Water Quality Improvement by Combined UF,RO, and Ozone/Hydrogen Peroxide System (HiPOx) in the Water Reclamation Process

Conventional water reclamation processes, such as membrane bioreactors, are not always effective in removal of pharmaceuticals and personal care products (PPCPs), endocrine disrupting chemicals (EDCs) and/or N-nitrosodimethylamine (NDMA), even with the reverse osmosis (RO) membrane process. A study was conducted, at a NEWater factory in Singapore, to compare a conventional ultrafiltration (UF) membrane /RO treatment process with a treatment train having the HiPOx unit, an advanced oxidation process (AOP), which was installed between the UF and the RO unit operations. By incorporating the HiPOx into the UF/RO treatment process, following results were observed; 1) increased removal of PPCPs, EDCs and NDMA, 2) improvement in ultraviolet transmission (UVT) of the RO permeate, 3) enhanced removal of TOC and color, and increased UVT of the RO brine, 4) suppression of the increase in the RO transmembrane pressure by organic fouling.     

体外模拟亚硝化体系中优选阻断NDMA生成的香辛料精油复合抑制剂

为了有效抑制N-二甲基亚硝胺(N-nitrosodimethylamine,NDMA)的形成,在体外模拟亚硝化反应体系中,先通过单因素实验研究市售常见的9种香辛料精油对NDMA的抑制作用,再利用二次回归正交组合试验设计,筛选最佳精油复合抑制剂配比.结果 表明,9种香辛料精油对NDMA的形成均有抑制作用,二次回归正交组合...     

气相色谱—热能分析法测定啤酒中N—亚硝基二甲胺

本文采用硅藻土柱层析分离、气相色谱——热能分析法测定啤酒中N—亚硝基二甲胺的含量,并对方法的灵敏度、准确度及各种影响因素进行探讨。用于样品测定取得较为满意的结果。     

壳聚糖及其衍生物对亚硝化反应的抑制作用

为了解壳聚糖及其衍生物对亚硝化反应的抑制作用,在体外模拟人胃液的条件下,用比色法及紫外光解法测定了壳聚糖及其衍生物对亚硝胺合成的阻断作用和对亚硝酸钠的清除作用。结果表明,壳聚糖及其衍生物对亚硝化反应均具有较强的抑制作用,对亚硝胺的阻断率达 52. 41% ~73 .20%,对亚硝酸钠的清除率达 50 .57%~73 .31%;在被测物中,脱乙酰度为 90%的壳聚糖在加入量为 6g/L时,对亚硝化反应的抑制作用最强。     

UV/H_2O_2降解水中痕量NDMA的效能研究

采用UV/H2O2降解水中的痕量NDMA,考察了水中NDMA初始浓度、H2O2投量、pH、天然有机物及常见阴离子等因素的影响,并分析了NDMA的降解产物。结果表明,在UV辐照度为1 000μW/cm2、NDMA初始浓度为0.1 mmol/L、H2O2投量为20 mg/L、pH值为4的条件下,UV/H2O2对NDMA的降解效果较好(反应5 min后对NDMA的去除率接近100%);水中的天然有机物和Cl-、SO42-、NO3-、HCO3-等阴离子对NDMA的降解均有抑制作用,腐殖酸浓度越大其抑制作用越强,阴离子的抑制作用由大到小依次为HCO3-、NO3-、SO24-、Cl-;NDMA的主要降解产物为二甲胺和硝酸盐,此外还有少量亚硝酸盐、甲酸盐和甲胺生成。     

Occurrence and removal of N-nitrosamines in wastewater treatment plants

The presence of nitrosamines in wastewater might pose a risk to water resources even in countries where chlorination or chloramination are hardly used for water disinfection. We studied the variation of concentrations and removal efficiencies of eight N-nitrosamines among 21 full-scale sewage treatment plants (STPs) in Switzerland and temporal variations at one of these plants. N-nitrosodimethylamine (NDMA) was the predominant compound in STP primary effluents with median concentrations in the range of 5-20 ng/L, but peak concentrations up to 1 μg/L. N-nitrosomorpholine (NMOR) was abundant in all plants at concentrations of 5-30 ng/L, other nitrosamines occurred at a lower number of plants at similar levels. From concentrations in urine samples and domestic wastewater we estimated that human excretion accounted for levels of <5 ng/L of NDMA and <1 ng/L of the other nitrosamines in municipal wastewater, additional domestic sources for <5 ng/L of NMOR. Levels above this domestic background are probably caused by industrial or commercial discharges, which results in highly variable concentrations in sewage. Aqueous removal efficiencies in activated sludge treatment were in general above 40% for NMOR and above 60% for the other nitrosamines, but could be lower if concentrations were below 8-15 ng/L in primary effluent. We hypothesize that substrate competition in the cometabolic degradation explains the occurrence of such threshold concentrations. An additional sand filtration step resulted in a further removal of nitrosamines from secondary effluents even at low concentrations. Concentrations released to surface waters were largely below 10 ng/L, suggesting a low impact on Swiss water resources and drinking water generation considering the generally high environmental dilution and possible degradation. However, local impacts in case a larger fraction of wastewater is present cannot be ruled out.     

Chloramination of nitrogenous contaminants (pharmaceuticals and pesticides): NDMA and halogenated DBPs formation

Disinfection with chloramines is often used to reduce the production of regulated disinfection by-products (DBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs). However, chloramination can lead to the formation of N-nitrosamines, including N-nitrosodimethylamine (NDMA), a probable human carcinogen. Previous research used dimethylamine (DMA) as a model precursor of NDMA, but certain widely used tertiary dimethylamines (e.g. the pharmaceutical ranitidine) show much higher conversion rates to NDMA than DMA. This study investigates the NDMA formation potential of several tertiary amines including pharmaceuticals and herbicides. The reactivity of these molecules with monochloramine (NH₂Cl) is studied through the formation of NDMA, and other halogenated DBPs such as haloacetonitriles (HANs) and AOX (Adsorbable Organic Halides). Several compounds investigated formed NDMA in greater amounts than DMA, revealing the importance of structural characteristics of tertiary amines for NDMA formation. Among these compounds, the pharmaceutical ranitidine showed the highest molar conversion to NDMA. The pH and dissolved oxygen content of the solution were found to play a major role for the formation of NDMA from ranitidine. NDMA was formed in higher amounts at pH around pH 8 and a lower concentration of dissolved oxygen dramatically decreased NDMA yields. These findings seem to indicate that dichloramine (NHCl₂) is not the major oxidant involved in the formation of NDMA from ranitidine, results in contradiction with the reaction mechanisms proposed in the literature. Dissolved oxygen was also found to influence the formation of other oxygen-containing DBPs (i.e. trichloronitromethane and haloketones). The results of this study identify several anthropogenic precursors of NDMA, indicating that chloramination of waters impacted by these tertiary amines could lead to the formation of significant amounts of NDMA and other non-regulated DBPs of potential health concern (e.g. dichloroacetonitrile or trichloronitromethane). This could be of particular importance for the chloramination of wastewater effluents, especially during water reuse processes.