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Viabilidade da utilização de leitos de macrófitas no tratamento das águas residuais do cozimento da cortiça
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A presente investigação foi realizada no âmbito do projeto PRIMA/0010/2021 destinado, na componente nacional, a investigar a viabilidade da utilização de leitos de macrófitas com configuração vertical na depuração dos efluentes produzidos pela indústria corticeira na etapa inicial destinada à purificação da matéria-prima concretizada através da imersão das pranchas de cortiça em água quente durante 1 a 1,5 horas. Para obter a eliminação completa dos contaminantes da cortiça, nomeadamente de compostos fenólicos (ácido gálico, ácido vanílico, ácido siríngico, taninos, etc.), e salvaguardar que a principal e mais valiosa produção (i.e., diversos tipos de rolhas), estão isentas de compostos cuja migração para o vinho pode determinar a sua degradação organolética, a reutilização da água é limitada. Consequentemente, o consumo específico de água é elevado (400-1200 L/ton de cortiça) e o efluente apresenta intensa coloração castanho-escuro, elevada carga orgânica (CQO entre 1382 e 4290 mg/L) e reduzida biodegradabilidade (CBO5/CQO entre 0,19 e 0,38).
As características desta água residual determinam que a viabilidade dos tratamentos biológicos convencionais seja muito limitada, prevalecendo a opção por tratamentos físico-químicos, nomeadamente processos de coagulação/floculação, os quais não promovem a efetiva redução da carga poluente, mas somente a sua concentração numa lama química, cujo processamento e destino final são cada vez mais dispendiosos. Os leitos de macrófitas são sistemas de tratamento que pretendem maximizar os processos físicos (filtragem, sedimentação), químicos (adsorção, precipitação, troca iónica) e biológicos (biodegradação, absorção pela planta, decomposição bacteriana) típicos das zonas húmidas naturais.
Duas unidades a escala piloto foram preparadas, uma contendo apenas Leca como enchimento e outra contendo Leca e uma camada intermediária de biocarvão. A distinta constituição das unidades permitiu efetuar a avaliação da influência do enchimento na remoção dos poluentes presentes no efluente do cozimento da cortiça. Os leitos foram plantados com Phragmites australis e o desempenho avaliado em termos de remoção de CQO, CBO5, CBO20, Fenóis totais, Cor, Azoto e Fósforo para operação com tempo de residência de 3 dias e tempo de retenção hidráulica de aproximadamente 7 dias, estes sistemas foram testados em 3 distintas etapas onde variou-se a carga orgânica alimentada. Nas 3 etapas os leitos foram alimentados com cargas médias de (50,8; 79,3 e 135,7) g CQO/m2.d; (10,9; 22,6 e 28,7) g CBO5/m2.d; (13,9; 27,0 e 32,3) g CBO20/m2.d e (3,8; 4,7 e 5,0) g FT/m2.d e obteve-se remoções de (56,1; 76,4 e 64,3)% de CQO; (56,3; 92,9 e 73,6)% de CBO5; (75,6; 90,8 e 78,0) % de CBO20 e (72,4; 62,8 e 62,8) % de FT para o leito #1 e (57,7; 88,9 e 64,8) % de CQO; (59,2; 94,0 e 76,5) % de CBO5; (69,6; 93,9 e 74,8) % de CBO20 e (84,1; 87,5 e 80,3) % de FT para o leito #2. O desempenho dos leitos de macrófitas na configuração vertical foi superior ao anteriormente obtido pela configuração horizontal apesar das cargas orgânicas serem mais elevadas. A adição de biocarvão determinou uma vantagem estatisticamente significativa na remoção de fenóis totais e da cor. No entanto, a coloração do efluente tratado por ambos os leitos, apresentou sempre coloração visível e características incompatíveis com os requisitos legais de descarga.
This research was carried out as part of the national PRIMA/010/2021 project to investigate the feasibility of using vertically configured macrophyte beds to purify the effluents produced by the cork industry in the initial stage of purifying the raw material by immersing the cork planks in hot water for 1 to 1.5 hours. In order to achieve the complete elimination of cork contaminants, namely phenolic compounds (gallic acid, vanillic acid, syringic acid, tannins, etc.), and to ensure that the main and most valuable production (i.e. various types of cork stoppers) are free of compounds whose migration into the wine can lead to its organoleptic degradation, the reuse of water is limited. Consequently, specific water consumption is high (400-1200 L/ton of cork) and the effluent has an intense dark brown color, a high organic load (COD between 1382 and 4290 mg/L) and low biodegradability (BOD5/COD between 0.19 and 0.38). The characteristics of this wastewater mean that the viability of conventional biological treatments is very limited, leading to the option of physical-chemical treatments, namely coagulation/flocculation processes, which do not promote the effective reduction of the pollutant load, but only its concentration in a chemical sludge, the processing and final destination of which is increasingly expensive. Macrophyte beds are treatment systems that aim to maximize the physical (filtration, sedimentation), chemical (adsorption, precipitation, ion exchange) and biological (biodegradation, plant absorption, bacterial decomposition) processes typical of wetlands. Two pilot-scale units were prepared, one containing only Leca as a filler and the other containing Leca and an intermediate layer of biochar. The different constitution of the units made it possible to evaluate the influence of the filler on the removal of pollutants present in the cork cooking effluent. The beds were planted with Phragmites australis and the performance evaluated in terms of COD, BOD5, BOD20, total phenols, color, nitrogen and phosphorus removal for operation with a residence time of 3 days and a hydraulic retention time of approximately 7 days. These systems were tested in 3 different stages where the organic load fed was varied. In the 3 stages the beds were fed with average loads of (56.1; 76.4 and 135.7) g COD/m2.d; (10.9; 22.6 and 28.7) g BOD5/m2.d; (13.9; 27.0 and 32.3) g BOD20/m2.d and (3.8; 4.7 and 5.0) g FT/m2. d and obtained removals of (50.8; 79.3 and 64.3) % COD; (56.3; 92.9 and 73.6) % BOD5; (75.6; 90.8 and 78.0) % BOD20 and (72.4; 62.8 and 62.8) % FT for bed #1 and (57.7; 88.9 and 64.8) % COD; (59.2; 94.0 and 76.5) % BOD5; (69.6; 93.9 and 74.8) % BOD20 and (84.1; 87.5 and 80.3) % FT for bed #2. The performance of the macrophyte beds in the vertical configuration was superior to that obtained in the horizontal configuration, despite the higher organic loads. The addition of biochar gave a statistically significant advantage in the removal of total phenols and color. However, the color of the effluent treated by both beds was always visible and had characteristics incompatible with the legal discharge requirements.
This research was carried out as part of the national PRIMA/010/2021 project to investigate the feasibility of using vertically configured macrophyte beds to purify the effluents produced by the cork industry in the initial stage of purifying the raw material by immersing the cork planks in hot water for 1 to 1.5 hours. In order to achieve the complete elimination of cork contaminants, namely phenolic compounds (gallic acid, vanillic acid, syringic acid, tannins, etc.), and to ensure that the main and most valuable production (i.e. various types of cork stoppers) are free of compounds whose migration into the wine can lead to its organoleptic degradation, the reuse of water is limited. Consequently, specific water consumption is high (400-1200 L/ton of cork) and the effluent has an intense dark brown color, a high organic load (COD between 1382 and 4290 mg/L) and low biodegradability (BOD5/COD between 0.19 and 0.38). The characteristics of this wastewater mean that the viability of conventional biological treatments is very limited, leading to the option of physical-chemical treatments, namely coagulation/flocculation processes, which do not promote the effective reduction of the pollutant load, but only its concentration in a chemical sludge, the processing and final destination of which is increasingly expensive. Macrophyte beds are treatment systems that aim to maximize the physical (filtration, sedimentation), chemical (adsorption, precipitation, ion exchange) and biological (biodegradation, plant absorption, bacterial decomposition) processes typical of wetlands. Two pilot-scale units were prepared, one containing only Leca as a filler and the other containing Leca and an intermediate layer of biochar. The different constitution of the units made it possible to evaluate the influence of the filler on the removal of pollutants present in the cork cooking effluent. The beds were planted with Phragmites australis and the performance evaluated in terms of COD, BOD5, BOD20, total phenols, color, nitrogen and phosphorus removal for operation with a residence time of 3 days and a hydraulic retention time of approximately 7 days. These systems were tested in 3 different stages where the organic load fed was varied. In the 3 stages the beds were fed with average loads of (56.1; 76.4 and 135.7) g COD/m2.d; (10.9; 22.6 and 28.7) g BOD5/m2.d; (13.9; 27.0 and 32.3) g BOD20/m2.d and (3.8; 4.7 and 5.0) g FT/m2. d and obtained removals of (50.8; 79.3 and 64.3) % COD; (56.3; 92.9 and 73.6) % BOD5; (75.6; 90.8 and 78.0) % BOD20 and (72.4; 62.8 and 62.8) % FT for bed #1 and (57.7; 88.9 and 64.8) % COD; (59.2; 94.0 and 76.5) % BOD5; (69.6; 93.9 and 74.8) % BOD20 and (84.1; 87.5 and 80.3) % FT for bed #2. The performance of the macrophyte beds in the vertical configuration was superior to that obtained in the horizontal configuration, despite the higher organic loads. The addition of biochar gave a statistically significant advantage in the removal of total phenols and color. However, the color of the effluent treated by both beds was always visible and had characteristics incompatible with the legal discharge requirements.
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Keywords
Cortiça Efluente do Cozimento da Cortiça Biodegradabilidade Zonas Húmidas Construídas Cork Cork Boiling Wastewater Biodegradability Constructed Wetlands