Análise de fatores que influenciam a proliferação de cianobactérias e algas em lagoas de estabilização.

Abstract

Cianobacteria bloom in aquatic water bodies are main concern to the Water companies due to their production and liberation of neuro and hepatic toxins which can affect human health when water is used for several activities. This phenomenon is not restricted to clean water bodies but also happens in waste stabilization ponds, a hipereutrophic environment and is favored by certain climatic and operational conditions. This research was carried out to investigate the causes of excessive cianobacteria growth in some stabilization ponds in Paraíba State - Northeast Brazil, particularly those of Sapé, Monteiro, Sousa and Cajazeiras municipalities. The literature emphasizes that different intervals of N/P rate allows cianobacteria bloom. In this work N/P rate were calculated using different forms of N and P. Wastewater Treatment Plants (WTP) final effluents were monitored from August 2000 to May 2004 with samples analysis carried out at the Laboratory of Environmental Sanitation of the Academic Unit of Civil Engineering - CTRN - UFCG. The variables analyzed were water temperature, pH, dissolved oxygen, electric conductivity, BOD, COD, ammonia, nitrate, soluble orthophosphate, total phosphorous and chlorophyll "a". Municipalities climatic data (precipitation, insolation and air temperature) were supplied by Paraíba State Water Adminístration Agency. Data analyses were carried out using Excel® 2003 available in Microsoft Office with descriptive statistical analysis and multiple correlations. Monitoring data showed that dry and rainy seasons influenced variation of final effluent quality. For raw sewage samples, most values N/P < 10 occurred when ammonia/total phosphorous were used. When ammonia/ soluble orthophosphate was used to estimate N/P rate, most values were in the 10-16 interval. In final effluent samples no matter which nitrogen and phosphorous forms used to calculate N/P rate, the prevailing rate was N/P < 10. Both rates favour algae and cianobacteria intensive growth. Intensive cianobacteria growth were evident in Sapé, Monteiro, Sousa and Cajazeiras WTP due to certain conditions such as iong insolation period, finai effluent, temperature above 25°C and pH around 7,5. The excessive cianobacteria proliferation happened in those systems configurated as primary facultative pond (except Monteiro WTP) and intermittent feeding. Attention must be given to systems with these features in tropical climate as they can favour the excessive growth of those microorganisms particularly in final effluent is discharged into supply water bodies.