Influência de agente quelante na formação do lodo granular aeróbio

Abstract

Aerobic granular sludge is a recent and promising biological wastewater treatment technology. The granules are of special importance in the treatment process and are responsible for the simultaneous treatment of organic matter and nutrients. In this sense, studies indicate that divalent cations, such as Ca2+, Mg2+ and Fe3+, are essential for granulation, as the positive charge of the bivalent cations neutralizes the negative charge on the surface of the microbial biomass and on the molecules of extracellular polymeric substances, which are essential for stability of the granules. However, chelating agents, such as ethylenediaminetetraacetic acid (EDTA), used, for example, in the manufacture of cleaning products to reduce water hardness, dissolve calcium precipitates from the granules and destabilize them. The presence of these substances in domestic or industrial wastewater can compromise the stability of the aerobic granule and limit the application of this treatment technology on a full scale. The objective of this work is to evaluate the formation of granular sludge in the presence of synthetic chelating agents and the addition of divalent cations to favor granulation. For this, two reactors were operated in sequential batches on bench scale, in parallel, and the first reactor was fed with synthetic effluent with addition of Ca2+, and the second reactor, in addition to effluent with the same characteristics of the first reactor, had the addition of EDTA. The cycle time will be 720 minutes, with 660 minutes for the reaction. The operation lasted 120 days, with the sedimentation time being gradually reduced, from 60 minutes to 1 minute. It was possible to notice a significant increase in the frequency of particles with diameters greater than 0.2 mm, being considered granules, only after day 75, when the sedimentation time was reduced to 1 minute. Most of the observed granule sizes were were between the diameters of 0.2 and 2.0 mm. For Biological Reactor 1, day 104 showed the highest ratio of granules, with 49.3% frequency inside the reactor; for Biological Reactor 2 this happened on day 99, with 57.5% of granules inside the reactor. The average values of SVI5 and SVI30 were 31.25 and 28.13 mL.g-1, respectively, for Reactor 1; and 27.59 and 26.64 mL.g-1, respectively, for Reactor 2. The sedimentation velocity verified was 16.33 m.h-1 and 12.87 m.h-1, for Reactors 1 and 2, respectively. Results were verified for the removal of organic matter always above 95%, both for COD and BOD. Finally, statistical analyzes showed significant differences only regarding the SVI30/SVI5 ratio and COD removal between treatments, after the granulation period.