General Description

1-Methoxy-2-propanol, a versatile solvent with uses in various industries, poses slight hazards to water and health upon prolonged exposure. An effective analytical method utilizing headspace gas chromatography has been developed for detecting urinary biomarkers, offering improved sensitivity and simplicity compared to traditional techniques. In wastewater treatment, anaerobic removal of 1-Methoxy-2-propanol using EGSB reactors has shown promising results, achieving high COD removal efficiencies under different operational conditions. It sheds light on efficient removal methods and microbial activities associated with 1-Methoxy-2-propanol in wastewater treatment processes.

Figure 1. 1-Methoxy-2-propanol

Overview

1-Methoxy-2-propanol, also known as propylene glycol methyl ether, is an organic compound with the molecular formula C4H10O2. It is a colorless transparent liquid with a boiling point of 118°C and a density of 0.922 g/mL at 25°C. This solvent is miscible with water and can dissolve various substances like rubber, resins, and cellulose. However, it is slightly hazardous to water and should be handled with caution. Its toxicity is relatively low, but prolonged or high-dose exposure may pose health risks. ¹

Analytical Method

1-Methoxy-2-propanol is a dominant glycol ether used on an industrial scale, and its unmetabolized urinary fraction serves as a good biological indicator of exposure to this compound. Thus, sensitive analytical methods for detecting biomarkers of exposure are of interest in the field of occupational exposure assessment. An alternative method for determining urinary 1-Methoxy-2-propanol based on headspace gas chromatography has been developed. This method offers several advantages over the existing method, including a tenfold lower limit of detection (0.1 mg/L), good accuracy, and precision, which were determined using several urinary 1-Methoxy-2-propanol analyses carried out on a series of urine samples obtained from a human volunteer study. The method involves the direct headspace analysis of urine samples, which eliminates the need for solid-phase extraction and derivatization before GC/FID analysis, thus simplifying the overall process. The inter-method comparison based on a Bland-Altman analysis showed that both techniques can be used interchangeably. The differences between the results obtained with both methods are not clinically relevant in comparison to the current biological exposure index of urinary 1-Methoxy-2-propanol. Overall, the headspace gas chromatography technique provides a more sensitive, accurate, and simple method for the determination of urinary 1-Methoxy-2-propanol compared to the existing method. As chronic occupational exposures to low levels of xenobiotics become increasingly relevant, this method will be useful in occupational exposure assessment for detecting biomarkers of exposure to glycol ethers such as 1-Methoxy-2-propanol. ²

Anaerobic Removal

1-Methoxy-2-propanol is a key component in the treatment of synthetic wastewater, often presenting challenges in removal due to its chemical properties. In a study, the anaerobic removal of 1-Methoxy-2-propanol was investigated using expanded granular sludge bed (EGSB) reactors operating under ambient temperatures. The experiment utilized two laboratory-scale EGSB reactors, operated at 18 and 25°C, treating synthetic wastewater consisting of ethanol and 1-Methoxy-2-propanol in a mass ratio of 4:1. Initially, continuous wastewater supply was employed, resulting in impressive chemical oxygen demand (COD) removal efficiencies exceeding 95% at both temperatures. This high efficiency was achieved with organic loading rates (OLR) of 29 and 43 kg COD m(-3) day(-1) at 18 and 25°C, corresponding to 1-Methoxy-2-propanol OLR of 6.4 and 9.3 kg COD m(-3) day(-1) respectively. Furthermore, the study simulated shift working conditions by implementing discontinuous substrate supply, which also yielded promising results. Even with intermittent substrate supply, good performance was maintained at both temperatures with an OLR of 30 kg COD m(-3) day(-1) (M2P OLR of 6.6 kg COD m(-3) day(-1)). However, a decline in methane yield of 15-30% was observed after 56 hours without substrate supply, attributed to biomass deactivation. Moreover, specific methanogenic activity (SMA) assays conducted at the end of the experiments provided insights into the microbial activity involved. SMA values using 1-Methoxy-2-propanol as a substrate were 24.3 and 7.8 ml CH4 gVSS(-1) day(-1) at 25 and 18°C respectively. This study represents a pioneering effort in investigating the anaerobic removal of 1-methoxy-2-propanol using EGSB reactors, shedding light on its efficacy and challenges in wastewater treatment processes. ³

Reference

1. 1-Methoxy-2-propanol. National Center for Biotechnology Information. 2024; PubChem Compound Summary for CID 7900.

2. Tomicic C, Berode M. Sensitive headspace gas chromatography analysis of free and conjugated 1-methoxy-2-propanol in urine. Anal Bioanal Chem. 2010;396(7):2709-2714.

3. Lafita C, Penya-roja JM, Gabaldón C. Anaerobic removal of 1-methoxy-2-propanol under ambient temperature in an EGSB reactor. Bioprocess Biosyst Eng. 2015; 38(11): 2137-2146.