/g和76.36%。光Fenton反应在有效破解污泥的同时,提高了污泥的脱水性能,有利于污泥的减量化。
Activated sludge process to treat municipal and industrial wastewater produces huge amounts of excess sludges. The treatment of these excess sludge becomes a difficult problem in sewage treatment because of its large volume, complex components and high cost. The water content of it is as high as 95%-99.5%. Therefore dewatering is the key of sludge reduction. The bottleneck of sludge reduction is dewatering because of much of extracellular polymeric substances (EPS). EPS are a complex high-molecular-weight mix coture of excreted by microorganisms, produced by cellysis and hydrolysis, which absorbed organic matter from wastewater. The physical-chemical properties and microbial characteristics of sludge are certainly determined by EPS, which compose 80% of the weight of solid sludge, and the main components of EPS are polysaccharide, protein, nucleic acid, lipid and DNA, etc.
Mechanical dewatering is the most common method in sludge reduction. Chemical condition has been adopted widely to improve sludge mechanical dewatering.
After using Fenton oxidation to processed excess sludge, in which sludge dewatering capacity was described by the specific resistance to filtration (SRF) and capillary suction time (CST). The effect of pH, reaction time, the dosage of Fe2+ and H2O2 on sludge dewatering capacity was investigated. The objective of this study was to optimize the operational conditions for sludge dewatering capacity with Fenton oxidation. Based on the best condition, the effects of various pH on SRF, CST and static balance time (SV30) were investigated. The results showed that the sludge dewatering capacity improvement by Fenton reaction was higher than that by acid treatment. The optimal operational conditions for the experimental sludge were: pH=2.5, reaction time=60 min, H2O2 dosage=6 g/L and Fe2+ dosage=4 g/L. Under these conditions, SRF and CST reduced from 34×1010s2/g and 69.6s to 1.31×109s2/g and 20.6s, dewatering capacity was improved obviously. After Fenton reaction, raising pH can improve dewatering capacity but affects settlement of sludge seldom.
Photo-Fenton reaction was used to oxidize excess sludge, in which sludge EPS disintegration was characterized by the concentration of soluble chemical oxygen demand (SCOD), polysaccharide and protein of sludge supernate, and sludge dewatering capacity was described by the SRF and the water content of the sludge cake. The results showed that the effect of EPS disintegration and sludge dewatering capacity improvement by photo-Fenton reaction was higher than that by Fenton reaction or UV radiation. The optimal operational conditions for the experimental sludge were:pH=3, reaction time=2 h, H2O2 dosage=4 g/L and Fe2+ dosage=0.6 mg/L. Under these conditions, the concentration of SCOD, polysaccharide and protein of the sludge supernate increased from 67.46 mg/L,12.53 mg/L and 8.62 mg/L to 568.12 mg/L,448.62 mg/L and 292.94 mg/L, respectively; and the SRF and the water content of filter cake reduced from 2.4x109 s2/g and 88.52% to 5.26x108 s2/g and 76.36%, respectively. The efficient EPS disintegration and dewatering capacity improvement of the excess sludge was simultaneously achieved by photo-Fenton, which benefits the further sludge reduction.
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