1- Introduction

2- Materials and methods

3- Results and discussion

4- Conclusion

References

Abstract

In this study, two bacteria strains (Enterobacter sp. SL and Acinetobacter sp. SL-1) and waste molasses (carbon source) were used to remove Zn(II), Cd(II), Cr(VI), and Cr(Total) in the liquid solution (87 mg·L). The results showed the removal efficiencies of Cr(Total) and Cr(VI) could reach over 98.00% after reaction, and the removal efficiencies of Zn(II) and Cd(II) were all about 90.00% by the synergistic actions of microorganisms and waste molasses. In this process, waste molasses provides nutrients for microorganisms and has the characteristics and capability of Cr, Zn, and Cd. Microorganisms mainly use biological adsorption (36.95% and 45.69%) and metabolism (24.37% and 17.05% by producing humic-acid and fulvic-acid like substances) to remove Zn(II) and Cd(II), while waste molasses could to remove Cr(Total) (81.24%) and Cr(VI) (75.90%). This study has potential application value for the treatment of wastewater containing high concentrations of heavy metals.

Introduction

Heavy metal-containing wastewaters are produced in many industries, and their direct discharge has caused serious impacts on human health and environment (Zhu et al., 2018). The popular methods for treatment of heavy metal-containing wastewater include the ion exchange method (Dai et al., 2015), electrochemical method (Kobya et al., 2017), photocatalysis (Luo et al., 2017), and biological method (Wen et al., 2018). Among them, biological method has been widely studied due to the low energy consumption, small secondary pollution, and environmental friendliness. (Zhou et al., 2013). However, applying survivable microbes for biological treatments in toxic environments has become the main challenge (Pradhan et al., 2019) because heavy metal-containing wastewater not only has complex heavy metal compositions but also may contain other toxic substances such as cyanide (a phenolic organic matter) (Wen et al., 2018). In addition, the characteristics of heavy metal-containing wastewater may vary moderately; especially the change of pH can significantly inhibit the bacterial activities (Alexandrino et al., 2014). Moreover, biological treatments of heavy metals normally have been used for low concentration ranges (10–50 mg·L−1) of heavy metals (Guo et al., 2017), and some bacteria can only work with specific single heavy metal [e.g., Zn(II) or Cr(VI)] in the wastewater (Peng et al., 2019; Singh et al., 2011; Wang et al., 2018). Due to the high concentration of heavy metals on microbial stress, it is extremely difficult for microorganisms to remove many kinds of heavy metals simultaneously (Dhal et al., 2013; Guo et al., 2017). Therefore, previous studies have used chemical pretreatment (Mejias Carpio et al., 2016) or the addition of substances such as iron ore (Guo et al., 2017) to reduce heavy metal content or toxicity. Although these methods can improve the activity of microorganisms, they also bring trouble to the subsequent treatment of the final effluent. Alexandrino et al. (2014) and Yan et al. (2018) applied a high concentration of sodium lactate (7.0 g·L−1) as a carbon source to stimulate bacteria growth and heavy metal removal. However, these expensive carbon sources burden wastewater treatment (Li et al., 2019; Wang et al., 2018). In addition, it has been reported that microorganisms need specific nutrient composition to be able to function, and the complex wastewater system (containing heavy metals) will inhibit its activity (Mejias Carpio et al., 2016; Peng et al., 2019; Pradhan et al., 2019). Therefore, biotreatments are usually limited in industrial application due to the multi heavy metals contained wastewater. So, it is important that to develop an economic biotreatment method with multi heavy metals tolerance performance. Moreover, it is critical to differentiate the contributions of biotic (e.g., via microbial metabolisms) and abiotic (the chemical properties of the carbon source) reactions for heavy metals removal in complex wastewater system.

1. Introduction

2. Material and methods

3. Results and discussion

4. Conclusions

Acknowledgments

Appendix A. Supplementary data

References

Abstract

Petrochemical industries are widely distributed in China. As a negative consequence, heavy metals in petrochemical area can result in soil contamination. However, the relevant research of heavy metals contamination in petrochemical area was few. In this study, a total of 103 topsoil samples (<20 cm) and 25 profile soil samples were collected and examined in a retired petrochemical industrial area, South China. The results showed the mean contents of Hg, Cd, As, Pb, Ni and Cu were 0.18, 0.69, 16.22, 47.24, 31.62 and 93.06 mg kg−1, respectively. The spatial distribution of six metals in topsoil was largely attributed to the industrial activities during the petroleum refining and transshipment process. Ni was the main pollutant in the petroleum refining process. While, the contamination of other metals mainly were caused by the leakage of the oil during transshipment. The migration of six metals to subsoil layers was also observable. In accordance, Hg, Cd, As, Pb, Cu, and Ni dropped by 95.02, 71.91, 89.45, 90.88, 99.22, and 65.07%, respectively, compared to their contents in topsoil. The contamination of the heavy metals was mainly caused during the process of petroleum refining and transshipment. The distribution of heavy metals in the factory was mainly affected by the industrial activities or the lateral infiltration of Lianhuashan River. Soil ingestion was the primary pathway for children and adults exposure to heavy metals. The total non-cancer human health risk induced by heavy metals was within the limit of USEPA (10−6 a−1). While the cancer risks alone induced by As through soil ingestion to children was 1.14 × 10−6 a−1, which exceeded the limit of USEPA. This study indicated that not only petroleum hydrocarbon but also heavy metals can cause soil contamination in a retired petrochemical industrial area, which provides a novel cognition. Altogether, measures should be taken in practice to substantially improve the soil quality in petrochemical industrial area.

Introduction

Heavy metals’ pollution has become one of the main environmental soil problems worldwide (Asgari and Cornelis et al., 2015; Hossein et al., 2019). Anthropogenic activities such as agriculture, urbanization and industrialization are the main driving forces of soil heavy metal contamination rather than occurring from soils naturally (e.g., due to the erosion of parent rocks, atmospheric deposition, and volcanic activities) in recent years (Wu et al., 2013; Latare et al., 2014; Özkul et al., 2016; Wang et al., 2019 ). Industrialization has been noted as the primary source of heavy metal contamination (Martín et al., 2014; Meisam et al., 2017; Hossein et al., 2019). This pollution not only affects the quality of soil, but also poses serious health risks to individuals (Chabukdhara et al., 2013; Asgari and Cornelis, 2015). Human exposure to heavy metals takes place through soil ingestion, dermal contact, and inhalation (Mungai et al., 2016). Upon exposure, heavy metals can damage the body’s immune, reproductive and nervous systems (USEPA 2004).

The heavy metals present in sludge are very harmful to the environment and the human body. It is necessary to remove them before sludge disposal. In this study, an ex situ method for removing heavy metals from sludge using electroosmosis was designed, and experiments were conducted to study the effects of electroosmosis voltages (30 V, 40 V and 50 V), citric acid concentrations (0.03 mol/kg, 0.06 mol/kg, 0.09 mol/kg and 0.12 mol/kg) and the power supply (continuous and interrupted) on the removal rate of heavy metals (Cu, Cr, Cd, Zn and Pb). The study found that the combination of the citric acid pretreatment and electroosmosis can effectively improve the removal rate of heavy metals. An appropriate increase in the voltage and citric acid concentration can improve the removal rate of heavy metals. The best combination was determined to be 40 V and 0.09 mol/kg. Under these conditions, the removal rates of Cu, Cr, Cd, Zn and Pb, were 14.39%-41.28% (continuous power supply) and 21.78%-42.36% (interrupted power supply). The interrupted power supply effectively improved the removal rates of Cd and Zn but reduced the removal rates of Cr and Pb. The power supply mode had no significant effect on the removal rate of Cu. Heavy metal speciation was analyzed by the BCR method, and the relationship between the ratio of easily removed metal speciation and the removal rate was studied. The increase in the ratio of easily removed speciation was accompanied by an increase in the removal rate, indicating that citric acid and electroosmosis increased the removal rate by increasing the ratio of easily removed speciation. However, the high pH value around the cathode caused by the electrochemical reaction was not conducive to the removal of heavy metals.

Introduction

Sewage sludge, a byproduct of sewage treatment processes, is rich in nitrogen (N), phosphorus (P), potassium (K) and organic matter. It is a popular practice to dispose of sewage sludge via land use, and many countries currently use this method. However, it can be difficult to convince the government and land users to agree on this method because of the presence of toxic metals and bacteria in the sludge. Therefore, it is necessary to separate the heavy metals from the sludge [1,2]. The methods for the removal of heavy metals from sludge are chemical extraction, electrokinetic remediation, filtration, ion exchange, adsorption on activated carbon, membrane technologies, microbiological leaching, phytoremediation, etc. [3-9]. The electrokinetic process aims to remove the heavy metals using an electric field, which promotes several complex mechanisms such as electrodialysis electric migration, electrophoresis, and electrolysis. This approach is conducive to the transportation of pollutants [10,11]. These effects cause the heavy metals to concentrate around the cathode, which allows for their removal. The advantages of electrokinetic remediation are that it is simple (i.e., simple equipment), flexible (i.e., can be used for in situ or ex situ treatments), relatively inexpensive, effective and environmentally friendly [12,13].

Introduction

Materials and method

Results and discussion

Conclusion

References

Abstract

Adsorption is one of the most commonly used methods for the wastewaters treatment. In this work, we studied the impact of experimental conditions on the adsorption of heavy metals M(II) (M=Cd, Ni, Cu, Pb and Zn) in batch system using chitin obtained from crab shells. This biomaterial is selected because of its low cost, availability and efciency. The M(II) adsorption was found to be dependent on the initial pH, contact time, initial concentration of M(II) and biomass dose. The kinetic models of Elovich, pseudo-frst-order and pseudo-second-order kinetic models were successfully applied, providing the best ftting of the experimental data. The Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms and the thermodynamic parameters were also discussed. The adsorption capacity peaks at: 50, 47.61, 43.4, 40 and 38.46 (mg L−1) for Pb(II), Cu(II),Ni(II), Cd(II) and Zn(II), respectively. The negative free energy (∆G°) and positive enthalpy (∆H°) indicated spontaneous and endothermic adsorption.

Introduction

The natural environment is constantly contaminated by various pollutants coming from industrial sectors, which in turn showed a considerable change. Toxic metals are widespread and hazardous and afect the environment with a negative impact on the ecosystem, causing dangerous diseases to both animals and humans. Among toxic metals, one can cite Cd, Hg, Pb, As, Cr and Cu (Salem et al. 2012) which must be removed before discharge to the aquatic environment. Unlike organic pollutants, heavy metals are refractory and cannot be degraded and accumulate in living organisms (Ali and Ateeg 2015). The elimination of metals has been the subject of several works using diferent techniques like ion electrodialysis (Esalah et al. 2000), sedimentation (Gupta et al. 2001), ion exchange (Da̧browski et al. 2004; Kang et al. 2008), biological operations (Rashid et al. 2014), coagulation/focculation (Yue et al. 2009), nanofltration (Hafane et al. 2000), solid-phase extraction (Khezami and Capart 2005), adsorption (Abolhasani and Behbahani 2015; Behbahani et al. 2014) and electrokinetic remediation (Sawada et al. 2004). However, all these techniques sufer from high costs of capital and operations as well as the elimination of metallic sludge (Malairajan 2011). On the other hand, the adsorption has become advantageous for removing toxic metals because of its environmentally friendly characteristic, efciency and low cost. In this regard, many marine wastes were used as adsorbents for both inorganic and organic pollutants (Copat et al. 2012; Izquierdo et al. 2014; Samiey and Ashoori 2012; Vilar et al. 2008).

Municipal solid waste incineration (MSWI) fly ash contains significant amounts of heavy metals (e.g., Cd, Cu, Pb and Zn) and is therefore considered to be a hazardous waste requiring proper treatment prior to its disposal. In this work, an integrated hydrometallurgical process for treatment of MSWI fly ash was evaluated. Valuable metals, e.g. Cu and Zn, were first recovered by combining leaching and extraction sequentially. In the next step, the t removal of Cd and Pb from the remaining leachate using four types of iron-based adsorbents was evaluated. The leaching was optimized with respect to pH, leaching time and liquid to solid ratio. A test done under optimal conditions gave metal releases of 100% and 80% for Cu and Zn as well as 100% and 85% for Cd and Pb, respectively. The resulting leachate was contacted with organic phases based on kerosene containing the extractants LIX860NeI for Cu extraction and Cyanex 572 for Zn extraction in two consecutive steps. Efficient extractions were achieved, thus demonstrating that the combination of leaching and extraction can be successfully used for the recovery of Cu and Zn. Adsorption of heavy metal ions on various iron based sorbents to detoxify the aqueous effluent from the extraction showed good removal efficiency (more than 95%) for both Cd and Pb. The results of this study show that the proposed integrated process is a promising tool that can be used in the strategy for metal recovery and detoxification of MSWI fly ash.

Introduction

Over the past few decades, incineration has become a widely prevalent alternative for municipal solid waste management all over the world (Song et al., 2017), due to the energy recovery and reduction in the volume and mass of waste (Narayana, 2009). However the MSWI process produces a considerable amount of fly ash which is commonly rich in leachable heavy metals, thus posing a serious threat to the environment and human health. Fly ashes have been classified as a hazardous waste (MEE, 2016), which must be treated properly to prevent environmental pollution (GarciaLodeiro et al., 2016). China is one of the largest municipal solid waste producing countries in the world. It is reported that the MSW generated was approximately 170 Mt in 2016, with an annual increase of 8e10% (Xin-gang et al., 2016). Meanwhile, for the aim of proper treatment, the proportion of incineration in the waste disposal (waste to energy) will be increased from 31% in 2015 to 54% in 2020 in China according to the “13th Five-Year” National Municipal Solid Waste Disposal Facilities Construction Plan. The amount of municipal solid waste incineration fly ash generated will increase rapidly as a consequence. However, only a few landfill sites designed for the disposal of hazardous waste like MSWI fly ash in China are now in service (Cheng and Hu, 2010) while the construction of new sites lags behind the construction of incineration plants. Therefore, it is urgent to drive the processing options available due to the huge capacity gap.

The integrated utilization of wastes in a cement kiln has become an international megatrend. Various hazardous compounds containing in wastes might be enriched in the particulate matter (PM) emitted during the waste disposal and cause adverse environmental consequences. In order to evaluate the potential environmental issues caused by the PM emission from the cement kiln for co-processing wastes, the chemical characteristics and formation mechanism of the PM was investigated for the first time by using a laboratory-scale tube furnace to simulate this process. PM was collected to analyze the major components (heavy metals, inorganic and organic components) and morphologies. The results reveal that volatile heavy metals in municipal sewage sludge (MSS) can be enriched in PM. The process can elevate the levels of sulfate and the organic contents in PM, and the existence of organic moieties such as CNþ and CHNþ suggest that the co-processing of MSS can affect the PM organic compositions. Single particle imaging analyses indicate that PM can be classified into nine types based on their elemental compositions. Further analysis reveals that most particles usually mix with other types of particles and those mixed particles may cause a more serious impact on the environment. Based on the TEM observation, a two-step formation mechanism of PM is proposed. Our findings point out the potential environmental adverse effects and call attentions to a full environment assessment of this new type of cement production process, and also indicates stringent measures should be taken to reduce PM emissions during this process.

Introduction

Municipal sewage sludge (MSS) is a common waste worldwide, and its production has reached 30 Mt/y with an annual increasing rate of 8e10% (Xiao et al., 2017). The accumulation of MSS has become a serious environmental concern. Landfill and incineration are the two most common routes for MSS disposal in China (Zhou et al., 2014). Such methods have their own bottlenecks. For example, the reduction of land resource and undesired emissions (e.g., leachate and landfill gas) to ambient water, soil and air restricts the implementation of landfills (Jin et al., 2017). Incineration can also aggravate emissions of hazardous substances such as heavy metals and some organic species into the environment. The methods of gasification, pyrolysis and digestion have been proposed for the disposal of MSS, but the associated intensive energy consumption, complex operation, etc., may also limit further development of those methods. The integrated utilization of wastes such as MSS in cement kiln has become a promising method and attracts public interests due to its multiple advantages. For example, the MSS contains Ca, Si and Al, which are similar to the raw materials for cement production and the co-processing of MSS in a cement kiln can save natural resources. Dried MSS also contains significant calorific values, which could save energy at the same time. The silicate in the cement clinker such as tricalcium silicate and dicalcium silicate can help stabilize the heavy metals during the high temperature calcination process. Hazardous organic substances might also be decomposed due to the high temperature and long residence time in a cement kiln. The co-processing of wastes in cement kiln can also receive subsidies from the government. Despite aforementioned advantages, this disposal method may pose some environmental problems, such as the emission of particulate matter (PM) into the air.

Porous pavements are commonly used stormwater management systems. However, the understanding of their long-term capacity to retain heavy metals is limited. This study aims to investigate the longterm removal of heavy metals in three different porous pavements – Porous Asphalt (PA), Hydrapave (HP) and Permapave (PP) over accelerated laboratory experiments representing 26 years with varying hydrological conditions (drying/wetting periods and flow rates). A treatment model that simulates adsorption and desorption processes was developed for the first time to predict the long-term heavy metal removal by porous pavements. Unsurprisingly, all tested porous pavements performed better in removing metals that tend to attach to solid particles (e.g. Pb, Al, Fe) than more soluble ones (e.g. Cu, Zn, and Mn). There was a general increase of heavy metal concentrations at the outlet of the pavements over time as a result of a decrease in adsorption capacity of the systems, especially after the occurrence of clogging; the soluble heavy metals removal decreased with a reduction in flow rates which was speculated to be due to more time being available for desorption of metals and breakdown of accumulated sediments. The proposed model simulated the trend, fluctuations and peaks of heavy metal concentrations reasonably well, achieving the Nash-Sutcliffe coefficient (NSE) values of 0.53- 0.68 during model calibration. The model was most promising in predicting Al and Cu release from porous pavements (50%-91% of the observed data within the 90% uncertainty bands, NSE=0.44-0.74), followed by Fe and Pb (27-77% observations within the bands, NSE=0.20-0.69). Further improvements of the model are needed for it to be applicable for Zn and Mn.

Introduction

Due to the increase in impervious areas alongside rapid urbanisation, urban stormwater runoff and pollution have increased significantly (Goonetilleke et al., 2005;Zgheib et al., 2012). This causes adverse impacts not only on downstream water quality (Jeng et al., 2005), but also on stream health (Booth and Jackson, 1997). Meanwhile stormwater can also be an alternative resource if collected and treated properly. To manage stormwater issues in cities, a variety of techniques have been developed under the concept of Water Sensitive Urban Design (WSUD, also called Low Impact Development in USA, Sustainable Urban Drainage Systems in the UK, and Sponge City in China – Fletcher et al. (2015)). Porous pavements are one WSUD technology that can be easily retrofitted within dense urban areas, providing unique opportunities to infiltrate stormwater on site as source control measures without taking up space in urban landscape (Mullaney and Lucke, 2014).

1- Introduction

2- Microorganisms- the key players in bioremediation

3- Factors affecting heavy metal bioremediation

4- Role of enzymes in bioremediation

5- Phytoremediation

6- Immobilization techniques in bioremediation

7- Nanoparticles in bioremediation

8- Conclusion

References

Abstract

Pollution by heavy metals has been identified as a global threat since the inception of industrial revolution. Heavy metal contamination induces serious health and environmental hazards due to its toxic nature. Remediation of heavy metals by conventional methods is uneconomical and generates a large quantity of secondary wastes. On the other hand, biological agents such as plants, microorganisms etc. offer easy and eco-friendly ways for metal removal; hence, considered as efficient and alternative tools for metal removal. Bioremediation involves adsorption, reduction or removal of contaminants from the environment through biological resources (both microorganisms and plants). The heavy metal remediation properties of microorganisms stem from their self defense mechanisms such as enzyme secretion, cellular morphological changes etc. These defence mechanisms comprise the active involvement of microbial enzymes such as oxidoreductases, oxygenases etc, which influence the rates of bioremediation. Further, immobilization techniques are improving the practice at industrial scales. This article summarizes the various strategies inherent in the biological sorption and remediation of heavy metals.

Introduction

Recent years have evinced an unparalleled population growth and an accelerated pace of industrialization in line with it. Although, the quality of human life has substantially improved over the years, it is inevitable not to ignore that these developmental activities have taken place at the cost of the quality of our environment. During the last century, mining, electroplating, smelting, fertilizer, pesticides, tanneries, paper and electronic industries have accounted for the release of large amounts of heavy metals and petroleum hydrocarbons into the natural ecosystem, which has been reported to have disrupted the physiological functions in biological systems (Taiwo et al., 2016; Arivalagan et al., 2014). Environmental contamination can also occur through leaching of heavy metals, metal corrosion, atmospheric deposition, sediment resuspension to soil and ground water and metal evaporation from the water resources (Weerasundara et al., 2017; Francov
a et al., 2017). Hence, sediments constitute the major phase of contamination by metals in the aquatic systems (Nagajyoti et al., 2010). Among the pollutants, the hazardous heavy metals such as Arsenic (As), Cadmium (Cd), Lead (Pb), Copper (Cu), Chromium (Cr), Nickel (Ni), Zinc (Zn), Aluminum (Al) and Manganese (Mn) have known to be the major threats to the environment (Ullah et al., 2015; Dhanarani et al., 2016; Karthik et al., 2017a). These heavy metals impart serious health issues both to humans and ecosystems (Zeraatkar et al., 2016; Chen et al., 2015; Ullah et al., 2015). Source of various heavy metals are listed in Table 1. The heavy metal pollutants can enter into the environment through natural and anthropogenic ways and can be deposited in soils, water bodies or in the air (Kuppusamy et al., 2017; Chen et al., 2015).

Heavy metals cannot be biodegraded and they remain in the environment until being removed. Thus, the removal of heavy metals from contaminated water is of special concern for the protection of human and aquatic lives. Studies on polymer inclusion membranes (PIMs) started more than 50 years ago and have shown outstanding separation performance of metal ions. The potential and capabilities of PIMs have made it more favorable than ion exchange and liquid-liquid extraction process. To achieve efficient transport of metal ions, different types of extractant with compatible base polymer have been successfully used along with suitable targeted metal ions. However, selectivity of metal ion is only limited to one type of metal ion based on the extractant used in PIMs. The present review describes the current literature on heavy metal removal using PIMs for the past 3 years. The compatibility of extractant with base polymer and plasticizer is discussed. Most of PIM studies used cellulose triacetate (CTA) and polyvinyl chloride (PVC) as the base polymer, and only a few studies have used other base polymers. These new base polymers have shown better PIMs in terms of stability and separation performance compared to the CTA- and PVC-based PIMs. Moreover, a new invention of dual PIM separation system has allowed simultaneous separation of multiple metal ions. Such improvement in PIM technology can speed up commercialization process and make it viable for large scale and industrial use especially in hydrometallurgy and wastewater treatment.

Introduction

Industrial applications do not only use heavy metals in their manufacturing process but also produce heavy metals in their discharge wastewater and effluents. Without adequate treatment, these heavy metals will be released into water bodies and cause severe damage to the environment and ecosystem. Ion exchange [1], adsorption [2], and liquid-liquid extraction [3] are among methods used to separate heavy metal compounds from wastewater. However, these methods are often inefficient and costly. For example, liquid-liquid extraction has been widely used in separating heavy metals based on their relative solubility in water and organic solvents. Liquid-liquid extraction is highly risky due to toxicity and flammable nature of organic solvents, especially when they are used at industrial scale [4]. The evolution in membrane development and widely acceptance of membrane technology has developed new technology for treatment of heavy metals in wastewater. Over the last four decades, liquid membranes notably polymer inclusion membranes (PIMs) have been proven to be a better alternative than ion exchange and liquid-liquid extraction methods in extracting and recovering various metal ions [5, 6•]. This is because PIMs can simultaneously conduct extraction and back extraction at the same time unlike liquid-liquid extraction where back extraction only happens after the extraction process takes place. Although PIMs are initially used as sensing component in ion-selective electrodes (ISEs) and optodes, research on PIM-based separation especially in removing heavy metals has become very popular due to their excellent stability and versatility compared to other liquid membrane types especially supported liquid membranes (SLMs) [7••].

The aim of this work is to evaluate an efective fltration technique for residual organic pollutants and heavy metals removal using two types of sand rich in iron oxide as a massive flter (sieved and gross sand). X-ray difraction, X-ray fuorescence (XRF), scanning electron microscopy, energy dispersive spectroscopy (EDS) and specifc surface area BET were investigated to characterize the sand. Experimental results showed that the BOD5 removal was found to be 93% for gross sand (GS) and 96% for sieved sand (SS). The COD removal was equal to 98.9 and 99.7% for GS and SS, respectively. The hydrogen bonding, complexation/precipitation process, ions exchanges and electrostatic interactions are the main phenomena proposed to describe residual organic pollutants removal. For heavy metals adsorption, results show a great efciency removal between 90 and 100% for both cases. The adsorption mechanism was proposed based on zero-point charge, FTIR analysis, fuorescence (XRF) and EDS. The fxation of heavy metals onto the sand could be referred to hydrogen bonding, electrostatic interaction, ion exchange and electron donor–acceptors.

Introduction

Increased urbanization and population growth have resulted in an increase in water requirements, which has resulted in excessive use of water resources with a large volume of pollutants. Moreover, wastewater becomes an important source of pollution and a major human health problem (Chaves et al. 2016; Ellis and Butler 2015; Miao et al. 2015). In recent years, several environmental problems were observed as a result of water contamination by organic and inorganic pollutants characterized by their persistence, toxicity and bioaccumulation capacity. Therefore, they must be removed before being discharged into a receiver medium (Albishri and Mahmoud 2013; Ji et al. 2012; Gebru and Das 2017; Karnib et al. 2014; Tunali et al. 2006; Liu et al. 2013; Shannon et al. 2008). Heavy metals are the most common environmental water pollutants and pose a potentially carcinogenic risk to humans, such as anemia, nervous system deterioration, failure of kidneys, and DNA-protein cross-linkage leading to cancer of the kidneys, liver and gastric tract (An et al. 2001; Chaudhry et al. 2016a, 2017a; Yan and Viraraghavan 2003; Inglezakis et al. 2002). Unlike organic pollutant waste, heavy metals are characterized by a long-term persistence and high non-biodegradability (O’Carroll et al. 2013; Jiang et al. 2010; Hongjie et al. 2009; Zhong et al. 2014). For these reasons, efective elimination of organic pollutants and inorganic pollutants has become an important issue today (Gaikwad 2004; Uzun and Güzel 2000). Today, innovative and cost-efective solutions to wastewater treatment and wastewater reutilization with new materials and techniques become a priority (Ding et al. 2014). Iron oxide sand fltration can be an efective innovative technique to solve these problems. A number of papers have used diferent types of sand rich in iron oxide such as sand coated with iron oxide modifed with sulfate (Vaishya and Gupta 2005), iron impregnated quartz sand (IIS) (Vaishya and Gupta 2003), Ce(IV) doped iron oxide (Zhang et al. 2003), silica-containing iron(III) oxide (Zeng 2003), iron-oxide-coated polymeric materials (Katsoyiannis and Zouboulis 2002) and iron oxide coated sand (Gupta et al. 2005), iron-zirconium oxide-coated sand (Chaudhry et al. 2017b; Chaudhry and Khan 2017), iron oxide activated red mud (Khan et al. 2015), and zirconium oxide-coated marine sand (Khan et al. 2013). Various techniques have been explored to remove heavy metals and organic pollutants from wastewater such as electrocoagulation (Adhoum et al. 2004; Hanay and Hasar 2011; Heidmann and Calmano 2008; Kabdasli et al. 2009), ion exchange (Sapari et al. 1996), precipitation, adsorption (Chen and Wang 2000; Siddiqui and Chaudhry 2017), and ion exchange-assisted membrane separation (Dzyazko and Belyakov 2004; Vasilyuk et al. 2004). Among these techniques, fltration using sand is an innovative method for treating water contaminated by toxic pollutants. The simplicity, low energy consumption and relatively low operational costs make sand fltration one of the most common pretreatments currently used in large installations (Bar-Zeev et al. 2012).

Enzyme-mediated bioremediation is an eco-friendly process for removing hazardous toxic heavy metals from the environment. The potential use of mutant alkaline phosphatase H412R for bioprecipitation of heavy metals such as Co2+, Cd2+, Cr6+, Ni2+, Mn2+ and Zn2+ from single-ion solutions and electroplating efuents was analysed in the present study. Purifed wild-type and H412R mutant alkaline phosphatase enzymes were incubated with an initial concentration of 100 ppm metal solutions for various time periods along with the substrate p-nitrophenol phosphate. Upon catalysis, the enzyme–substrate reaction liberates inorganic phosphate which in turn binds to heavy metals and precipitates them as metal-phosphates. The amount of metal ions precipitated as a result of formation of metal ion-phosphate complexes was determined by estimating the amount of free metal ions present in the solution using atomic absorption spectroscopy. Based on the results obtained, maximum bioprecipitation of metal ions, in general, was observed at 180 min of incubation period. The H412R mutant enzyme exhibited higher efciency and precipitated 96% of Mn2+ from electroplating efuent and 92% of Co2+ from the metal ion solution. The pattern of precipitation of various metal ions was in the order Co2+>Cr6+>Ni2+>Cd2+>Mn2+>Zn2+ for H412R mutant enzyme and Co2+>Cr6+>Zn2+>Ni2+>Cd2+>Mn2+ for wild-type enzyme. The results emphasise the use of novel H412R, a mutated alkaline phosphatase enzyme in its catalytic site, as an efcient way of achieving bioremediation of heavy metals from real-time efuents.

Introduction

Release of hazardous wastes into the environment as a result of tremendous increase in industrialisation and urbanisation is of major public health concern. Contamination of ground water occurs because of discharge of efuents from industries such as tannery and electroplating which are known to contain considerable amount of toxic elements causing toxicity in the ecosystem with consequences to health of humans and animals (Bai et al. 2008; Benazir et al. 2010). Investigations with animal models revealed severe damage to the kidney in mice when exposed to heavy metals at levels beyond the limits set by WHO (Wasana et al. 2017). Among various metals, the trivalent and hexavalent chromium is the metal of concern that has reached a hazardous level of 120 µg/L in the ground water which is alarmingly high (Kazakis et al. 2017). It has been reported that upon continuous exposure chromium could increase the risk of bladder cancer in humans (Wise et al. 2016), while cadmium, even when present in low concentration, accumulates in kidney eventually causing renal failure and cardiovascular diseases (Burke et al. 2016). On the other hand, co-contamination of groundwater with other heavy metals such as iron, cobalt and zinc was found to increase the toxicity of nickel causing severe eczema of skin (Sankhla et al. 2016). Heavy metals are known also to disrupt endocrine system when exposed to prolonged periods of time (Chiu et al. 2016). Because of long persistence of heavy metals and their associated health hazards several methods have come into existence for the treatment of efuents. Diverse techniques such as physical, chemical, phytoremediation (Huang et al. 2017; Sharma et al. 2016; Zheng et al. 2017), bioleaching (Xu et al. 2017) and nanoparticles (Yurekli 2016) were employed during wastewater treatment. Some of these methods involve membrane fltration, ion exchange, adsorption (Zhao et al. 2016; Zhang et al. 2016) and electro-chemical techniques such as electro-winning, electro-dialysis and electro-deionisation (Dermentzis et al. 2011; Xu et al. 2017). Most of these methods are often considered to be expensive, time-consuming and requiring utmost energy during the process. Further, bioremediation processes involving whole organisms face limitations with respect to the availability of metal interactive sites, metal toxicity, biosorption and bioaccumulation. The search for alternate methods which are resourceful, cost-efective, biological and environment-friendly has led to what is known as the feld of the green chemistry with emphasis to use of biocatalysts such as enzymes for bioremediation of pollutants (Tischer and Wedekind 1999; Alcalde et al. 2006). Enzymatic bioremediation has become an attractive alternative for the treatment of pollutants since enzymes provide simpler systems than using whole organisms. The added beneft of employing enzymes is that they remain relatively stable during the reactions and being proteins they are readily biodegradable (Ruggaber and Talley 2006).

Aluminum manufacturing has been reported as one of the largest industries and wastewater produced from the aluminum industry may cause significant environmental problems due to variable pH, high heavy metal concentration, conductivity, and organic load. The management of this wastewater with a high pollution load is of great importance for practitioners in the aluminum sector. There are hardly any studies available on membrane treatment of wastewater originated from anodic oxidation. The aim of this study is to evaluate the best treatment and reuse alternative for aluminum industry wastewater using membrane filtration. Additionally, the performance of chemical precipitation, which is the existing treatment used in the aluminum facility, was also compared with membrane filtration. Wastewater originated from anodic oxidation coating process of an aluminum profile manufacturing facility in Kayseri (Turkey) was used in the experiments. The characterization of raw wastewater was in very low pH (e.g., 3) with high aluminum concentration and conductivity values. Membrane experiments were carried out with ultrafiltration (PTUF), nanofiltration (NF270), and reverse osmosis (SW30) membranes with MWCO 5000, 200–400, and 100 Da, respectively. For the chemical precipitation experiments, FeCl3 and FeSO4 chemicals presented lower removal performances for aluminum and chromium, which were below 35% at ambient wastewater pH ~ 3. The membrane filtration experimental results show that, both NF and RO membranes tested could effectively remove aluminum, total chromium and nickel (>90%) from the aluminum production wastewater. The RO (SW30) membrane showed a slightly higher performance at 20 bar operating pressure in terms of conductivity removal values (90%) than the NF 270 membrane (87%). Although similar removal performances were observed for heavy metals and conductivity by NF270 and SW30, significantly higher fluxes were obtained in NF270 membrane filtration at any pressure that there were more than three times the flux values in SW30 membrane filtration. Due to the lower heavy metal (<65%) and conductivity (<30%) removal performances of UF membrane, it could be evaluated as pretreatment followed by NF filtration to protect and extend NF membrane life. The water treated by both NF and RO could be recycled back into the process to be reused with economic and environmental benefits.

Introduction

The aluminum industry contributes to the global economy and to the individual national economies of more than 30 countries. Primary aluminum production, the second most used metal in the world, has been recorded as 51 million tonnes (Das and Yin 2007; IAI 2013). Aluminum is used for varied applications in the construction industry, in transport, in electrical engineering, in packing, and in all kinds of equipment. Among them, production of fencing construction such as windows, doors, and wall and roof profile systems are common usages (Sergey 2011). Finished aluminum is produced by extrusion of the ingots and then the extruded pieces are anodized or covered (Dufour et al. 2001). The aluminum surface is converted to aluminum oxide in the anodizing process. Anodic coatings are impregnated with organic and inorganic dyes and pigments (Lyle et al. 2000) and sulfuric acid solutions are widely employed as electrolytes in anodizing (Sakon et al. 2005; Sanders 2012). The conventional anodizing process has environmental problems that producing huge amounts of wastewater with toxic reagents, heavy metals, and wide variation in pH (Sakon et al. 2005). Wastewater is one of the main issues for the aluminum industry because of significant environmental concerns and public health problems, since they usually contain a notable amount of heavy metals and even toxic elements with relatively high solubility (Agrawal and Sahu 2009). Heavy metals released into the environment bioaccumulate in living organisms and have a serious impact even in trace quantities (Lin et al. 2005; Murthy and Chaudhari 2008).

Heavy metal pollution has become one of the most serious environmental problems nowadays. The removal of heavy metals from wastewaters has attracted a considerable attention because of their adverse efects on public health and ecosystems. The main objective of this work was to investigate the efciency of the coupling of infltration-percolation process with adsorption on activated carbon in the removal of heavy metals contained in urban wastewater efuents. The adsorption of heavy metals on a commercial sample of activated carbon was studied in a static mode. Several laboratory experiments made it possible to distinguish the optimum quantity of powdered activated carbon necessary to remove a large range of heavy metals. Results showed that the equilibrium of the adsorption was reached very quickly for cadmium (Cd2+), i.e., after 15 min of contact with the activated carbon. On the other hand, the equilibrium of zinc (Zn2+), lead (Pb2+) and copper (Cu2+) was achieved after 45 min. The withdrawal rates were 70.77% for Zn2+, 64.75% for Pb2+, 67.07% for Cu2+ and 78.42% for Cd2+. The adsorption isotherms determined for Zn2+, Pb2+, Cu2+ were of type I, while the shape of the Cd2+ curve showed a type II isotherm. These isotherms confrm the capacity of the powdered activated carbon to adsorb cadmium better than the other studied heavy metals.

Introduction

Heavy metals are dangerous species which induce various environmental and health problems (Göde et al. 2017). Most industries unload wastewater and efuent containing toxic materials, mainly heavy metals, into aquatic systems without treatment, which is a major environmental problem. The excessive release of these pollutants presents a particular problem because they are not biodegradable (Boussahel 2001). These pollutants do not all have the same risks to the environment (Houas et al. 1999) and to health because of their diferent physicochemical properties. Efuents are still treated at wastewater treatment plants (WWTPs), apart from exceptional cases of storm spills, and thus the future of the toxic pollutants contained in wastewater will very much depend on the purifcation efciency of these stations (Varrault 2011). This author has shown that during the treatment, a small quantity of metallic trace elements is not eradicated and will, therefore, pass into the aquatic environment. Furthermore, the uppermost proportion of metals is trapped in the sewage sludge and can, therefore, be transferred either to unloading stations or to agriculture which receives this type of sludge. Heavy metals can reach concentrations that threaten the survival of certain populations and pose dangers. Indeed, heavy metals in water are absorbed by plants and animals. When the amount of these elements exceeds the norms, they can accumulate in the organisms of the food chain (Lacoue-Labarthe 2007). There are several methods for heavy metal detection including inductively coupled plasma-mass spectrometry (Liao and Jiang 1999), spectrophotometry (Jankiewicz et al. 2000), fame-atomic absorption spectrometry (Bortoleto et al. 2004) or electrochemical methods that include ion-selective electrodes, polarography and other modifed electrodes (Yola et al. 2012; Gupta et al. 2013a, b; Yola et al. 2014; Göde et al. 2017).