【作者】 魏亮亮；

【导师】 赵庆良；

【作者基本信息】 哈尔滨工业大学 ， 环境科学与工程， 2011， 博士

【摘要】 将城市污水处理厂(WWTP)二级出水经土壤含水层处理(SAT)后回用对于解决当前我国水资源短缺意义显著。由于溶解性有机物(DOM)是再生水加氯消毒过程中三氯甲烷(THMs)等消毒副产物的前体物质,受到环境学者越来越多的关注。本研究首先采用XAD树脂分级技术将DOM分为疏水性有机酸(HPO-A)、过渡亲水性有机酸(TPI-A)、疏水性中性有机物(HPO-N)、过渡亲水性中性有机物(TPI-N)和亲水性有机物(HPI),并借助加氯消毒实验、红外光谱、三维荧光光谱等多种实验手段分别考察了WWTP各构筑物在冬夏两季运行过程中对生活污水中DOM的去除特点,二级出水DOM在后续SAT处理过程中的去除机制;在此基础上,为了强化传统SAT的去处效果,进而研究了粉煤灰及炉渣改良SAT系统对二级出水中DOM的去除机理;最后本文对粉煤灰及炉渣对DOM的吸附机制及吸附特性进行了系统研究。HPI为生活污水DOM最主要的组分(夏季占原生活污水总有机物的60.5%,而冬季为57.4%),其次为HPO-A组分(夏季为20.3%,冬季为23.2%),而HPO-N、TPI-A及TPI-N组分的含量相对较低。通过WWTP的运行,生活污水中89.7%的溶解性有机碳(DOC)、52.6%的UV-254及86.4%的THMs前体物质在夏季运行过程中被有效去除,在冬季运行过程中,生活污水中DOC和THMs前体物质在污水处理厂运行过程中的去除率分别下降至88.2%和85.5%。WWTP中初次沉淀池(PST)构筑物对生活污水DOM中疏水性组分中芳香性物质及THMs前体物质去除有效(特别在冬季低温条件下)。A/O构筑物能够有效去除生活污水中含量最高、分子量最小的HPI组分,尤其在夏季运行条件下。与此同时,PST构筑物对酸性组分和疏水性组分中THMs前体物(C=C和C=O相关)的去除上意义显著。HPI和HPO-A为二级出水DOM中最主要组分(分别占总DOC含量的45.5%和30.0%),其中HPO-A为二级出水DOM中最主要的芳香性物质(占总UV-254的50.0%)和三氯甲烷(THMs)前体物质(占总THMFP的45.4%)。二级出水DOM经SAT系统运行后去除了65.1%,其中HPI能够在SAT系统中优先去除(去除率76.6%),HPO-A和HPO-N的去除率亦相对较高。但SAT系统对二级出水中芳香性物质和THMs前体物质的去除率分别为45.7%和45.2%,相对较低。SAT中的吸附作用对二级出水中HPO-A、HPO-N及TPI-A的去除效果较好,而生物作用对TPI-N和HPI组分优先降解。SAT系统中土壤吸附作用较生物降解作用对DOM的去除贡献率较低,可通过在SAT处理前进行GAC强化吸附来达到对二级出水THMs和芳香性物质的高效去除。通过在SAT系统中添加粉煤灰(FA)及炉渣可大幅提升SAT系统对二级处理出水中DOM的吸附去除效果,但须降低FA/炉渣的加入对SAT中生物降解作用的不利影响。二级出水DOM中芳香性有机化合物及THMs前体物质在FA及炉渣改良SAT系统中去除率大幅提升。由于FA及炉渣的添加增强系统吸附性的同时降低了土壤中生物活性,故有必要在SAT系统表层(表层25 cm)保留土壤层。总体上,HPI易于被土壤微生物降解,而HPO-A更易于被FA/炉渣吸附去除。炉渣在SAT系统中的添加较FA的添加对二级出水中DOM的去除效率较高。在15 g/L的粉煤灰投加量、303K和3 h接触时间的情况下,粉煤灰对二级处理出水中DOC、UV-254及THMs前体物质的去除率分别为22.5%、23.7%和25.9%。FA对DOM各组分的吸附均符合准二级吸附动力学模型,其中粉煤灰对DOM中HPI组分的吸附亦符合内扩散模型。从FA对DOM各组分的最大吸附量(Q0)和吸附过程吉布斯自由能的变化(ΔG0)可得出FA对HPI组分的吸附最强,但对DOM中酸性组分的吸附能力较弱。相较于Freundlich吸附方程,FA对DOM酸性组分的吸附更符合Langmuir模型,但对HPI的吸附模拟方面,Freundlich模型要优于Langmuir模型。炉渣较粉煤吸附需要较长的吸附平衡时间(12 h),且其吸附受到炉渣粒径的影响,粒径大于250目的炉渣在15 g/L的投加量、303K和12 h条件下,可去除二级出水中28.6%的DOM。此外,酸性条件有利于炉渣对DOM的高效吸附。炉渣对二级出水DOM各组分的吸附均符合准二级吸附方程和Freundlich吸附等温式,且其对HPO-A组分优先吸附,且吸附能力较强。粉煤灰/炉渣改良SAT可用于实际SAT系统对二级出水的处理厂,在粉煤灰(炉渣)和土壤混合比为1:1,混合层高度为1 m,覆土厚度为0.25 m的情况下运行并对二级出水进行处理,粉煤灰(炉渣)的吸附饱和时间分别为602天(1541天)。更多还原

【Abstract】 Soil aquifer treatment (SAT) with the secondary effluent of wastewater treatment plant (WWTP) is an increasingly valued practice to renovate domestic effluents for potable and non-potable purpose in those arid and semi-arid regions. Dissolved organic matter (DOM) is a major water quality issue associated with SAT systems, which is present in the recovered water and can be converted to carcinogenic disinfection by-products. DOM was fractionated by XAD-8/XAD-4 resins into five different fractions: hydrophobic acid (HPO-A), transphilic acid (TPI-A), hydrophobic neutral (HPO-N), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). Removal trend of the DOM in raw wastewater (RW) during the different units of WWTP were investigated firstly. Then the reduction mechanisms of the DOM during the SAT operation were explored via the comparison of the different advanced treatments. Finally, fly ash (FA) and coal slag were used as low-cost adsorbents for further removal of the DOM in secondary effluent.XAD fractionation results demonstrated that majority DOM of the RW was contributed by HPI (60.5% in summer and 57.4% in winter), followed by HPO-A, the remainder fractions were averaged 12.1%, 5.1% and 1.9% for HPO-N, TPI-A and TPI-N, respectively. 89.7% of the bulk dissolved organic carbon (DOC), 52.6% of UV-254, as well as 86.4% of trihalomethanes (THMs) precursors were efficiently removed by WWTP in summer, while the removal efficiency of DOC and THMFP decreased to 88.2% and 85.5% in winter. Removal of HPI related organics were effective by the facilities of A/O tanks, particularly in summer. On the other hand, PST played a key role in removing the THMs precursors in acidic and hydrophobic fractions (C=C and C=O related), especially in winter.Both HPI and HPO-A were the major components in the secondary effluent (accounting for 45.5% and 30.0% of the bulk organics), and that of the HPO-N, TPI-A and TPI-N were quite low. HPO-A was the predominant THMs precursors and aromatic components in secondary effluent, accounting for 50.0% of the bulk UV-254 and 45.4% of the THMFP, respectively. The DOC of the secondary effluent decreased 65.1% after SAT operation, in which HPI was preferentially removed when the SAT operation progressed (with a removal efficiency of 76.6%). Moreover, fractions of HPO-A and HPO-N were also efficiently removed. The adsorption mechanisms of the SAT system tended to adsorb more HPO-A, HPO-N and TPI-A and could reduce the aromaticity of those DOM fractions efficiently. On the other hand, the biodegradation mechanism would remove more HPI and TPI-N and lead an increased aromaticity. The most important removal process responsible for DOM in SAT was biodegradation instead of adsorption. Thus, the combination of the biodegradation (for TPI-N and HPI removal) and adsorption (for HPO-A, HPO-N and TPI-A removal) is essential DOM removal during the practicial recharging of the secondary effluent, which could be proven by the operation of GAC+SAT.In order to enhance the removal of DOM in secondary effluent during the SAT operation, fly ash (FA) and coal slag were used as supplementary materials to improve the adsorption mechanism of the SAT system. FA and coal slag additive in SAT system would efficiently enhance the bulk removal of the DOC, UV-254 and THMs precursors in secondary effluent, ascribing to their high surface-area. Experimental results indicated that FA and coal slag additive within the SAT columns would enhance the bulk adsorption of the hydrophobic fractions, while the removal of HPI were mainly accomplished by the biodegradation within the soli. Since the additive of FA and coal slag would negatively affect the biodegradation of the soil biomass (especially for the FA modified SAT), thus, the combination of an upper 0.25 m soil layer and a mixture of FA/coal slag and soil underneath is essential. In overall, the additive of coal slag showed a high removal of DOM in comparison with that of FA additive.Experimental results revealed that 22.5% of dissolved organic carbon (DOC), 23.7% of UV-254, 25.9% of trihalomethanes (THMs) precursors in secondary effluent were efficiently adsorbed by FA at the optimum conditions (15 g/L FA dosage, 303 K and 180 min contact time). Kinetic studies indicated that the adsorption of each DOM fractions by FA fitted the pseudo-second-order kinetic model quite well; moreover, the adsorption of hydrophilic fraction (HPI) also followed the intraparticle diffusion model. The maximum adsorption capacities (Q0) and the Gibbs free energy (ΔG0) value obtained from the adsorptions showed that FA was more efficient in adsorbing the fraction of HPI, while less effective in removing the acidic fractions. In addition, Langmuir model yielded a much better fit than Freundlich model in simulating the adsorption of the acidic DOM fractions, while contrary for the adsorption of hydrophilic fraction. The adsorption of coal slag needs a longer time to reach equilibrium (12 h), and the adsorption was affected by the particle sizes of the coal slag. At the condition of 15 g/L dosage, 303 K and 12 h contact time, the coal slag with a particle size of >250 mech would lead to a 28.6% removal of the DOM in secondary effluent. More organics would be removed at the acidic condition during the coal slag adsorption. In addition, the Freundlich model could well simulate the coal slag adsorption of all DOM fractions in comparison with that of Langmuir isotherm.For a purpose of the practical designing of the FA/coal slag modifie SAT, the adsorption saturation period of the FA/coal slag additive SAT were practically evaluated. At the additive ratio of FA/coal slag and soil was 1:1, the thickness of the mixture layer was 1 m, and the top soil layer was 0.25 m, the adsorption saturation period of the FA additive SAT was 602 d, while 1541 d for coal slag additive SAT.更多还原