Determination of maximum annual rate of application sewage sludge sanitized by alkaline process in soils of the metropolitan region of Curitiba, Brazil

O objetivo deste estudo foi analisar as curvas de pH de três solos representativos da Região de Metropolitana de Curitiba para determinação das taxas de aplicação máxima anual de lodo de esgoto higienizado pelo processo de estabilização alcalina prolongada (lodo EAP), conforme estabelece a legislação, e para comparação com a metodologia de saturação por bases (V%). Os solos foram incubados com seis doses de lodo EAP (pH 9,2) e o pH avaliado em 5 datas até 75 dias. O solo Cambissolo Húmico Distrófico típico, com a capacidade de troca de cátions e teor de carbono mais elevados, atingiu o pH 7 com 49 t ha-1 de sólidos totais (ST); o Latossolo Bruno Distrófico típico com 38 t ha-1 de ST, e o Cambissolo Háplico Distrófico típico, o mais restritivo, indicou que a aplicação anual de lodo EAP não deverá ultrapassar a 31 t ha-1 de ST. Sugeriu-se cautela na seleção do solo representativo. O método V% recomendou quantidades de lodo EAP iguais ou ligeiramente superiores às que atingiram pH 6 pelo método de incubação.The objective of this study was to analyze the pH curves of three representative soils of the Metropolitan Region of Curitiba for determining the maximum annual application rates of sewage sludge sanitized by prolonged alkaline stabilization process (EAP sludge), as stated in the legislation, and for comparison with the methodology of base saturation (V%). The soils were incubated with six doses of sludge EAP (pH 9.2) and pH measured on 5 dates, up to 75 days. The Inceptisol from Piraquara with the cation exchange capacity and higher carbon content reached the pH 7 with 49 t ha-1 of total solids (ST); the Oxisol with 38 t ha-1 of ST, and to Inceptisol from Pinhais, the most restrictive, indicated that the annual application of sludge EAP shall not exceed the 31 t ha-1 of ST. Caution in selecting representative soil was suggested. The method V% recommended EAP sludge quantities equal or slightly higher than that reached pH 6 by the method of incubation