The anaerobic digestion (AD) technology is widely used in the treatment of waste and wastewater. To ensure the treatment efficiency and to increase the biogas production, it is crucial to control and estimate the AD process. This can be achieved by monitoring the pH, temperature, and volatile fatty acids (VFAs) levels. The control and estimation of the AD process can be done using various methods such as online monitoring, model-based control, and machine learning algorithms. By controlling and estimating the AD process, it is possible to optimize the biogas production, reduce the energy consumption, and minimize the environmental impact.