ABSTRACT Covered lagoon biodigesters (CLB) have been widespread in Brazil in the treatment of pig manure. However, the quantification of biogas production in CLB using mathematical models is still limited and scarce. This study aimed to evaluate and compare six mathematical models—Chen-Hashimoto (Chen, 1983), CETESB (2006), COD Conversion (Chernicharo, 2016), IPCC (2006), Deng (Deng et al., 2014), and modified Stover-Kincannon (Yu et al., 1998)—usually used to estimate methane (CH 4 ), and propose improvements to the models, if necessary. The results were compared with the monitored production (P actual ) in a farm with CLB using the t-test (α = 5%). The Chen-Hashimoto, IPCC, Deng, and modified Stover-Kincannon models showed no statistical difference compared to P actual (405.0 m 3 CH 4 d −1 ), whereas the CETESB and COD Conversion models presented no statistical difference after the proposed improvements. All models can be considered reliable for estimating volumetric methane production after the adaptations, being relevant tools for diagnosis and decision-making regarding the energy recovery of biogas with CLB operation in pig farms.

ABSTRACT 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.

ABSTRACT This study aimed to evaluate the total contents of As, Cu and Zn in the profile of a Haplic Cambisol cultivated with crambe and corn and fertilized with sanitary sewage sludge and to compare them with those obtained in other forms of fertilization, as well as the content of metals in the grain of these crops. Two experiments were carried out in the field, one with maize cultivation and another with crambe, both were delineated as randomized blocks with four treatments and six replicates, which were: without fertilization, fertilization with sewage sludge dewatered and dried in the sun, with dry sewage sludge and with mineral fertilizers. At the end of the experiments soil samples were collected at 15, 50, 100, 150 and 200 cm depth for analysis of the total contents of As, Cu and Zn, as well as the grain of the crops. No differences were observed among the treatments. The total contents of As, Cu and Zn in the soil in both experiments and in the corn grains are below the limits of prevention and the maximum limit in grains established by the Brazilian resolutions. In relation to depth, the metal contents in the samples collected from the soil submitted to the fertilization treatments were similar to those quantified in the plots that did not received fertilization, but there was accumulation of Cu and Zn in the upper layers of the soil that received fertilization.

RESUMO 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.

ABSTRACT In 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.

RESUMO 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.

ABSTRACT One 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.