纳米银和银离子对2种微藻的急性毒性效应

为了探讨AgNPs对典型微藻的急性毒性效应及其机制,采用柠檬酸钠还原法制备AgNPs,以摇瓶实验法评估了不同浓度的AgNPs和Ag+对铜绿微囊藻和普通小球藻叶绿素a含量、形态结构和叶绿素荧光参数的影响。实验结果表明:AgNPs对普通小球藻和铜绿微囊藻的96 h-EC50分别为1.113 mg·L-1和0.697 mg·L-1,而Ag+对2种藻的96 h-EC50分别为0.106 mg·L-1和0.032 mg·L-1。扫描电镜结果表明:AgNPs处理使普通小球藻细胞表面出现褶皱,细胞变形甚至向内塌陷。对铜绿微囊藻部分细胞出现变形变得不规则,且出现某些胞外物质使细胞粘附在一起。透射电镜观察发现,高浓度Ag+处理使2种藻的细胞均发生质壁分离,部分细胞转变为孢子。而AgNPs处理使普通小球藻细胞蛋白核增大,蛋白核与类囊体区无明显连接通道。铜绿微囊藻拟核区膨大,类囊体和色素体被推向四周,部分类囊体断裂,同时,发现该藻可以分泌胞外物质在细胞周围吸附AgNPs颗粒。对于普通小球藻,0.6 mg·L-1AgNPs处理后细胞光系统Ⅱ的最大光化学量子产率ΦP0相对于CK没有显著差异,但0.09 mg·L-1Ag+处理使ΦP0显著增加。在高浓度AgNPs或Ag+处理时,ΦP0均显著降低。AgNPs未对普通小球藻光系统II性能参数PI_Abs造成影响,但不同浓度Ag+处理均使得该参数显著升高。对于铜绿微囊藻,2种毒物均使其ΦP0显著降低。而PI_Abs仅在2种毒物的最高浓度处理时显著降低。综上,AgNPs对2种藻的急性毒性远小于Ag+,而两者对铜绿微囊藻的毒性均大于普通小球藻。AgNPs胁迫使2种藻叶绿素a含量显著降低,并诱导2种藻在形态结构和光合生理方面发生了显著变化,造成不同程度的损伤,但与Ag+的毒性效应存在一定的差异。提高光吸收能通量补偿耗散能量和分泌胞外物质结合Ag+是微藻2种重要的解毒机制。     

污水厂尾水中消毒副产物对小球藻的生长生理影响

通过检测无锡某污水厂疫情期间排放尾水中消毒副产物的种类和浓度，发现一氯乙酸(CAA)占全年总检出量的30.22%.采用毒性标准实验方法研究CAA对小球藻生长和抗氧化系统的影响.结果表明在CAA胁迫下，小球藻生长速率减慢，最大光化学量子产量(Fv/Fm)较空白组出现明显下降，96 h叶绿素a浓度明显降低. CAA对小球藻的96 h半数效应浓度(EC₅₀)为14.734 mg·L^-1.中、低浓度CAA胁迫会诱导超氧化物歧化酶(SOD)、过氧化氢酶(CAT)活性和还原型谷胱甘肽(GSH)含量的上升，减少丙二醛(MDA)含量的积累；而高浓度胁迫下，SOD、CAT活性和GSH含量持续下降，MDA含量先升高再下降.     

5氟尿嘧啶对蛋白核小球藻和羊角月芽藻生长及叶绿素含量的影响

近年来,抗癌药的环境污染特征及其生态风险引起了广泛关注。为获取典型抗癌药5氟尿嘧啶的基础生态毒性数据,以蛋白核小球藻(Chlorella pyrenoidosa)和羊角月芽藻(Selenastrum capricornutum)为受试生物,考察了5氟尿嘧啶对2种绿藻的生长和叶绿素含量的影响。结果表明,5氟尿嘧啶对蛋白核小球藻和羊角月芽藻的生长具有抑制作用,随着暴露浓度升高,细胞生长抑制率增强。5氟尿嘧啶对2种绿藻的96 h半数抑制浓度(EC50)分别为450.36 mg·L~(-1)和692.30 mg·L~(-1),属于低毒性物质。暴露96 h后,低浓度5氟尿嘧啶(32 mg·L~(-1))对蛋白核小球藻和羊角月芽藻叶绿素含量有一定的促进作用,高浓度5氟尿嘧啶(32~500 mg·L~(-1))则抑制了2种绿藻的叶绿素含量,且两者具有明显的负相关关系。和叶绿素b相比,叶绿素a对5氟尿嘧啶胁迫更为敏感。     

Cr~(3+)胁迫对小球藻生理生化特性的影响

水体重金属污染较难处理,且会对水生物造成严重的影响。为探讨水体中重金属对藻类的毒性影响,以普通小球藻(Chlorella vulgaris)和铬(Cr~(3+))为材料,研究不同浓度Cr~(3+)对普通小球藻生理、生化特性的影响,检测不同浓度的Cr~(3+)对小球藻的毒性效应。结果表明,小球藻的最优生长温度为31℃。此条件下,Cr~(3+)浓度为3 mg·L~(-1)时,小球藻的生物量最大。Cr~(3+)的浓度低于3 mg·L~(-1)时,Cr~(3+)能促进小球藻的生长,且藻细胞中光合色素、蛋白质、可溶性糖、丙二醛(MDA)的含量及超氧化物歧化酶(SOD)的活性也逐渐增加。当各胁迫组的Cr~(3+)浓度超过3 mg·L~(-1)时,随着Cr~(3+)浓度的提高,C.vulgaris的生长受到明显的抑制,藻细胞的光合色素、蛋白质和可溶性糖含量呈现逐渐下降的趋势,而MDA含量持续增加,SOD和脯氨酸则表现出先持续增高后降低(Cr~(3+)浓度为7 mg·L~(-1)时)的趋势。证明不同浓度的Cr~(3+)对小球藻的生理生化特性有不同程度的毒性效应。     

pH对鱼腥藻和普通小球藻生长竞争的影响

pH值是藻类生长环境的重要理化指标,它可以通过改变环境酸碱度和碳酸盐平衡系统及不同形态无机碳分配关系来影响藻类的生长。为揭示水体中常见藻类的生长过程及其与pH的相互关系,设置了6.0,7.0,8.0和9.0等4个pH梯度,通过室内实验模拟水体条件,研究不同pH条件下主要水华藻类--鱼腥藻（Anabaena sp.strain PCC）和常见淡水藻类--普通小球藻（Chlorella vulga）的生长和种间竞争。结果表明,无论是在单种培养还是在共同培养体系中,4个pH条件下两种藻类的最大生物量差异显著（P〈0.05）,鱼腥藻和普通小球藻的最适pH均为9.0,其中单种培养时鱼腥藻和普通小球藻的最大生物量分别为4473.5×104,689.6×10^4 cells·mL-1;共同培养时鱼腥藻和普通小球藻的最大生物量分别为2798.0×10^4,296.5×10^4 cells·mL-1。竞争试验结果表明,pH对藻类种间竞争抑制参数能够产生显著影响,pH 7.0时普通小球藻对鱼腥藻的竞争抑制参数（β）最大,为12.91;鱼腥藻对普通小球藻的竞争抑制参数（α）则是pH 6.0时最大,为1.778。在4个pH条件下普通小球藻对鱼腥藻的竞争抑制参数（β）均大于鱼腥藻对普通小球藻的竞争抑制参数（α）,与单种培养相比,鱼腥藻最大藻细胞数受到明显削弱,说明普通小球藻在竞争中占优势。因此,在水产养殖过程控制和精准培水技术研究,以及控制养殖水体富营养化的过程中,可以通过调节养殖水体pH值以及普通小球藻的浓度来控制鱼腥藻的生长。     

渔业养殖区藻源溶解性有机质性质特征对汞甲基化影响

溶解性有机质(dissolved organic matter,DOM)是水生生态系统中的重要成分,能够显著影响汞的甲基化等形态变化过程.以近岸渔业养殖区藻源DOM为研究对象,运用傅里叶变换红外光谱和三维荧光光谱技术,对其结构特征进行表征;并选取总有机碳浓度TOC_DOM=10 mg·L^-1(DOM₁₀)和TOC_DOM=50 mg·L^-1(DOM₅₀)两种水平藻源DOM提取液,分析其在不同汞浓度条件下对汞甲基化过程的影响.结果表明,藻源DOM主要由类蛋白和类腐殖质组分组成,其中前者含量较高,疏水及芳香组分含量较低;红外光谱显示藻源DOM中含有—OH、—CH₃、—CH₂、芳香性C=C等官能团.甲基化实验表明,在溶液中DOM含量相对较少时(DOM:Hg浓度比≤15625),DOM表现出抑制汞甲基化的趋势,而当溶液中DOM含量逐渐升高(DOM:Hg浓度比>15625),DOM可以显著促进水体中汞向甲基汞的转化.藻源...     

锌与双酚A复合暴露对普通小球藻的联合毒性作用评估

为探究重金属与环境激素的联合毒性效应,以普通小球藻为受试生物,开展了锌与双酚A的单一及复合暴露对普通小球藻的急性毒性、叶绿素含量、可溶性蛋白含量及抗氧化应激的影响.结果显示,在单一暴露条件下,锌和双酚A对普通小球藻的EC50分别为5.10 mg·L-1和17.37 mg·L-1,仅在锌离子质量浓度低于0.25 mg·L-1时可促进普通小球藻叶绿素合成,而其他各暴露组中锌和双酚A对普通小球藻的光合作用具有抑制效应,采用等毒性配比法进行联合毒性试验,由相加指数法判断锌与双酚A对普通小球藻的联合作用类型为协同作用;藻细胞可溶性蛋白含量、抗氧化酶活性及丙二醛含量随锌与双酚A暴露浓度的增加被显著诱导,且高浓度的复合暴露对普通小球藻造成明显的氧化损伤.研究表明,锌与双酚A复合暴露会加强其在水环境中的毒性效应.     

g-C3N4-MoS2/WSe2自偏压系统构建与不同类型污染物同时去除性能研究

由于工业化进程的不断推进,染料与重金属废水被非法排入自然水体,水体污染问题日益严峻.为实现两种污染物的同时去除,本文通过调控合成MoS₂/WSe₂（MW）异质结复合催化材料,提高其催化活性.黑暗条件下,以MoS₂、WSe₂以及MW为阳极材料,g-C₃N₄为阴极材料组建自偏压燃料电池系统,实现在降解有机染料的同时,去除水体中的重金属离子.通过调控参数,探究影响染料与重金属去除的因素.研究表明,影响重金属和有机染料去除效果的因素有pH、电解质溶液浓度、重金属溶液浓度.当溶液pH=5,电解质溶液浓度为0.1 mol·L^-1,铜离子浓度为4 mg·L^-1时,重金属的去除率为64.3%.当溶液pH=5,电解质溶液浓度为0.2 mol·L^-1,铜离子浓度为2 mg·L^-1时,有机染料罗丹明B的去除率为99.5%.该系统在无外加光照条件下,实现不同类型污染物同时去除,并产生约240 ...     

氮磷质量浓度对普通小球藻和鱼腥藻生长竞争的影响

研究氮磷质量浓度对藻类生长竞争的影响,对于揭示如何通过控制环境因子促进有益藻类生长繁殖、抑制有害藻类生长繁殖,并利用藻类调节养殖环境和提高水体初级生产力具有重要意义。设置了4个氮磷质量浓度梯度(N 0.18μg·m L-1,P0.025μg·m L-1;N 0.36μg·m L-1,P 0.050μg·m L-1;N 0.72μg·m L-1,P 0.100μg·m L-1;N 3.60μg·m L-1,P 0.500μg·m L-1),通过测算比生长速率、生长曲线、竞争抑制参数,研究了不同氮磷质量浓度对普通小球藻(Chlorella vulgaris)和鱼腥藻(Anabaenasp.strain PCC)生长和种间竞争的影响。结果表明,在单种培养体系中,普通小球藻和鱼腥藻的最大藻细胞数量均随氮磷质量浓度的增加而增加,最大藻细胞数量分别为198.9×105 cells·m L-1和424.8×105 cells·m L-1;氮磷质量浓度对藻类的竞争能够产生明显影响,在共培养体系中,鱼腥藻的最大藻细胞数量表现为:中高氮磷组(208.9×105 cells·m L-1)中低氮磷组(98.3×105 cells·m L-1)高氮磷组(64.7×105 cells·m L-1)低氮磷组(45.3×105 cells·m L-1)。同时,种间竞争抑制参数的测算结果表明,4组氮磷质量浓度下鱼腥藻对普通小球藻的竞争抑制参数(α)分别为2.599、0.564、0.772、1.618,普通小球藻对鱼腥藻的竞争抑制参数(β)分别为0.434、0.321、0.466、-8.899,鱼腥藻对普通小球藻的竞争抑制参数(α)均大于普通小球藻对鱼腥藻的竞争抑制参数(β);低氮磷质量浓度时,鱼腥藻对普通小球藻的竞争抑制参数(α)最大,为2.599;中高氮磷质量浓度时,普通小球藻对鱼腥藻的竞争抑制参数(β)最大,为0.466。根据Lotka-Volterra竞争模型中的两物种竞争结局可初步判断,低、中高氮磷、高氮磷质量浓度时,鱼腥藻在竞争中占优势;中低氮磷质量浓度时,鱼腥藻和普通小球藻稳定共存。     

三亚河营养盐时空分布及富营养化研究

为了解三亚河营养盐污染状况,于2018年6月—2019年5月对三亚河流域进行逐季调查,分析水体中氮磷营养盐的时空分布特征及影响因素,评估河流富营养化状况,并进一步估算三亚河营养盐入海通量.结果表明,三亚河水体中营养盐浓度季节变化显著,三亚河水体中DIN的浓度范围为0.028—2.096 mg·L^-1,平均浓度为(0.700±0.279)mg·L^-1,冬季>秋季>夏季>春季,NO₃^--N和NH₄⁺-N是水体中DIN的主要存在形式.DIP浓度范围为0.007—0.442 mg·L^-1,平均浓度为(0.140±0.066) mg·L^-1,夏季>春季>冬季>秋季.空间分布上,N、P营养盐均呈现出上游及入海口河段浓度低,中下游河段浓度高的特点.河段环境特征、人为活动、降雨、潮汐作用是影响三亚河营养盐分布的主要因素.综合富营养盐指数(EI)结果显示,各季节三亚河上游及入海口河段均处于中富营...     

Reduction of hexavalent chromium with scrap iron in a fixed bed reactor

The reduction of hexavalent chromium by scrap iron was investigated in continuous long-term fixed bed system. The effects of pH, empty bed contact time (EBCT), and initial Cr(VI) concentration on Cr(VI) reduction were studied. The results showed that the pH, EBCT, and initial Cr(VI) concentration significantly affected the reduction capacity of scrap iron. The reduction capacity of scrap iron were 4.56, 1.51, and 0.57 mg Cr(VI)·g^-1 Fe⁰ at pH 3, 5, and 7 (initial Cr(VI) concentration 4 mg·L^-1, EBCT 2 min, and temperature 25°C), 0.51, 1.51, and 2.85 mg Cr(VI)·g^-1 Fe⁰ at EBCTs of 0.5, 2.0, and 6.0 min (initial Cr(VI) concentration 4 mg·L^-1, pH 5, and temperature 25°C), and 2.99, 1.51, and 1.01 mg Cr(VI)·g^-1 Fe⁰ at influent concentrations of 1, 4, and 8 mg·L^-1 (EBCT 2 min, pH 5, and temperature 25°C), respectively. Fe(total) concentration in the column effluent continuously decreased in time, due to a decrease in time of the iron corrosion rate. The fixed bed reactor can be readily used for the treatment of drinking water containing low amounts of Cr(VI) ions, although the hardness and humic acid in water may shorten the lifetime of the reactor, the reduction capacity of scrap iron still achieved 1.98 mg Cr⁶⁺·g^-1 Fe. Scanning electron microscope equipped with energy dispersion spectrometer and X-ray diffraction were conducted to examine the surface species of the scrap iron before and after its use. In addition to iron oxides and hydroxide species, iron-chromium complex was also observed on the reacted scrap iron.     

Selective recovery of Cu2+ and Ni2+ from wastewater using bioelectrochemical system

As the bioelectrochemical system, the microbial fuel cell (MFC) and the microbial electrolysis cell (MEC) were developed to selectively recover Cu²⁺ and Ni²⁺ ions from wastewater. The wastewater was treated in the cathode chambers of the system, in which Cu²⁺ and Ni²⁺ ions were removed by using the MFC and the MEC, respectively. At an initial Cu²⁺ concentration of 500 mg·L^-1, removal efficiencies of Cu²⁺ increased from 97.0%±1.8% to 99.0%±0.3% with the initial Ni²⁺ concentrations from 250 to 1000 mg·L^-1, and maximum power densities increased from 3.1±0.5 to 5.4±0.6 W·m^-3. The Ni²⁺ removal mass in the MEC increased from 6.8±0.2 to 20.5±1.5 mg with the increase of Ni²⁺ concentrations. At an initial Ni²⁺ concentration of 500 mg·L^-1, Cu²⁺ removal efficiencies decreased from 99.1%±0.3% to 74.2%±3.8% with the initial Cu²⁺ concentrations from 250 to 1000 mg·L^-1, and maximum power densities increased from 3.0±0.1 to 6.3±1.2 W·m^-3. Subsequently, the Ni²⁺ removal efficiencies decreased from 96.9%±3.1% to 73.3%±5.4%. The results clearly demonstrated the feasibility of selective recovery of Cu²⁺ and Ni²⁺ from the wastewater using the bioelectrochemical system.     

低碳氮比废水好氧颗粒污泥系统稳定性及微生物种群多样性研究

低碳氮比(C/N)废水处理是含氮废水处理中的难题之一.本实验在C/N为4:1和2:1(COD和NH₄⁺-N浓度分别为400 mg·L^-1和100 mg·L^-1,400 mg·L^-1和200 mg·L^-1)条件下,考察好氧颗粒污泥系统对低碳氮比废水的处理效果、长期运行稳定性,研究C/N对好氧颗粒微生物结构变化的影响.研究结果表明,在C/N为4:1的废水中接种活性污泥培养好氧颗粒污泥,形成的颗粒沉降性能良好,MLSS为4.94 g·L^-1,SVI30为40 mL·g^-1,COD去除率90%以上,氨氮去除率接近100%.降低碳氮比,即C/N为2:1后,好氧颗粒的物理及硝化性能无明显变化,MLSS为11.38 g·L^-1,SVI₃₀/SVI₅维持在1左右,COD去除率大于85%,氨氮去除率98%.碳氮比降低使颗粒微生物多样性减少,其中陶厄氏菌受影响较小,而硝化功能菌出现更替:噬氢菌、食酸菌、里德拜特氏菌消失,鞘氨醇单胞菌、束缚杆菌等成为优势菌种.实验表明,该低碳氮比条件下好氧颗粒污泥系统能够稳定运行,且具有优良的处理性能.     

Validation of polymer-based nano-iron oxide in further phosphorus removal from bioeffluent: laboratory and scaledup study

The efficient removal of phosphorous from water is an important but challenging task. In this study, we validated the applicability of a new commercially available nanocomposite adsorbent, i.e., a polymer-based hydrated ferric oxide nanocomposite (HFO-201), for the further removal of phosphorous from the bioeffluent discharged from a municipal wastewater treatment plant, and the operating parameters such as the flow rate, temperature and composition of the regenerants were optimized. Laboratory-scale results indicate that phosphorous in real bioeffluent can be effectively removed from 0.92 mg·L^-1 to<0.5 mg·L^-1 (or even<0.1 mg·L^-1 as desired) by the new adsorbent at a flow rate of 50 bed volume (BV) per hour and treatable volume of 3500–4000 BV per run. Phosphorous removal is independent of the ambient temperature in the range of 15°C–40°C. Moreover, the exhausted HFO-201 can be regenerated by a 2% NaOH+ 5% NaCl binary solution for repeated use without significant capacity loss. A scaled-up study further indicated that even though the initial total phosphorus (TP) was as high as 2 mg·L^-1, it could be reduced to<0.5 mg·L^-1, with a working capacity of 4.4–4.8 g·L^-1 HFO-201. In general, HFO-201 adsorption is a choice method for the efficient removal of phosphate from biotreated waste effluent.     

Optimization of thermophilic anaerobic-aerobic treatment system for Palm Oil Mill Effluent (POME)

Optimization of an integrated anaerobic-aerobic bioreactor (IAAB) treatment system for the reduction of organic matter (Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) concentrations) in Palm Oil Mill Effluent (POME) to legal standards with high methane yield was performed for the first time under thermophilic condition (50°C–55°C) by using response surface methodology (RSM). The experiments were conducted based on a central composite rotatable design (CCRD) with three independent operating variables, organic loading rates in anaerobic compartment (OLR_an) and mixed liquor volatile suspended solids (MLVSS) concentration in anaerobic (MLVSS_an) and aerobic compartments (MLVSS_a). The optimum conditions for the POME treatment were determined as OLR_an of 15.6 g COD·L^-1·d^-1, MLVSS_an of 43100 mg·L^-1, and MLVSS_a of 18600 mg·L^-1, where high aerobic COD, BOD and TSS removal efficiencies of 96.3%, 97.9%, and 98.5% were achieved with treated BOD of 56 mg·L^-1 and TSS of 28 mg·L^-1 meeting the discharge standard. This optimization study successfully achieved a reduction of 42% in the BOD concentrations of the final treated effluent at a 48% higher OLR_an as compared to the previous works. Besides, thermophilic IAAB system scores better feasibility and higher effectiveness as compared to the optimized mesophilic system. This is due to its higher ability to handle high OLR with higher overall treatment efficiencies (more than 99.6%), methane yield (0.31 L CH₄·g^-1 COD_removed) and purity of methane (67.5%). Hence, these advantages ascertain the applicability of thermophilic IAAB in the POME treatment or even in other high-strength wastewaters treatment.     

Upgrade of three municipal wastewater treatment lagoons using a high surface area media

Lagoon-based municipal wastewater treatment plants (WWTPs) are facing difficulties meeting the needs of rapid population growth as well as the more stringent requirements of discharge permits. Three municipal WWTPs were modified using a high surface area media with upgraded fine-bubble aeration systems. Performance data collected showed very promising results in terms of five-day biochemical oxygen demand (BOD₅), ammonia (NH₃) and total suspended solids (TSS) removal. Two-year average ammonia effluents were 4.1 mg·L^-1 for Columbia WWTP, 4 mg·L^-1 for Larchmont WWTP and 2.1 mg·L^-1 for Laurelville WWTP, respectively. Two- year average BOD₅ effluents were 6.8, 4.9 and 2.7 mg·L^-1, and TSS effluents were 15.0, 9.6 and 7.5 mg·L^-1. The systems also showed low fecal coliform (FC) levels in their effluents.     

Performance of an ANAMMOX reactor treating wastewater generated by antibiotic and starch production processes

A pilot-scale anaerobic ammonia oxidation (ANAMMOX) reactor was used to treat mixed wastewater resulting from a chlortetracycline and starch production process. The results, collected over the course of 272 days, show that the ratio of influent ammonium to nitrite, pH, and temperature can all affect the efficiency of nitrogen removal. The ratio of influent ammonium to nitrite was maintained at about 1:1 at a concentration below 200 mg·L^-1 for both influent ammonium and nitrite. The total nitrogen (TN) loading rate was 0.15–0.30 kgN·m^-3·d^-1, pH remained at 7.8–8.5, and temperature was recorded at 33±1°C. The rate of removal of ammonia, nitrite, and TN were over 90%, 90%, and 80%, and the effluent ammonium, nitrite and TN concentrations were below 50, 30, and 100 mg·L^-1.     

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.     

Adsorption property of direct fast black onto acid-thermal modified sepiolite and optimization of adsorption conditions using Box-Behnken response surface methodology

The adsorption of direct fast black onto acid-thermal modified sepiolite was investigated. Batch adsorption experiments were performed to evaluate the influences of experimental parameters such as initial dye concentration, initial solution pH and adsorbent dosage on the adsorption process. The three-factor and three-level Box-Behnken response surface methodology (RSM) was utilized for modeling and optimization of the adsorption conditions for direct fast black onto the acid-thermal modified sepiolite. The raw sepiolite was converted to acid-thermal modified sepiolite, and changes in the fourier transform infrared spectrum (FTIR) adsorption bands of the sample were noted at 3435 cm^-1 and 1427 cm^-1. The zeolitic water disappeared and the purity of sepiolite was improved by acid-thermal modification. The decolorization rate of direct fast black adsorbed increased from 68.2% to 98.9% on acid-thermal modified sepiolite as the initial solution pH decreased from 10 to 2. When the adsorbent dosage reached to 2.5 g·L^-1, 2.0 g·L^-1, 1.5 g·L^-1 and 1.0 g·L^-1, the decolorization rate was 90.3%, 86.7%, 61.0% and 29.8%, respectively. When initial dye concentration increased from 25 to 200 mg·L^-1, the decolorization rate decreased from 91.9% to 60.0%. The RSM results showed that the interaction between adsorbent dosage and pH to be a significant factor. The optimum conditions were as follows: the adsorbent dosage 1.99 g·L^-1, pH 4.22, and reaction time 5.2 h. Under these conditions, the decolorization rate was 95.1%. The three dimensional fluorescence spectra of direct fast black before and after treatment showed that the direct fast black was almost all adsorbed by the acid-thermal modified sepiolite.     

Migration of manganese and iron during the adsorption-regeneration cycles for arsenic removal

Fe-Mn binary oxide incorporated into porous diatomite (FMBO-diatomite) was prepared in situ and regenerated in a fixed-bed column for arsenite [As(III)] and arsenate [As(V)] removal. Four consecutive adsorption cycles were operated under the following conditions: Initial arsenic concentration of 0.1 mg·L^-1, empty bed contact time of 5 min, and pH 7.0. About 3000, 3300, 3800, and 4500 bed volumes of eligible effluent (arsenic concentration≤0.01 mg·L^-1) were obtained in four As(III) adsorption cycles; while about 2000, 2300, 2500, and 3100 bed volumes of eligible effluent were obtained in four As(V) adsorption cycles. The dissection results of FMBO-diatomite fixed-bed exhibited that small amounts of manganese and iron were transferred from the top of the fixed-bed to the bottom of the fixed-bed during As(III) removal process. Compared to the extremely low concentration of iron (<0.01 mg·L^-1), the fluctuation concentration of Mn²⁺ in effluent of the As(III) removal column was in a range of 0.01–0.08 mg·L^-1. The release of manganese suggested that manganese oxides played an important role in As(III) oxidation. Determined with the US EPA toxicity characteristic leaching procedure (TCLP), the leaching risk of As(III) on exhausted FMBO-diatomite was lower than that of As(V).