Movement of Water and Solutes in a Wastewater Irrigated Piedmont

Risk transfer from a megacity to a peri-urban agricultural community: wastewater reuse and effects on groundwater quality

Urban wastewater is a resource that can be reused, but its management must be carefully executed, considering its potential impact on public and environmental health. Unfortunately, marked differences in the quality of treatment, management, collection, and the monitoring of wastewater exist among low-, middle-, and high-income countries. This is the case of the Mezquital Valley, a semi-rural area that is composed of agricultural and industrial communities on the outskirts of Mexico City. For over 100 years, wastewater from Mexico City and its areas of conurbation has been sent to the Mezquital Valley, with few studies having been conducted to assess the existence and severity of bacterial and pathogen infiltration into the local aquifer. In this research, we present an assessment of wastewater infiltration transported from Mexico City, used for irrigation, with potential infiltration into the Mezquital Valley aquifer. We utilized stable isotope analysis of deuterium and oxygen-18 to determine whether a mixture of untreated wastewater from the Mexico City Metropolitan Area (MCMA) flows into the Mezquital aquifer. Also, tests for adenovirus, rotavirus, fecal coliform, fecal enterococci, Giardia lamblia, and Cryptosporidium parvum were employed to determine the presence of fecal indicators and pathogens in different water sources in the study area. The results show the presence of indicators and pathogens in local wells used as water supply in Mezquital Valley. The presence of such indicators suggests that pathogens can reach the water consumed by the inhabitants, posing a hazard to persons exposed to these waters during their normal daily-life activities.

Temporal analysis of the microbial communities in a nitrate-contaminated aquifer and the co-occurrence of anammox, n-damo and nitrous-oxide reducing bacteria

Groundwater-N pollution derives from agricultural and urban activities, and compromises water quality in shallow aquifers, putting human and environmental health at risk. Nonetheless, subsurface microbiota can transform dissolved inorganic nitrogen into N₂. In this study, we surveyed the microbial community of a shallow aquifer by sampling one well, one piezometer and a spring within an agricultural area that receives N-inputs of more than 700 kg/ha per year through irrigation with wastewater. The survey was conducted during a year with a 16S rRNA next-gen approach. In parallel, we quantified the number of gene copies and transcripts related to anaerobic ammonium oxidation (anammox, hzo), nitrite-dependent anaerobic methane oxidation (n-damo, nod and pmoA) and nitrous oxide reduction (last step of denitrification, nosZ), during the dry and rainy seasons. Our results showed that the groundwater samples had 17.7 to 22.5 mg/L of NO₃^--N. The bacterial and archaeal community structure was distinctive at each site, and it remained relatively stable over time. We verified the co-occurrence of N-transforming bacteria, which was correlated with the concentration of NO₂^-/NO₃^- and ORP/DO values (DO: ~3.0 mg/L). Our analyses suggest that these conditions may allow the presence of nitrifying microorganisms which can couple with anammox, n-damo and denitrifying bacteria in interrelated biogeochemical pathways. Gene density (as the number of gene copies per litre) was lower in the rainy season than in the dry season, possibly due to dilution by rainwater infiltration. Yet, the numbers of hzo gene copies here found were similar to those reported in oceanic oxygen minimum zones and in a carbonate-rock aquifer. The transcript sequences showed that Candidatus Brocadia spp. (anammox), Candidatus Methylomirabilis spp. (n-damo) and autotrophic denitrifying Betaproteobacteria coexist in the groundwater environment, with the potential to attenuate the concentration of dissolved inorganic nitrogen by reducing it to N₂ rather than N₂O; delivering thus, an important ecosystem service to remove contaminants.

Megacity Wastewater Poured into A Nearby Basin: Looking for Sustainable Scenarios in A Case Study

Megacity sewage creates socioeconomic dependence related to water availability in nearby areas, especially in countries with hydric stress. The present article studies the past, current, and future water balance progression of realistic scenarios from 2005 to 2050 in the Mezquital Valley, the receptor of Mexico City untreated sewage since 1886, allowing for agriculture irrigation under unsustainable conditions. The Water Evaluation and Planning System (WEAP) was used to estimate water demand and supply, and validation was performed by comparing results with outflow data from the Tula River. Simulated scenarios were (1st) steady-state based on inertial growth rates (2nd) transient scenario concerning the influence of forecasted climate change perturbations in surface water and hydric stress for 2050; and (3rd) the previous scenario appending scheduled actions, such as 36% reduction in imported wastewater and the startup of a massive Wastewater Treatment Plant, allowing for drip and sprinkler irrigation from the year 2030. The main results are as follows: (a) in the period 2005–2017, 59% of the agriculture depended on flood irrigation with megacity sewage; (b) the outcomes of water balance scenarios up to 2050 are presented, with disaggregated sectorial supply of ground and superficial water; (c) drip irrigation would reduce agriculture demands by 42% but still does not guarantee the downflow hydroelectric requirements, aggravated by the lack of wastewater supply from 2030. This research highlights how present policies compromise future Valley demands.

GHG and black carbon emission inventories from Mezquital Valley: The main energy provider for Mexico Megacity

The greenhouse gases and black carbon emission inventory from IPCC key category Energy was accomplished for the Mezquital Valley, one of the most polluted regions in Mexico, as the Mexico City wastewater have been continuously used in agricultural irrigation for more than a hundred years. In addition, thermoelectric, refinery, cement and chemistry industries are concentrated in the southern part of the valley, near Mexico City. Several studies have reported air, soil, and water pollution data and its main sources for the region. Paradoxically, these sources contaminate the valley, but boosted its economic development. Nevertheless, no research has been done concerning GHG emissions, or climate change assessment. This paper reports inventories performed by the 1996 IPCC methodology for the baseline year 2005. Fuel consumption data were derived from priority sectors such as electricity generation, refineries, manufacturing & cement industries, transportation, and residential use. The total CO2 emission result was 13,894.9 Gg, which constituted three-quarters of Hidalgo statewide energy category. The principal CO2 sources were energy transformation (69%) and manufacturing (19%). Total black carbon emissions were estimated by a bottom-up method at 0.66 Gg. The principal contributor was on-road transportation (37%), followed by firewood residential consumption (26%) and cocked brick manufactures (22%). Non-CO2 gas emissions were also significant, particularly SO2 (255.9 Gg), which accounts for 80% of the whole Hidalgo State emissions. Results demonstrated the negative environmental impact on Mezquital Valley, caused by its role as a Megacity secondary fuel and electricity provider, as well as by the presence of several cement industries.