Rosa M. Quinta-Ferreira

The influence of pH on the leaching behaviour of inorganic components from municipal solid waste APC residues

The influence of pH on the leaching behaviour of air pollution control (APC) residues produced in municipal solid waste incineration (MSWI) is addressed in this study. The residue is considered hazardous waste, and in accordance with their chemical properties, the leaching of contaminants into the environment is the main concern. Several leaching tests can be used for research studies or regulatory purposes, where a wide variety of conditions may be tested. Our work deals mainly with the leaching behaviour of toxic heavy metals (Pb, Cd, Zn, Cr, Ni, Cu) and inorganics associated with soluble salts (Na, K, Ca, Cl). The main goal is to obtain an overview of the leachability of APC residues produced in a Portuguese MSWI process. Among the different variables that may have influence on the leaching behaviour, pH of the leachant solution is the most important one, and was evaluated through pH static tests. The acid neutralization capacity (ANC) of the residue was also determined, which is in the range of 6.2-6.8 meq g(-1) (for pH=7) and 10.1-11.6 meq g(-1) (for pH=4). The analysis of the leaching behaviour is particularly important when the leaching is solubility controlled. The amphoteric behaviour of some elements was observed, namely for Pb and Zn, which is characterized through high solubilization at low and high pH and moderate or low solubility at neutral or moderate high pH. The solubility curves for Pb, Cd, Zn, Cr, Ni and Cu as a function of pH were obtained, which are very useful for predicting the leaching behaviour in different scenarios. The solubility of K and Na reveals to be nearly independent of the solution pH and the released amount is mainly availability-controlled. Moreover, the pH static test showed that Cl(-) is the most pH-independent species. The APC residue turns out to be a hazardous waste because of the high leaching of lead and chloride. On the other hand, leaching of elements like cadmium, nickel and copper is limited by the high pH of the residue, and as long as the waste keeps its ANC, the risk of mobilization of these elements is low.

Fenton's oxidation process for phenolic wastewater remediation and biodegradability enhancement

A mixture of six phenolic acids, corresponding to an initial TOC of 370 mgC/L, was studied by Fentons peroxidation aiming to improve the biodegradability of agro-industrial wastewaters. Input operating variables including the concentration of pollutants, iron and hydrogen peroxide as well as the reaction time were used to assess the mineralization degree through a factorial experimental methodology. A TOC removal in the range of 15.0-58.8% was attained within the operational conditions used. A reduced model was achieved using the statistically important independent factors and interactions to predict TOC degradation. On the hydrogen peroxide injection methodology, the results showed that the continuous introduction of small volumes is advantageous when compared with one single addition of the overall volume at the zero reaction time with a mineralization improvement of 11%. The use of FeSO(4).7H(2)O correspondent to a Fe(2+) load of 271 mg; [H(2)O(2)]=488.0 mM, injected in twelve aliquots each 30 min during 6h of reaction reached optimal efficiencies with the parent compounds (quantified by HPLC and the Folin-Ciocalteau method) quickly totally removed and TOC, COD and BOD(5) final values of 123 mgC/L, 180 mgO(2)/L and 146 mgO(2)/L, respectively. Toxicity assessment by Vibrio fischeri light inhibition revealed that Fentons process reduces the effluent ecological impact related with the decomposition of the toxic phenolic acids. Indeed, EC(50) changed from 32.2% dilution to no-dilution needed. The analysis of BOD(5)/COD ratio pointed out a high improvement of the treated wastewater biodegradability from 0.30 to 0.80 meaning that the application of Fentons oxidation as a pre-treatment enables a further application of an efficient post-biological technology which was also confirmed by respirometry.

Catalytic studies in wet oxidation of effluents from formaldehyde industry

Abstract Development and design of active catalysts for the oxidation of formaldehyde present in wastewaters is of great importance. In this context, catalytic performance studies for oxidation of high formaldehyde containing solutions (1500 ppm ) were carried out in a semibatch high-pressure reactor at 190–220°C and 15–35 bar of oxygen partial pressure. The removal efficiency of total organic carbon (TOC) was evaluated experimentally under different solid catalysts, using several heterogeneous composite oxides prepared in our laboratory (Mn/Ce, Co/Ce and Ag/Ce), as well as a commercial catalyst (CuO–ZnO/Al 2 O 3 ). The Mn/Ce catalyst was the more active leading to high TOC conversions (99.4%). The TOC reductions were lower using Co/Ce, Ag/Ce and CuO–ZnO/Al 2 O 3 , respectively, 71.3%, 54.2% and 78.7%. Attempts were made to identify the influence of different Mn/Ce ratios. A high molar fraction of Mn leads to high TOC abatements. During the preparation procedure of catalysts the drying temperature does not affect significantly the catalytic area while increasing calcination temperature leads to lower surface areas. Carbon capacity adsorption was not observed for the Mn/Ce and CuO–ZnO/Al 2 O 3 catalyst and leaching of the correspondent metals, Mn, Cu and Zn, was not significant. The catalytic wet oxidation (CWO) process was studied with an industrial high formaldehyde concentration effluent (800 ppm ) . Using an Mn/Ce catalyst the formaldehyde concentration decreased from 800 to 0.1 ppm and ammoniacal nitrogen from 420 to 155 ppm while 91.7% in TOC reduction was observed. These conversions were higher than those obtained with the commercial CuO–ZnO/Al 2 O 3 catalyst. Therefore, Mn/Ce catalysts seem to be interesting options for the treatment of effluents from formaldehyde industry by CWO process.

Application of ozonation for pharmaceuticals and personal care products removal from water

Due to the shortening on natural water resources, reclaimed wastewater will be an important water supply source. However, suitable technologies must be available to guaranty its proper detoxification with special concern for the emerging pharmaceutical and personal care products that are continuously reaching municipal wastewater treatment plants. While conventional biological systems are not suitable to remove these compounds, ozone, due to its interesting features involving molecular ozone oxidation and the possibility of generating unselective hydroxyl radicals, has a wider range of action on micropollutants removal and water disinfection. This paper aims to review the studies dealing with ozone based processes for water reuse by considering municipal wastewater reclamation as well as natural and drinking water treatment. A comparison with alternative technologies is given. The main drawback of ozonation is related with the low mineralization achieved that may lead to the production of reaction intermediates with toxic features. The use of hydrogen peroxide and light aided systems enhance ozone action over pollutants. Moreover, scientific community is focused on the development of solid catalysts able to improve the mineralization level achieved by ozone. Special interest is now being given to solar light catalytic ozonation systems with interesting results both for chemical and biological contaminants abatement. Nowadays the integration between ozonation and sand biofiltration seems to be the most interesting cost effective methodology for water treatment. However, further studies must be performed to optimize this system by understanding the biofiltration mechanisms.

Chemical stabilization of air pollution control residues from municipal solid waste incineration.

The by-products of the municipal solid waste incineration (MSWI) generally contain hazardous pollutants, with particular relevance to air pollution control (APC) residues. This waste may be harmful to health and detrimental to the environmental condition, mainly due to soluble salts, toxic heavy metals and trace organic compounds. Solidification/stabilization (S/S) with binders is a common industrial technology for treating such residues, involving however, a significant increase in the final mass that is landfilled. In our work, the chemical stabilization of APC residues by using NaHS x xH(2)O, H(3)PO(4), Na(2)CO(3), C(5)H(10)NNaS(2) x 3 H(2)O, Na(2)O x SiO(2) was investigated, and it was possible to conclude that all these additives lead to an improvement of the stabilization process of the most problematic heavy metals. Indeed, compliance leaching tests showed that after the stabilization treatment the waste becomes non-hazardous with respect to heavy metals. Chromium revealed to be a problematic metal, mainly when H(3)PO(4), Na(2)CO(3) and Na(2)O x SiO(2) were used for stabilization. Nevertheless, soluble phosphates are the most efficient additives for stabilizing the overall metals. The effect of the additives tested on the elements associated with soluble salts (K, Na, Cl(-)) is almost negligible, and therefore, the soluble fraction is hardly reduced without further treatment, such as pre-washing.

Percolation and batch leaching tests to assess release of inorganic pollutants from municipal solid waste incinerator residues

In this study, percolation and batch leaching tests were considered in order to characterize the behaviour of air pollution control (APC) residues produced in a municipal solid waste incinerator (MSWI) as a function of the liquid to solid ratio (L/S). This waste is hazardous, and taking into account their physical and chemical properties, leaching of contaminants into the environment is the main concern. In our work the leaching behaviour of toxic heavy metals (Pb, Zn, Cr, Ni and Cu) and inorganics associated with soluble salts (Na, K, Ca and Cl) was addressed. Although pH of the leaching solution is the most important variable, L/S may also play an important role in leaching processes. In our work, results from column and batch tests were compared in terms of concentration (mg/L) and releasing (mg/kg). The APC residues revealed to be hazardous according to both tests, and both Pb and Cl(-) far exceeded the regulatory thresholds. The material exhibits high solubility, and when the liquid to solid ratio was high, more than 50% can be solubilised. The patterns of release may be in some cases availability or solubility controlled, and the former was easier to identify. When the results from column and batch experiments were compared by representing the cumulative released amounts (in mg/kg) as a function of L/S, both curves match for Zn, Ni, Cu, K, Na, Cl and Ca, but for Cr and Pb a significant difference was observed. In fact, the column experiments revealed that under percolation conditions it should be expected slow releasing of Pb along time. From this study, it can be concluded that the released amounts obtained in batch experiments for a certain L/S should be considered as the worst case for medium term. Some simple models proposed on the literature and based on local equilibrium assumption showed good fitting to experimental data for soluble species (non-reactive solutes).

Recycling of air pollution control residues from municipal solid waste incineration into lightweight aggregates

This work focuses on the assessment of technological properties and on the leaching behavior of lightweight aggregates (LWA) produced by incorporating different quantities of air pollution control (APC) residues from municipal solid waste (MSW) incineration. Currently this hazardous waste has been mostly landfilled after stabilization/solidification. The LWA were produced by pelletizing natural clay, APC residues as-received from incineration plant, or after a washing treatment, a small amount of oil and water. The pellets were fired in a laboratory chamber furnace over calcium carbonate. The main technological properties of the LWA were evaluated, mainly concerning morphology, bulk and particle densities, compressive strength, bloating index, water adsorption and porosity. Given that APC residues do not own expansive (bloating) properties, the incorporation into LWA is only possible in moderate quantities, such as 3% as received or 5% after pre-washing treatment. The leaching behavior of heavy metals from sintered LWA using water or acid solutions was investigated, and despite the low acid neutralization capacity of the synthetic aggregates, the released quantities were low over a wide pH range. In conclusion, after a washing pre-treatment and if the percentage of incorporation is low, these residues may be incorporated into LWA. However, the recycling of APC residues from MSW incineration into LWA does not revealed any technical advantage.

Advanced oxidation processes for treatment of effluents from a detergent industry

Ozonation, catalytic ozonation, Fenton’s and heterogeneous Fenton‐like processes were investigated as possible pretreatments of a low biodegradable and highly toxic wastewater produced by a detergent industry. The presence of a Mn–Ce–O catalyst in ozonation enhances the biodegradability and improves the degradation at low pH values. However, a high content of carbonyl compounds adsorbed on the recovered solid indicates some limitations for real‐scale application. A commercial Fe2O3–MnOx catalyst shows higher activity as well as higher stability concerning carbon adsorption, but the leaching of metals is larger than for Mn–Ce–O. Regarding the heterogeneous Fenton‐like route with an Fe–Ce–O catalyst, even though a high activity and stability are attained, the intermediates are less biodegradable than the original compounds, indicating that the resulting effluent cannot be conducted to an activated sludge post‐treatment. The highest enhancement of effluent biodegradability is obtained with the classic homogeneous Fenton’s process, with the BOD5/COD ratio increasing from 0.32 to 0.80. This process was scaled up and the treated effluent is now safely directed to a municipal wastewater treatment plant.

Photocatalytic ozonation using doped TiO2 catalysts for the removal of parabens in water

Conventional wastewater treatments are inefficient for the removal of parabens. The aim of this study was finding a suitable solution using ozone and UVA irradiation combined with TiO2 catalysts doped with different noble metals (Ag, Pt, Pd, Au). Photocatalytic ozonation required lower amounts of ozone for higher efficiency on the removal of parabens, chemical oxygen demand (COD) and total organic carbon (TOC). The best catalyst for the initial contaminants degradation was 0.5% Ag-TiO2 leading to total parabens removal using 46mgO3/L. Due to the relative low mineralization achieved, the toxicity of the treated solutions was still compared with the initial one over several species (Vibrio fischeri, Lepidium sativum and Corbicula fluminea). All the treatments applied led to a clear decrease on the toxicity compared with initial mixture of parabens. From an economical point of view, it was concluded that the presence of UVA irradiation increased the energy consumption compared with catalytic ozonation with these catalysts but it can decrease the time of reaction. From the by-products analysis, it was concluded that hydroxylation appears to be the most significant reaction pathway and the main responsible for parabens degradation.

Adopting strategies to improve the efficiency of ozonation in the real‐scale treatment of olive oil mill wastewaters

In this experimental work the ozone action on the depuration of olive oil mill wastewater is studied for different operational conditions based on an actual industrial treatment plant. It was verified that the application of a Mn–Ce–O catalyst prepared at the laboratory, with a Mn/Ce molar proportion of 70/30, enhances the depuration efficiency and the effluent biodegradability. Ozonation operation at the natural pH of the effluent is recommended. Moreover, the integration of the Fenton process as a pretreatment improves the final chemical oxygen demand removal and enables a totally biodegradable effluent to be obtained, as confirmed by respirometric techniques.