A B S T R A C TOne of the major limitations of sewage sludge agricultural use is the presence of chlorobenzenes (CBs), which are toxic to the environment. The use of techniques of sewage sludge phytoremediation can be an important alternative for the degradation of these substances in the waste. The aim of this study was to evaluate the effect of Pennisetum purpureum cultivation time on the reduction of the concentrations of 1,4-CB and 1,3,5-CB in sewage sludge. The experiment was conducted in a greenhouse, using a randomized block design. The treatments consisted of five periods of Poaceae cultivation in sewage sludge plots (30, 60, 90, 120 and 150 days) and a control (sludge plots not cultivated). At 150 days, the control, in the layer of 0-20 cm, showed higher concentrations of 1,3,5-CB, compared with the same layer of cultivated sludge. In the cultivated sludge, in the 10-20 cm layer, there was a decrease in the concentrations of 1,4-CB, while in the layer of 20-30 cm, both concentrations decreased. The observed reductions may be the result of mutualistic interactions between decomposer organisms and the roots of P. purpureum, favoring the decomposition process.Fitorremediação de clorobenzenos em lodo de esgoto cultivado com Pennisetum purpureum em diferentes períodos R E S U M O Uma das grandes limitações do uso agrícola de alguns lodos de esgotos é a presença de clorobenzenos (CBs) que são tóxicos ao meio ambiente. O uso de técnicas de fitorremediação no lodo de esgoto pode ser uma importante alternativa para a degradação dessas substâncias no resíduo. Objetivou-se, neste trabalho, avaliar o tempo de cultivo de Pennisetum purpureum na redução das concentrações de 1,4-CB e 1,3,5-CB em lodo de esgoto. O experimento foi realizado em casa de vegetação, utilizando-se o delineamento em blocos casualizados. Os tratamentos corresponderam a cinco períodos do cultivo da Poaceae em parcelas de lodo de esgoto (30; 60; 90; 120 e 150 dias a partir do plantio de estacas) e uma testemunha (parcelas de lodo não cultivado). Aos 150 dias a testemunha, na camada de 0-20 cm, apresentou maiores concentrações de 1,3,5-CB, quando comparada à mesma camada do lodo cultivado. Já no lodo cultivado na camada de 10-20 cm, houve decréscimo das concentrações de 1,4-CB, enquanto, na camada de 20-30 cm, tanto as concentrações de 1,4-CB quanto de 1,3,5-CB diminuíram. As reduções observadas podem ser resultado das interações mutualísticas entre organismos decompositores e as raízes de P. purpureum, favorecendo o processo de remediação.

A B S T R A C TIn order to reduce the effect of heavy metals on the biosolid, it is necessary to promote its phytoremediation. It is important to know the total content and chemical forms of these elements in the residue for analyzing its behavior and potential toxicity. Thus, the aim of this study was to evaluate the fractionation and behavior of Cu and Zn in biosolid cultivated with Pennisetum purpureum in different periods. The experiment was carried out using a randomized complete block design. The treatments, with five replicates, corresponded to Pennisetum purpureum cultivation in biosolid for 30, 60, 90, 120 and 150 days after planting. The total contents of Cu and Zn in the biosolid remained below the critical limits established by the CONAMA Resolution 357, and there was a reduction in these values with Pennisetum purpureum cultivation. Furthermore, the increment in the grass cultivation period caused intense reduction of Zn contents bound to organic matter, but there was an increase in soluble Zn and residual Zn. Additionally, there was an intense reduction in the content of Cu bound to sulfides. Therefore, for biosolid phytoremediation purposes, the grass should be cultivated for 150 days.Fracionamento de cobre e zinco em biossólido cultivado com Pennisetum purpureum em diferentes períodos R E S U M O Para atenuar o efeito da presença de metais pesados no biossólido, faz-se necessária a sua fitorremediação, sendo fundamental o conhecimento das concentrações totais e das formas químicas destes elementos no resíduo para fins de análise do seu comportamento e potencial toxicidade. Assim, objetivou-se avaliar o comportamento e fracionamento do Cu e Zn em biossólido cultivado com Pennisetum purpureum em diferentes períodos. O experimento foi realizado utilizando-se delineamento em blocos casualizados. Os tratamentos, em cinco repetições, corresponderam ao cultivo de Pennisetum purpureum em biossólido por 30, 60, 90, 120 e 150 dias a partir do plantio. As concentrações totais de Cu e Zn no biossólido ficaram abaixo dos limites críticos da Resolução CONAMA 375, havendo redução destes valores com o cultivo de Pennisetum purpureum. Além disso, o incremento do período de cultivo da gramínea causou intensa redução da concentração de Zn ligado à matéria orgânica; por outro lado, houve aumento do Zn solúvel e residual. Já para o Cu houve intensa redução da concentração do elemento ligado a sulfetos. Assim, para fins de fitorremediação do biossólido, recomenda-se o plantio da gramínea por 150 dias. Key words:sequential extraction sewage sludge speciation of heavy metals Palavras-chave: especiação de metais pesados extração sequencial lodo de esgoto

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The biogas produced in UASB-based Sewage Treatment Plants (STPs) is rarely used for energy purposes and its potential is often unknown. This study aimed to propose a simple and reliable method based on energy balance to determine the technical feasibility of biogas use and the energy self-sufficiency of UASB reactors. To this end, we considered (i) electric power production (E) and (ii) electric power consumption (Econ) ascribed to Sewage Pumping Stations (SPSs) at different pressure heads (0 to 4 m, 4.1 to 8 m, 8.1 to 12 m, and 12.1 to 16 m). The technical feasibility of biogas use was assessed by evaluating if the flow of biogas produced in the STPs would be sufficient for the functioning of a commercial motor-generator. The linear model fit to estimate the biogas energy potential (y-axis) in STPs and the sewage flow (x-axis) is represented by y = 122.65x (R2 = 0.64). A total of 1,054 STPs in Brazil use UASB reactors as treatment units, of which nearly 31% are located in the southeast. However, only 11.2% of these STPs, which serve populations of over 29,981, presented technical feasibility to recover biogas. The mathematical equations proposed in this study to estimate the net electric power production in UASB-based STPs are relevant tools for sanitation companies and can enable studies to be performed for the implementation of energy self-sufficiency projects in Brazil.

Pig farming stands out as an alternative for decentralized electrical energy production from the use of biogas energy. However, its use is still limited. Thus, this study aimed to estimate and map the biogas production, as well as determine the electric power originated by the use of biogas produced in covered lagoon biodigester from pig farms of different sizes in the state of Minas Gerais, Brazil. The research was based on data provided by the Instituto Mineiro de Agropecuária (IMA). Three forms of electric power were estimated, as follows: (i) total, (ii) current, and (iii) installed. They were estimated from the volume of manure generated at each development stage of the animals. The total electric power corresponded to 31 MW, while the current electric power was equal to 20 MW. The installed electric power was still low and corresponded to 35.4% of the current electric power. The results showed that 55% of the current electric power was concentrated in only two mesoregions (Triângulo Mineiro/Alto Paranaíba and Zona da Mata). Therefore, the use of biogas contributed to providing energy self-sufficiency in pig farms and the generation of decentralized electrical energy.