Decomposition of sewage sludge using grass cultivation and aeration for use as organic fertilizer

The cultivation of grasses in sewage sludge (SS) with aeration improves the quality of this fertilizer, since the growth of the roots, the release of exudates and oxygenation, favor the mineralization of nutrients and the humification of organic matter. Thus, the present work aimed to evaluate the decomposition of SS using grass cultivation and aeration for use as organic fertilizer. The experiment was carried out in a randomized block design with four replications, in a 2 x 5 factorial scheme, corresponding to the presence or absence of culture with Pennisetum purpureum in SS, combined with five periods of aeration: 0, 14, 28, 42, and 60 days, with an air flow of 1,059 dm(3).h(-1).kg(-1) of volatile solids. The analyses showed that the air injection in the SS did not influence the decomposition of organic matter and the cultivation of the grass in SS increased the levels of N, Ca, S, Na and soluble mineral residues, as well as the electrical conductivity, indicating its mineralization. On the other hand, cultivation decreased the total levels of Fe and Pb, providing a reduction in the risk of toxicity of these elements. For application in agricultural soils and degraded areas, the sewage sludge is classified as Class 2, completely complying with the current regulation. Due to the low organic C values of the sludge used, the vegetable biomass produced can be incorporated into it for suitability and registration as organic fertilizer.