【作者】 裴烨青；

【导师】 陈东辉；

【作者基本信息】 东华大学 ， 环境工程， 2014， 博士

【摘要】 CMC,英文名Carboxymethyl Cellulose (Sodium),中文名羧甲基纤维素(钠),是一种羧甲基团(-CH2-COOH)结合至羟基(-OH)上的纤维素衍生物。CMC在民用、工业各类产品中被广泛用作增稠剂、乳化剂等,是当今全球产量最大、用途最广的纤维素类工业产品。CMC生产废水的主要化学组分是：水、羟乙酸钠和氯化钠,另含少量纤维素(及其杂质)、氢氧化钠、乙醇和CMC。CMC生产废水是典型的高浓度高盐度有机废水,最高COD浓度可达80000mg/L以上、盐度150000mg/L以上,较低COD浓度也在20000mg/L左右、盐度40000mg/L左右,因此在纳入排污管网前,必需得到有效处理。本文源于低浓度CMC生产废水好氧生物处理的一个工程案例,针对工程中出现的三项棘手问题,分析问题成因、研究解决方案。首先,本文分析归纳江苏省泰兴市一家特种化学品工厂采用好氧膜生物反应器(MBR)处理低浓度CMC生产废水的三个工程技术问题,进水COD浓度约20000mg/L、盐度约40000mg/L的,处理目标是出水COD浓度低于500mg/L。经过三个月污泥驯化期,生物处理系统在随后的四个月正式运行期内表现较为理想,大部分时间出水浓度都能达到预订排放目标。不过存在三个问题。第一,超滤系统产水通量下降速度过快,降速随盐度升高更快；常规的气水反洗物理清洗手段无法有效地恢复产水通量,只能缩短化学清洗的周期；虽然提高物理清洗的频率和强度可以起到一定的缓解作用,可是效果仍然非常有限。第二,生物处理系统对于进水盐度冲击出现明显不适应,特别是在污泥驯化期内,尚未稳定的生物系统对于废水盐度变化非常敏感,因此在这个阶段内必须严格遵循缓步提升进水盐度的原则；进入运行期后,生物系统对于盐度冲击的耐受能力明显增强,但是CMC生产废水水质较大波动(一波高于35000mg/L的盐度冲击)使得生物系统遭受严重损害。第三,大量的黄褐色泡沫层层叠叠溢出好氧池外,尽管泡沫问题不会对生物处理系统的处理效率造成影响,但是却破坏厂区的卫生环境状况。本文通过参阅大量科研文献,关注废水成分,分析得出：CMC生产废水的主要有机组分羟乙酸钠可能是造成这些工程问题的原因之一；CMC生产废水缺乏微量营养物质可能是造成这些工程问题的原因之二。再次基础上,提出了采用耐冲击性更佳、悬浮污泥更少的移动床生物膜反应器(MBBR)的工艺改进方案。接着,本文通过实验室试验,考察和比较了添加微量营养物质的活性污泥反应器和未添加微量营养物质的移动床生物膜反应器对于过滤性能、沉降性能和耐盐冲击性能的改善作用。其中,添加微量营养物质又分别通过向废水中添加天然水和投加化学药剂两种途径来实现的。结果,向废水中添加天然水可以明显改善混合液的过滤性能和耐盐冲击性能,不过对于沉降性能却无特别显著的改善作用；向废水中投加化学药剂没有任何改善作用,甚至还有一定负作用：移动床生物膜反应器内混合液的过滤性能最差,远远差于任何一个活性污泥反应器；三项方案对于处理效果皆无明显改善效果,同时发现维持活性污泥浓度的食微比介乎0.3-0.5kg COD/kg MLSS之间。根据试验结果得出结论：天然水中的微量营养物质能够有效改善活性污泥在处理CMC生产废水时的过滤性能和耐盐冲击性能,而在实际工程中可以将CMC生产废水与生活废水混合来补充微量营养物质。还采用珀金埃尔默Optima8300电感耦合等离子体发射光谱仪测定试验中所用天然水的微量元素成分和含量。然后,通过实验室小试和工程中试,研究了CMC生产废水与生活废水混合之后对于过滤性能的改善作用。小试结果表明CMC生产废水与生活废水混合可以明显改善活性污泥的过滤性能,不过效果略次于天然水。中试在生产现场进行,高浓度CMC生产废水与生活废水按照1：3混合,混合废水的SCOD浓度约18000mg/L、盐度约32000mg/L；采用推流好氧膜生物反应器进行处理,设计有机负荷为0.4kgSCOD/kgMLSS。结果：出水COD浓度低于1000mg/L,超滤系统通量下降缓慢,化学清洗周期延长至两个月以上。再后,针对泡沫问题,经过查阅科研文献,明确稳定泡沫是在发泡物质(表面活性剂)和稳泡物质的协同作用下所形成的。通过对过滤前后的CMC生产废水进行曝气,以及对过滤前后的CMC生产废水与活性污泥的混合液进行曝气,从而确定在CMC生产废水好氧生物处理中泡沫问题的成因。根据试验结果得到结论：表面活性剂CMC是CMC生产废水中的发泡物质；CMC生产废水中的悬浮固体天然纤维及其杂质是稳泡物质,具有非常良好的稳泡效果。在实际工程中可以采用以下两种解决方案：一是对CMC生产废水进行一段时间的预曝气,撇去浮渣之后进入好氧生物处理；二是滤去CMC生产废水中的悬浮固体之后进入好氧生物处理。最后,本文选用国际水协会(IWA)开发的活性污泥一号模型(ASM1),构建一个可以模拟活性污泥处理CMC生产废水过程的数学模型。活性污泥一号模型以死亡再生理论为基础,模拟活性污泥处理废水中的8个生物反应,涉及到13个反应组分,在数学模拟中用到了5个化学计量参数和14个动力学参数。经仔细研究活性污泥一号模型的内涵,同时结合CMC生产废水的水质特点,构建了CMC生产废水—活性污泥一号模型。这个模型将原本活性污泥一号模型中的8个生物反应简化为3个,将13个反应组分简化为8个,将5个化学计量参数简化为4个,其中需要测算的是1个,将14个动力学参数简化为5个,其中需要测算的是2个。经过测算,获得了活性污泥处理CMC生产废水的异养菌的产率系数YH、异养菌的最大比生长速率μH、异养菌的衰减系数bH在环境盐度10000-80000mg/L之间的数据变化情况。更多还原

【Abstract】 CMC, the initials of "Carboxymethyl Cellulose (Sodium)", is a cellulose derivative with carboxymethyl groups (-CH2-COOH) bound to some of the hydroxyl groups. CMC, which is applied as thickening agent, emulsifying agent and so forth in various civil and industrial products, has been the most abundantly produced and most widely applied cellulose products currently and globally.The main chemical constituents of CMC wastewater are:water, sodium glycolate and sodium chloride, and there is a little raw cellulose (and some impurities), sodium hydroxide, ethanol and CMC in it. CMC wastewater is typical high concentration and high salinity organic wastewater, whose COD and salinity can at highest be above80000mg/L and150000mg/L respectively, and at lowest be around20000mg/L and40000mg/L respectively, so it must be effectively treated before being discharged into sewerage.The study of the dissertation originates from a project of aerobic biological treatment of low concentration CMC wastewater, and fouceses on the three serious problems found in the project by analysing on the causes and experimenting on the solutions.Firstly, the dissertation discusses a full scale project:in a specialty chemical factory located in Taixing City, Jiangsu Province, low concentration CMC wastewater, whose COD and salinity was20000mg/L and40000mg/L respectively, was treated with aerobic membrane biological reactors (MBR), and the target COD of the treated effluent was below500mg/L. After three-month acclimatization period, the biological treatment system showed a relatively ideal performance in the subsequent four-month operation period. Namely, the treated effluent met the discharge standard most of the time. However, three great problems were found during the two periods. The first problem was that the permeate flux of the ultrafiltration system descended too fast, and even faster as the salinity ascended. During operation, the regular physical wash (air-water backwash) was unable to effectively restore the permeate flux, so the intervals between chemical washes had to be shortened. Heightening the frequency and intensity of physical washes had some mitigation effect, but the effect was quite limited. The second problem was that the biological treatment system showed obvious untoward reaction to salinity shocks. Especially during the acclimatization period, the yet unstable biological system was very sensitive to the ambient salinity change, so the principle of increasing influent salinity gradually must be strictly followed. During operation period, the biological system showed better tolerance to salinity shock. However, the CMC wastewater fluctuated in water quality fairly widely, and a wave of salinity shock over35000mg/L still caused considerable damage to the biological system. The third problem was that huge amounts of big tawny bubbles piled up layer upon layer, overflowed out of the aerobic reactor and drifted everywhere blown by the wind. Although the foaming problem had less negative effect on the treatment efficiency of the biological system, it was destructive to the factory environment.Secondly, the causes of these problems are analysed from the viewpoint of the wastewater constituents. Upon review of research literature, sodium glycolate, the main organic constituent in CMC wasterwater, is inferred to be one probable cause of these problems, and the abscence of micronutrients in CMC wasterwater is probably the principal cause of the problems. The improvements to these problems are discussed from the viewpoint of the wastewater treatment process. With better shock tolerance and less suspended sludge, Moving Bed Biofilm Reactor (MBBR) is supposed to make improvements.Thirdly, a comparison upon improvement effects on filterability, settleability and salinity shock tolerance is made between the AS reactors with micronutrients added and the MBBR without micronutrients added. The addition of micronutrients is realized through two ways:adding natural water into the wastewater and adding chemical agents into the wastewater. The experiment results show:adding natural water into the wastewater notably improves the filterability and salinity shock tolerance, but fails to make improvement in settleability; adding chemical agents into the wastewater makes no improvement, but negative effects; the MBBR makes the worst filterability, even far worse than any of the AS reactors; all the three trial solutions make no improvement in treatment efficiency; the minimum Food to Microorganism (F/M) that can maintain the current activated sludge concentration is0.3-0.5kg COD/kg MLSS. The following conclusions are made on the basis of the experiment results:the micronutrients in natural water can effectively improve the filterability and salinity shock tolerance of the activated sludge for treating CMC wastewater, and then for full scale projects, mixing CMC wastewater with municipal sewage is expected to be a more practicable option of acquiring micronutrients and improving the performance of the activated sludge.Fourthly, whether mixing CMC wastewater with municipal sewage can improve the filterability is studied through bench scale experiment and intermediate scale experiment. The bench scale experiment results show:mixing municipal sewage can effectively improve the filterability of the activated sludge, but slightly less effective than adding natural water. In the intermediate scale experiment held in a CMC factory, high concentration CMC wastewater and municipal sewage was mixed by ratio1:3, and treated with a plug flow aerobic MBR. The SCOD and salinity of the wastewater was18000mg/L and32000mg/L respectively; the design organic loading was0.4kgSCOD/kgMLSS. The intermediate scale experiment results show:the COD of the treated effluent was constantly below1000mg/L; the ultrafiltration flux descended slowly, and the interval between chemical washes was more than two months.Fifthly, the trace elements in the natural water utilised in the experiments are qualitatively analysed and quantitatively determined by a Perkin Elmer Optima8300Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES), and the results could be the reference for natural water synthesis.Sixthly, the formation mechanism of stable foam is defined upon review of research literature: stable foam is formed under the synergy of foaming agent (surfactant) and foaming stabiliser. The causes of foaming problem in the aerobic treatment of CMC wastewater are analysed by aerating unfiltered, filtered CMC wastewater, the mixed liquid of unfiltered, filtered CMC wastewater and activated sludge. The following conclusions are made on the basis of the experiment results:as a surfactant, CMC is the foaming agent; as the suspended solid in CMC wastewater, natural cellulose and its impurities is the foaming stabiliser, which has very excellent foam stabilising effect. For full scale projects, there can be two solutions to the foaming problem:the first is to pre-aerate the CMC wastewater for a period of time and then skim the scum before aerobic biological treatment; the second is to filter the CMC wastewater before aerobic biological treatment.Seventhly, the dissertation discusses the building of a mathematical model which can model the treatment of CMC wastewater with activated sludge process within the framework of the Activated Sludge Model No.1(ASM1) developed by the International Water Association (IWA). ASM1is on the theoretical basis of the death-regeneration hypothesis, modelling8dynamic processes, involving13state variables, utilising5stoichiometric parameters and14kinetic parameters. After studying ASM1detailedly and analysing the water quality of CMC wastewater deliberately, the "CMC wastewater-ASM1", which simplifies the original ASM1from8dynamic processes to3, from13state variables to8, from5stoichiometric parameters to4, from14kinetic parameters to5, has been built. Among the model parameters,1toichiometric parameter and2kinetic parameters need measuring and calculating. After measurement and calculation, the heterotrophic yields YH, the heterotrophic maximum specific growth rates μM and the heterotrophic decay rates6H for CMC wastewater treatment at different ambient salinity within range from10000mg/L to80000mg/L have been acquired.更多还原