Biodiversity of Duckweeds in Eastern China and Their Potential for Bioremediation of Municipal and Industrial Wastewater

Duckweed is a group of aquatic plants with the potential of wastewater remediation and fast accumulation of biomass. The accumulated biomass, rich in cellulose, starch and protein, can be used for biofuel, bio-fertilizer, animal feed and human food. Characterization of natural biodiversity of duckweed species is essential for the germplasm preservation and various practical applications. We have collected samples of duckweed in eastern China and characterized species biodiversity by genotyping, using chloroplast (atpF-atpH and psbK-psbI spacers). Spirodela polyrhiza was revealed as a clear dominant duckweed species in all locations of the area. Other duckweed species were identified as Landoltia punctata, Lemna aequinoctialis and Lemna turionifera. Selected isolates of these four species were used in the experiments to estimate their potential in removing nitrogen and phosphorus nutrients from municipal and industrial wastewater sampled at the local sewage plants. Duckweed was able to reduce the concentration of nitrogen up to 98% and phosphorus up to 96%. The presented data demonstrates high efficiency of the local duckweed isolates for bioremediation of different types of wastewater and the great potential of duckweed for wastewater treatment when incorporated into the purification chain.

Aquatic toxicity of di (2-eihylhexyl) phthalate to duckweeds

This study is concerned with the effects of di （2-ethylhexyl） phthalate （DEHP） on two kinds of duckweeds （Spirodela polyrhiza and Lemna minor）.The results indicate that DEHP has aquatic toxicity to Spirodela polyrhiza at 0.4 mg/L and to Lemna minor at over 0.1 mg/L by changing their physiologic-biochemical characteristics.The contents of duckweed chlorophyll and soluble protein decrease with increasing DEHP concentration after 7 d of exposure.DEHP shows the stimulating role in catalase （CAT） and superoxide dismutase （SOD） systems at relative low levels.At 0.01 mg/L and 0.005 mg/L,SOD activities of Spirodela polyrhiza and Lemna minor reach their peak values respectively,while CAT activity reaches its maximum value at 0.05 mg/L and 0.01 mg/L.When DEHP levels are too high,the protection enzyme system would be destroyed and plant growth is inhibited.The analysis of malondialdehyde （MDA） and Fourier transform infrared spectroscopy manifest that DEHP could affect the tested duckweeds by destroying its cell membranes,and Spirodela polyrhiza is more resistant to DEHP exposure than Lemna minor.

Influence of Salinity on Duckweed Growth and Duckweed Based Wastewater Treatment System

The growth of duckweed (Spirodela polyrrhiza) was investigated in an outdoor batch system under 15 different conductivities ranging from 200 μS/cm to 3000 μS/cm with average 110 μmol/m2 daylight intensity. The growth was performed in an anaerobically treated domestic wastewater using an initial plants population of 50 fronds. Increase in Relative Growth Rate—RGR—(in terms of fresh weight and number of fronds) had a significant non-linear (polynomial) relationship with the conductivity. The maximum RGR related to fresh weight of 0.176 was observed at the conductiviity of 1200 μS/cm while the maximum RGR related to fronds number was 0.193 at the conductivity of 800 μS/cm. The optimum range for duckweeds growth was found to be between conductivities of 600 μS/cm and 1400 μS/cm. The maximal rates of removal of COD of 14.5 mg/day, of 0.65 mg/day, NTK of 15.68 mg/day, faecal coliforms of 100% and turbidity of 80.8% were observed in this range. The COD and PO42- removal rates were highly correlated to the growth rate, with the correlation factor of up to 0.783 and, then to the conductivity. The NTK reduction was positively related to the conductivity.

TWO DIMENSIONAL PROPERTIES OF REVERSED DUCKWEED AMPHIPHILIC POLYMER

The surface pressure-Area isotherms of Reversed Duckweed amphiphili polymer were examined in view of their chemical structure and two- dimentional properties of polymer monolayer were studied.

Arsenic uptake, accumulation and phytofiltration by duckweed (Spirodela polyrhiza L.)

This study investigates arsenic （As） accumulation and tolerance of duckweed Spirodela polyrhiza L. and its potential for As phytofiltration. S. polyrhiza was able to survive in high concentration of As（V） solution. The EC 50 values （± SE） based on the external As（V） were （181.66 ± 20.12） μmol/L. It accumulated （999 ± 95） mg As/kg dw when exposed in 320 μmol/L As（V） solution for one week, and was able to take up appropriately 400 mg As/kg dw in tissues without a significant biomass loss. The EC 50 values （the effective concentration of As（V） in the nutrient solution that caused a 50% inhibition on biomass production） was （866 ± 68） mg/kg dw for the tissues, indicating that S. polyrhiza had a high capability of As accumulation and tolerance. The uptake kinetic parameters V max was （55.33 ± 2.24） nmol/（g dw·min） and K m was （0.144 ± 0.011） mmol/L. Within 72 hr, S. polyrhiza decreased As concentration in the solution from 190 to 113 ng/mL with a removal rate of 41%. The study suggested that this floating aquatic plant has some potential for As phytofiltration in contaminated water bodies or paddy soils.

Effects of duckweed(Spriodela polyrrhiza)remediation on the composition of dissolved organic matter in effluent of scale pig farms

The swine effluent studied was collected from scale pig farms,located in Yujiang County of Jiangxi Province,China,and duckweed（Spriodela polyrrhiza） was selected to dispose the effluent.The purpose of this study was to elucidate the effects of duckweed growth on the dissolved organic matter composition in swine effluent.Throughout the experiment period,the concentrations of organic matter were determined regularly,and the excitationemission matrix（3DEEM） spectroscopy was used to characterize the fluorescence component.Compared with no-duckweed treatments（controls）,the specific ultra-violet absorbance at 254 nm（SUVA254） was increased by a final average of 34.4%as the phytoremediation using duckweed,and the removal rate of DOC was increased by a final average of 28.0%.In swine effluent,four fluorescence components were identified,including two protein-like（tryptophan,tyrosine） and two humic-like（fulvic acids,humic acids） components.For all treatments,the concentrations of protein-like components decreased by a final average of 69.0%.As the growth of duckweed,the concentrations of humic-like components were increased by a final average of 123.5%than controls.Significant and positive correlations were observed between SUVA254 and humic-like components.Compared with the controls,the humification index（HIX） increased by a final average of 9.0%for duckweed treatments.Meanwhile,the duckweed growth leaded to a lower biological index（BIX） and a higher proportion of microbial-derived fulvic acids than controls.In conclusion,the duckweed remediation not only enhanced the removal rate of organic matter in swine effluent,but also increased the percent of humic substances.

The Potential of Lemna minor to Uptake Iron in Water

Heavy metal,even necessary element(e.g.iron)may pose risks to human being and environment.This laboratory study investigated the potential of duckweed Lemna minor to uptake iron from solutions.The levels of iron in duckweed did not increase with the concentrations of iron in solutions.The amounts of iron in plants also did not enhance with the culture time.The results indicated that the capability of duckweed to uptake iron was limited as iron was easy to be precipitated and form metal plaque.The use of chelators to increase the bioavailability of iron is necessary to enhance the phytoremediation efficiency.

Highly efficient fermentation of glycerol and 1,3-propanediol using a novel starch as feedstock

As a potential cost-effective feedstock for highly efficient fermentation of glycerol and its downstream product 1,3-propanediol(1,3-PD),duckweed starch was characterized and used for glycerol fermentation,for the first time,in this study.Genes involved in glycerol biosynthesis(gpd1 and gpp2)were overexpressed in Escherichia coli,and genes involved in glycerol catabolism(glpK and gldA)were disrupted,which led to significantly decreased residual sugar levels and dramatically increased glycerol production.The maximum glycerol concentration in fed-batch fermentation reached 102.72 g L^(-1) at 28 h,and the glycerol productivity was 3.67 g L^(-1) h^(-1),which,to our knowledge,is the highest productivity thus far reported.Subsequently,glycerol broth was fermented into 1,3-PD by Klebsiella pneumoniae.The concentration,conversion rate and productivity of 1,3-PD reached 35.54 g L^(-1),40.28%and 0.89 g L^(-1) h^(-1),respectively,without optimization.In summary,the duckweed starch-to-glycerol-to-1,3-PD process is feasible and shows potential for improving glycerol industry competitiveness.