Lamella design (high rate) and conventional flotation units applied to the post-treatment of the effluent from a system made up anaerobic reactor followed by aerobic reactor treating domestic sewage / Emprego da flotação lamelar de alta taxa e convencional como pós-tratamento do efluente de sistema constituído de reator anaeróbio seguido de reator aeróbio tratando esgoto sanitário

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The aim of this research was the study of the lamella design (high rate) and conventional dissolved air flotation (DAF) process potentiality of application as the final part of a domestic sewage sequential treatment system made up anaerobic reactors (UASB) followed by aeration tank. The work, developed at the Jardim das Flores WWTP of Rio Claro city, was separated in three phases. In the first phase, using the flotatest apparatus, the most suitable values of chemical (synthetic cationic polymer, arrow-root starch, ferric chloride and ferric chloride combined with polymer or arrow-root starch) dosages, air to solids ratio (A/S), as well as rapid mix and flocculation time and mean velocity gradient values, were investigated. In this phase, the best DAF performances were obtained with the application of cationic polymer, alone and associated to ferric chloride. The use of ferric chloride was essential to obtain better phosphorus removal results. The mixed liquor flotation using ferric chloride alone as primary coagulant presented extremely unsatisfactory performance, with the formation of flocks showing bad characteristics of flotability. Moreover, it was observed that flotation of this kind of effluent had requested gentler mixture conditions. In many cases, the best results were obtained by means of rapid mix or flocculation step elimination. In the second and third phases, using the lamella design and conventional flotation units respectively and cationic polymer as the only flocculation/flotation aid (dosage around 1 g of polymer/kg TSS), the most suitable values of Overflow Rate (OR), Solids Application Rate (SAR) and amount of air supplied to the flotation process, expressed as the A/S ratio or air dosage (AD, in g of air/ M POT.3 of influent) depending on influent total suspended solids concentration (TSSinfl), were investigated. The flotation essays results showed that the A/S ratio is more suitable for the air supply estimation in flotation of concentrated suspensions (TSSinfl above 1100 mg/L in this study). Contrarily, the parameter AD is more representative in cases of flotation of diluted suspensions. Using the lamella design unit, fed with aeration tank mixed liquor presenting good bio-flocculation conditions, it was possible to obtain adequate results applying OR as high as 350 M POT.3 /( M POT.2 .day) combined with SAR values between 120 and 250 kg of TSS/( M POT.2 .day), since the adequate amount of air has been provided for the process (AD values between 15,0 and 18,0 g of air/ M POT.3 of influent), for TSSinfl between 800 and 1100 mg/L. For the lamella flotation, it was noticed that the best performance has been directly associated to lower values of TSSinfl. The recommendations for flotation using the conventional DAF unit had to be more conservative, taking into account the poor bio-flocculation conditions presented by the mixed liquor during the third phase of work. In theses essays, the more adequate results were obtained by applying OR around 200 M POT.3 /( M POT.2 .day), SAR under 200 kg of TSS/( M POT.2 .day) and A/S ratio around 0,020 (AD of 21,0 g of air/ M POT.3 of influent), for TSSinfl around 1400 mg/L

ASSUNTO(S)

lodo ativado polyelectrolytes clarification using flotation clarificação por flotação polieletrólitos high rate flotation flotação lamelar flotação de alta taxa lamella flotation activated sludge

ACESSO AO ARTIGO

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