Carbon and chemical energy balance investigation on four wastewater treatment plants: PRESENTATION ONLY

Dai, Z., Aqua Enviro


With the assistance of modelling (GPS-X 7.0), a carbon and chemical energy balance investigation was conducted on four different wastewater treatment plants for discovering the potential opportunities for energy recovery improvement,

This study firstly discovered that there is a strong linear relationship between the organic carbon content and chemical energy content in both the wastewater and sludge and it thereby considered the chemical energy balance and the carbon mass balance are in good agreement. The result suggested that 55-83% of the influent chemical energy were captured in primary sludge and the surplus activated sludge. Meanwhile, 8-14% of the influent chemical energy remained in the final effluent that was discharged back to the environment, and the rest 12-32% of the influent chemical energy was considered lost to the atmosphere as CO2. The investigation of a sludge treatment process suggested that 39% of the chemical energy fed to the sludge treatment can be recovered as biomethane. Meanwhile, 20% of the sludge chemical energy remained in the dewatered digested sludge (known as biosolid), and approximately 31% of the sludge chemical energy was distributed to the filtrates and centrates that were returned to head of the work.

This work subsequently exploited a conceptual model built from one of the investigated treatment plants to simulate the impact of process optimization on the energy balance of the treatment system. The simulation looked into measures of reducing the sludge storage time from 17 days to minimal and improving the primary settlement from 40% solids removal to 70% solids removal. The former measure could elevate the biomethane production by up to 19%. The latter measure could improve the biomethane production by up to 37% and could simultaneously reduce the energy consumption on the aeration of activated sludge process by up to 20% due to the primary effluent with a reduced strength requires less oxygen for the treatment.

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