Effects of organic loading rate and pretreatments on digestion performance of corn stover and chicken manure in completely stirred tank reactor (CSTR)

Dual optimization in anaerobic digestion of rice straw: Effects HRT and OLR coupling on methane production in one-stage and two-stage systems

This experiment reports an energy-saving, cost-effective and environmental-friendly method to recover energy from high-cellulose waste: anaerobic digestion (AD) by extending hydraulic residence time (HRT) from 50d to 70d with ultra-high organic loading rate (OLR) of 2.28-2.80 g TS·L-1 d-1. The results indicate that biogas yield per VS and methane yield per VS increase with the extended HRT, with a maximum increase of up to 67.9%, while both yields decrease as OLR increases. The volumetric gas production (VGP) and volumetric methane production (VMP) improve by 20.2-37.3% when HRT is extended to 57 days and OLR is 2.80 g TS·L-1 d-1, reaching a peak at this point. As the biogas production capacity of the two-stage anaerobic digestion reaches its peak, the gap between the one-stage system and the two-stage system decreases from 23% to 7% under the same conditions. This demonstrates that optimizing HRT and OLR not only enhance the gas production efficiency of the AD system but also reduce the gas production disparity between single-stage and two-stage systems, thus serving as a cost-effective method for engineering operations. Microbial community analysis of each system reveals that extending HRT increases the abundance and diversity of microbial communities, while changes in HRT and OLR result in significant shifts in the distribution of methanogens. Through reasonable regulation of HRT and OLR, a balance can be found between the full degradation of organic matter and the system load, so as to maximize biogas production and efficiency.

Modelling of technical, environmental, and economic evaluations of the effect of the organic loading rate in semi-continuous anaerobic digestion of pre-treated organic fraction municipal solid waste

The study concerned technical feasibility, economic profitability, and carbon footprint (CF) analysis of semi-continuous anaerobic digestion (sAD) of organic fraction of municipal solid waste (OFMSW). The research assessed the pre-treatment effect on sAD by varying organic loading rates (OLR) from 3.38 to 6.75 kgvs/m3d. Three sAD configurations were investigated: hydrodynamic-cavitated (HC-OFMSW), enzymatically pre-treated (EN-OFMSW), and non-pre-treated (AD-OFMSW). Principal Component Analysis and Supervised Kohonen's Self-Organizing Maps combined the experimental, economic, and environmental evaluations. The sAD configurations were grouped predominantly according to the OLR however, within each OLR group the configurations were clustered according to the pre-treatments. The finding highlighted that pre-treatments offset inhibition in sAD of OFMSW due to the OLR increase, being economically profitable and CF negative up to 4.50 kgvs/m3d for EN-OFMSW and to 5.40 kgvs/m3d for HC-OFMSW. Whereas sAD-OFMSW remained economically and environmentally viable only up to 3.87 kgvs/m3d. HC-OFMSW reached the highest performance. In detail, for HC-OFMSW the NPV and CF ranged from 17679.30 to 43827.12 euros and from -51.08 to -407.210 kg CO2eq/1 MWh daily produced, by decreasing the OLR from 5.40 to 3.87 kgvs/m3d. These results are fundamental since pre-treatment is usually expensive due to additional energy or chemical requirements.

Adding Granular Activated Carbon and Zerovalent Iron to the High-Solid Anaerobic Digestion System of the Organic Fraction of Municipal Solid Waste: Anaerobic Digestion Performance and Microbial Community Analysis

Anaerobic digestion (AD) performance and microbial dynamics were investigated in a high-solid anaerobic digestion (HSAD) system of the organic fraction of municipal solid waste (OFMSW). 1, 5, 10, and 15% (w/w, dry weight of the OFMSW) of granular activated carbon (GAC) and zerovalent iron (ZVI) were added to the HSAD system. The results showed that adding ZVI and GAC can improve the methane yield of the OFMSW. Notably, R-(GAC + ZVI) exhibited the highest cumulative methane yield of 343.0 mL/gVS, which was 57.1% higher than that of the R-control. At the genus level, the dominant bacteria included norank_f__norank_o__MBA03, norank_f__norank_o__norank_c__norank_p__Firmicutes, Fastidiosipila, norank_f__Rikenellaceae, and Sphaerochaeta, while Methanoculleus, Methanobacterium, and Methanosarcina were the dominant archaea. The highest relative abundance of norank_f__norank_o__norank_c__norank_p__Firmicutes was 30.8% for the R-(GAC + ZVI), which was 71.4% higher than that of the R-control. The relative abundance of Methanoculleus and Methanobacterium for the R-(GAC + ZVI) and the R-control group accounted for 79.0 and 90.8% of the total archaeal abundance, respectively. Additionally, the relative abundance of Methanosarcina was 10.6% for R-(GAC + ZVI), which was higher than that of the R-control (1.1%). After the addition of GAC and ZVI, the electron transfer capacity of the HSAD system was enhanced, resulting in promoted methane production. Thus, the simultaneous addition of GAC and ZVI to the HSAD system can be an effective strategy to promote the cumulative methane yield of the OFMSW.

Green and chemical-free pretreatment of corn straw using cold isostatic pressure for methane production

In this study, the effect of cold isostatic pressure (CIP) pretreatment on the physicochemical properties and subsequent anaerobic digestion (AD) performance of corn straw (CS) was explored. The CS was subjected to CIP pretreatment by pressures of 200, 400 and 600 MPa, respectively, while AD was carried out at medium temperature (35 ± 2 °C). The results showed that CIP pretreatment disrupted the dense structure of the CS and altered the crystallinity index and surface hydrophobicity of the CS, thereby affecting the AD process. The presence of CIP pretreatment increased the initial reducing sugar concentration by 0.11-0.27 g/L and increased the maximum volatile fatty acids content by 112.82-436.64 mg/L, which facilitated the process of acidification and hydrolysis of the AD. It was also observed that the CIP pretreatment maintained the pH in the range of 6.37-7.30, maintaining the stability of the overall system. Moreover, the cumulative methane production in the CIP pretreatment group increased by 27.17 %-64.90 % compared to the control group. Analysis of the microbial results showed that CIP pretreatment increased the abundance of cellulose degrading bacteria Ruminofilibacter from 21.50 % to 27.53 % and acetoclastic methanogen Methanosaeta from 45.48 % to 56.92 %, thus facilitating the hydrolysis and methanogenic stages. The energy conversion analysis showed that CIP is a green and non-polluting pretreatment strategy for the efficient AD of CS to methane.

Energy generation from bioelectrochemical techniques: Concepts, reactor configurations and modeling approaches

The process industries play a significant role in boosting the economy of any nation. However, poor management in several industries has been posing worrisome threats to an environment that was previously immaculate. As a result, the untreated waste and wastewater discarded by many industries contain abundant organic matter and other toxic chemicals. It is more likely that they disrupt the proper functioning of the water bodies by perturbing the sustenance of many species of flora and fauna occupying the different trophic levels. The simultaneous threats to human health and the environment, as well as the global energy problem, have encouraged a number of nations to work on the development of renewable energy sources. Hence, bioelectrochemical systems (BESs) have attracted the attention of several stakeholders throughout the world on many counts. The bioelectricity generated from BESs has been recognized as a clean fuel. Besides, this technology has advantages such as the direct conversion of substrate to electricity, and efficient operation at ambient and even low temperatures. An overview of the BESs, its important operating parameters, bioremediation of industrial waste and wastewaters, biodegradation kinetics, and artificial neural network (ANN) modeling to describe substrate removal/elimination and energy production of the BESs are discussed. When considering the potential for use in the industrial sector, certain technical issues of BES design and the principal microorganisms/biocatalysts involved in the degradation of waste are also highlighted in this review.

Modeling and optimization of photo-fermentation biohydrogen production from co-substrates basing on response surface methodology and artificial neural network integrated genetic algorithm

The main aim of the present study was to establish a relationship model between bio-hydrogen yield and the key operating parameters affecting photo-fermentation hydrogen production (PFHP) from co-substrates. Central composite design-response surface methodology (CCD-RSM) and artificial neural network-genetic algorithm (ANN-GA) models were used to optimize the hydrogen production performance from co-substrates. Compared to CCD-RSM, the ANN-GA had higher determination coefficient (R² = 0.9785) and lower mean square error (MSE = 9.87), average percentage deviation (APD = 2.72) and error (4.3%), indicating the ANN-GA was more suitable, reliable and accurate in predicting biohydrogen yield from co-substrates by PFHP. The highest biohydrogen yield (99.09 mL/g) predicted by the ANN-GA model at substrate concentration 35.62 g/L, temperature 30.94 °C, initial pH 7.49 and inoculation ratio 32.98 %(v/v), which was 4.20 % higher than the CCD-RSM model (95.10 mL/g).