Aplicação da dinâmica de sistemas na implementação de modelo computacional para estimação da qualidade do efluente de lagoas facultativas

Abstract

This paper presents the preliminary results of the development of a computer model to predict the quality of the facultative pond effluent proposed by FRITZ (1985) with a system dynamics approach, using the software VenSim PLE ®. The model considers the mass balance applied in a complete mixing reactor, consisting of the simultaneous resolution of twelve differential equations in time for the determination of effluent concentrations of crude COD, soluble COD, dissolved oxygen, Organic and Inorganic Nitrogen, Total Kjeldhal Nitrogen, Ammoniacal Nitrogen, Organic and Inorganic Phosphorus, Alkalinity, Hydrogenionic Concentration (pH). For its calibration there was the division into two stages: verification and validation. For the verification, the following parameters were simulated: soluble COD, Ammoniacal Nitrogen, Total Phosphorus, pH, DO and temperature, were compared with the results obtained by Silva (1982) for a pilot scale facultative lagoon located in Campina Grande (PB), which operates as a complete mixing reactor and whose sampling were composed. The results of the simulations obtained for the verification were considered satisfactory, standing out the soluble COD, OD and temperature, which were similar to those obtained in the field. For validation, the following parameters were analyzed: crude COD, soluble COD, Kjeldhal Total Nitrogen, Ammoniac Nitrogen, pH, OD and Alkalinity, which were compared with the results obtained by Pedrelli (1997) for a full scale facultative lagoon located in Balneário Camburiú (SC). The results of the simulations obtained for Alkalinity and pH were the ones that presented the greatest similarity with those obtained in the field, soluble COD had satisfactory results, but for the other parameters the simulation results were slightly higher than those observed. Such variations may be associated to disregarding the variability of the affluent quality in the facultative pond, the possibility of compartmentalization of the liquid volume, which would remove the model from the complete mixing condition, as well as the fact that the samples used in the validation were obtained punctually and not in a compound way.