Abstract
This work aims to investigate the influence of polishing ponds (PP) depth on the post-treatment of sanitary sewers. Two treatment systems were designed and monitored. One system was an upflow anaerobic sludge blanket (UASB) rector and intermittent flow sand filter; followed by a PP of 0.20 m depth with low superficial application rate (24.9 kgBOD5.ha-1.day-1), high sunlight incidence (597 Wm-2) and enough biological carbon dioxide used to raise the average pH to 9.6, ensure an average removal of 81% orthophosphate and concentration of Escherichia coli lower than 103UFC/100 ml, which are the meeting requirements for unrestricted irrigation. The other system was a UASB followed by two PPs operated in parallel, at 0.20 and 0.60 m depths. The 0.20 m PP depth removed 80% of total Kjeldahl nitrogen, 53% of total phosphorus and 44% of orthophosphate. The 0.60 m pond depth showed low nutrient removal and a poor E. coli removal efficiency, 98.33% equivalent to 2 logs units. The ponds were fed by continuous systems. Key words: Nutrient removal, polishing ponds, disinfection, sunlight.
Highlights
The setup of a upflow anaerobic sludge blanket (UASB) reactor followed by a polishing pond is highly consolidated, mainly at a tropical climate region and in developing countries like Brazil
One system was an upflow anaerobic sludge blanket (UASB) rector and intermittent flow sand filter; followed by a polishing ponds (PP) of 0.20 m depth with low superficial application rate (24.9 kgBOD5.ha-1.day-1), high sunlight incidence (597 Wm-2) and enough biological carbon dioxide used to raise the average pH to 9.6, ensure an average removal of 81% orthophosphate and concentration of Escherichia coli lower than 103UFC/100 ml, which are the meeting requirements for unrestricted irrigation
Two experimental treatment systems were built to treat the raw sewage (RS) from the CAGEPA’s interceptor: the first system was a compact station (UASB reactor coupled to a decanter followed by an intermittent flow sand filter); and the second system was the combination of UASB reactor and decanter
Summary
The setup of a UASB reactor followed by a polishing pond is highly consolidated, mainly at a tropical climate region and in developing countries like Brazil. The main nitrogen removal mechanisms used for the domestic sewage treatment in stabilization ponds are: Ammonia volatilization, biological nitrogen uptake, nitrification, denitrification, dead biomass sedimentation and sludge layer accumulation (Craggs, 2005). The operational and environmental conditions in which the removal occurs need more studies (Valero et al, 2010), because there are those who affirm that under favourable conditions for the algae growth, the main nitrogen removal occurs by algae absorption, despite the high pH values (Valero and Mara, 2007)
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