Parabens in aerobic granular sludge systems: Impacts on granulation and insights into removal mechanisms.

This work assessed the impact of methylparaben, ethylparaben, propylparaben, and butylparaben (200 µg L-1 each) on the granulation process as well as on the organic matter and nutrient removal of an aerobic granular sludge (AGS) system (6-h cycle). Additionally, some insights into the main paraben removal mechanisms were provided. In the presence of parabens, aerobic granules with good settleability, but with fragile and irregular structure, were grown. No significant effect of parabens on organic matter (>90%) and nitrogen (~70%) removal was evidenced. On the other hand, phosphorus removal was slightly impaired, although high removal efficiencies (~70%) were reached. High paraben removal efficiencies were achieved (>85%) in the AGS system, with methylparaben being the most recalcitrant compound. Concerning the removal mechanisms, biotransformation was the main mechanism in the removal of all parabens (85.5% for methylparaben and 100% for the others), whereas, apparently, adsorption played a role only in the removal of methylparaben. In addition, this compound was also suggested as a probable intermediate of the degradation of the larger alkyl-chain parabens. Lastly, regarding the microbial community, with the exception of Mycobacterium, the reactors shared the same genera, which may explain their comparable operational performances. Additionally, some genera that developed more in the presence of parabens may be related to their degradation. Therefore, although antimicrobial agents such as parabens compromised the granule structure, AGS system maintained a good operational performance and showed to be very efficient in paraben removal.

Effect of calcium addition to aerobic granular sludge systems under high (conventional SBR) and low (simultaneous fill/draw SBR) selection pressure.

This paper investigated the effect of calcium addition on the formation and properties of aerobic granules under high (conventional SBR) and low (simultaneous fill/draw SBR) selection pressure. Additionally, the simultaneous removal of carbon, nitrogen, and phosphorus, and the operational stability were assessed. The conventional SBRs showed earlier granule development (20 days) than the simultaneous fill/draw SBRs. The effect of calcium on granulation was more accentuated in conventional SBRs, forming larger granules in a shorter interval of time due to the higher EPS production. Additionally, higher amounts of calcium were found in the EPS matrix, mainly during the formation of granules. The operation regime and the addition of calcium did not affect the removal of carbon, nitrogen, and phosphorus. However, they both influenced the granulation time, settleability characteristics, size, and granule composition.

Effects of coal ash supplementation on aerobic granular sludge cultivated in a simultaneous fill/draw sequencing batch reactor / Efeitos da suplementação de cinzas de carvão mineral em lodo granular aeróbio cultivado em reator em batelada sequencial de alimentação/descarte simultâneos

ABSTRACT This study aimed to verify if coal ash, a residue from thermal power plants, could act as a granulation nucleus, cations source, and abrasive element to favor granules formation and stability in aerobic granular sludge (AGS) systems. Two simultaneous fill/draw sequencing batch reactors (SBRs) (R1 and R2) were operated with 6-h cycles, i.e., the filling and drawing phases occurred simultaneously, followed by the reaction and settling phases. R1 was maintained as control, while R2 was supplemented with coal ash (1 g·L-1) on the first day of operation. Granulation was achieved in both reactors, and no significant differences were observed in terms of settleability, biomass retention, morphology, resistance to shear, and composition of the EPS matrix. However, the ash addition did not change the settleability, biomass retention, granule morphology, shear resistance, and extracellular polymeric substances (EPS) content significantly. COD removal was high (≥ 90%), while nitrogen (~50%) and phosphorus (~40%) removals were low, possibly due to the presence of nitrate during the anaerobic phase. With granulation, microbial population profile was altered, mainly at the genus level. In general, the operational conditions had a more considerable influence over granulation than the ash addition. The possible reasons are because the ash supplementation was performed in a single step, the low sedimentation rate of this particular residue, and the weak interaction between the ash and the EPS formed in the granular sludge. These factors appear to have decreased or prevented the action of the ash as granulation nucleus, source of cations, and abrasive element.

RESUMO O objetivo deste estudo foi verificar se a cinza de carvão mineral, um resíduo de usinas termelétricas, poderia atuar como núcleo de granulação, fonte de cátions e elemento abrasivo em sistemas de lodo granular aeróbio (LGA) para favorecer a formação e estabilidade dos grânulos. Dois reatores em batelada sequencial (RBS) (R1 e R2) foram operados em regime de alimentação/descarte simultâneos com ciclos de 6 h, ou seja, as fases de alimentação e descarte do efluente ocorreram simultaneamente, seguidas das fases de reação e de decantação. O R1 foi mantido como controle, enquanto o R2 foi suplementado com as cinzas (1 g·L-1) no primeiro dia de operação. A granulação foi alcançada em ambos os reatores, não havendo diferenças marcantes em termos de sedimentabilidade, retenção de biomassa, morfologia do grânulo, resistência ao cisalhamento e conteúdo de substâncias poliméricas extracelulares (SPE). A remoção de DQO foi alta (≥ 90%), enquanto as remoções de nitrogênio (~50%) e fósforo (~40%) foram baixas, possivelmente pela presença de nitrato na fase anaeróbia. Após a granulação, o perfil da comunidade microbiana mudou, especialmente em termos de gênero. Globalmente, as condições operacionais tiveram maior influência sobre a granulação do que a adição das cinzas, possivelmente porque elas só foram adicionadas uma vez e possuem baixa velocidade de sedimentação, bem como devido a uma fraca interação das cinzas com a matriz de SPE formada no lodo aeróbio. Esses fatores podem ter diminuído, ou mesmo impedido, a ação das cinzas como núcleo de grânulo, fonte de cátions ou elemento abrasivo.

Effect of calcium addition on the formation and maintenance of aerobic granular sludge (AGS) in simultaneous fill/draw mode sequencing batch reactors (SBRs).

This work investigated the effect of Ca2+ (100 mg L-1) addition on the formation and maintenance of aerobic granular sludge in a simultaneous fill/draw mode sequencing batch reactor (SBR), operated with a low liquid upflow velocity (0.92 m h-1), in order to verify if Ca2+ presence compensates the low selection pressure imposed. Additionally, carbon and nutrients removals, granules characteristics and microbial community were evaluated. For this, two SBRs (R1, control, and R2, Ca2+-supplemented) were operated (6-h cycle). In general, Ca2+ supplementation affected positively the sludge settleability, although a larger fraction of inert solids was found in the granules. The total extracellular polymeric substances were the same for both reactors, and no remarkable differences were observed between their polysaccharides and proteins contents. Overall, Ca2+ addition in a simultaneous fill/draw mode SBR neither accelerated the granule formation nor improved the operational performance. The microbial community structure, especially in terms of bioactivity, was not affected as well. Therefore, the effect of divalent cations might be more pronounced in conventional SBRs, in which the selection pressure is higher.

Effects of carbon source on the formation, stability, bioactivity and biodiversity of the aerobic granule sludge.

Three aerobic granular sludge systems were operated as sequencing batch reactors (SBR) with acetate, ethanol and glucose as carbon source. The SBR cycle was 6 h, with an anaerobic phase followed by an aerobic phase. The acetate granules (>1.5 mm) had the greatest microbial diversity and better results in terms of removal efficiency for carbon and nutrients (TN ≈ 72% and TP ≈ 42%) and also in the resistance tests. However, partial disintegration was observed. On the other hand, when ethanol was the substrate, the granules were stable, good nitrogen removal was achieved (TN ≈ 53%), but phosphorus removal was not favored (TP ≈ 31%). Glucose presented the lowest efficiency values for nitrogen (TN ≈ 44%) and phosphorous removal (TP ≈ 21%), and the granules formed (<1 mm) had the lowest microbial diversity. Therefore, the carbon source had a high impact on the characteristics of the granules.

Seleção de substratos padrões para ensaios respirométricos aeróbios com biomassa de sistemas de lodo ativado / Standards substrate selection for aerobic respirometric tests with biomass of activated sludge systems

Nesta pesquisa investigou-se a influência de diferentes substratos na determinação da taxa específica de consumo de oxigênio de biomassa com cultura mista heterotrófica e autotrófica nitrificante, visando à caracterização do substrato mais adequado no desenvolvimento de ensaios respirométricos aeróbios. Foram utilizadas diferentes biomassas derivadas de quatro variantes de sistemas de lodo ativado. Os grupos heterotróficos e autotróficos nitrificantes foram avaliados em relação à sua velocidade de consumo dos substratos testados, sendo utilizada a técnica da respirometria aeróbia aberta semi-contínua de distintos pulsos, descrita em Van Haandel e Catunda (1982). Um respirometro automático acoplado a um computador foi utilizado em todos os testes respirométricos. Para identificar a taxa de consumo dos organismos heterotróficos, os substratos de fonte de carbono selecionados foram acetato de sódio (C2H3NaO2), acetato de etila (C4H8O2), etanol (C2H6O), glicose (C6H12O6) e fenol (C6H6O). Para o grupo autotrófico nitrificante foram utilizados bicarbonato de amônio (NH4HCO3), cloreto de amônio (NH4Cl) e nitrito de sódio (NaNO2). Os resultados referentes ao grupo heterotrófico indicaram significativa diferença da taxa metabólica desses organismos na utilização dos substratos avaliados, exercendo maiores taxas de consumo de oxigênio para o acetato de sódio, enquanto para o grupo nitrificante o bicarbonato de amônio mostrou-se mais adequado. Comparando todos os sistemas estudados, observa-se a mesma tendência de maior biodegradabilidade ou afinidade aos substratos acetato de sódio e bicarbonato de amônio.

The influence of different substrates on the oxygen uptake rate (OUR) of sludge composed of heterotrophic and autotrophic bacteria was determined, in order to characterize the most suitable substrate for aerobic respirometric tests was the object of this research. Four different sludges were used, generated in variants of activated sludge systems. The OUR of the heterotrophic and autotrophic (nitrifying) bacteria was determined after additions of the different tested substrates by the technique of open semi-continuous aerobic respirometry, described in Van Haandel and Catunda (1982). An automated respirometer coupled to a computer was used in all respirometric tests. The OUR of the heterotrophic organisms, substrates was determined after adding separately sodium acetate (C2H3NaO2), ethyl acetate (C4H8O2), ethanol (C2H6O), glucose (C6H12O6) and phenol (C6H6O). For the autotrophic nitrifying group ammonium bicarbonate (NH4HCO3), ammonium chloride (NH4Cl) and sodium nitrite (NaNO2) were used as substrates. The results of the tests with the heterotrophic group of bacteria showed that significant differences in the OUR and hence in the metabolic rate by these organisms when the selected substrates were used, with sodium acetate exerting the highest OUR. For the group of nitrifying bacteria ammonium bicarbonate was the most appropriate substrate. The tendency of highest biodegradability and substrate affinity for sodium acetate and ammonium bicarbonate was observed for all four sludges from the different systems that were used in the investigation.