One of the major environmental issues and research challenges have been to reduce emissions and effluents without compromising the production performance. The renewable energy recovery from waste to energy is less emitting than using fossil fuels. It can compete with the other renewables if properly generated, transferred, transmitted and used. Anaerobic digestion (AD) is a potential production process to improve the security of energy supply. It also serves as a promising alternative to waste disposal. The feasibility of AD technologies for power generation has been proven in some of the technologically and agriculturally advanced countries however world-wide implementation still needs some development. Presented work focuses to overview the challenges and practices for energy efficiency improvement of AD that have been reported recently, mainly between the years of 2015 - 2016. The assessment suggests the consideration and/or attentions for substrate, pre-treatment and operation mode of digesters for a better risk minimisation and feasibility maximisation. The characteristics and supply of the substrate were suggested as the initial susceptible factor for the energy efficiency of AD. The systematic review serves as an overview of the AD development and an establishment of technically feasible technologies for further study and extended implementation.