Aproveitamento do lodo de ETA: biodegradabilidade e implicações ecotoxicológicas
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2023-03-02
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Universidade Estadual Paulista (Unesp)
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Devido às atividades antrópicas, a qualidade das águas dos mananciais está cada vez mais comprometida. Então, antes da água ser distribuída aos seus consumidores, ela precisa passar por um processo de tratamento que visa eliminar as impurezas que podem oferecer risco à saúde pública. Durante esse tratamento, é gerado um resíduo (lodo de ETA), resultado das etapas de coagulação e filtração. Geralmente, este resíduo é constituído de microrganismos, algas, materiais suspensos, matéria orgânica, compostos orgânicos, minerais e, também, alta concentração de ferro ou alumínio, por causa do coagulante utilizado na etapa de coagulação. Como o lodo é produzido em larga escala, pois está relacionado com a demanda de água potável, há uma preocupação em encontrar um descarte adequado, ou seja, que não ofereça risco de contaminação ambiental, à saúde humana e que seja economicamente viável. Dentro das diversas possibilidades para seu aproveitamento, a disposição em solos agrícolas é bastante promissora e sustentável. Entretanto, esse resíduo pode conter contaminantes orgânicos, metais pesados e microrganismos de caráter patogênico, o que tornaria sua disposição em solo inviável. A deposição inapropriada desse resíduo oferece alto risco ambiental, então, este trabalho teve como objetivo propor uma metodologia de baixo custo, empregando outros resíduos, de origem agroindustrial (bagaço de cana-de-açúcar e fibra de coco), como agentes descompactantes e estimulantes para biodegradar os possíveis compostos tóxicos existentes no lodo e biotransformá-lo em um insumo agrícola. Adicionalmente, também foram avaliados os efeitos ecotoxicológicos sobre organismos de diferentes níveis tróficos. Foi realizada a caracterização físico-química e a patogenicidade do lodo, avaliando a presença de coliformes totais, Escherichia coli e ovos de Ascaris ssp.. As amostras foram misturadas em solo, utilizando duas concentrações de lodo (10% e 15%), com e sem incorporação de bagaço de cana-de-açúcar e fibra de coco. O ensaio de respirometira foi aplicado para verificar a biodegradabilidade do lodo de ETA, quantificando a produção de CO2 das diferentes amostras, durante 120 dias. As amostras, antes e após a biodegradação, foram avaliadas quanto ao seu potencial fitotóxico (sementes de Lactuca sativa e Eruca sativa), toxicidade aguda (Daphnia similis e Folsomia candida) e teste de reprodução (F. candida). Quanto ao resultado da patogenicidade, o lodo de ETA, antes do processo de biodegradação, apresentou ausência de E. coli e ovo de Ascaris ssp., e número muito baixo de colônias de coliformes totais. Dentre as características físico químicas, o lodo apresentou pH próximo da neutralidade e baixa concentração de metais, porém continha excesso de líquidos livres, o que tornou indispensável o processo de secagem. A utilização dos resíduos agroindustriais, otimizou a produção de CO2, no entanto não contribuiu para a biodegradação do lodo de ETA. No teste de fitotoxicidade, as amostras que continham lodo associado com o bagaço de cana-de-açúcar apresentaram toxicidade moderada a alta, havendo inibição de germinação e diminuição do crescimento da radícula e do hipocótilo. Resultados semelhantes foram observados para D. similis, indicando que o bagaço liberou compostos tóxicos hidrossolúveis. No entanto, após a biodegradação, nenhum efeito tóxico foi observado demonstrando que o processo de biotransformação empregado levou à detoxificação das amostras. No teste com F. candida, não houve letalidade significativa, porém as amostras que continham lodo na concentração de 10% interferiram negativamente na reprodução desses organismos. Assim, o lodo estudado apresenta características físico-químicas interessantes para utilização como condicionantes e fertilizantes de solos agrícolas, entretanto, pela toxicidade observada, é indispensável a realização de um processo de biodegradação/bioestimulação para promover a eliminação desse efeito e, desse modo, garantir a segurança ambiental, proporcionando um destino sustentável.
Due to anthropic activities, the quality of water is increasingly compromised. So, before the water is distributed to its consumers, the raw water needs to undergo a treatment process that aims to eliminate impurities that may pose a risk to public health. During this treatment, a residue (WTP sludge) is generated, resulting from the coagulation and filtration steps. Generally, this residue consists of microorganisms, algae, suspended materials, organic matter, organic compounds, minerals, and also a high concentration of iron or aluminum, due to the coagulant used in the coagulation stage. As sludge is produced on a large scale, as it is related to the demand for drinking water, there is a concern to find an adequate disposal, to avoid posing a risk of environmental contamination and damage to human health, besides being economically viable. Within the various possibilities for its use, disposal in agricultural soils is very promising and sustainable. However, this residue may contain organic contaminants, heavy metals, and pathogenic microorganisms that would make its disposal in soil unfeasible. The inappropriate disposal of this residue poses a high environmental risk, so this work aimed to propose a low-cost methodology, using other residues, of agro-industrial origin (sugar cane bagasse and coconut fiber), as decompacting and stimulants agents to biodegrade the possible toxic compounds existing in the sludge and biotransform it into an agricultural input. Additionally, the ecotoxicological effects on organisms of different trophic levels were also evaluated. The physical-chemical characterization and the pathogenicity of the sludge were carried out, assessing the presence of total coliforms, Escherichia coli, and Ascaris ssp. eggs. The samples were mixed in the soil, using two concentrations of sludge (10% and 15%), with and without the incorporation of sugarcane bagasse and coconut fiber. The respirometer test was applied to verify the biodegradability of the WTP sludge, quantifying the CO2 production of the different samples, for 120 days. The samples, before and after biodegradation, were evaluated for their phytotoxic potential (Lactuca sativa and Eruca sativa seeds), acute toxicity (Daphnia similis and Folsomia candida), and reproduction test (F. candida). As for the result of pathogenicity, the WTP sludge showed the absence of Ascaris ssp. and E. coli, and very low numbers of total coliform colonies. Among the physical-chemical characteristics, the sludge showed a pH close to neutrality and a low concentration of metals, but it contained excess free liquids, which made the drying process indispensable. The use of agro-industrial residues optimized the production of CO2, however, it did not contribute to the biodegradation of the WTP sludge. In the phytotoxicity test, the samples that contained sludge associated with sugarcane bagasse showed moderate to high toxicity, with germination inhibition and reduction of radicle and hypocotyl growth. Similar results were observed for D. similis, indicating that the bagasse released water-soluble toxic compounds. However, after biodegradation, no toxic effect was observed, demonstrating that the biotransformation process employed led to detoxification of the samples. In the test with F. candida, there was no significant lethality, but the samples that contained sludge at a concentration of 10% negatively interfered with the reproduction of these organisms. Thus, the sludge studied presented interesting physicochemical characteristics for use as conditioners and fertilizers for agricultural soils. However, due to the observed toxicity, it is essential to carry out a biodegradation/biostimulation process to promote the elimination of this effect and, thus, guarantee environmental security, providing a more sustainable destination.
Due to anthropic activities, the quality of water is increasingly compromised. So, before the water is distributed to its consumers, the raw water needs to undergo a treatment process that aims to eliminate impurities that may pose a risk to public health. During this treatment, a residue (WTP sludge) is generated, resulting from the coagulation and filtration steps. Generally, this residue consists of microorganisms, algae, suspended materials, organic matter, organic compounds, minerals, and also a high concentration of iron or aluminum, due to the coagulant used in the coagulation stage. As sludge is produced on a large scale, as it is related to the demand for drinking water, there is a concern to find an adequate disposal, to avoid posing a risk of environmental contamination and damage to human health, besides being economically viable. Within the various possibilities for its use, disposal in agricultural soils is very promising and sustainable. However, this residue may contain organic contaminants, heavy metals, and pathogenic microorganisms that would make its disposal in soil unfeasible. The inappropriate disposal of this residue poses a high environmental risk, so this work aimed to propose a low-cost methodology, using other residues, of agro-industrial origin (sugar cane bagasse and coconut fiber), as decompacting and stimulants agents to biodegrade the possible toxic compounds existing in the sludge and biotransform it into an agricultural input. Additionally, the ecotoxicological effects on organisms of different trophic levels were also evaluated. The physical-chemical characterization and the pathogenicity of the sludge were carried out, assessing the presence of total coliforms, Escherichia coli, and Ascaris ssp. eggs. The samples were mixed in the soil, using two concentrations of sludge (10% and 15%), with and without the incorporation of sugarcane bagasse and coconut fiber. The respirometer test was applied to verify the biodegradability of the WTP sludge, quantifying the CO2 production of the different samples, for 120 days. The samples, before and after biodegradation, were evaluated for their phytotoxic potential (Lactuca sativa and Eruca sativa seeds), acute toxicity (Daphnia similis and Folsomia candida), and reproduction test (F. candida). As for the result of pathogenicity, the WTP sludge showed the absence of Ascaris ssp. and E. coli, and very low numbers of total coliform colonies. Among the physical-chemical characteristics, the sludge showed a pH close to neutrality and a low concentration of metals, but it contained excess free liquids, which made the drying process indispensable. The use of agro-industrial residues optimized the production of CO2, however, it did not contribute to the biodegradation of the WTP sludge. In the phytotoxicity test, the samples that contained sludge associated with sugarcane bagasse showed moderate to high toxicity, with germination inhibition and reduction of radicle and hypocotyl growth. Similar results were observed for D. similis, indicating that the bagasse released water-soluble toxic compounds. However, after biodegradation, no toxic effect was observed, demonstrating that the biotransformation process employed led to detoxification of the samples. In the test with F. candida, there was no significant lethality, but the samples that contained sludge at a concentration of 10% negatively interfered with the reproduction of these organisms. Thus, the sludge studied presented interesting physicochemical characteristics for use as conditioners and fertilizers for agricultural soils. However, due to the observed toxicity, it is essential to carry out a biodegradation/biostimulation process to promote the elimination of this effect and, thus, guarantee environmental security, providing a more sustainable destination.
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Resíduos sólidos orgânicos, Biodegradação, Bioestimulação, Fitotoxicidade, Toxicidade aguda, Teste de reprodução, Organic solid waste, Biodegradation, Biostimulation, Phytotoxicity, Acute toxicity, Reproduction test