Effect of algal flocculation on dissolved organic matters using cationic starch modified soils

Modified soils(MSs) are being increasingly used as geo-engineering materials for the sedimentation removal of cyanobacterial blooms. Cationic starch(CS) has been tested as an effective soil modifier, but little is known about its potential impacts on the treated water.This study investigated dissolved organic matters in the bloom water after algal removal using cationic starch modified soils(CS-MSs). Results showed that the dissolved organic carbon(DOC) could be decreased by CS-MS flocculation and the use of higher charge density CS yielded a greater DOC reduction. When CS with the charge density of 0.052, 0.102 and0.293 meq/g were used, DOC was decreased from 3.4 to 3.0, 2.3 and 1.7 mg/L, respectively.The excitation–emission matrix fluorescence spectroscopy and UV254 analysis indicated that CS-MS exhibits an ability to remove some soluble organics, which contributed to the DOC reduction. However, the use of low charge density CS posed a potential risk of DOC increase due to the high CS loading for effective algal removal. When CS with the charge density of 0.044 meq/g was used, DOC was increased from 3.4 to 3.9 mg/L. This study suggested, when CS-MS is used for cyanobacterial bloom removal, the content of dissolved organic matters in the treated water can be controlled by optimizing the charge density of CS. For the settled organic matters, other measures(e.g., capping treatments using oxygen loaded materials) should be jointly applied after algal flocculation.     

Modeling level-of-safety for bus stops in China

Objective: Safety performance at bus stops is generally evaluated by using historical traffic crash data or traffic conflict data. However, in China, it is quite difficult to obtain such data mainly due to the lack of traffic data management and organizational issues. In light of this, the primary objective of this study is to develop a quantitative approach to evaluate bus stop safety performance.

Methods: The concept of level-of-safety for bus stops is introduced and corresponding models are proposed to quantify safety levels, which consider conflict points, traffic factors, geometric characteristics, traffic signs and markings, pavement conditions, and lighting conditions. Principal component analysis and k-means clustering methods were used to model and quantify safety levels for bus stops.

Results: A case study was conducted to show the applicability of the proposed model with data collected from 46 samples for the 7 most common types of bus stops in China, using 32 of the samples for modeling and 14 samples for illustration. Based on the case study, 6 levels of safety for bus stops were defined. Finally, a linear regression analysis between safety levels and the number of traffic conflicts showed that they had a strong relationship (R² value of 0.908).

Conclusions: The results indicated that the method was well validated and could be practically used for the analysis and evaluation of bus stop safety in China. The proposed model was relatively easy to implement without the requirement of traffic crash data and/or traffic conflict data. In addition, with the proposed method, it was feasible to evaluate countermeasures to improve bus stop safety (e.g., exclusive bus lanes).     

电化学辅助微电解法处理焦化废水

制备了锰粉改进的规整化微电解填料,采用电化学辅助改进微电解填料处理初始COD为6 153.6 mg/L、ρ(NH_3-N)为182.6 mg/L的焦化废水,优化了工艺条件。实验结果表明,电化学辅助微电解法处理焦化废水的最佳工艺条件为电压8 V,填料投加量20 g/L,初始废水pH 6,反应时间30 min。在此条件下废水COD去除率为75.3%,NH_3-N去除率为65.4%;在其他工艺条件相同的情况下,未通过电化学辅助的填料微电解反应的COD去除率为33.0%,NH_3-N去除率为16.2%,电化学辅助后的COD去除率和NH_3-N去除率均明显提高。     

粉末活性炭的Fenton氧化再生

采用Fenton氧化法对吸附处理染料废水后的饱和粉末活性炭(饱和炭)进行再生,考察了饱和炭的再生效果及其主要影响因素。实验结果表明:饱和炭的最佳再生条件为H2O2投加量6.5 mmol/g、再生p H 3.0、H2O2与Fe2+的摩尔比10、再生时间1 h;最佳条件下的再生率(再生粉末活性炭(再生炭)与新粉末活性炭对废水COD去除率的百分比)约为60%;使用最佳再生条件下得到的再生炭对废水进行吸附处理,废水的COD去除率和脱色率分别约为27%和67%。     

水体中几种无机离子对硝酸根敏化甲芬那酸光降解影响研究

以中压汞灯为光源,研究环境浓度范围内硝酸根对甲芬那酸(MEF)光降解的影响机制.结果表明,甲芬那酸在不同浓度硝酸根溶液中的光解反应符合准一级动力学规律,其降解速率常数随硝酸根离子浓度增大而增大,当硝酸根离子浓度由0增至1 mmol·L-1时其速率常数由0.00627 min-1增至0.0232 min-1;以异丙醇为分子探针检测到羟基自由基存在于MEF光解过程中;光解过程中产生亚硝酸根,其浓度随着反应的进行而不断增大;碱性水环境对硝酸根敏化甲芬那酸的光解反应有利;碳酸盐、氯离子、三价铁对硝酸根敏化甲芬那酸光解产生抑制作用.采用UPLC/MS/MS对硝酸根敏化MEF光降解产物进行鉴定,并提出3条可能的光解路径.毒性研究表明,在硝酸根敏化甲芬那酸光降解过程中,生成了具有较甲芬那酸而言更高风险的中间产物.     

Feasibility of bubble surface modification for natural organic matter removal from river water using dissolved air flotation

A novel, functionalized bubble surface can be obtained in dissolved air flotation (DAF) by dosing chemicals in the saturator. In this study, different cationic chemicals were used as bubble surface modifiers, and their effects on natural organic matter (NOM) removal from river water were investigated. NOM in the samples was fractionated based on molecular weight and hydrophobicity. The disinfection byproduct formation potentials of each fraction and their removal efficiencies were also evaluated. The results showed that chitosan was the most promising bubble modifier compared with a surfactant and a synthetic polymer. Tiny bubbles in the DAF pump system facilitated the adsorption of chitosan onto microbubble surfaces. The hydrophobic NOM fraction was preferentially removed by chitosan-modified bubbles. Decreasing the recycle water pH from 7.0 to 5.5 improved the removal of hydrophilic NOM with low molecular weight. Likewise, hydrophilic organic compounds gave high dihaloacetic acid yields in raw water. An enhanced reduction of haloacetic acid precursors was obtained with recycle water at pH values of 5.5 and 4.0. The experimental results indicate that NOM fractions may interact with bubbles through different mechanisms. Positive bubble modification provides an alternative approach for DAF to enhance NOM removal.

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Greenhouse gas emissions from dairy open lot and manure stockpile in northern China: A case study

The open lots and manure stockpiles of dairy farm are major sources of greenhouse gas (GHG) emissions in typical dairy cow housing and manure management system in China. GHG (CO₂, CH₄ and N₂O) emissions from the ground level of brick-paved open lots and uncovered manure stockpiles were estimated according to the field measurements of a typical dairy farm in Beijing by closed chambers in four consecutive seasons. Location variation and manure removal strategy impacts were assessed on GHG emissions from the open lots. Estimated CO₂, CH₄ and N₂O emissions from the ground level of the open lots were 137.5±64.7 kg hd^-1 yr^-1, 0.45±0.21 kg hd^-1 yr^-1 and 0.13±0.08 kg hd^-1 yr^-1, respectively. There were remarkable location variations of GHG emissions from different zones (cubicle zone vs. aisle zone) of the open lot. However, the emissions from the whole open lot were less affected by the locations. After manure removal, lower CH₄ but higher N₂O emitted from the open lot. Estimated CO₂, CH₄ and N₂O emissions from stockpile with a stacking height of 55±12 cm were 858.9±375.8 kg hd^-1 yr^-1, 8.5±5.4 kg hd^-1 yr^-1 and 2.3±1.1 kg hd^-1 yr^-1, respectively. In situ storage duration, which estimated by manure volatile solid contents (VS), would affect GHG emissions from stockpiles. Much higher N₂O was emitted from stockpiles in summer due to longer manure storage.

Implications: This study deals with greenhouse gas (GHG) emissions from open lots and stockpiles. It’s an increasing area of concern in some livestock producing countries. The Intergovernmental Panel on Climate Change (IPCC) methodology is commonly used for estimation of national GHG emission inventories. There is a shortage of on-farm information to evaluate the accuracy of these equations and default emission factors. This work provides valuable information for improving accounting practices within China or for similar manure management practice in other countries.     

Vinegar residue compost as a growth substrate enhances cucumber resistance against the Fusarium wilt pathogen Fusarium oxysporum by regulating physiological and biochemical responses

Environmental Science and Pollution Research - Fusarium wilt caused by the fungus Fusarium oxysporum f. sp. cucumerinum (FOC) is the most severe soil-borne disease attacking cucumber. To assess the...     

国内外冷却服的发展现状及关键技术

本文论述了国内外冷却服的发展现状,介绍了3种制冷技术路线,指出了其各自的关键技术,有利于人们对冷却服的发展趋势进一步的了解和认识.