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BioCH4 from the Anaerobic co-Digestion of the Organic Fraction of Municipal Solid Waste and Maize Cob Wastes
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Resumo(s)
Maize Cob Waste (MCW) is available in high amounts, as maize is the most
produced cereal in the world. MCW is generally left in the fields despite its
negligible impact in soil fertility. It can be used as substrate in Anaerobic co-Digestion
(AcoD) and as precursor to produce Activated Carbons (ACs). In this
context, a biorefinery concept was developed based on two purposes: 1) the pretreated
MCW can be valorised as co-substrate in the AcoD with Organic Fraction
of Municipal Solid Wastes (OFMSW), and 2) MCW can be used as a precursor of
ACs for biomethane (bioCH4) conditioning.
The AcoD of OFMSW with chemically pre-treated MCW in presence of
H2O2 at 23 ºC increased the biogas and CH4 yields by 65% and 48%, respectively,
when compared to AD of standalone OFMSW., providing higher biogas quality
and a more stable AcoD process than with non-pre-treated MCW.
Among the ACs produced, the physically MCW(PA)3h AC performed better
in H2S removal than commercial and impregnated by liquid digestate ACs.
Textural properties seemed to be more important than the mineral content for
H2S removal and the presence of O2 on MCW(PA)3h surface may have favoured
H2S catalytic oxidation.
The MCW(PA)3h AC was also the most suitable candidate for CO2 separation
due to its more favourable textural properties, sufficient selectivity and
higher working capacity than the others ACs produced. The adsorption equilibrium
measurements of CO2 and CH4 showed that the Sips isotherm model and
the Adsorption Potential Theory (APT) can be confidently employed to correlate
the experimental data, as well as the axial dispersed plug-flow and Linear Driving
Force (LDF) model is able to correlate the fixed bed experimental data.
The environmental Life Cycle Assessment of a biorefinery case study was
performed on the hypothesis of implementing, at an existing Portuguese
Anaerobic Digestion plant processing OFMSW, (i) an AcoD unit using MCW as
co-substrate; (ii) an H2S unit using MCW(PA)3h as adsorbent, and (iii) a Pressure
Swing Adsorption (PSA) upgrading unit. The cogeneration of the biogas produced
during AcoD with non-pre-treated MCW is more sustainable than with
pre-treated MCW. The environmental impacts associated with biogas upgrading
to bioCH4 at optimized H2S adsorption capacity of MCW(PA)3h, if fossil natural
gas used for the OFMSW transport is substituted by the produced bioCH4, decreased
significantly, giving lower impacts than cogeneration in five categories.
Descrição
Palavras-chave
Activated Carbon Anaerobic Digestion Biorefinery Biogas Upgrading to Biomethane Maize Cob Waste Pre-treatment