Sludge digestion efficiency was improved by separating the time sludge stays in the system from the time water flows through it. By reducing the water flow time to 10 days, the sludge became thicker and was digested better, producing more biogas. Different types of bacteria helped break down the sludge, with some becoming more common when the water flow time was shorter. This change also led to more efficient energy production from methane, using less energy overall.