Evaluation of sludge from pond system for treatment of piggery wastes

Stabilization ponds used for the treatment of piggery wastes accumulate sludge over time, which is commonly used in agriculture. The objective of this study was to evaluate the agronomic potential of this kind of sludge. The samplings were collected in two different phases. The first in two anaerobic ponds (AP1 and AP2) and in one facultative pond with 5 transverse baffles and, the second in the same facultative pond with aeration. The removed sludge of AP1 and AP2 was characterized as rich sludge in volatile solids and with low stabilization, there was a great accumulation of the total phosphorus in the sludge of AP2. The facultative pond presented greater retention of nutrients in the sludge in relation to the anaerobic ponds. The annual accumulation of sludge was 13.3 cm/year in the AP1 and 6.70 cm/year in the AP2, while in the pond with aeration this was on the average of 0.5 cm/year, due to the aeration regime. The sludge can be used as a fertilizer in agriculture, if the chemical characteristics of the soil are taken into account so as to avoid the accumulation of nutrients and damage to plants.