Nanoscale Zero-Valent Iron(nZVI)for Heavy Metal Wastewater Treatment:A Perspective

Industries such as non-ferrous metal smelting discharge billions of gallons of highly toxic heavy metal wastewater(HMW)worldwide annually,posing a severe challenge to conventional wastewater treatment plants and harming the environment.HMW is traditionally treated via chemical precipitation using lime,caustic,or sulfide,but the effluents do not meet the increasingly stringent discharge standards.This issue has spurred an increase in research and the development of innovative treatment technologies,among which those using nanoparticles receive particular interest.Among such initiatives,treatment using nanoscale zero-valent iron(nZVI)is one of the best developed.While nZVI is already well known for its site-remediation use,this perspective highlights its application in HMW treatment with metal recovery.We demonstrate several advantages of nZVI in this wastewater application,including its multifunctionality in sequestrating a wide array of metal(loid)s(>30 species);its capability to capture and enrich metal(loid)s at low concentrations(with a removal capacity reaching 500 mg·g^(-1)nZVI);and its operational convenience due to its unique hydrodynamics.All these advantages are attributable to nZVI’s diminutive nanoparticle size and/or its unique iron chemistry.We also present the first engineering practice of this application,which has treated millions of cubic meters of HMW and recovered tons of valuable metals(e.g.,Cu and Au).It is concluded that nZVI is a potent reagent for treating HMW and that nZVI technology provides an eco-solution to this toxic waste.

Efficiency and effectiveness of systems for the treatment of domestic wastewater based on subsurface flow constructed wetlands in Jarabacoa, Dominican Republic

Constructed wetlands(CwW)are well known nature-based systems for water treatment.This study evaluated the efficiency and effectiveness of seven domestic wastewater treatment systems based on horizontal flow CWs in Jarabacoa,the Dominican Republic.The results showed that the CWs were efficient in reducing the degree of contamination of wastewater to levels below the Dominican wastewater discharge standards for parameters such as the 5-day biochemical oxygen demand(BOD5)and chemical oxygen demand,but not for the removal of phosphorus and fecal coliforms.In addition,a horizontal flow subsurface wetland in the peri-urban area El Dorado was evaluated in terms of the performance of wastewater treatment in tropical climatic conditions.The concentrations of heavy metals,such as zinc,copper,chromium,and iron,were found to decrease in the effluent of the wetland,and the concentrations for nickel and manganese tended to increase.The levels of heavy metals in the effluent were lower than the limit values of the Dominican wastewater discharge standards.The construction cost of these facilities was around 200 USD per population equivalent,similar to the cost in other countries in the same region.This study suggested some solutions to the improved performance of CWs:selection of a microbial flora that guarantees the reduction of nitrates and nitrites to molecular nitrogen,use of endemic plants that bioaccumulate heavy metals,combination of constructed wetlands with filtration on activated carbon,and inclusion of water purification processes that allow to evaluate the reuse of treated water.

Magnesium oxide(MgO)nanoadsorbents in wastewater treatment:A comprehensive review

Wastewater contamination by heavy metals and synthetic dyes presents a significant environmental challenge,necessitating effective and sustainable separation techniques.This review article provides a detailed examination of magnesium oxide(MgO)nanoparticles as an innovative nanoadsorbent for wastewater treatment,with a specific focus on heavy metal and dye removal.The review comprehensively explores various aspects of MgO nanoparticles,including their structural characteristics and synthesis techniques.The article delves into the morphology and crystallographic arrangement of MgO nanoparticles,offering insights into their structural attributes.Given the complexity of adsorption processes,the review identifies and analyzes parameters influencing the adsorption efficiency of MgO nanoparticles,such as temperature,pH,contact time,initial concentration,and co-existing ions.The interplay between these parameters and the adsorption capability of MgO nanoparticles emphasizes the importance of optimizing operational conditions.Furthermore,the review assesses various synthesis methods for MgO nanoparticles,including sol-gel,hydrothermal,precipitation,green synthesis,solvothermal,and template-assisted techniques.It discusses the advantages,limitations,and resulting nanoparticle characteristics of each method,enabling readers to grasp the implications of synthesis processes on adsorption efficiency.This comprehensive review consolidates current insights into the effectiveness of MgO nanoparticles as a potent nanoadsorbent for removing heavy metals and dyes from wastewater covering a wide spectrum of aspects related to MgO nanoparticles.Moreover,there is a need to investigate the use of MgO in the treatment of actual wastewater or river water,in order to leverage its cost-effectiveness and high efficiency for practical water treatment applications in real-time.

Damage to DNA of effective microorganisms by heavy metals:Impact on wastewater treatment

The research is to test the damage to DNA of effective microorganisms(EMs)by heavy metal ions As3+,Cd2+,Cr3+,Cu2+,Hg2+, Pb2+,and Zn2+,as well as the effects of EM bacteria on wastewater treatment capability when their DNA is damaged.The approach applied in this study is to test with COMET assay the damage of EM DNA in wastewater with different concentrations of heavy metal ions As3+,Cd2+,Cr3+,Cu2+,Hg2+,Pb2+,Zn2+,as well as the effects of EM treated with As3+,Cd2+,Cr3+,Cu2+,Hg2+,Pb2+,and Zn2+ on COD degradin...

Superior adsorption performance of graphitic carbon nitride nanosheets for both cationic and anionic heavy metals from wastewater

Water pollution caused by highly toxic Cd(II), Pb(II), and Cr(VI) is a serious problem. In the present work,a green and low-cost adsorbent of g-C_3N_4 nanosheets was developed with superior capacity for both cationic and anionic heavy metals. The adsorbent was easily fabricated through one-step calcination of guanidine hydrochloride with thickness less than 1.6 nm and specific surface area of 111.2 m^2·g^(-1). Kinetic and isotherm studies suggest that the adsorption is an endothermic chemisorption process, occurring on the energetically heterogeneous surface based on a hybrid mechanism of multilayer and monolayer adsorption. The tri-s-triazine units and surface N-containing groups of g-C_3N_4 nanosheets are proposed to be responsible for the adsorption process.Further study on pH demonstrates that electrostatic interaction plays an important role. The maximum adsorption capacity of Cd(II), Pb(II), and Cr(VI) on g-C_3N_4 nanosheets is 123.205 mg·g^(-1), 136.571 mg·g^(-1),and 684.451 mg·g^(-1), respectively. The better adsorption performance of the adsorbent than that of the recently reported nanomaterials and low-cost adsorbents proves its great application potential in the removal of heavy metal contaminants from wastewater. The present paper developed a promising adsorbent which will certainly find applications in wastewater treatment and also provides guiding significance in designing adsorption processes.

Effects of Wastewater Discharge on Heavy Metals Pollution in Fadama Soils in Kano City, Nigeria

Objective To present the results of a research project on 6 heavy metals （Cd, Cu, Zn, Pb, Hg, and Cr） at 30 Fadama fields scattered around Kano. Methods Following a reconnaissance conducted, 30 representative Fadama lands being irrigated with wastewater were selected from zones of the city under residential, industrial, commercial, and mixed but largely residential landuses. Five additional Fadama lands not being irrigated with wastewater were selected to serve as control. Using grid sampling procedure, soil samples were selected from 0-15 cm and 20-30 cm depths and analyzed for the above listed heavy metals using atomic absorption spectrophotometry. T-test was used to compare the mean values of the metals for the Fadama lands under different landuse zones with those of the control. Results Analyses of the soil data collected showed that the metals were concentrated in higher amounts in the lower （20-30 cm） than the upper （0-15 cm） depths, which was an indication of downward movement of the metals in profile of the soils. In the two soil depths, Zn was generally the most abundant, followed by Cr, then Pb, Cu, and Cd while Hg was the least. The Fadama soils in areas of mixed landuses with industrial as the dominant ones maintained the highest concentrations of the various metals. Conclusions These results indicate clearly that the Fadama soils are significantly polluted by industrial and household wastewater and that there is a particular threat from Cr and Pb pollution. There is also evidence that the metals are accumulating at lower layers of the soil profile, suggesting that not only plants and soil, but even water bodies could be under the threat of heavy metal pollution in the area.

Physico-chemical characterization of a farmland affected by wastewater in relation to heavy metals

This study investigated selected properties of soils affected by wastewater and its relationship with some heavy metals. A free survey technique involving target sampling was used in siting soil profile pits. Soil samples were collected based on horizon differentiation and analyzed using routine and special analytical techniques. Soil data were subjected to correlation analysis using SAS program. Results show that all heavy metals studied had values above critical limits in the polluted soils using known standards and that these biotoxic metals decreased with soil depths. Highly significant (P=0.01 and 0.05) relationships were established between investigated heavy metals and some soil properties, especially soil pH and organic matter. Further studies involving more edaphic properties, biotoxic metals and their bioaccessibility in crops growing on wastewater soils will surely enhance knowledge and management of these highly anthropogenically influenced soils of the study site.

Heavy Metals Removal from Swine Wastewater Using Constructed Wetlands with Horizontal Sub-Surface Flow

The removal efficiency of Cu and Zn from swine wastewater was evaluated as effected by three variables: the hydraulic retention time (HRT) (24, 48, 72 and 96 hours), two different plant species (Typha domingensis Pers. and Eleocharis cellulosa) and two different sizes of filter media (5 and 15 mm) using a horizontal sub-surface flow constructed wetland. From the results, a significant difference was observed in the removal efficiency of Cu and Zn with respect to different hydraulic retention times. The best results were obtained in the HRT of 96 hours for Zn where 96% removal of Zn with Typha domingensis Pers. specie with gravel of 15 mm (experimental unit 6) was achieved. For Cu, at 72 hours of HRT, the efficiency was nearly 100% in five of the six study units (1, 2, 3, 5 and 6). In contrast, in experimental unit 4 with gravel of 15 mm and without plants, only 86% Cu removal was achieved.

Evaluation of Nutrients and Trace Metals and Their Enrichment Factors in Soil and Sugarcane Crop Irrigated with Wastewater

The study was conducted to investigate enrichment factor of wastewater (WW) irrigation to agricultural soils and the bioconcentration factor of trace metals uptake by sugarcane and to determine the concentrations of nutrients in sugarcane by growing the same on a contaminated soil, during the growth period of crop in Vidyaranyapuram area in the South West of Mysore, Karnataka. The concentrations of macronutrients and trace metals in the soil sampled sugarcane crop were found highly significant in Ca, Mg, K, Na, N, Mn, Cu, Ni and Cr. The enrichment factor was maximum for N and Na, and the values of N and Na were in the significant enrichment category. Whereas the values of following elements (K, P, Ca, SO4, Cu, Cr, Mg, Mn, Ni, Cd, Fe, Pb, Cl, Co and Zn) in soil irrigated with WW were in moderate enrichment category. The mean concentrations of N, P, K, Ca, Na, Fe, Mn, and Pb in sugarcane leaves in wastewater treatment crops were significantly higher than those with ground water (GW) treated which showed the lowest concentrations. Calculation of the bioconcentration factor (BCF) indicated that the accumulation of heavy metals in sugarcane crop was in the order Cd > Zn > Co > Pb > Mn > Ni > Cu > Cr > Fe. Pearson’s correlation coefficient indicated the relationship between different elements content in soil and plant. The results showed that the elements, Ca, Mg, Na, K, N, P, Mn, Zn and Cr, were significantly positively correlated, between the soil and the plant.

Removal of Some Heavy Metals from Wastewater by Using of Fava Beans

The Fava Beans were used in this work as low cost adsorbent material for removal of Pb(II), Cd(II) and Zn(II) ions from aqueous solutions. The samples were prepared without farther treatment and sorted according to the particles diameter by standard sieves 250 - 500 μm. Batch adsorption experiments were carried out to study the adsorption process, several parameters such as Initial pH of adsorbent, effect of contact time, effect of adsorbent amount and effect of metal concentration were conducted in these experiments. The effects of any one of those previously mentioned parameters on the adsorption capacity were studied while the other parameters were kept constant. It was found that the obtained maximum adsorption capacities of Fave beans for the removal of selected heavy metals were very high. This provide us to use Fava beans as a low coast adsorbent material to clean up the water in the environment from toxic heavy metals such as Pb(II), Cd(II) and Zn(II) ions.

Susceptibility of Some Selected Nitte Municipal Wastewater Sources to Trace Metals Pollution

The negative impacts of pollution due to trace metals in wastewater on aquatic ecosystem and related organisms in water bodies are on the increase. This paper deals with the investigation on the pollution indices of trace metals in selected wastewater samples of Nitte Town, Udupi District, Karnataka State, India. Twelve wastewater samples were obtained from Students Hostels, Auto-Service Workshop Station, Foundry, Laundry, Landfill Leachate and Wastewater Treatment Plant Inlet. The measured heavy metals in the samples include: Copper (Cu), Lead (Pb), Magnesium (Mg), Chromium (Cr), Nickel (Ni), Zinc (Zn), Manganese (Mn) and Cadmium (Cd), using the air-acetylene-operated Flame Atomic Absorption Spectrometer (FAAS), Avanta GM model. The results were all compared with the EPA Effluent Standards. Findings revealed that all samples recorded dwindling levels of trace metals pollution when compared with the Standards. The heaviest concentration occurred in Cd with as high as 1856.4 ppm as found in the Stale Landfill Leachate sample, while the least contaminating metal in the samples is Manganese which was detected in only Aerated Wastewater Treatment Plant sample (2.3 ppm). This study is therefore recommending Electro-coagulation treatment method for trace metals with high concentration levels like Cd, Pb, Mg and Cu, while those with lesser concentration such as Mn, Cr, Ni and Zn in the samples are suggested to be treated with chemical precipitation method.

Surface Modification of the Biowaste for Purification of Wastewater Contaminated with Toxic Heavy Metals—Lead and Cadmium

The surface of a biowaste was modified by introduction of amino group for the purification of wastewater contaminated with heavy metals. In this study waste tea leaf was used as a biowaste which was an economic and efficient bioadsorbent. The aminated tea leaves were characterized by spectral and elemental analysis. The adsorption capacity of the surface modified biosorbent was studied as the function of solution pH, concentration of metal ions and contact time of adsorption. The applicability of Langmuir isotherm was tested. The adsorption capacities were found to be 83.04 mg/g and 57 mg/g for Pb (II) and Cd (II), respectively. The biosorbent was regenerated by desorption of the metal loaded adsorbent with 0.1 M HNO3. These results showed that the aminated tea leaves may be an attractive alternative for treatment of wastewater contaminated with heavy metals.

Treatment of Wastewater Containing Heavy Metals Using Dissolved Air Released Flotation Column

A new type of dissolved air released flotation column is developed to treat wastewater containing Cr（Ⅵ） based on advantages of both dissolved air floatation and column floatation. By using a column with a diameter of 50 mm and a specially made dissolved air releaser, micro-bubbles inside the column can be formed. N2H4H2O was used as reductant, AlCl3 as flocculant, C12H25SO3Na（SDS） as surfactant in the experiment. The effects of pH of wastewater, pressure of dissolved air, ratio of return water, and concentration of flocculant and surfactant on the removal efficiency are studied. The results show that the efficiency of dissolved air released flotation column is much higher than that of other approaches after the operation parameters are optimized, with the reduction ratio of Cr（Ⅵ ） in wastewater reaching 98%. So this technique can be widely used in wastewater treatment

Examination of the Level of Heavy Metals in Wastewater of Bandar Abbas Wastewater Treatment Plant

One of the main environmental pollutants is heavy metals. Due to extensive usage in industry, these metals enter biological cycle rapidly and contaminated water and soil resources rapidly. In this work, lead, copper, zinc and chromium of Bandar Abbas wastewater are examined. For this research, nine stations were set for measurement in urban level in Bandar Abbas and sampling of aforesaid metals was performed in fall and winter 2006 in these stations. After extraction and preparation operations using APDC-MIBK, samples were measured using flame atomic absorption system. According to results, concentrate of studied metals was lower than allowable standard value set by Iran environmental protection organization for agricultural purposes and sewage to ground level waters. In addition, efficiency of Bandar Abbas wastewater treatment plant to remove these metals is 40% - 70% from which highest removal is for zinc as much as 71.1% and lowest level is for copper as much as 40.5%. However, copper level was higher than allowable level for agricultural purposes in spring and summer (0.21 mg/L and 0.23 mg/L, respectively) and lower in fall and winter (0.103 mg/L and 0.098 mg/L, respectively). Furthermore, changes in concentration of metals in these stations in various seasons were measured and analyzed using one-way variance analysis and simultaneous effects of time and place on measured variables were analyzed using two-way variance analysis.

Removal of Heavy Metals （Copper, Manganese and Zinc） from Industrial Wastewater of Baiji Refinery by Granular Activated Carbon

The aim of the present work is to remove heavy metals （copper, manganese, and zinc） from industrial wastewater of Baiji refinery using GAC （granular activated carbon）. The most important factors affecting adsorption process have been studied, which are granular activated carbon thickness, H, inlet pollutant concentration, Cv, and liquid hourly space velocity, LHSV. All experiments were performed under constant temperature at 25℃ and pH = 7. The experimental apparatus was designed and constructed to enable controlling of the operating conditions. Employing five levels for each of H and LHSV and three levels for Co required 75 runs for each metal. Box-Wilson method was used to reduce the number of experiments to 15 for each metal. The results indicated that copper, manganese, and zinc can be completely removed from wastewater using activated carbon. However, breakthrough time for zinc is low. It is also shown that breakthrough time （TB） and exhaustion time （TE） are inversely proportional with pollutant concentration and LHSV （liquid hour space velocity） while it is directly proportional with the thickness of activated carbon column.

Study and Solutions to the Issue of Heavy Metals from Wet FGD Wastewater

The conventional wet FGD process has been applied in more than 85% units for SO2 removal in China. There are a great number of pollution components in the wastewater from wet FGD process,and the removal process of these components is very complicated and difficult,especially the removal of heavy metals in the wastewater. Even if a foreign advanced technology was applied,it is still difficult to meet the discharge requirements of heavy metals in spite of its much higher investment,operation and maintenance cost than that from the domestic widely-used and simple wastewater treatment process. Under the background of increasingly stringent environmental requirements,to improve the existing wastewater treatment process or to change the existing wet FGD process has become extremely urgent.

Soil Microbial Characteristics Under Long-Term Heavy Metal Stress:A Case Study in Zhangshi Wastewater Irrigation Area,Shenyang

Soil samples were collected from Zhangshi Wastewater Irrigation Area in the suburb of Shenyang City,China,an area with a 30-year irrigation history with heavy metal-containing wastewater.The chemical properties and microbial characteristics of the soils were examined to evaluate the present situation of heavy metal pollution and to assess the soil microbial characteristics under long-term heavy metal stress.In light of the National Environmental Quality Standards of China,the soil in the test area was heavily polluted by Cd and to a lesser degree by Zn and Cu,even though wastewater irrigation ceased in 1993.Soil metabolic quotient (qCO_2) had a significant positive correlation,while soil microbial quotient (qM) had a negative correlation with content of soil heavy metals.Soil microbial biomass carbon (MBC) had significantly negative correlation with Cd,but soil substrate-induced respiration (SIR),dehydrogenase activity (DHA),cellulase activity, and culturable microbial populations had no persistent correlations with soil heavy metal content.Soil nutrients,except for phosphorous,showed positive effects on soil microbial characteristics,which to a certain degree obscured the adverse effects of soil heavy metals.Soil Cd contributed more to the soil microbial characteristics,but qM and qCO_2 were more sensitive and showed persistent responses to heavy metals stress.It could be concluded that qM and qCO_2 can be used as bioindicators of heavy metal pollution in soils.

BOD Exertion and OD600 Measurements in Presence of Heavy Metal Ions Using Microbes from Dairy Wastewater as a Seed

BOD measurements in presence of cobalt, nickel, copper, zinc, silver and cadmium are reported using wastewater from dairy industry as a seed. Extent of inhibition in BOD is studied for variables like, concen-tration of metal ions (0.2 mM to 1.4 mM), pH (3 to 8) and temperature of incubation (15℃, 20℃, 25℃, 30℃ and 35℃). Results of BOD inhibition are supported by absorbance measurement (OD600) studies of microbial matter preserved in Luriya broth medium. OD measurement results are used to derive minimum inhibitory concentration, i.e., threshold concentration of each metal showing toxicity towards microbes. Sil-ver is found to be the most toxic element.

Heavy Metal Contaminated Food Crops Irrigated with Wastewater in Peri Urban Areas, Zambia

Studies on peri urban farming in Zambia have not adequately tackled the issues pertaining to heavy metal contaminated wastewater irrigation farming. The study investigated heavy metal contamination of water, soils and crops at two peri urban areas in Zambia. Two study sites were New Farm Extension in Mufulira Town in the Copperbelt Province and Chilumba Gardens in Kafue Town in Lusaka Province. The heavy metals investigated were lead, copper, cobalt, nickel and chromium. These heavy metals were found to be higher than acceptable limits in wastewater used to irrigate crops and there are potential human health risks associated with consumption of heavy metal contaminated food crops which have implications on the livelihoods of people. Samples of water, soil and crops were collected and analysed for lead (Pb), copper (Cu), chromium (Cr), cobalt (Co) and nickel (Ni) using the Atomic Absorption Spectrometer (AAS). The data on heavy metals was analysed using mean, standard error and T-test. The results indicated that the levels of heavy metals in wastewater, soil and food crops were above acceptable limits at two study sites. It can be concluded that there was heavy metal contamination of wastewater, soil and food crops at the two peri-urban areas in Zambia. The study highlighted the actual levels of heavy metal contaminant uptake in food crops consumed by the peri urban population. The information from this study can be used by the relevant authorities to develop appropriate measures for monitoring and control of heavy metal contamination in wastewater irrigation farming systems in peri urban areas inZambia.

A Review on Constructed Wetlands Components and Heavy Metal Removal from Wastewater

Constructed wetlands are man-made complex of substrates, emergent/submergent vegetation, and water. Constructed wetlands have been known as an efficient and low-cost treatment process. Constructed wetland is a natural treatment system that physical, chemical, and biological processes occur when water, soil, plants, and microorganisms interact. They are considered as natural treatment ecosystems that are designed to take advantages of the natural processes to provide wastewater treatment. Constructed wetlands treat different types of wastewaters such as municipal, industrial, agricultural, and storm water. The removal of heavy metals within wetlands is performed generally by plant uptake and by adsorption onto sediments. Heavy metal treatment examples and some specifications and regulations are finally discussed.