Design and Techno-economic Analysis of Ammonia Production from Human Waste via Anaerobic Digestion

Abstract

The increasing concern on climate change has prompted scientists across the world to find new sources of renewable and sustainable energy to reduce the over 75% of global energy dependence on fossil fuels. Improper disposal and treatment of human waste threaten the environmental and public health, and it requires immediate treatment of which anaerobic digestion comes as a rescue for effective and sustainable waste treatment technology. Hence, the objective of this work was to design and evaluate the techno-economic analysis of ammonia production from human waste (HW) via anaerobic digestion (AD) through two process schemes using Aspen Plus process simulator. The models were validated using an existing data, with 4.48 and 4.33% percentage error for the anaerobic digestion (new developed model) and anaerobic digestion with carbon capture and reuse (existing model) respectively. The sensitivity analysis showed that the AD reactors produced the best ammonia outputs at 60°C and 1 atm of 0.172 and 0.0189 kg/h respectively. The highest amount of ammonia for process schemes 1 and 2 is 0.0905 kg/h and 1.2792 kg/h for 10 L/day of organic loading rate (OLR), respectively. The organic loading rate rose as ammonia yield increased. For process scenarios 1 and 2, the best amounts are 0.1423 and 0.001609 kg/h for hydraulic retention durations of 1 and 10 days. Additionally, the net present value (NPV) values of $128,825.54 and $291,876.33, the internal rate of return (IRR) of 17 and 12%, and the payout periods of 6 and 7 years show that both schemes are promising in terms of payout period, although scheme 2 has a higher NPV than scheme 1 and a higher internal rate of return than scheme 1.