RESUMO
This study investigated the effect of magnetite nanoparticles (Np-magnetite) added to a pilot-scale sequencing batch reactor (SBR) treating domestic wastewater, to improve aerobic granular sludge (AGS) formation and the effects of granule disintegration. Np-magnetite additions (75 mg L-1) were made during the start-up of the reactor and repeated after 100 and 170 days, when granule disintegration was observed. From the first Np-magnetite addition, SVI5 was reduced from 1315 to 85 mL g-1. The granular biomass was observed on the 56th day, when 57% of the granules presented diameters bigger than 212 µm. The 100-day disintegration episode disturbed the granular biomass, reducing the volatile suspended solids by 51%, increasing the SVI values to above 200 mL g-1. Np-magnetite addition recovered all the granular biomass parameters to the values observed before disintegration. The treatment efficiency was stable during operation of the reactor for nutrients (52.8 ± 23.4% NH4+-N; 54.5 ± 12.2% PO43--P) and carbonaceous organic matter (71.7 ± 12.7% BOD5; 77.5 ± 10.0% CODt). Np-magnetite addition changed the microbial community of the granular sludge, analysed via high-throughput 16S RNA sequencing, and recovered the treatment efficiency previously disturbed by the disintegration processes. These results indicate the potential of Np-magnetite as an agent for sludge aggregation in an aerobic granular reactor.
Assuntos
Reatores Biológicos , Nanopartículas de Magnetita/química , Águas Residuárias/microbiologia , Purificação da Água , AerobioseRESUMO
Aerobic granular sludge (AGS) is a microbial biofilm self-aggregation, which is effective for nutrient and pollutant removal, through the development of dense microbial layers bound together with extracellular polymeric substances (EPSs). However, long start-up times and granule disintegration are still challenges ahead. An array of external additives, including ion chelating agents, sludge-based enhancers, and magnetic influence have been tested to overcome these barriers. The application of such additives may promote enhanced EPS production, neutralization of charges on the bacterial surface, acts as a core-induced agent, or as a bridge to connect EPSs and cell surfaces. Although additives may improve the granule formation without reducing treatment efficiencies, there are still environmental concerns due to the fate and toxicity of discharged excess sludge. This mini-review identifies an array of external additives and their mechanisms to improve granulation properties, and proposes discussion about the technical and economic viability of these additives. KEY POINTS: ⢠Additives reduce granulation time and repair granule disintegration. ⢠Biopolymer-based additives fulfill technical and environmental requirements. ⢠Sludge-based additives are cheap and in line with the resource recovery concept. ⢠The need for environmental-friendly additives for aerobic granular sludge process. ⢠External additives affect granular biomass size distribution.
Assuntos
Biopolímeros/farmacologia , Esgotos/microbiologia , Eliminação de Resíduos Líquidos , Aerobiose , Bactérias/efeitos dos fármacos , Bactérias/metabolismo , Biofilmes/efeitos dos fármacos , Biofilmes/crescimento & desenvolvimento , Biomassa , Reatores Biológicos , Quelantes/farmacologia , Matriz Extracelular de Substâncias Poliméricas/efeitos dos fármacos , Matriz Extracelular de Substâncias Poliméricas/metabolismo , Nanopartículas de Magnetita , Esgotos/químicaRESUMO
The formation and application of aerobic granules for the treatment of real wastewaters still remains challenging. The high fraction of particulate organic matter (XS) present in real wastewaters can affect the granulation process. The present study aims at understanding to what extent the presence of XS affects the granule formation and the quality of the treated effluent. A second objective was to evaluate how the operating conditions of an aerobic granular sludge (AGS) reactor must be adapted to overcome the effects of the presence of XS. Two reactors fed with synthetic wastewaters were operated in absence (R1) or presence (R2) of starch as proxy for XS. Different operating conditions were evaluated. Our results indicated that the presence of XS in the wastewater reduces the kinetic of granule formation. After 52 d of operation, the fraction of granules reached only 21% in R2, while in R1 this fraction was of 54%. The granules grown in presence of XS had irregular and filamentous outgrowths in the surface, which affected the settleability of the biomass and therefore the quality of the effluent. An extension of the anaerobic phase in R2 led to the formation of more compact granules with a better settling ability. A high fraction of granules was obtained in both reactors after an increase of the selection pressure for fast-settling biomass, but the quality of the effluent remained low. Operating the reactors in a simultaneous fill-and-draw mode at a low selection pressure for fast-settling biomass showed to be beneficial for substrate removal efficiency and for suppressing filamentous overgrowth. Average removal efficiencies for total COD, soluble COD, ammonium, and phosphate were 87 ± 4%, 95 ± 1%, 92 ± 10%, and 87 ± 12% for R1, and 72 ± 12%, 86 ± 5%, 71 ± 12%, and 77 ± 11% for R2, respectively. Overall our study demonstrates that the operating conditions of AGS reactors must be adapted according to the wastewater composition. When treating effluents that contain XS, the selection pressure should be significantly reduced.