Oxidation mechanisms of amoxicillin and paracetamol in the photo-Fenton solar process.

The present study shows the results of solar photo-Fenton oxidation of paracetamol (PCT) and amoxicillin (AMX). Fe2(SO4)3 was used as the source of iron and EDDS as the iron complexing agent, employing different doses of hydrogen peroxide. Two aqueous matrices, a synthetic wastewater and real wastewater from El Ejido WWTP effluent (Almeria) were used. In all cases, the process was operated under conditions of natural sunlight. Results showed that the degradation of both drugs is favoured when the aqueous matrix presents low concentration of carbonates. Under the conditions studied here, degradation percentages above 90% were obtained in the synthetic wastewater and 80% in the actual effluent. The degradation products were determined using liquid chromatography coupled to high-resolution mass spectrometry with hybrid quadrupole time-of-flight analyser. The intermediates detected throughout the oxidative process for both micro-contaminants were mainly products of hydroxylation reactions. The toxicity of the samples was determined using the bacterium Vibrio fischeri. In the acute toxicity test, it was observed that the bacteria did not undergo inhibition in any of the cases. However, chronic toxicity studies showed that the higher the Hydraulic Retention Time (HRT) employed in the assays, the higher the bacterial inhibition.

An assessment of heavy metal contamination in surface sediment using statistical analysis.

The distribution and accumulation of heavy metals in the sediments, especially those nearest of wastewater discharges of south of Spain, were investigated. Sediment samples from 14 locations were collected and characterised for metal content (e.g. Ni, Cu, Zn, Cr, Pb, Mn, Cd and Hg), organic carbon, total nitrogen, total phosphorous, n-hexane-extractable material, carbonates and grain size. Concentration data were processed using correlation analysis and factor analysis. The correlation analysis of concentrations data showed important positive correlations among organic carbon, total phosphorus, Cu, Zn, Cd and Hg, otherwise weak correlations among Mn, Cr, Ni and CO(3) (2-), indicating that these metals have complicated geochemical behaviours. The use of statistical factor analysis also confirmed these results. Sediments pollution assessment was carried out using geoaccumulation and metal pollution indexes (MPI(8)). The results revealed that sediments of Cádiz bay and Sancti Petri channel were uncontaminated with the studied metals.

A new approach to toxicity determination by respirometry.

Respirometry, as used in wastewater treatment, is the measurement and interpretation of the respiration rate of microorganisms in activated sludge. The respiration rate is the amount of the oxygen per unit of volume and time that is consumed by the microorganisms. For a long time respirometry has been recognized as a valuable basis for controlling the activated sludge process. The reason for this is that respiration rate is directly linked to two important biochemical processes that must be controlled in a wastewater treatment plant: biomass growth and substrate consumption. This paper shows different experiments to quantify toxic or inhibitory effects as determined by the toxicity protocol for respirometry. The protocol used was based on the utilization of the respiration of activated sludge to measure and quantify toxic effects of compounds. Our purpose was for both the protection and treatment ability determination of wastewater plants, depending on the problems (e.g. pollution), needs of customers and possibilities for biodegradation of the tested products.

Modelling of reactivation after UV disinfection: effect of UV-C dose on subsequent photoreactivation and dark repair.

The increased use of UV radiation as a wastewater treatment technology has stimulated studies of the repair potential of microorganisms following treatment. In this study, samples of unfiltered secondary effluent were irradiated with seven levels of UV-C doses (50-200 mW s/cm(2)) from six low-pressure lamps in an open-channel UV disinfection system. Following irradiation, samples were incubated at 20 degrees C under photoreactivating light or in darkness. Samples were analysed for 240 min following incubation. The logistic model is proposed to explain the relation between photoreactivation and the UV-C dose received by the microorganisms. That model accurately fitted the data obtained in photoreactivation experiments, permitting interpretation of the estimated kinetic parameters: S(m) and k(2). In the experiments carried out in darkness, a slight reactivation is observed (<0.1%), followed by a decay period in which survival decreases. In order to model this last period, a modification was made to the logistic model by including a term of mortality that assumes a zero-order kinetic. The parameters S(m) and k(2), in both photoreactivation and darkness, show an exponential dependence on the UV-C inactivating dose. It is possible to predict their values, and hence the reactivation curve, from the equations proposed in this work.

Use of microbial activity parameters for determination of a biosolid stability index.

Variations in microbial activity during the aerobic digestion of sludge generated at wastewater treatment plants were studied. Results obtained by the measurement of enzymatic activity and microbiological parameters were compared with those determined by traditional methods (COD, suspended solids, etc.). Their variation with digestion time was monitored for batch digestion over a period of 135 days. The relationship between these measurements and control parameters of the sludge was also investigated. It was found that the traditional physicochemical and microbiological parameters present a series of problems which detract from their usefulness. The enzymatic parameters dehydrogenase activity (primary metabolism) and esterase activity (secondary metabolism) are better able to characterise the process, and the ratio of these two variables may be used to estimate the degree of endogenesis and, consequently, the degree of stability of the aerobic sludge digestion. In addition, these techniques are swift and simple to employ.