Occurrence and hazard assessment of natural radioactivity in drinking water in South Lebanon.

This study is intended to assess the natural radioactivity in the drinking water in the southern region of Lebanon and to determine its suitability for human consumption. In this context, activity concentrations for gross alpha, gross beta, 238U, 234U, and radon from selected drinking water sources, wells, and springs and the corresponding tap water, in the area under investigation, were determined during both the wet and the dry seasons. The maximum recorded activities of gross alpha, gross beta, and radon measured using liquid scintillation counter were found to be 374.6 ± 11.5 mBq L-1 for gross alpha, 418 ± 12 mBq L-1 for gross beta, and 42,900 ± 370 mBq L-1 for radon. Whereas, alpha spectroscopy analysis for uranium content showed maximum activities of 53.7 ± 2.1 mBq L-1 for 238U and 55.9 ± 2.3 mBq L-1 for 234U. Significant seasonal activity variation between wet and dry season was noticed only in gross alpha concentrations. In addition, significant variation between sources and tap water was recorded only in radon concentrations. Whereas, no significant variation was noted in radioactivity concentrations in waters from springs and those from wells. In contrast to all sampled locations, the annual effective dose of only one sampled well (Aitaroun) exceeded the WHO individual dose criterion (IDC) level of 100 µSv year-1 and recorded an annual effective dose of 170 µSv year-1, 103 µSv year-1, and 127 µSv year-1 for infants, children, and adults, respectively.

Spatio-temporal variation of the microbial community of the coast of Lebanon in response to petroleum hydrocarbon pollution.

In this study, the coast of Lebanon was analyzed for the dynamic changes in sediment microbial communities in response to a major petroleum oil spill and tar contamination that occurred in the summer of 2021. Spatio-temporal variations in the microbial structure along the shores of Lebanon were assessed in comparison to baseline microbial structure determined in 2017. Microbial community structure and diversity were determined using Illumina MiSeq technology and DADA2 pipeline. The results show a significant diversity of microbial populations along the Lebanese shore, and a significant change in the sediment microbial structure within four years. Namely, Woeseia, Blastopirellula, and Muriicola were identified in sediment samples collected in year 2017, while a higher microbial diversity was observed in 2021 with Woeseia, Halogranum, Bacillus, and Vibrio prevailing in beach sediments. In addition, the results demonstrate a significant correlation between certain hydrocarbon degraders, such as Marinobacter and Vibrio, and measured hydrocarbon concentrations.

Precipitation softening: a pretreatment process for seawater desalination.

Reduction of membrane fouling in reverse osmosis systems and elimination of scaling of heat transfer surfaces in thermal plants are a major challenge in the desalination of seawater. Precipitation softening has the potential of eliminating the major fouling and scaling species in seawater desalination plants, thus allowing thermal plants to operate at higher top brine temperatures and membrane plants to operate at a reduced risk of fouling, leading to lower desalinated water costs. This work evaluated the use of precipitation softening as a pretreatment step for seawater desalination. The effectiveness of the process in removing several scale-inducing materials such as calcium, magnesium, silica, and boron was investigated under variable conditions of temperature and pH. The treatment process was also applied to seawater spiked with other known fouling species such as iron and bacteria to determine the efficiency of removal. The results of this work show that precipitation softening at a pH of 11 leads to complete elimination of calcium, silica, and bacteria; to very high removal efficiencies of magnesium and iron (99.6 and 99.2 %, respectively); and to a reasonably good removal efficiency of boron (61 %).