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As Estações de Tratamento de Águas Residuais (ETAR) são fundamentais para garantir a saúde pública e o equilíbrio dos ecossistemas, uma vez que permitem o tratamento de águas residuais e a sua devolução segura ao meio hídrico. Porém, nas atividades decorrentes da exploração das ETAR são geradas grandes quantidades de resíduos, destacando-se as lamas, os gradados e as areias, sendo os dois últimos, geralmente, encaminhadas para aterro sanitário. Os princípios preconizados na legislação levantam a necessidade de encontrar alternativas à deposição dos resíduos em aterro sanitário, dando prioridade à prevenção, reutilização e valorização dos mesmos. Assim, o presente projeto teve como objetivo principal a otimização da gestão dos resíduos provenientes da etapa de desarenamento da ETAR de Valongo, Campo e Sobrado e da ETAR de Ermesinde e Alfena. Neste trabalho foi estudada a viabilidade de valorização deste resíduo na construção civil e em processos de co-compostagem. Para tal, numa primeira fase, efetuou-se um pré-tratamento aos resíduos das duas instalações, com vista à redução da matéria orgânica presente para avaliar a possibilidade da sua reutilização (por exemplo, na construção civil). A valorização (por exemplo, através da co-compostagem) foi também avaliada, tendo sido analisados alguns parâmetros considerados críticos para o processo de compostagem, tais como pH, teor de humidade, razão C/N e razão C/N/P. Procedeu-se a uma caraterização dos resíduos e seus respetivos eluatos de acordo com a Norma EN 12457-4. Foram também efetuados ensaios de pré-tratamento que consistiram na realização de lavagens com água residual tratada e água de abastecimento da rede pública. Para ambos os resíduos, verificouse que o ensaio de lixiviação (eluato) foi o que apresentou uma maior quantidade de matéria orgânica lixiviada, e após as lavagens, os valores de carbono orgânico total (COT) na fase líquida foram de 20000 e de 2037 mg/kg matéria seca, para os resíduos da ETAR de Valongo, Campo e Sobrado e da ETAR de Ermesinde e Alfena, respetivamente. Nos ensaios em foi utilizada água residual tratada foi possível obter resíduos com menor teor de COT (em base seca) do que naqueles em foi usada água da rede pública, 44,66 % no resíduo de Valongo, Campo e Sobrado e 6,10 % no de Ermesinde e Alfena. Concluiu-se que as lavagens efetuadas não permitiram extrair matéria orgânica suficiente de forma a cumprir os requisitos exigidos para sua utilização na construção civil. A introdução de um lavador de areias HUBER Coanda RoSF4/1 na ETAR de Ermesinde e Alfena, permitiria a remoção de matéria orgânica para valores inferiores a 3 %, valor máximo admitido para a incorporação em camadas não-ligadas em pavimentações. Sob o ponto de vista económico, a aquisição do lavador de areias seria amortizada ao fim de 6 anos. No que diz respeito à valorização orgânica, verificou-se que o resíduo de Valongo, Campo e Sobrado apresentava um valor de pH de 5,62 e uma razão C/N/P (140,4:8,3:1), que se enquadram nos intervalos de valores de referência, respetivamente 5 a 7,5 e 100:10:1 a 200:2:1. No resíduo de Ermesinde e Alfena apenas o parâmetro pH (7,20) se encontra dentro da gama adequada. No entanto, os restantes parâmetros poderão ser equilibrados pela incorporação de outro resíduo, nomeadamente, lamas de ETAR, através do processo de co-compostagem. O encaminhamento dos resíduos de ambas as unidades de tratamento para co-compostagem permitiria a poupança de, pelo menos, 4 618,8 € por ano. Assim, as sugestões apresentadas permitiriam a minimização do impacte relacionado com a geração e gestão de resíduos de desarenamento, seguindo os princípios da economia circular. Além disso, originariam uma redução de custos, o que poderia gerar novas oportunidades económicas.
Wastewater Treatment Plants (WWTP) are essential to guarantee public health and equilibrium of ecosystems, as they allow wastewater to be treated and safely returned to the aquatic environment. However, large quantities of residues are generated in the activities resulting from the operation of WWTPs, particularly sludge, screenings and grit, the last two of which are generally sent to landfill. The principles laid down in the legislation led to find alternatives to the disposal of residues in landfill, prioritizing the prevention, reuse and recovery. The main aim of this project was therefore to optimize the management of residue from the grit removal stage of the Valongo, Campo and Sobrado WWTP and the Ermesinde and Alfena WWTP. This work studied the feasibility of valorizing this residue in the construction industry and in co-composting processes. The waste from the two facilities was initially pre-treated in order to reduce the organic matter present and assess the possibility of reusing it (e.g. in construction). Valorization (e.g. in co-composting) was also assessed and some critical parameters for the composting process were analyzed, such as pH, moisture content, C/N ratio and C/N/P ratio. The waste and its respective eluates were characterized in accordance with Standard EN 12457-4. Pre-treatment tests were also carried out, consisting of washing with treated wastewater and water from the public water supply. For both wastes, it was found that the leaching test (eluate) was the one with the highest amount of organic matter leached, and after washing, the total organic carbon (TOC) values in the liquid phase were 20000 and 2037 mg/kg dry matter, for the waste from the Valongo, Campo and Sobrado WWTP and the Ermesinde and Alfena WWTP, respectively. In the tests where treated wastewater was used, it was possible to obtain a waste with a lower TOC content (on a dry basis) than when tap water was used, 44,66 % in the Valongo, Campo and Sobrado waste and 6,10 % in the Ermesinde and Alfena waste. It was concluded that the washes carried out did not extract enough organic matter to meet the requirements for use in construction. The introduction of a HUBER Coanda RoSF4/1 sand scrubber at the Ermesinde and Alfena wastewater treatment plant would allow organic matter to be removed to contents lower than 3 %, the maximum value allowed for incorporation into non-bonded paving layers. From an economic point of view, the purchase of the sand washer would be amortized after 6 years. With regard to organic recovery, it was found that the waste from Valongo, Campo and Sobrado had a pH value of 5,62 and a C/N/P ratio (140,4:8,3:1), which fall within the range of reference values, respectively 5 to 7,5 and 100:10:1 to 200:2:1. In the Ermesinde and Alfena waste, only the pH parameter (7,20) is within the appropriate range. However, the other parameters could be balanced by incorporating other wastes, namely sludge from wastewater treatment plants, through the co-composting process. The incorporation of these wastes in the co-composting process would save at least €4 618,8 per year. Thus, the presented suggestions would minimize the impact related to the generation and management of grit, following the principles of the circular economy. They would also lead to a reduction in costs and could generate new economic opportunities.
Wastewater Treatment Plants (WWTP) are essential to guarantee public health and equilibrium of ecosystems, as they allow wastewater to be treated and safely returned to the aquatic environment. However, large quantities of residues are generated in the activities resulting from the operation of WWTPs, particularly sludge, screenings and grit, the last two of which are generally sent to landfill. The principles laid down in the legislation led to find alternatives to the disposal of residues in landfill, prioritizing the prevention, reuse and recovery. The main aim of this project was therefore to optimize the management of residue from the grit removal stage of the Valongo, Campo and Sobrado WWTP and the Ermesinde and Alfena WWTP. This work studied the feasibility of valorizing this residue in the construction industry and in co-composting processes. The waste from the two facilities was initially pre-treated in order to reduce the organic matter present and assess the possibility of reusing it (e.g. in construction). Valorization (e.g. in co-composting) was also assessed and some critical parameters for the composting process were analyzed, such as pH, moisture content, C/N ratio and C/N/P ratio. The waste and its respective eluates were characterized in accordance with Standard EN 12457-4. Pre-treatment tests were also carried out, consisting of washing with treated wastewater and water from the public water supply. For both wastes, it was found that the leaching test (eluate) was the one with the highest amount of organic matter leached, and after washing, the total organic carbon (TOC) values in the liquid phase were 20000 and 2037 mg/kg dry matter, for the waste from the Valongo, Campo and Sobrado WWTP and the Ermesinde and Alfena WWTP, respectively. In the tests where treated wastewater was used, it was possible to obtain a waste with a lower TOC content (on a dry basis) than when tap water was used, 44,66 % in the Valongo, Campo and Sobrado waste and 6,10 % in the Ermesinde and Alfena waste. It was concluded that the washes carried out did not extract enough organic matter to meet the requirements for use in construction. The introduction of a HUBER Coanda RoSF4/1 sand scrubber at the Ermesinde and Alfena wastewater treatment plant would allow organic matter to be removed to contents lower than 3 %, the maximum value allowed for incorporation into non-bonded paving layers. From an economic point of view, the purchase of the sand washer would be amortized after 6 years. With regard to organic recovery, it was found that the waste from Valongo, Campo and Sobrado had a pH value of 5,62 and a C/N/P ratio (140,4:8,3:1), which fall within the range of reference values, respectively 5 to 7,5 and 100:10:1 to 200:2:1. In the Ermesinde and Alfena waste, only the pH parameter (7,20) is within the appropriate range. However, the other parameters could be balanced by incorporating other wastes, namely sludge from wastewater treatment plants, through the co-composting process. The incorporation of these wastes in the co-composting process would save at least €4 618,8 per year. Thus, the presented suggestions would minimize the impact related to the generation and management of grit, following the principles of the circular economy. They would also lead to a reduction in costs and could generate new economic opportunities.
Description
Keywords
Águas residuais Co-compostagem Construção civil Matéria orgânica Reutilização Valorização Wastewater Co-composting Construction Organic matter Reuse Valorization