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Os efluentes gerados no processo de refinação do açúcar devem ser tratados de forma respeitar normas de descarga e a minimizar o impacto que os mesmos criam. Existem algumas vantagens no tratamento de efluentes industriais em conjunto com as águas residuais domésticas, nomeadamente ao nível dos nutrientes (muitas vezes em falta nas águas residuais industriais), mas também devem ser evitadas concentrações elevadas de alguns poluentes, que poderiam ser prejudiciais aos tratamentos biológicos implementados nas estações de tratamento de águas municipais. Desta forma existem valores máximos para a descarga dos efluentes industriais nos coletores municipais, que são definidos pela entidade gestora do sistema, neste caso pelas Águas do Porto. Os valores máximo admissíveis (VMA) aplicados à RAR Açúcar são os seguintes, 3 mS/cm para a condutividade, 2000 mg/L para os cloretos, 6-9 para o pH, 1000 mg/L para os sólidos suspensos totais (SST) e 1000 mg O2/L para a carência química de oxigénio (CQO). Os efluentes das várias etapas do processo de refinação, incluem condensados, águas residuais provenientes do vazamento/lavagem de equipamentos, da purga das caldeiras, da descoloração e da nanofiltração. Após um estudo realizado anteriormente na RAR Açúcar, que se baseou na caracterização (quantitativa e qualitativa) dos efluentes processuais, concluiu-se que o efluente proveniente da nanofiltração possuía uma carga poluente muito elevada. Desta forma, começou-se por estudar o processo de nanofiltração e percebeu-se que o efluente gerado por este continha salmoura (mistura de água e cloreto de sódio) e corantes. A salmoura é usada para a regeneração das resinas de permuta iónica usadas na descoloração. Quando as concentrações de sal no efluente proveniente desta etapa são suficientemente elevadas, realiza-se o seu tratamento por nanofiltração, resultando o permeado que é reaproveitado e inserido novamente no sistema e o retido, ou concentrado, que é enviado para a estação elevatória e daí para o coletor municipal. Para estimar as quantidades de sal que são enviadas para a estação elevatória, realizouse um balanço material, onde se concluiu que na regeneração das resinas era usado um total 1568 kg de sal, sendo que deste, 52% (815 kg) é reaproveitado através da nanofiltração, 34% (528 kg) fica retido nas resinas e 14% (225 kg) é desperdiçado. Como diariamente ocorrem duas regenerações das resinas e duas nanofiltrações, concluiu-se que a quantidade de sal enviada para a estação elevatória é significativa e aumenta a carga inorgânica do efluente global devido à elevada quantidade de cloretos que estas águas residuais contêm. Assim, procedeu-se a uma análise geral com o intuito de perceber o impacto que cada uma destas águas residuais poderia causar no efluente global. A definição do plano de amostragem baseou-se num trabalho realizado anteriormente, e foram definidos quatro pontos de recolha: à saída da regeneração das resinas de permuta iónica, à saída da nanofiltração e no início da estação elevatória (A), local onde chegam as várias correntes que contribuem para o efluente global, e no fim (B), de onde é feita a bombagem para o coletor municipal. A recolha de amostras realizou-se em cinco dias diferentes, e foram medidos os seguintes parâmetros: cloretos, condutividade, pH, SST e CQO. Concluiu-se que a contribuição do efluente proveniente da regeneração das resinas é muito significativa para o efluente final, já que os valores dos parâmetros são muito superiores aos admitidos para descarga no coletor municipal, excetuando o pH que não é muito afetado por este efluente. Foram analisados separadamente os dois processos, regeneração das resinas e nanofiltração. Retiraram-se amostras da regeneração das resinas e quinze minutos depois retiraram-se amostras da estação elevatória nos dois pontos de recolha, A e B. Para a nanofiltração realizou-se o mesmo procedimento, no entanto, como a descarga é direta, apenas se retirou uma amostra do efluente da nanofiltração e várias amostras nos dois pontos de recolha A e B da estação elevatória durante a descarga deste. As amostras da estação elevatória, durante a descarga do efluente da regeneração das resinas e da nanofiltração apresentaram as seguintes médias: no ponto de recolha A respetivamente, 18,5 e 3,68 mS/cm, 8634 e 847 mg/L de cloretos, 5,0 de pH, 1733 e 6822 mg/L de SST, 17,0 e 36,0 g O2/L de CQO; no ponto de recolha B obtiveram-se os seguintes valores, 13,6 e 5,23 mS/cm, 5431 e 1562 mg/L de cloretos, 4,2 e 4,1 de pH, 3179 e 5984 mg/L de SST, 47,9 e 49,3 g O2/L de CQO. A partir da análise destes valores concluiu-se que o efluente da regeneração das resinas de permuta iónica afeta de forma mais acentuada o efluente final, devido ao elevado volume que é enviado para a estação elevatória. Apesar das águas residuais provenientes da nanofiltração apresentarem concentrações mais elevadas do que as provenientes da regeneração, devido ao seu baixo volume (1 m3), não afetam tão significativamente as concentrações das águas residuais finais.
The effluents generated from the sugar refining process must be treated to respect discharge standards and minimize the impact they create. There are some advantages in treating industrial effluents together with domestic wastewater, namely in terms of nutrients (often lacking in industrial wastewater), but high concentrations of some pollutants should also be avoided, which could be harmful to the biological treatments implemented in municipal wastewater treatment plants. Thus, there are maximum values for the discharge of industrial effluents in municipal collectors, which are defined by the managing entity of the system, in this case Águas do Porto. The maximum admissible values (MAV) applied to the RAR Açúcar are the following: 3 mS/cm for conductivity, 2000 mg/L for chlorides, 6-9 for pH, 1000 mg/L for total suspended solids (TSS) and 1000 mg O2/L for chemical oxygen demand (COD). The effluents from the various stages of the refining process, include condensate, wastewater from equipment leakage/washing, boiler purge, decolorization and nanofiltration. After a previous study carried out at RAR Açúcar, which was based on the characterization (quantitative and qualitative) of the process effluents, it was concluded that the effluent from nanofiltration had a very high pollutant load. Thus, the nanofiltration process was studied and it was noticed that the effluent generated by this process contained brine (a mixture of water and sodium chloride) and dyes. The brine is used for regeneration of the ion exchange resins used in decolorization. When the salt concentrations in the effluent from this stage are high enough, it is treated by nanofiltration, resulting in the permeate that is reused and fed back into the system and the retained, or concentrate, that is sent to the pumping station and from there to the municipal collector. To estimate the quantities of salt that are sent to the pumping station, a material balance was carried out, which allowed to conclude that in the regeneration of resins a total of 1568 kg of salt was used, of which 52% (815 kg) is reused through nanofiltration, 34% (528 kg) is retained in the resins and 14% (225 kg) is wasted. As two regenerations of the resins and two nanofiltrations occur daily, it was concluded that the quantity of salt sent to the pumping station is significant and increases the inorganic load of the global effluent due to the high quantity of chlorides that these wastewaters contain. Therefore, a general analysis was carried out aiming to understand the impact that each of these wastewaters could cause in the global effluent. The definition of the sampling plan was based on previous work, and four collection points were defined: at the exit of the ion exchange resin regeneration, at the exit of the nanofiltration and at the beginning of the pumping station (A), where the various currents that contribute to the overall effluent arrive, and at the end (B), from where the pumping to the municipal collector is done. Sampling took place on five different days, and the following parameters were measured: chlorides, conductivity, pH, TSS and COD. It was concluded that the contribution of the wastewater from the regeneration of resins is very significant for the final effluent, since the values of the parameters are much higher than those allowed for discharge into the municipal collector, except the pH that is not much affected by this effluent. Samples were also taken from the nanofiltration effluent, and it was noticed that its load was quite high. The two processes, resin regeneration and nanofiltration, were analyzed separately. Samples were taken from the resin regeneration as well as from the pumping station (fifteen minutes later) at sampling points A and B. For nanofiltration the same procedure was performed, however, as the discharge is direct, only one sample was taken from the nanofiltration effluent, and several samples were taken from the pumping station during its discharge. The samples from the pumping station, during the discharge of the effluent from resin regeneration and nanofiltration revealed the following averages at collection point A respectively, 18.5 and 3.68 mS/cm conductivity, 8634 and 847 mg/L chlorides, 5.0 pH, 1733 and 6822 mg/L TSS, 17.0 and 36.0 g O2/L COD. At collection point B, the following values were obtained: 13.6 and 5.23 mS/cm conductivity, 5431 and 1562 mg/L chlorides, 4.2 and 4.1 pH, 3179 and 5984 mg/L TSS, 47.9 and 49.3 g O2/L COD. From the analysis of these values, it was concluded that the effluent from the regeneration of ion exchange resins affects the final effluent more markedly, due to the high volume that is sent to the pumping station. Although wastewater from nanofiltration has higher concentrations than wastewater from regeneration, due to its lower volume (1 m3 ), it does not significantly affect the final wastewater.
The effluents generated from the sugar refining process must be treated to respect discharge standards and minimize the impact they create. There are some advantages in treating industrial effluents together with domestic wastewater, namely in terms of nutrients (often lacking in industrial wastewater), but high concentrations of some pollutants should also be avoided, which could be harmful to the biological treatments implemented in municipal wastewater treatment plants. Thus, there are maximum values for the discharge of industrial effluents in municipal collectors, which are defined by the managing entity of the system, in this case Águas do Porto. The maximum admissible values (MAV) applied to the RAR Açúcar are the following: 3 mS/cm for conductivity, 2000 mg/L for chlorides, 6-9 for pH, 1000 mg/L for total suspended solids (TSS) and 1000 mg O2/L for chemical oxygen demand (COD). The effluents from the various stages of the refining process, include condensate, wastewater from equipment leakage/washing, boiler purge, decolorization and nanofiltration. After a previous study carried out at RAR Açúcar, which was based on the characterization (quantitative and qualitative) of the process effluents, it was concluded that the effluent from nanofiltration had a very high pollutant load. Thus, the nanofiltration process was studied and it was noticed that the effluent generated by this process contained brine (a mixture of water and sodium chloride) and dyes. The brine is used for regeneration of the ion exchange resins used in decolorization. When the salt concentrations in the effluent from this stage are high enough, it is treated by nanofiltration, resulting in the permeate that is reused and fed back into the system and the retained, or concentrate, that is sent to the pumping station and from there to the municipal collector. To estimate the quantities of salt that are sent to the pumping station, a material balance was carried out, which allowed to conclude that in the regeneration of resins a total of 1568 kg of salt was used, of which 52% (815 kg) is reused through nanofiltration, 34% (528 kg) is retained in the resins and 14% (225 kg) is wasted. As two regenerations of the resins and two nanofiltrations occur daily, it was concluded that the quantity of salt sent to the pumping station is significant and increases the inorganic load of the global effluent due to the high quantity of chlorides that these wastewaters contain. Therefore, a general analysis was carried out aiming to understand the impact that each of these wastewaters could cause in the global effluent. The definition of the sampling plan was based on previous work, and four collection points were defined: at the exit of the ion exchange resin regeneration, at the exit of the nanofiltration and at the beginning of the pumping station (A), where the various currents that contribute to the overall effluent arrive, and at the end (B), from where the pumping to the municipal collector is done. Sampling took place on five different days, and the following parameters were measured: chlorides, conductivity, pH, TSS and COD. It was concluded that the contribution of the wastewater from the regeneration of resins is very significant for the final effluent, since the values of the parameters are much higher than those allowed for discharge into the municipal collector, except the pH that is not much affected by this effluent. Samples were also taken from the nanofiltration effluent, and it was noticed that its load was quite high. The two processes, resin regeneration and nanofiltration, were analyzed separately. Samples were taken from the resin regeneration as well as from the pumping station (fifteen minutes later) at sampling points A and B. For nanofiltration the same procedure was performed, however, as the discharge is direct, only one sample was taken from the nanofiltration effluent, and several samples were taken from the pumping station during its discharge. The samples from the pumping station, during the discharge of the effluent from resin regeneration and nanofiltration revealed the following averages at collection point A respectively, 18.5 and 3.68 mS/cm conductivity, 8634 and 847 mg/L chlorides, 5.0 pH, 1733 and 6822 mg/L TSS, 17.0 and 36.0 g O2/L COD. At collection point B, the following values were obtained: 13.6 and 5.23 mS/cm conductivity, 5431 and 1562 mg/L chlorides, 4.2 and 4.1 pH, 3179 and 5984 mg/L TSS, 47.9 and 49.3 g O2/L COD. From the analysis of these values, it was concluded that the effluent from the regeneration of ion exchange resins affects the final effluent more markedly, due to the high volume that is sent to the pumping station. Although wastewater from nanofiltration has higher concentrations than wastewater from regeneration, due to its lower volume (1 m3 ), it does not significantly affect the final wastewater.
Description
Keywords
Águas residuais Cloretos Indústria da refinação do açúcar Nanofiltração Regeneração Resinas de permuta iónica Chlorides Ion exchange resins Nanofiltration Regeneration Sugar refining industry Wastewaters