Alkali-activated geopolymers based on calcined phosphate sludges and metakaolin.

The extraction of phosphorite ore in Tunisia has resulted in the discharge of substantial amounts of phosphatic sludge into the region's water system. To mitigate this environmental issue and prevent heavy metal leaching, a geopolymerization process was employed using two types of Tunisian calcined phosphate sludges (Cal-PS1 and Cal-PS2) as substitutes for alkali-activated metakaolin. This study aimed to investigate and compare the physical and mechanical properties of the resulting geopolymers. The optimal substitution ratio of metakaolin with calcined phosphate sludge was determined to be 1.5, equivalent to 20 wt.% of calcined phosphate sludge. Compressive strength tests conducted after 28 days of curing revealed values of 37 MPa for Cal-PS1 specimens and 28 MPa for Cal-PS2 geopolymers while compressive strength of geopolymers soaked in water for 28 days showed a decrease with the addition of phosphate sludges. The specific surface areas of Cal-PS1 geopolymers ranged from 16.3 to 16.9 m2/g and from 17.62 to 18.73 m2/g for Cal-PS2 specimens exhibiting a mesoporous structure. The elasticity modulus of the geopolymers was found to increase with the increase of the apparent density of geopolymers and with the sludges content but it tended to be lower than the Portland cement elasticity modulus. Leaching test was conducted to evaluate the potential environmental applications of the geopolymers. This test demonstrated effective containment of heavy metals within the geopolymers' network, except for low levels of arsenic.

Removal of phosphate from synthetic wastewater: A comparative study between both activated clays using an experimental design methodology.

Phosphate-loaded industrial wastewaters have resulted in numerous environmental issues that have hard hit the Gulf of Gabes-Tunisia, making the environmental protection one of the most compelling priorities. Consequently, this study aimed first to compare the amounts of phosphate adsorbed by two types of Tunisian activated clays. The second goal was to assess and optimize the phosphate removal efficiency of these clays, using Box-Behnken design (BBD) under response surface methodology. Results showed that the highest adsorption amounts of 130.16 mg g-1 , 125.42 mg g-1 were yielded for Jebel Haidoudi clay and Douiret clay, respectively. These values demanded an initial phosphate concentration of 300 mg L-1 , a contact time of 5 h, and a pH of 2). Thus, kinetic and isotherm studies of phosphate elimination from synthetic solutions demonstrated that for both activated clays, the pseudo-second-order and Langmuir equation fitted very well the experimental data, respectively. These results indicate that phosphate adsorption might be mainly a chimisorption phenomenon and a monolayer process. All these findings confirmed that both activated clays could be considered as a competent, cost-effective, efficient and ecological alternative for the elimination of phosphate from industrial wastewaters. PRACTITIONER POINTS: Activated clay could be adopted as an efficient and cost-effective adsorbent. The optimum conditions were nominated as 300 mg L-1 of initial phosphate concentration, 5 h contact times and pH = 2. The probable uptake mechanism of phosphate followed predominantly the acid-base interaction and hydrogen bond.

Biological and biochemical assessment in Phorcus articulatus (Lamarck 1822): contamination and seasonal effect.

This work aims to diagnose the state of the northeastern coasts of Tunisia using P. articulatus species. Biological parameters, protein and metallothionein content, enzymatic activities, and metallic concentration were assessed at four stations during four seasons and analyzed by multiple regressions. The comparison of biological ratios showed minima at Sidi Daoued and maxima at Korbous where metallothioneins were maximal. The catalytic activity was low during summer and higher during cold periods contrary to acetylcholinesterase activity. Concerning glutathione S-transferase, its activity was important at Kelibia in autumn and at La Goulette and Sidi Daoued in warm seasons. The metallic concentrations were low at Korbous and maximal at Kelibia and Sidi Daoued stations. Kelibia seems to be the most polluted site followed by Sidi Daoued and La Goulette (industries, urbanization and fishing ports). The pollution seems to be reduced at Korbous station having more suitable conditions for the proliferation of monodonts.

Bio-monitoring of metal impact on metallothioneins levels in the gastropod Phorcus turbinatus (Born, 1778) in the northeastern and the eastern coasts of Tunisia.

This work is an evaluation of metal contamination degree in Phorcus turbinatus and a monitoring of metals impact on metallothioneins functioning. The gastropod was sampled from six stations along the northeastern and eastern coasts of Tunisia during four seasons (2014-2015). Our results suggested that sedimentological metallic contents (Copper, Zinc and Cadmium) vary significantly depending on stations and not significantly according to seasons except for copper. Nevertheless, differences were no significant between stations and significant between seasons as for ambient factors, metallic intrinsic contents and metallothioneins rates. The monodonta tissue seems to be enriched in the four analyzed metals (Cu, Zn, Cd and Hg) and this species seems to have an ability to accumulate metals. Metal effect on the protein induction may be linked to physicochemical factors (temperature, O2 and Cu contents in sediment). In fact, metallothioneins levels were positively correlated to the dissolved oxygen rates and negatively linked to temperature.

Lead removal from aqueous solutions by raw sawdust and magnesium pretreated biochar: Experimental investigations and numerical modelling.

Lead removal from aqueous solutions by raw cypress (Cupressus sempervirens L.) sawdust (RCS) and its derivative magnesium pretreated biochar (Mg-B) was investigated under static and dynamic conditions through batch and column assays. The Hydrus-1D model was used to estimate the transport parameters of the lead measured breakthrough curves. The batch experiments results showed that Mg-B was very efficient in removing lead compared to RCS and several other previously tested natural and modified materials. The column experiments results indicated that for both RCS and Mg-B, lead breakthrough curves and the related removal efficiencies were mainly dependent on the used initial concentration and the adsorbents bed height. The use of Hydrus-1D showed that the two-site chemical non-equilibrium model describes better the experimental lead breakthrough curves for both RCS and Mg-B as the equilibrium model.

Quantification of Groundwater - Saline Surface Water Interaction in a Small Coastal Plain in North-East Tunisia using Multivariate Statistical Analysis and Geophysical Method.

Amultivariate statistical analysis used with geophysical investigation enabled the assessment of interaction between saline surface water and groundwater in the coastal plain of Wadi Al Ayn and Daroufa in CapBon peninsula, north-east Tunisia. The application of the Principal Component Analysis (PCA) identified the end members which contribute to groundwater recharge: the wastewater infiltrated from Wadi Al Ayn, the oilfield brine infiltrated to the aquifer through the sandy bed of Wadi Al Ayn, the intruded seawater near Wadi Daroufa in the downstream region and the fresh groundwater flowing from the upstream region. The contribution of wastewater in groundwater recharge varies from 1.4% in the upstream region of Wadi Al Ayn to 77% near its downstream part. The fraction of oilfield brine mixed with groundwater in the alluvial aquifer under Wadi Al Ayn varies from 1% to 13%; whereas the fraction of intruded seawater into the coastal part of the aquifer near Daroufa region varies from 2% to 21%.

Heavy elements in the phosphorite from Kalaat Khasba mine (North-western Tunisia): potential implications on the environment and human health.

Tunisia is one of the largest phosphate producers in the world (more than 10 million tons per year since the early nineties). The Kalaat Khasba mine (NW of Tunisia) has operated from 1893 until 1993 and data demonstrate that, in the phosphorites of Kalaat Khasba, Cd is enriched 105-208 times, when compared with shales, and U is enriched by a factor varying between 18 and 44. The general trend shows an increase in heavy elements content with decreasing particle size. On the other hand, concentrations of Sr, Cr and U exhibit the same distribution for the different size fractions. It was found that Cd concentrations exceed the allowed EC soil limits for growing crops. Hence, owing to the tailings exposure and to the mobilisation of the finest particles by rainfall and wind, Cd could have detrimental effects on human health and on the environment because a significant portion of Cd was found in the exchangeable form.

Multimarker approach analysis in common carp Cyprinus carpio sampled from three freshwater sites.

The aim of this study is to assess the response of a multimarker approach in common carp Cyprinus carpio sampled from three Tunisian dam lakes selected according to different environmental and ecological characteristics. Glutathione-S-transferase (GST) activity was analyzed in carp liver and used as a phase II detoxification enzyme, hepatic metallothionein content (MTs) was used as a metallic stress indicator, and cholinesterase activities were analyzed in muscle and brain and used as neurotoxicity biomarker. Micronucleus frequency test (MN) as a genotoxicity marker. GST and MT levels showed an increase in fish from the Bir Mcherga site and a decrease in Sidi Saâd site with respect to fish from Nebhana site. Results showed a strong inhibition of cholinesterase activities in fish from Bir Mcherga and Sidi Saâd sites compared to Nebhana site. Relatively high level of MN is reported specially in fish blood from the Bir Mcherga site.