A bioseparation process for removing heavy metals from waste water using biosorbents

of conventional adsorbents to the use of biosorbents. The presence of heavy metals in the environment is of major concern because of their toxicity, bioaccumulating tendency, and threat to human life andthe environment. In recent years, many low cost sorbents such as algae, fungi bacteria and lignocellulosic agricultural by-products have been investigated for their biosorption capacity towards heavy metals. In this comprehensive review, the emphasis is on outlining the occurrences and toxicology of heavy metals and the biosorption capacity of biosorbents compared to conventional adsorbents. A detailed description of the adsorption properties and mode of action of these biosorbents is offered in order to explain the heavy metal selectivity displayed by these biosorbents. The role of cell structure, cell wall, micropores and macropores is evaluated in terms of the potential of these biosorbents for metal sequestration. Binding mechanisms are discussed, including the key functional groups involved and the ion-exchange process. Quantification of metal-biomass interactions is fundamental to the evaluation of potential implementation strategies, hence, sorption isotherms, sorption kinetics, intraparticle diffusivities as well as models used to characterize biosorbent sorption are reviewed. The sorption behavior of some biosorbents with various heavy metals is summarized, their relative performance evaluated and a bioseperation process flow diagram for heavy metal removal from wastewater using biosorbents was propose

Potential Use of Agro/Food Wastes as Biosorbents in the Removal of Heavy Metals

The production of large quantities of agro/food wastes from food processing industries and the release of pollutants in the form of heavy metals from various metallurgical industries are the grave problems of the society as well as serious threats to the environment. It is estimated that approximately one–third of all food that is produced goes to waste, meaning thereby that nearly 1.3 billion tonnes of agro/food wastes are generated per year. This readily available and large amount waste can be utilized for the removal of toxic metals obtained from metallurgical industries by converting it into the adsorbents. For example, mango peel showed adsorption capacity of 68.92 mg/g in removing cadmium II ions. Similarly, coconut waste showed a higher adsorption capacity of 285 and 263 mg/g in removing cadmium and lead ion, respectively. Biosorption and bioaccumulation are recommended as novel, efficient, eco-friendly, and less costly alternative technologies over the conventional methods such as ion exchange, chemical precipitation, and membrane filtration, etc. for the removal of toxic metal ions. Because of the presence of metal-binding functional groups, the industrial by-products, agro-wastes and microbial biomass are considered as the potential biosorbents. Thus they can be used for the removal of toxic metal ions. This chapter highlights the available information and methods on utilizing the agro/food waste for the eradication of toxic and heavy metal ions. Furthermore, this chapter also focuses on the sorption mechanisms of different adsorbents as well as their adsorbing capacities

Remediation of metal ions in aqueous solution using activated carbon from Zea may stem

Zea mays stem and its activated carbon were prepared through chemical activation method using four different activating reagents (NaOH, H₃PO₄, H₂SO₄, KOH) and were used as adsorbents for the removal of Pb(II), Cu(II), Hg(II) and Cr(III) from aqueous solution. The results shows that activated carbon has high surface area and pore volume compared to the powdered raw Zea mays stem. Prepared activated carbon was characterized using physico-chemical properties such as carbon yield, iodine number, moisture content, percentage adsorption, and analytical instruments such as Fourier transform Infrared spectroscopy (FTIR), atomic absorption spectrometer (AAS), scanning electron microscopy (SEM), Energy Dispersive X-ray analysis (EDS), powder X-ray Diffraction (pXRD). The adsorption of Pb(II), Cu(II), and Cr(III) ions were pH, contact time, and concentration dependent. Based on the results obtained from the batch experiments, activated carbon prepared from Zea mays stem is not good enough for the removal of Hg(II) from aqueous solution. Adsorption ability was calculated and found to be 66.67% for activated carbon obtained from H₂SO₄, 21.21% for activated carbon obtained from KOH, and 20% for activated carbons obtained from NaOH and H₃PO₄. The pH 5-6 was chosen for all experiments, contact time was 2 hours, and adsorbent dosage was 2 g, initial concentration range from 200, 400, 600, 800, and 1000 ppm at room temperature. The metal ion removal trend was found in the order Pb(II)>Cu(II)>Cr(III)>>Hg(II). The Langmuir model fitted well in most of the cases with > 0.99. Consequently, the adsorption of Pb(II) and Cu(II) followed Langmuir isotherm model while that of Cr(III) best fitted the Freundlich isotherm model. The results indicated that the adsorption process followed two possible mechanisms. (I) Metal ion – adsorbent complex model and (II) Metal ion – ion-exchange adsorbent complex model

Eesti substraatide biokeemilise metaanitootlikkuse potentsiaali määramine ja anaeroobse kääritamise mõnede inhibiitorite uurimine

Energia sõltuvus fossiilsetest kütustest on sundinud riike üle maailma leidma uusi alternatiive energia tootmiseks. Võimalike taastuvate ener-giaallikate seas peetakse üheks potentsiaalseks energia saamise alternatii-viks biogaasi tootmist, kuna samaaegselt lahendatakse ökoloogilisi prob-leeme. Anaeroobse kääritamise protsess, milles rühm spetsialiseerunud anaeroobseid baktereid muudab orgaanilist biomassi biogaasiks, on hästi dokumenteeritud. Siiski ei ole andmed tavaliste keemiliste näitajate ja biomassi metaanitootlikkuse potentsiaali kohta alati esitatud standardi-seeritud vormis, mis teeb nende interpretatsiooni raskeks nii teadlaste kui ka biogaasijaamade operaatorite jaoks. Levinumad substraadid biogaasi tootmiseks Eestis võiksid olla looma-sõnnik, energiakultuurid, silod. Hinnanguliselt on Eestis umbes 286 000 ha vabanenud põllumajanduslikku maad, mida võib kasutada ener-giakultuuride kasvatamiseks, ja umbes 128 000 ha poollooduslikku rohumaad. Siiski on Eestis 2011. aastal ainult üks põllumajanduslikul toormel töötav biogaasijaam. Biogaasi toodetakse Eestis reoveepuhastites ja prügilates. Palju uurimusi on läbi viidud eesmärgiga suurendada biogaasi tootmi-se efektiivsust. Need uuringud keskenduvad uute reaktorite konfigurat-sioonile, erinevate substraatide kooskääritamisele ja samuti anaeroobse kääritamise inhibiitorite väljaselgitamisele. Kirjandusest teadaolevad inhibiitorid on ammoniaak, pika ahelaga rasvhapped, raskmetallid ja teised. Viimastel aastatel on erinevates teadusvaldkondades (pinnateadu-sed, orgaaniline keemia, molekulaarbioloogia, pooljuhtide füüsika ja ka põllumajandusteadused) suurenenud huvi nanotehnoloogia vastu, mis võib põhjustada uute toksiliste ainete sattumist keskkonda. Uute kemi-kaalide – nanoosakeste – ökotoksilisus ja mõju anaeroobsetele mikro-organismidele pole veel teada. Käesoleva doktoritöö peamisteks eesmärkideks olid 1) andmebaasi loomine, mis koondaks kirjanduses avaldatud teadustöö-de ja rakenduslike projektide andmeid erinevate substraatide keemili-se koostise ja metaanitootlikkuse potentsiaali kohta (artikkel I); 2) Eesti põllumajandusliku biomassi ja põllumajandustootmise jäätmete metaanitootlikkuse potentsiaali ja metaani tootmise kineetika uuri-mine (artiklid II ja III); 3) metallioksiidide nanoosakeste kahjuliku mõju uurimine biogaasi tootmisel, võrreldes neid tava- ehk mikrosuuruses osakestega (artikkel IV). Metoodika Metaanitootlikkuse potentsiaali andmebaas loodi elektrooniliselt, kasu-tades kolme programmeerimiskeelt: HTML, PHP ja MySQL. See on kättesaadav aadressil http://bioconversion.emu.ee/. Juurdepääs andme-baasile on vaba peale e-registreerimist ja andmebaasi administraatori heakskiitu. Andmed on organiseeritud substraadi tüübi alusel. Iga subst-raadi jaoks on lisatud andmed koos viidetega algallikatele nii substraadi kui olemasolul ka kääritusjäägi keemilise koostise ja metaanitootlikkuse potentsiaali kohta pärast ühikute standardiseerimist (artikkel I). Analüüsiti 61 Eestist pärit substraadi (rohtne biomass ja põllumajan-dustootmise jäätmed) keemilist koostist ja määrati nende metaanisaagis, kasutades biokeemilise metaanitootlikkuse potentsiaali testi (artiklid II ja III). Lisaks viidi läbi anaeroobne inhibeerimistest CuO ja ZnO nano-osakeste ja tavasuuruses osakestega (artikkel IV). Inokulum mõlemate katsete jaoks saadi Tallinna reoveepuhasti anaeroobsest reaktorist. Testid teostati hapnikuvabas keskkonnas temperatuuril 36 °C, metaani teket mõõdeti gaaskromatograafiliselt. Metaani kumulatiivne saagis arvutati, lahutades inkubatsiooni aja jooksul tekkinud metaani summast substraa-dita võrdluskatses tekkinud metaani saagis. Gaasi produktsiooni väljen-dati metaani liitrites, arvutatuna 0 °C ja 1 atm tingimustele katses lisatud substraadi kuivaine või orgaanilise aine kilogrammi kohta (artiklid II ja III). Metaanitootlikkuse potentsiaali (kõrgeim kumulatiivne metaani saagis testi jooksul) ja protsessi kiiruskonstandi väärtuse sõltuvust subst-raadi keemilisest koostisest analüüsiti Pearsoni korrelatsioonanalüüsi abil (artikkel III). Biogaasi ja metaani tootmise inhibeerumine arvuta-ti inhibiitorit sisaldavates katsetes tekkinud biogaasi ja metaani koguste võrdlemisel kontrollkatsetega. REGTOXi programmi Log-Normali mu- delit kasutades arvutati üldlevinud toksilisusparameetrid EC10, EC20 ja EC50 (artikkel IV). Tulemused ja arutelu Loodud metaanitootlikkuse potentsiaali andmebaas sisaldas 2011. a septembriks andmeid 226 erineva substraadi kohta 88 kirjandusallikast. Sama substraadi kohta on sageli andmeid erinevatest publikatsioonidest. Andmebaasis on 535 erinevat kirjet energiakultuuride, 63 sõnniku, 98 kooskääritamise ja 102 jäätmete rühmas (artikkel I). Katsetöös uuritud substraatide keemilise koostise andmed sarnanesid teis-te autorite poolt avaldatud tulemustega. Rohtse biomassi (energiakultuu-rid, silod, hein) metaanisaagised olid vahemikus 286-323 L CH4/kg VS. Vedelsõnniku proovidest oli sea vedelsõnnikul kõrgem metaanisaagis (317 L CH4/kg VS) kui veise vedelsõnnikul (238 L CH4/kg VS). Ana-lüüsitud energikultuuridest oli metaanitootlikkus kõige kõrgem aas-rebasesaba korral (323 L CH4/kg VS). Uuritud toiduainetööstuse ülejää-kidest oli kõrgeim metaanisaagis juustul (658 L CH4/kg VS), samas kui madalaim saagis leiti teraviljaveski jääkidest (328 L CH4/kg VS) (artiklid II ja III). Kõrgeim kineetiline kiiruskonstant määrati piima (0,344 ± 0,03 1/d) ja madalaim (0,061 1/d) energiarohu Szarvasi-1 korral. Põllumajandus-liku rohtse biomassi (rohusilo, maisisilo, silosegu ja hein) korral olid kiiruskonstandid vahemikus 0,086–0,230 1/d. Sea vedelsõnnikust oli metaani tekkimine kiirem kui veise vedelsõnnikust, kiiruskonstandid vastavalt 0,139 ja 0,092 1/d. Tööstuslikest jääkidest oli metaani tekki-mine aeglaseim katsetes piiritustööstuse praagaga. Erinevused protsessi kiirustes on seletatavad substraatide erineva keemilise koostisega (artik-kel III). Analüüsides substraatide metaanisaagise sõltuvust keemilisest koosti-sest, ilmnes metaani saagise positiivne korrelatsioon orgaanilise aine ja valkude sisaldusega substraadi koostises. Ligniinisisaldus substraatides mõjutas metaani produktsiooni negatiivselt. Olulised positiivsed seosed keemilise koostise ja kiiruskonstandi vahel leiti P, Ca, Mg ja K puhul. Mida kõrgem oli aga lignotselluloosse materjali (hemitselluloos, tsellu-loos, ligniin) sisaldus substraatides, seda väiksem oli metaani tekke kiirus (artikkel III). Inhibeerimistestides näitasid CuO ja ZnO nanoosakesed negatiivsemat mõju anaeroobsele käärimisprotsessile kui nende tava- ehk mikrosuuru-ses osakesed. Katsetes ZnO nanoosakestega oli biogaasi ja metaani teke vähem inhibeeritud kui katsetes CuO nanoosakestega. Metaani teket uurides leitud EC50 väärtused tava- ja nanosuuruses CuO-osakestega katsetes olid vastavalt 129 ja 10,7 mg Cu/L, ZnO puhul vastavalt 101 ja 57,3 mg Zn/L. Keemiline analüüs näitas CuO nanoosakeste suuremat lahustuvust, võrreldes mikrosuuruses osakestega (artikkel IV). Tulemus-test selgus, et nanosuuruses CuO inhibeeriv mõju võib osaliselt olla põh-justatud lahustunud Cu2+-ioonidest katsekeskkonnas. Järeldused Loodud andmebaas võimaldab kasutajatel koondatult ja ühtsetele ühi-kutele viidult kätte saada andmeid erinevate kultuuride ja orgaaniliste jäätmete keemilise koostise ja metaanitootlikkuse potentsiaali kohta koos vastavate kirjandusviidetega Open Accessi keskkonnas. Teadlased saaksid andmebaasi kasutada substraatide võrdlemisel, uurides biomassi koostise mõju metaani saagisele, ja statistilise analüüsi eesmärgil. Inseneride jaoks võiks andmebaas olla oluline abivahend biogaasijaamade projekteerimi-sel ja opereerimiseks vajalike andmete koondamisel. Doktoritöö tulemused näitasid Eesti rohtse biomassi, loomade vedel-sõnniku ja põllumajandusjäätmete kõrget metaani tootlikkuse potent-siaali. Saadud metaanisaagised varieerusid vahemikus 238 L CH4/kg VS (veise vedelsõnnik) kuni 658 L CH4/kg VS (juustujäägid). Kiireim substraadi biokonversioon metaaniks toimus katsetes piimaga, kus ku-lus ainult kolm päeva ultimatiivsest metaani saagisest 80% saavutami-seni. Samas kulus energiarohu korral selleks 31 päeva. Kuigi tulemused näitasid põllumajanduslikest substraatidest biogaasi tootmise suurt po-tentsiaali, on kääritamisprotsessi erinevate aspektide ja kommertsiaalse süsteemi toimimise analüüsimiseks vajalik ka pilootseadmetega uurin-gute läbiviimine. Nanoosakeste mõju kohta anaeroobsetes süsteemides on avaldatud üksi-kuid andmeid. Doktoritöös saadud tulemused on olulised, täiendamaks nanoosakeste potentsiaalse mõju iseloomustamist anaeroobses käärita-misprotsessis. Tulemused näitasid, et CuO- ja ZnO-osakeste suurusel oli otsene mõju biogaasi ja metaani saagisele. Nanoosakeste suurem inhi-beeriv toime võib osaliselt olla selgitatud toksiliste metalliioonide (Cu2+, Zn2+) sattumisega vette. Edasised uuringud inhibeerimise mehhanismide osas on olulised, et selgitada teiste võimalike tegurite mõju. Rohtsest biomassist biogaasi tootmine, kasvatades vabanenud maal kõr-ge energiapotentsiaaliga sobivaid kultuure, võimaldaks Eestil täita taas-tuvenergia tootmise vajadust. Loomade vedelsõnnik ja tööstuse jäätmed on sobivateks substraatideks kooskääritamisel, nende kasutamine bio-gaasi tootmiseks on tähtis ka jäätmetekke vältimise ning õhu ja veeko-gude keskkonnakaitse seisukohast. Võtmeküsimuseks on koostöö põllu-majandustootjate ja valitsusringkondade vahel, et soodustada investeeri-mist uute biogaasijaamade rajamisse.Publication of this thesis is supported by the Estonian University of Life Sciences and by the Doctoral School of Earth Sciences and Ecology created under the auspices of European Social Fund

Using agricultural wastes to treat lead-contaminated water in Western Australia

Aqueous solutions are becoming increasingly contaminated in all parts of the world (2015). Heavy metals are toxic contaminants that are mainly distributed in urban stormwater run-off and industrial wastewaters as a result of some mining operations, electronic assembly planting, battery manufacturing, and etching operations (Kadirvelu et al. 2001). Pb (II) is a heavy metal that causes significant damage in the human body. Drinking lead-contaminated water even at low concentrations may cause lifethreatening conditions such as cancer, kidney damage, brain damage, and liver problems (El-Said 2010). Therefore, it is necessary to remove lead from aqueous solutions. Several conventional physical, chemical, and biological systems have been used to eliminate Pb (II) ions from contaminated aqueous solutions, including membrane filtration (Song et al. 2011), electrolysis (Deng et al. 2010), chemical precipitation (Cort 2005), magnetic base methods (Ma et al. 2017), water filtration (Gohari et al. 2013, Magni et al. 2015), and adsorption techniques (Pehlivan et al. 2009). However, the cost of some of the cited techniques is prohibitively high, while others cannot remove low Pb (II) ion concentrations efficiently (Babel and Kurniawan 2003, Volesky and Holan 1995). Although adsorption is a reasonable process for removing dissolved lead from contaminated water, the cost of using conventional media (e.g. activated carbon and resin) make it cost inhibitive for the treatment of large quantities of wastewater (Cutillas-Barreiro et al. 2016, Demirbas 2008). It also takes a long time in some cases to achieve adsorption equilibrium (Czinkota et al. 2002). In recent decades, interest in the use of cost-effective adsorbents to reduce the expense of water treatment processes has intensified. Attention has been focused on natural agricultural waste materials such as seeds (Gilbert et al. 2011), fruit peel (Mallampati et al. 2015), nut shells (Taşar et al. 2014) , crop residues (El-Said 2010), and fruit shells (Zein et al. 2010) as low-cost and environmentally friendly adsorbents which are highly efficient and generally available in large quantities (Ibrahim et al. 2010). Against this backdrop, many agricultural residues are being produced every day, and they need to be managed. Using agricultural wastes to treat contaminated water is a low-cost and effective approach that deal with waste management and water treatment at the same time. This project describes an economically viable and practical way to utilize crop residues as adsorbents to remove toxic Pb (II) ions from lead-contaminated water. These agricultural waste adsorbents have a number of advantages; they are cheap and biodegradable, they have a porous surface, and are able to eliminate Pb (II) ions from contaminated water quickly and effectively. Therefore, in this research two Western Australian crop residues were used as adsorbents to eliminate lead ions from aqueous solutions. The study was carried out in four phases: the first phase involved the selection and preparation of different local Western Australian agricultural wastes. Lupin straw and canola stalk were collected from local farms and studied for their efficiency as two low-cost natural adsorbents that can remove dissolved Pb2+ ions from synthetic wastewater. In the second phase, experiments were carried out to understand the equilibria of Pb (II) adsorption onto adsorbents. The effect of various environmental conditions such as contact time, pH, initial adsorbent dosage and adsorbate concentration were investigated. The presence of different functional groups, chemical compositions, and the surface characteristics of the adsorbents were analysed in the third phase using energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) devices. In the final phase, the obtained experimental data were validated using different isotherm models developed by Langmuir, Freundlich, Harkins-Jura, Redlich- Peterson and Halsey to describe the adsorption process based on the homogeneity of the surfaces of the adsorbents. Pseudo-first-order, pseudo-second-order, intra-particle diffusion, Elovich, and fractional power kinetic models were utilized to investigate the dynamic mechanism of lead adsorption onto adsorbents over time

Perspective Chapter: Environmental-Friendly Agro Waste Management

Abundant amount of agro wastes is produced day by day globally to manage the escalating needs of billons of human population. The agro wastes are produced from various sources mainly crops left out, agro industries, aquaculture, and livestock. The major ingredient of agro wastes are of cellulose, lignin, hemicelluloses, etc. Conventionally, most of the crops left out were used for composting, animal fodder, domestic fuel, etc. Due to modernization technology in agriculture sector, people from Third World countries prefer cost-effective methods such as combustion process. Improper management of agro waste generated in the process has been contributing toward escalating air, soil, and water pollution. A proper environmental-friendly management of agro waste is the need of the time for sustainability, food, and health security of human. Lignin and hemicellulose can be used for generation of biofuels and biofertilizer. Cellulose can be sustainably used for the production of nanosilica, biodegradable polymer, paper, pulp, etc. This chapter emphasizes sustainable agro waste management without affecting the environment at lower cost in timely manner. In particular, the agro waste biomass could be used as a source of value-added bio-product, which has wide applications and impacts the bio-economy without hampering the climatic change issue

Alkaline Urine Dehydration : how to dry source-separated human urine and recover nutrients?

Human urine is a renewable resource from which water, nutrients and energy can be recovered and safely recycled. This thesis presents a novel on-site technology, called alkaline dehydration, for recovering nutrients from source-separated urine. To recover urea (the major nitrogenous compound in fresh urine) and prevent its urease enzyme-catalysed hydrolysis to ammonia, fresh urine was alkalised to pH ≥10 by anion exchange or use of alkaline substrates. To reduce the volume and concentrate the nutrients, the alkalised urine was dried in different substrates at temperatures of 40-60 °C. To evaluate alkaline urine dehydration at pilot-scale, a prototype dryer with capacity to treat 30 L urine d–1 was built and field-tested for three months at a military camp in Finland. More than 90% of the urine mass was reduced and dehydration rates of up to 40 L urine d–1 m–2 were obtained. Up to 98% of the nitrogen (N) and 100% of the phosphorus (P) and potassium (K) in urine were recovered. A dry solid containing 10% N, 1.5% P and 6.0% K, with similar salt and heavy metal content to synthetic fertilisers available in Sweden was produced. At least 12.5 g Ca(OH)2 or 6.8 g MgO per litre of fresh urine was required to buffer the pH of urine against absorption of CO2 during dehydration. The energy demand for evaporating urine was similar to that of incineration toilets, but could be reduced if heat energy from the dryer’s exhaust air were recovered. Overall, this thesis shows that a new sanitation system that safely collects, treats, transports and applies urine as fertiliser could be created by integrating alkaline urine dehydration with existing infrastructure. If implemented globally, this system could recycle 31 Tg N y–1 and 2.8 Tg P y–1, which would reduce the transgression of the planetary boundary for N and P by 35% and 25%, respectively

Production of high-value nanoparticles via biogenic processes using aquacultural and horticultural food waste

The quantities of organic waste produced globally by aquacultural and horticulture are extremely large and offer an attractive renewable source of biomolecules and bioactive compounds. The availability of such large and diverse sources of waste materials creates a unique opportunity to develop new recycling and food waste utilisation strategies. The aim of this review is to report the current status of research in the emerging field of producing high-value nanoparticles from food waste. Eco-friendly biogenic processes are quite rapid, and are usually carried out at normal room temperature and pressure. These alternative clean technologies do not rely on the use of the toxic chemicals and solvents commonly associated with traditional nanoparticle manufacturing processes. The relatively small number of research articles in the field have been surveyed and evaluated. Among the diversity of waste types, promising candidates and their ability to produce various high-value nanoparticles are discussed. Experimental parameters, nanoparticle characteristics and potential applications for nanoparticles in pharmaceuticals and biomedical applications are discussed. In spite of the advantages, there are a number of challenges, including nanoparticle reproducibility and understanding the formation mechanisms between different food waste products. Thus, there is considerable scope and opportunity for further research in this emerging field

DISTRIBUTION AND BIOAVAILABILITY OF METALS IN GASOLINE CONTAMINATED SITES IN LAGOS, NIGERIA

Distribution of metals in soil of two gasoline contaminated sites in Lagos were studied. Total Concentrations of twenty-five elements were investigated in composite samples collected at different depths within the sites. The elements were determined by ICP-AES after microwave assisted acid digestion of the samples. Chemical fractionation, mobility and potential bioavailability of some of the toxic and EU priority metals e.g., Pb, Cu, Cd, and Fe were evaluated in the topsoil (0-15 cm) by sequential extraction. There were great variation in the concentrations of the elements in both sites with depth. Speciation analysis showed that Pb and Cd dominated the Fe-Mn oxide fraction while the concentrations of Fe and Cu were higher in the residual fraction in site A. In site B, Pb, Cu and Cd was mainly associated with the Fe-Mn oxide fraction, while Fe was in the residual fraction. Cd has the highest mobility factors, 33.2% (site A) and 29.5% (site B), respectively. The concentrations of most of the toxic heavy metals (e.g., Pb, Zn, Cu, Cr, Cd etc.) exceed that of the control samples and heavy metal baseline values around the world. Thus, proper management of these potentially contaminated sites is imperative to prevent human health risk

Biochar applications for treating potentially toxic elements (PTEs) contaminated soils and water: a review

Environmental pollution with potentially toxic elements (PTEs) has become one of the critical and pressing issues worldwide. Although these pollutants occur naturally in the environment, their concentrations are continuously increasing, probably as a consequence of anthropic activities. They are very toxic even at very low concentrations and hence cause undesirable ecological impacts. Thus, the cleanup of polluted soils and water has become an obligation to ensure the safe handling of the available natural resources. Several remediation technologies can be followed to attain successful remediation, i.e., chemical, physical, and biological procedures; yet many of these techniques are expensive and/or may have negative impacts on the surroundings. Recycling agricultural wastes still represents the most promising economical, safe, and successful approach to achieving a healthy and sustainable environment. Briefly, biochar acts as an efficient biosorbent for many PTEs in soils and waters. Furthermore, biochar can considerably reduce concentrations of herbicides in solutions. This review article explains the main reasons for the increasing levels of potentially toxic elements in the environment and their negative impacts on the ecosystem. Moreover, it briefly describes the advantages and disadvantages of using conventional methods for soil and water remediation then clarifies the reasons for using biochar in the clean-up practice of polluted soils and waters, either solely or in combination with other methods such as phytoremediation and soil washing technologies to attain more efficient remediation protocols for the removal of some PTEs, e.g., Cr and As from soils and water