RESUMEN
Characterisation of the water treatment sludge (WTS) generated in drinking water treatment plants (DWTPs) is crucial to define alternatives for its adequate management, including potential reuse options. To define these alternatives, it is necessary to evaluate rainfall seasonality effect on WTS production and its physical and chemical characteristics. This study assessed the production and characterisation of four types of alum-based WTS. The WTS was generated in a pilot-scale system from different raw water turbidities (i.e., low: <5 NTU, medium: 5-10 NTU, high: ≥10 NTU, and very high turbidity: â¼300 NTU) and coagulant doses. To estimate WTS production, mathematical models based on variables such as raw water turbidity, coagulant dosage, and organic matter removed were used. The WTS characterisations included physical (solids and particle size distribution), chemical (metallic oxides, pH, mineral phases), and surface properties (functional groups and zero-charge point pH). The modified Kawamura model presented the best fit (R2 = 1.0, RMSE = 0.1062 and the lower Akaike Information Criterion) for the estimation of WTS production, indicating that at the DWTPs, it is possible to make sludge production projections using only two simple variables: coagulant dose and the raw water turbidity. The four types of WTS consist mainly of amorphous materials (45-65 %), featuring some mineral phases and exhibiting high contents of Al (Al2O3: 30-34 %), Si (SiO2: 21-26 %) and Fe (Fe2O3: 11-13 %). Nevertheless, very high turbidity WTS shows variations in its characteristics, notably a heightened content of clays. As a result of the high concentrations of Al and Fe, the WTS has the potential to be used as coagulants or for the recovery of coagulants, especially low turbidity WTS, which is produced from water with low turbidity and organic matter. The presence of aluminium-silicate clays and the surface functional groups of the silica network suggest that WTS, particularly very high turbidity WTS, also has the potential to be raw materials for generating adsorbents. The potential applications of WTS in coagulation and adsorption can be leveraged in wastewater treatment, promoting the circular economy in the water sector.
RESUMEN
This study describes the development, optimization and validation of a method for the extraction of 15 pesticides of different chemical classes in drinking water treatment sludge (DWTS) by vortex-assisted Matrix Solid Phase Dispersion (MSPD) with determination by gas chromatography coupled to mass spectrometry. It focused on the application of alternative and different solid supports to the extraction step of the MSPD. The main parameters that influenced the extraction were studied in order to obtain better recovery responses. Recoveries ranged from 70 to 120% with RSD below 20% for all analytes. Limits of quantification (LOQ) of the method ranged from 5 to 500 µg kg-1 whereas the analytical curves showed correlation coefficients above 0.997. The method under investigation used low volume of solvent (5 mL), low sample mass (1.5 g) and low mass of chitin (0.5 g), an environmentally friendly support. It has advantages, such as speed, simplicity and low cost material, over other methods. When the method was applied, 4 out of 15 pesticides were detected in the DWTS samples in concentrations below the LOQ.