Nitrogen recovery from wastewater using gas-permeable membranes: Impact of inorganic carbon content and natural organic matter.

Gas-permeable membranes coupled with low-rate aeration is useful to recover ammonia (NH4+) from livestock effluents. In this study, the role of inorganic carbon (bicarbonate, HCO3-) to enhance the N recovery process was evaluated using synthetic effluents with various NH4+ to HCO3- molar ratios of 0.5, 1.0, 1.5 and 2.0. The study also evaluated the effect of increased organic matter on the NH4+ recovery using humic acids (3000-6000 mg L-1), and the N recovery from high-strength swine manure. The release of hydroxide from the HCO3- with aeration increased the wastewater pH and promoted gaseous ammonia formation and membrane uptake. At the same time, the recovery of gaseous ammonia (NH3) through the membrane acidified the wastewater. Therefore, an abundant inorganic carbon supply in balance with the NH4+ is needed for a successful operation of the technology. NH4+ removal efficiencies >96% were obtained with NH4+ to HCO3- ratios ≤1. However, higher molar ratios inhibited the N recovery process resulting in lower efficiencies (<65%). Fortunately, most swine manures contain ample supply of endogenous inorganic carbon and the process can be used to more economically recover the ammonia using the natural inorganic carbon instead of expensive alkali chemicals. In 4 days, the recovered NH4+ from swine manure contained 48,000 mg L-1. Finally, it was found the process was not inhibited by the increasing levels of organic matter in the wastewater evaluated.

Use of organic acids in the composting of municipal solid waste: a pilot-scale study.

Compost made from municipal solid waste (MSW) contains heavy metals that can interfere with the use of organic amendment in soil. In order to find effective ways to reduce the potential risk of heavy metals, we have investigated a novel approach by use of organic acid during MSW composting. Citric and oxalic acid dissolutions (0.25 mol x (-1)) were used at determined ratios (kg dried MSW: cm(3) acid). Cr and Ni concentrations were similar in compost, independent of acid contribution. By contrast, Cu concentrations decreased by 63% (at citric acid ratio 1:15), 65% (at citric acid ratios 1:20 and 1:40) and 83% (at oxalic acid ratio 1:40); furthermore, Pb concentrations reduced by 71% (at citric acid ratios 1:20 and 1:40 and at oxalic acid ratio 1:40) and Zn concentrations reduced by 67% (at citric acid ratios 1:10 and 1:20) and 70% (at oxalic acid ratio 1:40). The total metal mass decreased by an average of 12% in the compost fraction, whereas the total percentage of the residual fraction increased by an average of 20%. The acid addition in the studied ratios improved compost quality without negatively influencing biostabilization.

Production of pulp and energy using orange tree prunings.

The aim of this work was to chemically characterize orange tree prunings and use it in pulping and combustion processes. Soda-anthraquinone pulping of the main fraction of orange pruning (stems with a diameter > 0.5 cm) was simulated with polynomial and neurofuzzy models, that predicted pulp properties as a function of operating variables (155-185°C, 40-90 min, soda concentration, 10-16%) with errors less than 20%. The heating values (16,870 kJ/kg), the flame temperature (1150-2150 °C) and dew point temperature of fuel gas (47-53 °C) for the residual fraction from orange pruning (stems diameter < 0.5 cm and leaves) was determined and compared with other non-wood lignocellulosic materials. As a consequence the price of kJ obtained by combustion of this residual fraction is less than other lignocellulosic materials, much lower than those of fossil fuels.

Exploitation of hemicellulose, cellulose and lignin from Hesperaloe funifera.

This work seeks the integral use of all major components of Hesperaloe funifera, separating hemicelluose by hydrothermal treatments; cellulose by pulping processes; and exploitation of lignin of pulping liquor by pyrolysis and gasification processes. By using sulfuric acid in the hydrothermal treatment (150-190 °C, 0-20 min after reaching operating temperature, 6-10 liquid/solid ratio, 0.1-0.5% sulfuric acid), the glucose and xylose of liquid fraction increase from 1.5% to 5.9%, and 4.0% to 12.4%, respectively; the yields of solid fraction decrease from 91.6% to 79.5%, and the lignin content increase from 23% to 32%. Pulps and paper sheets obtained from solid fractions hydrothermal treatments and from raw material pulped with diethanolamine, are worse than those obtained with soda-anthraquinone (Yield 57.8%; kappa number 24.9; Viscosity 711 mL/g; Brightness 54.8%; Tensile index 73.6 Nm/g; Stretch 2.84%; Burst index 6.13 kN/g and Tear index 1.69 mNm2/g). By acidification (pH 6) of soda pulping liquor it separate lignin-rich solids, which by pyrolysis gave a gas containing 1.13% H2, 31.79% CO and 1.86% CH4 by weight. Gasification of the same sample provided a gas containing 0.18% H2, 24.50% CO and 17.75% CH4.

El contraste de medias recortadas ante la violación de los supuestos paramétricos / No disponible

En la presente investigación se estudia, mediante simulación por ordenador, el comportamiento del contraste de t de Student con medias recortadas (Wilcox, 1996), con tamaños muestrales pequeños, bajo la violación de los supuestos de normalidad y homocedasticidad. Se concluye que este contraste es útil cuando las distribuciones son asimétricas, pero se asegura el supuesto de homocedasticidad (AU)

The trimmed means test under the violation of parametric assumptions. In this study, using computer simulation, we test the behavior of Student’s test with trimmed homoscedasticity assumptions. It is concluded that this test is useful when both distributions are asymmetric but homoscedastic (AU)