Enhanced renewable-energy production from co-digestion of waste biomass and sewage sludge based on bio-economic prospects

Summary

The exponential demand for energy and the environmental pollution that results from the reliance 
on fossil fuels represent a great challenge to humanity. Additionally, great volumes of wastes such 
as food waste, agricultural waste and animal manure can be generated annually and require proper 
management. Traditional management approaches of solid wastes such as landfilling, and 
incineration can contaminate soil, air and groundwater. Anaerobic digestion (AD) is a technique 
that can harness natural resources (e.g., biomass waste) to generate biogas and digestate. The 
generated biogas can be used as an energy source and digestate can be employed as a biofertilizer 
and replace chemical fertilizers. The mono-digestion of wastes cannot achieve efficient anaerobic 
digestion due to the unsuitable C/N ratio. In this work, the co-digestion by adding different wastes 
in anaerobic digestion process can be attained to achieve high biogas production rate due to the 
appropriate C/N ratio, balanced nutrients, and high buffer capacity. The generated methane from 
the anaerobic digestion process has lower energy content compared to hydrogen. Additionally, the 
produced biogas includes some impurities (e.g., H2S) which requires separation. Traditional 
techniques used for the production of H2 such as steam reforming of methane, coal gasification 
and partial oxidation have some shortcomings such as the release of high volumes of greenhouse 
gases and the high energy consumption. Thus, in the proposed work, microbial electrolysis cell 
can be integrated in anaerobic digestion process (AD-MEC) to efficiently reduce solids, generate 
H2 and improve the efficiency and stability. In the hybrid system, low voltage can be applied to 
AD leading to the oxidation of organic waste via the anodic bacterial consortia and the generation 
of protons and electrons. Then, electrons can be transferred to the cathode electrode via the circuit
wire to generate H2 at the cathode. Further, an ion exchange membrane will be introduced to MEC 
to achieve the charge balance and prevent the consumption of the generated H2 by methanogens, 
thereby maximizing the production rate of hydrogen. Different electrode materials will be tested 
to specify the best electrode material. Different doses of biochar prepared from agricultural wastes
will be added to AD-MEC to show the effect of biochar on hydrogen production rate. On the other 
hand, the discharged digestate from AD-MEC will be characterized to check its properties to be 
used as a biofertilizer for improving the soil quality. A feasibility study will be performed to check 
the profitability of the hybrid system. The expected low-cost, high H2 production rate, maximum 
solid reduction and profits via microbial electrolysis cell coupled with anaerobic digestion can 
encourage decision makers to apply this technique on a wider scale to overcome the problems of 
energy and waste management. 

Achievements

List of Publications from the Project

Partners

• Prof. Cesar Torres,

Project Members

Project Leaders