Phosphorus removal by adding ferric chloride in upflow anaerobic sludge blanket (UASB) followed by aerobic sequential batch reactor (RSB)

Um sistema de tratamento de esgotos sanitários por reator UASB seguido de RSB foi operado durante 27 semanas objetivando-se verificar seu desempenho na remoção de matéria orgânica carbônácea, nitrogênio amoniacal e fósforo. O reator UASB, com 145 litros foi operado com tempo de detenção hidráulica médio de 8 horas durante todo o experimento. O reator RSB, de 106 litros, foi operado com tempos de ciclio de 24, 12 e 6 horas, em seis etapas distintas. Os tempos de ciclo no RSB variaram de 24, 12, 6, 24, 24 e 24 para as etapas 1, 2, 3, 4, 5 e 6 respectivamente. As últimas três etapas foram caracterizadas pela adição de cloreto férrico, respectivamente. O sistema UASB/RSB apresentou eficiência média de remoção de DQO de 92% nas etapas 1, 2, 5, e 6. Na etapa 3, com tempo de ciclo de 6 horas e na etapa 4, quando o RSB recebeu 50mg/L de cloreto férrico, a eficiência média de remoção de DQO foi de 83%. Quando FeCl3 foi adicionado no afluente do reator UASB, obteve-se excelente desempenho na remoção de fósforo, cujas concentrações afluentes foram da ordem de 1,0 mg/L e 4,0 mg/L para a adição de 200 e 100 mg/L de cloreto férrico, respectivamente.The performance evaluation of a pilot scale system composed by a UASB reactor followed by an SBR reactor treating domestic sewage is presented. The UASB reactor with 145 L of volume, was operated with an average hydraulic detention period of 8 hours. The SBR reactor had a volume of 106 litters being operated with cyclic time of 24, 12, and 6 hours. These different operational conditions characterized three stages of the work from a total of six stages. The three last stages were the addition of 50, 100, and 200 mg/L of ferric chloride in the aerobic, anaerobic, and anaerobic reactors, respectively. In the three last stages the UASB reactor worked with an average hydraulic detention time of 8 hours and the aerobic reactor worked with a cyclic time of 24 hours. After 27 weeks of continuous operation, the UASB/SBR system produced very good results in terms of COD removal. The average results of the COD removal were of 92% to the first, second, fifth, and sixth stages, having a reduction to 83% on the average to the stages where the SBR received 50 mg/L of ferric chloride and in which it worked with a six hour cyclic period. The addition of ferric chloride in the anaerobic reactor had great efficiency in the phosphorus removal. It was reached absolute values of until 1 mg/L of PO43- in the aflluent of the system, promoting an average effluent of 4 mg/L of PO43- with the addition 200 mg/L of FCl3. The UASB/SBR system can become a very promising alternative for domestic sewerage treatment in Brazil, since the system can be projected with shorter times of hydraulic detention times, resulting in a low cost compact installation. Furthermore, excellent results can be gotten to the ammonium and phosphorus removal