As energy consumption and waste generation from human activities continue to rise, the technology of anaerobic digestion (AD), which converts waste into bioenergy, has gained popularity. Biogas produced from AD commonly contains 60 % CH4, 40 % CO2 and a minor fraction of impurities. Currently, several anaerobic reactors have been designed to upgrade the biogas with biomethane content above 90 %. This review summarizes the current trends in the biological upgradation of biogas from a bio-circular economy perspective to achieve sustainable energy goals. Examples of applications reporting the latest advancements in treating industrial effluents using high-rate anaerobic reactors have been mentioned. The integrated anaerobic-aerobic hybrid reactor offers a solution to the limitations of traditional methods in treating diverse effluents. A special focus on biological upgradation techniques such as in-situ, ex-situ, and hybrid mechanisms have been briefed. The key advantage of hybrid upgradation is its ability to address the pH rise during in-situ process. Additionally, the applications of artificial neural networks and optimization to upgrade biogas production have been discussed. The review concludes with future research directives with emphasis on the economic viability of the approaches.

Experience mapping based predictive controller (EMPC) is a recently developed controller based on the concepts of Human Motor Control. It has been demonstrated to out-perform other classical controllers like proportional-derivative (PD), model reference based adaptive controller (MRAC), linear quadratic regulator (LQR) and the linear quadratic Gaussian (LQG) for both Type-1 and Type-0 systems. This paper analyses the stability and efficiency of EMPC for Type 1 systems. EMPC uses rectangular pulse input as control action for well-damped Type 1 systems and a first order decay input for under-damped Type 1 systems. The simulation results of EMPC for position control of a DC motor with a load coupled through a flexible shaft are presented as a case study to derive and prove the stability criterion. The efficiency of EMPC on a practical system is analysed in terms of energy dissipated in the armature resistance of the motor and the same is compared with PD, MRAC, LQR, LQG controller. Further, the computational cost of EMPC is discussed and compared with traditional controllers from the point of view of implementation.