Estudo da evolução da camada de lodo da lagoa anaeróbia profunda da pedreira nº 7 do sistema de tratamento de esgotos do Róger na grande João Pessoa-PB.

Abstract

The results presented in this research were obtained from an experimental investigation accomplished at Roger's deep anaerobic pond during the period from March 2005 to November 2005. The pond was developed in a deactivated quarry of calcareous rock exploration located in the pole of sewer treatment in Paraiba River Basin in Joao Pessoa City - PB (7° 10" S; 34° 49" W), Northeast of Brazil. The main objective of this research was the study of the evolution of the sludge layer in an anaerobic pond. The specific objectives were: the study of the distributions of affluent flow; the monitoring of the physicochemical variables in the sewer and in the effluent of the pond; the study of the wastewater drainage speed distribution in the desaerator, to esteem the volume of the accumulated sludge in the pond and to determine its stability. To accomplish these objectives, physicochemical variables of the sewer, effluents from the desaerator and from the anaerobic pond were analyzed; the flow of sewer was monitored in a period of 42 days; samples of sludge from the pond entrance zone and from the pond exit zone had been analyze; the wastewater drainage speed in the desaerator was measured; and an hydrographic survey of the accumulated sludge layer in the pond was made. The average flow of the affluent sewer in the pond was esteemed in 25890 mVd and it represents an increase of 38.8% compared to the one esteemed two years ago. The performance of the pond was inferior to the observed one in studies realized by Arruda (2003), although the efficiencies of removal of BOD5 (67.67%), COD (60.79%) and SS (70.98%) had been reduced for 53.64; 7.12 and 37.70% respectively. The wastewater flow speed in the desaerator is in agreement with the norms of NBR 12209 when only one canal is in operation. With the data from the hydrographic survey it was evidenced that the accumulated sludge layer in Roger's anaerobic pond had a mean thickness of 1.82m and a volume esteemed in 14122.82 m3 , corresponding to 16.7% of the useful capacity of the reactor. The mean hydraulic detention time of Roger's pond was 2.76 days and this value is among the typical limits recommended by the literature for that reactor type. The sludge from the anaerobic pond presents a volatile solid reduction of 5.8%, value that is below the maximum limit of 17.0% recommended by EPA. According to this investigation it was observed that the decrease of the pond efficiency seems to be associated to the progressive increase of sludge layer and the consequent dragging of solids. According to the results presented here it becomes evident that to recover the efficiency of the anaerobic pond it is necessary to take immediate providences to remove, treat and dispose the accumulated sludge.