The researchers studied two sewage treatment systems to see how well they remove contaminants. They looked at things like pH, nutrients, metals, and organic matter in the sludge produced by each system. The system with an anaerobic sludge mantle reactor had higher levels of phosphorus, potassium, and organic matter in the sludge compared to the system with stabilization ponds. Metal ion concentrations were higher in the anaerobic system's sludge, except for manganese and nickel. Iron levels were similar in both systems. Overall, the anaerobic system had higher metal ion levels in the sludge compared to the stabilization ponds.