Effects of humic acid on residual Al control in drinking water treatment plants with orthophosphate addition

This study aimed to investigate the effects of humic acid (HA) on residual Al control in drinking water facilities that used orthophosphate addition. The results showed that adding orthophosphate was an effective method for residual Al control for the raw water without HA. When orthophosphate was added at 1.0 min before the addition of poly aluminum chloride (PACl), the concentrations of soluble aluminum (Sol-Al) and total aluminum (Tot-Al) residue were 0.08 and 0.086 mg·L^-1, respectively; both were reduced by 46% compared with the control experiment. The presence of HA would notably increase the residual Al concentration. For the raw water with 5 mg·L^-1 of HA, the concentrations of Sol-Al and Tot-Al increased from 0.136 and 0.174 mg·L^-1 to 0.172 and 0.272 mg·L^-1, respectively. For water with a HA concentration above 5 mg·L^-1, orthophosphate was ineffective in the control of residual Al, though there were still parts of orthophosphate were removed in coagulation. The amounts of Al removal were positively correlated with the solids freshly formed in coagulation. Similar to the raw water without HA, the best Al control was obtained with orthophosphate salt added at 1.0 min before PACl. HA concentrations in the raw water, solution pH, and the orthophosphate dosage suitable for residual Al control by orthophosphate precipitation were also investigated.     

Life cycle assessment and environmental improvement of residential and drinking water supply systems in Hanoi,Vietnam

In many Asian cities the public water supply is characterised by low pressure, frequent interruptions and occasional contamination. Hence, private households have to store water and increase pressure individually to ensure an uninterrupted supply at sufficient pressure and water for drinking has to be boiled or supplied separately in bottles. In this study the present water supply system in Hanoi and a number of modification options were analysed from an environmental point of view through life cycle assessment (LCA) in order to identify the most sustainable solutions for future water supply. It was found that the boiling of water for drinking was the largest source of impacts in the present system. Impacts could be reduced significantly if the public supply network was improved and private pumping and storage could be avoided and if the water could be used directly for drinking. It was also found that impacts could be reduced if consumers used bottled water for drinking instead of boiling tap water. Finally, it was demonstrated that even if drinking water cannot be supplied directly through the public network, a reliable public water supply at high pressure is environmentally advantageous. Sensitivity analyses revealed that the conclusions of this study are likely to be applicable to other cities with similar water supply systems.     

碟形沼泽湿地水中氮的动态变化及影响因素分析

通过对三江平原碟形湿地不同植被类型沼泽水体中氮含量的研究表明,漂筏苔草、毛果苔草和乌拉苔草沼泽水体中各形态氮含量具有明显的季节变化特征.总氮(TN)含量在5-10月份的植物生长季节表现为先增加后降低的趋势,不同植被类型沼泽水体TN含量明显不同.NH4+-N是无机氮的主要存在形态,含量比例在44.81%～98.89%之间.在整个生长季,乌拉苔草沼泽水NH4+-N含量呈先增加后降低的趋势,毛果苔草沼泽水NH4+-N含量在8月份具有峰值,漂筏苔草沼泽水NH4+-N含量较低,波动不大.硝态氮(NO3--N)在生长季中期含量较低,而亚硝态氮(NO2--N)含量较高;生长季末期NO3--N含量增高,而NO2--N含量降低.沼泽水体中不同形态氮浓度与植被类型、植被生长阶段密切相关,并且受到水温、降雨、蒸发、农田排水等因素的影响.     

A red water occurrence in drinking water distribution systems caused by changes in water source in Beijing,China: mechanism analysis and control measures

A red water phenomenon occurred in several communities few days after the change of water source in Beijing, China in 2008. In this study, the origin of this problem, the mechanism of iron release and various control measures were investigated. The results indicated that a significant increase in sulphate concentration as a result of the new water source was the cause of the red water phenomenon. The mechanism of iron release was found that the high-concentration sulphate in the new water source disrupted the stable shell of scale on the inner pipe and led to the release of iron compounds. Experiments showed that the iron release rate in the new source water within pipe section was over 11-fold higher than that occurring within the local source water. The recovery of tap water quality lasted several months despite ameliora- tive measures being implemented, including adding phosphate, reducing the overall proportion of the new water source, elevating the pH and alkalinity, and utilizing free chlorine as a disinfectant instead of chloramine. Adding phosphate was more effective and more practical than the other measures. The iron release rate was decreased after the addition of 1.5 mg. L-1 orthophosphate- P, tripolyphosphate-P and hexametaphosphate-P by 68%, 83% and 87%, respectively. Elevating the pH and alkalinity also reduced the iron release rate by 50%. However, the iron release rate did not decreased after replacing chloramine by 0.5-0.8 mg. L-1 of free chlorine as disinfectant.     

Impact of total organic carbon and chlorine to ammonia ratio on nitrification in a bench-scale drinking water distribution system

Nitrification occurs in chloraminated drinking water systems and is affected by water quality parameters. The aim of this study was to investigate the impact of total organic carbon and chlorine to ammonia ratio on nitrification potential in a simulated drinking water distribution system as during chloramination. The occurrence of nitrification and activity of nitrifying bacteria was primarily monitored using four rotating annular bioreactors (RAB) with different chlorine to ammonia ratios and total organic carbon (TOC) levels. The results indicated that nitrification occurred despite at a low influent concentration of ammonia, and a high concentration of nitrite nitrogen was detected in the effluent. The study illustrated that reactors 1(R1) and 3 (R3), with higher TOC levels, produced more nitrite nitrogen, which was consistent with the ammonia-oxidizing bacteria (AOB) counts, and was linked to a relatively more rapid decay of chloramines in comparison to their counterparts (R2 and R4). The AOB and HPC counts were correlated during the biofilm formation with the establishment of nitrification. Biofilm AOB abundance was also higher in the high TOC reactors compared with the low TOC reactors. The chlorine to ammonia ratio did not have a significant impact on the occurrence of nitrification. Bulk water with a high TOC level supported the occurrence of nitrification, and AOB development occurred at all examined chlorine to ammonia dose ratios (3:1 or 5:1).     

Presence,dissemination and removal of antibiotic resistant bacteria and antibiotic resistance genes in urban drinking water system: A review

Reviewed the change of ARGs and ARB in full-scale urban drinking water systems. Conventional processes are more promising than BAC process in ARGs removal. Mechanisms of ARGs enrichment and spread in BAC filter and DWDSs are discussed. Raise the need of future research on ARGs and ARB change in building plumbing systems. Antibiotic resistance in aquatic environment has become an important pollution problem worldwide. In recent years, much attention was paid to antibiotic resistance in urban drinking water systems due to its close relationship with the biosafety of drinking water. This review was focused on the mechanisms of antibiotic resistance, as well as the presence, dissemination and removal of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in the urban drinking water system. First, the presence of ARB and ARGs in the drinking water source was discussed. The variation of concentration of ARGs and ARB during coagulation, sedimentation and filtration process were provided subsequently, in which filtration was proved to be a promising technology to remove ARGs. However, biological activated carbon (BAC) process and drinking water distribution systems (DWDSs) could be incubators which promote the antibiotic resistance, due to the enrichment of ARGs and ARB in the biofilms attached to the active carbon and pipe wall. Besides, as for disinfection process, mechanisms of the inactivation of ARB and the promotion of conjugative transfer of ARGs under chlorine, ozone and UV disinfection were described in detail. Here we provide some theoretical support for future researches which aim at antibiotic resistance controlling in drinking water.     

Effect of the ultraviolet/chlorine process on microbial community structure,typical pathogens,and antibiotic resistance genes in reclaimed water

• UV/chlorine can effectively remove VBNC pathogens, ARGs and MGEs in reclaimed water. • Microbial community was changed with reduced diversity during UV/chlorine process. • CRBs-carried MGEswere the predominant groups during UV/chlorine process. • No direct co-selection strategy was shared between UV/chlorine and resistome. Urban wastewater contains a wide range of pathogens and antibiotic resistance genes (ARGs), which are a serious concern if reusing treated wastewater. However, few studies have explored the microbial communities in reclaimed water using ultraviolet (UV)/chlorine treatment and assessed the changes of the resistome. This study investigated the occurrence of typical pathogens, ARGs, and bacterial communities in UV/chlorine-treated reclaimed water samples. The numbers of culturable and viable but non-culturable pathogens were effectively reduced to 0 CFU/mL within 1–10 and 10–30 min after UV/chlorine treatment, respectively. Meanwhile, the physicochemical indices of water quality were not affected. UV/chlorine treatment could significantly change the bacterial community structure of reclaimed water, showing a decrease in bacterial abundance and diversity. Chlorine-resistant Acinetobacter and Mycobacterium were the dominant bacterial genera (>50%) after UV/chlorine treatment. Moreover, the number of ARGs and mobile genetic elements (MGEs) decreased with an increase in UV/chlorine exposure. However, eight ARGs and three MGEs were consistently detected in more than three seasons, making these major concerns because of their potential role in the persistence and dissemination of antibiotic resistance. Overall, the results of this study suggest that UV/chlorine treatment can potentially improve the microbiological safety of reclaimed water. And more attention should be paid to the pathogens that are both chlorine-resistant and carry MGEs because of their potential for resistance transmission.     

南京东郊蔬菜种植基地地表水氮、磷、重金属含量及影响因素

南京东郊典型蔬菜基地地表水环境质量的调查分析表明:(1)在当前的生产和生活条件下,地表水尚未受Pb、Cu、Zn、Cd和Cr污染,但有不同程度的氮、磷污染。(2)河流氮、磷污染比池塘严重。河流水中氨氮和水溶性磷的比例相对较高,而池塘水中硝态氮、有机氮和有机磷的比例相对较高,这种差别有助于识别地表水中氮、磷的来源。河流底泥中总氮、总磷和重金属含量(Cr除外)比塘泥高,表明河水氮、磷及重金属污染风险比池塘水高。(3)南京东郊蔬菜基地地表水中氮、磷及重金属主要来自城市生活污水的排放,其次来自蔬菜栽培中有机肥过量投入造成的流失。因此,保护城郊地表水应从城市生活污水净化和蔬菜栽培中有机肥的合理施用入手。     

贵州草海湿地农田渠系水质空间分异特征及影响分析

为了解草海湿地农田渠系水质现状、空间分异特征及影响因素,于2011年秋季对草海湿地进行大空间尺度的采样,分析了氮磷等理化指标,采用单因子污染指数法和营养状态指数法分别对农田渠系水质和湖泊营养状态进行评价.结果表明,草海湿地农田渠系水质污染严重,多数水质为V类或劣V类,总氮和溶解氧是水体中的主要污染因子;上游水质劣于下游,尤其是上游靠近县城区域的水质最差;多等级排水渠系对氮磷具有一定的截留作用,干渠V级水质好于低级渠系水质;不同的土地利用方式对水质的影响不同,城镇用地>集中式村落>农田;草海湿地水体上、中、下游营养水平分别为中度富营养、轻度富营养和中营养,外源污染物的累积和湖泊营养水平的提高导致其沼泽化,而流域不合理的土地利用结构加剧了沼泽化的进程.