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Abstract(s)
A tese de mestrado aqui apresentada teve como principal objetivo estudar e avaliar a eficiência de diferentes tecnologias de tratamento na redução da carga orgânica dos efluentes da Estação de Tratamento de Águas Residuais (ETAR) da empresa Dias Ruivo Curtumes e Produtos Industriais Lda.
Inicialmente avaliou-se o funcionamento atual da ETAR, verificando-se que são consistentemente cumpridos os valores de descarga estipulados na licença ambiental da empresa, para os parâmetros sólidos suspensos totais (SST), crómio III (Cr) e pH. Durante o período de análises, a ETAR permitiu reduções na carência química de oxigénio (CQO) de 72% (2332,00 mg O2/L),, embora ultrapassasse os valores limite de descarga (300 mg O2/L). Relativamente ao azoto total, o valor deste parâmetro manteve-se inalterado, e superior (205,30 a 404,50 mg N/L) ao limite de descarga (15 mg N/L).
Foi realizado um estudo posterior durante um período de 3 semanas com o objetivo de determinar qual o impacto que a zona de fitorremediação de fim de linha, previamente construída traria ao tratamento atual. Durante este período foram analisadas as diferentes etapas de tratamento (primário, secundário e terciário), e pôde-se concluir que a fitorremediação de fim de linha apresentou a capacidade de reduzir o carbono orgânico total (COT) em 44% (724,80 mg/L) e a CQO em 51% (1532,00 mg O2/L), provenientes do tratamento secundário, embora não atingindo o valor estipulado na licença. A zona de tratamento secundário não foi além de uma redução de 20% para o COT (1283,90 mg/L) e 3% para a CQO (1791,00 mg O2/L) , provenientes do tratamento primário, este que, novamente apresentou as maiores reduções de contaminantes.
Foram realizados estudos com recurso a técnicas de oxidação química convencional, usando peróxido de hidrogénio (H2O2) como agente oxidante, adicionado nos últimos dois tanques do tratamento secundário da ETAR. Esta técnica conduziu a uma redução da CQO em 3%, de COT em 3% e não influenciou a remoção do azoto total.
Laboratorialmente realizou-se um teste de arejamento em reator fechado, de modo a avaliar a influencia da adição de oxigénio por via de ar comprimido para degradação de compostos orgânicos. Foi inserido ar comprimido num intervalo de 0,1-0,2 barg, durante um período de 48 horas. Nestas condições não se observou qualquer vantagem na utilização desta tecnologia.
Foi ainda estudado um processo avançado de oxidação (PAO) de forma a analisar a eficiência de redução de matéria orgânica. Avaliou-se a eficiência da reação de Fenton em 3 conjuntos de ensaios onde foram variadas as condições de temperatura, pH inicial e razão mássica [Fe2+:H2O2], com percentagem mássica de 35% m/m de H2O2. No primeiro, avaliou-se o uso desta tecnologia como pré-tratamento da etapa biológica; no segundo conjunto estudou-se a sua aplicação a montante do tratamento primário e a influência da sedimentação e no terceiro (montante do tratamento primário) foram também variadas as condições operatórias.
Para a primeira situação estudada, os ensaios realizados nas condições iniciais de pH 3, razão [Fe2+:H2O2] de 1/3 e temperatura inicial de 20 º C apresentaram os melhores resultados, com reduções de carbono total (CT) de 62% e de CQO de 61%, o que permitirá que na entrada da fase posterior de tratamento (tratamento secundário) o efluente apresente valores inferiores de CQO e COT (626,67 mg O2/L e 377,10 mg/L) possibilitando, eventualmente um melhor desempenho desta etapa de tratamento e, consequentemente, da ETAR.
No segundo conjunto de ensaios foi confirmada a importância da etapa de sedimentação dos complexos férricos: a redução da CQO passou de 71% para 78% (354,80 mg O2/L) e de COT de 57% para 71% (255,90 mg/L) (pH igual 3, temperatura igual a 20º C e razão mássica [Fe2+ : H2O2] de 1/3). Com o objetivo de estudar a diminuição da formação de lamas, realizou-se um conjunto de ensaios variando a quantidade de oxidante adicionado. Atingiram-se remoções de CQO de 70% (628,00 mg O2/L) e de COT de 55% (511,25 mg/L) para pH igual 3, temperatura igual a 20 ºC e razão mássica [Fe2+ : H2O2] de 1/3 e metade da concentração estequiométrica de H2O2. Estes valores foram ligeiramente inferiores aos obtidos no segundo conjunto de ensaios. Em todas os três ensaios não foi conseguida a redução de azoto total.
Assim, com base nos resultados obtidos, é expectável que os tratamentos alternativos estudados contribuam para melhorar o funcionamento da ETAR, cumprindo os objetivos pretendidos, no que diz respeito aos valores de CQO regulamentados na licença de descarga
The main objective of the treatment plant presented here was to study and evaluate the efficiency of different treatment technologies in reducing the organic load of effluents from the wastewater treatment plant (WWTP) of the company Dias Ruivo- Curtumes e Produtos Industriais Lda. Initially, the current functioning of the WWTP was evaluated, verifying that the discharge values stipulated in the company's environmental license are consistently met, for the total suspended solids (SST), chromium III (Cr) and pH parameters. During the analysis period, the WWTP allowed reductions in chemical oxygen demand (COD) of 42%, although it exceeded the discharge limit values (150 mg O2/L). Regarding total nitrogen, the value of this parameter remained unchanged, and above the discharge limit (15 mg/L). A subsequent study was carried out over a period of 3 weeks to determine what impact a previously constructed phytoremediation zone would have on the current treatment. During this period, the different stages of treatment (primary, secondary and tertiary) were analyzed, and it was concluded that phytoremediation had the ability to reduce total organic carbon (TOC) by 44% and COD by 51%, although not reaching the amount stipulated in the license. The secondary treatment zone did not go beyond a 20% reduction for TOC and 3% for COD. Studies were carried out using conventional chemical oxidation techniques, using hydrogen peroxide (H2O2) as an oxidizing agent, and added to a secondary treatment tank at the WWTP. This technique led to a reduction of COD by 3%, of TOC by 3% and did not influence the removal of total nitrogen. In the laboratory, an aeration test was carried out in a closed reactor, under conditions of 0.1-0.2 bar, for a period of 48 hours. Under these conditions, no advantage was observed in the use of this technology. An advanced oxidation process (PAO) was also studied in order to analyze the efficiency of organic matter reduction. The efficiency of the Fenton reaction was evaluated in 3 sets of tests where the conditions of temperature, initial pH and mass ratio [Fe2+:H2O2] were varied. In the first one, the use of this technology as a pre-treatment of the biological stage was evaluated; in the second set, its application was studied upstream of the primary treatment and the influence of sedimentation and in the third (amount of the primary treatment) the operating conditions were varied. For the first situation studied, the tests carried out in the initial conditions of pH 3, [Fe2+:H2O2] ratio of 1/3 and initial temperature of 20 º C presented the best results, with reductions of total carbon (TC) of 62% and of COD of 61%, which will allow the effluent to present lower COD and TOC values (626.67 mg O2/L and 377.10 mg/L) at the entrance of the subsequent treatment phase (secondary treatment) allowing, eventually, a better performance of this stage of treatment and, consequently, of the WWTP. In the second set of tests, the importance of the sedimentation stage of the ferric complexes was confirmed: the reduction of COD went from 71% to 78% and of TOC from 57 to 78% (pH equal to 3, temperature equal to 20º C and mass ratio [ Fe2+: H2O2] of 1/3). In order to study the reduction of sludge formation, a set of tests was carried out, varying the amount of oxidant added. COD removals of 70% and TOC of 54% were achieved for pH equal to 3, temperature equal to 20 ºC and mass ratio [Fe2+: H2O2] of 1/3 and half the stoichiometric concentration of H2O2. These values, although slightly lower than those obtained in the second set, are satisfactory. Thus, based on the results obtained, it is expected that the alternative treatments studied can help the WWTP to comply with the values regulated in the discharge license with regard to COD
The main objective of the treatment plant presented here was to study and evaluate the efficiency of different treatment technologies in reducing the organic load of effluents from the wastewater treatment plant (WWTP) of the company Dias Ruivo- Curtumes e Produtos Industriais Lda. Initially, the current functioning of the WWTP was evaluated, verifying that the discharge values stipulated in the company's environmental license are consistently met, for the total suspended solids (SST), chromium III (Cr) and pH parameters. During the analysis period, the WWTP allowed reductions in chemical oxygen demand (COD) of 42%, although it exceeded the discharge limit values (150 mg O2/L). Regarding total nitrogen, the value of this parameter remained unchanged, and above the discharge limit (15 mg/L). A subsequent study was carried out over a period of 3 weeks to determine what impact a previously constructed phytoremediation zone would have on the current treatment. During this period, the different stages of treatment (primary, secondary and tertiary) were analyzed, and it was concluded that phytoremediation had the ability to reduce total organic carbon (TOC) by 44% and COD by 51%, although not reaching the amount stipulated in the license. The secondary treatment zone did not go beyond a 20% reduction for TOC and 3% for COD. Studies were carried out using conventional chemical oxidation techniques, using hydrogen peroxide (H2O2) as an oxidizing agent, and added to a secondary treatment tank at the WWTP. This technique led to a reduction of COD by 3%, of TOC by 3% and did not influence the removal of total nitrogen. In the laboratory, an aeration test was carried out in a closed reactor, under conditions of 0.1-0.2 bar, for a period of 48 hours. Under these conditions, no advantage was observed in the use of this technology. An advanced oxidation process (PAO) was also studied in order to analyze the efficiency of organic matter reduction. The efficiency of the Fenton reaction was evaluated in 3 sets of tests where the conditions of temperature, initial pH and mass ratio [Fe2+:H2O2] were varied. In the first one, the use of this technology as a pre-treatment of the biological stage was evaluated; in the second set, its application was studied upstream of the primary treatment and the influence of sedimentation and in the third (amount of the primary treatment) the operating conditions were varied. For the first situation studied, the tests carried out in the initial conditions of pH 3, [Fe2+:H2O2] ratio of 1/3 and initial temperature of 20 º C presented the best results, with reductions of total carbon (TC) of 62% and of COD of 61%, which will allow the effluent to present lower COD and TOC values (626.67 mg O2/L and 377.10 mg/L) at the entrance of the subsequent treatment phase (secondary treatment) allowing, eventually, a better performance of this stage of treatment and, consequently, of the WWTP. In the second set of tests, the importance of the sedimentation stage of the ferric complexes was confirmed: the reduction of COD went from 71% to 78% and of TOC from 57 to 78% (pH equal to 3, temperature equal to 20º C and mass ratio [ Fe2+: H2O2] of 1/3). In order to study the reduction of sludge formation, a set of tests was carried out, varying the amount of oxidant added. COD removals of 70% and TOC of 54% were achieved for pH equal to 3, temperature equal to 20 ºC and mass ratio [Fe2+: H2O2] of 1/3 and half the stoichiometric concentration of H2O2. These values, although slightly lower than those obtained in the second set, are satisfactory. Thus, based on the results obtained, it is expected that the alternative treatments studied can help the WWTP to comply with the values regulated in the discharge license with regard to COD
Description
Keywords
ETAR H2O2 Arejamento Reação de Fenton CQO COT Azoto total Tecnologias de tratamento de efluentes WWTP Aeration Fenton’s Reaction TOC Total nitrogen Wastewater treatment Technologies