The choice of activating agent for the thermochemical production of high-grade activated carbon (AC) from agricultural residues and wastes, such as feedstock, requires innovative methods. Overcoming energy losses, and using the best techniques to minimise secondary contamination and improve adsorptivity, are critical. Here, we review the importance and influence of activating agents on agricultural waste: how they react and compare conventional and microwave processes. In particular, adsorbent pore characteristics, surface chemistry interactions and production modes were compared with traditional methods. It was concluded that there are no best activating agents; rather, each agent reacts uniquely with a precursor, and the optimum choice depends on the target adsorbent. Natural chemicals can also be as effective as inorganic activating agents, and offer the advantages that they are usually safe, and readily available. The use of a microwave, as an innovative pyrolysis approach, can enhance the activation process within a duration of 1–4 h and temperature of 500–1200 °C, after which the yield and efficiency decline rapidly due to molecular breakdown. This study also examines the biomass milling process requirements; the influence of the dielectric properties, along with the effect of washing; and experimental setup challenges. The microwave setup system, biomass feed rate, product delivery, inert gas flow rate, reactor design and recovery lines are all important factors in the microwave activation process, and contribute to the overall efficiency of AC preparation. However, a major issue is a lack of large-scale industrial demonstration units for microwave technology.

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HighlightsOn dry basis, typical human faeces contain 83 wt.% organic fraction and 17 wt.% ash.The LHV of dry human faeces ranged from 19 to 22 MJ/kg, values similar to wood biomass.Syngas from dry human faeces had LHV of 15–17 MJ/kg at equivalence ratio of ∼0.31.Energy is best recovered from moist human faeces at equivalence ratio above 0.6.Recoverable exergy potential from moist human faeces can be up to 15 MJ/kg.

HighlightsDry human faeces have a Higher Heating Value (HHV) of 24 MJ/kg.Faeces combustion was investigated using a bench-scale downdraft combustor test rig.Combustion temperature of 431–558 °C was achieved at air flow rate of 10–18 L/min.Fuel burn rate of 1.5–2.3 g/min was achieved at air flow rate of 10–18 L/min.Combustion temperature of up to 600 ± 10 °C can handle 60 wt.% moisture in faeces.

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Sustainable land use has been identified as one way of tackling challenges related to climate change, population expansion, food crisis and environmental pollution. Disposal of oil palm fresh fruit bunch (FFB) solid wastes is becoming a challenge with an increased demand and production of palm oil. Whilst this poses a challenge, it could be turned into an opportunity by utilising it as a resource and fully valorise it to meet soil and crop demands. This review presents the potentials of FFB solid wastes, which include empty fruit bunch (EFB), mesocarp fibre (MF), palm kernel shell (PKS), as soil ameliorants. The major findings are the following: 1) pyrolysis, gasification, combustion, and composting are processes that can enhance the value of FFB solid wastes.