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The objective of the present study was to investigate the ability of water hyacinth (Eichhornia crassipes) to absorb organic compounds (potassium hydrogen phthalate, sodium tartrate, malathion, 2,4-dichlorophenoxy acetic acid (2,4-D), and piroxicam). For the aforementioned purpose, an artificial wetland system (AWS) was constructed and filled with water hyacinth collected from the Valsequillo Reservoir, Puebla, Mexico. Potassium hydrogen phthalate and sodium tartrate were measured in terms of chemical oxygen demand (COD) and biological oxygen demand (BOD). The present study indicated that the water hyacinths absorbed nearly 1.8-16.6 g of COD kg dm (dry mass of water hyacinth), while the absorbance efficiency of BOD was observed to be 45.8%. The results also indicated that the maximum absorbance efficiency of malathion, 2,4-D, and piroxicam was observed to be 67.6%, 58.3%, and 99.1%, respectively. The kinetics of organic compounds fitted different orders as malathion followed a zeroth-order reaction, while 2,4-D and piroxicam followed the first-order reactions. Preliminary assessment of absorption of heavy metals by the water hyacinth in the AWS was observed to be (all values in mg g) 7 (Ni), 13.4 (Cd), 16.3 (Pb), and 17.5 (Zn) of dry biomass, thus proving its feasibility to depurate wastewater.

The present work aims to elucidate the possibility of injecting ozone into surface waters combined with urban wastewaters in order to improve the water quality of the High Atoyac Sub-basin (HAS) in Central Mexico. For this purpose, twenty physicochemical parameters, eight heavy metals, seven organic compounds, and one biological indicator were assessed in water from different sites of the studied area (the Alseseca River, the Atoyac River and the Valsequillo Reservoir). Results demonstrated that O3 injection led to the decrease of the aromatic fraction of organic molecules since the Spectral Absorption Coefficient at 254 nanometers (SAC254) reduction was found to be 31.7% in the Valsequillo Reservoir water samples. Maximum Chemical Oxygen Demand (COD) removal was observed to be 60.2% from the Alseseca River with a 0.26 mg O3/mg initial COD dose. Among all the phthalates studied in the present work, Di(2-ethylhexyl) phthalate (DEHP) exhibited the highest concentration (5.8 μg/L in the Atoyac River). Treatment with O3 was not effective in eliminating fecal coliforms (FC) in waters that host high organic matter (OM) loads as opposed to waters with low OM. After the injection of 4.7 mg O3/mg COD in the VO3-AT water sample, a 90% removal of Iron (Fe) and Aluminum (Al) was registered; while Manganese (Mn), Nickel (Ni), Zinc (Zn), and Cooper (Cu) showed a 73%, 67%, 81%, and 80% removal, respectively; Chromium (Cr) registered the highest removal (~100%). The present work demonstrated that while finding a suitable O3 dose to improve the quality of water in the HAS, the 5-days Biochemical Oxygen Demand (BOD5)/COD ratio (i.e., biodegradability) is more important than the overall OM removal percentage proving that O3 injection is a feasible process for the treatment of eutrophic waters from HAS.

The Valsequillo reservoir is a Ramsar wetland due to its importance as a point of convergence of migratory waterfowl. It is located in Central Mexico and is currently endangered by the constant spill of municipal and industrial discharges from Puebla city. On this context, we evaluated thirteen potential toxic metals (PTMs) in water, Water hyacinth (E. crassipes) plants and sediments at this site. A combined number of 31 samples were collected from the study area. The degree/extent of metal contamination in sediments was assessed through different geochemical indexes, namely: Geoaccumulation index (Igeo), Enrichment Factor (EF) and Potential Ecological Risk Index (PERI). The ability of Water hyacinth plants residues as a phytodepurator in the Ramsar site was tested in terms of the bioaccumulation factor (BF) and the translocation factor (TF). The results concerning sediments showed that Pb, Cu and Hg pose a threat to the aquatic environment since Igeo and EF indicate sediments ranging from moderately contaminated to contaminated. Moreover, PERI pointed out Hg as the main contributor to the ecological risk in sediments, especially in the part of the reservoir covered by E. crassipes. Water hyacinth plants displayed good capacity to absorb PTMs from the water, since the content of Co, Zn, As, Ni, Cu, Pb, Ti, Cr, Ba, Mo and V in the total plant was (all values in mg/kg of dry weight) 21 ± 9, 408 ± 300, 12 ± 6, 93 ± 21, 93 ± 69, 53 ± 29, 1067 ± 643, 78 ± 55, 362 ± 39, 14 ± 0.6 and 96 ± 35, respectively. Metal content in sediments resembles to that of E. crassipes; especially in the roots, suggesting a constant deposition of plants at the bottom of the reservoir, which contributes to the eutrophication of the water. The present work encourages the need for a sustainable management of Water hyacinth plants in the Ramsar site, since they represent a plague and a natural phyto-depurator at the same time.

This work shows the results for the first time of calibrating and validating a mathematical model, capable of predicting the amounts of O3 and O2 necessary to reduce pollution levels in a lake based on the Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD5), Total nitrogen (TN), Total phosphorus (TP) and Fecal coliforms (FC) concentrations. The model was designed to treat a natural or artificial lake as though it were an aerated lagoon operating as an idealized Continuous flow complete-mix reactor. The O3 yield constant for eliminating the non-biodegradable fraction of COD and for deactivating fecal coliforms were laboratory derived and calibrated with field values. Based on the field parameters, the model accurately predicted a reduction in BOD5, COD, TN, TP and FC of 53 %, 51 %, 39 %, 42 % and 98 %, respectively. The model proved to be effective in predicting O2 and O3 demand and time of recovery of a polluted water body.

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