Proposta de metodologia para determinação da atividade hidrogênica específica


IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia




Hydrogen production by fermentation process is influenced by the concentration and characteristics of organic substrate, the effluent pH value and biomass concentration. The determination of specific hydrogenic activity of organic substrates and biomass can be a tool to analyze the hydrogen volume produced during the fermentation, the volatile fatty acids production, the degree of acidification and evaluated compounds toxicity to the hydrogen producing microorganisms. To determine the ideal conditions for the measurement of specific hydrogen activity were realized batch tests using glucose as source of organic matter at concentrations of 1,000, 2,000, 4,000, 8,000, 12,000, 16,000 and 20,000mg.COD.L-1. The pH values tested were 5.0, 5.5, 6.0 and 6.5 and the biomass concentration of 1,250, 2,500, 5,000 and 7,500mgTVS.L-1. The higher hydrogen activity was 483mLH2.gTVS-1.h-1 for the organic matter concentration of 12,000mg.L-1, pH value of 6.0 and biomass concentration of 2,500mgTVS.L-1. The higher hydrogen volume produced was 38mL.gCOD-1 in the initial organic matter concentration of 16,000mg.L-1, at pH value 5.5 and sludge concentration of 5,000mgTVS.L-1. Volatile fatty acids analysis indicated that the highest percentage of acetic acid and propionic acid were obtained when the pH tested was 6.5, at biomass concentration of 7,500mgTVS.L-1. In other studied conditions, the butyric acid was the predominant volatile fatty acids in the effluent. The degree of acidification value was probably affected by organic matter from sludge, resulting in values above 1.0. Tests measuring the specific hydrogen activity were performed with different organic substrates (propionic acid, butyric acid, proteic effluent, glycerol and fungicide production effluent) permitted to evaluate the applicability of the activity test and the potential that organic substrates have to produce hydrogen. Using the organic matter concentrations presented above, initial pH value equal to 6.0 and biomass concentration of 2,500mgTVS.L-1. The higher hydrogen activity and hydrogen volume produced were obtained for the proteic effluent, 6.8mLH2.gTVS-1.h-1 and 1,74mL.gCOD-1, respectively. The volatile fatty acid found in highest percentage after fermentation of organic substrates was acetic acid. A high degree of acidification was observed on tests with butyric acid due the high residual concentration in the effluent. The influence of pH control on hydrogen producing microorganisms was evaluated in tests with and without pH control, using glucose as organic matter source at concentration of 12,000mg.COD.L-1, the pH values tested was 5.0, 5.5 and 6.0 and the biomass concentration was 2,500mgTVS.L-1. The results indicated that the higher hydrogen percentages, volatile fatty acid production, degree of acidification and organic matter removal occurred when the pH was not controlled; indicating that an initial adjustment in the pH was needed, but the control may affect the process performance. Additional studies about the optimization of hydrogen production from raw swine waste using two batch anaerobic reactors, one acidogenic reactor and other methanogenic reactor were performed. The influence of sludge age and the pH and temperature effects on acidogenic phase were analyzed. In acidogenic reactor were tested the sludge ages of 1.4, 1.7 and 2.5 days, pH values of 5.0 and 6.0 and temperatures: ambient (15 to 25°C), 35°C and 55°C .The higher hydrogen concentration in the biogas was 21.3% for the sludge age of 1.4 days, initial pH equal to 5.0 and temperature 35 °C. In this condition there was an increase in volatile fatty acids concentration in the acidogenic reactor effluent, indicating the occurrence of complex substances hydrolysis and consequently the increase in hydrogen concentration.


reatores dejetos suinos lodo Ácidos graxos biogás hidrogênio : produção

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