Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

A simple method for the isolation of chitin is described. It is based on the solubility of the biopolymer in concentrated aqueous HCl at low temperature. The solubility diagram of the system chitin-HCl-H2O is discussed as well as the kinetics of the acid-catalyzed hydrolysis of the biomaterial. The hydrolytic degradation of the polymer is estimated to be less than 0,3 %, during the procedure.

The investigation of tropical gramineous in guinea pigs in the area of La Mana. The following objectives were pursued: To increase the productive indexes in improved peruvian guinea pigs (Cavia porcellus Linnaeus) under the effect of the consumption of the saboya grass (Panicum maximun Jack), leaves of Corn (Zea mays) and cane of sugar (Saccharum officinarum L) in the area of La Mana, and to determine the profitability of the treatments. 48 improved peruvian guinea pigs separated by sex of 35 days of age were used with a weight average of 305 g. A factorial form 2 (sex) x 3 (gramineous) with four replications was applied, arranged in a (CRBD). For the mean comparisons the Tukey (P≤ 0.05%) test was used. To obtain the profitability of the treatments the Benefit-Cost Relationship was used. The consumption of gramineous (g), consumption of food (g), gain of weight (g), nutritious conversion, live weigh (g) and yield to the channel (%) was evaluated. The male guinea pigs presented the major (P<0.05) consumption of gramineous, gain of weight and alive weight (81.65 g day-1 of MS; 8.66 g animal-1 day-1; 827.7 g, respectively). The gramineous of more consumption (P<0.05) was the saboya grass (99.31 g animal-1 day-1 of MS). However it shows the less efficient (13.82) nutritious conversion (P<0.05). The biggest gain of weight (P<0.05) was registered by the treatment based on leaf of corn (9.16 g animal-1 day-1). The yield to the channel (P>0.05) was not affected by the effect of the consumption of gramineous. The biggest profitability was registered by the male guinea pigs fed with leaf of corn + balanced (52.4%).

In order to increase production and profitability of common bean (Phaseolus vulgaris L.) crop, two types of commercial zeolites were assessed: “Zeolite C” and “Roca Magica” both of the Clinoptilolite type, in doses of 25, 50 and 75% of the recommended fertilization (80-40-00) for this crop in Quevedo city area. The variety of common bean used was “EVG-6”. The treatments were generated in the factorial form as follows 2 (types of zeolite) x 3 (doses of zeolite) + 1 (fertilization without zeolite as control), arranged in a Complete Randomized Blocks Design with four replications. To compare the means of the treatments, the Tukey test was used (P ≤ 0.05). Days to flowering, pests and diseases damages number of pods per plant, number of grains per pod, weight of 100 seeds and yield per hectare was measured in the plot. With the highest dose of zeolite along with chemical fertilizers an early flowering of about two days was observed. The minor pests and diseases damage was registered with the application of natural zeolite along with fertilizers. Among the types of zeolite statistical differences were found only in weight of 100 seeds and yield per plant; no statistical differences were found in the other variables. In the “zeolite vs. without zeolite” contrast a major production per plant and per hectare was found in favor of the application of zeolite. The higher profitability was obtained with the use of fertilizer plus “75% of Zeolite C” and “25% of Roca Magica”.

An agroforestry system trial with coffee (Coffea arabica L.) was implanted in “La Represa” Farm, nearby Quevedo on 1997. Four forest species associated with coffee and it was also established plots of coffee and trees in monoculture systems, at the next plots. The forest species utilized were guayacán blanco (Cybistax donnell-smithii Rose), laurel prieto (Cordia megalantha Chadat), fernansánchez (Triplaris cumingiana Wedd) and teca (Tectona grandis L. F.). The intention was to compare the agroforestry systems and the monoculture system in both components trees and coffee. The production by hectare of coffee was major in monoculture system. The incidence (%) of mining of the coffee (Perileucoptera coffeella Green) was low in the two systems; also, there were no significant differences among both coffee plantation systems. The volume of the forest species was major in the agroforestry systems. According to the evaluation of the land efficiency usage, anyone of the agroforestry systems evaluated is better than the pure cultivations of these species.

With the purpose of getting to know the energy and protein required by the Pekin duck (Anas platyrhinchos) in growth and finishing phases, isoenergetic and isoproteic diets were used, five treatments with four repetitions for the energy and the equal form for the protein. The variables studied were: consumption of food, gain of weight, nutritious conversion and yield to the channel. In the growing phase significant differences in the variable gain of weight and nutritious conversion was registered. It didn’t seize in the food consumption. Although, it was observed that the best consumption of food, gain of weight and nutritious conversion, were achieved, with 3010 kcal EM kg-1 and 22% PB (T3), based on the energy and with 2975 kcal EM kg-1 and 19% PB based on the protein, respectively. In the finishing phase, significant differences among the treatments were not registered, however, based on the energy, the treatment with 2833 kcal EM kg-1 and 18% PB (T2) registered the best answers in the productive variables as well as the diet with 2991 kcal EM kg-1 and 18 PB (T5) based on the protein.

A new simplified mass-transfer model was developed to describe the volatile organic compounds (VOC) emission rates from diffused aeration systems. The model takes into consideration that the VOC mass transfer occurs in two separate mass-transfer zones instead of lumping the overall VOC transfer in the whole aeration tank as is done in the conventional ASCE-based model. A series of batch VOC emission tests were performed in a 1000 l tank equipped with a fine pore diffuser at 0,50 to 1,33 - 10-3 normal m3/s diffused air flow rate and a water temperature of 293 K. The unsteady-state dissolved concentrations of p-xylene, benzene, toluene, trichloroethylene and tetrachlorethylene were measured during the tests and these data were used to find the proportional coefficient Ψ and with it, the volumetric mass-transfer coefficients of the VOCs. It was found that the Ψ coefficients were not dependent upon the diffused air flow rate, but do depend on the nature of the volatile compound used. A semiempirical set of equations that predict successfully the Ψ coefficients based on the critical volume and the normal boiling temperature of the compound was found. It was concluded that the new model provides better insight of the VOC mass transfer process and requires only oxygen aeration performance data, besides the critical volume and the normal boiling point of the compound, to predict accurately the VOC emission rates.

A series of unsteady-state reaeration tests were performed in a 1000 l tank at 1-10-3 normal m3/s diffused-air flow rate and 298,65 K water temperature. Three different types of impurities: soybean oil, surfactant, and diatomaceous earth were doped to simulate the impurities in wastewaters and the effects of the impurities on the oxygen transfer rate were investigated. The ASCE and the new simplified two-zone oxygen mass-transfer models were used to analyze the unsteady-state reaeration data and the volumetric mass-transfer coefficients determined from them were correlated as a function of the impurity concentration. An empirical correlation that predicts successfully the volumetric oxygen-transfer coefficient in an aqueous system with mixed impurities was found. The results showed that the mass-transfer coefficients of the surface aeration zone are more sensitive to the impurity concentration than those of the gas bubble zone.         

A new two zone simplified oxygen mass-transfer model with an analytical solution was proposed and used to analyze the unsteady state reaeration data of diffused reaeration systems in order to find the volumetric mass-transfer coefficients. Series of unsteady state reaeration tests in a 1000 l tank was performed to validate the model. The effect of the air flow rate and the temperature upon the mass-transfer coefficients was studied and empirical equations were used to successfully correlate them. The air flow rate was varied from 0,50 to 1,33 - 10-3 normal m3/s and the water temperature was varied from 293,25 to 303,25 K. It was found that the new model describes mathematically the aeration process very well and gives a better physical understanding of it.          

Esterification of carboxylic acids with alcohols is considered as AAC2 type reaction. The specific rate of esterification of acetic acid with methanol, in mixtures of acetonitrile-methanol showed a quadratic dependence on the alcohol concentration. This second order dependence suggests a general base catalyzed mechanism analogous to the [H2O]2 kinetic dependence observed in the acidcatalyzed hydrolysis of carboxylic esters, in highly aqueous media.   

Fischer esterification of the mixture of palm fatty acids can be achieved in 80% conversion, under conditions of reactive distillation and methanesulphonic acid as catalyst. The volatility of the H2O/alcohol azeotrope by-product confines the kinetic acceleration, relative to batch conditions.