Microbiological and physicochemical quality enhancement of treated wastewater using raw and chemically modified clays from Sidi Bouzid region, Tunisia.

Environmental discharge of wastewater represents a source of chemical and biological pollutants. This study firstly evaluates the microbiological and physicochemical quality of treated wastewaters collected from two wastewater treatment plants (WWTPs) located in two different Tunisian cities namely Sidi Bouzid (SB) and Gafsa (G). Then, the capacity of three raw and acid/base-activated local clays to enhance the quality of wastewaters was assessed. The results indicate that the quantities of enteric bacteria (oscillating from 1.381 × 103 to 1.4 × 108 CFU/100 mL), fungi (between 1.331 × 103 and 1.781 × 104 CFU/100 mL), as well as SARS-CoV-2 (between 4.25 × 103 and 5.05 × 105 CFU/100 mL) and Hepatitis A virus RNA (form 4.25 × 103 to 7.4 × 104 CFU/100 mL) detected in effluent wastewaters were not in compliance with the Tunisian standards for both studied WWTPs. Likewise for other indicators such as electrical conductivity (ranging 4.9-5.4 mS/cm), suspended matter (145-160 g l-1), chemical oxygen demand (123-160 mg l-1), biological oxygen demand 5 (172-195 mg l-1), chloride, Total Kjeldahl nitrogen (TKN) and phosphorus contents (710, 58-66 and 9.47-10.83 mg l-1 respectively), the registered values do not agree with the set standards established for wastewater treatment. On the other hand, the pH values fitted (oscillating from 6.86 (at G) to 7.24 (at SB) with the Tunisian standards for both WWTPs. After treatment, wastewaters showed better values for the microbiological parameters, especially for the clays designed as AM and HJ1, which eliminated 100% of viruses. In addition, when acid-activated AM clays were applied, a marked improvement in the quality of physicochemical parameters was obtained, especially for suspended matter (2 and 4 g l-1 for SB and G, respectively), TKN (5.2 (SB) and 6.40 (G) mg/l), phosphorus (1.01 (SB) and 0.81 (G) mg/l). Our results open perspectives for the possibility of efficiently using these specific clays in the enhancement of the quality of treated wastewaters.

Adsorption of antibiotics on bio-adsorbents derived from the forestry and agro-food industries.

Antibiotic consumption at high levels in both human and veterinary populations pose a risk to their eventual entry into the food chain and/or water bodies, which will adversely affect the health of living organisms. In this work, three materials from forestry and agro-food industries (pine bark, oak ash and mussel shell) were investigated as regards their potential use as bio-adsorbents in the retention of the antibiotics amoxicillin (AMX), ciprofloxacin (CIP) and trimethoprim (TMP). Batch adsorption/desorption tests were conducted, adding increasing concentrations of the pharmaceuticals individually (from 25 to 600 µmol L-1), reaching maximum adsorption capacities of ≈ 12000 µmol kg-1 for the three antibiotics, with removal percentages of ≈ 100% for CIP, 98-99% adsorption for TMP onto pine bark, and 98-100% adsorption for AMX onto oak ash. The presence of high calcium contents and alkaline conditions in the ash favored the formation of cationic bridges with AMX, whereas the predominance of hydrogen bonds between pine bark and TMP and CIP functional groups explain the strong affinity and retention of these antibiotics. The Freundlich's model provided the best prediction for AMX adsorption onto oak ash and mussel shell (heterogeneous adsorption), whereas the Langmuir's model described well AMX adsorption onto pine bark, as well as CIP adsorption onto oak ash (homogeneous and monolayer adsorption), while all three models provided satisfactory results for TMP. In the present study, the results obtained were crucial in terms of valorization of these adsorbents and their subsequent use to improve the retention of antibiotics of emerging concern in soils, thereby preventing contamination of waters and preserving environment quality.

Cu and As(V) Adsorption and Desorption on/from Different Soils and Bio-Adsorbents.

This research is concerned with the adsorption and desorption of Cu and As(V) on/from different soils and by-products. Both contaminants may reach soils by the spreading of manure/slurries, wastewater, sewage sludge, or pesticides, and also due to pollution caused by mining and industrial activities. Different crop soils were sampled in A Limia (AL) and Sarria (S) (Galicia, NW Spain). Three low-cost by-products were selected to evaluate their bio-adsorbent potential: pine bark, oak ash, and mussel shell. The adsorption/desorption studies were carried out by means of batch-type experiments, adding increasing and individual concentrations of Cu and As(V). The fit of the adsorption data to the Langmuir, Freundlich, and Temkin models was assessed, with good results in some cases, but with high estimation errors in others. Cu retention was higher in soils with high organic matter and/or pH, reaching almost 100%, while the desorption was less than 15%. The As(V) adsorption percentage clearly decreased for higher As doses, especially in S soils, from 60−100% to 10−40%. The As(V) desorption was closely related to soil acidity, being higher for soils with higher pH values (S soils), in which up to 66% of the As(V) previously adsorbed can be desorbed. The three by-products showed high Cu adsorption, especially oak ash, which adsorbed all the Cu added in a rather irreversible manner. Oak ash also adsorbed a high amount of As(V) (>80%) in a rather non-reversible way, while mussel shell adsorbed between 7 and 33% of the added As(V), and pine bark adsorbed less than 12%, with both by-products reaching 35% desorption. Based on the adsorption and desorption data, oak ash performed as an excellent adsorbent for both Cu and As(V), a fact favored by its high pH and the presence of non-crystalline minerals and different oxides and carbonates. Overall, the results of this research can be relevant when designing strategies to prevent Cu and As(V) pollution affecting soils, waterbodies, and plants, and therefore have repercussions on public health and the environment.

Potential of low-cost bio-adsorbents to retain amoxicillin in contaminated water.

Sewage sludge as agricultural amendment is the main route of human-medicine antibiotics to enter soils. When reaching environmental compartments, these compounds can cause significant risks to human and ecological health. Specifically, the antibiotic amoxicillin (AMX) is highly used in medicine, and the fact that more than 80% of the total ingested is excreted increases the chances of causing serious environmental and public health problems. As the use of low-cost bio-adsorbents could help to solve these issues, this research focuses on the retention of AMX onto four by-products of the forestry industry (eucalyptus leaf, pine bark, pine needles, and wood ash) and one from food industry (mussel shell). To carry out this study, batch-type tests were performed, where increasing concentrations of the antibiotic (0, 2.5, 5, 10, 20, 30, 40 and 50 µmol L-1) were added to samples of 0.5 g of each bio-adsorbent. Eucalyptus leaf, pine needle and wood ash showed adsorption scores higher than 80%, while it was up to 39% and 48% for pine bark and mussel shell, respectively. For pine bark, wood ash and mussel shell, adsorption data showed good adjustment to the Freundlich and Linear models, while pine needles and eucalyptus leaf did not fit to any model. There was not desorption when the maximum concentration of AMX (50 µmol L-1) was added. Overall, eucalyptus leaf, pine needles and wood ash can be considered good bio-adsorbents with high potential to retain AMX, which has significant implications regarding their eventual use to reduce risks of environmental pollution by this antibiotic.

Competitive adsorption and desorption of tetracycline and sulfadiazine in crop soils.

In view of the environmental issues caused by antibiotics, this research studies competitive adsorption/desorption for tetracycline (TC) and sulfadiazine (SDZ) in agricultural soils. Competitive adsorption was studied in binary systems (adding equal concentrations of both antibiotics). In addition, it was compared with results from simple systems. In all cases, batch-type adsorption/desorption experiments were carried out. In the binary systems, for the highest antibiotic concentration added, adsorption percentages were always higher for TC (close to 100%) than for SDZ (10-90%). In these systems, TC desorption was lower than 5% for all soils, and generally <10% for SDZ. Comparing TC and SDZ adsorption for the different systems, SDZ was clearly affected by the presence of TC, with SDZ adsorption percentages being was much higher (with differences generally above 65%) in the binary than in the simple systems. On the contrary, comparing the results of TC adsorption in simple and binary systems, TC was not affected by the presence of SDZ, obtaining similar adsorption percentages in both systems. Kd and KF values (in the Linear and Freundlich models), were higher in the simple systems in the case of TC, which could be due to competition with SDZ, while for SDZ Kd and KF were higher in the binary systems, with a synergistic effect of TC favoring SDZ adsorption. Regarding desorption, it reached 100% for SDZ in some soils in simple systems, dropping to 10% in the presence of TC. TC desorption was <4%, not affected by SDZ. The results indicate that environmental risks would be higher for SDZ, showing differences when both antibiotics are present. This can be considered relevant as regards public health and environmental preservation, in view of direct toxicities and the promotion of resistance to antibiotics associated with the presence of these contaminants in the environment.

Amoxicillin Retention/Release in Agricultural Soils Amended with Different Bio-Adsorbent Materials.

The antibiotic amoxicillin (AMX) may reach soils and other environmental compartments as a pollutant, with potential to affect human and environmental health. To solve/minimize these hazards, it would be clearly interesting to develop effective and low-cost methods allowing the retention/removal of this compound. With these aspects in mind, this work focuses on studying the adsorption/desorption of AMX in different agricultural soils, with and without the amendment of three bio-adsorbents, specifically, pine bark, wood ash and mussel shell. For performing the research, batch-type experiments were carried out, adding increasing concentrations of the antibiotic to soil samples with and without the amendment of these three bio-adsorbents. The results showed that the amendments increased AMX adsorption, with pine bark being the most effective. Among the adsorption models that were tested, the Freundlich equation was the one showing the best fit to the empirical adsorption results. Regarding the desorption values, there was a decrease affecting the soils to which the bio-adsorbents were added, with overall desorption not exceeding 6% in any case. In general, the results indicate that the bio-adsorbents under study contributed to retaining AMX in the soils in which they were applied, and therefore reduced the risk of contamination by this antibiotic, which can be considered useful and relevant to protect environmental quality and public health.

Relevance of sorption in bio-reduction of amoxicillin taking place in forest and crop soils.

The fate of antibiotics reaching soils is a matter of concern, given its potential repercussions on public health and the environment. In this work, the potential bio-reduction of the antibiotic amoxicillin (AMX), affected by sorption and desorption, is studied for 17 soils with clearly different characteristics. To carry out these studies, batch-type tests were performed, adding increasing concentrations of AMX (0, 2.5, 5, 10, 20, 30, 40, and 50 µmol L-1) to the soils. For the highest concentration added (50 µmol L-1), the adsorption values for forest soils ranged from 90.97 to 102.54 µmol kg-1 (74.21-82.41% of the amounts of antibiotic added), while the range was 69.96-94.87 µmol kg-1 (68.31-92.56%) for maize soils, and 52.72-85.40 µmol kg-1 (50.96-82.55%) for vineyard soils. When comparing the results for all soils, the highest adsorption corresponded to those more acidic and with high organic matter and non-crystalline minerals contents. The best adjustment to adsorption models corresponded to Freundlich's. AMX desorption was generally <10%; specifically, the maximum was 6.5% in forest soils, and 16.9% in agricultural soils. These results can be considered relevant since they cover agricultural and forest soils with a wide range of pH and organic matter contents, for an antibiotic that, reaching the environment as a contaminant, can pose a potential danger to human and environmental health.

SARS-CoV-2 and other main pathogenic microorganisms in the environment: Situation in Galicia and Spain.

In the context of the current COVID-19 pandemic, and mostly taking a broad perspective, it is clearly relevant to study environmental factors that could affect eventual future outbreaks due to coronaviruses and/or other pathogenic microorganisms. In view of that, the authors of this manuscript review the situation of SARS-CoV-2 and other main pathogenic microorganisms in the environment, focusing on Galicia and Spain. Overall, in addition to showing local data, it is put in evidence that, summed to all efforts being carried out to treat/control this and any other eventual future epidemic diseases, both at local and global levels, a deep attention should be paid to ecological/environmental aspects that have effects on the planet, its ecosystems and their relations/associations with the probability of spreading of eventual future pandemics.

Optimization of synergistic biosorption of oxytetracycline and cadmium from binary mixtures on reed-based beads: modeling study using Brouers-Sotolongo models.

The first aim of this study was to synthesize and characterize reed-based-beads (BBR), an enhanced adsorbent from Tunisian reed. The second purpose was to evaluate and optimize the BBR efficiency for the simultaneous removal of oxytetracycline (OTC) and cadmium (Cd(II)), using central composite design under response surface methodology. The third goal was to elucidate the biosorption mechanisms taking place. It was shown that under optimum conditions (4.19 g L-1 of BBR, 165.54 µmol L-1 of OTC, 362.16 µmol L-1 of Cd(II), pH of 6, and 25.14-h contact time) the highest adsorption percentages (63.66% for OTC and 99.99% for Cd(II)) were obtained. It was revealed that OTC adsorption mechanism was better described by Brouers-Sotolongo fractal equation, with regression coefficient (R2) of 0.99876, and a Person's chi-square (χ2) of 0.01132. The Weibull kinetic equation better explained Cd(II) biosorption (R2 = 0.99959 and χ2 = 0.00194). FTIR and isotherm studies confirmed that the BBR surface was heterogeneous, and that adsorption mechanisms were better described by the Freundlich/Jovanovich equation (R2 = 0.99276 and χ2 = 0.04864) for OTC adsorption, and by the Brouers-Sotolongo model (R2 = 0.9851 and χ2 = 0.77547) for Cd(II) biosorption. Overall results indicate that, at last, the BBR lignocellulosic biocomposite beads could be considered as cost-effective and efficient adsorbent, which could be of socioeconomic and environmental relevance. Graphical abstract.

Competitive adsorption and desorption of three tetracycline antibiotics on bio-sorbent materials in binary systems.

Batch-type experiments were used to study competitive adsorption/desorption for the antibiotics tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC), onto by-products from forest and food industries (oak ash, pine bark, and mussel shell). These antibiotics are frequently present in manures and slurries spread on agrosystems. Binary competitive systems were performed by setting the dose of one antibiotic to 200 µmol L-1, and varying the concentration of a second antibiotic from 50 to 600 µmol L-1. In the cases where a concentration of 200 µmol L-1 was used for each antibiotic, the results of the binary experiments were also compared with those obtained in parallel tests corresponding to simple and ternary systems using the same concentration. The results indicated that pine bark can adsorb most of the antibiotics added, with desorption being less than 5% in most cases. Oak ash showed high adsorption for all three antibiotics in the simple systems (100% of CTC, 90% of TC, and 80% of OTC), but clearly decreased in the binary systems (up to values below 40%), especially for higher antibiotics concentrations, although desorption was generally less than 5%. Mussel shell showed adsorption results lesser than 25% for OTC and CT in simple systems, while increased up to 65% in binary systems in which CTC was present at high concentrations, but desorption was generally very high. CTC was the antibiotic with the highest adsorption onto all three by-products, and the one showing less decrease for its adsorption in the binary systems. Overall, the smallest differences among the various competitive systems were obtained when the adsorbent used was pine bark, and especially for the CTC antibiotic. These results could aid to develop management practices, based on the use of low-cost bio-sorbents, which would decrease risks of pollution due to tetracycline antibiotics spread in agroecosystems and affecting the environment.

Adsorption/desorption of three tetracycline antibiotics on different soils in binary competitive systems.

Taking into account environmental and public health issues due to emerging pollutants, and specifically to antibiotics spread into environmental compartments, this work focused on the competition among three tetracycline antibiotics (tetracycline, CT; oxytetracycline, OTC; and chlortetracycline, CTC) for adsorption sites in six different soils. Batch-type adsorption/desorption tests were carried out, with 24 h as contact time. The six soils were from two different farming areas, and were selected according to pH values and organic matter contents. Binary systems (pairs of antibiotics present simultaneously) were used to study competition, setting the dose of one antibiotic at 200 µmol L-1, and varying the concentration of another from 50 to 600 µmol L-1. In the case of the concentration of 200 µmol L-1, the results of the binary systems were also compared with those obtained in simple and ternary systems. The results showed that those soils with the highest organic matter content (soils 50AL and 71S) adsorbed 100% of the three antibiotics, with desorption being <10% in all cases. The other four soils showed some degree of competition for adsorption sites in binary systems, with adsorption decreasing between 25 and 47% compared to simple systems, and with desorption increasing, especially in soils with higher pH and less organic matter. This competition was even more pronounced in ternary systems, affecting to these same soils, while the effects were very scarce in soils with higher organic matter content. The results indicate that most of the studied soils have high adsorption capacity for tetracycline antibiotics, retaining them with high energy even in the case of multiple systems. It was also shown that hysteresis affected adsorption/desorption processes. These results have relevance at environmental and social levels, given the growing concern regarding antibiotics pollution, and the need of promoting their retention and inactivation when spread in environmental compartments.

Competitive adsorption/desorption of tetracycline, oxytetracycline and chlortetracycline on pine bark, oak ash and mussel shell.

We studied competitive adsorption for the tetracycline antibiotics (TCs) tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC) on three bio-adsorbents (mussel shell, oak wood ash, and pine bark). The results were compared for individual systems (with antibiotics added separately) and ternary systems (with all three antibiotics added simultaneously). In all cases batch-type experiments were carried out, with 24 h of contact time. In the individual systems, concentrations of 200 µmol L-1 were used for each of the three antibiotics, separately. In the ternary system, all three TCs were added simultaneously, using the following total concentrations: 50, 100, 200, 400, 600 µmol L-1, each antibiotic being 1/3 of the total. Taking into account that ionic strength of a solution is related to a measure of the concentration of ions in that solution, the use of individual and ternary systems allows to compare, for each antibiotic, systems having equal concentrations and similar ionic strength (concentrations of 200 µmol L-1), and systems having different concentrations and ionic strength (200 µmol L-1 in the individual systems, and 600 µmol L-1 in the ternary systems, resulting from the sum of 200 µmol L-1 corresponding to each of the three antibiotics). Adsorption/desorption results indicated that these processes were in all cases closely related to pH values, and to carbon and non-crystalline minerals contents in the bio-adsorbents. Both oak ash and pine bark adsorbed close to 100% of TCs in individual and ternary systems, with desorption <4% for oak ash, and <12% for pine bark. However, mussel shell gave clearly poorer results, only relatively acceptable for CTC, with adsorption <56% and desorption even >30% for TC and OTC. In view of the results, oak ash and pine bark can be recommended as effective bio-adsorbents for the three TCs studied, and could be useful to retain/inactive them in wastes, and soil or liquid media receiving these emerging pollutants, thus reducing risks of damage for public health and the environment.

Competitive adsorption of tetracycline, oxytetracycline and chlortetracycline on soils with different pH value and organic matter content.

Antibiotics spread into the environment can cause soil and water degradation. Specifically, tetracycline antibiotics (TCs) are among those most consumed in veterinary medicine, and near 90% of the doses administered to animals are excreted as original compounds, due to poor absorption. In this study we investigated competitive soil adsorption/desorption for three tetracycline antibiotics (tetracycline: TC, oxytetracycline: OTC, and chlortetracycline: CTC), usually spread on soils by slurry fertilization, affecting to soil degradation due to chemical pollution. The study was carried out on six soils selected according to their pH values (4.49-7.06), and organic matter contents (1.07-10.92%). The competitive experiments were performed in ternary systems (adding all three TCs simultaneously, using five equal and increasing concentrations, from 17 to 200 µmol L-1). The results were compared with those obtained in simple systems (adding individual antibiotics separately), for the same final concentration (in this case, 200 µmol L-1) and for different concentrations (200 µmol L-1 in the simple systems, versus 600 µmol L-1 in the ternary systems, resulting from the sum of 200 µmol L-1 of each of the three antibiotics). In all cases, batch-type adsorption/desorption experiments were carried out, with 24 h as contact time. Those soils with higher organic matter content adsorbed 100% of the TCs, with desorption being always lower than 3%. In soils with less organic matter, adsorption decreased as the dose of added antibiotic increased, due to competition for adsorption sites. CTC was the most retained among the three TCs (up to 20% more than the other when high doses of antibiotic were added). In the simple systems, percentage adsorption was always high (>85%) for the three TCs; however, percentage adsorption decreased in the ternary systems, reaching just 65% and 40% (for equal and different ionic strength, respectively) in soils with low organic matter contents. These results show the environmental and public health relevance of competition among the three TCs. In fact, the highest risk of entering the food chain takes place when these antibiotics are spread together on soils with low organic matter content, especially in the case of TC and CTC, which are the least adsorbed and the most desorbed molecules.

Controlling risks of P water pollution by sorption on soils, pyritic material, granitic material, and different by-products: effects of pH and incubation time.

Batch experiments were used to test P sorbent potential of soil samples, pyritic and granitic materials, mussel shell, mussel shell ash, sawdust, and slate waste fines for different pH and incubation times. Maximum P sorption varied in a wide range of pH: < 4 for pyritic material, 4-6 for forest soil, > 5 for slate fines, > 6 for shell ash, and pH 6-8 for mussel shell. P sorption was rapid (< 24 h) for forest soil, shell ash, pyritic material, and fine shell. On the opposite side, it was clearly slower for vineyard soil, granitic material, slate fines, pine sawdust, and coarse shell, with increased P sorption even 1 month later. For any incubation time, P sorption was > 90% in shell ash, whereas forest soil, pyritic material, and fine shell showed sorption rates approaching 100% within 24 h of incubation. These results could be useful to manage and/or recycle the sorbents tested when focusing on P immobilization or removal, in circumstances where pH changes and where contact time may vary from hours to days, thus aiding to diminish P pollution and subsequent eutrophication risks, promoting conservation and sustainability.

Chromium and fluoride sorption/desorption on un-amended and waste-amended forest and vineyard soils and pyritic material.

Using batch-type experiments, chromium (Cr(VI)) and fluoride (F-) sorption/desorption were studied in forest and vineyard soil samples, pyritic material, pine bark, oak ash, hemp waste and mussel shell, as well as on samples of forest and vineyard soil, and of pyritic material, individually treated with 48 t ha-1 of pine bark, oak ash, and mussel shell. Pine bark showed the highest Cr(VI) sorption (always > 97% of the concentration added) and low desorption (<1.5%). Pyritic material sorbed between 55 and 98%, and desorbed between 0.6 and 9%. Forest and vineyard soils, oak ash, mussel shell and hemp waste showed Cr(VI) sorption always < 32%, and desorption between 22 and 100%. Pine bark also showed the highest F- retention (sorption between 62 and 73%, desorption between 10 and 15%), followed by oak ash (sorption 60-69%, desorption 11-14%), forest soil (sorption 60-73%, desorption 19-36%), and pyritic material (sorption 60-67%, desorption 13-15%), whereas in vineyard sorption was 49-64%, and desorption 24-27%, and in hemp waste sorption was 26-36%, and desorption 41-59%. Sorption data showed better fitting to the Freundlich than to the Langmuir model, especially in the case of Cr(VI), indicating that multilayer sorption dominated. The addition of by-products to the forest and vineyard soils, and to the pyritic material, caused an overall increase in F- sorption, and decreased desorption. Furthermore, the pine bark amendment resulted in increases in Cr(VI) retention by both soils and the pyritic material. These results could be useful to favor the recycling of the by-products studied, aiding in the management of soils and degraded areas affected by Cr(VI) and F- pollution, and in the removal of both anions from polluted waters.

Effects of Changing pH, Incubation Time, and As(V) Competition, on F- Retention on Soils, Natural Adsorbents, By-Products, and Waste Materials.

The purpose of this work was to elucidate the repercussion of changing pH, incubation time and As(V) competition on fluoride (F-) sorption on forest and vineyard soil samples, pyritic, and granitic materials, as well as on the by-products pine sawdust, oak wood ash, mussel shell ash, fine and coarse mussel shell, and slate processing waste fines. To reach this end, the methodological approach was based on batch-type experiments. The results indicate that, for most materials, F- sorption was very high at the start, but was clearly diminished when the pH value increased. However, oak wood ash and shell ash showed high F- sorption even at alkaline pH, and pine sawdust showed low F- sorption for any pH value. Specifically, F- sorption was close to 100% for both ashes at pH < 6, and around 70% at pH 10, while for forest soil it was close to 90% at pH < 2, and around 60% at pH values near 8. Regarding the effect of incubation time on F- sorption, it was very low for both soils, pyritic material, granitic material, and both kinds of ashes, as all of them showed very rapid F- sorption from the start, with differences being lesser than 10% between sorption at 30 min and 1 month of incubation. However, sawdust and slate fines sorbed 20% of added F- in 30 min, remaining constant up to 12 h, and doubling after 30 days. And finally, mussel shell sorbed 20% at 30 min, increasing to close to 60% when incubation time was 30 days. This means that some of the materials showed a first sorption phase characterized by rapid F- sorption, and a slower sorption in a second phase. As regards the effect of the presence of As(V) on F- sorption, it was almost negligible, indicating the absence of competition for sorption sites. In view of that all, these results could aid to appropriately manage soils and by-products when focusing on F- removal, in circumstances where pH value changes, contact time vary from hours to days, and potential competition between F- and As(V) could take place.

As(V) Sorption/Desorption on Different Waste Materials and Soil Samples.

Aiming to investigate the efficacy of different materials as bio-sorbents for the purification of As-polluted waters, batch-type experiments were employed to study As(V) sorption and desorption on oak ash, pine bark, hemp waste, mussel shell, pyritic material, and soil samples, as a function of the As(V) concentration added. Pyritic material and oak ash showed high sorption (90% and >87%) and low desorption (<2% and <7%). Alternatively, hemp waste showed low retention (16% sorption and 100% desorption of the amount previously sorbed), fine shell and pine bark sorbed <3% and desorbed 100%, the vineyard soil sample sorbed 8% and released 85%, and the forest soil sample sorbed 32% and desorbed 38%. Sorption data fitted well to the Langmuir and Freundlich models in the case of both soil samples and the pyritic material, but only to the Freundlich equation in the case of the various by-products. These results indicate that the pyritic material and oak ash can be considered efficient As(V) sorbents (thus, useful in remediation of contaminated sites and removal of that pollutant), even when As(V) concentrations up to 6 mmol L-1 are added, while the other materials that were tested cannot retain or remove As(V) from polluted media.

Heavy metals fractionation and desorption in pine bark amended mine soils.

The European Community Bureau of Reference method (BCR) was used for evaluating the effects of pine bark amendment (0, 24 and 48 g kg-1) and ageing (1 and 30 days) on Cd, Cu, Ni, Pb and Zn fractionation, on samples from an acid mine soil. In addition, the stirred flow chamber technique was applied for analyzing heavy metals desorption from the unamended and pine bark amended mine soil. When the unamended soil were not subjected to ageing, the added heavy metals were mainly accumulated as soluble fraction (>90% for Cd, Ni and Zn; 71% for Cu; and 45% for Pb). Pine bark amendment and ageing had little effect on Cd, Ni and Zn fractionation, whereas important changes were detected for Cu and Pb in response to both pine bark amendment and ageing (decrease in the soluble fractions, and increase in less mobile fractions). Desorption experiments showed that both pine bark amendment and ageing decreased heavy metals release from the mine soil. The results of this study indicate that pine bark amendment could be used to increase heavy metals retention (especially in the case of Cu and Pb) in acid mine soils, thus reducing the risks of metal transfer to uncontaminated environmental zones.

As(V)/Cr(VI) retention on un-amended and waste-amended soil samples: competitive experiments.

Focusing on simultaneous arsenic and chromium pollution, we used batch-type experiments to study As(V)/Cr (VI) competitive sorption on soil samples, pyritic material, mussel shell, oak ash, pine bark and hemp waste, as well as on binary mixtures (50 % mussel shell and 50 % another material-oak ash, pine bark, or hemp waste), and on forest and vineyard soil samples and pyritic material amended with 48 t ha-1 of mussel shell, oak ash, pine bark, or hemp waste. Equal As(V) and Cr(VI) concentrations (0 to 6 mmol L-1) were added to the individual materials, binary mixtures, and 48 t ha-1 amended materials. The individual forest soil sample, pyritic material, and oak ash showed clearly higher As(V) sorption, whereas Cr(VI) sorption was higher on pine bark. Sorption was up to 50 % higher for As(V) than for Cr(VI) on the forest soil sample, oak ash, and pyritic material, while pine bark sorbed 95 % more Cr(VI). Regarding binary mixtures, the presence of mussel shell increased As(V) sorption on pine bark and Cr(VI) sorption on hemp waste. As regards the amendments, in the case of the forest soil sample, the amendments with oak ash and mussel shell increased As(V) sorption, while pine bark amendment increased Cr(VI) sorption; in the vineyard soil sample, the mussel shell amendment increased As(V) sorption; in the pyritic material, pine bark amendment increased Cr(VI) sorption. These results could be useful to appropriately manage the soils and individual or mixed by-products assayed when As(V) and Cr(VI) pollution occurs.