Biossólidos: produção, efeitos no crescimento de mudas de eucalipto e avaliação de risco à saúde humana

Abstract

This work involved the production of biosolids by means of lime treatment and green house drying of UASB reactor sludge, the use of these biosolids to produce Eucalyptus urophylla seedlings, and an approach of microbiological risk assessment to estimate human health risks (occupational risks) associated with the production of the seedlings. In trials conducted in an experimental site in Viçosa - MG, three lots of biosolids attaining to Class A and B standard qualities (according to the criteria of the Brazilian regulation on biosolids use in agriculture) were produced, and the following variables were monitored:: moisture content, pH, total solids, viable helminth eggs, Salmonella spp., total coliforms, and E. coli. Based on the results of helminth eggs and E.coli, the limed sludge (adding 50% CaO in relation to the sludge dry weight) reached Class B standard within 12 days in Lot 1 and seven days in lots 2 and 3; Class A biosolids was reached after 70, 62 and 29 days respectively in lots 1, 2 and 3. Regarding the green house dried sludge, Class B was achieved in lots 1, 2 and 3 within 42, 35 and 56 days, respectively; Class A standard was achieved only after 100 days in Lot 1 but was not reached after 80 and 62 days in lots 2 and 3, respectively. In both cases (lime and green house treatment) biosolids handling was not feasible before 40 days storage due to high humidity, and this required additional conditioning procedures in order to plant the eucalyptus seedlings in plastic tubes. The sludge drying in the green house resulted in biosolids with better agricultural properties than those produced by lime treatment. The sowing and growth of the eucalyptus seedlings were carried out in nursery and greenhouse facilities at the Federal University of Viçosa. The eucalyptus seedlings were planted in polypropylene tubes containing biosolids (limed and dried, Classes A and B) and Plantmax mixed in different proportions (0, 25, 50, 75 and 100% of biosolids). Each treatment received four replications in plots with 10 seedlings each, which were arranged in a complete randomized design. Altogether 800 seedlings were planted (2 types of biosolids x 2 classes of biosolids x 5 proportions of biosolids / substrate x 4 replicates x 10 seedlings per replicate). 90 days after sowing, the following parameters were measured in the saplings: survival, height, stem diameter and dry biomass (aerial and root).. In general, the best seedling’s developments were obtained with 50% biosolids + 50% Plantmax and/or 75% biosolids + 25% Plantmax. Overall, the biosolids produced in the greenhouse promoted better results than the limed sludge.The quantitative microbiological risk assessment was based on the construction of exposure scenarios for the use of biosolids in the cultivation of tree seedlings, using those treatments with 100% of biosolids (limed and dried, classes A and B) and those that resulted in the highest agronomic yield. The results suggested that this activity involves occupational risk (arising from involuntary ingestion of biosolids particles), in particular risks of helminth infection in continuing activities of seedlings planting and transplanting. However, due to limitations inherent to and some assumptions made in this study, the risks may have been overestimated.