Abstract
This research was carried out with the aim to evaluate the anaerobic digestion (AD) of llama and dromedary dungs (both untreated and trampled) in batch mode at mesophilic temperature (35 °C). The biochemical methane potential (BMP) tests with an inoculum to substrate ratio of 2:1 (as volatile solids (VS)) were carried out. The methane yield from trampled llama dung (333.0 mL CH4 g−1 VSadded) was considerably higher than for raw llama, raw and trampled dromedary dungs (185.9, 228.4, 222.9 mL CH4 g−1 VSadded, respectively). Therefore, trampled llama dung was found to be the best substrate for methane production due to its high content of volatile solids as well as its high nitrogen content (2.1%) and more appropriate C/N ratio (23.6) for AD. The experimental data was found to be in accordance with both first-order kinetic and transference function mathematical models, when evaluating the experimental methane production against time. By applying the first-order kinetic model, the hydrolysis rate constants, kh, were found to be 19% and 11% higher for trampled dungs in comparison with the raw dung of dromedary and llama, respectively. In addition, the maximum methane production rate (Rm) derived from the transference function model for trampled llama dung (22.0 mL CH4 g−1 VS d−1) was 83.3%, 24.4% and 22.9% higher than those obtained for raw llama manure and for raw and trampled dromedary dungs, respectively.
Highlights
Three-quarters of the global heating demand is met by coal, gas and oil, which implies a strong dependence on fossil fuels, and the rest, approximately 27%, comes from renewable energy sources [1]
The volatile solids (VS) content was similar in all substrates, it should be noted that the lowest VS content was found in raw llama dung (665.3 ± 3 g kg−1), while the highest VS content was found for the trampled llama dung (779.5 ± 9.2 g kg−1)
Methane yield values in the range of 185.9–333.0 mL CH4 g−1 VS were found in biochemical methane potential (BMP) experiments of llama and dromedary dungs carried out at mesophilic temperature (35 °C)
Summary
Three-quarters of the global heating demand is met by coal, gas and oil, which implies a strong dependence on fossil fuels, and the rest, approximately 27%, comes from renewable energy sources (bioelectricity) [1]. Developed countries are committed to developing, manufacturing and increasing the use of green energies, which would enhance the population life’s quality by reducing the effects of climate change and aiming for a more sustainable economic development [5]. In the last 20 years, greenhouse gas (GHG) emissions generated by population growth and technological development design to new records; from 1990, global emissions have increased by almost 50% [6]. In 2015 the United Nations designed the 17 Sustainable Development Goals (SDG) included in the 2030 Agenda with the aim to achieve a better sustainable world for all, The main source of GHG emissions is directly linked to fossil fuels being burned for the production of thermal, electrical and mechanic energy, representing two-thirds of total emissions, where transport and industry have the major impact [7].
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