【作者】 何莉；

【导师】 吉芳英；

【作者基本信息】 重庆大学 ， 环境科学与工程， 2014， 博士

【摘要】 近年来，城市污水处理厂普遍存在污泥有机质（MLVSS）含量低、混合液有机质和悬浮固体比值（MLVSS/MLSS）通常在0.25~0.5之间，远低于0.75的正常水平，生化池底部泥沙淤积严重，大多数污水厂尤其是氧化沟等取消初沉池的污水厂运行1~2年，其生化池底部就可能产生0.5~2m的淤泥，使生物处理系统难以正常运行。这种现象在三峡库区山地城镇污水厂表现得尤为突出。究其原因，这种现象可能和污水中外源性无机固体含量增加、取消初沉池后无机固体去除受阻、化学除磷导致无机物含量的增加、延长污泥龄导致无机固体颗粒及无机物在污水处理系统中长期停留等因素有关。但是，在查阅资料范围内发现，鲜有学者进行相关研究，更缺乏对污水处理系统无机固体分布特性以及污泥MLVSS/MLSS下降的机制的研究。在分析无机固体迁移机制时，作者认为粒径是影响颗粒物分布特性的重要因素。基于此，研究了细微泥沙对活性污泥性质的影响；研究了化学除磷对活性污泥无机组份的累积贡献；重点研究了不同粒径的细微泥沙在生化处理系统中的分布特性和归趋行为；最后研究了细微泥沙累积对污水处理厂运行的综合影响。主要结论如下：1）进水的泥沙浓度对活性污泥的无机固体累积及恢复能力有重要影响。研究发现，粒径为43um的进水细微泥沙含量（ISS/COD）≦0.6时，MLVSS/MLSS可以维持在0.6以上的较正常水平；ISS/COD≧1.2时，MLVSS/MLSS下降到0.44以下；ISS/COD≧2.4时，MLVSS/MLSS下降到0.25以下。研究进一步发现ISS/COD≧1.8时，会持续影响活性污泥系统的恢复能力，经过60d后MLVSS/MLSS和MLSS难以恢复到初始值。细微泥沙能提高活性污泥的沉降性能和脱水性能，但同时也增大了活性污泥的比重，使得污泥容易在生化池沉积。细微泥沙不会抑制微生物活性，但会降低单位质量活性污泥的比好氧呼吸速率。2）采用硫酸铁和硫酸铝作为化学除磷剂，根据《室外排水设计规范》（GB50014-2006）对除磷剂投加量和污水厂对投加方式的要求进行化学除磷。研究结果表明在运行50d以后，MLVSS/MLSS仍能维持在0.6以上的较正常水平。化学除磷产生的化学污泥与COD的比值仅为0.1，但对MLVSS/MLSS和污泥浓度的影响却大于细微泥沙含量为（ISS/COD）0.1的影响。化学除磷也能提高污泥的沉降性能和脱水性能，但会抑制好氧微生物活性，导致比好氧呼吸速率下降。3）进入生化处理系统的无机固体除极少数细微泥沙可能随着出水排出生化系统外，其余部分或悬浮在混合液中、或沉积在构筑物底部、或随剩余污泥排出。研究发现，粒径＜73um的细微颗粒在混合液、剩余污泥和沉积污泥中的分布比分别为>21%、>31%、<47%,分布相对均匀；粒径>106um的颗粒在混合液、剩余污泥和沉积污泥中的分布比分别为<4%、<20%、>75%,主要沉积在构筑物底部。研究进一步发现,细微颗粒进入生化处理系统后,极易引起污泥MLVSS/MLSS比值下降,在粒径<73um颗粒的连续影响下,生化处理系统运行40d后,MLVSS/MLSS从0.84下降到0.26。结果表明,大颗粒固体更容易沉积在反应器底部,导致泥沙淤积,细微颗粒更容易悬浮在混合液中,引起污泥MLVSS/MLSS比值下降。4)通过对重庆市A污水厂连续一年的现场跟踪监测发现,污水厂进水的细微泥沙浓度年均值为809mg/L,ISS/COD的年均值为1.27,远远高于普通生活污水0.1的比值。降雨过程导致大量的泥沙进入生化处理系统,ISS高达1243mg/L,ISS/COD最大值达到1.98,比背景期增加113%,造成MLVSS/MLSS下降。经过多次降雨后,污水厂的MLVSS/MLSS从旱季的0.57下降到雨季的0.25,污水厂以提高污泥浓度的方式保证污水处理效果,导致MLSS从3000mg/L增加8000mg/L。这种调控方式阻碍了氧气传递,导致供气量上升,最终使污水厂的运行成本增加了44%以上。研究进一步发现进水中的泥沙浓度高和进水泥沙粒径小于73um是造成污水厂混合液MLVSS/MLSS降低的主要原因。通过对B污水厂的现场研究发现,氧化沟底部的泥沙沉积现象严重。细微泥沙主要沉积在缺氧段,其沉积厚度为0.36m～1.68m,沉积量为1061m3,使缺氧段的水力停留时间减少了57%,TN去除率降低了20%。细微泥沙在污水处理构筑物的累积定期为污水厂增加了4-5万的清淤费用,同时也使污水处理构筑物停止运行,影响污水厂的正常运作。5)基于细微泥沙在生化处理系统中的分布特性,建立无机固体的累积模型,其公式为化学污泥与混合液均匀混合,不存在沉积现象,其在混合液中的分布系数0为1。经验证,该模型能较准确预测细微泥沙含量、化学污泥和不同粒径的无机固体对混合液MLVSS/MLSS以及MLISS浓度的影响。更多还原

【Abstract】 In recent years, there are some problems in urban wastewater treatmentplants(WWTP), such as low organic components in sewage sludge,mixtureMLVSS/MLSS is between0.25~0.5, much lower than the normal value0.75, anddeposited sludge height in oxidation ditch which cancelled primary settling tank is up to1~2m. These phenomenon have become a great problem for the normal operation ofWWTP. This phenomenon in the mountainous urban WWTP of the three gorgesreservoir area is especially prominent. This maybe have relations with the increase ofexogenous inorganic suspended solid(ISS), caused by the cancellation of primarysettling tank, chemical phosphorus removal and extension of sludge rententiontime.Based on existing research, few relative studies have been done, and there are alsolack of studies about the fate of ISS in wastewater treatment system and the mechanismof MLVSS/MLSS decline. Based on the analysis of ISS distribution characteristic,particle size is considered as an important factor affecting the fate of particles. Based onthis, the effect of fine sediment and chemical phosphorus removal on inorganic solidaccumulation in the activated sludge system was studied first; second, typical particlesize distribution characteristic of fine sediment in sewage treatment system was studied;finally, the comprehensive effect of fine sediment accumulation on WWTP’s operationwas also researched.The main conclusions are as follows:1) Influent fine sediment concentration had important influence on ISSaccumulation and recoverycapability of activated sludge.When influent fine sedimentcontent(ISS/COD) with particle size less than43um was not more than0.6,MLVSS/MLSS can remain above0.6;when ISS/COD was more than1.2,MLVSS/MLSS dropped to below0.44; when ISS/COD was more than2.4,MLVSS/MLSS dropped to below0.25. Further study found that if ISS/COD was morethan1.8, it would continue to affect therecoverycapability of activated sludge system,and MLVSS/MLSS and MLSS is difficult to return to the initial value after60d. Finesediment can improve the settleability of activated sludge and dewatering performance,but also increase the density of the activated sludge at the same time, making sludgeeasier to settling in the biochemical treatment tank, increasing the difficulty of agitationand aeration, even resulting in a decrease of working volume of biochemical treatmenttank. Fine sediment will not inhibit microbial activity, but will reduce the oxygen uptake rate of unit mass sludge.2)According to the dosage stipulated in theCode for design of outdoor wastewaterengineeringand operation manner in WWTP,use ferric sulfate and aluminum sulfate aschemical phosphorus removal agent. The results showed that MLVSS/MLSS can stillmaintain at0.6after operation for50d. The chemical sludge’s contribution to the ISSwas equivalent to the ISS/COD of0.1, but the effect on MLSS and MLVSS/MLSS wasgreater than that of fine sediment. Chemical phosphorus removal can also improve thesludge settleability and dewatering performance, but will inhibit microbial activity,reducing the oxygen uptake rate.3)The influent fine sediment in an activated sludge system may be discharged fromthe reactors via effluent, or suspend in the activated sludge, or deposite at the bottom ofthe reactors, or discharged from the reactors via excess sludge. The results showed thefine sediment with particle size less than73um had a uniform proportion in mixture,excess sludge and deposited sludge, and the value was＞21%、＞31%、＜47%respectively. The fine sediment with particle size more than106um mainly deposited inthe bottom of reactor, and the proportion was＜4%、＜20%、＞75%respectively.Studies further found that the sludge MLVSS/MLSS ratio decreased easily. Under thecontinuous influence offine sediment with particle size less than73um, MLVSS/MLSSdecreased from0.84to0.26after40d. In a word, large solid particles were more likelyto deposit in the bottom of the reactor, causing sediment deposition, but fine particlessuspended in mixture more easily, causing sludge MLVSS/MLSS ratio decrease.4)Through1year on-site monitor of A WWTP in Chongqing, it found that theannual average concentration of fine sediment was809mg/L, and ISS/COD was1.27,much higher than the ordinary sewage of0.1. During rainfall process, fine sedimentcontent increased to1243mg/L, and the maximum of ISS/COD was1.98, increased by113%than the background period.After a rainfall, MLVSS/MLSS only decreased from0.37to0.32, but MLSS rised from5380to6700mg/L.Rainfall caused a lot of sedimentinto the activated sludge, resulting in MLVSS/MLSS decreased. In order to ensure thewastewater treatment efficiency, WWTP had to improve MLSS, leading to MLSSincreased from3000mg/L in the dry season to8000mg/L in the rainy season, andMLVSS decreased from0.57to0.25. This operation manner of WWTP will hinder theoxygen transfer, increase the oxygen supply, eventually make WWTP’s operating costsincrease more than44%. Study further found that high sediment concentration ininfluent and sediment particle size less than73um were the main reason for MLVSS/ MLSS reducing.The study of B WWTP showed that the sediment deposition in the bottom of biochemical treatment tank was very serious. For oxidation ditch, fine sediment deposited mainly in the anoxic period. Its deposition height was from0.36m to1.68m, and deposition volume was1061m3, leading to hydraulic retention time of anoxic period decreased by57%, and TN removal rate reduced by20%. The accumulation of fine sediment increased40000～50000yuan cost for WWTP regularly, stopped WWTP running at the same time, affectting the normal operation of the WWTP.5) Based on the distribution characteristics of fine sediment in sewage treatment system, the accumulation model of ISS is established, the formula was Chemical sludge mixed with mixture evenly and did not deposited in the bottom, thus, its distribution coefficient was1. It verified that the model can predict the effect of fine sediment content, chemical sludge and fine sediment with different particle size to MLVSS/MLSS and MLISS concentration.更多还原