Regeneration of granular activated carbon clogged in the treatment of leachates.

Landfill leachates are highly contaminated liquids and complex to treat. Two of the processes which are promising for the treatment are the advanced oxidation and adsorption methods. With the combination of the Fenton and adsorption methods, practically all the organic load of leachates can be removed; however, this combination of processes is limited due to the soon clogging of adsorbent material, which leads to high operation costs. In the present work, the results of the regeneration of clogged activated carbon are shown after the application of the Fenton/adsorption process in leachates. This research consisted of four stages: sampling and leachate characterization, clogging of the carbon through the Fenton/adsorption process, carbon regeneration through the oxidative Fenton process, and lastly, evaluation of regenerated carbon adsorption through jar and column tests. In the experiments, HCl 3 M was used, and different concentration of hydrogen peroxide (0.15 M, 0.2 M, 0.25 M) were tested at different times (16 h and 30 h). The activated carbon regeneration through the Fenton process and the optimal peroxide dosage was 0.15 M for 16 h. The regeneration efficiency was obtained from comparing the adsorption efficiency between regenerated and virgin carbon, reaching 98.27% and can be applied up to 4 times without losing regeneration efficiency. These results prove that it is possible to restore the clogged activated carbon adsorption capacity during the Fenton/adsorption process.

Pesticide treatment in biobed systems at microcosms level under critical moisture and temperature range using an Orthic Solonchaks soil from southeastern Mexico amended with corn husk as support.

Agriculture effluents from cleaning and handling equipment used in pesticide applications can contaminate superficial and groundwater sources when not correctly disposed of. Biobeds using soil enriched with amendments represent a viable technology to control and minimize pesticide pollution of soil and water in farmlands. They are usually installed outdoors without protection, making them vulnerable to rain flooding, lack of moisture, drought, and intense heat or cold. Temperature (T) and moisture (M) of the biomixture are considered two of the most important physical factor affecting pesticide dissipation. This study aimed to evaluate the effect of T and M on the dissipation of five of the most used pesticides (carbofuran, atrazine, 2,4-D, diazinon, and glyphosate) in Yucatan State, Mexico. Three experiments using miniaturized biobeds considering optimal temperature and moisture (T of 30 ± 2 °C and 90% water holding capacity [WHC]) were performed. The optimal dissipation time and the effect of T, M variations, and volatilization was determined. The optimal dissipation time was over 14 days. Carbofuran was the least dissipated pesticide and glyphosate the most. The primary factor affecting pesticide dissipation was T (P < 0.05), reaching rates of dissipation of 99% at 45 °C. Variations of M in the biomixture were not significant on pesticide dissipation (P > 0.05). The white-rot fungi were observed; its presence was related to increments of T. Head Space analysis (at 45 °C) showed low pesticide volatilization (≤0.03%) for all pesticide used were quantified; water vapor condensation could reduce the pesticide volatilization for experimental conditions.

Identification of microbial species present in a pesticide dissipation process in biobed systems using typical substrates from southeastern Mexico as a biomixture at a laboratory scale.

Biobed systems are an important option to control point pollution in agricultural areas. Substrates used and microbial diversity present in a biomixture perform an essential function in pesticide dissipation. In this study, the effects of soil (50% of volume/volume [V/V] proportion for all biomixtures) and four soil-based biomixtures (miniaturized biobeds; addition of novel substrates from southeastern Mexico) on dissipation of high concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D), atrazine, carbofuran, diazinon, and glyphosate and on microbial diversity in biomixtures were evaluated. Small residual amounts of all pesticides at 20 (<2%) and 41 (<1%) days were observed; however, the lowest efficiency rates were observed in soil. Glyphosate was the only pesticide that completely dissipated in soil and biomixtures. Archaea, bacteria, and fungi were identified in biobeds, with bacteria being the most diverse microorganisms according to the identified species. The presence of white-rot fungi (normally related to pesticide degradation in biomixtures) was observed. Effects of the pesticide type and of biomixtures on pesticide dissipation were significant (P<0.05); however, only the effect of biomixtures on microbial diversity was significant (P<0.05); microbial diversity and richness had a significant effect on the residual amount of pesticides (P<0.05). Microbial diversity in terms of phyla was directly related to physicochemical parameters such as organic matter, lignin, water-holding capacity, and pH of soil and biomixtures.

Agricultural effluent treatment in biobed systems using novel substrates from southeastern Mexico: the relationship with physicochemical parameters of biomixtures.

Misuse of pesticides in farming activities leads to contamination of drinking water sources and is responsible for animal and human health problems. The biobeds are practicable option to minimize contamination by pesticides during preparation, use and washing of equipment for pesticide treatments. This research aimed at testing substrate mixtures to optimize biobed efficiency to remove pesticides under the climate of the Yucatan (México). Agricultural soil and 11 mixtures adding vegetable compost, sisal pulp, corn stover and seaweed were tested under controlled conditions. Each biomixture was exposed to a mixture of five pesticides (2,4-diclorophenoxyacetic acid "2,4-D" [1.08 mg cm-3], atrazine [2.50 mg cm-3], carbofuran [0.23 mg cm-3], diazinon [0.34 mg cm-3], and glyphosate [0.36 mg cm-3]) in a period of 41 days. Monitoring of the dissipation of pesticide residues showed that pesticides were quickly dissipated in soil at microcosm level experiment, while at two critical times of 20 and 41 days, all mixtures of substrates (biomixtures) were efficient in dissipation of high concentrations of pesticide in a short time (>99%). Time, biomixture and type of pesticide were shown to be the main parameters influencing pesticide dissipation (P < 0.05). Several other physicochemical parameters of the biomixtures, such as organic matter (OM), lignin, water holding capacity (WHC), and pH, were also significant on pesticide dissipation (P < 0.05), being pH the most significant.

Physico-chemical treatment of Merida landfill leachate for chemical oxygen demand reduction by coagulation.

In order to determine the optimal dosage and type of coagulant for the physico-chemical treatment of leachate from the sanitary landfill of Merida, Mexico, a total of 864 jar tests were performed. Four metallic coagulants (ferric chloride, ferric sulphate, aluminium polychloride and aluminium sulphate) with doses ranging between 50 and 300 mg L(-1) and two polyelectrolytes (high-density anionic and cationic reagents) with doses from 2 to 12 mg L(-1) were tested. Neither an adequate type of coagulant nor an optimal dose could be found. The removal of contaminants was measured as total and dissolved chemical oxygen demand (COD). Soluble COD removal efficiencies were low, from 0 to 47%, with a 4% average value only. These low values of organic material removal were attributed to the particular characteristics of the Merida landfill leachate (low suspended solids concentration), so even with sweep-floc coagulation (300 mg L(-1) dose) only low COD removal efficiencies were obtained. A study of the suspended particle size distribution of the leachate was conducted in order to explain the poor performance. The particle size distribution ranged from 0.375 to 948.2 microm, with an average value of 22.97 microm. In a second step the optimal pH for physico-chemical treatment of these leachates was determined. Finally a greater than 90% removal of organic material, measured as suspended COD, was obtained at pH 2, which was considered as the optimal value.