Operating Performance of Full-Scale Agricultural Biogas Plants in Germany and China: Results of a Year-Round Monitoring Program

Abstract

Germany (DE) and China (CN) have different political approaches in supporting the biogas sector. Three German and three Chinese large-scale biogas plants (BGPs) were evaluated as part of a year-round monitoring program. Laboratory methods were utilized to analyze the chemical indicators. Results showed a stable anaerobic digestion process without system failures in all BGPs. The methane yield had a range of 0.23–0.35 m3CH4/kgODM for DE BGPs and 0.11–0.22 m3CH4/kgODM for CN BGPs, due to different substrates and working temperatures. Financial analyses indicated that DE BGPs are viable under their current feed-in tariffs contracts. Their financial internal rate of return (IRR) ranged between 8 and 22%. However, all CN BGPs had negative IRRs, indicating that they are financially unfeasible. Risk analyses illustrated that DE BGPs will face financial nonviability if benefits decrease by 9–33% or costs increase by 10–49%, or if a combined worse case (benefit decrease and cost increase) of 5–20% occurs. Incentives to BGP operations are particularly important in China, where the government should consider switching the construction-based subsidy to a performance-based subsidy system to motivate the operators. BGP monitoring is necessary to understand the performance, in addition to briefing policymakers in case a policy reform is needed.

Comparison of Biological Efficiency Assessment Methods and Their Application to Full-Scale Biogas Plants

“…This leads to a high CE BMP found in this study and also to a small spread in the values, which corresponds to results by Ruile et al of 21 German biogas plants [5]. The CE BMP reveals a small potential in increasing the digestion duration nowadays compared to lower CE BMP in other former studies [5,33,40], which is supported by a comparison of the SMP BMP to the SMP BMP of former studies [34,41]. Further optimization cannot be done for most BPs based on this.…”

Anaerobic Digestion of Pig Slurry in Fixed-Bed and Expanded Granular Sludge Bed Reactors

“…Compared with currently operating large-scale and laboratory-scale CSTRs for treating animal residues, which typically have an HRT of ≥15 d, EGSB and FB reactors can be used to reduce the HRT for the AD of PS [10][11][12][13][14]52]. This reduction in HRT, in turn, leads to a higher OLR and a higher MPR, shown by the comparison between the results of Reguiero et al [53] and this study in Table 4.…”

“…In Germany, based on Brosowski et al [6], it can be calculated that only 16% of the theoretical biomass potential of liquid pig manure is used. Biogas plants that use animal residues such as manure or pig slurry (PS) as the substrate often employ continuously stirred tank reactors (CSTRs) [2,[7][8][9], which have hydraulic retention times (HRTs) of more than 30 d [10][11][12][13][14]. Reducing the HRT below the doubling rate of the active biomass in the CSTR could wash out the microorganisms and cause the process to destabilize or fail [15].…”

Hydrothermal Treatment of Residual Forest Wood (Softwood) and Digestate from Anaerobic Digestion—Influence of Temperature and Holding Time on the Characteristics of the Solid and Liquid Products

“…Depending on the feedstock of the AD plant, the physicochemical characteristics of DG vary. The DG of agricultural AD plants from stirred tank reactors, for instance, is often characterized by DM concentrations below <5% [13] to remain suitable for pumping. Alternative utilization approaches for DG such as the coupling of AD with hydrothermal processes could open up new opportunities for plant operators [14,15].…”