Post-treatment of anaerobic filters on intermittent sand filters : performance in critical operation

Author(s)

Daniel Augusto Camargo Bueno

• Document type: Master's Dissertation
• Defense date: 2017
• Advisor: Adriano Luiz Tonetti

Abstract

The lack of simplified methodologies for wastewater treatment, which are applicable to the unique conditions of small communities, has resulted in worsening problems of national importance, since in many cases their untreated effluents are dumped into water bodies. This study aims to the performance and operation of a sewage treatment prototype consisting by a linear combination of upflow anaerobic filters filled with coconuts shells (Coco nucifera) followed by intermittent sand filters. The research was divided in four experimental stages called Analytical Periods (1st, 2nd, 3rd and 4th AP), in which it was used different Hydraulic Retention Times (HRT) in the Anaerobic Reactors (AR) of 24, 12, 8 and 4 hours for their inversely proportional Surface Application Rates (SAR) of 200, 400, 600 and 1,200 L.m-2.day-1 in the intermittent sand filters (ISF). The objective was to evaluate the removal potential or transformation of organic compounds, solids and nutrients, as well as considering the efficiency levels, the frequency of maintenance and the principles of operation and clogging of the combined anaerobic-aerobic system. Physical and chemical parameters were statistically evaluated using the Kruskal-Wallis test at a 5% trust level. The results showed that in lowers SAR (200 and 400 L.m-2.day-1) the ISF with additional aeration tube had greater solids removal and nitrification, however, there were no statistical differences regarding to the removal of COD and BOD, but it was shown an optimization in the reduction of the average diameter of organic particles. On the other hand, at higher SAR (600 and 1,200 L.m-2.day-1) in what concerns about the depurative capacity, there were no statistically significant differences between the ISF with and without the sub-surface aeration tube. In view of the multiple operating conditions (1st, 2nd, 3rd and 4th AP), the performance analysis of the AR-ISF system units showed that AR reached average COD removal of 83, 73, 67 and 63%, respectively to Organic Loading Rates (OLR) of 0.8, 2.2, 3.4 and 8.1 kg COD.m-3.day-1, whereas for the ISF, the removal rates were 71, 84, 81 and 57% for Organic Surface Application Rates (OSAR) of 27, 108, 221 and 590 g COD.m-2.day-1. That is, even under critical operating conditions it was possible to maintain the high levels of efficiency in the AR-ISF system. Removal of SST of the AR was ~90% for all the AP due to their filling material, but for the ISF it was observed a decreasing removal of 84, 94, 79 and 27%, probably, this is result of the greater brittleness in the polishing of increasing loading rates of SST. Finally, the nitrification mesuared by the Conversion Rates of TKN to nitrate, presented a gradual decrease with an increase in SAR (95, 88, 45 and 12%). So, the ISF was unable to operate at critical rates, mainly due to the reduction in its useful life time (AU)

• FAPESP's process: 13/14853-5 - Wastewater treatment by anaerobic filters operated in multiple hydraulic retention times followed by sand filters
• Grantee: Daniel Augusto Camargo Bueno
• Support type: Scholarships in Brazil - Master