The remediation potential and kinetics of Pb2+ adsorbed by the organic frameworks of Cladophora rupestris.

Cladophora rupestris is ubiquitous in many kinds of waterbodies, and C. rupestris biomass can serve as a carrier for adsorbing and transferring heavy metals. Batch experiments and characterization were performed. Results showed that the organic frameworks of C. rupestris (CROF) had a specific surface area of 2.58 m2/g and an external surface area of 2.06 m2/g. Many mesopores were present in CROF, mainly distributed in 2.5-7.5 nm. The zeta potentials were within the range of - 4.46 to - 13.98 mV in the tested pH of 2.0-9.0. CROF could effectively adsorb Pb2+ in large pH range. The maximum adsorption capacity (qmax) of Pb2+ on CROF was 15.02 mg/g, and 97% of Pb2+ was adsorbed onto CROF after 25 min. CROF had a preferential adsorption of Pb2+. The protein secondary structures and carbon skeletons of CROF all worked in adsorption. The main Pb2+ adsorption mechanisms were pore filling, electrostatic attraction, Pb-π interaction, and surface complexation. Therefore, it is valuable as a biosorbent for the removal of Pb2+ from waterbodies.

XPS and NMR analyze the combined forms of Pb in Cladophora rupestris subcells and its detoxification.

In this study, the combined forms of Pb in Cladophora rupestris (L.) (C. rupestris) were investigated via X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR), different Pb concentrations (0, 0.5, and 5.0 mg/L), and C. rupestris subcells were explored. Results showed that combined forms of Pb mainly account for Pb-polysaccharides (Pb-OH of carbohydrates) in the cell wall, Pb-protein (Pb-N= and (C-N-)2Pb) in the organelle, and Pb-organic acid (Pb-sulfates, (CO)2-Pb and (COO)2-Pb) in the soluble fraction. Pb-S-containing group (Pb-C-S) could formed in subcelluar when C. rupestris was subjected to high Pb stress. Meanwhile, Pb2+ could penetrate the C. rupestris cells via the formed chelate between GSH/MT and -OH functional groups. Results could help understand the role of subcellular fraction in the algae remediation and detoxification to heavy metal.

Combined forms of Pb and its detoxification and absorption in Cladophora rupestris subcells.

This study aims to analyze the combined form, detoxification, and adsorption mechanism of Pb in Cladophora rupestris subcells. The chemical form analysis at different concentrations (0, 0.5, 1.0, 2.5, 5.0, 7.5, and 10 mg/L) indicated that most of the Pb (37%-76%) were integrated with oxalate and undissolved phosphate, which were important to the detoxification of C. rupestris. The characterization of Pb (0, 0.5, and 5.0 mg/L) at the subcellular was conducted via Fourier-transform infrared spectroscopy (FTIR), Three-dimensional excitation-emission matrix spectroscopy (3D-EEM), and protein secondary structure fitting. Results revealed that Pb-polysaccharides ((C6H5)-OO-Pb-OH, C-O-Pb, and symmetric Pb-O-Pb), Pb-functional-groups ((C6H5)-COO-Pb and (C6H5)-P = O-Pb), and Pb-protein complexes (OH-C7H6-CN-Pb-COOH, C9H10-NH-CN-C = O-Pb, Pb-S-C, and Pb-S) were formed. The cell wall produced transport proteins, such as metallothionein and glutathione, which bound and helped Pb2+ enter the cell. After entering the soluble fraction, the Pb-organic acid ((C6H5)-COO-Pb, (C6H5)-O-Pb, and (C6H5)-P = O-Pb) and Pb-sulfhydryl compound (Pb-S-C/Pb-S) assumed the most important role in resisting the toxicity of Pb2+. Pb2+ was absorbed in the organelle and formed (C6H5)-C-O-Pb and (C6H5)-P = O-Pb, and complexed with protein (Pb-C-N) when treated with 5.0 mg/L Pb. Results could help understand the role of subcellular fraction in the algal adaptation to stressful heavy metal conditions.

Response of sulfhydryl compounds in subcells of Cladophora rupestris under Pb stress.

This study aimed to determine the role of sulfhydryl compounds in the subcells of C. rupestris under Pb stress. Different concentrations (0, 0.5, 1.0, 2.5, 5.0, 7.5, and 10 mg/L) and different exposure days (1, 3, 5, and 7 days) were designed to analyze the subcellular distribution of non-protein thiols (NPT), glutathione (GSH), and phytochelatins (PCs) in C. rupestris. NPT, GSH, and PCs increased significantly with increasing Pb stress in the cell wall and soluble fraction, especially NPT. NPT and GSH slowly increased, and PCs showed no significant difference in the organelle of C. rupestris at low concentrations (< 5.0 mg/L). PCs slightly increased under 5.0 mg/L of Pb stress. PCs/NPT gradually increased with Pb stress at a low Pb concentration. GSH detoxification response lagged behind those of NPT and PCs in response to time. PCs/NPT initially increased and then decreased with Pb stress duration. This study suggested that NPT, GSH, and PCs played an important role in the detoxification of the cell wall and the soluble fraction of C. rupestris under Pb stress. PCs were important in the organelle.

The remediation potential and kinetics of cadmium in the green alga Cladophora rupestris.

This study determined the subcellular distribution, chemical forms, and effects of metal homeostasis of excess Cd in Cladophora rupestris. Biosorption data were analyzed with Langmuir and Freundlich adsorption models and kinetic equations. Results showed that C. rupestris can accumulate Cd. Cd mainly localized in the cell wall and debris (42.8-68.2%) of C. rupestris, followed by the soluble fraction (22.1-38.4%) observed in C. rupestris. A large quantity of Cd ions existed as insoluble CdHPO4 complexed with organic acids, Cd(H2PO4)2, Cd-phosphate complexes (FHAC) (43.2-56.0%), and pectate and protein-integrated Cd (FNaCl) (30.8-43.2%). The adsorption data were well fitted by the Freundlich model (R2 = 0.933) and could be described by the pseudo-second-order reaction rate (R2 = 0.997) and Elovich (R2 = 0.972) equations. Related parameters indicated that Cd adsorption by C. rupestris is a heterogeneous diffusion. Cd promoted Ca and Zn uptake by C. rupestris. Cu, Fe, Mn, and Mg adsorption was promoted by low Cd concentrations and inhibited by high Cd concentrations. Results suggested that cell wall sequestration, vacuolar compartmentalization, and chemical morphological transformation are important mechanisms of Cd stress tolerance by C. rupestris. This study suggests that C. rupestris has bioremediation potential of Cd.

Biodegradation of triphenylmethane dye crystal violet by Cedecea davisae.

The present study focuses on the biodegradation of triphenylmethane dye crystal violet (CV) by Cedecea davisae. The degradation of CV was evaluated via ultraviolet absorbance at 254 nm (UV254) and chemical oxygen demand (COD) removal, and the kinetics was used to evaluate the degradation efficiency. Intermediate products were analyzed via UV-vis spectroscopy (UV), Fourier transform infrared spectroscopy (FTIR), and high-performance liquid chromatography (HPLC). Results showed that C. davisae was able to decolorize the CV, and the maximum decolorization ratio reached 97%. COD reduction was observed after decolorization, with average removal rates of >90% after 48 h. Moreover, 50% of UV254 can be removed after 14 h. The removal efficiency of CV by C. davisae followed first- and second-order reaction kinetics at temperature ranged from 20 °C to 40 °C and pH 4.0 to 6.0, respectively. By using UV, the peak representing the CV disappeared 14 h after CV decolorization, and the degradation of aromatic and naphthalene rings was attributed to the formation of a new metabolite. The FTIR spectra of metabolites showed that a new functional group of OH, CH, CH2, CH3, NH, CN, CN, or CO was produced. The chromatograms of HPLC recorded at 589 nm at retention time decreased and were not detected following incubation for 8 h by C. davisae.

Absorption and subcellular distribution of cadmium in tea plant (Camellia sinensis cv. "Shuchazao").

A hydroponic experiment was performed to investigate the Cd absorption and subcellular distribution in tea plant, Camellia sinensis. Increased Cd accumulation potential was observed in the tea plant in a Cd-enriched environment, but most of the Cd was absorbed by the roots of C. sinensis. The Cd in all the root fractions was mostly distributed in the soluble fraction, followed by the cell wall fraction. By contrast, the Cd was least distributed in the organelle fraction. The adsorption of Cd onto the C. sinensis roots was described well by the Langmuir isotherm model than the Freundlich isotherm. Most of the Cd (38.6 to 59.4%) was integrated with pectates and proteins in the roots and leaves. Fourier transform infrared spectroscopy (FTIR) analysis showed that small molecular organic substances, such as amino acids, organic acids, and carbohydrates with N-H, C=O, C-N, and O-H functional groups in the roots, bonded with Cd(II). The Cd accumulation in the C. sinensis leaves occurred in the cell wall and organelle fractions. C. sinensis has great capability to transport Cd, thereby indicating pollution risk. The metal homeostasis of Fe, Mn, Ca, and Mg in C. sinensis was affected when the Cd concentration was 1.0-15.0 mg/L.

Effect of solid-state NaOH pretreatment on methane production from thermophilic semi-dry anaerobic digestion of rose stalk.

The effects of solid-state NaOH pretreatment on the efficiency of methane production from semi-dry anaerobic digestion of rose (Rosa rugosa) stalk were investigated at various NaOH loadings (0, 1, 2, and 4% (w/w)). Methane production, process stability and energy balance were analyzed. Results showed that solid-state NaOH pretreatment significantly improved biogas and methane yields of 30-day anaerobic digestion, with increases from 143.7 mL/g volatile solids (VS) added to 157.1 mL/g VS -192.1 mL/g VS added and from 81.8 mL/g VS added to 88.8 mL/g VS-117.7 mL/g VS added, respectively. Solid-state NaOH pretreatment resulted in anaerobic digestion with higher VS reduction and lower technical digestion time. The 4% NaOH-treated group had the highest methane yield of 117.7 mL/g VS added, which was 144% higher compared to the no NaOH-treated group, and the highest net energy recovery. Higher rate of lignocellulose breakage and higher process stability of anaerobic digestion facilitated methane production in the NaOH-pretreated groups.

Effects of cadmium on bioaccumulation and biochemical stress response in rice (Oryza sativa L.).

This study investigated the effects of various Cd concentrations on the bioaccumulation, antioxidative defense, and stress responses of rice (Oryza sativa L.). The distribution characteristics of Cd in rice were in the following order: roots>stems>grains. The bioconcentration factor values of Cd increased at concentrations lower than 3.00 mg Cd/kg and approximately decreased to a constant value at concentrations higher than 3.00 mg Cd/kg. Rice showed a higher Cd accumulation potential at low Cd concentrations than at high Cd concentrations. The Freundlich isotherm model described well the adsorption isotherms of Cd in rice roots. The biosorption mechanism of rice roots was determined to be cooperative adsorption. The malondialdehyde (MDA) content increased at a concentration range of 0.00-5.00 mg/L, indicating the enhancement of lipid peroxidation. By contrast, the MDA content slightly decreased at concentrations higher than 5.00 mg/L. Peroxidase (POD) activity exhibited active response to oxidative stress at concentrations lower than 5.00 mg/L but was inhibited at concentrations higher than 5.00 mg/L. The response to Cd stress of the N-H, O-H and C-O functional groups in rice shoots was observed via Fourier transform infrared spectroscopy.

Effects of Cu(2+) and Zn(2+) on growth and physiological characteristics of green algae, Cladophora.

Effects of various concentrations of Cu(2+) and Zn(2+) (0.0, 0.1, 0.25, 0.5, or 1.0 mg/L) on the growth, malondialdehyde (MDA), the intracellular calcium, and physiological characteristics of green algae, Cladophora, were investigated. Low Zn(2+) concentrations accelerated the growth of Cladophora, whereas Zn(2+) concentration increases to 0.25 mg/L inhibited its growth. Cu(2+) greatly influences Cladophora growth. The photosynthesis of Cladophora decreased under Zn(2+) and Cu(2+) stress. Cu(2+) and Zn(2+) treatment affected the content of total soluble sugar in Cladophora and has small increases in its protein content. Zn(2+) induced the intracellular calcium release, and copper induced the intracellular calcium increases in Cladophora. Exposure to Cu(2+) and Zn(2+) induces MDA in Cladophora. The stress concent of Cu(2+) was strictly correlated with the total soluble sugar content, Chla+Chlb, and MDA in Cladophora, and the stress concent of Zn(2+) was strictly correlated with the relative growth rate (RGR) and MDA of Cladophora.

Effects of lead on tolerance, bioaccumulation, and antioxidative defense system of green algae, Cladophora.

Effects of various concentrations (0.5, 1.0, 2.5, 5.0, 7.5, and 10.0 mg/L) of lead (Pb(2+)) on the growth, bioaccumulation, and antioxidative defense system of green algae, Cladophora, was investigated. Low concentrations of Pb(2+) accelerated Cladophora growth, but concentrations of 10.0 mg/L and above inhibited the growth because of the hinderance to photosynthesis. The total soluble sugar content of Cladophora was affected by Pb(2+) treatment, but the protein content showed no significant changes. The malondialdehyde (MDA) content and peroxidase(POD) activity of Cladophora gradually increased whereas superoxide dismutase(SOD) decreased with Pb(2+) concentrations. Catalase (CAT) activity exhibited no significant changes following Pb(2+) treatment. Pb(2+) accumulated in Cladophora and that the lead content in Cladophora was correlated with POD growth, MDA, and Metallothionein (MT). POD and MT play a role in the survival of Cladophora in Pb-contaminated environments. This study suggests that Cladophora can be a choice organism for the phytoremediation of Pb-polluted coastal areas.