The researchers used a process called reversed A2/O to remove nitrogen from a mix of leachate and municipal wastewater. They found that the key factor for efficient nitrogen removal is the hydraulic retention time, which should be at least 9 hours. Increasing the dissolved oxygen in the aerobic basin can actually reduce total nitrogen removal. Adjusting the sludge return ratio can improve organic and denitrification removal, while changing the mixed-liquor return ratio can enhance denitrification removal. By maintaining specific conditions like water temperature, solids retention time, and oxygen levels, they achieved optimal organic and nitrogen removal simultaneously, meeting A-level standards for wastewater treatment.