Hydrothermal conversion of water lettuce biomass at 473 or 523 K

The high moisture content of an aquatic biomass was used advantageously in a hydrothermal process. Reducing sugars, amino acids, proteins, and crude oil were extracted from water lettuce (Pistia stratiotes L.) using subcritically heated water. The highest yields of reducing sugars and amino acids were obtained after treatment at 473 K for 30 min (23.70 ± 0.52 g kg⁻¹ and 4.35 ± 0.09 g kg⁻¹ dry mass respectively), while protein was obtained at 3.60 ± 0.04 g kg⁻¹ feedstock after treatment at 523 K for 60 min. The greatest solubilization occurred at 523 K after 60 min. The solid residues could be applied as fertilizers as hemicellulose and cellulose were hydrothermally converted to humus. The crude oil components that were extracted from the liquid residues differed markedly between the two treatment temperatures. The conversion of furan compounds to cyclopentenone and its derivatives only occurred at the higher reaction temperature and was increased by a longer reaction time.     

Phytoremediation potential of three aquatic macrophytes in manganese‐contaminated water

Manganese (Mn) uptake capacities of water hyacinth (Eichhornia crassipes (Mart.) Solms, water lettuce (Pistia stratiotes L.) and slligator alternenthera (Alternanthera philoxeroides) were investigated with four Mn levels: 0(control), 50, 200, 400 mg/L. With increased Mn exposure, the tested plants showed similar responses with a decrease in relative growth rate and an increase in plant Mn concentrations. Comparatively, water lettuce had the significantly higher total Mn concentrations, shoots enrichment factor and translocation factor at all Mn‐treated treatments and the much greater total Mn removal at concentrations of 200 and 400 mg/L Mn. In most cases, Mn pollution significantly decreased Mg concentrations for all three plants. Concomitantly, increment trends of Fe, Cu and Zn concentrations were observed for water lettuce with the increasing external Mn concentrations, which could partly contribute to its higher Mn concentrations. The results indicated that water lettuce have standout potentials as a phytoremediation plant for Mn contaminated waters.     

水生植物大薸和凤眼莲对水中铀的去除

通过室内水培和静态吸附实验,研究了铀矿区土著水生植物大薸(Pistia stratiotes L.)和凤眼莲(Eichhornia crassipes)对真实铀矿坑水和不同铀浓度水中铀的去除能力。结果表明:干体大薸和凤眼莲根系以1g/L(干重)的比例投加至铀矿坑水(ρ0(U)=1.93mg/L,pH0=7.83)中,1h后,矿坑水中铀去除率分别达58%和48%,5d后铀质量浓度降至0.3mg/L以下;活体大薸和凤眼莲对水体中铀的去除作用主要集中在第1d内,单株鲜重约为400g左右的活体大薸在10min内可以将1Lρ0(U)=0.045~4.5mg/L的水体中铀质量浓度降至30μg/L以下,符合世界卫生组织建议的饮用水标准;单株鲜重约为400g左右的活体凤眼莲在1d内可以将1Lρ0(U)=0.5~4.5mg/L的水体中铀质量浓度降至国家标准(GB 23727—2009)规定值(0.05mg/L)以下。     

Chromium bioaccumulation: comparison of the capacity of two floating aquatic macrophytes

The capacity of Salvinia herzogii and Pistia stratiotes to remove Cr (III) from water and their behaviour at different Cr (III) concentrations were studied in outdoor experiments. Cr distribution in aerial parts and roots with time and the possible mechanisms of Cr uptake were analyzed. Both macrophytes efficiently removed Cr from water at concentrations of 1, 2, 4 and 6 mgCrL(-1). S. herzogii was the best adapted species. At a greater initial concentration, greater bioaccumulation rates were observed. Root Cr uptake was a rapid process that was completed within the first 24h. Cr uptake through direct contact between the leaves and the solution is the main cause of the increase of Cr in the aerial parts, Cr being poorly translocated from the roots to the aerial parts. Both mechanisms were fast processes. The Cr uptake mechanism involves two components: a fast component and a slow one. The former occurs mainly due to the roots and leaves adsorption and is similar for both species. The slow component is different for each species probably because in P. stratiotes a Cr precipitation occurs induced by the roots.     

水浮莲叶挥发性化学成分的GC/MS法分析

采用气相色谱-质谱联用方法(GC/MS)分析了水浮莲叶中挥发性化学成分。以水蒸气蒸馏法从水浮莲叶中提取挥发油,以毛细管柱为分离柱,在最佳分析条件下共分离出30个化合物,用归一化法测定其相对含量,并用气相色谱-质谱法对分离出的化学成分进行鉴定,共鉴定了26个成分,占挥发油总成分的95·20%。该法对挥发油化学成分的分离效果满意。     

不同水分测定方法对水浮莲水分测定结果的影响

采用烘箱法和红外法两种不同的方法测定水浮莲中水分含量,通过设置不同温度、不同时间和不同称样量测定水浮莲的水分含量,分析三者对水浮莲水分含量测定的影响。结果表明：烘箱法测定水浮莲含水率的最佳条件是称样量1g、温度100℃、时间6h,含水率为（91．1±0．2）％;红外法测定的最佳条件是称样量为1g、温度105oC、时间9min,含水率为（87．3±0．3）％。温度、时间、称样量均是影响水浮莲含水率测定的因素,在实验过程中需对三者进行优化,并且烘箱法的精密度高于红外法,应用中需准确测定水分含量时可优先考虑烘箱法。     

低浓度镉胁迫下2种水生植物体内植物络合素的响应

采用溶液培养方式,研究了水环境低浓度镉(Cd)(0.01～0.64 μmol/L)较长时间胁迫下漂浮植物水浮莲(Pistia stratiotes L.)和沉水植物伊乐藻(Elodea nuttallii)体内植物络合素(PCs)的响应规律.结果显示,2种水生植物对外界Cd胁迫表现出明显的吸收和积累效应,水浮莲体内PCs的响应明显强于伊乐藻.水浮莲体内的PCs诱导量与Cd处理浓度存在良好的剂量-效应关系,Cd浓度≥0.08 μmol/L水浮莲根系产生明显毒害效应并伴随根系PCs的诱导量急剧增加.回归分析显示,2种水生植物体内PCs的合成水平与Cd的生物毒性呈现一定的线性关系,表明PCs可作为重金属Cd胁迫的生物标记物指示水体中重金属的毒害程度.比较而言,水浮莲体内PCs对Cd污染更为敏感,可通过检测其根系PCs的含量来评价和预测实际水环境中Cd的污染.     

Performance evaluation of hybrid constructed wetlands for the treatment of municipal wastewater in developing countries

In developing countries, high cost of conventional wastewater treatment is a major hindrance in its application. Constructed wetlands (CWs) offer low-cost and effective solution to this issue. The current study aimed to evaluate an innovative maneuver of CWs i.e. hybrid flow constructed wetlands (HCWs) for municipal wastewater (MWW). The HCWs included two lab scale CWs; one horizontal and one vertical, in series. Local plant species were used. HCWs were operated in both, batch and continuous mode. Batch mode was used to (1) optimize detention time and (2) find pollutants removal efficiency. Continuous operation (at batch optimized retention time) was carried out for the evaluation of mass removal rate, r (g·m^-2·d^-1), volumetric rate constant, K_v (per day) and areal rate constant, K_a (m·d^-1). Among two local plants tested, Pistia stratiotes gave better removal efficiency than Typha. Optimum detention time in HCWs was found to be 8 days (4 + 4 each). The optimum COD, BOD, TSS, TKN and P removal observed for Pistia stratiotes planted HCWs was 80%, 84%, 82%, 71% and 88% respectively. Effluent standards for COD, BOD and TSS were met at optimum conditions. The values of K_a and K_v demonstrated that more removal occurred in vertical flow as compared to horizontal flow CW.     

Potential allelochemicals fromPistia stratiotes L.

Among the substances isolated from ethyl ether extract ofPistia stratiotes L., linoleic acid,-linolenic acid, (12R,9Z,13E,15Z)-l2-hydroxy- 9,13,15-octadecatrienoicacid, (9S,10E,12Z,15Z)-9-hydroxy-10,12,15-octadecatrienoic acid, -asarone, and 24S-ethyl-4,22-cholestadiene-3,6-dione were found to inhibit the growth of some microalgae in solid medium. Toxicity of -asarone on the growth of sensitive algal strains in liquid medium is discussed.     

两种土著水生植物对铀矿坑水的修复能力研究

通过野外采样、室内分析和水培实验,研究了某废弃铀矿坑水中的土著水生植物大薸(Pistia stratiotes L.)和凤眼莲(Eichhornia crassipes)对铀矿坑水的原位修复能力。野外采样分析结果表明,大薸和凤眼莲对废弃铀矿坑水中的铀有极强的富集能力。废弃铀矿坑水中铀浓度在0.4~0.6mg/L之间,高出国家排放标准(GB 23727—2009)规定值(0.05mg/L)的10倍左右。废弃铀矿坑水中土著水生植物大薸和凤眼莲根系平均铀含量分别为1 015.40mg/kg(干重)和504.87mg/kg(干重);富集系数分别为2 071和1 001。水培实验结果表明,大薸对铀矿坑水中铀的去除能力与植物生长期、生物量和覆盖水体面积呈正相关。生长后期(单株生物量鲜重≥100g)的大薸、凤眼莲,投加量为100g/L时,10d可将铀矿坑水中铀浓度由1.93mg/L降至0.03mg/L以下,去除率达到98%以上。SEM-EDS结果表明,大薸和凤眼莲在酸性条件下与水体中的铀结晶矿化,生成纳米片状晶体堆簇在根系表面;在碱性条件下(接近废弃铀矿坑水的pH值时),未出现类似矿化结晶体。表明大薸和凤眼莲对于不同酸度的铀废水体系有不同的修复机理。