Energy efficiency improvement of wastewater treatment processes subjected to load fluctuations

The objective of this study is to create methodology assisting the design or redesign of energy efficient wastewater treatment (WWT) plants. The focal points of the reported investigation are (a) methodology for analysis and evaluation of existing WWT facilities; (b) targeting, showing eventual scope for energy efficiency improvement; (c) bottlenecks identification; (d) design guidelines, assisting the redesign/retrofit design for efficiency improvement, and (e) support of decision making in case of alternative centralised/ decentralised/combined wastewater treatment options. The reported methodology utilises the process systems integration approach and extends the integration concepts to the specific area of wastewater treatment. The target area of application is the anaerobic wastewater treatment facilities, but the general discussion addresses the aerobic activated sludge biodegradation as well. In the first instance the energy management intent utilises the well-known process integration concept. Special account is made of long-term disturbances and dynamics as a result of rapid seasonal changes of the population in tourist areas (such as Killarney, County Kerry, Ireland). Flexibility and operability improvement are targeted; analysis and guided design changes are proposed. The paper analyses important quantitative characteristics of systems dynamic. Discusses the formulation of operating regions in dynamic operation situations and focuses on long-term disturbances and their best consideration in the quest for better energy efficiency and maximisation of possible capacity fluctuation absorption. Oversedign, structure changes and bypass placements are amongst the measures to be undertaken. The energy efficient redesign framework will include agitation electrical energy, process heat recovery, heat generation, bio-gas generation, etc. Further, a special attention is paid to environmental issues (dealing with wastewater effluents, odours, etc.). It includes a strategy for environmental impact analysis and sustainability analysis in dynamic conditions. In addition, a decision-assisting procedure will advise strategy for centralised/decentralised wastewater treatment accounting for the dynamics of the changeable financial environment. Suggested and discussed are possible links and integration between municipal and industrial wastewater treatment plants as overall wastewater treatment strategy in the area concerned. A discussion and practical guidelines drawing the importance of the energy management advances for more cost attractive wastewater treatment operations in cases of anaerobic/aerobic bio-treatment, centralised or distributed strategies are drown as a conclusion of the reported investigation.