Marta Otero

Silica coated magnetite particles for magnetic removal of Hg2+ from water

The magnetic removal of Hg(2+) from water has been assessed using silica coated magnetite particles. The magnetite particles were first prepared by hydrolysis of FeSO(4) and their surfaces were modified with amorphous silica shells that were then functionalized with organic moieties containing terminal dithiocarbamate groups. Under the experimental conditions used, the materials reported here displayed high efficiency for Hg(2+) uptake (74%) even at contaminant levels as low as 50 μg l(-1). Therefore these eco-nanomagnets show great potential for the removal of heavy metal ions of polluted water, via magnetic separation.

Dye adsorption by sewage sludge-based activated carbons in batch and fixed-bed systems.

The present research work deals with the production of activated carbons by chemical activation and pyrolysis of sewage sludges. The adsorbent properties of these sewage sludges based activated carbons were studied by liquid-phase adsorption tests. Dyes removal from colored wastewater being a possible application for sludge based adsorbents, methylene blue and saphranine removing from solution was studied. Pure and binary adsorption assays were performed in batch and fixed bed systems. In all cases studied, the adsorbents produced from sewage sludges were able to adsorb both the compounds considered here. Nevertheless, time required for reaching equilibrium, adsorptive capacity and fixed bed characteristic parameters were different for these two compounds. Methylene blue adsorption occurred faster than that of saphranine, and it was preferably adsorbed when treating binary solutions. It could be concluded that the sewage sludge-based activated carbons may be promising for dyes removal from aqueous streams.

Kinetic and equilibrium modelling of the methylene blue removal from solution by adsorbent materials produced from sewage sludges

Abstract Sewage sludge utilisation must be the preferred management solution for a residue which does not show the desired improvement on wastewater treatment. This research work’s aim was to study the dye binding capacity of adsorbents produced from sewage sludges. The quality of sewage sludges as starting materials has been investigated by using sludges both from an urban and from an agrofood industry wastewater treatment plant. Dried sewage sludges, pyrolysed sewage sludges and both chemically activated and pyrolysed sewage sludges have been used as adsorbent materials in single batch liquid-phase adsorption tests. The adsorption equilibriums of methylene blue by these materials have been described in terms of both Langmuir and Freundlich equations. In order to investigate the mechanisms of adsorption, the first- and second-order kinetic models have been used. All the sludge-derived adsorbents produced have been able to uptake methylene blue from solution, the second-order rate expression being preferred to the first-order one. Nevertheless, the time needed for reaching the equilibrium and adsorptive capacity have differed from one to another adsorbent. Equilibrium and kinetic results have showed that dried urban sewage sludges are the most efficient materials for removing the methylene blue from the solution.

Processes for the elimination of estrogenic steroid hormones from water: A review

Natural estrogens such as estrone (E1), 17β-estradiol (E2), estriol (E3), and the synthetic one, 17α-ethinylestradiol (EE2), are excreted by humans and animals and enter into environment through discharge of domestic sewage effluents and disposal of animal waste. The occurrence of these substances in aquatic ecosystems may affect the endocrine system of humans and wildlife so it has emerged as a major concern for water quality. Extensive research has being carried out during the last decades on the efficiency of the degradation and/or removal of these hormones in sewage treatment plants (STPs). Conventional and advanced treatments have been investigated by different authors for the elimination of estrogens from water. This paper aims to review the different processes and treatments that have been applied for the elimination of E1, E2, E3 and EE2 from water. With this purpose, physical, biological and advanced oxidation processes (AOP) have been addressed.

Elimination of organic water pollutants using adsorbents obtained from sewage sludge

Sewage sludge valorisation must be the preferred management solution for a residue which minimising does not keep with a desirable improvement on wastewater treatment. This research work deals with the potential application of adsorbents produced from sewage sludge in organic pollutants removal. After chemical activation and pyrolysis treatment, sewage sludge provides materials of great porosity and high surface area. The properties of this type of material was studied by liquid-phase adsorption using crystal violet, indigo carmine and phenol as adsorbates, experiments being performed for two different adsorbent particle sizes. Firstly, single adsorption batch experiments were carried out to obtain kinetic and equilibrium data. The adsorbates preferential adsorption was then investigated by studying adsorption from mixed solutions. The sludge-derived activated carbon produced could adsorb the three adsorbates considered with the time required to reach equilibrium and full adsorptive capacity varying between the adsorbates. Crystal violet adsorption has been higher and faster than indigo carmine or phenol. It is proposed that activated carbons made from sewage sludge show promise for the removal of organic pollutants from aqueous streams.

Adsorption of heavy metals onto sewage sludge-derived materials.

Two materials were produced from sewage sludge by: (1) pyrolysis of dried sewage sludge (PS); (2) chemical activation of dried sewage sludge with ZnCl(2) followed by pyrolysis (AS). The aim was to study the application of these materials for metal purification from water and to determine the efficiency of each material. Although AS displayed higher capacity, both PS and AS were able to adsorb these metals and the preferential order was equal: Hg(II)>Pb(II)>Cu(II)>Cr(III). For each metal-adsorbent pair, metal adsorption was highly pH dependent. In all cases the equilibrium was well described both by the Langmuir and the Freundlich isotherms. At the corresponding optimum pH, AS showed the following adsorption capacities: 175.4, 64.1, 30.7 and 15.4 mg/g of Hg(II), Pb(II), Cu(II) and Cr(III), respectively. These results indicate the potential application of these sewage sludge based adsorbents for the treatment of metal polluted effluents.

Analysis of the co-combustion of sewage sludge and coal by TG-MS

Combustion of sewage sludge may be a viable solution for its management in some cases and so is its co-combustion with coal. The aim of the present paper is to study the behavior of three different sludges during combustion and the modifications of combustion parameters that take place when sludges are mixed with coal, all measurements being done by thermogravimetry. The combustion of pyrolyzed sewage sludges has also been studied, related to the possibility of combining combustion with pyrolysis when trying to valorize sludges by producing active carbon. From the burning profile data it has been possible to observe that a rapid devolatilization occurs during sludge combustion compared to coal and previously pyrolyzed sludge. The exact temperatures of devolatilization and of maximum speed of weight loss have also been ascertained together with differential thermal analysis and measurements of gas emissions during combustion. The behavior of the sludges tested is qualitatively similar but quantitatively different, so tests have to be carried out before they are put in the furnace.

Co-combustion of different sewage sludge and coal: A non-isothermal thermogravimetric kinetic analysis

The kinetics of the combustion of coal, two different sewage sludge and their blends (containing different dried weight percentages of sewage sludge) was studied by simultaneous thermogravimetric analysis. Once the weight percentage of sludge in the blend was 10%, the effects on the combustion of coal were hardly noticeable in terms of weight loss. The Arrhenius activation energy corresponding to the co-combustion of the blends was evaluated by non-isothermal kinetic analysis. This showed that, though differences between coal and sewage sludge, the combustion of their blends kept kinetically alike to that of the coal. This work illustrates how thermogravimetric analysis may be used as an easy rapid tool to asses, not only mass loss, but also kinetics of the co-combustion of sewage sludge and coal blends.

Mercury pollution in Ria de Aveiro (Portugal): a review of the system assessment

The Ria de Aveiro (Portugal) is a coast al lagoon adjacent to the Atlantic Ocean and it has an inner bay (Laranjo bay) that received a highly contaminated effluent discharged by a mercury cell chlor-alkali plant from the 1950s until 1994. The aim of this study is to review in a holistic way several research studies that have been carried out in the Ria de Aveiro, in order to evaluate the remobilization of the mercury accumulated within the system and the recovery of the lagoon. The spatial distribution of the total mercury in the surrounding terrestrial environment has also been considered. Results indicate that the main mercury contamination problems in the Ria de Aveiro are confined to the Laranjo bay. Mercury export to the coastal waters and its impact on the nearshore compartments (water column, sediment and biota) are low. No direct effects of the mercury from nearby industrial activities were detected in Aveiro’s urban soils, although historical mercury contamination is still affecting soil quality in the immediate vicinity of the chlor-alkali plant, located in Estarreja. Moreover, macrophyte harvesting for human direct or indirect use and the consumption of mussels, crabs and the sea bass from the Laranjo bay may constitute a health risk. Further studies focusing on developing skills for the restoration of the ecosystem are presently underway.

Anaerobic digestion and co-digestion of slaughterhouse waste (SHW): influence of heat and pressure pre-treatment in biogas yield.

Mesophilic anaerobic digestion (34+/-1 degrees C) of pre-treated (for 20 min at 133 degrees C, >3 bar) slaughterhouse waste and its co-digestion with the organic fraction of municipal solid waste (OFMSW) have been assessed. Semi-continuously-fed digesters worked with a hydraulic retention time (HRT) of 36 d and organic loading rates (OLR) of 1.2 and 2.6 kg VS(feed)/m(3)d for digestion and co-digestion, respectively, with a previous acclimatization period in all cases. It was not possible to carry out an efficient treatment of hygienized waste, even less so when OFMSW was added as co-substrate. These digesters presented volatile fatty acids (VFA), long chain fatty acids (LCFA) and fats accumulation, leading to instability and inhibition of the degradation process. The aim of applying a heat and pressure pre-treatment to promote splitting of complex lipids and nitrogen-rich waste into simpler and more biodegradable constituents and to enhance biogas production was not successful. These results indicate that the temperature and the high pressure of the pre-treatment applied favoured the formation of compounds that are refractory to anaerobic digestion. The pre-treated slaughterhouse wastes and the final products of these systems were analyzed by FTIR and TGA. These tools verified the existence of complex nitrogen-containing polymers in the final effluents, confirming the formation of refractory compounds during pre-treatment.