BACKGROUND Aerobic granular sludge (AGS) technology has been widely investigated for wastewater treatment. The morphological and structural characteristics of granules and nitrogen pathways have not been fully clarified using real domestic wastewater. To address this issue, microbial community distribution, diversity and functional pathways towards nitrogen conversions in a sequencing batch reactor were investigated. RESULTS Granules (d ∼ 300 µm) were formed with low‐strength domestic wastewater (COD influent < 200 mg CODsoluble L−1). COD and ammonium effluent concentrations (55 mgCOD L−1, 14 mgNH4−‐N L−1) achieved national treatment standards. Nitrite accumulation was observed (16.5 mgNO2−‐N L−1) and N2O emissions (2.8% of nitrogen load) were detected. Granules were composed of protozoa and bacteria, with an outer layer dominated by ammonium‐oxidizing bacteria (AOB) and deeper layers with nitrite‐oxidizing bacteria (NOB) and denitrifiers. Partial nitrification, denitrification via nitrite, nitrifier denitrification, complete and incomplete denitrification pathways were assessed by qPCR. CONCLUSIONS AGS process showed the establishment of partial nitrification in a low‐strength real wastewater condition. The granular system showed N2O emission in a lower range than others known partial nitrification processes. In order to achieve nitrogen removal saving costs in terms of energy and space, engineering wastewater designers can consider AGS as an attractive technology. © 2016 Society of Chemical Industry

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-The following sludge reduction alternatives were tested in wastewater biological reactors: oxic-settling-anaerobic (OSA-process); ultrasonic disintegration (UD); chlorination (CH); 3,3',4',5-tetrachlorosalicylanilide (TCS); and folic acid (FA). Compared to the control system, UD reduced 55% of the sludge production, and greater substrate and nutrient removal efficiency was achieved. CH worsened the sludge settleability and increased the SVI values; the system achieved 25% of sludge reduction. OSA showed 50% and 60% of sludge reduction after 16 and 10 hours under anaerobic conditions, respectively. The observed sludge yield during TCS addition was decreased by 40%, and the sludge settleability worsened. FA presented the highest sludge reduction (75%), and the system improved the nutrient removal efficiency by 30% compared to the control system and maintained the sludge properties. Acute toxicity conducted with Daphnia magna classified the effluent from the sludge reduction systems as non-toxic for discharge into water sources.

NO-production was investigated during nitrogen removal using aerobic granular sludge (AGS) technology. A pilot sequencing batch reactor (SBR) with AGS achieved an effluent in accordance with national discharge limits, although presented a nitrite accumulation rate of 95.79% with no simultaneous nitrification-denitrification. NO production was 2.06 mg L during the anoxic phase, with NO emission during air pulses and the aeration phase of 1.6% of the nitrogen loading rate. Batch tests with AGS from the pilot reactor verified that at the greatest COD/N ratio (1.55), the NO production (1.08 mgNO-N L) and consumption (up to 0.05 mgNO-N L), resulted in the lowest remaining dissolved NO (0.03 mgNO-N L), stripping the minimum NO gas (0.018 mgNO-N L). Conversely, the carbon supply shortage, under low C/N ratios, increased NO emission (0.040 mgNO-N L), due to incomplete denitrification. High abundance of ammonia-oxidizing and low abundance of nitrite-oxidizing bacteria were found, corroborating the fact of partial nitrification. A denitrifying heterotrophic community, represented mainly by Pseudoxanthomonas, was predominant in the AGS. Overall, the AGS showed stable partial nitrification ability representing capital and operating cost savings. The SBR operation flexibility could be advantageous for controlling NO emissions, and extending the anoxic phase would benefit complete denitrification in cases of low C/N influents.

RESUMO Os reatores operados em bateladas sequenciais (RBS) com biomassa granular aeróbia são uma tecnologia compacta e promissora no tratamento de águas residuárias. Porém, sua utilização com esgoto sanitário ainda é um desafio, devido à instabilidade e desintegração dos agregados. O presente trabalho avaliou a granulação da biomassa em um RBS em escala piloto, sem a adição de inóculo, para o tratamento de esgoto sanitário. O estudo foi dividido em três estratégias operacionais com ciclos compostos pelas fases: enchimento, anóxica, aeróbia, sedimentação, descarte e repouso. Trabalhou-se com variações no tempo dos ciclos, 4 horas (estratégias I e II) e 6 horas (estratégia III), e na fase anóxica, 13, 30 e 90 minutos nas estratégias I, II e III, respectivamente. O desenvolvimento dos grânulos ocorreu de forma natural, sem inoculação, e o reator tratou o esgoto sanitário atendendo às exigências nacionais de padrões de lançamento de efluentes. As características do lodo granular aeróbio e o desempenho do reator no tratamento de esgoto melhoraram com o aumento da fase anóxica. Grânulos (200 a 400 µm) compreenderam mais de 80% da biomassa com boas características de sedimentabilidade (a razão entre os índices volumétricos de lodo após 30 e 10 minutos de sedimentação - IVL30/IVL10 - esteve entre 0,7 e 1,0) na estratégia III. As variáveis de maior relevância no processo foram a razão IVL30/IVL10 e a razão entre a demanda química de oxigênio solúvel do efluente e do anóxico (DQOS efluente/DQOS anóxico), polissacarídeos e temperatura, indicando a importância desses parâmetros para a manutenção da estabilidade operacional de um RBS com grânulos.