Water pollution is one of the global challenges that society must address in the 21st century aiming to improve water quality and reduce human and ecosystem health impacts. Industrialization, climate change, and expansion of urban areas produce a variety of water pollutants. In this work, we discuss some of the most recent and relevant findings related to the release of heavy metals, the possible risks for the environment and human health, the materials and technologies available for their removal. Anthropogenic activities are identified as the main source of the increasing amounts of heavy metals found in aquatic environments. Some of the health hazards derived from repeated exposure to traces of heavy metals, including lead, cadmium, mercury, and arsenic, are outlined. We also give some perspectives about several techniques used to detect heavy metals, as well as about the factors that could affect the contaminant removal. The advantages and drawbacks of conventional and non-conventional heavy metal removal methods are critically discussed, given particular attention to those related to adsorption, nanostructured materials and plant-mediated remediation. Some of the commercial products currently used to eliminate heavy metals from water are also listed. Finally, we point out some the requirements and opportunities linked to developing efficient methods for heavy metal removal, such as the ones that exploit nanotechnologies.

Heavy metal water pollution: A fresh look about hazards, novel and conventional remediation methods

Olive stones have been widely used as a renewable energy biowaste source. As they are rich in elemental carbon (40–45 wt%), much research focussed on effectively converting olive stones, as precursors, into activated carbon adsorbents. However, only a few studies have concentrated on summarising the various techniques used to produce activated carbon from olive stone. This article reviews the research undertaken on the production and application of activated carbon as an adsorbent from olive stones for wastewater treatment. Various physical, chemical and physico-chemical treatments to remove heavy metals, organics and dyes are discussed, and the resultant adsorption capacities are reported. In several cases, very high adsorption capacities are recorded. Finally, the future prospects of these materials as adsorbents are discussed, and after further development work, olive stone-derived activated carbons have great potential especially in the area of organic polluted wastewaters.

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Production and applications of activated carbons as adsorbents from olive stones

Heavy metal contamination has been a serious threat to environment and human health Carbon-based materials, from biochar/activated carbon to modified materials (ie carbon nanotubes-based materials, and graphene-based materials), have been widely studied as efficient adsorbents for the heavy metal removal from aqueous solutions This review discussed the recent achievements in adsorption isotherms, adsorption kinetics and adsorption mechanism according to the existing forms of heavy metals in water The effect of process conditions, such as temperature, pH value, and coexisting ions, on adsorption performance are combed, and the universal guidance law is obtained The physical adsorption, electrostatic interaction, ion exchange, surface complexation, and precipitation/coprecipitation play important roles in heavy metals adsorption process In addition to the common activated carbon(AC), biochar(BC) and the emerging carbon nanotubes(CNTs) and graphene(GN) adsorbent show good development potentials Meanwhile, though the modified carbonaceous materials can achieve high adsorption capacity and removal efficiency of heavy metals, the modification operation is complex, especially chemical modification Acid and alkali solution are often used to regenerate spent materials in desorption, however, further studies of other desorption reagent are really needed This review highlights the removal of heavy metal ions from aqueous solution using carbon-based materials as adsorbents, and discusses the existing deficiencies and suggestions on further study

Removal of heavy metals from aqueous solution using carbon-based adsorbents: A review

Wastewater contains many organic and inorganic pollutants and discharging them into received waters leads to serious environmental problems. The wastewater that is produced from various industries contains a noticeable amount of dyes; heavy metals and metalloids this has remained one of the major environmental problems facing public health. Unfortunately, the conventional wastewater remediation process is unable to remove dyes and heavy metals completely. One of the widely used water treatment technologies is biosorption, biosorbents are considered to be an emerging green, cost-effective, and efficient alternative. Therefore, the search for locally or regionally available biomasses for heavy metals/metalloids and dyes removal gained rapid attention. Methylene blue, Crystal violet, Reactive black 5, and Congo red; Cd, Cr, Cu, Pb, Hg, Ni, and Zn; and As were selected as examples for dyes, heavy metals, and metalloids, respectively, In this regard, a comprehensive understanding of the biosorption capability of different biosorbents is necessary to know how they can remove inorganic and organic contaminants in wastewater. Biosorption is an ion exchange, complexation, and coordination process. Besides, the recent advances in various biomaterials-based biosorbents and different approaches of pollutants removal from wastewater with several examples to provide a backdrop for future research have been reviewed. This can be beneficial for developing more effective technologies to eliminate contaminants, thus bridging the gap between laboratory results and industrial use. crustacean shells, algae, chitosan are the most effective biosorbents. These biosorbents can serve as good alternatives to synthetic materials for pollutants removal from wastewater.

A critical review of biosorption of dyes, heavy metals and metalloids from wastewater as an efficient and green process

https://pureadmin.qub.ac.uk/ws/files/190290035/water_treatment_revised_Review_Accepted_for_publication.pdf

Insight on water remediation application using magnetic nanomaterials and biosorbents

Typical chemical precipitation methods using lime (Ca(OH)2), soda ash (Na2CO3) and sodium sulfide (Na2S) for removals of heavy metals (i.e. Zn (II), Cu (II) and Pb (II)) from aqueous solutions were compared by jar tests. A focus was especially given to particle size differences and chemical phase conversion of precipitates. A removal of 99.99% from aqueous solutions with three precipitants was achieved for copper and zinc at an initial concentration of 100 mg/L. And lead was efficiently removed (99.75%) by sodium sulfide. In contrast, the maximal lead removals with lime or soda ash precipitation were only 76.14% and 97.78%. The mean particle size of precipitates was in the range of 55 nm–45 μm, depending on properties of precipitants and heavy metal to precipitant ratios. The settling performance of the sludge derived from precipitation was dominated by particle size and Zeta-potential of precipitates. It was observed that ultra-fine copper sulfide particles resulted from the precipitation were around 55 nm and did not settle in 12 h due to electrostatic repulsion force between particles. The main compounds in the sludge obtained from precipitation were metal hydroxides and metal sulfides. However, spontaneous dehydration of metal hydroxide, oxidation of sulfide and atmospheric carbonation were identified by means of XRD and thermal analyses, which is invaluable to the disposal and utilization of the sludge.

Comparison of heavy metal removals from aqueous solutions by chemical precipitation and characteristics of precipitates

The long term catalytic activity of pyrite in advanced oxidation for wastewater treatment is vital for the practical application. In this work, the efficacy of pyrite catalyzed Fenton-like oxidation for tertiary treatment of dyeing wastewater was investigated for a period of two years. The influence of pyrite oxidation and dissolution on the catalytic activity was studied based on surface characterizations and chemistry studies. Experimental results demonstrated that pyrite can effectively catalyze H2O2 to oxidize recalcitrant pollutants in the biological effluent of dyeing wastewater. At initial pH 3–6, H2O2 of 10 mM and pyrite of 24 g L−1, COD and color removals reached 76.67% and 97.09% in 180 min of reaction time. The higher treatment efficacy of pyrite catalyzed Fenton-like oxidation was due to appropriate conversion rate of H2O2 to hydroxyl radicals compared with the classic Fenton oxidation. Heterogeneous catalysis by Fe(II) on the pyrite surface was much more significant than Homogeneous catalysis by dissolved iron ions of pyrite. The latter contributed only 28.25% abatement of COD at pH 3 and can be negligible at wastewater initial pH > 5. The oxidation of pyrite resulted in acidic pH environment for recalcitrant organic compound destruction even if the initial pH of wastewater was 6.5. It was found that the catalytic activity of pyrite can maintain at least two years, as the surface regeneration of pyrite in that period of time occurred spontaneously due to the slow dissolution of oxidation products.

Long term catalytic activity of pyrite in Heterogeneous Fenton-like oxidation for the tertiary treatment of dyeing wastewater

Four kinds of iron-bearing materials including chalcopyrite, pyrite, sponge iron and iron–carbon composite were exploited as catalysts and 3D electrodes (particle electrode) for heterogeneous electro-Fenton oxidation processes. Their catalytic activities were compared according to decolorization (i.e. 1 − C ∕ C 0) and COD removal efficacies, using Reactive Red X-3B as a model organic pollutant in dyeing wastewater. The iron–carbon composite was found to be the most effective catalyst, and 99.63 ± 1 % of decolorization and 79.86 ± 2 % of COD removal can be achieved. The addition of sodium chloride reduced catalytic efficacies of sponge iron and iron–carbon composite slightly, but promoted those of chalcopyrite and pyrite. Furthermore, the stability and reusability of catalysts were examined and insignificant reduction on catalytic activity was observed for 5 cycles of electro-Fenton processes.

Catalytic activity comparison of typical iron-bearing particle electrodes in heterogeneous electro-Fenton oxidation processes

Micro-bubbles enhanced removal of diesel oil from the contaminated soil in washing/flushing with surfactant and additives.

The biosurfactant was used to remove diesel from contaminated montmorillonite, which was enhanced by humic acid sodium salt (HASS) addition or microbubbles resulted from sonication It was found that montmorillonite exhibited strong adsorption for saponin, causing the effective critical micelle concentration shift of saponin from 02 g L−1 to 06 g L−1 The washing efficacy (diesel removal) with 06 g L−1 saponin and 2% HASS (HASS/saponin ratio = 2%) increased 149 % compared to the control condition (without HASS), whereas the diesel removal with microbubble enhancement (25 min sonication) increased 152 % compared to the control condition Bright-field microscopy, microscope, DLS, PSS, and TEM were used to measure the size of micelles and count micelle numbers In the addition of 2% HASS, the mean diameter of saponin micelles decreased from 8249 ± 123 nm to 913 ± 76 nm, and the number of micelles increased from 42,000 to 110,000 at saponin solution of 03 g L−1 The hydrophobic core volume increased accordingly HASS molecule might cause the extension of hydrophobic interior space in micelles to solubilize the hydrocarbon contaminant In addition to micelles solubilization, the microbubbles enhancement washing process increased the diesel removal by floatation, cavitation in sonication

Yuan Yao

Papers

Comparison of heavy metal removals from aqueous solutions by chemical precipitation and characteristics of precipitates

Long term catalytic activity of pyrite in Heterogeneous Fenton-like oxidation for the tertiary treatment of dyeing wastewater

Catalytic activity comparison of typical iron-bearing particle electrodes in heterogeneous electro-Fenton oxidation processes

Micro-bubbles enhanced removal of diesel oil from the contaminated soil in washing/flushing with surfactant and additives.

Solubilization mechanism of diesel in saponin micelle for contaminated montmorillonite washing