摘要
污泥浓缩是城市污水处理厂污泥处理处置的重要环节,污泥浓缩工艺主要有重力浓缩,机械浓缩和气浮浓缩。
来自二沉池的剩余活性污泥含水率一般在99.2～99.6%,一些新工艺,如重庆大学自行研究开发的一体化氧化沟工艺,其剩余污泥经过固液分离器分离后排放,还有其它新工艺剩余污泥直接从曝气池排放,排放的剩余污泥含水率高,浓度低,在此我们称之为低浓度剩余污泥。
涡凹气浮技术在工业废水处理中得到广泛应用,但在城市污水处理厂污泥浓缩领域中尚没有应用。
本研究将涡凹气浮工艺引入到城市污水处理厂污泥浓缩领域;对调理剩余活性污泥用调理剂进行了优选;研究了絮凝剂、表面活性剂、固体负荷、水力负荷、刮泥方式、曝气机功率及温度等因素对低浓度剩余活性污泥涡凹气浮浓缩工艺的影响;研制并生产出了一台用于浓缩低浓度剩余活性污泥的MCAF-10改进型涡凹气浮设备,并研究了絮凝剂、表面活性剂、固体负荷、水力负荷、刮泥方式、曝气机功率及温度等因素对剩余低浓度活性污泥改进型涡凹气浮浓缩工艺的影响;对涡凹气浮及改进型涡凹气浮浓缩污泥脱水性能及出水性质进行了研究;对污泥浓缩工艺的有关机理进行了一些探讨;对涡凹气浮污泥浓缩工艺的特点进行了总结,并进行了能耗、技术经济分析。得到了以下结论:
1、采用FO4190SH、FO4248、FO4440SH、FA920SH、AN926SHU和 PAC单污泥调理剂和PAC+FO4440SH、PAC+FO4190SH、PAC+FA920SH、PAC+AN926SHU FO4440SH+FA920SH、 FO4440SH+AN926SHU复合调理剂对污泥进行调理, 综合考虑污泥调理效果和运行管理及费用等因素,对于南昌市朝阳洲污水处理厂污泥调理,优选单污泥调理剂阳离子型聚电解质FO4440SH。
2、采用CAF-5型涡凹气浮浓缩低浓度活性污泥时,絮凝剂采用FO4440SH,最佳投加量为1.0kg/tDS,表面活性剂采用1227,最佳投加量0.2kg/tDS,固体负荷为230kgMLSS/m3?d,水力负荷为90 m2/m3?d,出水SS为200～250mg/L,溶解性COD为30～40mg/L,污泥中的磷在浓缩过程中不会释放。
3、研制出一台适用于低浓度剩余活性污泥浓缩的MCAF-10型改进型涡凹气浮设备,采用MCAF-10型改进型涡凹气浮工艺浓缩低浓度剩余活性污泥时,絮凝剂采用FO4440SH,最佳投加量1.0kg/tDS,表面活性剂采用1227,最佳投加量0.2kg/tDS,固体负荷为270kgMLSS/m3?d,水力负荷为110 m2/m3?d,出水SS为100～150mg/L,溶解性COD为30mg/L左右,污泥中的磷在浓缩过程中不会释放。
4、改进型涡凹气浮用于浓缩低浓度剩余活性污泥时浓缩效果好,固体负荷高,出水SS低,比涡凹气浮更适合于低浓度剩余活性污泥浓缩。
5、适量的表面活性剂能够提高污泥的浓缩效果,过多的表面活性剂由于胶束的存在,亲水性增强,降低污泥絮体与气泡的粘附,从而降低污泥浓缩效果。
随着表面活性剂的加入,污泥表面胞外多聚物释放到外界环境中,污泥絮体比以前更容易压缩,结合水数量减少,脱水性能改善。
涡凹气浮产生的气泡较大,污泥絮粒大小不是影响涡凹气浮污泥浓缩工艺的主要因素,污泥絮体只要达到300～400μm能够与气泡粘附即可。
6、涡凹气浮浓缩工艺具有污泥停留时间短,污泥浓缩效果好,浓缩污泥脱水性能好,设备简单,操作方便,费用低,污泥无磷的释放等特点,适宜于低浓度剩余活性污泥的浓缩。
7、污水处理厂剩余污泥以混合液的形式排放,不进入二沉池,直接进入涡凹气浮工艺进行浓缩,较伟统污泥浓缩工艺,可缩短污泥处理流程,避免在污泥中的磷在二沉池和重力浓缩池中释放,在经济上合理,技术上可行。
Sludge thickening process is one of the important links of waste sludge treatment and disposal in the municipal wastewater treatment plant (WWTP). It includes mainly gravity thickening, mechanical thickening and air floatation thickening.
The water content of excess sludge from secondary settling tank varies from 99.2% to 99.6%, but the water content of excess sludge, which is discharged from solid-liquid seperator for the Integrated Oxidation Ditch developed by Chongqing University, or discharged from aeration tank for some new wastewater treatment process is higher than 99.2～99.6%, Its water content is high and solid content is low, it is called low concentration excess activated sludge.
Cavitation Air Floatation (CAF) technology has been widely applied industrial wastewater treatment, but hasn’t been used in sludge thickening field.
In this research, CAF technology was introduced into sludge thickening in WWTP, conditioner for excess activated sludge was selected. Factors such as flocculants, surfactant, solid loading, hydraulic loading, sludge skimming method, the aerator power and temperature were investigated. A Modified Cavitation Air Floatation (MCAF) equipment for low concentration activated sludge was developed and the factors such as flocculants, surfactant, solid loading, hydraulic loading, sludge skimming method, the aerator power and temperature were investigated, too. The dewatering characteristics of thickened sludge and effluent quality from CAF and MCAF were studied. The correlative mechanism of CAF and MCAF sludge thickening process were discussed. The features of CAF thickening process were summarized. Energy consumption, technology and economic analysis were illustrated. The results are as follows:
1、Single conditioners such as FO4440SH, FO4248, FO4190SH, PAC, FA920SH and dual conditioners such as PAC + FO4440SH, PAC + FO4190SH, PAC + FA920SH, PAC+AN926SHU, FO4440SH+FA920SH, FO4440SH+AN926SHU were used, given a comprehensive consideration of the sludge conditioning effect, operation management and cost, single conditioner FO4440SH was selected for the sludge conditioning from Chaoyangzhou WWTP.
2、As CAF-5 was employed to thicken low concentration sludge, flocculant FO4440SH was added with an optimal dosage of 1.0kg/tDS, 1227 was adopted as surfactant with an optimal dosage of 0.2kg/tDS,solid loading was 230kgMLSS/m3?d,and hydraulic loading was 90 m2/m3?d. The SS and dissolved COD in the effluent was 200～250mg/L and 30～40mg/L,respectively. And P in the sludge wouldn’t release during the thickening process.
3、MCAF-10, which is aimed to low concentration excess activated sludge, has been developed. When MCAF-10 was used to thicken low concentration activated sludge, with optimal dosage of FO4440SH and 1227 at 1.0kg/tDS and 0.2kg/tDS respectively, and with solid loading at 270kgMLSS/m3?d, hydraulic loading at 110 m2/m3?d, the SS and dissolved COD of the effluent was 100～150mg/L and 30mg/L or so,respectively. There was no P release of the sludge during the thickening process.
4、MCAF exhibits excellent thickening efficiency with high solid loading and low SS effluent, therefore is more suitable for thickening low concentration excess sludge.
5、A certain amount of surfactant enhances sludge thickening efficiency, while too much of it decreases the thickening efficiency due to the fact that the existing of micelle exhibits stronger hydrophilicity and decreases the adherence between sludge flocs and gas bubbles.
With the addition of surfactant, the extra-cellular polymers in sludge surface is released to outside environment, which yields more compactable activated sludge flocs with less interstitial moisture and improved dewaterability.
Since bubbles produced by CAF or MCAF are relatively large, the size of sludge flocs is not the key factor that affects sludge thickening for CAF or MCAF process. As long as the flocs’ size reach 300~400μm, they can adhere to gas bubbles.
6、Besides its simple unit, convenient operating and low cost, CAF thickening process possesses a short
引文
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