Abstract The present study evaluated the phosphorus removal in a Sequencing Batch Reactor (SBR - 2,500L) used to treat the wastewater from an office building in two steps: phase I-Enhanced biological phosphorus removal (EBPR) and phase II-co-precipitation using FeCl3 as precipitant. The raw sewage presented a high organic load variation ranging from 0.11 (phase I) to 0.66 (phase II) kgCOD.m-3.d-1. A better phosphorus removal performance was obtained during co-precipitation (from 19.0 to 1.2 mg.L-1 = 93% of efficiency) compared with biological removal (from 15.6 to 9.0 mgL-1 = 42% of efficiency). FISH analyses did not demonstrate a strong PAO inhibition; however, nitrifying and denitrifying organisms (NSO and PAE) showed a significant activity reduction during phase II. Therefore, the bench tests made to obtain the oxygen uptake rate (OUR) revealed a heterotrophic organisms activity significantly lower in phase II (46.8 mgDQOT.L-1) than phase I (211.8 mgDQOT.L-1), indicating metabolic inhibition. The co-precipitation processes enhanced phosphorus removal, bringing the SBR effluent into accord with state law requirements; however, the inhibitory effect of ferric chloride on microorganism activity was highlighted.

ResumoO objetivo deste trabalho é apresentar o desempenho dos wetlandsconstruídos de fluxo vertical (WCFV) submetidos a diferentes carregamentos orgânicos e hidráulicos, a fim de incorporar esta tecnologia como opção no tratamento descentralizado de esgotos em empreendimentos comercial e residencial. Avaliou-se ao longo de dois anos dois sistemas de tratamento: (i) sistema 1 - empreendimento comercial: composto por um Reator Aneróbio Compartimentado (RAC) seguido de WCFV (área superficial total de 189 m2); (ii) sistema 2 - condomínio residencial: composto pela sequência RAC e WCFV com fundo saturado (área superficial total de 3.141 m2). Com o monitoramento operacional e analítico junto aos wetlands, determinaram-se taxas hidráulicas aplicadas variando de 130 a 12 mm.d-1 e carregamentos médios aplicados variando de 87 a 1,9 gDQO m-2.d-1 para os sistemas 1 e 2, respectivamente. Os distintos carregamentos foram resultantes da demanda atual dos empreendimentos, sendo que os sistemas 1 e 2 apresentaram eficiências médias globais de remoção em termos de concentração de 75% e 93% para DQO, de 88% e 97% para DBO e de 83% e 94% para SS, respectivamente. A partir dos resultados obtidos, recomenda-se a utilização dos WCFV como alternativa tecnológica de tratamento de esgoto sob o contexto da descentralização.

AbstractThe aim of this study is to show the performance of vertical flow constructed wetlands (VFCW) applied to wastewater treatment from commercial and residential buildings under different organic and hydraulic loading rates. During two years two systems were evaluated: (i) system 1 - commercial building: compound by one Baffle Anaerobic Reactor (BAC) followed by VFCW (superficial area 189 m2); (ii) system 2 - residential building: compound by one BAC followed by VFCW (superficial area 3,141 m2). The operational and analytic monitoring of the wetlands systems determined hydraulic loading rate applied from 130 to 12 mm.d-1 and organic loading rate applied from 87 to 1.9 gCOD, for systems 1 and 2 respectively. The different loadings applied were due to actual demand and the systems 1 and 2 showed average concentration removals efficiencies of 75% and 93% to COD, of 88% and 97% to BOD and of 83% and 94% to SS, respectively. These results lead us to recommend the use of VFCW as a decentralized wastewater treatment technology.

Os problemas provocados pela nitrificação no esgoto com baixa alcalinidade foram analisados num reator piloto do tipo lodos ativados seqüencial por batelada (RSB), alimentado por esgoto urbano. A diminuição do pH se mostrou em três níveis: com pH de 6,8 - 6,0 os protozoários, responsáveis para a filtração da fase liquida, desaparecerem; os flocos de lodos ativados começaram a se destruir abaixo pH 6,5 resultando em elevação da turbidez no efluente final e abaixo de pH 6,2-6,0 a nitrificação foi afetada. A influência da desnitrificação para manter o pH foi analisada. Devido a baixa relação C:N no esgoto pré-tratado, a desnitrificação não se mostrou suficiente para manter o pH estável. Este trabalho apresenta o cálculo da alcalinidade que considera a influência da nitrificação e desnitrificação, de acordo com os resultados obtidos no RSB. Baseado nesse cálculo, foi desenvolvida uma recomendação na forma gráfica para usar em ETE´s afetadas por baixa alcalinidade.

In this study, the problems provoked by nitrification of wastewater with low alkalinity were analyzed in a pilot sequencing batch activated sludge reactor (SBR). Decrease in pH resulted in disappearence of protozoa. De-flocculation of the activated sludge floc started below pH 6.5, resulting in enhanced effluent turbidity and loss of bacteria. Nitrification efficiency was affected below pH 6.2. The denitrification activity was not sufficient to keep up the pH, due to a low C/N ratio of the wastewater. Based on alkalinity and ammonia concentration of the wastewater and the necessary denitrification rate to prevent operational problems, was developed a prognostic diagram. The applicability of this diagram was tested for the SBR with excellent results. The diagram could be applied to optimize the operation of wastewater treatment plants affected by problems with low alkalinity wastewater.