【作者】 胡保安；

【导师】 顾平；

【作者基本信息】 天津大学 ， 环境工程， 2008， 博士

【摘要】 随着水质标准的提高和膜法水处理成本的降低,混凝微滤工艺在处理微污染原水和低放废水领域越来越受到重视。混凝工艺能提高出水水质,同时其絮体在膜表面沉积也有效延缓了膜污染;微滤膜工艺则能有效的发挥过滤功能。在天津市某水厂建立了两套浸没式混凝微滤中试系统,即浸没式混凝膜过滤(SCMF)工艺和浸没式膜混凝反应器(SMCR)工艺,处理规模分别为150和300 m3/d,目的在于为建设混凝微滤工艺的自来水厂提供必要的基础参数和运行管理经验。与中国工程物理研究院合作开发了混凝微滤工艺处理低放废水的装置,在相关的设计中,对聚偏氟乙烯中空纤维微滤膜的耐辐射性能也进行了研究。SCMF工艺稳定运行时,膜通量为53.3 L/(h·m2),过滤时间为30 min,气水联合反洗为80 s。在稳定运行的154 d内,共进行了5次化学清洗。原水的水质状况显著影响膜污染的速率和出水的水质。低温低浊时期的原水水质较好,混凝剂FeCl3的投加量为6 mg/L;常温时期投加混凝剂聚合氯化铝10~20 mg/L,并增大了强化通量维护(EFM)的频率;夏季高温高藻期的原水水质较差,需要进一步采取预氯化和降低膜通量等措施来控制膜污染。SMCR工艺采取连续曝气,出水8 min停歇2 min的运行方式,气水比为15:1,排泥周期可由24小时延长为48小时,膜通量为16.7 L/(h·m2),FeCl3的投加量为3~4 mg/L。SMCR工艺在稳定运行的134 d内,从未进行化学清洗。在原水水质变差时同样需要采取加大混凝剂投剂量和增加预氯化等措施来控制膜污染和提高出水水质。混凝微滤工艺的出水水质稳定可靠,满足《生活饮用水卫生标准》(GB 5749-2006)。SCMF、SMCR工艺的平均出水浊度均为0.09 NTU,出水浊度≤0.1 NTU的部分所占比例分别为89.5%和92.0%,表明混凝微滤工艺对浊度有良好的去除效果。SCMF工艺的平均出水CODMn为2.03 mg/L,SMCR工艺为2.25 mg/L。出水细菌指标良好。SCMF工艺的产水率为90.9%,SMCR工艺的产水率可达98.8%。SCMF、SMCR工艺的电耗分别为0.20、0.42 kW·h/m3,考虑电费和药剂费用之和,SMCR工艺为0.247元/m3,高于SCMF工艺低温低浊时期的0.162元/m3,而低于其常温期0.264元/m3。混凝微滤工艺对微污染原水中可溶性有机物和消毒副产物前体物的去除研究发现,原水中的溶解性有机物以小分子为主,其中分子量介于3k-1k Da之间的有机物THMs的生成能力最强;膜分离出水中大分子有机物的含量具有较大幅度的降低,而小分子物质去除效果较差,甚至出现负增长的现象;比较不同有机物指标的去除效果,在各个分子量区间,UV254的去除率高于DOC;两套处理系统对THMFP的去除率在40%左右。采用粉末活性炭吸附工艺可以提高THMFP的去除效果,烧杯试验确定了吸附平衡时间为45 min;在相同投加吸附时间的情况下,发现PAC在投加量为20 mg/L时,去除率为57%。采用不同的剂量和剂量率对浸泡在pH=10的氢氧化钠溶液中的PVDF中空纤维微滤膜进行辐照。对辐照前后的样品作相关的性能测试,得到了膜耐辐射的剂量限值和辐射后的膜性能变化,辐射与PVDF膜的化学反应机理表明,膜表面生成-OH、-COOH和不饱和键,从而影响了通量、最大孔径、力学强度等指标,最后对装置的设计提出了工程化建议。更多还原

【Abstract】 With the stringent water quality standards and the decreased cost of membrane, the coagulation-microfiltration process was increasingly concerned in the field of micro-polluted water and low-level radioactive wastewater treatment. Coagulation process could improve the treated water quality, and it could effectively retard membrane fouling because of the floc deposition on the membrane surface.Microfitration process could effectively exert liquid-solid separation function. Two pilot-scale devices of coagulation-mircofiltration processes, which were submerged coagulation membrane filtration (SCMF) with a capacity of 150 m3/d and submerged membrane coagulation reactor (SMCR) with a capacity of 300 m3/d, were constructed in a water treatment plant in Tianjin. The aim was to offer the basic data and the operational experience for new water treatment plant. A study on the resistance to radiation of poly(vinylidene fluoride) (PVDF) hollow fiber membrane was carried out. The aim was to design a device to treat the low-level radioactive wastewater for China Academy of Engineering Physics.The SCMF process, with a flux of 53.3 L/(h·m2), was backwashed after every 30 minutes’filtration. The membrane was chemically cleaned five times during 154 days’steady operation. The membrane fouling rate and the quality of treated water were remarkedly influenced by the quality of the raw water, which was relatively well during low temperature and turbidity period. The dosage of FeCl3 was 6 mg/L in this period. The dosage of polyaluminium chloride was 10~20 mg/L during normal temperature period, and a higher frequency of EFM was needed. The quality of the raw water was worst during high temperature and alga bloom period, so that further measures such as prechlorination and reduction of the flux were required. The SMCR process was operated under continuous aeration, with a 2 minutes’interval after every 8 minutes’filtration. The ratio of air to water was 15:1, and the sludge discharging period was 24 h firstly, then 48 h finally. The membrane flux was 16.7 L/(h·m2) and the dosage of FeCl3 was 3~4 mg/L. The SMCR, whose fouling rate was much lower than that of SCMF, was never chemically cleaned during 134 days’steady operation. Higher coagulation dosage and prechlorination were also required to control the membrane fouling and improve treated water quality when the raw water quality was poor.The quality of the treated water by both coagulation-microfiltation processes met the Standards for Drinking Water Quality (GB 5749-2006). Results showed that the turbidity was removed almost completely in this process. The treated water from SCMF and SMCR had the same average turbidity of 0.09 NTU, with 89.5% and 92.0% of turbidity less than 0.1 NTU respectively. The average CODMn of the treated water from two systems was 2.03 mg/L and 2.25 mg/L respectively. The quality of the treated water from two systems was excellent in microorganic indexes. Compared with SMCR water productivity of 98.8%, SCMF was only 90.9%. The power consumption of SCMF and SMCR process was 0.20 kW·h/m3 and 0.42 kW·h/m3 respectively. But the reagent cost of SMCR process was less than that of SCMF. As the total cost of the power and reagent was concerned, SMCR process was 0.247 yuan/m3,higher than that of SCMF during low temperature period and lower than that of SCMF during normal temperature period.A study on the remove of soluble organic compound and THMFP with coagulation-microfiltration process was carried out. The results of ultrafiltration test showed that the organic matters with low MW were the major THMs precursors and the organic matters with MW between 3k-1k Da had the greatest THMFP in raw water. The organic matters with high MW were removed efficiently, and that with low MW even had minus-increase reversely. UV254 had a better removal than DOC in various MW fractions. THMFP removal efficiency of the two systems is nearly 40%. Powered actived carbon (PAC) absorption test was performed to remove THMFP. By the jar test, the contact time and dosage were 45 min and 20 mg/L respectively, and the remove rate of THMFP was 57%.The effect of low-level doses of gamma radiation on the properties of the PVDF hollow fiber membrane was studied. In the experiment, different radiation doses were chosen with the certain dose rate. The membranes dipped in the sodium hydroxide solution with pH of 10 were irradiated and some performance tests were carried out. The radiant chemic reaction mechanism showed that–OH, -COOH and unsaturated chemical bond were appeared on membrane functional surface, so the flux, the maximal pore size and the mechanical property were affected. Based on the results of the tests, suggestion for the engineering application was proposed.更多还原