Hydrothermal carbonization of sewage sludge and corn cobs to produce solid recovered fuel: Parametric synergistic analysis through deep machine learning, economic feasibility and contribution in circular economy

The biowaste production rate is escalating globally, contributing towards greenhouse gas emmissions and becoming a challenge for the waste management authorities. The co-pyrolysis of biowaste provides an alternative path for energy security, sustainability and biowaste contribution towards renewable energy streams. The current study focuses on production of novel hydrochar from sewage sludge and corn cobs through hydrothermal carbonization process along with enhanced energy contents and hydrochar yield. Four different mixing ratios (1/4, 1/3, 1/2 and 1/1), three different carbonization temperatures (180, 200, 220) 0C and different residence times (1, 2 and 3) hr were applied to produce the higher energy containing hydrochar. To validate combustion efficiency of hydrochar, detailed elemental and proximate analysis were carried out. The elevated fuel ratio of 0.41, hydrochar production of 81.45 % and higher heating value of 23.77 MJ/kg were achieved with lower ash contents up to 6.20 %. The combustion performance of hydrochar were compared to that of peat and lignite through Van Krevelen diagram. To evaluate the synergistic parametric influences in hydrochar production process, Pearson co-relation matrix, principal component analysis and machine learning modelling were applied to experimental data. Fixed carbon had provided 0.99 positive co-relation with fuel ratio and hydrochar yield. Fixed carbon was deduced as the most imperative parameter determining the quality of hydrochar. To determine commercial competitiveness, economic analysis was also carried out with 5.57 years as break-even period. The developed technology could play a dynamic role in developing biowaste circular economy in the rural sectors of the developing countries.