Luis G. Torres

Decontamination of soil washing wastewater using solar driven advanced oxidation processes

Decontamination of soil washing wastewater was performed using two different solar driven advanced oxidation processes (AOPs): the photo-Fenton reaction and the cobalt/peroxymonosulfate/ultraviolet (Co/PMS/UV) process. Complete sodium dodecyl sulphate (SDS), the surfactant agent used to enhance soil washing process, degradation was achieved when the Co/PMS/UV process was used. In the case of photo-Fenton reaction, almost complete SDS degradation was achieved after the use of almost four times the actual energy amount required by the Co/PMS/UV process. Initial reaction rate in the first 15min (IR15) was determined for each process in order to compare them. Highest IR15 value was determined for the Co/PMS/UV process (0.011mmol/min) followed by the photo-Fenton reaction (0.0072mmol/min) and the dark Co/PMS and Fenton processes (IR15=0.002mmol/min in both cases). Organic matter depletion in the wastewater, as the sum of surfactant and total petroleum hydrocarbons present (measured as chemical oxygen demand, COD), was also determined for both solar driven processes. It was found that, for the case of COD, the highest removal (69%) was achieved when photo-Fenton reaction was used whereas Co/PMS/UV process yielded a slightly lower removal (51%). In both cases, organic matter removal achieved was over 50%, which can be consider proper for the coupling of the tested AOPs with conventional wastewater treatment processes such as biodegradation.

Wastewater disinfection and organic matter removal using ferrate (VI) oxidation

The use of iron in a +6 valence state, (Fe (VI), as FeO4(-2)) was tested as a novel alternative for wastewater disinfection and decontamination. The removal of organic matter (OM) and index microorganisms present in an effluent of a wastewater plant was determined using FeO4(-2) without any pH adjustment. It was observed that concentrations of FeO4(-2) ranging between 5 and 14 mg l(-1) inactivated up to 4-log of the index microorganisms (initial concentration c.a. 10(6) CFU/100 ml) and achieved OM removal up to almost 50%. The performance of FeO4(-2) was compared with OM oxidation and disinfection using hypochlorite. It was observed that hypochlorite was less effective in OM oxidation and coliform inactivation than ferrate. Results of this work suggest that FeO4(-2) could be an interesting oxidant able to deactivate pathogenic microorganisms in water with high OM content and readily oxidize organic matter without jeopardizing its efficiency on microorganism inactivation.

Coagulation-flocculation process applied to wastewaters generated in hydrocarbon-contaminated soil washing: Interactions among coagulant and flocculant concentrations and pH value

Wastewater produced in the contaminated soil washing was treated by means of coagulation-flocculation (CF) process. The wastewater contained petroleum hydrocarbons, a surfactant, i.e., sodium dodecyl sulfate (SDS) as well as salts, brownish organic matter and other constituents that were lixiviated from the soil during the washing process. The main goal of this work was to develop a process for treating the wastewaters generated when washing hydrocarbon-contaminated soils in such a way that it could be recycled to the washing process, and also be disposed at the end of the process properly. A second objective was to study the relationship among the coagulant and flocculant doses and the pH at which the CF process is developed, for systems where methylene blue active substances (MBAS) as well as oil and greases were present. The results for the selection of the right coagulant and flocculant type and dose, the optimum pH value for the CF process and the interactions among the three parameters are detailed along this work. The best coagulant and flocculant were FeCl3 and Tecnifloc 998 at doses of 4,000 and 1 mg/L, correspondingly at pH of 5. These conditions gave color, turbidity, chemical oxygen demand (COD) and conductivity removals of 99.8, 99.6, 97.1 and 35%, respectively. It was concluded that it is feasible to treat the wastewaters generated in the contaminated soil washing process through CF process, and therefore, wastewaters could be recycled to the washing process or disposed to drainage.

Disinfection of a wastewater flow treated by advanced primary treatment using O3, UV and O3/UV combinations

This study was conducted to evaluate the ozone, UV and O3/UV processes for the reuse of sewage treatment plant effluent (Universidad Autonoma Metropolitana Azcapotzalco wastewater treatment plant). The ozone/UV process was compared to individual ozone and the UV processes and control parameters were total and fecal coliforms. Different ozone concentrations (6–12 mg O3/min) and different UV fluencies (6.7–20.12 mJ/cm2) were tested. It is possible to conclude than none of the processes achieved the disinfection levels required to comply with the Mexican standard NOM-003-SEMARNAT-1997. The continuous ozone process offered the lower total and fecal coliforms reductions, while UV light resulted a disinfection agent with higher germicide power than ozone. The maximum logarithmic reduction achieved due to the combined ozone/UV process was of 2.04 for fecal coliforms and of 2.17 for total coliforms. The next 8 combinations showed lower removal efficiencies, but always higher than those obtained with the single ozone or UV processes. The ozone/UV process was highly effective for the disinfection and a synergistic effect was observed.

Two-Stage Optimization of Coliforms, Helminth Eggs, and Organic Matter Removals from Municipal Wastewater by Ozonation Based on the Response Surface Method

In this study, a set of municipal wastewater (MWW) samples from an actual residual water treatment plant was treated by ozone. The residual water was characterized in terms of organic load and biological contaminants: total coliforms (TC), fecal coliforms (FC) and helminth eggs (HE). Initial values of these parameters were 2.8 × 107 MPN/100 mL, 8.48 × 106 MPN/100 mL, and 470 L−1, respectively. The experimental setup considered the modification of pH and ozone dose as independent variables. Three different initial pH values (4.0, 7.0, and 11.0) and three different ozone concentrations (6, 15, and 30 mg/L) were used to investigate the pH ozone dose effect. The efficiency of ozone-based treatment was determined by the reduction of the microbiological indicators (TC, FC, and HE) and physicochemical parameters (COD and turbidity). The response surface method was used to determine suboptimal reaction conditions. These conditions were obtained using a two-stage procedure. The conditions under which both microbiological and organics were better removed corresponded to pH 7.8 and ozone concentration of 15.5 mg/L. A decline of biological indicators of 99% for TC, 99% for FC, and 99% for HE was obtained under the same reaction conditions. The reduction of chemical oxygen demand (COD) and turbidity was 75% and 85% under the same operation conditions, respectively.

Scaling-up parameters for site restoration process using surfactant-enhanced soil washing coupled with wastewater treatment by Fenton and Fenton-like processes

Estimation of scaling-up parameters for a site restoration process using a surfactant-enhanced soil washing (SESW) process followed by the application of advanced oxidation processes (Fenton and photo-Fenton) was performed. For the SESW, different parameters were varied and the soil washing efficiency for pesticide (2,4-D) removal assessed. The resulting wastewater was treated using the Fenton reaction in the absence and presence of ultraviolet (UV) radiation for pesticide removal. Results showed that agitation speed of 1550 rpm was preferable for the best pesticide removal from contaminated soil. It was possible to wash contaminated soils with different soil concentrations; however the power drawn was higher as the soil concentration increased. Complete removal of the pesticide and the remaining surfactant was achieved using different reaction conditions. The best degradation conditions were for the photo-Fenton process using [Fe(II)]=0.3 mM; [H2O2]=4.0 mM where complete 2,4-D and sodium dodecylsulfate (SDS) removal was observed after 8 and 10 minutes of reaction, respectively. Further increase in the hydrogen peroxide or iron salt concentration did not show any improvement in the reaction rate. Kinetic parameters, i.e. reaction rate constant and scaling-up parameters, were determined. It was shown that, by coupling both processes (SESW and AOPs), it is possible the restoration of contaminated sites.

Variation of Mechanical and Hydraulic Properties of Oil-Contaminated Soil Due to a Surfactant-Enhanced Washing Process

Soil contaminated with a high level of hydrocarbons was obtained from an area near an oil extraction facility located in the Tamiahua region, Veracruz, Mexico, and submitted to a surfactant enhanced washing (SEW) process to remove contaminants. The purpose of this article was to characterize the variations in the mechanical and hydraulic properties of the soil after the application of the SEW process, as these characteristics are important in soil mechanics and might affect the behavior of the material for construction purposes. During the experimental assessment, each test was conducted several times for three different soil conditions (contaminated, non-contaminated, and washed soil), applying the same specifications and features to each one to allow accurate comparison of data. Results show that the soil washing process produces a loss of fine particles that affect the mechanical and hydraulic behavior of the tested materials. Data also indicates that the presence of the contaminant modifies soil characteristics generating different soil properties under all the conditions studied.

Viscosity, Surface Tension, and Other Physical-chemical Characteristics of Three Crude Oils Arising From Chicontepec, Mexico

Three dead crude oil samples, arising from Chicontepec, Veracruz (Mexico), were characterized in terms of water content; sediment volume; the fraction of insoluble components in pentane; the fraction of saturated, polar, and aromatic compounds; and the acid and base numbers. In addition, the API density, viscosity at various temperatures, and surface tension were measured for each crude. At the end, some correlations between oil composition and surface properties and viscosity are presented. Viscosity and surface tension of these samples are correlated with the fraction of n-pentane insoluble components (asphaltenes) and inversely correlated with the fraction of aromatic compounds. The acid components in the crude oils are correlated with surface tension while the basic components are negatively correlated with it. Finally the base number is correlated with viscosity.