The performance of a pilot scale sewage treatment system composed of an upflow anaerobic sludge blanket (UASB) digester and a sequencing batch activated sludge reactor (SBR) is described. The system constitutes a simple, economic, and compact treatment option and is able to produce consistently a final effluent quality that is equal or better than that of a conventional activated sludge plant. The entire treatment system had a retention time of only 9h and an average operational temperature of 25 degrees C. Due to the efficient anaerobic pre treatment the aerobic sludge production was low and could easily be accommodated for stabilisation in the UASB reactor. The system exhibited excellent operational stability with full nitrification for aerobic sludge ages longer than 9 days. At shorter sludge ages there was excessive wash out of sludge particles and the sludge mass could not be maintained in the SBR reactor. Sludge settleability was good throughout the experimental investigation period of one year. The reduction of the reactor volume and oxygen consumption was more than 50% compared to conventional activated sludge. The anaerobic excess sludge had a high concentration and good stability so that its dewatering and final disposal was a relatively minor problem.
This study investigated the potential of laboratory- scale columns of immobilized micro-algae to disinfect effluents using thermo-tolerant coliforms (TTC) as a model system. Cells of a Chlorella species isolated from a waste stabilization pond complex in Northeast Brazil were immobilized in calcium alginate, packed into glass columns and incubated in contact with TTC suspensions for up to 24 hours. Five to six log removals of TTC were achieved in 6 hours and 11 log removals in 12 hours contact time. The results were similar under artificial light and shaded sunlight. However little or no TTC removal occurred in the light in columns of alginate beads without immobilized algae present or when the immobilized algae were incubated in the dark suggesting that the presence of both algae and light were necessary for TTC decay. There was a positive correlation between K(b) values for TTC and increasing pH in the effluent from the immobilized algal columns within the range pH 7.2 and 8.9. The potential of immobilized algal technology for wastewater disinfection may warrant further investigation.
The system consists of a partially aerated facultative pond with a polished area that treats the effluents of a soft drink industry in Brazil. This work concerns on the study of the longitudinal distribution as well as the analysis of the vertical profile of the main control parameters which exerts a direct influence on the metabolism of the system.
The results show the existence of a horizontal thermal gradient between aerated and polishing zones, which is more intense at the surface of the first 40 metres. The vertical profile did not identify a tendency to thermal stratification. The constant gradient vertical of 0.1°C in the aerated and polishing zones characterizes an almost isothermal condition.
The decrease of the effluent pH values was observed in the bottom layer of the pond. This indicates that the anaerobic digestion on the sedimented sludge incorporates acids in the liquid mass.
The dissolved oxygen vertical distribution presents negative clinographic profile. The isolines in the aerated zone indicate good efficiency of oxygen transfer. In the polishing zone, concentrations above 2.0 mg/l were observed down to a depth of 1 m, possibly caused by photosynthetic activities.
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