Desempenho de um sistema wetland no tratamento de um córrego afluente ao açude de Bodocongó: segundo ano de funcionamento.

Abstract

The treatment of polluted surface water by simple and economic methods is becoming more and more necessary for the survival of rivers and lakes as well as it presents an opportunity of reusing these waters for irrigation. With this purpose the present research was carried out at Campus II of the Federal Paraiba University (Campina Grande, Paraiba, Brazil), to evaluate an artificial wetland system using Typha spp. The system consisted of 10 Brasilit tanks of 250 L, filled with small stone pieces ( 19 mm) and was fed in batch with stream water, that passes through Campus II of this University, with calculated discharge for a hydraulic detention of 5 and 10 days and having a subsurface flow. In 8 of these tanks 8 propagulos of Typha spp were planted while the other two tanks having no macrofitas were used as controls. The efficiency of the system was evaluated in terms of physical, chemical and biological water quality parameters measured for affluent and effluent water of the tanks. The statistical analysis of the results was made on two data groups: one that obtained along with six months of the preset research work ( January to June 2001) and the other obtained during first year of the work ( January to December 2000 ), making a total of eighteen months. The results showed that the system presented significant efficiency for the water purification. For the two periods of the water hydraulic detention the verified mean removals in the last six months were: 82 and 89% turbidity; 83 to 88% biochemical demand of oxygen BOD5; 100% ammoniacal nitrogen; 84 to 86% total phosphrorus; 96% of the soluble ortophosphate and 99% of feacal coliforms. The temperature and the pH stayed practically constant, while other parameters suffered higher increments as: electric conductivity (83 to 106%), bicarbonates (64 to 90%), chlorates (134 to 220%), sodium (165 to 228%), calcium (96 to 114%), magnesium (103 to 141%), total alkalinity (67 to 92%) and total hardness (92 to 111%). A comparison of these results with those of previous 12 months, especially corresponding to similar climatic period (first semester) it can be said that the performance of the system improved along with time with the growth of the plants and their radicule system. The variance analysis at 5% level of significance showed differences for the following parameters: total solids, ammoniacal nitrogen, nitrates, phosphorous, feacal coliforms and estreptococos coliforms. The Tukey test also applied to these two periods did not indicate any significant difference for the effluents of the vegetated tanks for the hydraulic detention time of 5 and 10 days on the variables as: electrical conductivity, turbidity, pH, alkalinity, hardness, BOD5, ammoniacal nitrogen, total phosphorous; feacal coliforms and estreptococos eoliforms. These effluents when compared with those of controle tanks, showed significant differences for: electrical conductivity, bicarbonate, sodium, calcium, magnesium, hardness, coliforms and estreptococos feacal. It is concluded that the surface waters contaminated with domestic drain can be treated through the constructed wetlands use with 5 days hydraulic detention time. These systems are characterized by their construction simplicity and maintenance and presents an alternative for the better utilization of the scarce hydraulic resources of semi-arid region of Northeast of Brazil.