Abstract
ABSTRACT Nitrogen is a very important parameter for water pollution control since nitrification implies in aquatic environment oxygen consumption and some nitrogen forms are toxic. In the present study, an optimization model was developed and applied aiming at simultaneous organic matter and nitrogen compounds minimum removal efficiencies determination. A water quality model and the Genetic Algorithm Metaheuristic were associated in order to solve the optimization problem. The estimated minimum efficiencies conditioned the sewage treatment systems pre-selection. The study area was the Pardo River watershed (Espírito Santo State, Brazil). The results indicate that the treatment systems need to be more efficient in ammonia removal when the treated effluents disposed in watercourses that present high pH values because ammonia toxicity increases with pH. Considering the boundary conditions assumed in this study, the pre-selection process indicated activated sludge systems, submerged aerated biofilter with nitrification, or with biological nitrogen removal, for Ibatiba city. Simpler systems such as primary treatment with septic tanks, stabilization ponds, UASB reactors and biological filters were pre-selected for Santíssima Trindade and Nossa Senhora das Graças towns.
Highlights
Effluents treatment before discharge, either individual or collective, is the main strategy for water bodies’ pollution control
The ammonia compounds toxicity in freshwater bodies is influenced by temperature, salinity and pH values (REIS; MENDONÇA, 2009), the present study considered only the effect of pH, since the environmental quality standards established in Brazil did not include temperature and/or salinity effects
From water quality modeling combined with an optimization technique, aiming at Biochemical Oxygen Demand (BOD) and nitrogen compounds minimum treatment efficiencies determination and sewage treatment systems pre-selection within a river basin, the main conclusions can be summarized as follows:
Summary
Either individual or collective, is the main strategy for water bodies’ pollution control. The required treatment level depends on effluent characteristics, receiving watercourse class and self-purification capacity. Treatment cost can be as important as the water quality goals to be achieved. High investments in pollution control may not be feasible in developing countries (CHO; SUNG; HA, 2004). An ideal treatment plant should be associated with minimum contaminant discharges, minimum treatment costs, and maximum sociocultural benefits (ZENG et al, 2007). Watercourses self-purification capacity studies become relevant allies of the decision-making processes associated to the effluent treatment systems selection. Watercourses self- depuration consideration can provide significant treatment costs reduction
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