Estudo sobre a viabilidade de incorporação do lodo de estação de tratamento de água no substrato para produção de espécies nativas da Mata Atlântica (Brasil)

Abstract

The main method of a water treatment plant (WTP) and its inadequate disposal can cause damage to human health and the environment. The different alternatives of disposal of WTP can be employed and mainly alternatives that can be valued as raw material. This study was evaluated the incorporation of the WTP in substrate to production of seedlings of species natives of Atlantic Forest. The sludge used in the experiment comes from WTP Porto das Caixas, located in the municipality of Itaboraí / RJ. The nursery is located in the municipality of Magé / RJ and both are operated by the State Water and Sewage Company (CEDAE). The species Schinus terenbinthifolius (Aroeira Pimenteira) and Pterocarpus violaceus (Aldrago) were used. Currently, the nursery uses 50% of the sludge from the sewage treatment plant (WTS) and 50% of a commercially purchased soil in the substrate. The objective of this work was to replace the commercial soil with WTP sludge. For this, percentages of WTP sludge with percentages of WTS sludge were produced. The first trace, trace testimony (T1), corresponds to that used in the nursery, the others have the following compositions: T2 with 100% of WTP sludge, T3 with 75% of WTP sludge and 25% of WTS sludge, T4 with 50% of WTP sludge and 50% of WTS sludge, T5 with 25% of WTP sludge and 75% of WTS and T6 sludge with 100% WTS sludge. Some analyzes were carried out to verify the possibility of incorporation of WTP sludge. Analyzing the results it was verified that it is possible to incorporate WTP sludge for seedling production, but the composition of the trace is primordial for the use. The trace that presented the best results was the T5 trace, as it was the only trace that achieved 100% survival and higher growth rates in relation to the height and collection diameter, as well as the higher Dickson Quality Index (DQI). A limiting factor verified for the use of sludge in seedling production is the moisture content that is directly related to the amount of WTP sludge incorporated into the trace. The higher the moisture content the more difficult is the workability of the traces, which affects the production in the forest nurseries. It was verified that the traces with higher percentage and WTP sludge do not have enough nutrients for the seedlings production, since the concentrations of nutrients such as Calcium and Phosphorus needed for seedling growth were below the concentrations found in the WTS. About the economic and environmental benefits, it was verified that it is possible to avoid the annual use of approximately 7,500 m3 of soil, generating an economy in the purchase of this material of approximately R$ 432 thousand a year. Considering the volume of WPA sludge that would no longer be disposed of in a sanitary landfill, it would be possible to obtain annual savings of over R$ 290,000. Thus, overall, the annual savings for seedlings production could currently exceed R $ 720 thousand. In this way the work contributes with an important tool of management of the sludge generated in water treatment plants, that until the present day still presents deficiency in the environmentally adequate destination.