Tools for evaluation and prediction of industrial noise sources. Application to a wastewater treatment plant.

In recent years, acoustic pollution caused by noise has considerably increased in many countries. Particularly in Spain, the noisiest country in Europe. It is sometimes difficult to predict the noise levels that a new installation or an expansion of industrial equipment will cause in the surroundings. This work introduces a new methodology for the prediction, evaluation, and analysis of industrial noise sources, as well as a novel tool for predicting and categorizing outdoor noise from its measurement at their sources. A Wastewater Treatment Plant (WWTP) has been used to demonstrate the applicability and validity of this methodology. The continuous level of acoustic pressure equivalent has been measured in different points of the plant using an integrating sound level meter. From these values, noise maps have been built to obtain detailed information of the industrial noise generated in the installation. Also, the typical frequency patterns of each type of source have been used for the calculation of source noise apportionments. To achieve this objective, several noise sources have been selected to provide information about their contribution to the industrial noise in the WWTP surrounding area. Finally, predictions have been validated using actual measurements. This methodology is a useful tool to predict personal exposure to noise and the impact on the environment. This information can be used, in particular, to propose mitigation actions.

Biosorption of cadmium (II) from aqueous solutions by natural and modified non-living leaves of Posidonia oceanica.

Natural, HCl-treated, and formaldehyde-treated non-living leaves of Posidonia oceanica, a marine plant, were investigated as potential biosorbents to remove Cd2+ from aqueous solutions. The studied biosorbents were characterized by elemental analysis and Fourier transform infrared spectroscopy (FTIR) and it was observed that the adsorption capacity of the biosorbents strongly depended on the pH, increasing as the pH rises. The adsorption process was fast. The adsorption kinetic was analyzed using five kinetic models: pseudo-first order, pseudo-second order, Elovich, intraparticle diffusion, and Bangham models. The adsorption isotherms were analyzed by the Langmuir, Freundlich, Dubinin-Radushkevich, Sips, Redlich-Peterson, and Toth models. The maximum biosorption capacity was attained by the biosorbent treated with HCl (1.11 mmol g-1). The distribution equilibrium constant and the Gibbs free energy change were calculated. The effects of the presence of Na+, K+, Mg2+, and Ca2+ ions in the solution on Cd2+ uptake were studied. Results indicate that non-living leaves of P. oceanica, natural or treated, can be considered as effective and low-cost biosorbents for the removal of cadmium from aqueous solutions.

Comparative study of six different sludges by sequential speciation of heavy metals.

The presence of heavy metals in the sludges produced in wastewater treatment plants restricts their use for agricultural purposes. This study looks at different types of sludge (aerobic, anaerobic, unstabilised, sludge from a waste stabilisation pond, sludge from an extended aeration plant and heat treated sludge) and compares the distribution of heavy metals with the treatment that they have undergone. In addition, the total quantity of metals (Cd, Cr, Cu, Ca, K, Fe, Mg, Ni, Na, Pb and Zn) and some agronomic parameters necessary for characterising a sludge as suitable for use as amendment were determined. The BCR method for heavy metal speciation was followed. Principal component analysis (PCA) was applied in order to obtain more information about metal speciation in the sewage sludges. It was confirmed that the concentration of heavy metals did not exceed the limits set out by European legislation and that the stabilisation treatment undergone by the sludges strongly influenced the heavy metal distribution and the phases to which they were associated. The waste stabilisation pond sludge, which has undergone a higher degree of mineralisation than the others, shows a lower metal bioavailability index since practically all the heavy metals in it are associated to the oxidisable and residual fraction. On the other hand the unstabilised sludge, which, along with that exposed to extended aeration, contains the highest accumulations of heavy metals in the most easily assimilable fractions.

Ecotoxicity, phytotoxicity and extractability of heavy metals from different stabilised sewage sludges.

The presence of heavy metals in the sludges produced in wastewater treatment plants restricts their use for agricultural purposes. This study compares different types of sludges (aerobic, anaerobic, unstabilised and sludge from a waste stabilisation pond) in order to assess the extractability of heavy metals using simple extraction, water and DTPA. The stabilisation treatment undergone by the sludges influenced the heavy metals extractability. The least mineralised sludges (unstabilised and aerobic) showed higher metal extractability. The sewage sludges were subjected to chemical characterisation and toxicity testing (ecotoxicity and phytotoxicity assays) in absence of substrate, to provide a preliminary assessment of their suitability for land application. The ecotoxicity assays confirmed that no sludge constituted a hazardous waste. The sludge extracts had significant adverse effect on the germination index (GI) of barley (Hordeum vulgare L.) and cress (Lepidium sativum L.), a fact which indicates that some characteristics affected root growth.

Phytotoxicity and heavy metals speciation of stabilised sewage sludges.

The presence of heavy metals in the sludges produced in wastewater treatment restricts plants growth and hence their use for agricultural purposes. This study looks at different types of sludges (aerobic, anaerobic, unstabilised and sludge from a waste stabilisation pond) and compares the distribution of the heavy metals that they contain according to the treatment that they have undergone. The sewage sludges were subjected to chemical characterisation and phytotoxicity testing (in absence of substrate) to provide a preliminary assessment of their suitability for land application. In addition, the total quantity of metals (Cd, Cr, Cu, Ca, K, Fe, Mg, Ni, Na, Pb and Zn) was determined. The Community Bureau of Reference (BCR) method for heavy metal speciation was followed. It was confirmed that the total concentration of heavy metals did not exceed the limits set out by European legislation and that the stabilisation treatment undergone by the sludges strongly influenced the heavy metal distribution and the phases to which they were associated. The sludge extracts did not exert any significant adverse effect on the relative seed germination (RSG) of barley (Hordeum vulgare L.) or cress (Lepidium sativum L.), although the reduction in germination index (GI) indicates that some characteristics existed did have an adverse effect on root growth.

Simple and sequential extractions of heavy metals from different sewage sludges.

The presence of heavy metals in the sludges produced in waste-water treatment plants restricts their use for agricultural purposes. This study looks at different types of sludges (aerobic, anaerobic, unstabilised and sludge from a waste stabilisation pond) and compares the distribution of the heavy metals they contain according to the treatment that they have undergone. Some agronomic parameters necessary for characterising a sludge as suitable for use as amendment were determined. The aim of this study is to compare the availability and the localisation of heavy metals in different sewage sludges using simple (water and DTPA) extraction and the BCR (Community Bureau of Reference) sequential extraction procedure. It was confirmed that the total concentration of heavy metals did not exceed the limits set out by European legislation and that the stabilisation treatment undergone by the sludges strongly influenced the heavy metal distribution and the phases to which they were associated and their bioavailability level. The DTPA extraction procedure is cheap and easy to perform and the obtained results are similar to those obtained with the sequential procedure.