Chicken is a favorite, inexpensive meat across the globe. But the bird’s popularity results in a lot of waste that can pollute soil and water. One strategy for dealing with poultry poop is to turn it into biofuel, and now scientists have developed a way to do this by mixing the waste with another environmental scourge, an invasive weed that is affecting agriculture in Africa. They report their approach in ACS’ journal Energy & Fuels.
Convert the waste into fuel
Poultry sludge is sometimes turned into fertilizer, but recent trends in industrialized chicken farming have led to an increase in waste mismanagement and negative environmental impacts, according to the United Nations Food and Agriculture Organization. Droppings can contain nutrients, hormones, antibiotics and heavy metals and can wash into the soil and surface water. To deal with this problem, scientists have been working on ways to convert the waste into fuel. But alone, poultry droppings don’t transform well into biogas, so it’s mixed with plant materials such as switch grass. Samuel O. Dahunsi, Solomon U. Oranusi and colleagues wanted to see if they could combine the chicken waste with Tithonia diversifolia (Mexican sunflower), which was introduced to Africa as an ornamental plant decades ago and has become a major weed threatening agricultural production on the continent.
The researchers developed a process to pre-treat chicken droppings, and then have anaerobic microbes digest the waste and Mexican sunflowers together. Eight kilograms of poultry waste and sunflowers produced more than 3 kg of biogas — more than enough fuel to drive the reaction and have some leftover for other uses such as powering a generator. Also, the researchers say that the residual solids from the process could be applied as fertilizer or soil conditioner.
Bioconversion of Tithonia diversifolia (Mexican Sunflower) and Poultry Droppings for Energy Generation: Optimization, Mass and Energy Balances, and Economic Benefits
Anaerobic co-digestion of pretreated and untreated samples of Tithonia diversifolia with poultry droppings was carried out to establish a permanent solution to the menace of this stubborn weed present in crops worldwide. The physicochemical and microbial characteristics of the substrates (T. diversifolia, poultry droppings, and rumen contents) were evaluated using standard methods. The initial high chemical oxygen demand (COD) values were significantly reduced by 60.45 and 56.33% after digestion. In all the experiments, biogas production was progressive until between the 16th and 21st days in most cases, after which a decrease was observed until the end of the experiments. The most desirable actual/experimental biogas yields from both experiments were 2984.20 and 1408.02 m3/kg total solids (TS) fed, with desirability of 100% for both experiments. Gas chromatographic analysis revealed the CH4 and CO2 contents of both experiments to be 67 ± 1.5%; 22 ± 2% and 60 ± 1%; 23 ± 2%, respectively. The response surface methodology (RSM) model and the artificial neural networks (ANNs) model were employed in data optimization, and the optimal values for each of the five major parameters optimized are as follows: temperature (A) = 37.20 °C, pH (B) = 7.50, retention time (C) = 27.95 days, total solids (D) = 11.97 g/kg, and volatile solids (E) = 8.50 g/kg. The root-mean-square error of biogas for RSM (105.61) was much higher than that for ANNs (84.65). In the pretreated experiment, the most desirable predicted yield for RSM model was 3111.07 m3/kg TS fed, while that of ANNs model was 3058.50 m3/kg TS fed; for the experiment without pretreatment, it was 1417.39 and 1412.50 m3/kg TS fed, respectively. In all, there was a 54.44% increase in predicted biogas yield in the experiment with pretreatment over the untreated. Based on the coefficient of determination (R2), the mean error, and predicted biogas yields, the ANNs model was found to be more accurate than RSM in the study. The energy balance revealed a positive net energy which adequately compensated for the thermal and electrical energies used in carrying out thermo-alkaline pretreatment. The co-digestion of these substrates for bioenergy generation is hereby advocated.
The authors acknowledge funding from Landmark University (Nigeria).
The abstract that accompanies this study is available here.
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