Parametrização de daos fundamentais em lagoas de polimento operadas em regime de bateladas sequenciais visando a remoção de nutrientes.

Abstract

In this research, the use of Sequential Batch Polishing Ponds (SBPP) was studied in the post-treatment of the UASB reactor. The variation of depth and average temperature on the performance of the UASB+SBPP system was investigated. Four ponds were used: PP1, PP2, PP3 and PP4, with depths of 0.20, 0.40, 0.60 and 1.00 m, respectively. It is operated in the Hot Period (HP) (between September and May) with an average temperature of 25°C, and the Cold Period (CP) (between June and August) with an average temperature of 21°C in city of Campina Grande/PB. The objective of this work was to determine and parameterize fundamental data in SBPP, analyzing the influence of operational conditions such as depth and temperature, in order to enable the development of predictive models, to facilitate the optimized design of these systems based on nutrient removal. Initially, the influence of depth and average temperature on system performance was analyzed, comparing the results with bibliographic data on Stabilization Pond Systems (SPS), as well as with the use of Continuous Flow Polishing Ponds (CFPP) in the UASB post-treatment. The efficient anaerobic treatment allowed the elevation of the pH in the SBPP, regardless of the period of the year, and the process was favored in PP1, PP2 and PP3, with the best performance during the HP, resulting in a lower HTR, thus, demanding a smaller area. It was verified that the UASB+SBPP system needs an area close to the UASB+CFPP system in the HP and similar to the SPS in the CP. Having the advantage of nutrient removal, which in these systems is not high. Subsequently, the transfer constants of volatile compounds were determined since the exchange of compounds with air is important because they affect the pH and the availability of dissolved oxygen in LPs. It has been shown that the transfer kinetics of compounds is governed by Fick's law. After obtaining the constants, we proceeded to develop a predictive model of pH variation and ammonia desorption in SBPP. To validate the model, tests were carried out in the two conditions of average temperature and in the four lakes with different depths. The model was validated by the good correspondence between simulated and experimentally obtained values in all cases. For the HP, the model stood out, presenting a high linear correlation, with R2 greater than 0.90 for all lakes. As for the CP, the smallest R2 obtained was 0.74 for the four lakes. Thus, the proposed model is adequate to describe pH variation and ammonia desorption in SBPP. Therefore, it is possible to determine the desired minimum pH for the desorption of ammonia and, in this way, obtain with good precision the HTR necessary to reach this pH. As for phosphorus, an empirical model based on thermodynamic equilibrium was developed. It was found that it is possible to obtain a concentration (<1.0 mgP.L-1) when the pH in the pond reaches values close to 9.5 regardless of the temperature conditions. The empirical model developed makes it possible to correlate the logarithm of phosphorus concentration and the pH in SBPP, which can be used to calculate the expected pH and thus have a good approximation of the desired concentration of phosphorus. Thus, it is concluded that when using the UASB+SBPP system, it is possible to obtain an effluent with superior quality than that of the SPS and UASB+CFPP, especially with regard to the removal of nutrients. Finally, the empirical model of phosphorus removal helps to determine the desired pH and thus dimension the system based on such data for phosphorus removal.