Enhancing methane production from the invasive macroalga Rugulopteryx okamurae through anaerobic co-digestion with olive mill solid waste: process performance and kinetic analysis

Abstract

The biomass valorisation of the invasive brown alga Rugulopteryx okamurae (Dictyotales, Phaeophyceae) is key to curbing the expansion of this invasive macroalga which is generating tonnes of biomass on southern Spain beaches. As a feasible alternative for the biomass management, anaerobic co-digestion is proposed in this study. Although the anaerobic digestion of macroalgae barely produced 177 mL of CH4 g−1 VS, the co-digestion with a C-rich substrate, such as the olive mill solid waste (OMSW, the main waste derived from the two-phase olive oil manufacturing process), improved the anaerobic digestion process. The mixture improved not only the methane yield, but also its biodegradability. The highest biodegradability was found in the mixture 1 R. okamurae—1 OMSW, which improved the biodegradability of the macroalgae by 12.9% and 38.1% for the OMSW. The highest methane yield was observed for the mixture 1 R. okamurae—3 OMSW, improving the methane production of macroalgae alone by 157% and the OMSW methane production by 8.6%. Two mathematical models were used to fit the experimental data of methane production time with the aim of assessing the processes and obtaining the kinetic constants of the anaerobic co-digestion of different combination of R. okamurae and OMSW and both substrates independently. First-order kinetic and the transference function models allowed for appropriately fitting the experimental results of methane production with digestion time. The specific rate constant, k (first-order model) for the mixture 1 R. okamurae- 1.5 OMSW, was 5.1 and 1.3 times higher than that obtained for the mono-digestion of single OMSW and the macroalga, respectively. In the same way, the transference function model revealed that the maximum methane production rate (Rmax) was also found for the mixture 1 R. okamurae—1.5 OMSW (30.4 mL CH4 g−1 VS day−1), which was 1.6 and 2.2 times higher than the corresponding to the mono-digestions of the single OMSW and sole R. okamurae (18.9 and 13.6 mL CH4 g−1 VS day−1), respectively.

Performance and kinetic evaluation of the anaerobic digestion of olive pomace derived from a novel manufacturing process based on an olive cold-pressing system: influence of the fruit ripening level

“…The anaerobic inoculum used was a mesophilic granular sludge from a full-scale UASB reactor treating wastewater from a brewery industry. The reactors were prepared with the addition of the inoculum and the substrate together with a micronutrient solution [5,6]. The main characteristics of the inoculum were pH: 7.5 ± 0.2, total solids (TS): 25.0 ± 1.1 g/ kg, volatile solids (VS): 19.9 ± 1.2 g/kg.…”

A Concise Review on the Potential Applications of Rugulopteryx okamurae Macroalgae

“…The use of R. okamurae biomass as a substrate in anaerobic digestion has emerged as a solution for the problem of accumulating tons of algal biomass along the coasts. Anaerobic digestion is a biological process ( Figure 4 ) that occurs in the absence of oxygen, in which microorganisms metabolize organic matter, generating high calorific value biogas as a final product (mainly methane, 60–70%) [ 11 ]. Biogas is produced for energy purposes, as a renewable energy source.…”

“…Despite still being incipient, research on potential applications of the macroalgae is also being performed as a way of minimizing the accumulation of macroalgae residue and the costs associated with its removal and elimination from affected regions [ 10 ]. This research gives value to the residue [ 11 ], transforming a problem into an opportunity for obtaining new marketable products [ 12 ].

Figure 1 Schematic representation of the taxonomic position of [ 13 ].

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Evaluation of batch mesophilic anaerobic digestion of raw and trampled llama and dromedary dungs: methane potential and kinetic study

“…The anaerobic inoculum used was a mesophilic granular sludge from a full-scale UASB reactor treating wastewater from a brewery industry. The reactors were prepared by the addition of the inoculum and the substrate together with a micronutrient solution [19,20]. The main characteristics of the inoculum were pH: 7.5 ± 0.2, total solids (TS): 24.4 ± 1.3 and volatile solids (VS): 20.3 ± 1.0.…”

“…These values indicated the high carbon and the low mineral content of the substrates, being balanced substrates for the AD process [27]. The substrates nitrogen content was also considered optimal for the AD process since the C/N ratio of all the substrates studied was within the range of 20-30, although other authors established a more restrictive ratio, placing the most optimal C/N ratio for the AD process between 25 and 30 [20][21][22][23][24][25][26][27][28]. The C/N content of the dungs used in these experiments were 26.8 ± 5.5 and 23.6 ± 0.9 for the llama dung (raw and trampled, respectively) and 22.2 ± 0.6 and 23.7 ± 0.7 for the dromedary dung substrates (raw and trampled, respectively).…”