Tratamento de efluentes da indústria de processamento de castanha pela combinação de processos biológicos e químicos
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2012
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As empresas de transformação de castanha geram grandes quantidades de sub-produtos. Estes são essencialmente compostos por águas usadas na lavagem e no processamento do fruto, águas residuais e diferentes tipos de resíduos sólidos.
As águas residuais devem ser geridas de um modo adequado para evitar impactos ambientais negativos: desde a sua separação, passando pelo tratamento adequado e finalmente poderem ser eliminados sem causar danos ao ambiente nem à saúde pública. Para serem lançados em águas superficiais, os efluentes tem de respeitar certos limites paramétricos exigidos legalmente.
Este trabalho teve como objetivos tratar um efluente resultante de uma indústria de transformação de castanha, otimizar alguns aspetos no seu tratamento e avaliar quais os melhores coagulantes/floculantes na ótica dum tratamento complementar biológico/químico. De início o efluente foi submetido a um tratamento biológico aeróbio. Numa segunda etapa o efluente foi submetido a um tratamento químico complementar de coagulação/floculação.
Durante o tratamento biológico, o efluente, foi sujeito a diversos ensaios de biodegradabilidade aeróbia. Estes ensaios basearam-se na utilização de reatores descontínuos aeróbios aos quais foram adicionadas diferentes quantidades pré determinadas de lamas ativadas, e um determinado volume de efluente previamente estabelecido. Nesta etapa avaliou-se a atuação das lamas ativadas na redução da carga poluente do efluente em estudo.
Posteriormente, foi efetuado um tratamento complementar químico por coagulação/floculação em sistema jar-test. Foi feita a avaliação de diferentes coagulantes/floculantes nomeadamente hidróxido de cálcio, sulfato de alumínio, sulfato ferroso e cloreto férrico. Para cada coagulante químico foi avaliado o efeito do pH do meio e otimizando-se a sua dosagem para melhor valor pH obtido. Para cada processo (biológico/químico) foi efetuada a determinação de vários parâmetros nomeadamente CQO solúvel (CQOs), turvação, sólidos suspensos totais, sólidos suspensos voláteis, polifenóis totais, pH e aromaticidade.
Na primeira etapa do trabalho experimental, etapa em que se recorreu a ensaios de biodegradabilidade aeróbia, verificou-se que em ensaios de 48 horas, a percentagem de remoção de CQOs foi em média de 76,5%. Nestes ensaios verificou-se que com o passar do tempo de arejamento, os parâmetros em estudo diminuíram. No entanto de forma geral, esta diminuição foi mais notória nas primeiras 24 horas de arejamento, após o que já não é tão significativa.
Quanto ao tratamento biológico, as condições mais eficientes para a remoção de CQO obtiveram-se para a combinação X2S2,5; corresponde a 2 g/L de biomassa inicial e 2,5 g/L de carga poluente inicial.
Numa segunda etapa do trabalho experimental, usaram-se ensaios de coagulação/floculação química após o tratamento biológico. De todos os coagulantes em estudo selecionou-se o sulfato de alumínio como o coagulante mais eficiente para um pH inicial de 7,0.
Com a otimização das dosagens do sulfato de alumínio a pH=7,0 verificou-se que a concentração de coagulante que se mostrou mais eficiente na redução dos parâmetros em estudo corresponde a uma dosagem de 6,0 g/L. Para este valor obteve-se uma redução dos seguintes parâmetros: CQOs redução de 86,7%, SST de 96,0%, SSV de 97,3%, turvação de 86,9%, polifenóis totais de 77,6% e aromaticidade de 82,5%.
De acordo com os resultados obtidos, conclui-se que a estratégia que se revelou mais acertada para o tratamento de efluente da indústria de processamento de castanha será a combinação de processos biológicos aeróbios com processos de coagulação/floculação química. No entanto, este efluente ainda não se encontra de acordo com a legislação para descarga em águas superficiais, necessitando de sofrer um tratamento de acabamento numa ETAR municipal ou outra.
The chestnut processing companies generate large quantities of by-products. These are essentially composed by water used for washing and processing of fruit, wastewater and different types of solid waste. Wastewater must be managed in an appropriate way to avoid negative environmental impacts, since their separation, through appropriate treatment and finally can be eliminated without harming the environment or public health. To be released into surface waters, the effluent must meet certain limits parametric legally required. This study aimed to treat a wastewater resulting from a chestnut processing industry, to optimize their treatment and to evaluate what the best coagulants / flocculants in view of a complementary biological/chemical treatment. Initially the effluent was subjected to an aerobic biological treatment. In a second stage the effluent is subjected to a supplementary treatment chemical coagulation/ flocculation. During the biological treatment, the effluent was subjected to various aerobic biodegradation conditions. These tests were based on the use of batch aerobic reactor to which were added various quantities of predetermined activated sludge, and a specific predetermined volume of effluent. In this step we evaluated the performance of activated sludge in reducing the pollution load of the effluent under study. A complementary treatment was made later by chemical coagulation/ flocculation jar-test-system. This treatment was performed to evaluate different coagulants/ flocculants, in particular, calcium hydroxide, aluminum sulphate, ferrous sulphate and ferric chloride. For each chemical coagulant was evaluated the effect of pH and was optimize the dosage for better pH obtained. Each process (biological and chemical) was monitored by determination of various parameters including COD, turbidity, total suspended solids, volatile suspended solids, total polyphenols, pH and aromaticity. In the first step of the experimental work, aerobic biodegradation tests, it was found that in assays of 48 hours, the percentage removal of COD averaged 76.5%. In these trials it was found that over time of airing, the parameters under study decreased. However in general, this was more noticeable in the first 24 hours of aeration, after which it is not so significant. In the biological treatment, the more efficient conditions for removal of COD was obtained for the combination X2S2,5 and corresponds to 2 g/L initial biomass and 2.5 g/L initial pollution load. A second step of the experimental work, use coagulation/ flocculation chemicals tests after the biological treatment. In these coagulants studies was selected aluminum sulfate as the most efficient coagulant to an initial pH of 7.0. By optimizing the dosages of aluminum sulfate to pH = 7.0 was found that the concentration of coagulant is more efficient in reducing the parameters under study is a dosage corresponds to 6.0 g/L. For this value was obtained a reduction of the following parameters: COD reduction of 86.7%, TSS of 96.0%, 97.3% of VSS, turbidity of 86.9%, 77.6% of total polyphenols and aromatic of 82.5%. According to the results obtained, the strategy that has proved most correct for the treatment of effluent from chestnut processing industry is the combination of biological aerobic processes with chemical coagulation/flocculation. However, this effluent is not yet in accordance with the rules for discharge into surface waters, need to undergo a finishing treatment in a municipal or other wastewater treatment plant.
The chestnut processing companies generate large quantities of by-products. These are essentially composed by water used for washing and processing of fruit, wastewater and different types of solid waste. Wastewater must be managed in an appropriate way to avoid negative environmental impacts, since their separation, through appropriate treatment and finally can be eliminated without harming the environment or public health. To be released into surface waters, the effluent must meet certain limits parametric legally required. This study aimed to treat a wastewater resulting from a chestnut processing industry, to optimize their treatment and to evaluate what the best coagulants / flocculants in view of a complementary biological/chemical treatment. Initially the effluent was subjected to an aerobic biological treatment. In a second stage the effluent is subjected to a supplementary treatment chemical coagulation/ flocculation. During the biological treatment, the effluent was subjected to various aerobic biodegradation conditions. These tests were based on the use of batch aerobic reactor to which were added various quantities of predetermined activated sludge, and a specific predetermined volume of effluent. In this step we evaluated the performance of activated sludge in reducing the pollution load of the effluent under study. A complementary treatment was made later by chemical coagulation/ flocculation jar-test-system. This treatment was performed to evaluate different coagulants/ flocculants, in particular, calcium hydroxide, aluminum sulphate, ferrous sulphate and ferric chloride. For each chemical coagulant was evaluated the effect of pH and was optimize the dosage for better pH obtained. Each process (biological and chemical) was monitored by determination of various parameters including COD, turbidity, total suspended solids, volatile suspended solids, total polyphenols, pH and aromaticity. In the first step of the experimental work, aerobic biodegradation tests, it was found that in assays of 48 hours, the percentage removal of COD averaged 76.5%. In these trials it was found that over time of airing, the parameters under study decreased. However in general, this was more noticeable in the first 24 hours of aeration, after which it is not so significant. In the biological treatment, the more efficient conditions for removal of COD was obtained for the combination X2S2,5 and corresponds to 2 g/L initial biomass and 2.5 g/L initial pollution load. A second step of the experimental work, use coagulation/ flocculation chemicals tests after the biological treatment. In these coagulants studies was selected aluminum sulfate as the most efficient coagulant to an initial pH of 7.0. By optimizing the dosages of aluminum sulfate to pH = 7.0 was found that the concentration of coagulant is more efficient in reducing the parameters under study is a dosage corresponds to 6.0 g/L. For this value was obtained a reduction of the following parameters: COD reduction of 86.7%, TSS of 96.0%, 97.3% of VSS, turbidity of 86.9%, 77.6% of total polyphenols and aromatic of 82.5%. According to the results obtained, the strategy that has proved most correct for the treatment of effluent from chestnut processing industry is the combination of biological aerobic processes with chemical coagulation/flocculation. However, this effluent is not yet in accordance with the rules for discharge into surface waters, need to undergo a finishing treatment in a municipal or other wastewater treatment plant.
Descrição
Dissertação de Mestrado em Segurança Alimentar
Palavras-chave
Águas residuais , Tratamento químico , Transformação de castanha , Tratamento biológico aeróbio , Coagulação/floculação , CQO , Sulfato de alumínio