UV disinfection is cost-effective and easy to maintain for decentralized areas. However, to ensure its effectiveness, some parameters need to be considered. In this study, a general search of Web of Science articles was performed to determine the possible influence of these parameters on the reactivation of microorganisms in UV systems; in addition, different search strings were used focusing exclusively on wastewater treatment, UV systems and Advanced Oxidation Processes (AOPs). It was found that in order to maintain low transmittance, it is essential to remove suspended solids and reduce water hardness. It is recommended to control the zeta potential in the range of 0–5 mV to avoid the aggregation of particles and bacteria. Determining the appropriate UV dose is essential to mitigate the reactivation of microorganisms. A minimum dose of 40 mJ/cm² can contribute to effective disinfection and reduce the likelihood of reactivation. In addition, maintaining a residual chlorine level of at least 0.5 mg/L provides an additional barrier to reactivation. It is also important to optimize the design flow rate of the UV system as recommended for each individual unit. These measures, together with the combination of UV disinfection and chemical or AOP_S, can effectively reduce the reactivation.

In this study, two hormones 17β-estradiol (E₂) and 17α-ethynylestradiol (EE₂), and three phenolic compounds, bisphenol A (BPA), 4-N-nonylphenol (4-NP) and 4-tert-octylphenol (4-t-OP), were determined in surface water in the Cuautla River at the State of Morelos during the dry-season in Mexico. The endocrine disrupting compounds (EDCs) were extracted from water samples using solid-phase extraction (SPE) with end-capped C₁₈, and then the extracts were chemically derivatized to TMS (trimethylsylane)-compounds and analyzed by gas chromatography coupled to mass spectrometry (GCMS). The most abundant compound was BPA (22.46 ± 30.17 ng L⁻¹), followed by 4-t-OP (11.24 ± 11.76 ng L⁻¹), 4-NP (7.53 ± 14.88 ng L⁻¹), EE₂ (2.37 ± 4.36 ng L⁻¹) and E₂ (0.97 ± 1.82 ng L⁻¹). The residual amounts of target compounds could either reach stream surface water from direct domestic wastewater discharges, conventional wastewater treatment plant or can be a result from the use of agrochemicals in crop areas. The EDCs in Cuautla River exerted a high pressure on the aquatic ecosystem because their presences in surface water caused medium and high potential ecological risk. Besides, it was found that aquatic organisms were exposed to estrogenic activity.

La seguridad hídrica debe ser el objetivo estratégico de la política del agua en México. Es respecto de este principio normativo que debe evaluarse la situación actual de los recursos hídricos, en calidad y cantidad, así como de la gestión del agua en práctica. En este texto se elabora un diagnóstico general de la seguridad hídrica en México, así como de los retos que enfrenta ahora y en el futuro cercano. Se analiza la disponibilidad y escasez con un enfoque territorial, así como la condición de los acuíferos, la calidad del agua superficial y subterránea y los usos del agua. Se abordan los principales desafíos para la seguridad hídrica y las tendencias en las fuerzas modeladoras más relevantes. Para atender la problemática descrita, se proponen acciones específicas y, como conclusión general, la necesidad de una reforma del agua en México.

Herbicides have contributed to increased agricultural production. However, their residual amount can cause negative effects on environmental and public health. Therefore, this work aimed to determine the occurrence of both atrazine and diuron in surface and well water and investigate their link with drinking use. The samples were collected during dry and rainy seasons in three wells and surface water from a river and a pond located in the low plains of the Ixcatepec catchment, at the Amacuáhuitl community of the municipality of Arcelia, Guerrero State, in the center south of México, which is a rural community where farming is the main activity. The compounds were obtained by solid phase extraction and determined by HPLC-MS quadrupole with positive electrospray ionization mode. A geomorphic analysis was conducted inside the Ixcatepec catchment using the digital elevation model of the Shuttle Radar Topography Mission, SRTM-v4. The human risk for drinking water was calculated according to the Hazard Quotient. The concentrations of atrazine and diuron were between 5.77 and 402 ng L⁻¹. Atrazine was the most abundant and frequent pesticide found with an average concentration of 105.18 ng L⁻¹, while that of diuron was 86.56 ng L⁻¹. The highest levels were found in pond Ushe, likely being the result of the lowest flow and stagnation of water, and during the cold-dry season a consequence of mobilization by irrigation runoff. The morphological analysis indicated that the compounds mainly reached body water located in the lower surfaces from cultivated areas. Therefore, the occurrence is mainly linked to agriculture activity within the rural community. However, chemical properties of compounds, crop irrigation, and environmental conditions could be contributing to the dispersion of residual amounts of herbicides within the hydrological system. The estimation of risk showed that atrazine can mainly generate health problems for children using the Azul well as a source of drinking water.

The reuse of treated wastewaters could contribute to reducing water stress. In this research, ultrasound application on bacterial inactivation in municipal wastewater (MWW) was evaluated. Total and fecal coliforms were used as standard fecal indicators; volatile suspended solids (VSS) were analyzed too. Samples were taken from the effluent of secondary clarifiers. In addition, inactivation tests were carried out on pure cultures of E. coli (EC) and B. subtilis (BS). Sonication was performed at 20 kHz, 35% amplitude and 600 W/L for 15, 30 and 45 min. After 15 min of sonication, bacterial density was reduced by 1.85 Log₁₀ MPN/100 mL for EC and 3.16 Log₁₀ CFU/mL for BS. After 30 min, no CFU/mL of BS were observed in MWW and, after 45 min, the reduction of total and fecal coliforms was practically 6.45 Log₁₀ MPN/100mL. Inactivation mechanism was made by cavitation, which causes irreversible damage to the cell wall. Although high bacterial densities were employed, percentages of inactivation >99% were reached at 45 min. This research contributes to the implementation of ultrasound as a disinfection technique with high potential due to its high efficiency without producing byproducts. In fact, the water meets the guidelines for reuse in direct human contact services.