An evaluation of a proposed approach for overcoming the environmental and economic challenges of anaerobic digestion process through the production of more bio-products

Abstract

The transformation to renewable energy has become a requirement nowadays. Thermo-plastic starch (TPS) is a type of bio-plastic. Its quality and properties are examined by employing mechanical, physical, and other tests. Despite the proven advantages of using anaerobic digestion (AD) for the conversion of biomass into biogas and the developments on it, there still exist some environmental and economical challenges limiting prosperity and sustainability of AD. Economically, compared to fossil fuel market, biogas, which is the only major product of AD, is not competitive enough compared to the prices of its counterparts. With the aid of Design Expert software, the present study mainly aims to design and implement an integrated approach so as to potentially overcome these challenges and to make the AD more desirable. The approach incorporates the AD process with the process of producing TPS to form; biogas, bio-slurry and TPS/mango fibre bio-plastic sheet, from the residues of three starchy biomass: potato, mango and avocado. A Hollander Beater was employed as a multi-functional device, to: pre-treat the biomass, isolate the starch and to process mango seed coats. The study found that, the highest energy gain per gram of volatile solids of potato residues was 62.9% at 35 ⁰C, 1.62 g-VS organic concentration and 50% sludge concentration, which yielded a maximum CH4% of 72.4%. While, the highest energy gain by the gram of volatile solids of mango and avocado residues were 65% and 16.5% which yielded a maximum CH4% of 62.4% and 60.9% respectively. The production of a bio-plastic sheet with a dimension of 2440*1220*3.2 mm has the same specifications of the optimal bio-plastic sheet produced, resulting in a cost efficiency of up to 65%. To achieve this approximately 353.7 kg potato, 89.9 kg mango and 173.7 kg avocado requires processing. Therefore the proposed study has achieved its main aim. Economically, this was achieved as a result of an excess amount of the bio-energy been produced (approximately 29%) of the total bio-energy produced. Regarding the environmental challenges which mainly depend on the accumulation of large amounts of the generated digestate, the study has confirmed the bio-fertiliser potential of the digestate with a suggestion to carry out more tests to confirm its quality and increase the reliability. Countries such as Saudi Arabia which is emerging in this field, can greatly benefit from this study via identifying the obstacles, tackling and avoiding them to improve profitability.