Anaerobic Digestion, Codigestion of Food Waste, and Chicken Dung: Correlation of Kinetic Parameters with Digester Performance and On-Farm Electrical Energy Generation Potential

Abstract

Valorization of agro-food waste through anaerobic digestion (AD) is gaining prominence as alternative method of waste minimization and renewable energy production. The aim of this study was to identify the key parameters for digester performance subjected to kinetic study and semicontinuous operation. Biochemical methane potential (BMP) tests were conducted in two different operating conditions: without mixing (WM) and continuous mixing (CM). Three different substrates, including food waste (FW), chicken dung (CD), and codigestion of FW and CD (FWCD) were used. Further kinetic evaluation was performed to identify mixing’s effect on kinetic parameters and correlation of the kinetic parameters with digester performance (volatile solid removal (VS%) and specific methane production (SMP)). The four models applied were: modified Gompertz, logistic, first-order, and Monod. It was found that the CM mode revealed higher values of Rm and k as compared to the WM mode, and the trend was consistently observed in the modified Gompertz model. Nonetheless, the logistic model demonstrated good correlation of kinetic parameters with VS% and SMP. In the continuous systems, the optimum OLR was recorded at 4, 5, and 7 g VS/L/d for FW, CD, and FWCD respectively. Therefore, it was deduced that codigestion significantly improved digester performance. Electrical energy generation at the laboratory scale was 0.002, 0.003, and 0.006 kWh for the FW, CD, and FWCD substrates, respectively. Thus, projected electrical energy generation at the on-farm scale was 372 kWh, 382 kWh, and 518 kWh per day, respectively. Hence, the output could be used as a precursor for large-scale digester-system optimization.

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“…Hence, using the same ratio of substrate to working volume, the volume of the substrate used in the OFS was computed, and the electrical energy generation was calculated as shown in Table 10 . In comparison with a previous study on the co-digestion of chicken dung and food waste [ 39 ], the optimum OLRs for both the CSTR (OLR 5) and the AF (OLR 4) produced higher electrical energy generation, whereas the previous study achieved 0.002 kWh [ 39 ].…”

“…The kinetic study was analyzed using Microsoft Office 2021 Excel Solver, where all the kinetic parameters can be predicted for all the models (modified Gompertz model (MG), logistic model (LG), and first order model (FO)). The peak SMP rate and the lag phase can be derived by using the MG and LG; meanwhile, the FO can explain the hydrolysis stage [ 39 ]. In a batch study, the methane generation rate was estimated by the MG model to be proportional to the population growth rate of the methanogens.…”

“…In a batch study, the methane generation rate was estimated by the MG model to be proportional to the population growth rate of the methanogens. The LG, however, believed that the methane production was proportional to its maximum rate [ 39 ]. On the other hand, the FO model was used to describe hydrolysis as the rate limiting phase in the AD system [ 51 ].…”

“…In addition to the experimental work, modelling, which includes kinetic studies and artificial neural networks (ANNs), of the AD of CM and MR was also investigated and analyzed. Designing commercial-scale digesters can benefit from modelling since it provides a useful idea from which to initiate the design and operation and can be used to anticipate the AD system behavior and maximize the biogas output [ 39 ]. Kinetic studies use the application of pre-determined formulas [ 40 , 41 ]; meanwhile, the ANN is an intelligent system which involves computation and mathematics, inspired by the biological nervous system (human brain processes), and produces the equation (output) for the biogas prediction [ 42 , 43 ].…”

Performance Monitoring of Anaerobic Digestion at Various Organic Loading Rates of Commercial Malaysian Food Waste

“…Moreover, the study found that the modified Gompertz model for biogas production was fitted with food waste co-digested with the chicken manure. However, the chicken manure substrate fits well with a logistic model ( Jaman et al, 2022 ).…”