Browsing by Author "Kolajo, Oluwafemi"

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Strategies for enhancing methane production from coffee pulp via co-digestion, urea supplementation, and biochar-assisted process stabilisation
(Elsevier Ltd., 2026-07-29) Oyetade, Joshua; Nason, Abigail; Mulimi, Lilian; Kolajo, Oluwafemi; Adeeyo, Adeyemi; Fayemi, Omolola; Machunda, Revocatus L
offee pulp (CP), a lignocellulosic agro-industrial residue rich in organic matter, contains phenolic compounds and other constituents that can limit anaerobic digestion (AD) performance. This study evaluated semi-continuous AD of CP in continuously stirred tank reactors under mesophilic conditions (37 °C), comparing co-digestion with coffee wastewater (CWW) and sisal wastewater (SWW) against CP mono-digestion. Co-digestion achieved stable reactor performance, with methane production rates of 564 ± 89 and 624 ± 92 mL CH4/L/day and methane contents of 56–59%. This improved performance was associated with enhanced nutrient balance (C/N = 23.8), dilution of potential inhibitory compounds, and low VFA concentrations (<1 g/L). In contrast, CP mono-digestion resulted in process instability, characterised by reduced methane production, VFA accumulation (>1.5 g/L), pH decline, and nitrogen limitation (TAN = 56.0–64.8 mg/L). Urea supplementation restored nutrient availability and reactor stability, resulting in methane production of 343 ± 18 mL CH4/L/day. Although combined urea and biochar supplementation supported recovery (326 ± 26 mL CH4/L/day), the independent effect of biochar could not be isolated, and biochar did not prevent instability at increased organic loading rates. Batch assays further showed that inoculum adaptation enhanced initial methane production kinetics, whereas cattle manure inoculum achieved the highest final methane yield (328 ± 8 mL CH4/g VS). Overall, co-digestion with agro-industrial wastewaters represents an effective strategy for improving CP digestion, while maintaining adequate nitrogen availability is critical for stable CP mono-digestion.
Synthesis of bio-based polymeric hydrogels from a hybrid system of cellulose derived from selected invasive plant biomass grafted with poly(acrylic acid)
(Elsevier B.V., 2026-05-11) Oyetade, Joshua; Nason, Abigail; Mulimi, Lilian; Kolajo, Oluwafemi; Adeeyo, Adeyemi; Fayemi, Omolola; Machunda, Revocatus
The current study presented upcycling invasive plant biomass into high-purity cellulose, which offers a simultaneous solution for ecological management and sustainable production of bio-based materials. The preliminary proximate and lignocellulosic characterization for the biomass was carried out, while polyacrylic acid (PAA) was grafted via free radical polymerization onto the extracted cellulose from parthenium weed (PW) and water hyacinth (WH). The study revealed hemicellulose, lignin, and cellulose in PW to be 41.21%, 18.78%, and 31.13%, while WH has a value of 38.7%, 15.91% and 27.8%. The cellulose displayed a fibrous morphology with increased roughness compared to the amorphous sponge-like structure of pristine PAA. The cellulose exhibited functional groups characteristic of glucose, while PAA hydrogels contained hydrophilic groups (OH and COOH), enhancing water absorption. Thermal analysis indicated that the hydrogel's thermal stability improved with added cellulose. Among the formulations, PAA grafted onto 1% WH and PW-cellulose has the highest absorbency value of 95.43 and 89.46 g/g at 60 min, respectively, compared to pristine hydrogel (106.14 g/g). Also, the conditions for maximum water absorbency were observed at a pH of 7, a crosslinker amount of 0.05 g, and an initiator value of 0.010 g. The absorbency value increased to 95.47 g/g for PAA grafted to 1%PW-cellulose. Thus, the study revealed an effective strategy to convert invasive plant-derived cellulose and polyacrylic acid into valuable bio-based hydrogels, promoting material innovation consistent with circular economy and environmental sustainability principles.