Relationship between wastewater sludge quality and energy production potential

Relationship between wastewater sludge quality and energy production potential

A joint research and development project with University of Western Australia

Wastewater Treatment Plant (WWTP) plays an irreplaceable role in the overall wellbeing and development of societies. Wastewater treatment is an ongoing process that requires high-energy consumption, and this demand contributes negatively to climate change. Nonetheless, there are options available for energy production and recovery in WWTPs during its treatment process, which can also reduce the negative environmental impacts. This study aims to investigate the potential of energy production and recovery at one WWTP, and the reduction of environmental impacts achieved.

The study site is a WWTP situated at Subiaco of Western Australia, operated by Water Corporation. The research evaluated sludge samples from the Subiaco WWTP at the UWA SESE laboratory for the characteristics of the sludge. Laboratory batch scale anaerobic digestion studies were also carried out to evaluate the efficiency of the system. The results of this study were then compared with data from the neighbouring WWTPs that use anaerobic treatment for sludge stabilisation. Further analyses were carried out to determine the economical values of the generated energy potential and the reduced environmental impacts.

The experimental results showed that sludge samples from the Subiaco WWTP had a biogas production capacity of 0.015 m3/L sludge or 0.6 m3/VS, with a potential energy production of 40.4 megawatt-hour (MWh) per day. The biogas conversion to electricity used a combined heat and power (CHP) unit with an assumed efficiency factor of 70 %, and results indicated that Subiaco WWTP has the potential to recover 78 % of its overall energy consumption through anaerobic treatment, with a generated value of A$1,012,291 per year. The payback period of purchasing a CHP unit using this generated value alone in the Best Case scenario is between 2.2 to 9.6 years, and 4.2 to 12.5 years in the Worst Case scenario. The amount of avoided carbon dioxide (CO2) emission from the substitution of treatment system is 7,475 metric tons annually. This study had successfully demonstrated the sustainability and economical advantage of an anaerobic treatment process, and concluded that energy production and recovery is a feasible option for Subiaco WWTP.