Lagoas de polimento como pós-tratamento de reatores UASB: remoção de material orgânico

Abstract

The sequential batch regime in polishing ponds has two important advantages in comparison to continuous flow ponds: (1) it greatly reduces the time required for bacterial removal and (2) it opens the possibility of efficiently removing the nutrients nitrogen and phosphorus. However, the applicability of the sequential batch regime is limited by the concentration of organic material of the pond influent: if this concentration is too high, the oxygen demand exceeds the oxygen generation capacity in the pond and the environment will become anaerobic, which is undesirable: the anaerobic digestion leaves a high concentration of residual organic material. In this context, this work aims to evaluate the removal of residual organic material from the effluent of a UASB reactor in polishing ponds, operated in sequential batch mode. In addition, the influence of the initial concentration of organic material and depth on the performance of the ponds was evaluated. Additionally, the use of inoculum was tested to assess the possibility of increasing the treatment capacity. The operation of polishing ponds in sequential batches allowed efficient removal of organic material, BOD (on average 70%), but the time to reach the minim DBO increased with increasing depth. During the treatment of a batch, the BOD went through a minimum and then increased, presumably due to the production of algae. In all cases, when the organic material concentration applied in the LPBS increased, the concentration of the minimum residual BOD also increased. The elevation of organic material on LPBS did not lead to an anaerobic environment in the ponds. An increase was observed of the dissolved oxygen concentration and pH during the treatment period, although lower for greater depths and higher applied charges. With respect to the use of inoculum to improve the post-treatment in LPBS, it was viable in the LPBS with a depth of 0,2 m and 20% of inoculum. The inoculation did not lead to an increase of the treatment capacity of LPBS with a depth of 0,4 m.