Performance of a reciprocal shaker in mechanical dispersion of soil samples for particle-size analysis

The dispersion of the samples in soil particle-size analysis is a fundamental step, which is commonly achieved with a combination of chemical agents and mechanical agitation. The purpose of this study was to evaluate the efficiency of a low-speed reciprocal shaker for the mechanical dispersion of soil samples of different textural classes. The particle size of 61 soil samples was analyzed in four replications, using the pipette method to determine the clay fraction and sieving to determine coarse, fine and total sand fractions. The silt content was obtained by difference. To evaluate the performance, the results of the reciprocal shaker (RSh) were compared with data of the same soil samples available in reports of the Proficiency testing for Soil Analysis Laboratories of the Agronomic Institute of Campinas (Prolab/IAC). The accuracy was analyzed based on the maximum and minimum values defining the confidence intervals for the particle-size fractions of each soil sample. Graphical indicators were also used for data comparison, based on dispersion and linear adjustment. The descriptive statistics indicated predominantly low variability in more than 90 % of the results for sand, medium-textured and clay samples, and for 68 % of the results for heavy clay samples, indicating satisfactory repeatability of measurements with the RSh. Medium variability was frequently associated with silt, followed by the fine sand fraction. The sensitivity analyses indicated an accuracy of 100 % for the three main separates (total sand, silt and clay), in all 52 samples of the textural classes heavy clay, clay and medium. For the nine sand soil samples, the average accuracy was 85.2 %; highest deviations were observed for the silt fraction. In relation to the linear adjustments, the correlation coefficients of 0.93 (silt) or > 0.93 (total sand and clay), as well as the differences between the angular coefficients and the unit < 0.16, indicated a high correlation between the reference data (Prolab/IAC) and results obtained with the RSh. In conclusion, the mechanical dispersion by the reciprocal shaker of soil samples of different textural classes was satisfactory. The results allowed recommending the use of the equipment at low agitation for particle size- analysis. The advantages of this Brazilian apparatus are its low cost, the possibility to simultaneously analyze a great number of samples using ordinary, easily replaceable glass or plastic bottles.

Studies on hydrogen production by continuous culture system of hydrogen-producing anaerobic bacteria

Characteristics of continuous hydrogen production and fatty acid formation by an active hydrogen-producing anaerobic bacterium, Clostridium butyricum strain SC-E1, was examined under vacuum and non-vacuum culture systems. The continuous cultures were performed using 1040 ml anaerobic glass bottles containing 600 ml of medium including glucose and polypeptone at a concentration of 0.5 or 1.0% as substrate, and were conducted at pH 6.7, hydraulic retention time (HRT) 8h, and 30°C on a reciprocal shaker. The non-vacuum cultures at 16 days of incubation showed 2.0 to 2.3 mol-H2/mol-glucose and 1.4 to 2.0 mol-H2/mol-glucose of hydrogen productivity at 0.5 and 1.0% of substrate concentration, respectively. The vacuum cultures conducted at 0.28 atm gave 1.8 to 2.3 mol-H2/mol-glucose and 1.3 to 2.2 mol-H2/mol-glucose of hydrogen productivity at 0.5 and 1.0% of substrate concentration, respectively. The fatty acid production from the vacuum cultures exhibited approximately the same yield of fatty acids as those of the non-vacuum cultures. It was concluded that the maximal hydrogen production potential by anaerobic bacteria is 1.3 to 2.2 mol-H2/mol-glucose, which is less than 50% of theoretical. In addition, the total hydrogen production rate by a two-stage bioreactor consisting of a 1-litre anaerobic fermenter (HRT 10h) and a 4-litre photobioreactor (HRT 36h) feeding at 2.4-litre of 1.0% glucose per day was estimated at 1.4 to 5.6 mol-H2/mol-glucose, which is 12 to 47% theoretical.