Anaerobic digestion (AD) was utilized to treat the ever-growing amount of organic fraction of municipal solid waste (OFMSW) generated due to population growth and the expansion of the global economy. The widespread application of AD has led to a continuous increase in residual solid digestate that necessarily requires further disposal. Improving AD efficiency and reducing the large amount of digestate is necessary. This study investigated the chemical and physical characteristics of biochar derived from digestate at different pyrolysis temperatures (300 °C, 500 °C, and 700 °C), as well as corn stover biochar at 500 °C, and their effects on AD performance. The pH value of the biochar increased with an increase in pyrolysis temperature while the electrical conductivity decreased. Macropores dominated the biochar’s pore size, and decreased with an increased pyrolysis temperature. The biochar preparation temperature significantly influenced the AD efficiency. Biochar prepared at 700 °C outperformed the other groups, improving the biogas production yields by 10.0%, effectively shortening the lag time, and increasing the average chemical oxygen demand (COD) degradation rate by 14.0%. The addition of biochar (700 °C) and corn stover biochar increased the relative abundance of the volatile fatty acid (VFAs)-oxidizing bacteria Syntrophomonadaceae, which expedited the acid conversion in AD systems. Biochar facilitated direct interspecies electron transfer between DMER64 and Trichococcus with Methanosaeta, enhancing the biogas production performance. These findings confirmed that the biochar derived from digestate promoted biogas production and acid conversion in the AD system of OFMSW. Furthermore, biochar has an improved AD stability, which represents a promising approach to recycling digestate.

Compared with monotherapy, combination therapy is the first choice and the most promising method for the treatment of many complex diseases. Due to the wide variety of drugs, it is often difficult to choose desirable combination drugs with synergy and low risk. Additional research should always be done before combining drugs because the combinatorial effects can be synergistic, additive, or even antagonistic. Synergistic drugs work together to cause an effect greater than the sum of its parts. Some studies propose different approaches to detect synergism between two or more drugs. Based on the framework of bifurcation-based method, we propose an approach to screen another potential synergistic drug for a given drug. Different from other methods, the approach can help us screen and detect drugs which have a synergistic effect with a known drug, thus playing critical roles in combination therapy. In order to demonstrate the effectiveness of the approach, we apply it to three models, i.e. the zeroth-order reaction model, the galactose model, and the epithelial-to-mesenchymal transition network. The approach provides a theoretical basis for rational design of combination drugs and new use of old drugs.