A Cooper, W Bailey, C Rogers, D Solley, M Laginestra
Publication Date (Web): 12 February 2016

Wastewater treatment represents significant energy consumption, and authorities are becoming increasingly aware of the urgent need to provide sustainable services in delivering services.

Today, with a greater emphasis on energy efficiency and reducing resources, operators of wastewater treatment plants (WWTPs) must consider their role as resource recovery centres, focusing on purifying water for reclamation, beneficially using biosolids, and conserving or producing energy.

Biosolids management at WWTPs offers the opportunity to achieve energy sustainability through anaerobic digestion, the production of digester gas with high methane content, and heat and energy production. This potential can be enhanced if high-strength wastes are brought to the WWTPs for co-digestion with the generated sludge from the wastewater treatment process.

This paper looks at two treatment plants (significantly different in size) where biosolids are suitably managed in the US in an effort to achieve sustainability.

Blue Plains Wastewater Treatment Plant
Handling 1400ML a day, the DC Water’s Blue Plains plant in Washington encountered rapidly escalating costs in 2006 and new digestion facilities were placed on hold. After a strategic development investigation by a blue-ribbon panel, plant management opted away from thermophilic digestion, which was the original plan, and proceeded with thermal hydrolysis and mesophilic anaerobic digestion, dramatically reducing construction and O&M costs.

Since then, DC Water has implemented $450 million in improvements, including generation of 13MW of power.

DC Water continues to explore opportunities for becoming energy-neutral. The following options are actively being considered:

  • Solar panels over process tanks (potentially yielding 14,600 MW/year);
  • Solar panels over parking lots, building tops, etc. (potentially yielding 8700 MW/year); and,
  • Co-digestion of food waste of 15 dt/d (150 wt/d), which is estimated to yield 1.5 to 4.0 MW. 

Also, DC Water is actively looking at reducing energy usage and the following projects offer opportunities for additional savings:
  • Improving efficiency of secondary treatment blowers; changing to finer bubble air diffusion for secondary treatment to yield two MW;
  • Changing to Anammox for BNR to yield 4 MW benefit. 

Hill Canyon Treatment Plant
A Californian plant managing 50ML a day, Hill Canyon began to be transformed in 2006 after the plant operations team began an aggressive energy conservation program to enable 50% of the plant’s needs to be met by power production from biogas. Additional energy was provided by solar panels in 2007 (150 kW) and upsized cogeneration in 2013 (700 kW). To ensure production of adequate digester gas, HCTP now treats a variety of high-strength waste streams, and in 2014 HCTP achieved 100% production of its energy usage.

Some Australian authorities are also looking at WWTP energy efficiency and biosolids sustainability aspects, including co-digestion and alternative digestion enhancements, and these are outlined in context with the above US case studies.

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