自来水厂有机物去除规律的研究

某水厂通过混凝沉淀、臭氧氧化和生物降解去除有机物,对耗氧量的总去除率在50%～75%,其中混凝沉淀工艺为25%～50%,臭氧活性炭工艺为10%～30%。混凝沉淀去除了水中大部分分子量 10 kDa的有机物,臭氧活性炭工艺对分子量3 k Da的有机物的去除效果明显,能有效去除三卤甲烷前驱物。氯气消毒后产生三卤甲烷的有机物分子量大都小于1 k Da,但分子量在1～3 kDa之间的有机物具有最强的三卤甲烷生成能力。     

3级生物滤池挂膜启动分析

试验采用交替式进水的3级生物滤池处理校园生活污水,并分析讨论了3根滤柱的挂膜启动规律。在水温11.3～21.0℃条件下,3根滤柱均用接种挂膜法启动,分别历时23、20、23 d,3根滤柱出水的COD、BOD去除率稳定在80%左右,出水分别维持在95、29 mg/L以下。研究了NH4+-N的去除效果,一、三级滤柱为兼性厌氧滤柱,去除率范围为57%～67%;二级滤柱为好氧滤柱,去除率为71%～78%,此时3根滤柱挂膜启动成功。     

天津市纪庄子污水回用试验研究

为了研究城市污水回用技术,采用微絮凝和直接过滤新工艺对天津纪庄子污水处理厂的二级出水进行了深度处理的试验研究,处理水的COD、BOD、SS不仅去除率高,而且实际绝对值也低,尤其是出水浊度达到了饮用水的标准,磷也有一定的去除率。并发现滤柱中有生物絮凝和生物滤床作用,所以,直接过滤的COD去除率达77％。     

不同滤料对丹江口水库水的过滤效果研究

以丹江口水库中试基地的沉淀池出水作为试验用水,对比研究了细石英砂单层滤料、粗石英砂单层滤料、无烟煤单层滤料及无烟煤-石英砂双层滤料的过滤效果。结果表明,4组滤柱对浊度的去除效果相近,但无烟煤-石英砂双层滤柱受进水浊度变化的影响较小,抗冲击能力较强,出水浊度相对稳定;无烟煤-石英砂双层滤柱与无烟煤滤柱对有机物的去除效果优于细石英砂与粗石英砂滤柱,无烟煤-石英砂双层滤柱与无烟煤滤柱对CODMn的去除率分别为(31.45±10.39)%和(28.23±9.15)%,对UV254的去除率分别为(13.05±5.3)%和(14.23±4.97)%;细石英砂滤柱水位增长最快,且运行周期最短,无烟煤-石英砂双层滤柱与无烟煤滤柱水位增长相对较慢,运行周期是细石英砂与粗石英砂滤柱的2～3倍。     

生物预处理富营养化水源水的试验研究

采用生物陶粒滤柱作为预处理工艺,考察了其对滏阳河水的处理效果以及影响因素,并确定了运行参数。试验结果表明:生物滤柱对各种藻的去除效果不同,且去除率随滤速的上升而降低;有机物的去除率受滤速影响不大,但随着温度的上升而提高。生物预处理不但能够降低混凝剂的用量,而且使溶解氧增大,改善了水质。     

氯对活性炭吸附性能及孔隙结构的影响

通过中试研究了氯对活性炭滤料吸附性能和结构的影响。中试采用两根活性炭滤柱,其中1#活性炭滤柱进水不含氯,2#活性炭滤柱进水氯浓度为3 mg/L,连续运行21个月。试验末期,2#滤柱的碘值、亚甲基蓝值比1#滤柱的分别低40.7%、38.1%,比表面积和孔容积分别低34%和26%;2#滤柱对CODMn的平均去除率比1#滤柱低11%。可知,水中的氯会影响活性炭的吸附性能和结构,进而降低其对有机物的去除效率。     

串联微絮凝过滤工艺预处理低浊度海水研究

以三氯化铁和聚合氯化铝（PAC）作为絮凝剂，采用石英砂、沸石、锰砂和颗粒活性炭滤柱进行了单独及串联微絮凝过滤预处理低浊度海水的试验研究。结果表明，单独微絮凝过滤对浊度有较好的去除效果，其中锰砂的相对较差；颗粒活性炭滤柱对有机物的去除率较高，其余3种滤柱只能去除小部分的有机物；4种滤柱单独过滤的除盐能力均很弱。而串联过滤工艺明显提高了对有机物的去除率和除盐能力，几乎全部的浊度和绝大部分的有机物均能被有效去除。当采用三氯化铁作絮凝剂时，石英砂滤柱与颗粒活性炭滤柱串联的除盐效果最显著；而采用PAC作絮凝剂时，锰砂滤柱与颗粒活性炭滤柱串联的除盐能力最佳。     

生物陶粒柱深度处理水厂滤后水

采用生物陶粒柱（接种经筛选的工程菌）对水厂滤后水进行深度处理。结果表明,在水温为10～17℃、滤速为6 m/h、水力停留时间为40 min、气水比为1∶1的工况下,生物陶粒柱对滤后水中的CODMn、氨氮的去除率分别为30%和67.45%,优于水温为1～10℃、滤速为4 m/h、水力停留时间为30 min、气水比为1∶1工况下对两者的去除率（分别为10%和61.9%）;两种工况下的出水浊度均在0.3～0.4 NTU。     

铁碳内电解对生物反硝化脱氮的强化效能及机理

利用小试和中试研究了铁碳内电解工艺单元对深床滤柱生物反硝化作用的强化效能,在分析其作用机理的基础上,进行了长期的现场效能验证试验。结果表明,铁碳内电解可以有效强化深床滤柱利用二沉池出水中有机物进行生物反硝化的效能;铁碳内电解对水中有机物的分子质量、亲疏水性改变作用微弱,而其对有机物分子结构中部分基团的改变可能是导致其可利用性提升的重要原因。现场长期运行结果表明,组合工艺可显著提升二沉池出水水质,处理出水水质稳定达到一级A排放标准要求。     

珠江水中有机物分子量分布及其去除研究

采用超滤膜分级方法考察了常规混凝、高锰酸钾和粉末活性炭预处理等工艺对珠江水中各级分子量有机物的去除效果。结果表明,珠江水中有机物以分子量小于1kDa的小分子有机物为主,各级分子量有机物TOC和UV254具有良好的相关性。常规混凝工艺主要去除大分子有机物,且去除率随分子量的减小而降低。高锰酸钾预处理能够全面提高各级分子量有机物的去除效果;粉末活性炭主要吸附中小分子有机物,对各级分子量有机物的去除效果与常规混凝成互补。     

Characterization of natural organic matter adsorption in granular activated carbon adsorbers

The removal of natural organic matter (NOM) from lake water was studied in two pilot-scale adsorbers containing granular activated carbon (GAC) with different physical properties. To study the adsorption behavior of individual NOM fractions as a function of time and adsorber depth, NOM was fractionated by size exclusion chromatography (SEC) into biopolymers, humics, building blocks, and low molecular weight (LMW) organics, and NOM fractions were quantified by both ultraviolet and organic carbon detectors. High molecular weight biopolymers were not retained in the two adsorbers. In contrast, humic substances, building blocks and LMW organics were initially well and irreversibly removed, and their effluent concentrations increased gradually in the outlet of the adsorbers until a pseudo-steady state concentration was reached. Poor removal of biopolymers was likely a result of their comparatively large size that prevented access to the internal pore structure of the GACs. In both GAC adsorbers, adsorbability of the remaining NOM fractions, compared on the basis of partition coefficients, increased with decreasing molecular size, suggesting that increasingly larger portions of the internal GAC surface area could be accessed as the size of NOM decreased. Overall DOC uptake at pseudo-steady state differed between the two tested GACs (18.9 and 28.6 g-C/kg GAC), and the percent difference in DOC uptake closely matched the percent difference in the volume of pores with widths in the 1-50 nm range that was measured for the two fresh GACs. Despite the differences in NOM uptake capacity, individual NOM fractions were removed in similar proportions by the two GACs.     

Evaluation of biodegradability of NOM after ozonation

The major purpose of this study was to develop a simple procedure to describe the kinetics of biodegradation of natural organic matter (NOM) in drinking water and to use this procedure to evaluate changes in the concentration of biodegradable organic matter during ozonation and biotreatment. The proposed approach quantitatively describes the formation and removal of rapidly and slowly biodegradable fractions of NOM. This study showed that, depending on source water, ozonation of NOM may result in either minimal formation of biodegradable organic carbon (BDOC), or the formation of predominantly rapidly biodegradable NOM, or in the formation of both rapidly and slowly biodegradable NOM. The kinetic data obtained in this study suggest that while conventional biofiltration processes are capable of removing the rapidly biodegradable fraction, slowly biodegradable organic matter would remain in the filter effluent and may cause bacterial regrowth in the distribution system. An addition of a small amount of easily biodegradable carbon ("stimulated" biodegradation) to ozonated water appears to be effective for the removal of slowly biodegradable organic matter.     

Comparison of NOM removal and microbial properties in up-flow/down-flow BAC filter

The removal of natural organic matter (NOM) in term of COD_Mn by up-flow biologically activated carbon filter (UBACF) and down-flow biologically activated carbon filter (DBACF) was investigated in a pilot-scale test. The impacts of the molecular weight distribution of NOM on its degradation by the UBACF and DBACF were evaluated. The relationship between biodegradation and the microbial properties in the UBACF and DBACF were approached as well. The feed water of the UBACF and DBACF were pumped from the effluent of the rapid sand filtration (RSF) of Chengnan Drinking Water Treatment Plant (CDWTP), Huaian, Jiangsu Province, China. When the adsorption was the dominant mechanism of NOM removal at the initial stage of operation, the COD_Mn removal efficiency by the UBACF was lower than the DBACF. However, with the microbes gradually accumulated and biofilm formed, the removal of COD_Mn by the UBACF increased correspondingly to 25.3%, at the steady-state operation and was approximately 10% higher than that by the DBACF. Heterotrophy plate count (HPC) in the finished water of the UBACF was observed 30% higher than that of the DBACF. The UBACF effluent had higher concentration of detached bacteria whereas the DBACF harbored more attached biomass. The highest attached biomass concentration of the UBACF was found in the middle of the GAC bed. On the contrary, the highest attached biomass concentration of the DBACF was found on the top of the GAC bed. Furthermore, a total of 9479 reads by pyrosequencing was obtained from samples of the UBACF and DBACF effluents. The UBACF effluent had a more diverse microbial community and more even distribution of species than the DBACF effluent did. Alphaproteobacteria and Betaproteobacteria were the dominant groups in the finished water of the UBACF and DBACF. The higher organic matter removal by the UBACF was attributed to the presence of its higher biologically activity.     

Study of catalyzed ozonation for advanced treatment of pulp and paper mill effluents

Ozonation and catalytic ozonation (TOCCATA process) were used as tertiary treatments of wastewaters from three different pulp and paper mills. Laboratory batch experiments were conducted to assess the efficiency of each oxidation system for removal of organic matter. The investigations measured ozone consumption rate, variations in chemical oxygen demand (COD), total organic carbon (TOC), suspended solids (SS) and molecular weight distribution with contact time. For conventional ozonation, ozone consumption rate was dependent on the nature of the effluent. Organic matter elimination occurred both by oxidation and precipitation. Precipitation played a major role on TOC removal varying with the effluent, and was responsible for production of high final SS concentrations. However, the effluent type did not affect the ozone consumption rate for TOCCATA-catalyzed reactions. Using TOCCATA, it was shown that organic matter was removed through steady conversion of organic carbon to carbon dioxide. Finally the two oxidation systems were compared with respect to their impact on molecular weight distribution. A total removal of the two initial fractions of compounds (high and low molecular weights) was observed with two effluents. With the third effluent, only the initial fraction of low molecular weight compounds was removed by the two oxidizing systems. The results showed that ozonation and TOCCATA-catalyzed ozonation could achieve removals of COD of 36-76%. Depending on the effluent type, the amount of ozone consumed per gram of COD removed was lower for conventional or for catalytic ozonation.     

Long term case study of MIEX pre-treatment in drinking water; understanding NOM removal

Removal of natural organic matter (NOM) is a key requirement to improve drinking water quality. This study compared the removal of NOM with, and without, the patented magnetic ion exchange process for removal of dissolved organic carbon (MIEX DOC) as a pre-treatment to microfiltration or conventional coagulation treatment over a 2 year period. A range of techniques were used to characterise the NOM of the raw and treated waters. MIEX pre-treatment produced water with lower concentration of dissolved organic carbon (DOC) and lower specific UV absorbance (SUVA). The processes incorporating MIEX also produced more consistent water quality and were less affected by changes in the concentration and character of the raw water DOC. The very hydrophobic acid fraction (VHA) was the dominant NOM component in the raw water and was best removed by MIEX pre-treatment, regardless of the raw water VHA concentration. MIEX pre-treatment also produced water with lower weight average apparent molecular weight (AMW) and with the greatest reduction in complexity and range of NOM. A strong correlation was found between the VHA content and weight average AMW confirming that the VHA fraction was a major component of the NOM for both the raw water and treated waters.     

Natural organic matter (NOM) in a limed lake and its tributaries

The chemistry of a limed lake and its main tributaries were studied for 3 years (1992-94) with an emphasis on natural organic matter (NOM). Increased transparency and decreased water colour indicated a general reduction of NOM in the lake. Increased A(254 nm)/A(410 nm) ratios in the epilimnion during summer and early autumn suggested degradation of higher molecular size organic matter into low molecular size NOM. Increase in ammonium and dissolved inorganic carbon concentrations in the lake was possibly due to the NOM degradation. Using budget calculations and the literature values, photodegradation and microbial activity were estimated to be the main mechanisms of the NOM removal. These mechanisms accounted for about 30-35% and 60-65% of the total loss of organic matter, respectively, in the summer and early autumn period. Low sedimentation rates indicate that co-precipitation of organic matter with calcium, aluminium and/or iron was of minor importance in these seasons.     

Adsorption of natural organic matter oxidized with ClO2 on granular activated carbon

The paper describes the influence of the oxidation of natural organic matter (NOM) molecules with chlorine dioxide (ClO2) on granulated activated carbon (GAC) adsorption. In order to determinate the influence of ClO2 dosage on the NOM adsorption on GAC two parallel pilot scale experiments were performed. The raw water was treated respectively with 0.2 and 0.4 mg ClO2 L(-1) followed by the adsorption on GAC filters. Experiments were total organic carbon (TOC) measurements and size exclusion chromatography (SEC) controlled. The molecular weight distribution of NOM in the filtration bed outlet demonstrates that the low molecular weight molecules are less retained than the higher molecular weight components of NOM. It is shown that low molecular weight NOM causes less ClO2 demand. The oxidation of NOM molecules and very high capacity of GAC filter bed for NOM components can be used to control high ClO2 demand.     

Removal of natural organic matter and THM formation potential by ultra- and nanofiltration of surface water

Natural organic matter (NOM) and trihalomethane formation potential (THMFP) removal were evaluated by ultrafiltration (UF) and nanofiltration (NF). Ten different raw water sources in Alicante province (SE Spain) were analysed. Five types of membranes of different materials were tested with a dead-end-type stirred UF cell. Additional measurements, such as dissolved organic carbon, ultraviolet absorbance (254nm), THMFP, ion concentration, pH, conductivity, etc. were made on raw water, permeates and concentrates. The SUVA value was used to determine the hydrophobicity of the water analysed. The elimination of NOM and THMFP is correlated with the molecular weight (MW) of NOM determined by size exclusion chromatography (SEC). The flux decline trends were correlated with cation concentration. NOM removal by UF is low, which correlates with the average MW determined by SEC with an average value of 922g/mol (between 833 and 1031g/mol). However, the NOM removal obtained with the NF90 and NF270 NF membranes for all water sources is almost complete (90%). THMFP removal is related to hydrophobicity and permeability of membrane. The NFT50 membrane removes almost 100% of the THMFP of more hydrophobic waters.     

Pore blockage effect of NOM on atrazine adsorption kinetics of PAC: the roles of PAC pore size distribution and NOM molecular weight

Natural organic matter (NOM) in natural water has been found to have negative effects on the adsorption of various trace organic compounds by activated carbon through two major mechanisms: direct competition for sites and pore blockage. In this study, the pore blockage effect of NOM on atrazine adsorption kinetics was investigated. Two types of powdered activated carbon (PAC) and three natural waters were tested to determine the roles of PAC pore size distribution and NOM molecular weight distribution in the pore blockage mechanism. When PAC was preloaded with natural water, the pore blockage effect of the NOM was found to cause a reduction of up to more than two orders of magnitude in the surface diffusion rate of atrazine compared to simultaneous adsorption of atrazine and NOM with fresh PAC. The surface diffusion coefficient of atrazine for preloaded PAC decreased with a decrease in PAC dose or an increase in NOM surface concentration. Because of the pore blockage effect of NOM, a 30% drop in atrazine removal was observed in a continuous flow PAC/microfiltration (MF) system after 7 days of contact compared to the removal predicted from the batch isotherm test. Large micropores and mesopores were found to play an important role in alleviating the effect of pore blockage. A PAC with a relatively large fraction of large micropore and mesopores was shown to suffer much less from the pore blockage effect compared with a PAC that had a much smaller fraction of large pores. Natural waters with different NOM molecular weight distribution caused different extent of pore blockage. The NOM molecules with molecular weight between 200 and 700 Dalton appeared to be responsible for the pore blockage effect.     

Degradation of natural organic matter by TiO2 photocatalytic oxidation and its effect on fouling of low-pressure membranes

Natural organic matter (NOM) fouling continues to be the major barrier to efficient application of microfiltration (MF) and ultrafiltration (UF) in drinking water treatment. In this study, the potential of TiO2/UV photocatalytic oxidation to control fouling of membranes by NOM was evaluated. Decomposition kinetics of NOM was investigated using a commercial TiO2 catalyst, and the effect of various experimental parameters including TiO2 dosage and initial total organic carbon (TOC) concentration were also determined. The reaction kinetics was found to increase with increasing TiO2 dosage, but decrease with increasing initial TOC concentration. Even though the rate of TOC removal was relatively low, the TiO2/UV process was very effective in controlling membrane fouling by NOM. At a TiO2 concentration of 0.5 g/L, fouling of both an MF and a UF membrane was completely eliminated after 20 min of treatment. Careful analyses of specific UV absorbance (SUVA) and molecular weight (MW) distribution of NOM revealed that the effectiveness in membrane fouling control is the result of the changes in NOM molecular characteristics, namely MW and SUVA due to the preferential removal and transformation of large, hydrophobic NOM compounds. Results from this study show that TiO2/UV photocatalytic oxidation is a promising pretreatment method for MF and UF systems.