Caracterização e comportamento de uma série de lagoas de polimento tratando esgotos sanitários / Characterization and performance of a polishing pond series treating domestic wastewater

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

This work, conducted in Viçosa MG, presents the results of five years monitoring of a domestic wastewater treatment system including an anaerobic reactor (UASB) plus a submerged aerated biofilter (real scale), followed by a three to four shallow polishing / maturation ponds series (pilot scale, h ≤0,90 m), with operational flexibility in terms of depth and hydraulic retention time. The pond system took up the performance oscillations of the pre-treatment unities (UASB + BF), and the complementary organic matter removal took place, essentially, in the first pond, achieving average BOD and filtered COD removal efficiencies of 12 50% and 50 -60%, respectively. The Minas Gerais State BOD standard for discharge into water bodies (60 mg / L) was achieved, most of the time, in the first pond; the third and the fourth ponds did not contribute for BOD and COD removal anymore. The results suggested that ammonia volatilization is the main mechanism of nitrogen removal in the pond system. It well absorbed the ammonia increase in the pre-treatment unities, leading to a gradual but intense removal along the pond series, achieving average ammonia removal efficiencies within the range of 60 -90%. Under the experimental conditions of this study, the Brazilian standard for ammonia discharge into water bodies (20 mg NH3 / L), and more strict water quality criteria for aquaculture were achieved with hydraulic retention times of 15 and 35 days, respectively. On the other hand phosphorus removal was shown to be limited. All over the period of this study, E.coli removal in the UASB + BF system (mainly in the UASB reactor) was around 0.5 log unities, followed by an intense decay along the pond series. Under the experimental conditions of this study the WHO guidelines for unrestricted irrigation (103 E.coli / 100 mL), and for restricted irrigation and aquaculture were achieved within hydraulic retention times of 17 and 11 days, respectively. The results confirm that shallow polishing / maturation ponds are fully able to produce effluents in accordance with the Brazilian standard for ammonia discharge into water bodies and with the bacterial WHO guidelines for irrigation. In addition, the results provide relevant information for planning and designing polishing ponds: air x water temperature, organic matter removal coefficients, nitrogen removal coefficients, bacterial decay coefficients, and their variation along the pond series, pH values, and suitable ranges of hydraulic surface loading, ponds depth and hydraulic retention times. pH values were always above 7.0 along the whole water column and above 7.5 at mid depth. The following average pH values increasing (measured at the water surface and at mid depth) were recorded along the pond series: (i) pond 1 to pond 2: 3 - 5%; (ii) pond 2 to pond 3: 5 - 7%; (ii) pond 3 to pond 4: no increase - 2%. The calculated ammonia removal coefficients were virtually constant along the pond series, around 0.0058 d-1. In general, E. coli decay coefficients were quite high and increased along the pond series: average values of 0.98 d-1 in the first pond, followed by 13% and 22% increasing in the second and the third ponds, respectively. The fourth pond did not substantially add to additional removal.

ASSUNTO(S)

tratamento tratamento de aguas de abastecimento e residuarias domestic wastewater lagoas de polimento polishing pond esgotos sanitários treatment

ACESSO AO ARTIGO

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