Sludge Testing

Ferreira, Karen Chibana, et al. Microchemical Journal 207 (2024): 112057.

Hydrophobic deep eutectic solvents (HDES) were employed as extraction solvents in dispersive liquid-liquid microextraction (DLLME) for the determination of parabens and bisphenol A in sludge samples. Gas chromatography-mass spectrometry (GC–MS), with a pyrolizer for sample introduction, was utilized for analysis. Chemometric tools were applied to optimize the analysis conditions, considering both the sample introduction and DLLME parameters.

The HDESs were characterized using Fourier-Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TG). Univariate and multivariate strategies were employed to identify the optimal experimental conditions. The injection volume was set at 20 µL, with a pyrolizer temperature of 320 °C and a duration of 0.5 minutes. For DLLME, a full factorial design was used to identify the optimal conditions for each variable, including the salting-out effect, pH, dispersing solvent volume, and extraction solvent volume. The best DLLME conditions for sludge samples were found to be 300 µL of HDES, 350 µL of acetonitrile (ACN), pH 10, and 27% m/v NaCl.

After optimization, HDES was successfully applied as an extraction solvent for detecting endocrine disruptors in sludge samples. Future work will involve analyzing additional sludge samples (liquid and solid phases) using standard addition to quantify the analytes. The use of HDES in environmental samples aids in the identification of emerging contaminants, aligning with sustainable analytical chemistry principles. This was confirmed by applying the GREEnness Analytical (AGREE) evaluation system, which yielded values of 0.72 and 0.76 for the methodology and sample preparation, respectively.

Lin, Feng, et al. Journal of Chromatography A 1628 (2020): 461449.

This study presents a novel method for determining water distribution in sludge using a multiple headspace extraction (MHE) technique. The process involves stepwise removal of water vapor from a sealed vial containing a sludge sample, followed by gas chromatographic analysis (GC). By plotting the GC signal of water vapor against the extraction number, three distinct trend lines can be observed. Two transition points from these profiles allow for the division of water release into three stages: free water, capillary water, and adsorption water.

The water content of each type in the sludge is then calculated by summing the GC peak areas at each stage, using a method calibration. The results demonstrated that the MHE-GC method offers better repeatability (RSD < 18.6%) and sensitivity (limit of quantitation = 0.028%) compared to the thermal drying method, which was used as a reference. The MHE-GC method showed good agreement with the reference method for analyzing free and capillary water. Additionally, the results for adsorption water and bound water obtained through this method were found to be more accurate than those from the reference method.

Zeng, S., Qi, P., Ai, S., Sun, X., Kang, H., & Bian, D. (2024). Environmental Technology, 45(25), 5233-5243.

This study presents a method for accurately determining the total nitrogen (TN) content in activated sludge using an ultrasound-assisted wet digestion technique. A response surface methodology was applied to evaluate the individual and interactive effects of three factors: sludge dilution ratio, ultrasonic time, and ultrasonic power. The physico-chemical and digestion-oxidation parameters were also optimized.

The results showed that the optimal conditions for the method were: a sludge dilution ratio of 225 times, a stirring rate of 400 rpm, ultrasonic treatment for 22 minutes at 720 W, and the addition of 8 mL of potassium persulfate with a digestion time of 40 minutes. The relative standard deviation (RSD) for parallel TN determinations was ≤2.77%, with spike recovery rates ranging from 98.49% to 101.43%. This ultrasound-assisted wet method offers a simpler and more accurate approach for determining TN concentration in activated sludge.

Jovancicevic, Ivana, and Jan Schwarzbauer. Discover Water 3.1 (2023): 5.

The use of sewage sludge conditioned with polyacrylamides (PAA) results in the emission of these polymers into the soil. Due to their high adsorption capacity and low migration tendency, PAA polymer chains tend to remain fixed in the soil, minimizing the risk of leaching into groundwater. While PAA is not considered toxic, it can exhibit acute toxicity to aquatic organisms, with cationic polyacrylamide (cPAM) being more toxic than the anionic form. Moreover, increased concentrations of cPAM in aqueous solutions can lead to significant acidification and salinization, potentially harming plant growth, especially during early stages. Consequently, analyzing PAA in the environment is necessary.

In this study, a pyrolysis-based analytical method was applied to four sewage sludge samples from municipal wastewater treatment plants. All four relevant cPAA degradation products were successfully identified in three out of the four sludge samples. The correlation was confirmed by comparing retention times and mass spectra with those obtained from experiments on pure cPAA and spiked samples. The pyrograms showed retention time variations within an acceptable range.