Stability of an anaerobic single reactor filled with dolomitic limestone with increased organic load of sugarcane

Abstract

The anaerobic single-stage reactor was evaluated to treat vinasse and to evaluate its stability. This bench reactor was filled with dolomitic limestone with a horizontal plug flow to simulate a drainage channel. The experiment lasted 129 days while the reactor was submitted to different applied organic concentrations (chronologically applied: 3.0; 5.0; 12.0; 9.0 and 7.5 g L -1 as COD, chemical oxygen demand). COD removals were 50% and 9% with 3.0 and 7.5 g L -1 , respectively. With 12.0 g L -1 , reactor efficiency increased to 33%, with an abrupt drop to 3% on the 84 th day. Therefore, in order to avoid reactor collapse, a remedial measure was necessary. The system remained in batch without feeding for 19 days (from the 85 th to the 104 th day) with 9.0 g L -1 . Afterwards, it was observed that the performance of the system tended to stabilize, reaching 47% with 7.5 g L -1 in the 118 th day. At the end of the experiment, the potassium content of the wastewater decreased from 800 mg L -1 to 594 mg L -1 (on an average 25%) and calcium and magnesium increased within the reactor liquor. The dissolution of the limestone inside the liquor reactor probably caused this result. After the treatment with limestone, the average pH value of the effluent increased from 4.9 to over 6.0 in all organic concentrations. It could be concluded that the reactor filled with dolomitic limestone in these operational conditions assured a low efficiency in COD removal, potassium reduction, increasing values of pH, alkalinity, calcium and magnesium. The instability was observed when there was increase in organic load to 12 g L -1 with subsequent recovery. 5,0; 12,0; 9,0 e 7,5 g L -1 como DQO, demanda química de oxigênio). As remoções de DQO foram de 50% e 9% com 3,0 e 7,5 g L -1 , respectivamente. Com 12,0 g L -1 a eficiência do reator aumentou para 33%. Mas, houve uma queda abrupta para 3% aos 84 dias. Então, a fim de evitar o colapso do reator, uma medida corretiva foi necessária. O sistema permaneceu em regime batelada sem alimentação durante 19 dias (do 85º ao 104º dia) com 9,0 g de L -1 . Depois, observou-se que o desempenho do sistema tendeu à estabilidade, atingindo 47% com 7,5 g L -1 no 118º dia. No final do experimento, o teor de potássio do efluente diminuiu de 800 mg L -1 para 594 mg L -1 (em média 25%) e cálcio e magnésio aumentaram dentro do licor do reator. Provavelmente, isto pôde ser observado devido a dissolução do calcário dentro do reator. Após o sistema de tratamento com calcário, o valor médio do pH do efluente aumentou de 4,9 para mais de 6,0 em todas as concentrações orgânicas. Pôde-se concluir que o reator preenchido com rochas de calcário dolomítico nestas condições operacionais assegurou baixa eficiência na remoção de DQO, redução de potássio, valores crescentes de pH, alcalinidade, cálcio e magnésio. A instabilidade foi observada quando houve os aumentos da carga orgânica para 12 g L -1 com recuperação subsequente.Palavras-chave: carga biológica, destilaria de etanol, efluente agroindustrial, vinhaça, tra...