Study on Tolerance and Biosorption of Various Microalgae Species to Arsenic

[Objective] This study aimed to select microalgae species which are capable to effectively remove arsenic contamination from water under natural conditions. [Method] Four microalgae species [Chlorella sp. （zfsaia）, Chlorella minata, Chlorella vulgaris and Selenastrum capricormulum] were used as experimental materials and cultured with six different concentrations of As （Ⅲ） （0.5, 1.0, 2.0, 5.0, 10.0, 20.0 mg/L）. Biomass, chlorophyll a content and other physiological indicators were determined to investigate the arsenic tolerance and biosorption of four microalgae species. [Result] Chlorella sp. is sensitive to arsenic toxicity, its growth was inhibited when arsenic concentration exceeded 10 mg/L, with an EC 50 of 17.32 mg/L; when the arsenic concentration was 0-20 mg/L, growth of S.c, ww1 and C.v was not affected, which showed relatively high tolerance to arsenic, with arsenic removal rates of 77.02% , 72.18% and 81.36% respectively after 24 h. [Conclusion] This study indicates that microalgae have good application prospects for processing arsenic wastewater and being indicator plants of arsenic wastewater.

Arsenite oxidation by three types of manganese oxides

Oxidation of As（Ⅲ） by three types of manganese oxides and the effects ofpH, ion strength and tartaric acid on the oxidation were investigated by means of chemical analysis, equilibrium redox, X-ray diffraction （XRD） and transmission electron microscopy （TEM）. Three synthesized Mn oxide minerals, bimessite, cryptomelane, and hausmannite, which widely occur in soil and sediments, could actively oxidize As（Ⅲ） to As（Ⅴ）. However, their ability in As（Ⅲ）-oxidation varied greatly depending on their structure, composition and surface properties. Tunnel structured cryptomelane exhibited the highest ability of As （Ⅲ） oxidation, followed by the layer structured birnessite and the lower oxide hausmannite. The maximum amount of As （Ⅴ） produced by the oxidation was in the order （mmol/kg） of cryptomelane （824.2） 〉 bimessite （480.4） 〉 hausmannite （117.9）, As pH increased from the very low value（pH 2.5）, the amount of As（Ⅲ） oxidized by the tested Mn oxides was firstly decreased, then negatively peaked in pH 3.0 6.5, and eventually increased remarkably. Oxidation of As（Ⅲ） by the Mn oxides had a buffering effects on the pH variation in the solution. It is proposed that the oxidative reaction processes between As （Ⅲ） and biruessite（or cryptomelane） are as follows： （1） at lower pH condition： （MnO2）x＋ H3AsO3 ＋ 0.5H^＋=0.5H2AsO4^- ＋ 0.5HAsO4^2- ＋Mn〉^2＋ （MnO2）x-1 ＋ H2O; （2） at higher pH condition： （MnO2）x ＋ H3AsO3 = 0.5H2AsO4^- ＋ 0.5HAsO4^2- ＋ 1.5H^＋ ＋ （MnO2）x-1. MnO. With increase of ion strength, the As（Ⅲ） oxidized by bimessite and cryptomelane decreased and was negatively correlated with ion strength. However, ion strength had little influence on As （Ⅲ） oxidation by the hausmarmite. The presence of tartaric acid promoted oxidation of As（Ⅲ） by birnessite. As for cryptomelane and hansmannite, the same effect was observed when the concentration of tartaric acid was below 4 mmol/L, otherwise the oxidized As（Ⅲ） decreased. These findings are of great significance in improving our understanding of As geochemical cycling and controlling As contamination.

The oxidative and adsorptive effectiveness of hydrous manganese dioxide for arsenite removal

This study focuses on the effectiveness of hydrous manganese dioxides （ζMnO2） removing arsenite （As（Ⅲ）） from aqueous solution. Effects of such factors as permanganate oxidation, pH, humic acid and Ca^2＋ on As removal and possible mechanisms involved in have been investigated. Permanganate oxidation increases As removal to a certain extent; the higher pH results in the formation of more easily adsorbed As species, contributing to higher As removal; hmnic acid occupies adsorbing sites and decreases ζ potential of ζMnO2, therefore inhibiting As removal; Ca^2＋ facilitates As adsorption on ζMnO2, mainly through increasing ζ potential and decreasing repulsive forces between As and surface sites.ζMnO2 exhibits oxidative and adsorptive potential for As（Ⅲ）, and may be employed as adsorbents or filter coating for As removal in water treatment process.

Ethanol mediated As(Ⅲ) adsorption onto Zn-loaded pinecone biochar：Experimental investigation,modeling,and optimization using hybrid artificial neural network-genetic algorithm approach

Organic matters（OMs） and their oxidization products often influence the fate and transport of heavy metals in the subsurface aqueous systems through interaction with the mineral surfaces. This study investigates the ethanol（EtO H）-mediated As（Ⅲ） adsorption onto Zn-loaded pinecone（PC） biochar through batch experiments conducted under Box–Behnken design. The effect of EtO H on As（Ⅲ） adsorption mechanism was quantitatively elucidated by fitting the experimental data using artificial neural network and quadratic modeling approaches. The quadratic model could describe the limiting nature of EtO H and pH on As（Ⅲ） adsorption,whereas neural network revealed the stronger influence of Et OH（64.5%） followed by pH（20.75%）and As（Ⅲ） concentration（14.75%） on the adsorption phenomena. Besides, the interaction among process variables indicated that Et OH enhances As（Ⅲ） adsorption over a pH range of2 to 7, possibly due to facilitation of ligand–metal（Zn） binding complexation mechanism.Eventually, hybrid response surface model–genetic algorithm（RSM–GA） approach predicted a better optimal solution than RSM, i.e., the adsorptive removal of As（Ⅲ）（10.47 μg/g） is facilitated at 30.22 mg C/L of Et OH with initial As（Ⅲ） concentration of 196.77 μg/L at pH 5.8. The implication of this investigation might help in understanding the application of biochar for removal of various As（Ⅲ） species in the presence of OM.

Adsorptive removal of As(Ⅲ) ions from water using spent grain modified by polyacrylamide

In order to enhance the removal efficiency of As（III）, a pre-oxidation process is generally applied first to convert As（III） to As（V）, which may cause unwanted new contaminants. To overcome this problem, efforts were made to develop an effective way to remove As（III）directly without an oxidation step. The effect of polyacrylamide polymers（PAMs） such as anionic PAM, cationic PAM and nonionic PAM, on As（III） ion adsorption by spent grain（SG）was investigated. The physico-chemical properties of the three PAM-polymerized SGs（APSG（anionic PAM-polymerized modified spent grain）, CPSG（cationic PAM-polymerized spent grain） and NPSG（nonionic PAM-polymerized spent grain）） were analyzed using Fourier transform infrared（FT-IR）, scanning electron microscope（SEM） and zeta potential.Batch experimental data showed that the sequence of preferential adsorption for As（III） was APSG 〉 CPSG 〉 NPSG. Active functional groups such as amino group（NH2）, carbonyl group（C_O）, C–N bond of the amide group（CONH2）, and hydroxyl group（O–H） were responsible for As（III） adsorption. Many tubular structures occurring on the surface of APSG possibly increase the specific surface areas and favor the adsorption of As（III） ions. A fixed-bed study was carried out by using APSG as an adsorbent for As（III） from water. Three factors such as bed height, initial concentration and flow rate were studied, and breakthrough curves of As（III） were obtained. The Adams–Bohart model was used to analyze the experimental data and the model parameters were evaluated.

海洋真核微藻Ostreococcus tauri对砷的解毒机制研究

实验选取模式藻种——海洋真核微藻Ostreococcus tauri为材料,以毒性较强的三价砷(As(Ⅲ))为代表,采用液态纯培养法研究海洋微藻对As(Ⅲ)的解毒机制.结果表明,As(Ⅲ)的氧化是O.tauri体内主要的砷解毒机制.暴露于含30μmol·L-1和1.67μmol·L-1As(Ⅲ)的培养基时,该微藻分别在培养的60 h和72 h内将培养基中90%以上的As(Ⅲ)氧化为毒性较低的五价砷(As(V)).随着培养时间的增加,培养6 d后在添加30μmol·L-1As(Ⅲ)的培养基和藻体内均检测到二甲基砷(DMAs(V)),表明该海洋微藻同时具有砷甲基化功能.在O.tauri体内砷甲基化可作为另一种解毒机制,满足其对较高浓度砷的解毒需要.对O.tauri的气态砷挥发能力研究表明,该海洋微藻具有砷挥发功能,可通过将砷挥发出体外进行解毒.20、40、80μmol·L-1As(Ⅲ)培养4周后,O.tauri可分别产生气态砷16.7、4.0和1.3 ng.O.tauri通过对砷的氧化来降低细胞周围环境的砷毒性,通过砷甲基化及挥发降低细胞体内的砷毒性.