BACKGROUND Metallurgic wastewaters are acidic effluents containing large amounts of nitrate and heavy metals. Citric acid is one of the acids used by this industry and forms stable complexes with metal ions. The aim of this study was to elucidate the chemical aspects driving inhibitory or stimulatory effects of heavy metals on denitrifying processes, based on speciation analysis and monitoring key denitrification intermediates (nitrite and N2O). RESULTS Denitrifying sludge incubations were conducted with iron, chromium and nickel, in single and multi‐metal assays, using citrate and ethanol as electron donors. Ferric‐citrate complex, [Fe‐cit](aq), was readily consumed, while complexes of divalent metals, [Fe‐cit]‐ and [Ni‐cit2]4‐, remained very stable affecting denitrification. Nitrate reduction was affected by Ni2+, while nitrite and N2O accumulation was observed with NiCO3 and Ni(OH)2 oversaturation. [Cr‐cit2]4‐ resulted in overall denitrification inhibition, while species of [Cr‐cit]2‐ caused denitrification stimulation. CONCLUSION Fe and Cr inhibited the overall denitrification process, while Ni caused accumulation of intermediates. Synergistic inhibition imposed by multi‐metal systems revealed lower inhibitory effects compared with those observed by the sum of individual effects of metals. This study elucidates chemical aspects determining the effects of heavy metals on denitrification, which is relevant to develop efficient biological processes for metallurgic effluents. © 2017 Society of Chemical Industry

This study aimed to evaluate the influence of airflow (0.25, 0.50 and 0.75 L.L -1 .min -1 ) and cycle time (10.45 h, 14.25 h and 17.35 h) on a sequencing batch reactor (SBR) performance in promoting nitrification and denitrification of poultry slaughterhouse wastewater. The operational stages included feeding, aerobic and anoxic reactions, sedimentation and discharge. SBR was operated in a laboratory scale with a working volume of 4 L, keeping 25% of biomass retained inside the reactor as inoculum for the next batch. In the anoxic stage, C: N ratio was maintained between 5 and 6 by adding cassava starch wastewater. A factorial design (2 2 ) with five repetitions was designed at the central point to evaluate the influence of cycle time and airflow on total inorganic nitrogen removal (N-NH 4 + +N-NO 2 -+N-NO 3 -) and in the whole process (nitrification and denitrification). The highest total inorganic nitrogen removal (93.3%) was observed for airflow of 0.25 L.L -1 .min -1 and a cycle time of 14.25 h. At the end of the experiment, the sludge inside the reactor was characterized by fluorescent in situ hybridization (FISH), indicating the presence of ammonia and nitrite oxidizing bacteria.KEYWORDS: nitrification, denitrification, response surface methodology, fluorescent in situ hybridization. EFEITO DO TEMPO DE CICLO E DA VAZÃO DE AR NA REMOÇÃO BIOLÓGICA DE NITROGÊNIO DE EFLUENTE DE ABATEDOURO DE AVES UTILIZANDO REATOR EM BATELADAS SEQUENCIAISRESUMO: Este trabalho teve por objetivo avaliar a influência da vazão de ar (0,25; 0,50 e 0,75 L.L -1 .min -1 ) e do tempo de ciclo (10h45; 14h25 e 17h35) no desempenho de um reator em bateladas sequenciais (RBS) em promover a nitrificação e a desnitrificação de água residuária de abatedouro de aves. A operação contemplou as etapas de alimentação, reação aerada e anóxica, sedimentação e descarte. O RBS foi operado em escala de bancada com volume útil de 4 L, mantendo-se 25% do volume do reator como inóculo em cada batelada. Na fase anóxica, a relação C:N foi mantida entre 5 e 6, adicionando-se água residuária do processo de obtenção de fécula de mandioca. Elaborou-se um planejamento fatorial (2 2 ) com cinco repetições, no ponto central, para verificar a influência dos fatores, o tempo de ciclo e a vazão de ar, na variável resposta remoção de nitrogênio inorgânico total (N-NH 4 + +N-NO 2 -+N-NO 3 -), no processo completo (nitrificação e desnitrificação). A maior remoção de nitrogênio inorgânico total (93,3%) foi observada quando se utilizou vazão de ar de 0,25 L.L -1 .min -1 e tempo de ciclo de 14h25. No final do experimento, o lodo do reator foi caracterizado através de hibridização fluorescente in situ (FISH), indicando a presença de bactérias oxidadoras de amônia e de nitrito.

ABSTRACT:The aim of this study was to monitor the stabilization of a sequential batch reactor (SBR) regarding the partial nitritation of poultry slaughterhouse wastewater, aiming at preparing it for a reactor with bacteria that promote anaerobic ammonia oxidation (anammox). A cylindrical reactor with a useful volume of 3.5 L, mechanical agitation (50 rpm), and suspended biomass was used in the experiment. The strategies adopted for nitrite-oxidizing bacteria (NOB) inhibition were cycle time (CT: 24, 16, 6, 5, 4 h and real-time monitoring), free ammonia accumulation, alkalinity restriction and low concentrations of dissolved oxygen (DO). The ammonification process, observed at all experimental phases, negatively influenced the control of partial nitritation process. Alkalinity restriction under low cycle times (4 and 5 h) conditions, together with low dissolved oxygen concentration, was a key factor for nitrite-oxidizing bacteria inhibition. Stability of partial nitritation was only reached by real-time monitoring, being the cycles stopped when 50% N-NH4 + and 50% N-NO2 − were present in the reactor.

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A região Oeste do Paraná passou a ter grande destaque na produção avícola nos últimos anos, contribuindo para que o estado do Paraná se tornasse o maior produtor de frango de corte do Brasil. Por sua vez, a atividade avícola produz uma grande quantidade de resíduos, como a cama de aviário. Estas camas passam por diversos tratamentos, como adição de gesso agrícola, adição de cal, dentre outros componentes que são utilizados com diferentes finalidades. Este trabalho foi desenvolvido no município de Palotina - PR, de outubro de 2018 a dezembro de 2018. Foram coletadas dez amostras de cama tratada com gesso e dez tratadas com cal. Foram determinados os teores de nitrogênio, fósforo, potássio, cálcio, magnésio, carbono orgânico e enxofre. Os dados foram comparados pelo teste de Tukey a 5% de probabilidade. Os teores de nitrogênio e enxofre são maiores nas camas de aviário tratadas com gesso agrícola e os teores de magnésio são maiores nas camas tratadas com cal virgem.