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Chromium is a non-biodegradable element predominantly found in two chemical forms, Cr(VI) and Cr(III). Several remediation strategies have been implemented to achieve its removal from aquatic environments with limited results. This review article focuses on the analysis of removal strategies including the use of: (1) raw materials (agro-wastes, activated carbons, extracts and solutions) and (2) treated materials (alkaline and acid treatments). The article also reviews and analyses results obtained with surfactant modified organic biomasses. Although this review aims to summarise chromium removal techniques by highlighting relevant results of several studies, surface modification is outlined as a promising method to improve removal efficiency in aqueous solutions. The information presented in this article can help in the development of more efficient methods considering the improvements that surfactants may offer.

This research addresses the use of methane (CH4) for energy generation in a landfill located in Southern Mexico. To evaluate the feasibility of this renewable and sustainable energy project, a LandGEM model was used to estimate the CH4-emissions, the environmental benefits and the economic profitability. Taken together, results showed an average CH4-production of 2932 ft3/min, with a maximum CH4-generation flowrate of 4072 ft3/min (115.3 m3). Energy generation resulted in 32.396 million KW h/year with a hot water/steam production of 63.990 million BTU/year. The installed capital costs of a 15-years project were estimated in $9,034,907 USD; economic parameters showed a financial profitability with a net present value of $6,304,060 and an internal rate of return of 25%. The environmental benefits reported a total collection and destruction of CH4 at 9,824,469,979 ft3 (278,198,009.2 m3). The results obtained in this research can be used to conduct further studies to implement waste-to-energy technologies in Mexico and thus improve the sector of sustainable and renewable energy.

The presence of heavy metals in water for human use or consumption represents a major risk to human health. It is therefore important to find materials to remove or minimise the concentration of these pollutants. The adsorption process for the removal of heavy metals is favoured by the use of low-cost materials that exhibit a porous structure and a high cation exchange capacity, such as zeolites and clays. On the other hand, chemical treatments, e.g., using acids and bases, can modify the properties of these materials, but more recently the application of surfactants has also shown to be successful for broadening their metal affinity and allowing the removal of diverse organic and inorganic pollutants from water. This paper reviews the application of modified zeolites and clays for the removal of heavy metals from water.

In this study we report the characterization of a leachate contaminated site, by following a methodology that integrates geophysical and geohydrological data to better constrain a hydrogeological model. The characterization of the site (subsurface structure, soil characteristics) included six seismic refraction profiles, three electromagnetic lines using transient domain electromagnetic soundings (TDEM), two electric resistivity tomography (ERT) profiles, five vertical electrical sounding (VES) and geohydrological testings and analysis to support the delimitation of the contaminant plume. The study area corresponds to the leachate lagoon of Oaxaca City landfill, southern Mexico. Its inferred hydrogeological model constitutes an example of the uselfuness of the integration of several diverse methods applied with the same objective, thus reducing the ambiguity of applying a single characterization technique. The results indicate that low resistivity values from 1.5 to 2.5 Ohm-m are related to a leachate polluted soil underlying the leachate lagoon and also associated with an anomaly enclosed in the rockbed. A displacement of the polluted plume to the SW from the lagoon was also detected. Water quality is quite good but the human activity in the study area confers a risk to the Zaachila aquifer.