Efeito da adição de borras de café sobre a compostagem de resíduos de Acacia dealbata L. (mimosa)
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2014-01-24
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A utilização de borras de café e de resíduos de Acacia dealbata L. em compostagem para agricultura em modo de produção biológico pode ser uma solução para reduzir o impacte no meio ambiente e permitir a valorização agronómica destes materiais. No sentido de se estudar a incorporação de borras de café em compostados, efetuou-se um ensaio no qual se testaram quatro tratamentos com diferentes teores de borras de café com, tratamentos C0 (Testemunha), C10, C20 e C40, contendo respetivamente 0, 10, 20 e 40 % de borras no peso seco da mistura (10 kg) efetuada com resíduos de Acacia dealbata L. e palha de trigo. O ensaio foi conduzido com 3 repetições utilizando compostores termicamente isolados com capacidade de 135L e arejamento forçado. Ao longo do ensaio foi monitorizada a evolução da temperatura e foram determinadas as emissões de dióxido de carbono (CO2), metano (CH4) e óxido nitroso (N2O) e, nos dias 0, 3, 9, 22, 41, 64, 105 e 156, foram avaliadas as principais características físico-químicas dos compostados (humidade, pH, condutividade elétrica, relação C/N e teores de N mineral). Nas amostras iniciais e finais foi igualmente medida a concentração de compostos fenólicos e de taninos. Foi ainda determinada a fitotoxicidade dos compostados finais através da condução de um teste de germinação de sementes de alface, sorgo e Acacia dealbata L. com diluições de 0, 10, 20, 30 e 40% dos diferentes compostados.
A utilização de diferentes concentrações de borras de café nas misturas mostrou efeitos significativos sobre vários dos parâmetros avaliados. Os resultados obtidos sugerem que o valor de pH inicialmente ligeiramente ácido (pH <6) das misturas não impediu a obtenção do máximo de temperaturas ao 3ºdia (57,6 ± 0,1 °C). Nos tratamentos C20 e C40 foram observadas temperaturas altas durante um maior período de tempo. Os tratamentos C20 e C40 revelaram uma maior emissão acumulada de CO2 (181,3 e 148,7 g C-CO2 kg-1 MS inicial, respetivamente) e N2O (177,8 e 162,8 mg N-N2O kg-1 MS inicial) do que os tratamentos C0 e C10 (124,6 e 137,3 g C-CO2 kg-1 MS inicial e 160,3 e 151,2 mg N-N2O kg-1 MS inicial), tendo a análise de emissão de CH4 revelado que apenas existiram condições de emissão (anaerobiose) nos 3 primeiros dias, possivelmente devido ao grande consumo de O2 por parte dos microrganismos. Não foi observada a presença de N-NO3- no final do processo de compostagem, contudo os valores de carbono orgânico solúvel (COS) e azoto orgânico solúvel (AOS) mostraram aumentos consideráveis com o aumento dos teores de café presentes. Os compostados apresentaram na generalidade teores de matéria orgânica elevados, compreendidos entre 917,2±1,5 e 929,5±0,3 g kg-1 de MS e valores de condutividade elétrica (CE) baixos (entre 0, 78 e 1,62 dS m-1). As reduções da razão C/N variaram entre 18,7 - 22,2 no início do processo de compostagem para 8,6 - 12,1 no final. Nos ensaios de germinação efetuados observaram-se efeitos de toxicidade sobre a germinação de sementes de Lactuca sativa L. no tratamento C10, possivelmente devido á presença de taninos, contudo não foram observados efeitos sobre a germinação de Sorghum Sudanense L.
A utilização de borras de café permitiu de uma forma geral obter compostados com qualidade agronómica mais elevada na maioria dos parâmetros em estudo.
The use of coffee dregs and Acacia dealbata L. wastes in composting for organic farming production mode may be a viable solution to reduce the impact on the environment and to allow the agronomic valorization of these materials. In order to study the effect of incorporation of coffee dregs on the composting process progress and end-product quality characteristics, four treatments with different amounts of coffee dregs were established: C0 (Control), C10, C20 and C40, containing respectively 0, 10, 20 and 40% of coffee dregs in relation to the dry weight (10 kg). The mixtures were completed with Acacia dealbata L. wastes and wheat straw. Three repetitions were made and thermally insulated composters with 135L capacity and forced aeration were used. Throughout the trial the evolution of the temperature was monitored and the emission of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) was measured. At days 0, 3, 9, 22, 41, 64, 105 and 156, physicochemical key-characteristics of composts (moisture, pH, electrical conductivity, C / N, mineral N content) were evaluated. The concentrations of phenolic compounds and tannins were measured in the initial and final sampling days. Further it was determined the phytotoxicity of the final composts by conducting germination seed tests of Lactuca sativa L. (lettuce), Sorghum sudanense L. (sorghum) and Acacia dealbata L. using dilutions of 0, 10, 20, 30 and 40% of the different composts obtained. Different coffee dreg concentrations showed significant effects on several parameters assessed. The results suggest that the initial slightly acidic pH value (pH <6) of the mixtures did not prevent the attainment of maximum temperatures on day 3 (57.6 ± 0.1 ° C). In treatments C20 and C40 it was observed high temperatures over a longer period of time. C20 and C40 treatments showed greater cumulative CO2 emission (181.3 and 148.7 g CO2-C kg-1 MS initial, respectively) and N2O (177.8 and 162.8 mg N2O-N kg-1 MS initial) than treatments C0 and C10 (124.6 and 137.3 g CO2-C kg-1 MS initial and 160.3 and 151.2 mg N2O-N kg-1 MS initial) and CH4 emissions results revealed that there were only emission conditions (anaerobic) over the first 3 days, possibly due to O2 consumption by the microorganisms. No presence of NO3--N at the end of the composting process was observed. However the amounts of soluble organic carbon (COS) and soluble organic nitrogen (AOS) showed considerable increases when increasing the amount of coffee. The composts showed generally high levels of organic matter, comprised from 917.2 ± 1.5 to 929.5 ± 0.3 g kg-1 of dry matter and low values of electrical conductivity (EC) (between 0.78 and 1.62 dS m-1). The C/N ratio varied from 18.7 to 22.2 at the beginning of the composting process to 8.6 to 12.1 at the end. In the germination tests performed there were observed toxic effects on the germination of lettuce (C10 treatment), possibly due to the presence of tannins, but no effects were observed on the germination of sorghum. In general, the use of coffee dregs allowed obtaining composts with high quality relatively to most of the studied parameters.
The use of coffee dregs and Acacia dealbata L. wastes in composting for organic farming production mode may be a viable solution to reduce the impact on the environment and to allow the agronomic valorization of these materials. In order to study the effect of incorporation of coffee dregs on the composting process progress and end-product quality characteristics, four treatments with different amounts of coffee dregs were established: C0 (Control), C10, C20 and C40, containing respectively 0, 10, 20 and 40% of coffee dregs in relation to the dry weight (10 kg). The mixtures were completed with Acacia dealbata L. wastes and wheat straw. Three repetitions were made and thermally insulated composters with 135L capacity and forced aeration were used. Throughout the trial the evolution of the temperature was monitored and the emission of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) was measured. At days 0, 3, 9, 22, 41, 64, 105 and 156, physicochemical key-characteristics of composts (moisture, pH, electrical conductivity, C / N, mineral N content) were evaluated. The concentrations of phenolic compounds and tannins were measured in the initial and final sampling days. Further it was determined the phytotoxicity of the final composts by conducting germination seed tests of Lactuca sativa L. (lettuce), Sorghum sudanense L. (sorghum) and Acacia dealbata L. using dilutions of 0, 10, 20, 30 and 40% of the different composts obtained. Different coffee dreg concentrations showed significant effects on several parameters assessed. The results suggest that the initial slightly acidic pH value (pH <6) of the mixtures did not prevent the attainment of maximum temperatures on day 3 (57.6 ± 0.1 ° C). In treatments C20 and C40 it was observed high temperatures over a longer period of time. C20 and C40 treatments showed greater cumulative CO2 emission (181.3 and 148.7 g CO2-C kg-1 MS initial, respectively) and N2O (177.8 and 162.8 mg N2O-N kg-1 MS initial) than treatments C0 and C10 (124.6 and 137.3 g CO2-C kg-1 MS initial and 160.3 and 151.2 mg N2O-N kg-1 MS initial) and CH4 emissions results revealed that there were only emission conditions (anaerobic) over the first 3 days, possibly due to O2 consumption by the microorganisms. No presence of NO3--N at the end of the composting process was observed. However the amounts of soluble organic carbon (COS) and soluble organic nitrogen (AOS) showed considerable increases when increasing the amount of coffee. The composts showed generally high levels of organic matter, comprised from 917.2 ± 1.5 to 929.5 ± 0.3 g kg-1 of dry matter and low values of electrical conductivity (EC) (between 0.78 and 1.62 dS m-1). The C/N ratio varied from 18.7 to 22.2 at the beginning of the composting process to 8.6 to 12.1 at the end. In the germination tests performed there were observed toxic effects on the germination of lettuce (C10 treatment), possibly due to the presence of tannins, but no effects were observed on the germination of sorghum. In general, the use of coffee dregs allowed obtaining composts with high quality relatively to most of the studied parameters.
Descrição
Dissertação de Mestrado em Engenharia Agronómica
Palavras-chave
Compostagem , Acacia dealbata (mimosa) , Germinação , Gases com efeito de estufa , Borras de café