Worldwide, raw or treated wastewater is used for irrigation. However, this practice implies that the microbial content must be controlled. Unfortunately, detection techniques for microorganisms are costly, time consuming, and require highly trained personnel. For these reasons, this study used particle size distribution to measure the microbial quality of wastewater through correlations between the number or volume of particles and the concentration of fecal coliforms, Salmonella spp. and helminth ova. Such correlations were obtained for both raw and chemically treated wastewater. The best fit was the one for helminth ova, which applies for both the influent and effluent and also for all the coagulants involved. This technique allows the on-line quantification of helminth ova at a cost of US$3 and it takes only 5 minutes, instead of the US$70 and 5 days for the standard technique. With respect to the coagulants applied, their behavior is different only for particles smaller than 8 mm, and thus this value is considered as the critical size for this particular treatment. The best coagulant was the aluminium polychloride. In addition, this work establishes the distribution of COD, TSS, nitrogen, and phosphorous for particles smaller and larger than 20 mm.

The aim of the research was to show the presence of micropollutants contained in the wastewater of Mexico City within the distribution canals of the Mezquital Valley (MV), as well as their retention in agricultural soil and aquifers. This system constitutes the world’s oldest and largest example of the use of untreated wastewater for agricultural irrigation. The artificial recharge associated with the MV aquifers, with groundwater extracted for human consumption showing its importance as a water resource for Mexico City. The results of sampling show the presence of 18 compounds, with 10 of these considered as endocrine disruptor compounds (EDCs). The concentration of these pollutants ranged from 2 ng/L for 17 β-estradiol to 99 ng/L for DEHP, with these values decreasing throughout the course of the canals due to the wastewater dilution factor, their retention in agricultural soil, and their accumulation in the local aquifer. The main mechanisms involved in natural attenuation are adsorption, filtration, and biodegradation. Drinking water equivalent levels (DWELs) were estimated for 11 compounds with regard to acceptable daily intakes (ADIs), by assuming local exposure parameters for a rural Mexican population. These were compared with the maximum groundwater concentrations (Cgw) to screen the potential risks. The very low ratios of Cgw to DWELs indicate no appreciable human health risk from the presence of trace concentrations of these compounds in the source of drinking water in the MV. Despite this, far from being exceeded after more than 100 years of irrigation with residual water, the natural soil attenuation seems to remain stable.

Waterborne diseases produced by organisms of public health concern are prevalent worldwide, continuing to cause deaths annually. Conventional disinfectants (ozone, UV radiation, chlorine) have been insufficient in providing safe water as many studies revealed. TiO₂ is an attractive alternative to conventional methods because of its versatility and recently explored biocidal capacity due to advanced oxidation processes. The oligodynamic effect that TiO₂ seems to have on some microorganisms consists of effective lipid hyper oxidation of microorganism membranes, as well as protein interactions that lead to the alteration of the internal conditions and the inhibition of metabolic processes that eventually lead to their lysis. Nevertheless, a satisfactory description of other organisms is necessary to complete the disinfectant–organism interaction, and then the subsequent evaluation parameters of sanitation should proceed. In addition, solutions for feasibility, standardization of results for achieving consistent results and defined applications, lower costs, scalability, and security after its application need to be studied. Understanding its usage implies knowing the actual state of the art and its limitations for water disinfection purposes, as well as the potential benefits that overcoming such limitations would provide, thus allowing the possibility of establishing it as a feasible and popular technology.

Where there is a variation in quality and quantity of sewage, advanced primary treatment (APT) is a useful means of treating wastewater. Mexico City, which has a combined sewage network and variations of flow rates ranging from 45 m³ s⁻¹ during the dry season to 300 m³ s⁻¹ during the rainy season, is just such a case. The data presented in this paper show the suitability of APT for Mexico City, enabling the continued reuse of such waters in a very arid region of 85 000 ha of poor quality soils. Given the agricultural nature of the irrigation area, the objective of this treatment is determined mainly by health requirements (helminth eggs and bacterial removal) instead of the organic and nutrient contents of the effluent, which are needed for the agricultural purposes of the irrigated area. From tested conditions, alum in a dose of 100 mg l⁻¹ and 0.2 mg l⁻¹ of an anionic polymer produce an effluent with a helminth egg content of <1 egg l⁻¹, which allows its use for irrigation for any kind of crop. Removal efficiencies attained were of 63.87% for TSS, 28.36% for COD, 17.42% for N, 20.43% for P, and 97.7% for helminth eggs. However because faecal coliform content is 1.2 × 10⁶ NMP/100 ml⁻¹, an additional disinfection process is needed.

The treatment of reject water from a nanofiltration system by photo-oxidation with ultraviolet light and titanium dioxide (TiO₂) showed that degradation efficiency of the organic micropollutants (OMPs) varied depending on the reaction time analyzed. Thus, compounds such as diclofenac and ibuprofen exhibited greater than 95 % degradation within the first 15 min, while less than 65 % of naproxen and gemfibrozil was degraded after 15 min of reaction time. Salicylic acid had the lowest degradation efficiency in 15 min (<45 %) of all of the compounds studied. In addition to radical recombination, suspended particles limit potential homogeneous illumination in the reaction system while the presence of organic material causes parallel hydroxyl radical-consuming reactions, which may be responsible for low degradation efficiencies under these conditions.