【作者】 王晓霞；

【导师】 应维琪； 吕树光；

【作者基本信息】 华东理工大学 ， 环境工程， 2010， 博士

【摘要】 污泥减量化与资源化是当前环境领域的研究热点之一。通过溶胞技术,使得污泥中的微生物利用衰亡微生物形成的二次基质进行生长,可达到污泥减量化的目的。在采用溶胞法进行污泥减量的同时,必然伴随着细胞内有机物、氮、磷等物质的释放。全面了解剩余污泥减量化过程中细胞物质的释放规律,掌握污泥减量后上清液的可生化特性,为减量化后的污泥上清液寻找合理出路,同时对污泥中所释放的磷资源进行回收,对实现剩余污泥有效减排具有重要意义。论文以目前常用城市污水处理组合工艺—A/O, An/O, A2/O工艺的剩余污泥为研究对象,通过小试研究了污泥在超声波处理中细胞物质的破解效果和释放规律。首先对比考察了超声波工作方式对污泥中COD, TN, TP释放的影响,确定了脉冲比4：1作为本研究中的超声波工作方式。在本研究所选取的超声波处理条件下(声能密度0.167～0.500W／mL,超声时间10～60 min)下,A/O, An/O, A2/O三种工艺剩余污泥中的有机物、氮、磷的释放量与释放率均随超声时间而提高,其中0.500 W/mL,60 min时A/O, An/O, A2/O污泥所对应的COD释放率分别为50.8%、54.1%和56.9%,TN释放率分别为52.1%、47.2%和70.4%,TP释放率分别为45.3%、68.1%和88.2%。在本研究的实验条件下,声能密度对物质释放的贡献度要小于超声时间,由处理中细胞物质释放规律可判定,超声波临界声能密度介于0.330 W／mL与0.500 W／mL之间。经超声处理后,三种剩余污泥的上清液BOD5/COD提高到0.33～0.68,有机物均以MW≤2 kDa的低分子量物质为主,表明所释放的有机物具有良好的可生化性。所释放的TN均以有机氮为主,NH3-N次之,硝态氮含量甚微,可忽略不计。上清液中有机物及氮含量同时增加,但COD/TKN>9,表明污泥在超声处理中所释放的氮可通过生物法得到有效去除。由于A/O, An/O, A2/O工艺的剩余污泥含磷量不同,所以在超声处理中三种剩余污泥的磷释放特性差别较大。A／O污泥含磷量较低,在0.167～0.500 W／mL下处理时,TP释放率差别不大,并且所释放的P043--P大约占污泥TP量的13.0%-18.2%,磷回收价值不高。而含磷量较高的An／O和A2／O污泥在相同的超声波处理条件下所释放的TP量明显高于A／O污泥,并且其中PO43--P比例较高(An／O和A2／O污泥上清液中PO43--P/TP分别为73.6%-89.2%、89.9%～96.5%),是污泥TP量的46.8%-55.7%、57.2%-76.2%,有利于通过化学法进行磷回收。为验证超声处理剩余污泥的效果,本研究对另外两个处理方法进行了对比研究。剩余污泥的热处理实验结果表明,污泥减量化和物质释放效果受处理温度的影响较大,处理效果随处理温度的提高而提高,但不同温度下的处理效果及变化规律有所不同。较低温度(50℃时),处理效果随时间而提高,但最大污泥浓度减少率及物质释放率低于20%,而70℃、90℃时污泥减量化和细胞物质释放均呈现先快后慢的处理效果；三个温度下污泥中磷的释放规律相同,均表现为先快后慢。热处理中的污泥上清液的氮磷组成与超声波法接近。因此采用热处理法进行污泥减量和细胞物质释放时,宜采用高温短时的操作方案。采用酸碱调节实验进行剩余污泥的处理中,仅在强碱性(初始pH为12.0)条件下才有一定的污泥减量和细胞物质释放,但处理效果不如超声波法和热处理法。综合考虑处理效果和经济能耗,在本研究所选用的三种处理方法中,超声波法较为经济有效。为防止污泥减量化易造成污水处理系统中磷负荷的增加,论文对富磷污泥超声处理中所释放的磷进行了化学法回收研究。以An／O工艺剩余污泥在0.330 W/mL、60 min条件下得到的超声波上清液作为实验对象,通过单因素实验确定了磷酸铵镁沉淀法和磷酸钙盐沉淀法的最佳工艺条件,分别为反应初始pH 9.7、搅拌时间10 min、镁磷比1.5和反应初始pH 9.0、搅拌时间5 min、钙磷比3.87。在此条件下分别可回收污泥超声波上清液中96.3%、94.0%的PO43--P。因此超声波法进行污泥减量与化学法磷回收相结合后,可回收富磷污泥中大约50%的TP,这对缓解磷资源紧缺问题具有重要指导意义。最后对A/O、An/O、A2/O工艺剩余污泥经超声波处理和磷回收后的污泥上清液的可生化特性进行了静态间歇式实验研究。结果表明：A／O工艺剩余污泥超声波上清液,在好氧条件下的有机物生物降解性、有机氮与氨氮的硝化性、有机物对反硝化影响方面的可生化性均较好；An／O工艺剩余污泥经MAP法磷回收的超声波上清液,在好氧条件下的有机物生物降解性和富磷污泥的厌氧释放性均优于采用HAP法磷回收的污泥超声波上清液；经MAP法磷回收后的A2／O工艺剩余污泥的超声波上清液,在有机物生物降解性、硝化反应、反硝化反应、厌氧释磷四个方面的生化特性均不如生活污水,尤其在有机物的生物降解性方面；根据城市污水厂剩余污泥产生量,将A/O、An/O、A2/O工艺的剩余污泥超声波上清液与生活污水相混合后,混合液在各方面的生化特性均与生活污水接近。因此,A/O、An/O. A2/O工艺剩余污泥经超声波减量化处理和磷资源回收后,污泥上清液可回流至工艺流程中任意生化段,不会影响原工艺的生化处理效果。综上所述,通过超声波与化学法磷回收技术,可实现城市污水处理厂剩余污泥50%的减量化,回收污泥中约50%的总磷,而且减量化中所释放的细胞物质可回流至原处理工艺,不会影响生化系统的稳定运行。更多还原

【Abstract】 Reduction and reuse of waste activated sludge (WAS) are popular topics in environmental research. Biological utilization of the cellular materials released from sludge disintegration is an attractive approach to achieve the desired degree of sludge reduction. A full understanding of the release of many organics, nitrogen (N) and phosphorus (P) species during WAS treatment, biodegradability of supernatant of the treated WAS and P recovery will help to construct a cost effective program of WAS reduction and reuse.Batch ultrasound treatment (sonication) runs were performed on WAS of A/O, An/O and A2/O units to identify the important factors affecting sludge disintegration and releases of the cellular materials and their effects. The effects of sonication on the releases of COD, total N (TN) and total P (TP) were first investigated; the results suggested that the 4:1 pulse ratio sonication was the desired sonication pattern for the tests. Under the sonication conditions of this research (ultrasound intensity of 0.167-0.500 W/mL and treatment time of 10-60 min), the releases of organic, N and P species increased with the treatment time; under 60 min in sonication at 0.500 W/mL, COD release efficiences of 50.8%,54.1%and 56.9%, TN release efficiences of 52.1%,47.2%and 70.4%, and TP release efficiences of 45.3%,68.1%and 88.2%were observed for the A/O, An/O and A2/O WAS samples respectively. The ultrasound intensity was a less important factor than the treatment time; the critical ultrasound intensity was estimated at 0.330-0.500 W/mL.After sonication, the supernatants of the treated WAS samples were more biodegradable as evidenced by the higher BOD5/COD of 0.33-0.68 and the predominance of organic compounds of MW≤2 kDa, which are called as smaller molecular. Organic N species were the predominant in TN released, followed by ammonia N and negligible amounts of nitrified N species. A major part of the TN released can be biologically removed since these supernatants all had a high value of COD/TKN, which are more than 9.Different amounts of TP were released from the three kinds of WAS due to their different TP contents. For the A/O WAS with low TP, about the same TP release rates were observed under sonication at 0.167-0.500 W/mL; P recovery would not be practical given its small PO43--P content of 13.0%-18.2%. For the An/O and A2/O WAS with more TP (TP was 46.8%-55.7%and 57.2%-76.2%of the dry weight for the An/O and A2/O WAS respectively), much more TP species were released under sonication; the greater release of TP species of higher%of PO43--P (the values of PO43--P/TP were 73.6%-89.2%and 89.9%-96.5%for the An/O and A2/O WAS respectively) could make P recovery by chemical precipitation more attractive.Thermal treatment and acid-alkalia adjustment were also studied and compared with sonication for sludge reduction effectiveness. Results of thermal treatment of WAS have demonstrated the importance of temperature during the process; more release of dissolved cellular materials and greater sludge reduction were observed at a higher temperature and that the treatment efficiences and change patterns in the process were temperature dependent. At a relatively low temperature of 50℃, although the thermal treatment efficiencies improved with the treatment time, the max observed sludge reduction and material releases were all less than 20%. At a higher temperature of 70 and 90℃, the rates of sludge reduction and material releases were fast initially and then slow down gradually. The same pattern was observed in P releases during the thermal treatment at the three temperatures mentioned above. Composition of TN released by thermal treatment was about the same as that by sonication. So high temperature treatment in short duration would therefore be the most effective mode for sludge reduction. WAS reduction by pH adjustment was only marginally effective at a very high initial pH of 12. Considering the treatment efficiences and cost, sonication was clearly the best method of the three studied for sludge reduction.So that recycling of the sonicated WAS would not increase the P loading to the existing wastewater treatment system, P recovery by chemical precipitation was studied. Series of experiments were performed on the supernatant of the sonicated An/O WAS (60 min at 0.330 W/mL) to identify the best operation conditions for P recovery employing MAP and HAP methods. With the initial pH of 9.7, mixed contact time of 10 min and Mg/P of 1.5,96.3%of soluble PO43--P in the MAP precipitation was recovered, and the initial pH of 9.0, mixed contact time of 5 min and Ca/P of 3.87,94.0%of soluble PO43--P in the HAP precipitation was recovered. Incorporating P recovery in the sonication WAS reduction system, about 50% of TP may be recovered, which was an important benefit due to the current shortage of P resources.Batch biodegradability tests were performed on the supernatants of sonicated WAS of the A/O, An/O, A2/O units. The supernatants of the sonicated A/O WAS exhibited good results to aerobic degradability for organics and N by nitrification and denitrification. Aerobic COD reduction and anaerobic TP release of the supernatant of the sonicated An/O WAS+P recovery by MAP were better than that by HAP. Supernatant of the sonicated A2/O WAS+P recovery by MAP was less efficience than the raw domestic wastewater in terms of COD reduction, nitrification, denitrification and P release. Given the proper mixture of raw wastewater and the supernatants of all sonicated WAS had similar biodegradability as the raw wastewater, the supernatants of sonicated WAS (from A/O, An/O, A2/O units)+P recovery may be recycled to a biological treatment systems (of organic removal, nitrification, denitrification and P release) without any harm.The results of this study do demonstrate that the combined sonication of WAS and P recovery by chemical precipitation is capable of achieving 50%reduction in the amount of the wastewater treatment plant sludge and recovering 50%soluble TP of the sonicated WAS. Furthmore the remaining dissolved cellular materials of the recycle sonicated WAS would have no adverse effects on the stable performance in raw domestic biological treatment system.更多还原