Avaliação do desempenho de sistemas alagados construídos de escoamento horizontal subsuperficial tratando efluente de reator UASB, com base em quatro anos de monitoramento / Performance evaluation of horizontal subsurface flow constructed wetlands in the treatment of UASB reactor effluent, based on four years of monitoring

RESUMO Um sistema composto por um reator anaeróbio tipo upflow anaerobic sludge blanket (UASB), seguido de um sistema de alagados construídos (SAC) de escoamento horizontal subsuperficial compreendendo duas unidades em paralelo (50 habitantes cada), foi avaliado para o tratamento de águas residuárias geradas na cidade de Belo Horizonte, Minas Gerais, Brasil. Uma unidade foi plantada com Typha latifolia e a outra não foi vegetada. Amostras semanais do efluente do reator UASB e do efluente das unidades do SAC foram avaliadas por um período de quatro anos de operação do sistema. Nas taxas de aplicação praticadas (média de 0,11 m3.m-2.d-1), o efluente final apresentou excelente qualidade em termos de matéria orgânica e sólidos suspensos, mas baixa capacidade de remoção de nitrogênio. Os valores médios de concentração no efluente das unidades plantadas e não plantadas foram, respectivamente, demanda bioquímica de oxigênio: 25 e 23 mg.L-1; demanda química de oxigênio: 50 e 55 mg.L-1; sólidos suspensos totais: 10 e 8 mg.L-1; nitrogênio Kjeldahl total: 30 e 31 mg.L-1; e nitrogênio amoniacal: 27 e 28 mg.L-1. Não se observou diferença significativa entre as concentrações efluentes das unidades plantada e não plantada para a maioria dos constituintes investigados.

ABSTRACT A system composed of an upflow anaerobic sludge blanket (UASB) reactor followed by two horizontal subsurface flow wetlands (50 inhabitants each) constructed in parallel was evaluated for the treatment of municipal wastewater generated in the city of Belo Horizonte, Minas Gerais, Brazil. One unit was planted with Typha latifolia, and the other one was not planted. Weekly samples of the effluent from the UASB reactor and the effluent from both wetland units were evaluated for a period of four years of the system's operation. With the applied loads (average of 0.11 m3.m-2.d-1), the final effluent showed excellent quality in terms of organic matter and suspended solids, but it showed low capacity for nitrogen removal. Mean concentration values in the effluent from the planted and unplanted units were, respectively, biochemical oxygen demand: 25 and 23 mg.L-1; chemical oxygen demand: 50 and 55 mg.L-1; total suspended solids: 10 and 8 mg.L-1; total Kjeldahl nitrogen: 30 and 31 mg.L-1; and N-ammonia: 27 and 28 mg.L-1. There was no significant difference between the effluent concentrations from the planted and unplanted units for most of the evaluated constituents.

Role of vegetation (Typha latifolia) on nutrient removal in a horizontal subsurface-flow constructed wetland treating UASB reactor-trickling filter effluent.

The main objective of the work is to characterize the role of plants in a constructed wetland in the removal of nitrogen (N) and phosphorus (P). The experiments were carried out in a full-scale system in the city of Belo Horizonte, Brazil, with two parallel horizontal subsurface-flow constructed wetland units (one planted with Typha latifolia and one unplanted) treating the effluent from a system composed of an upflow anaerobic sludge blanket reactor and a trickling filter (TF). Each wetland unit received a mean flow of approximately 8.5 m³ d⁻¹ (population equivalent around 60 inhabitants each), with a surface hydraulic loading rate 0.12 m³m⁻²d⁻¹. The experiments were conducted from September 2011 to July 2013. Mean effluent concentrations from the wetlands were: (a) planted unit total nitrogen (TN) 22 mg L⁻¹, ammonia-N 19 mg L⁻¹, nitrite-N 0.10 mg L⁻¹, nitrate-N 0.25 mg L⁻¹, P-total 1.31 mg L⁻¹; and (b) unplanted unit TN 24 mg L⁻¹, ammonia-N 20 mg L⁻¹, nitrite-N 0.54 mg mL⁻¹, nitrate-N 0.15 mg L⁻¹, P-total 1.31 mg L⁻¹. The aerial part of the plant contained mean values of 24.1 gN (kg dry matter)⁻¹ and 4.4 gP (kg dry matter)⁻¹, and the plant root zone was composed of 16.5 gN (kg dry matter)⁻¹ and 4.1 gP (kg dry matter)⁻¹. The mean extraction of N by the plant biomass was 726 kgN ha⁻¹y⁻¹, corresponding to 17% of the N load removed. For P, the extraction by the plant biomass was 105 kgP ha⁻¹y⁻¹, corresponding to 9% of the P load removed. These results reinforce the reports that N and P removal due to plant uptake is a minor mechanism in horizontal subsurface-flow constructed wetlands operating under similar loading rates, typical for polishing of sanitary effluent.