Water Journal : Water Journal November 2011
technical features 70 NOVEMBER 2011 water greenhouse emissions 2. Pumping represents up to 90% of energy consumption for clean water and up to 30% for wastewater processes. Potential reductions include: a. Between 5% and 10% improvement on existing pump performance; b. Between 3% and 7% improvement on pump technology; c. Between 5% and 30% in some pumping situations where the operational set-up has been changed from the design condition. Energy savings are feasible in more complex and large- scale systems, but frequently show marginal payback using current financial analyses. 3. There is scope for up to 20% improvement in clean water processes, but the energy use in this category is low. There may be potential in clean water processes opportunities associated with older DAF, membrane packages, U/V systems and ozone plants. 4. Between 50% and 60% of the energy consumed in the wastewater cycle is used in Activated Sludge Plants. Potential reductions include: a. Up to 25% performance improvement depending on investment to date; b. Up to 50% reduction is possible by aligning control parameters with the consent; 5. There is potential for optimising wastewater processes towards increasing primary sludge production, reducing secondary treatment loads and increasing gas yields to Combined Heat and Power (CHP) plant with minimal investment. 6. There is potential for up to 15% improvement in building services. 7. Renewable energy, mainly in the form of CHP from sludge gas, could contribute significantly to reducing the net energy demand of the water industry. 8. 'Water supply only' companies will have limited opportunities for improvement compared with those wastewater companies deriving energy from sludge. 9. For the whole water cycle, overall energy efficiency gains of between 5 and 15% seem realistic. But gains will depend heavily on the characteristics and current performance of the system, its operational management, the regional environment and geography. 10. Cost-benefit analyses should use electricity price increases projected to about half the design life of the plant; ie, at least 10 years into the future. 11. Negotiations on consent standards should include a net pollution assessment to balance pollution removed by treatment against pollution caused through increased energy demand. The balance must include electrical power generation and distribution efficiency. All the above savings are indicative only, suggesting order of magnitude gains for companies that either have not started or have implemented only limited energy efficiency measures. Some companies have made significant progress installing new equipment and refurbishing existing equipment with energy use reduction in mind. They are less likely to realise gains at the upper end of the ranges through future interventions. One objective of the study was to use the case studies to understand regional, environmental, regulatory and operational management differences between companies. However, there was insufficient comparative data to be able to make such distinctions apart from geography; a utility's energy demand is very dependent on the locations of its sources and fresh water delivery regime and wastewater collection and disposal, the optimum being by gravity. This is particularly illustrated by a comparison of the major Australian cities, as shown in Figure 3. The study also made recommendations to progress knowledge in, and application of, energy efficiency throughout the water cycle. The recommendations included: 1. Consider whether incremental improvements or technologies described in the case studies are relevant to local or regional energy efficiency initiatives and follow the advice and examples where applicable. 2. Use future electricity prices in cost/ benefit analyses, projected to about presented at 100% 70% 60% 50% 40% 90% 80% 30% 20% 10% 0% Sydney Melbourne Brisbane Adelaide Other energy -- demand Wastewater -- treatment Wastewater -- pumping Water supply -- treatment Water supply -- pumping Figure 3. Energy demand for four Australian utilities, 2008 (WSAA, 2010).
Water Journal December 2011
Water Journal September 2011