Isolation of hexavalent chromium resistant bacteria from industrial saline effluents and their ability of bioaccumulation

The mixed cultures has been isolated from industrial saline wastewater contaminated with chromium(VI), using enrichment in the presence of 50 mg l⁻¹ chromium(VI) and 4% (w/v) NaCl at pH 8. In this study, the molasses (M) medium was selected a suitable medium for the effective chromium bioaccumulation by the mixed cultures. Eleven pure isolates obtained from mixed cultures and some of them showed high bioaccumulation in the M media containing about 100 mg l⁻¹ chromium(VI) and 4% NaCl. The strain 8 (99.3%) and 10 (99.1%) were able to bioaccumulate more efficient than the mixed culture (98.9%) in this media. But the highest specific Cr uptake was obtained by the mixed cultures followed by strain 8 and 10 with 56.71, 33.14 and 21.7 mg g⁻¹, respectively. Bioaccumulation of chromium(VI) ions by the strain 8 growing in the media with chromium(VI) and NaCl was studied in a batch system as a function of initial chromium(VI) (86.6–547.6 mg l⁻¹) and NaCl (0, 2, 4, 6% w/v) concentrations. During all the experiments, the uptake yield of the strain 8 was highly affected from NaCl concentrations in the medium at high initial chromium(VI) concentrations. But at low chromium(VI) concentration, strain 8 was not affected from NaCl concentrations in the medium. The maximum uptake yield were obtained in the M media with 2% NaCl as 98.8% for 110.0 mg l⁻¹, 98.6% for 217.1 mg l⁻¹, 98.6% for 381.7 mg l⁻¹ and 98.2% for 547.6 mg l⁻¹ initial chromium(VI) concentrations. The strain 8 tolerated a 6% (w/v) NaCl concentration was able to bioaccumulate more than 95% of the applied chromium(VI) at the 97.6–224.4 mg l⁻¹ initial chromium(VI) concentrations. The results presented in this paper was shown that these pure and mixed cultures might be of use for the bioaccumulation of chromium(VI) from saline wastewater.     

Predictive expressions of growth and Remazol Turquoise Blue-G reactive dye bioaccumulation properties of Candida utilis

The combined effects of initial sucrose and initial Remazol Turquoise Blue-G (RTBG) reactive dye concentrations on the specific growth rate and dye bioaccumulation efficiency of Candida utilis was investigated and optimized using response surface methodology (RSM) in this study. A 2² full factorial central composite design was successfully used for experimental design and analyses of the results. Two numerical correlations fitted to a second-order quadratic equation were obtained to estimate the responses of specific growth rate and dye uptake yield. The statistical analysis indicated that both the microbial growth and removal yield of dye enhanced with raising sucrose concentration up to 15 g l^?1 and diminished with the increase in initial RTBG dye concentration up to approximately 500 mg l^?1 due to inhibition caused by high concentrations of RTBG dye. The optimum combination predicted via RSM confirmed that C. utilis was capable of bioaccumulating RTBG with the maximum uptake yield of 82.0% in 15 g l^?1 sucrose and 50 mg l^?1 dye containing growth medium.     

Treatment of dye-rich wastewater by an immobilized thermophilic cyanobacterial strain: Phormidium sp.

The removal of Remazol Blue and Reactive Black B by the immobilized thermophilic cyanobacterial strain Phormidium sp. was investigated under thermophilic conditions in a batch system, in order to determine the optimal conditions required for the highest dye removal. In the experiments, performed at pH 8.5, with different initial dye concentrations between 9.1 mg l⁻¹ and 82.1 mg l⁻¹ and at 45 °C, calcium alginate immobilized Phormidium sp. showed high dye decolorization, with maximum uptake yields ranging from 50% to 88% at all dye concentrations tested. When the effects of high dye concentrations on dye removal were investigated, the highest uptake yield in the beads was 50.3% for 82.1 mg l⁻¹ Remazol Blue and 60.0% for 79.5 mg l⁻¹ Reactive Black B. The highest color removal was detected at 45 °C and 50 °C incubation temperatures for all dye concentrations. As the temperature decreased, the removal yield of immobilized Phormidium sp. also decreased. At about 75 mg l⁻¹ initial dye concentrations, the highest specific dye uptake measured was 41.29–41.17 mg g⁻¹ for Remazol Blue and 47.69–43.82 mg g⁻¹ for Reactive Black B at 45 °C and 50 °C incubation temperatures, respectively, after 8 days incubation.     

Chromate reduction by resting cells of Achromobacter sp. Ch-1 under aerobic conditions

Chromate reduction was carried out by resting cells of Achromobacter sp. Ch-1 with lactate as electron donor under aerobic conditions. The reduction activity of the samples supplemented with lactate was two times as those without lactate. The reduction rate was influenced by initial pH and lactate concentration. Under the optimal conditions, pH 9.0 and 4000 mg l⁻¹ lactate supplement, reduction rate was 5.45 mg l⁻¹ min⁻¹. The reduction rate decreased with increasing of Cr(VI) concentrations and increased with cell densities proportionally. The maximum reduction limit of Ch-1 cells was obtained at 2107 mg l⁻¹ of Cr(VI).     

Continuous Cr(VI) removal by Scenedesmus incrassatulus in an airlift photobioreactor

Cr(VI) removal by Scenedesmus incrassatulus was characterized in a continuous culture system using a split-cylinder internal-loop airlift photobioreactor fed continuously with a synthetic effluent containing 1.0 mg Cr(VI) l^?1 at dilution rate (D) of 0.3 d^?1. At steady state, there was a small increase (6%) on the dry biomass (DB) concentration of Cr(VI)-treated cultures compared with the control culture. 1.0 mg Cr(VI) l^?1 reduced the photosynthetic pigments content and altered the cellular morphology, the gain in dry weight was not affected. At steady state, Cr(VI) removal efficiency was 43.5 ± 1.0% and Cr(VI) uptake was 1.7 ± 0.1 mg Cr(VI) g^?1 DB. The system reached a specific metal removal rate of 458 μg Cr(VI) g^?1 DB d^?1, and a volumetric removal rate of 132 μg Cr(VI) l^?1 d^?1.     

Nitrogen transformation in the hybrid bioreactor landfill

The hybrid bioreactor landfill was promising in solid waste management. In the work, the nitrogen removal and nitrogen transformation in hybrid bioreactor landfill with sequencing of facultative anaerobic and aerobic conditions was explored. The result showed that the combination of facultative anaerobic and aerobic conditions in the hybrid bioreactor landfill was indeed effective in eliminating ammonia both from the leachate and the refuse thoroughly. About 72% of nitrogen was reduced from the landfilled fresh refuse through the operation of 357 days. At the end of the experiment, the concentrations of COD, ammonia, nitrate and TN in the leachate decreased to 399.2 mg l^?1, 20.6 mg N l^?1, 3.7 mg N l^?1 and 25.3 mg N l^?1, respectively.     

Comparative efficiency of algal biofilters in the removal of chromium and copper from wastewater

The performance of a macroalgae (Sargassum sp.), a laboratory-cultivated microalgae (Chlorococcum sp.) and a commercially available granulated activated carbon (GAC) for the removal of copper (Cu) and chromium (Cr) from aqueous solutions was evaluated using batch experiments. Kinetic and isotherm experiments were done at the optimal pH of 4.5 ± 0.1 for Cu (II) and 2.0 ± 0.1 for Cr (total). The equilibrium isotherms were determined and the results were analyzed using the Langmuir and Freundlich models. The best Cu removal performance was observed on Sargassum at a maximum removal of 87.3% obtained for an initial concentration of 20 mg L^?1 Cu. The maximum uptake capacities for Cu (II) were 71.4, 19.3 and 11.4 mg g^?1 of Sargassum, Chlorococcum and GAC, respectively. The biosorbents were also able to remove appreciable amounts of Cr, again with Sargassum showing maximum uptake capacity over the other materials. Kinetic studies also reveal that the removal rate is faster for both metals in Sargassum. Tests with an actual wastewater confirm the maximum uptake capacity of Cu by Sargassum. In all experiments the Sargassum biofilter outperformed GAC, which makes it a promising low-cost alternative to conventional filtration materials for wastewater treatment.     

Bacterial decolorization and degradation of the reactive dye Reactive Red 180 by Citrobacter sp. CK3

A bacterial strain, CK3, with remarkable ability to decolorize the reactive textile dye Reactive Red 180, was isolated from the activated sludge collected from a textile mill. Phenotypic characterization and phylogenetic analysis of the 16S rDNA sequence indicated that the bacterial strain belonged to the genus Citrobacter. Bacterial isolate CK3 showed a strong ability to decolorize various reactive textile dyes, including both azo and anthraquinone dyes. Anaerobic conditions with 4 g l^?1 glucose, pH = 7.0 and 32 °C were considered to be the optimum decolorizing conditions. Citrobacter sp. CK3 grew well in a high concentration of dye (200 mg l^?1), resulting in approximately 95% decolorization extent in 36 h, and could tolerate up to 1000 mg l^?1 of dye. UV–vis analyses and colorless bacterial cells suggested that Citrobacter sp. CK3 exhibited decolorizing activity through biodegradation, rather than inactive surface adsorption. It is the first time that a bacterial strain of Citrobacter sp. has been reported with decolorizing ability against both azo and anthraquinone dyes. High decolorization extent and facile conditions show the potential for this bacterial strain to be used in the biological treatment of dyeing mill effluents.     

Hexavalent chromium removal from aqueous solution by adsorption on treated sawdust

The studies on adsorption of hexavalent chromium were conducted by varying various parameters such as contact time, pH, amount of adsorbent, concentration of adsorbate and temperature. The kinetics of adsorption of Cr(VI) ion followed pseudo second order. Langmuir adsorption isotherm was employed in order to evaluate the optimum adsorption capacity of the adsorbent. The adsorption capacity was found to be pH dependant. Sawdust was found to be very effective and reached equilibrium in 3 h (adsorbate concentration 30 mg l⁻¹). The rate constant has been calculated at 303, 308, 313 and 318 K and the activation energy (E_a) was calculated using the Arrhenius equation. Thermodynamic parameters such as standard Gibbs energy (ΔG°) and heat of adsorption (ΔH_r) were calculated. The ΔG° and ΔH_r values for Cr(VI) adsorption on the sawdust showed the process to be exothermic in nature. The percentage of adsorption increased with decrease in pH and showed maximum removal of Cr(VI) in the pH range 4.5–6.5 for an initial concentration of 5 mg l⁻¹.     

Nitrification rates of algal–bacterial biofilms in wastewater stabilization ponds under light and dark conditions

The objective of this study was to investigate nitrification rates in algal–bacterial biofilms of waste stabilization ponds (WSP) under different conditions of light, oxygen and pH. Biofilms were grown on wooden plates of 6.0 cm by 8.0 cm by 0.4 cm in a PVC tray continuously fed with synthetic wastewater with initial NH₄-N and Chemical Oxygen Demand (COD) concentrations of 40 mg l^?1 and 100 mg l^?1, respectively, under light intensity of 85–95 μE m^?2 s^?1. Batch activity tests were carried out by exposure of the plates to light conditions as above (to simulate day time), dim light of 1.8–2.2 μE m^?2 s^?1 (to simulate reduced light as in deeper locations in WSP) and dark conditions (to simulate night time). Dissolved oxygen (DO) concentration and pH were controlled. At some experiments, both parameters were kept constant, and at others they were left to vary as in WSP. Results show biofilm nitrification rates of 945–1817 mg-N m^?2 d^?1 and 1124–1615 mg-N m^?2 d^?1 for light and dark experiments. When the minimum DO was 4.1 mg l^?1, the biofilm nitrification rates under light and dark conditions did not differ significantly at 95% confidence. When the minimum DO in the dim light experiment was 3.2 mg l^?1, the nitrification rates under light and dim light conditions were 945 mg-N m^?2 d^?1 and 563 mg-N m^?2 d^?1 and these significantly differed. Further decrease of DO to 1.1 mg l^?1 under dark conditions resulted in more decrease of the nitrification rates to 156 mg-N m^?2 d^?1. It therefore seems that under these experimental conditions, biofilm nitrification rates are significantly reduced at a certain point when bulk water DO is between 3.2 mg l^?1 and 4.1 mg l^?1. As long as bulk water DO under dark is high, light is not important in influencing the process of nitrification.     

Decolorization of Reactive Red 195 by a mixed culture in an alternating anaerobic–aerobic Sequencing Batch Reactor

The mono-azo dye Reactive Red 195 (RR 195) is a widely used color compound in the textile industry. As many other colors, it is persistent and difficult to be removed from water with conventional processes. The present study investigates biological decolorization of RR 195 under alternate anaerobic–aerobic conditions in a laboratory scale Sequencing Batch Reactor (SBR) containing a mixed culture and fed with a biodegradable carbon source. Different values of the Sludge Retention Time (SRT), Hydraulic Retention Time (HRT), influent color and organic carbon loadings were adopted during the experimental activity and their effects on color and Chemical Oxygen Demand (COD) removal efficiencies and process kinetics determined. The optimal operating conditions were found to be: 800 mg l⁻¹ influent COD, 50 d SRT and a 24 h-cycle. Under these conditions, the maximum color efficiency of 97% was achieved for a 40 mg l⁻¹ RR 195 in the feed. Some inhibition was present at influent color loadings above 40 mg l⁻¹, which was confirmed by the application of the Haldane model.     

Phosphogypsum biotransformation in cultures of sulphate reducing bacteria in whey

Assemblages of anaerobic sulphidogenic microorganisms were isolated from soil polluted by oil-derived products and grown using the microcosms method. The cultures were grown in minimal and Postgate media with phosphogypsum (PG) as the sole electron acceptor and with lactate, casein or lactose as the sole carbon source. The most effective was the assemblage in Postgate medium with lactose as the sole carbon source. A reduction of 980 mg COD l^?1 (reduction of about 40%) and 790 mg SO₄^2? l^?1 (reduction of 53% of phosphogypsum introduced to the medium) was noted in the culture. The lowest activity was observed for minimal medium with lactose as sole carbon source (reduction of 4.4% COD and 40% PG). The selected assemblage became an inoculum for a culture in Postgate, minimal and/or distilled water medium with PG (6 g l^?1) and cheese whey (2.5 and 4.5 g l^?1).A percentage reduction of COD and SO₄^2? of PG was observed in all cultures. After growth, the residues were weighed and in all cases a distinct mass reduction of PG was observed in comparison to the 6 g l^?1 introduced to the medium. Diffractometric studies of the residues confirmed the presence of calcite and apatite. The presence of these mineral phases in the residues allows their application as agricultural fertilisers.     

Multiple regeneration pathways in Spathoglottis plicata Blume — A study in vitro

Asymbiotic germination of immature seeds (embryos), and mature seeds and micropropagation of Spathoglottis plicata were described. Effects of three nutrition media namely, Murashige & Skoog (MS); Phytamax (PM); and Phyto-Technology orchid seed sowing medium (P₇₂₃), two carbon sources such as glucose and sucrose at 2–3% (w/v), two plant growth regulators such as 6-benzylaminopurine (BAP; 0.5–3.0 mg l^− 1) and α-naphthalene acetic acid (NAA; 0.5–2.0 mg l^− 1) and peptone (2.0 g l^− 1) were examined on seed germination, early protocorm development and micropropagation. The maximum germination of mature seeds (95%) was recorded in PM medium supplemented with 2% (w/v) sucrose + 2.0 g l^− 1 peptone. For germination of embryos P₇₂₃ medium supplemented with 1.0 mg l^− 1 BAP proved best. Multiple shoot buds or protocorm-like bodies (PLBs) were produced from stem segments of in vitro raised seedlings. Both direct organogenesis and embryogenesis were observed and the morphogenetic response was initiated by different concentrations and combinations of PGRs. The optimum PGR combination for maximal PLB regeneration was 1.0 mg l^− 1 NAA + 2.5 mg l^− 1 BAP, while 1.0 mg l^− 1 NAA + 1.0 mg l^− 1 BAP for shoot bud development. Strong and stout root system was induced in half strength PM medium supplemented with 0.5 mg l^− 1 IAA. The well-rooted plantlets were transferred to pots containing a potting mixture composed of saw dust, coconut coir, humus, and coal pieces at 1:1:1:2 (w/w) with 80% survival in outside environment and flowered after two years of transfer.     

Effects of nitrobenzene concentration and hydraulic retention time on the treatment of nitrobenzene in sequential anaerobic baffled reactor (ABR)/continuously stirred tank reactor (CSTR) system

The effects of increasing nitrobenzene (NB) concentrations and hydraulic retention times (HRT) on the treatment of NB were investigated in a sequential anaerobic baffled reactor (ABR)/aerobic completely stirred tank reactor (CSTR) system. In the first step of the study, the maximum COD removal efficiencies were found as 88% and 92% at NB concentrations varying between 30 mg L^?1 and 210 mg L^?1 in ABR. The minimum COD removal efficiency was 79% at a NB concentration of 700 mg L^?1. The removal efficiency of NB was nearly 100% for all NB concentrations in the ABR reactor. The methane gas production and the methane gas percentage remained stable (1500 mL day^?1 and 48–50%, respectively) as the NB concentration was increased from 30 to 210 mg L^?1. In the second step of the study it was found that as the HRT decreased from 10.38 days to 2.5 days the COD removal efficiencies decreased slightly from 94% to 92% in the ABR. For maximum COD and NB removal efficiencies the optimum HRT was found as 2.5 days in the ABR. The total COD removal efficiency was 95% in sequential anaerobic (ABR)/aerobic (CSTR) reactor system at a minimum HRT of 1 day. When the HRT was decreased from 10.38 days to 1 day, the methane percentage decreased from 42% to 29% in an ABR reactor treating 100 mg L^?1 NB. Nitrobenzene was reduced to aniline under anaerobic conditions while aniline was mineralized to catechol with meta cleavage under aerobic conditions.     

Subcellular distribution and chemical forms of cadmium in Bechmeria nivea (L.) Gaud.

Bechmeria nivea (L.) Gaud. (Ramie) is a promising species for Cd phytoextraction with large biomass and fast growth rate. Nevertheless, little information is available on its tolerance mechanisms towards Cd. Determination of Cd distribution and chemical speciation in ramie is essential for understanding the mechanisms involved in Cd accumulation, transportation and detoxification. In the present study, ramie plants were grown in hydroponics with increasing Cd concentrations (0, 1, 3, 7 mg l^?1). The subcellular distribution and chemical forms of Cd in different tissues were determined after 20 days exposure to this metal. To assess the effect of Cd uptake on plant performance, nitrate reductase activity in leaves and root activity were analyzed during the entire experimental period. Increased Cd level in the medium caused a proportional increase in Cd uptake, and the highest Cd concentration occurred in roots, followed by stems and leaves. Subcellular fractionation of Cd-containing tissues indicated that about 48.2–61.9% of the element was localized in cell walls and 30.2–38.1% in soluble fraction, and the lowest in cellular organelles. Cd taken up by ramie rapidly equilibrated among different chemical forms. Results showed that the greatest amount of Cd was found in the extraction of 1 M NaCl and 2% HAC, and the least in residues in all test tissues. In roots, the subdominant amount of Cd was extracted by d-H₂O and 80% ethanol, followed by 0.6 M HCl. While in stems and leaves, the amount of 0.6 M HCl-extractable Cd was comparable with that extracted by 80% ethanol or d-H₂O. 1 mg l^?1 Cd stimulated nitrate reductase activity in leaves and root activity, while a concentration-dependent inhibitory effect was observed with increasing Cd concentration, particularly at 7 mg l^?1 Cd. It could be suggested that the protective mechanisms evolved by ramie play an important role in Cd detoxification at relatively low Cd concentrations (below 3 mg l^?1 Cd) but become restricted to maintain internal homeostasis with higher Cd stress.     

Assessment of Lemna gibba L. (duckweed) as a potential ecological indicator for contaminated aquatic ecosystem by boron mine effluent

Duckweeds, as a group, are important early warning indicators for the assessment of contaminated ecosystems due to their propensity to accumulate pollutants. In the present study, we investigated the potential use of Lemna gibba L. (Lemnaceae) as an ecological indicator for boron (B) mine effluent containing B concentration above 10 mg l⁻¹. For this purpose, L. gibba fronds were grown for 7 days in simulated water contaminated with B mine effluent. The important note is that this study was carried out in Kırka (Eskişehir, Turkey) B reserve area, which is the largest borax reserve in all over the world, under natural climatic conditions in the field. The results demonstrated that accumulations of B by L. gibba gradually increased based on the initial B concentrations (10, 25, 50, 100, and 150 mg l⁻¹) of the mine effluent. B concentration in the dry weight of the plant reached 639 mg kg⁻¹ when the minimum initial dosage (10 mg l⁻¹) was applied and 2711 mg kg⁻¹ when the maximum initial dosage (150 mg l⁻¹) was applied during the study. However, significant reductions in their relative growth rates occurred in 50, 100 and 150 mg l⁻¹ initial B concentrations. Results suggest that 25 mg l⁻¹ B concentration in water seemed to be a sensitive endpoint for L. gibba that could be used as a critical bioindicator level of B contaminated water. Following our data, we also constructed a simple growth model under the climatic conditions in this region of Turkey, but in instructive as a worldwide model. L. gibba is, therefore, suggested to be able to use as both an indicator and a phytoremediation tool because of its high accumulation capacity for B contaminated water.     

Protocorm culture of Dendrobium candidum in balloon type bubble bioreactors

Protocorm cultures of Dendrobium candidum were established in balloon type bubble bioreactors using Murashige and Skoog (MS) medium with 0.5 mg l⁻¹ α-naphthaleneacetic acid (NAA), 2.5% (w/v) sucrose, 5:25 mM NH₄:NO₃ and 1% (v/v) banana homogenate for the production of biomass and bioactive compounds. In 3 l bioreactor containing 2 l medium, a maximum protocorm biomass (21.0 g l⁻¹ dry biomass) and also optimum quantities of total polysaccharides (389.3 mg g⁻¹ DW), coumarins (18.0 mg g⁻¹ DW), polyphenolics (11.9 mg g⁻¹ DW), and flavonoids (4.5 mg g⁻¹ DW) were achieved after 7 weeks of culture. Based on these studies, 5 and 10 l bioreactor cultures were established to harvest 80 g and 160 g dry biomass. In 10 l bioreactors, the protocorms grown were accumulated with optimal levels of polysaccharides (424.1 mg g⁻¹ DW), coumarins (15.8 mg g⁻¹ DW), polyphenols (9.03 mg g⁻¹ DW) and flavonoids (4.7 mg g⁻¹ DW). The bioreactor technology developed here will be useful for the production of important bioactive compounds from D. candidum.     

Decolorization of azo dye by immobilized Pseudomonas luteola entrapped in alginate–silicate sol–gel beads

Pseudomonas luteola was immobilized by entrapment in alginate–silicate sol–gel beads for decolorization of the azo dye, Reactive Red 22. The influences of biomass loading and operating conditions on specific decolorization rate and dye removal efficiency were studied in details. The immobilized cells were found to be less sensitive to changes in agitation rates (dissolved oxygen levels) and pH values. Michaelis–Menten kinetics could be used to describe the decolorization kinetics with the kinetic parameters being 36.5 mg g⁻¹ h⁻¹, 300.1 mg l⁻¹ and 18.2 mg g⁻¹ h⁻¹, 449.8 mg l⁻¹ for free and immobilized cells, respectively. After five repeated batch cycles, the decolorization rate of the free cells decreased by nearly 54%, while immobilized cells still retained 82% of their original activity. The immobilized cells exhibited better thermal stability during storage and reaction when compared with free cells. From SEM observation, a dense silicate gel layer was found to surround the macroporous alginate–silicate core, which resulted in much improved mechanical stability over that of alginate beads when tested under shaking conditions. Alginate–silicate matrices appeared to be the best matrix for immobilization of P. luteola in decolorization of Reactive Red 22 when compared with previous results using synthetic or natural polymer matrices.     

Potential of Typha angustifolia for phytoremediation of heavy metals from aqueous solution of phenol and melanoidin

Typha angustifolia was evaluated for various heavy metals (Cu, Pb, Ni, Fe, Mn, and Zn) bioremediation potential from aqueous solution containing variable concentrations of phenol (100–800 mg l^?1) and melanoidin (2500–8500 Co–Pt) at 20, 40, and 60 days. The concentration of phenol (200–400 mg l^?1) along with melanoidin 2500 Co–Pt showed optimum for phytoremediation of tested heavy metals, while, higher concentrations of melanoidin (5600–8500 Co–Pt) showed toxic effect on T. angustifolia along with phenol. Phenol and melanoidin showed adverse effect on T. angustifolia of up to 20 days incubation, but this leads to induction of peroxidase and ascorbic acid activity to cope with adverse conditions. Subsequently, as pollutants were decreased along with plant growth, peroxidase and ascorbic acid also declined. However, with reduction of peroxidase, catalase level was increased. The Cu, Zn, and Ni were accumulated at maximum in all tested conditions. The TEM observations of T. angustifolia showed clotted deposition of metals and shrinkage of cell in root, breakdown of spongy and palisade parenchyma of leaves at higher concentration of phenol (100 mg l^?1) and melanoidin (5500 Co–Pt). Thus, this study concluded that T. angustifolia could be a potential phytoremediator for heavy metals from metal, melanoidin, and phenol containing industrial wastewater at optimized condition.     

Response of miscanthus to toxic cadmium applications during the period of maximum growth

Plants of miscanthus were grown in a Cd-free solution up to 1 month before heading and then were exposed to 0, 0.75, 1.5, 2.25 and 3 mg l⁻¹ cadmium for 36 days. All cadmium levels were toxic to miscanthus. Growth response was not dose-dependent and two toxicity thresholds were identified: one between 0 and 0.75 mg l⁻¹ Cd, the other between 2.25 and 3 mg l⁻¹ Cd. The former caused a biomass decrease by about 50%, whereas the latter completely inhibited growth and disrupted the mechanisms that restricted Cd translocation to the shoot. Growth of the aerial part was affected by cadmium more than that of the hypogeal one. Cadmium did not change the N concentration of different plant parts, but markedly reduced the N uptake of the plant, the N net uptake rate (NUR) and the N net translocation rate (NTR) from the rhizome to the aerial part. These two indexes equalled zero when plants ceased to grow. Otherwise, the Cd-NUR increased with Cd supply and the Cd-NTR from rhizome to aerial part showed the highest increment when plants did not grow at all. This suggests different uptake pathways for the two elements, active for nitrogen and passive for cadmium. The Cd concentration and the Cd content markedly increased with all Cd levels, following the order roots ≫ rhizome > culms > leaves. The Cd concentration and the Cd content of aerial organs increased with Cd supply, but increments were highest between 2.25 and 3 mg l⁻¹ Cd. The highest Cd concentrations were recorded in plants grown with 3 mg l⁻¹ Cd and were 41 and 122 mg kg⁻¹, respectively, for the aerial and the hypogeal plant parts. The hypogeal plant part retained most of the cadmium taken up from solution, accounting for approximately 87% of total plant cadmium with the three lower Cd levels, and for 73% with the highest one. The maximum Cd content of the entire plant was achieved with the two higher Cd levels and was approximately 4.7 mg, while the Cd content of the aerial part was highest with 3 mg l⁻¹ Cd (1.2 mg Cd per plant) and that of the hypogeal one with 2.25 mg l⁻¹ Cd (4 mg Cd per plant). The highest aerial content achieved in this experiment was 10-fold that obtained in a previous research when small-sized plants were exposed to the same Cd level.