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Microbial Electrolysis Cells (MECs) are one of the bioreactors that have been used to produce bio-hydrogen by biological methods. The objective of this comprehensive review is to study the effects of MEC configuration (single-chamber and double-chamber), electrode materials (anode and cathode), substrates (sodium acetate, glucose, glycerol, domestic wastewater and industrial wastewater), pH, temperature, applied voltage and nanomaterials at maximum bio-hydrogen production rates (Bio-HPR). The obtained results were summarized based on the use of nanomaterials as electrodes, substrates, pH, temperature, applied voltage, Bio-HPR, columbic efficiency (CE) and cathode bio-hydrogen recovery (C Bio-HR). At the end of this review, future challenges for improving bio-hydrogen production in the MEC are also discussed.

Mechanical compaction is often used to densify building earth blocks by reducing the void between the particles. Compacted stabilised earth involves a binder, which holds the particles of the materials together. The compaction and addition of binders to the earth can modify its transport, mechanical, and acoustical properties. In this study, the acoustic transmission coefficient, porosity, and airflow resistivity were investigated by varying the concentrations of water hyacinth ash (WHA) and sugarcane bagasse ash (SBA) binders. An acoustic test rig comprising an acoustic wave guide made from joined water pipes was employed to analyse the influence of the WHA and SBA binders on the acoustical performance of the earth blocks. It was found out that the measured acoustic wave transmission was sensitive to the variation in the composition of WHA and SBA in the earth blocks. Increasing the WHA concentration led to an increase in the acoustic transmission coefficient and porosity, but reduced the airflow resistivity of the compressed earth blocks; while increasing the SBA reduced the transmission coefficient and porosity, but increased the airflow resistivity. This shows that SBA has a stronger binding property than WHA, which is ideal for the manufacture of stronger earth blocks, while the higher porosity of the earth blocks obtained with WHA is good for the construction of porous walls, which is good for maintaining the airflow between the inside of buildings and the surrounding.