Influence of the Substrate/Inoculum Ratio on Process Stability and Performance during Batch Digestion of Grass Silage

Impact of using glucose as a sole carbon source to analyze the effect of biochar on the kinetics of biomethane production

The adaptation of biochar in anaerobic digestion (AD) positively influences the conversion of substrate to biomethane and promotes system stability. This study investigated the influence of biochar (BC) doses (0 to 8 g/L) on the Biochemical Methane Potential (BMP) of glucose during a 60-day AD in a mesophilic batch-type reactor. The first 6.5 weeks of the experimentation were dedicated to the microorganism's adaptation to the biochar and degradation of organics from the used inoculum (3 phases of the glucose feeding). The last 2 weeks (4th phase of glucose feeding) represented the assumption, that glucose is the sole carbon source in the system. A machine learning model based on the autoregressive integrated moving average (ARIMA) method was used to model the cumulative BMP. The results showed that the BMP increased with the amount of BC added. The highest BMP was obtained at a dose of 8 g/L, with a maximum cumulative BMP of 390.33 mL CH4/g-VS added. Likewise, the system showed stability in the pH (7.17 to 8.17). In contrast, non-amended reactors produced only 135.06 mL CH4/g-VS and became acidic at the end of the operation. Reducing the influence of carbon from inoculum, sharpened the positive effect of BC on the kinetics of biomethane production from glucose.

Influence of Pre-Incubation of Inoculum with Biochar on Anaerobic Digestion Performance

The application of biochar as an additive to enhance the anaerobic digestion (AD) of biomass has been extensively studied from various perspectives. This study reported, for the first time, the influence of biochar incubation in the inoculum on the anaerobic fermentation of glucose in a batch-type reactor over 20 days. Three groups of inoculum with the same characteristics were pre-mixed once with biochar for different durations: 21 days (D21), 10 days (D10), and 0 days (D0). The BC was mixed in the inoculum at a concentration of 8.0 g/L. The proportion of the inoculum and substrate was adjusted to an inoculum-to-substrate ratio of 2.0 based on the volatile solids. The results of the experiment revealed that D21 had the highest cumulative methane yield, of 348.98 mL, compared to 322.66, 290.05, and 25.15 mL obtained from D10, D0, and the control, respectively. Three models-modified Gompertz, first-order, and Autoregressive Integrated Moving Average (ARIMA)-were used to interpret the biomethane production. All models showed promising fitting of the cumulative biomethane production, as indicated by high R2 and low RMSE values. Among these models, the ARIMA model exhibited the closest fit to the actual data. The biomethane production rate, derived from the modified Gompertz Model, increased as the incubation period increased, with D21 yielding the highest rate of 31.13 mL/gVS. This study suggests that the application of biochar in the anaerobic fermentation of glucose, particularly considering the short incubation period, holds significant potential for improving the overall performance of anaerobic digestion.

Effects of additives on physical, chemical, and microbiological properties during green waste composting

Composting is an environmentally friendly and sustainable way to transform Green waste (GW) into a useful product. GW, however, contains substantial quantities of lignocelluloses that extend the composting period unless substances that accelerate composting are added. The objective of this research was to assess the influence of the following additives on GW composting (w/w dry matter contents of the additives were indicated): sugarcane bagasse at 15%; bean dregs at 35%; silage at 45%; flue gas desulfurization gypsum at 5%; maifanite at 4%; and furfural residue at 20%. Based on the composting temperature, compost density, porosity, particle-size distribution, water retention, pH, cation exchange capacity, available nutrient contents, humification coefficient, organic matter loss, microbial populations, and phytotoxicity, the best additives were 45% silage and 5% flue gas desulfurization gypsum. The latter two additives produced a high-quality product in only 35 and 37 days, respectively.

Evaluation of maifanite and silage as amendments for green waste composting

Composting is a popular method for recycling organic solid wastes including agricultural and forestry residues. However, traditional composting method is time consuming, generates foul smells, and produces an immature product. The effects of maifanite (MF; at 0%, 8.5%, and 13.5%) and/or silage (SG; at 0%, 25%, and 45%) as amendments on an innovative, two-stage method for composting green waste (GW) were investigated. The combined addition of MF and SG greatly improved composting conditions, reduced composting time, and enhanced compost quality in terms of composting temperature, bulk density, water-holding capacity, void ratio, pH, cation exchange capacity, ammonia nitrogen content, dissolved organic carbon content, crude fibre degradation, microbial numbers, enzyme activities, nutrient contents, and phytotoxicity. The two-stage composting of GW with 8.5% MF and 45% SG generated the highest quality and the most mature compost product and did so in only 21 days. With the optimized composting, the degradation rate of cellulose and hemicellulose reached 46.3 and 82.3%, respectively, and the germination index of Chinese cabbage and lucerne was 153 and 172%, respectively, which were all far higher than values obtained with the control. The combined effects of MF and SG on GW composting have not been previously explored, and this study therefore provided new and practical information. The comprehensive analyses of compost properties during and at the end of the process provided insight into underlying mechanisms. The optimized two-stage composting method may be a viable and sustainable alternative for GW management in that it converts the waste into a useful product.