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This research work focuses on the development of a new process for the decontamination of municipal wastes incinerators fly ashes. The objective of this study was to evaluate different total and selective precipitation methods for metals removal from ash decontamination leachates. The tested options include 1) use of hydrated lime and caustic soda for selective (pH 5.0) and total (pH 8.5) metal precipitation; 2) addition of different chemicals (H3PO4, Na2S and FeCl3) in a pH range from 6.0 to 9.0. Fly ash decontamination assays using alkaline and acid washing steps were initially performed using optimal conditions previously established. Treated fly ashes respected the standards based on the TCLP leaching test for all studied metals and SPLP. Total metal precipitation tests carried out at pH 8.5 achieve removal yields for all metals > or = 90% using hydrated lime and > or = 83% using caustic soda. Selective precipitation tests alone at pH 5.0 show removal yields > or = 97% for Cr and between 75 and 87% for Al and Pb. Moreover, assays carried out using a stoechiometric addition of Na2S have allowed the separation of Cd (> or = 99%) and Zn (> or = 71%) as metal sulphides (CdS and ZnS). From an economical point of view, the most interesting option seems to be the leachates neutralization at pH 7.0 using Ca(OH)2 combined with the reuse of the treated leachates in the fly ash leaching steps. Metal precipitation cost at pH 7.0 has been estimated to be 22.7 CAN dollars tct-1 using Ca(OH)2, and 26.7 CAN dollars tct-1 using NaOH.

Adsorption tests were carried out in acidic synthetic solutions (pH 2.0) using 20 g l(-1) of various natural adsorbents and 0.25 mM of 11 different metals. In decreasing order, the most efficient adsorbents tested were: oyster shells, cedar bark, vermiculite, cocoa shells and peanut shells. In contrast, weak metal adsorption was demonstrated by: red cedar wood, peat moss, pine wood, corn cobs and perlite. Metal adsorption capacities in acidic synthetic solution followed the order: Pb2+> Cr3+> Cu2+> Fe2+> Al3+> Ni2+> Cd2+ > Mn2+ > Zn2+ >> Ca2+, Mg2+. Alkaline treatment (0.75 M NaOH) increased the effectiveness of metal removal for the majority of adsorbents. In contrast, acid treatment (0.75 M H2SO4) either reduced or did not affect the adsorption capacity of the materials tested. Finally, oyster shells, red cedar wood, vermiculite, cocoa shells and peanut shells, were effective natural adsorbents for the selective recovery of lead and trivalent chromium from acidic effluent.

The Montreal Urban Community (MUC) treatment plant produces approximately 270 tons of dry sludge daily (tds/day) during physicochemical wastewater treatment. The sludges are burned and contribute to the greenhouse effect by producing atmospheric CO2. Moreover, the sludge emanates a nauseating odour during its thermal stabilisation and retains unpleasant odours for the part (25%) that is dried and granulated. To solve this particular problem, the treatment plant authorities are currently evaluating an acidic chemical leaching (sulfuric or hydrochloric acid) process at a pH between 2 and 3, using an oxidizing agent such as ferric chloride or hydrogen peroxide (METIX-AC technology, patent pending; [20]). They could integrate it to a 70 tds/day granulated sludge production process. Verification of the application of METIX-AC technology was carried out in a pilot plant set up near the sludge production plant of the MUC. The tests showed that METIX-AC technology can be advantageously integrated to the process used at the MUC. The residual copper (274 +/- 58 mg/kg) and cadmium (5.6 +/- 2.9 mg/kg) concentrations in the treated sludge meet legislation standards. The results have also shown that odours have been significantly eliminated for the dewatered, decontaminated, and stabilized biosolids (> 97%) compared to the non-decontaminated biosolids. A high rate of odour elimination also was obtained for the liquid leached biosolids (> 93%), compared to the untreated liquid biosolids. The fertilising value (N and P) is well preserved by the METIX-AC process. Dissolved organic carbon measurements have showed that little organic matter is brought in solution during the treatment. In fact, the average concentration of dissolved organic carbon measured in the treated liquid phase is 966 +/- 352 mg/l, whereas it is 1190 +/- 325 mg/l in untreated sludge. The treated sludge was first conditioned with an organic polymer and a coagulant aid. It was successfully dewatered with various dehydration equipments (filter press, rotary press, centrifuge).

Thermodynamic calculations were performed in order to predict the formation of metal precipitates during the tannery sludge leaching. Gibbs free energy deltaG=RTln(Qc/Kc) of precipitation reaction was used to examine the formation of precipitates during the leaching process. The values of activity equilibrium constant (Ka) of various precipitation reactions were adopted from the literature. The Ka values were corrected to obtain the corresponding values of concentration product (Qc) and concentration equilibrium constant (Kc) using the activity coefficients (gamma) of the ions. The activity coefficients (gamma) of the ions was calculated using Davies equation Lngammai=-1.172Zi2((I0.5/(1+I0.5))-0.3I) (aqueous solution, 25 degrees C, 1 atm, I>0.3 mol x l(-1)). The values of ionic strength (I) at different sludge solids concentration and leaching pH were obtained by measuring the concentration of all ionic species in the leachate. The thermodynamic calculations indicated that the possible metal precipitates formed during the leaching process were (am)Cr(OH)3, (am)CrPO4, (am)Fe(OH)3, alpha-FeOOH(goethite), FePO4.2H2O, (am)AIPO4-2H2O, CaSO4.2H2O(gypsum). The solubility of these precipitates was found to decrease with the increase in the ionic strength (or sludge solids concentration). The results of computations were supported by the experimental observations.

Metal removal by biological solubilization in three strongly contaminated sediments was carried out in a two-liter stirred bioreactor. Biological treatment yielded metal removal efficiencies in the range of 11-30%, 43-57%, 60-79%, 61-90%, 18-21%, 0-10% for Pb, Cu, Zn, Cd, Ni and Cr, respectively. The treated sediments were then rinsed with a NaCl solution (0.5 M), resulting in an increase by nearly 47% in Pb removal for the three sediments, while for other metals (Cu, Zn, Cd, Ni, Cr), the NaCl rinse did not seem to allow any significant increase in metal solubilization. A standard procedure of sequential selective extraction (SSE) was applied to the sediments before and after each treatment. With regard to Pb, Zn and Cd, the carbonate bound fractions (2/3 sediments) represented 18-42% of metals prior to treatment, while the iron and manganese oxides bound fraction constituted 39-60% of metals for the three sediments. Between 90 and 100% of Pb, Zn and Cd removed by the process came from the fractions bound to carbonates and from those bound to Fe and Mn oxides. The organic matter and sulfide bound fractions contained 65-72% of total Cu present before treatment and the process removed, on average, 63% Cu present in this fraction. In contrast, Ni and Cr were found mainly in the residual fractions (50-80%). Finally, this biological treatment did not solubilize Cr appreciably, while removal of Ni mostly originated from the carbonate and Fe/Mn oxides fractions (70-80%).

A mixed culture of two fast-growing bacterial strains for heavy-metal solubilization of municipal sewage sludge has been developed. Strain VA-7 decreases the initial sludge pH (7-8.5) to a value between 4.0 and 4.5. Then, strain VA-4 begins growing and further reduces the pH to values below 2.0. The rapid decrease of sludge pH by a mixed culture through sulfur oxidation into sulfuric acid solubilizes the toxic metals (Cd 83-96%, Cr 16-54%, Cu 85-87%, Mn 91-94%, Ni 78-79%, Pb 28-46%, Zn 82-96%) to levels recommended for intensive use of residual sludge in agriculture. A study of the physiological and metabolic characteristics of these strains revealed that isolate VA-7 is a strain of Thiobacillus thioparus (ATCC 55127), while isolate VA-4 corresponds to a Thiobacillus thiooxidans (ATCC 55128). These bacterial strains possess distinctive physiological characteristics that allow them to easily grow and solubilize heavy metals in municipal sludge.

Le Maroc abrite le long de ses cotes des milieux paraliques tels que des lagunes, des estuaires et des baies qui comptent parmi les plus productifs au monde. Le site le plus important au Maroc est la baie de Dakhla, tant par sa superficie que par sa richesse halieutique. Ainsi, cette baie est un ecosysteme ayant une forte potentialite en termes d'aquaculture et, principalement, la conchyliculture, et abrite des zones propices pour la tapiculture, la mytiliculture et l'ostreiculture, conformement au plan d'amenagement base sur le concept de la planification ecologique. Un suivi hydrologique (temperature, salinite, chlorophylle “a”, matieres en suspension et matiere organique) a ete entame depuis avril 2004 sur un projet d'elevage d'huitres creuses (Crassostrea gigas) installe sur le site Duna Blanca depuis avril 2003. Aussi, au cours de cette etude, un suivi saisonnier de la structure sedimentaire a la fois granulometrique et metallique a ete realise. Les prelevements hydrologiques ont ete effectues mensuellement en surface et au fond, en periode des vives-eaux, a maree basse et maree haute. Les resultats issus de cette etude montrent bien que le site presente toujours une richesse en elements nutritifs et une biomasse chlorophyllienne importante. Un gradient de sursalure est bien net avec une variation saisonniere de la temperature. La structure sedimentaire est de type vaseux-sableux a sableux. Les concentrations en metaux dans les sediments ne depassent jamais les seuils de toxicite. Cependant, le potentiel de production du site ne peut etre sans limite ce qui necessite une attention particuliere au cours de l'extension et de l'installation des nouvelles fermes conchylicoles. Mots cles: Hydrologie, edaphique, baie de Dakhla, ostreiculture, metal ABSTRACT Morocco shelters lagoons, estuaries and bays along its paralic coasts which are among the most productive in the world. The Bay of Dakhla is the longest and the most important site in Morocco due to its halieutic richness. In fact, this bay is an ecosystem with great potential in terms of aquaculture, mainly shellfish farming, and shelters favorable zones for tapiculture, mytiliculture and ostreiculture, in accordance with ecological planning. A hydrological study (temperature, salinity, chlorophyll “a”, suspended matter and organic matter) was conducted on a breeding project of the cupped oyster (Crassostrea gigas) installed on the Duna Blanca site since April 2003. A seasonal follow-up of sediment structure was carried out involving granulometric and metallic studies. The hydrological sampling was performed monthly on the surface and at the bottom, during spring tides, low tide and high tide. The results confirmed that the site encompasses a wealth of nutritive elements and a significant chlorophyll-rich biomass. A gradient of hypersalinity is well correlated with seasonal variation of the temperature. The sedimentary structure ranges from muddy-sandy to sandy type. The metal concentrations in the sediments never exceeded the toxicity thresholds. However, the site's production potential cannot be limitless and could be affected by the extension and installation of new conchylaceous farms. [ABSTRACT FROM AUTHOR]

At the onset of 21st century, the pollution of surface and groundwater by toxic metals continues to represent a challenge for the authorities responsible for environmental protection. The uncontrolled rejection of metals in aquatic ecosystems such as Ag, As, Be, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Tl and Zn, constitute a serious threat to human and animal health. Several methods of treatment of waters polluted by metals have been proposed during the last several decades. However, the technique of precipitation of metals remains the most favorable option on an industrial scale due to reasons of cost-effectiveness, performance, and simplicity. The present review presents current knowledge on various technical alternatives for precipitation of metals. The discussion relates to the individual characteristics of the metal contaminants, as well as their behavior compared to various techniques of precipitation. [ABSTRACT FROM AUTHOR]

An investigation on the effect of sludge solids concentration on bioleaching of Cr(III) and other metals from tannery sludge by indigenous sulphur-oxidizing bacteria was carried out. The sludge solids concentrations ranged from 13 to 60 g/L. The concentration of elemental sulphur was fixed at 30 g/L. The results showed that the lowest pH reached after 25 days of bioleaching at all studied sludge solids concentration was about 1.3. The optimum sludge solids concentration for maximum metal leaching from tannery sludge was 40 g/L and about 87% of Cr(III), 73% of Al, 72% of Fe, 62% of Mg, and 73% of Zn could be leached in this case. During bioleaching, the concentrations of total and volatile suspended solids of the tannery sludge significantly decreased. The sulphur-oxidizing bacteria could tolerate a Cr(III) concentration as high as 5,930 mg/L at pH 1.3. The leaching efficiencies of Cr(III), Al, and Fe for both chemical leaching and bioleaching of tannery sludge were similar at pH 1.3. The leaching efficiency of Ca, Mg, and Zn in both leaching processes were identical for pH values in the range of 1.3 to 3.0. [ABSTRACT FROM AUTHOR]

The MUC (Montreal Urban Community) treatment plant produces approximately 270 tons of dry sludge daily (270 tds/day) during the physico-chemical treatment of wastewater. Recently, this treatment plant endowed a system of drying and granulation of sludge for valorization as an agricultural fertilizer having a capacity of 70 tds/day (25% of the daily sludge production). However, the metal content (mainly Cu and Cd) of the sludge surpasses the norms for biosolids valorization. In order to solve this problem, a demonstration project, from the lab scale to the industrial pilot plant, was carried out to test the Metix-AC technology for the removal of metals. A strongly metal-loaded filtrate was generated during the sludge decontamination. Tests concerned the study of the metal recovery by total precipitation and selective precipitation, as well as the use of alternative products for the metal precipitation. Other works consisted to simulate the acid filtrate recirculation from the decontaminated sludge (25% of the total volume) in the untreated sludge (75% of the total volume) intended for the incineration. The total precipitation with hydrated lime appeared effective for the recovery of metals (87% Cd, 96% Cr, 97% Cu, 98% Fe, 71% Ni, 100% Pb, 98% Zn). However, this option entails the production of an important quantity of metallic residue, which should be disposed of expensively as dangerous material. The selective iron precipitation does not appear to be an interesting option because the iron in solution within the leached sludge was principally present in the form of ferrous iron, which cannot be precipitated at pH lower than five. On the other hand, the use of commercial precipitating agents (TMT-15, CP-33Z, CP-NB and CPX) without pH adjustment of filtrate gave good results for the recovery of Cu and, to a lesser degree for the recovery of Pb. However, the efficiency for the other metals' (Cd, Cr, Fe, Ni and Zn) recovery was weaker (< 25%). Finally, the acid filtrate recirculation containing solubilised metals in untreated sludge destined for incineration appears to be the most interesting option. Metals in solution in the acid filtrate, precipitate or adsorb effectively (97% Cd, 97% Cr, 99% Cu, 82% Ni, 100% Pb and 87% Zn) on the solids of the untreated sludge. Moreover, TCLP tests were done on ashes produced during the incineration of sludge mixed with the acid filtrate produced during sludge decontamination. These tests showed that there were no significant differences, as regards the extractability of metals, between such ashes and those produced during the untreated sludge incineration without addition of filtrate. Therefore, it was predictable that this method can respect the current environmental standards required by the different governmental authorities. [ABSTRACT FROM AUTHOR]