Monitoring toxicity of an azo dye methyl red and a heavy metal Cu,using plant and animal bioassays

Toxicities of an azo dye methyl red and a heavy metal copper (Cu) were quantified, using growth and mortality as end points, in four plant species and three animal species by subjecting them to short-term (4 days for animals, 10 days for plants) static bioassays. Lemna aequinoctialis Welwitch (EC₅₀: 7–16 ppm) was found to be the most sensitive species for methyl red, Ceratophyllum demersum L. (EC₅₀: 25 ppm) and Lactuca sativa L. (EC₅₀: 56 ppm) were intermediate, while Oryza sativa L. shows reduction in seedling vigor (9–27%) of <50%, being the least sensitive amongst the tested plant species. Methyl red toxicity is almost 3–5-fold higher in growing medium (pH = 5.8–6.0), even at high nutrient levels, while Cu toxicity is higher in nutrient-poor alkaline medium at alkaline pH (8.3–8.7; EC₅₀: Ceratophyllum = 104–200 ppb; Lemna = 100–170 ppb) compared to nutrient-rich acidic medium (pH = 5.4–5.7; EC₅₀: Ceratophyllum = 2600–3175 ppb; Lemna = 4350–4715 ppb). Rice tolerance (EC₅₀: 6500 ppb) was found to be higher than hydrophytes while lettuce was most tolerant to Cu. Fish sensitivity toward the test chemicals was almost parallel to Ceratophyllum and Lemna [Gambusia affinis Baird and Gerard (LC₅₀: 250 ppb for Cu) and Poecilia reticulata Peters (LC₅₀: 24 ppm for methyl red)]. Similar to the plants, dye toxicity increased markedly (LC₅₀: 7 ppm) in the acidic medium (pH = 6.0). Amongst the tested organisms, Daphnia was found to be most sensitive to methyl red (EC₅₀: 6 ppm) while its sensitivity to Cu (EC₅₀: 230 ppb) was similar to hydrophytes and fish. Initially, the combination of dye and Cu (at their sublethal concentrations) had additive effects in duckweed, while dye concentration ruled afterward. These results indicate that hydrophytes and animals are equally sensitive toward the test chemicals. Dye toxicity in hydrophytes and fish was pH dependent, while in the case of Cu, it is related to the nutrient status of the growth medium of plants.     

Removal of Cr(VI) from aqueous solution using waste weed, Salvinia cucullata

Biosorption studies of Cr(VI) were carried out using waste weed, Salvinia cucullata. Various adsorption parameters were studied, such as agitation speed, contact time, pH, particle size, and concentrations of adsorbent and adsorbate. The equilibrium was achieved in 12 h. A lower pH favoured adsorption of Cr(VI). The kinetics followed pseudo-second-order rate equations. The adsorption isotherm obeyed both the Langmuir and Freundlich models. The calculated activation energy (1.1 kJ mol^-1) suggested that the adsorption followed a diffusion-controlled mechanism. Various thermodynamic parameters such as Δ G^°, Δ H^°, and Δ S^° were also calculated. The positive values of enthalpy indicated the endothermic nature of the reaction, and Δ S^° showed the increasing randomness at the solid liquid interface of Cr(VI) on the adsorbent, which revealed the ease of adsorption reaction. These thermo-dynamic parameters showed the spontaneity of the reaction. The maximum adsorption of uptake (232 mg g^-1) compared well with reported values of similar adsorbents. The rate-determining step was observed to follow an intra-particle diffusion model.     

硫酸盐废水生物处理产生的硫化物处理含Pb2+、Zn2+的钢丝酸洗废水

在一套小型搅拌反应器中,研究了碱沉淀(KOH,处理a)、碱沉淀及硫酸盐废水厌氧处理产生的硫化物出水混合(KOH+出水混合,处理b)、碱沉淀及N2吹脱硫酸盐废水厌氧处理产生的硫化物(KOH+N2吹脱,处理c),以及碱沉淀、硫酸盐废水厌氧处理产生的硫化物出水混合和N2吹脱硫化物联合(KOH+出水混合+N2吹脱,处理d)等4组处理方式对含Zn2+、Pb2+的钢丝绳酸洗废水处理效果的影响.废水pH值为0.7,Zn2+和Pb2+含量分别为450和3274 mg.L-1.结果表明,KOH+出水混合+N2吹脱的处理方式对废水有较好的处理效果,Zn2+和Pb2+的去除为氢氧化物、硫化物沉淀的共同作用结果,处理后,废水中Zn2+和Pb2+的去除率均达99.6%以上,满足污水综合排放标准(GB 8978—1996).     

Physicochemical aspects of using natural scavengers in removing methylene blue (basic dye) from solution

Effluent from dyeing and finishing processes is an important source of water pollution. The effectiveness of bentonite, kaolinite and sediment from a local deposit in removing methylene blue as a cationic dye from aqueous solutions has been investigated. The adsorption equilibrium (isotherm) has been determined according to Freundlich and Langmuir equations. The optimum amount is 0.5 g for all adsorbents, and the optimum pH ranges are 2–8 for bentonite and 2–6 for kaolinite and sediment. With respect to kinetic modelling, the adsorption of methylene blue on various adsorbents was fitted to a second-order equation. Also, the thermodynamic parameters were determined. The negative free energy values indicate the feasibility of the process and spontaneous nature of adsorption. The positive ΔH° values indicate the endothermic nature of the process. Thus, Egyptian clay minerals and sediments have a great tendency to remove the dye from solutions.     

Physicochemical aspects of using natural scavengers in removing methylene blue (basic dye) from solution

Effluent from dyeing and finishing processes is an important source of water pollution. The effectiveness of bentonite, kaolinite and sediment from a local deposit in removing methylene blue as a cationic dye from aqueous solutions has been investigated. The adsorption equilibrium (isotherm) has been determined according to Freundlich and Langmuir equations. The optimum amount is 0.5 g for all adsorbents, and the optimum pH ranges are 2-8 for bentonite and 2-6 for kaolinite and sediment. With respect to kinetic modelling, the adsorption of methylene blue on various adsorbents was fitted to a second-order equation. Also, the thermodynamic parameters were determined. The negative free energy values indicate the feasibility of the process and spontaneous nature of adsorption. The positive ΔH° values indicate the endothermic nature of the process. Thus, Egyptian clay minerals and sediments have a great tendency to remove the dye from solutions.     

Effective removal of Cd2+ and Pb2+ pollutants from wastewater by dielectrophoresis-assisted adsorption

Dielectrophoresis (DEP) process could enhance the removal the Cd²⁺ and Pb²⁺ with less absorbent. The removal rates of both Cd²⁺ and Pb²⁺ increased with the increase of voltage. The overall removal rate of Cd²⁺ and Pb²⁺ in the binary system is higher than that of Cd²⁺ or Pb²⁺ in the single system. DEP could cause considerable changes of the bentonite particles in both surface morphology and microstructure. Dielectrophoresis (DEP) was combined with adsorption (ADS) to simultaneously and effectively remove Cd²⁺ and Pb²⁺ species from aqueous solution. To implement the process, bentonite particles of submicro-meter size were used to first adsorb the heavy metal ions. These particles were subsequently trapped and removed by DEP. The effects of the adsorbent dosage, DEP cell voltage and the capture pool numbers on the removal rate were investigated in batch processes, which allowed us to determine the optimal experimental conditions. The high removal efficiency, 97.3% and 99.9% for Cd²⁺ and Pb²⁺, respectively, were achieved when the ions are coexisting in the system. The microstructure of bentonite particles before and after ADS/DEP was examined by scanning electron microscopy. Our results suggest that the dielectrophoresis-assisted adsorption method has a high capability to remove the heavy metals from wastewater.     

Biomonitoring of heavy metal (Cd,Cu, Pb,and Zn) concentrations in the west intertidal area of Peninsular Malaysia by using Nerita lineata

Snails, Nerita lineata, were collected from 15 sites along the west intertidal area of Peninsular Malaysia from December 2005 until April 2006. The concentrations of heavy metals (Cd, Cu, Pb, and Zn) were determined in the total soft tissues, operculums, and shells of the snails. Different patterns of heavy metal distributions were found in the different tissues (shell, operculums, and soft tissues) as well as spatial variations of heavy metal concentrations in the snails. This shows that the distribution of metals in the shells and the total soft tissues of N. lineata were not similar which could be due to different rates of metal accumulation, excretion, and sequestration. Since N. lineata is abundant on the rocky shores, below jetties and mangrove trees along the west intertidal area of Peninsular Malaysia and accumulate heavy metals, the snails are therefore potential biomonitors of heavy metal contamination for the west intertidal area of Peninsular Malaysia.     

Recovery of Ni(II) from real electroplating wastewater using fixed-bed resin adsorption and subsequent electrodeposition

Resin adsorption and subsequent electrodeposition were used for nickel recovery. Treated wastewater can meet the Electroplating Pollutant Discharge Standard. The spent resin is completely regenerated by 3 BV of 4% HCl solution. 95.6% of nickel in concentrated eluent was recovered by electrodeposition. Effective recovery of high-value heavy metals from electroplating wastewater is of great significance, but recovering nickel ions from real electroplating wastewater as nickel sheet has not been reported. In this study, the pilot-scale fixed-bed resin adsorption was conducted to recover Ni(II) ions from real nickel plating wastewater, and then the concentrated Ni(II) ions in the regenerated solution were reduced to nickel sheet via electrodeposition. A commercial cation-exchange resin was selected and the optimal resin adsorption and regeneration conditions were investigated. The resin exhibited an adsorption capacity of 63 mg/g for Ni(II) ions, and the average amount of treated water was 84.6 bed volumes (BV) in the pilot-scale experiments. After the adsorption by two ion-exchange resin columns in series and one chelating resin column, the concentrations of Ni(II) in the treated wastewater were below 0.1 mg/L. After the regeneration of the spent resin using 3 BV of 4% (w/w) HCl solution, 1.5 BV of concentrated neutral nickel solution (>30 g/L) was obtained and used in the subsequent electrodeposition process. Using the aeration method, alkali and water required in resin activation process were greatly reduced to 2 BV and 3 BV, respectively. Under the optimal electrodeposition conditions, 95.6% of Ni(II) in desorption eluent could be recovered as the elemental nickel on the cathode. The total treatment cost for the resin adsorption and regeneration as well as the electrodeposition was calculated.     

Removal of toxic chromium(VI) from aqueous solution by activated carbon using Casuarina equisetifolia

Highly activated carbon from the seed husk of Casuarina Casuarinas equisetifolia, a worldwide famous plant, have been prepared and tested for the removal of toxic Cr(VI) from its aqueous solution. The adsorbent was investigated for influences of initial chromium concentration (75, 100, 125, and 150 mg l^-1), pH, contact time, and quantity of carbon on removal of Cr(VI) from aqueous solution at room temperature (25±2 °C). The adsorption kinetic of Cr(VI) was studied, and the rates of sorption were found to conform to pseudo-second-order kinetics with a good correlation (R²≥0.99). The Langmuir and Freundlich models fit the isotherm data well. Furthermore, the Gibbs free energy was obtained for each system and was found to be-5.29 kJ mol^-1 for removal of Cr(IV). The negative value of Δ G° indicates the feasibility and spontaneous nature of adsorption. The results indicate that acidic pH (1.05) supported the adsorption of Cr(IV) on activated carbon. The maximum adsorption capacity of Cr(VI) on activated carbon was about 172.4 mg g^-1 at pH 1.05.     

Formation of ferric flocks to remove for the removal of Zn and Cu from dockyard wastewater

Wastewater from wash down of boat hulls contains typically Cu, Zn and organometallic biocides, e.g. tributyltin (TBT). In some cases this wastewater is led directly into the marine system. In the present paper, a cheap flocculation method (iron flocculants) for removal of Cu and Zn from the wastewater is investigated and the method was shown successful. TBT concentration in a sample from a German dockyard was also decreased during flocculation, but the TBT removed was already associated with small particulates in the original sample. Low concentrations of heavy metals were obtained by flocculation: <0.05 mg Cu/l and 0.2 mg Zn/l. An erratum to this article can be found at     

Bioremediation of aquaculture wastewater from Mugil cephalus (Linnaeus, 1758) with different microalgae species

Current aquaculture practices have a detrimental impact on the environment, in particular due to the release of high concentration of nitrogen and phosphorus that can induce eutrophication. This study investigates and compares the capacity of three microalgae species Tetraselmis suecica, Isochrysis galbana and Dunaliella tertiolecta, in the bioremediation of grey mullet Mugil cephalus wastewater. The experiment was conducted in batch conditions for 7 days using completely mixed bubble column photobioreactors. After two days, T. suecica and D. tertiolecta were able to remove more than 90% of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorous (DIP), whereas I. galbana removed only 32% and 79% of DIN and DIP, respectively. A higher biomass yield resulted for T. suecica (603?±?34?mg/L, mean?±?SE). This study confirms the potential to employ T. suecica in an Integrated Multi-Trophic Aquaculture system for bioremediation of wastewater and identifies D. tertiolecta as another valid candidate species. Moreover, these species can growth in unsterilized culture media, and this reduces energy consumption, costs and efforts.     

Selective recovery of Cu2+ and Ni2+ from wastewater using bioelectrochemical system

As the bioelectrochemical system, the microbial fuel cell (MFC) and the microbial electrolysis cell (MEC) were developed to selectively recover Cu²⁺ and Ni²⁺ ions from wastewater. The wastewater was treated in the cathode chambers of the system, in which Cu²⁺ and Ni²⁺ ions were removed by using the MFC and the MEC, respectively. At an initial Cu²⁺ concentration of 500 mg·L^-1, removal efficiencies of Cu²⁺ increased from 97.0%±1.8% to 99.0%±0.3% with the initial Ni²⁺ concentrations from 250 to 1000 mg·L^-1, and maximum power densities increased from 3.1±0.5 to 5.4±0.6 W·m^-3. The Ni²⁺ removal mass in the MEC increased from 6.8±0.2 to 20.5±1.5 mg with the increase of Ni²⁺ concentrations. At an initial Ni²⁺ concentration of 500 mg·L^-1, Cu²⁺ removal efficiencies decreased from 99.1%±0.3% to 74.2%±3.8% with the initial Cu²⁺ concentrations from 250 to 1000 mg·L^-1, and maximum power densities increased from 3.0±0.1 to 6.3±1.2 W·m^-3. Subsequently, the Ni²⁺ removal efficiencies decreased from 96.9%±3.1% to 73.3%±5.4%. The results clearly demonstrated the feasibility of selective recovery of Cu²⁺ and Ni²⁺ from the wastewater using the bioelectrochemical system.     

Assessment of individual and combined toxicities of three heavy metals (Cu,Cd and Hg) by using Tigriopus fulvus

The toxicities of copper, cadmium, and mercury ions and their binary and ternary mixtures were studied using the copepods Tigriopus fulvus. The LC50 values measured after 48 h exposure to single metal solutions revealed a toxicities rank as follows: CdT. fulvus. The combined effect of the metals was found to be antagonistic for Cu?Cd, Hg?Cd, and Cu?Cd?Hg, additive for Hg?Cu.     

Effects of three low-molecular-weight organic acids (LMWOAs) and pH on the mobilization of arsenic and heavy metals (Cu, Pb, and Zn) from mine tailings

Natural organic acids may play an important role in influencing the mobility of toxic contaminants in the environment. The mobilization of arsenic (As) and heavy metals from an oxidized Pb–Zn mine tailings sample in the presence of three low-molecular-weight organic acids, aspartic acid, cysteine, and succinic acid, was investigated at a mass ratio of 10 mg organic additive/g mine tailings in this study. The effect of pH was also evaluated. The mine tailings sample, containing elevated levels of As (2,180 mg/kg), copper (Cu, 1,100 mg/kg), lead (Pb, 12,860 mg/kg), and zinc (Zn, 5,075 mg/kg), was collected from Bathurst, New Brunswick, Canada. It was found that the organic additives inhibited As and heavy metal mobilization under acidic conditions (at pH 3 or 5), but enhanced it under neutral to alkaline conditions (at pH above 7) through forming aqueous organic complexes. At pH 11, As, Cu, Pb, and Zn were mobilized mostly by the organic additives, 45, 46, 1,660, and 128 mg/kg by aspartic acid, 31, 28, 1,040, and 112 mg/kg by succinic acid, and 53, 38, 2,020, and 150 mg/kg by cysteine, respectively, whereas those by distilled water were 6, 16, 260, and 52 mg/kg, respectively. It was also found that the mobilization of As and the heavy metals was closely correlated, and both were closely correlated to Fe mobilization. Arsenic mobilization by the three LMWOAs was found to be consistent with the order of the stability of Fe–, Cu–, Pb–, and Zn–organic ligand complexes. The organic acids might be used potentially in the natural attenuation and remediation of As and heavy metal–contaminated sites.     

Molecular characterisation of high-strength polycyclic aromatic hydrocarbon (PAH)-degrading and phenol-tolerant bacteria obtained from thermal power plant wastewater

This article reports the successful isolation and molecular characterisation of nine different phenol-tolerant and polycyclic aromatic hydrocarbon (PAH)-degrading Gram-positive bacterial species of diverse genera from the effluents of various industries. Based on similarity matrix studies, isolates Corynebacterium sp. DST1, Lysinibacillus sp. and Planococcus sp. showed<97% similarity, suggesting the possibility of new species in their respective genera.     

Fecundity of the freshwater fish, Notopterus notopterus (Pallas) in natural and heavy metal contaminated water

The knowledge of fecundity of fish from a specific aquatic body is extremely important in the successful management and exploitation of its fishery. In the present investigation the fecundity of the freshwater fish, Notopterus notopterus was studied in fish collected from a natural aquatic body (Sirnoor nala) near Gulbarga and also in fish exposed to some heavy metal contamination (HgCl2, CdCl2 and their combination) at sublethal concentration for 15 days in the laboratory. The mathematical relationship between fecundity and total length, body weight, ovary length and ovary weight were determined in both unexposed and exposed fish. The fish, N. notopterus has bigger oocytes and are few in number. Studies in the fish exposed to heavy metals indicate that significant reduction in these parameters after exposure to heavy metals at sublethal concentration was noticed. The fecundity has straight line relationship with total length, body weight, ovary length and ovary weight in control fish which did not alter after heavy metal exposure. This study provides the viability of species in only specific environment.     

Levels of heavy metals (Zn,Cu, Cd,and Pb) in mudskippers (Periophthalmodon schlosseri) and sediments collected from intertidal areas at Morib and Remis,Peninsular Malaysia

The concentrations of Zn, Cu, Cd, and Pb were determined in different tissues of mudskipper fishes Periophthalmodon schlosseri caught at two selected locations (Morib and Remis) of the intertidal mudflat area of Selangor state, West Coast of Peninsular Malaysia and in surface sediment samples. Metal concentrations in the mudskipper tissue and in the sediment samples tended to vary significantly (p < 0.05) between the two locations. Higher metal concentrations (except for Zn) were mostly found in the tissues of mudskippers from Remis. For sediment samples, significantly (p < 0.05) higher metal concentrations of all metals were also found at Remis. Generally, metal distribution between different tissues of mudskipper varied with scales being highly accumulative of Zn, Cd, and Pb, while for Cu, the highest mean concentrations were found in the liver. The lowest mean concentrations of Zn, Cu, and Cd were found in the muscles except for Pb, which was lowest in the liver. This study suggests that mudskippers can be potential biomonitoring organisms for heavy metal bioavailability and contamination of intertidal coastal mudflats. The concentrations of Cd and Pb were slightly above the acceptable limits of Malaysian and European food safety guidelines.     

Adsorptive removal of As(III) and As(V) from water and wastewaters using an anion exchanger derived from polymer-grafted banana stem

In this study, the adsorption characteristics of As(III) and As(V) from water and wastewater using polyacrylamide-grafted banana stem with quaternary ammonium functionality (PGBS-AE) were investigated. Infrared spectroscopic, and thermogravimetric analyses were performed to affirm the polymer grafting, functionality, morphology, and thermal stability. Batch experiments were carried out to understand the effect of contact time, concentration, pH, adsorbent dose, and temperature of the solution for the adsorption of As(III) and As(V) onto PGBS-AE. Equilibrium was achieved within 1 h and the optimum pH was found to be 9.0 and 3.0 for As(III) and As(V), respectively. Isotherm studies showed that the Langmuir equation fits best. Maximum adsorption capacities of 50 and 5.5?g?kg^?1 were obtained for As(III) and As(V) at 30°C. The endothermic nature of adsorption was evident as the adsorption efficiency increased with temperature. The thermodynamic parameters were evaluated to explain the feasibility of adsorption and to predict the nature of adsorption. The competence of the adsorbent for practical purposes was also analyzed by treating with a fertilizer industry effluent sample. Studies pertaining to adsorbent regeneration and readsorption of As(III) and As(V) were carried out for four consecutive cycles.     

Concurrent adsorption and reduction of chromium(VI) to chromium(III) using nitrogen-doped porous carbon adsorbent derived from loofah sponge

• A high-efficiency N-doped porous carbon adsorbent for Cr(VI) was synthesized. • The maximum adsorption capacity of Cr(VI) reached up to 285.71 mg/g at 318K. • The potential mechanism for Cr(VI) adsorption by NHPC was put forward. • DFT analyzed the adsorption energy and interaction between NHPC and Cr(VI). To develop highly effective adsorbents for chromium removal, a nitrogen-doped biomass-derived carbon (NHPC) was synthesized via direct carbonation of loofah sponge followed by alkali activation and doping modification. NHPC possessed a hierarchical micro-/mesoporous lamellar structure with nitrogen-containing functional groups (1.33 at%), specific surface area (1792.47 m²/g), and pore volume (1.18 cm³/g). NHPC exhibited a higher Cr(VI) adsorption affinity than the HPC (without nitrogen doping) or the pristine loofah sponge carbon (LSC) did. The influence of process parameters, including pH, dosage, time, temperature, and Cr(VI) concentration, on Cr(VI) adsorption by NHPC were evaluated. The Cr(VI) adsorption kinetics matched with the pseudo-second-order model (R²≥0.9983). The Cr(VI) adsorption isotherm was fitted with the Langmuir isotherm model, which indicated the maximum Cr(VI) adsorption capacities: 227.27, 238.10, and 285.71 mg/g at 298K, 308K, and 318K, respectively. The model analysis also indicated that adsorption of Cr(VI) on NHPC was a spontaneous, endothermal, and entropy-increasing process. The Cr(VI) adsorption process potentially involved mixed reductive and adsorbed mechanism. Furthermore, computational chemistry calculations revealed that the adsorption energy between NHPC and Cr(VI) (−0.84 eV) was lower than that of HPC (−0.51 eV), suggesting that nitrogen doping could greatly enhance the interaction between NHPC and Cr(VI).