Thermal Pretreatment of Harvest Residues and Their Use in Anaerobic Co-digestion with Dairy Cow Manure

Ensemble machine learning prediction of anaerobic co-digestion of manure and thermally pretreated harvest residues

This study aimed to clarify the statistical accuracy assessment approaches used in recent biogas prediction studies using state-of-the-art ensemble machine learning approach according to 10-fold cross-validation in 100 repetitions. Three thermally pretreated harvest residue types (maize stover, sunflower stalk and soybean straw) and manure were anaerobically co-digested, measuring biogas and methane yield alongside eight thermal preprocessing and biomass covariates. These were the inputs to an ensemble machine learning approach for biogas and methane yield prediction, employing three feature selection approaches. The Support Vector Machine prediction with the Recursive Feature Elimination resulted in the highest prediction accuracy, achieving the coefficient of determination of 0.820 and 0.823 for biogas and methane yield prediction, respectively. This study demonstrated an extreme dependency of prediction accuracy to input dataset properties, which could only be mitigated with ensemble machine learning and strongly suggested that the split-sample approach, often used in previous studies, should be avoided.

Anaerobic co-digestion of spent coconut copra with cow urine for enhanced biogas production

Laboratory-scale bioreactors were used to co-digest spent coconut copra (SCC) and cow urine (CU) as a co-substrate (SCC + CU) in a batch mode under thermophilic condition (45 ± 2°C) in order to enhance biogas production. The effect of CU pretreatment on the performance indicators (biogas and biomethane yields, total solids (TS), and volatile solids (VS) reduction, pH and volatile fatty acids (VFAs) concentrations) were also examined. This was compared with mono-digestion of SCC. The experiment was performed with different mixing ratios in reactors labelled as follows: A = 75 g SCC + 5 ml CU; B = 70 g SCC + 10 ml CU; C = 65 g SCC + 15 ml CU; and D (control) = 80 g SCC at a hydraulic retention time of 42 days. Co-digestion (SCC + CU) significantly improved anaerobic digestion (AD) performance resulting in a threefold and fivefold increase in biogas and biomethane production, respectively, with concomitant TS (44.9-57.7%) and VS (55.4-60.3%) removal efficiencies. But for mono-digestion (control experiment), all CU treated and co-digestion assays showed pH stability ranging between 6.6 and 7.4 and VFAs' concentrations ranging from 15-330 mgL^-1. By acting as a buffer, CU effectively enhanced the AD performance of SCC as demonstrated in this study.

Natural Communities of Microalgae and Cyanobacteria from Eutrophicated Waters as Potential Co-substrates for Small-scale Biogas Production

The purpose of this study was to determine the biogas potential of biomass produced by microbiotic communities developed under natural conditions in freshwater systems such as ponds incorporated into agricultural landscapes. Natural communities of microalgae were collected from a small eutrophicated pond where dominant species were euglenoids (Lepocinclis species). Cyanobacterial communities dominated by Lyngbya species were taken from a domestic aquarium and cultivated under makeshift conditions. Experiments were done using dairy cow manure (DCM) for codigestion with natural communities of microalgae (MDM) and cyanobacteria (CDM) and conducted during 42 days in thermophilic regime. The total biogas yields were 421.40 and 383.34 mL/g volatile solids (VS), while the average methane contents were 63.97 and 64.06% for MDM and CDM, respectively. Our results indicate that the natural communities of microalgae and cyanobacteria used in this study possess the potential for biogas production, which is, in comparison with particular algal and cyanobacterial strains cultivated under strictly controlled cultivation conditions, more promising. Therefore, this study aims to motivate further investigations into the diverse natural communities of microalgae and cyanobacteria and pretreatments that are environmentally friendly and cost-effective and will eventually enhance small-scale biogas production on agricultural farms.

Hydrothermal pretreatment of source separated organics for enhanced solubilization and biomethane recovery

The objective of this research was to evaluate the effect of the hydrothermal pretreatment on the solubilization of source separated organics (SSO) as well as the biomethane recovery through the mesophilic batch anaerobic digestion process. For this purpose, the SSO was subjected to fifteen different pretreatment conditions within five different severity index (SI) values (3, 3.5, 4, 4.5, and 5). The pretreatment temperature, holding time, and pressure ranged from 150 to 240 °C, 5 to 30 min, and 476 to 3367 kPa, respectively. The highest solubilization improvement of ∼50% was achieved under the pretreatment condition of "220 °C-10 min-2323 kPa" corresponding to the SI value of 4.5. However, the maximum biomethane production yield of 280 mL/g TCOD_added and biomethane production rate of 30 mL/g TCOD_added were obtained under the less intense pretreatment conditions of "190 °C-20 min-1247 kPa" and "170 °C-30 min-786 kPa", respectively.

Electroporation of harvest residues for enhanced biogas production in anaerobic co-digestion with dairy cow manure

The aim of this research was to develop a method for pretreatment of lignocellulose (LC) substrates (harvest residues (HR)) via electroporation (EP) for the purpose of improving the biogas production process. In addition, pretreated LC substrates were analyzed by scanning electron microscopy (SEM) and the energy balance of the total process was calculated. After the conducted pretreatment and anaerobic co-digestion with dairy cow manure (DCM), the statistical data analysis showed statistically significant differences in biogas and/or methane yield for all three LC substrates and their fractions. It was concluded that, after the pretreatment of LC substrates via EP, it is possible to improve the anaerobic co-digestion process and to achieve positive energy balance of the total process.