Thermally-induced changes in tropical soils properties and potential implications to sequential nature-based solutions.

Some remediation techniques, such as thermal remediation, can significantly change the soil properties. These changes can be beneficial or detrimental to the sequential application of Nature-based Solutions. This work evaluated the effects of thermal remediation on the properties of two tropical soils (Technosol and Oxisol), and discuss how these changes might impact both biotic and abiotic degradation processes. Bench tests using disturbed samples were performed under oxic and anoxic conditions, whereas 3D physical models were used to simulate the heat distribution along undisturbed samples. The changes in soils texture, density, hydraulic conductivity, iron concentration, mineralogy and microbiota were evaluated. The properties of Oxisol were more affected than those of Technosol due to the higher levels in Fe(III), organic carbon and finer texture. When heated in the range of 120 to 300 °C under oxic and anoxic conditions, the Fe(II) content and the magnetism intensity increased in Oxisol, probably due to the formation of magnetite. Under oxic conditions, the burning of Oxisol organic matter promoted an anoxic atmosphere, favoring the formation of Fe(II). However, the continuous increase of the temperature (>300 °C) lead to the decrease of Fe(II) due to the transformation of magnetite to maghemite, and then to hematite. The heating process also promoted some minerals decomposition and cementation of the clay fraction, increasing the soil texture. Bacterial populations were impacted, but showed ability to recover at 60 °C. However, above 100 °C no culturable cells were recovered and at temperatures above 270 °C soil sterilization occurred. The changes observed, especially in Oxisol samples, indicated that mild heating (between 120 and 240 °C), in turn, can increase the potential for abiotic degradation of some contaminants, such as chlorinated solvents. Therefore, heating conditions up to 240 °C during thermal remediation can be defined as to promote beneficial changes in soil properties, increasing its potential for natural attenuation by abiotic processes even when the microbiota is affected, and improving its sustainability.

Viabilidade técnica e econômica da regeneração de coagulantes a partir de lodos de estações de tratamento de água / Technical and economical feasibility of coagulant recovery from water treatment plant sludges

Esse trabalho teve como objetivo avaliar a viabilidade técnica e econômica da regeneração de coagulantes pela acidificação de lodos de ETA's e a posterior aplicação dos coagulantes regenerados no tratamento de esgotos. Foram realizados ensaios em escala de bancada visando o estudo das condições de regeneração, da qualidade do coagulante produzido e do lodo resultante. O coagulante regenerado teve desempenho satisfatório no tratamento de efluentes de reator UASB e foi observado que ocorreram reduções significativas de sólidos em suspensão nos lodos das ETA's. Com respeito à avaliação econômica, foi verificado que considerando as reduções de custos decorrentes da diminuição de lodo a ser tratado e disposto, o custo de produção do coagulante regenerado é muito próximo ao custo do coagulante comercial. Portanto, concluiu-se que hoje em dia essa tecnologia deve ser considerada como uma alternativa potencialmente viável dos pontos de vista técnico e econômico para o tratamento e reaproveitamento de lodo de ETA's.