Organic matter. Humic substances. Characterization. Lactuca sativa L.

Water for human consumption must meet a potability standard in order to be used for drinking, food preparation and personal hygiene. For this, it is necessary that, regardless of its origin, the water is submitted to different physical and chemical treatments, or a combination of both. Water treatment consists basically in the removal of suspended and colloidal particles, organic matter, microorganisms, and other substances possibly harmful to human health. After the removal of particles a residue called sludge is generated, which is a mixture of sand and clay, rich in organic matter (OM), micro and macro nutrients. This waste has still been disposed in water courses without any previous treatment. For its reuse is of fundamental importance the study of the structural characteristics, as well as the evaluation of the OM content present in this waste. Thus, the objective of this study was to extract and characterize the OM of the sludge from the Water Treatment Plant in the city of Arapiraca, Alagoas, and then apply it to the lettuce crop in order to evaluate the influence of OM on plant growth and development. The samples were collected and submitted to drying and then disaggregated and sieved. The results obtained in this study indicate that this waste is rich in OM, indicating that this matrix has a potential as an agricultural additive. The E4/E6 ratio shows that the humic substances (HS) contain few aromatic structures and a lower degree of humification. The E2/E3 ratio showed a high value, indicating a decrease in the molecular size of the structures that compose the HS. From the E2/E4 ratio it can be inferred that in the studied SH, there is the presence of structures derived from lignin. The HS, contributed to the growth and development of the lettuce plants. For most of the variables analyzed, the HS showed a significant effect. The HS dose of 100 mg L-1 was the best response dose. A decrease in the effects of the analyzed variables was observed as the concentration of HS increased.