Successful strategies for increasing energy self-sufficiency at Gruneck wastewater treatment plant in Germany by food waste co-digestion and improved aeration

Population growth, tightening effluent discharge requirements and increasing energy costs are driving the wastewater treatment sector to improve energy efficiency and strive towards energy self-sufficiency. Despite many strategies being proposed for improving energy self-sufficiency at wastewater treatment plants (WWTPs), limited case studies have been conducted. This full-scale case study at Gruneck WWTP evaluates the effectiveness of two different strategies and quantifies their plant-wide impact. Gruneck WWTP increased energy self-sufficiency by 24% (from 64 to 88%) through reducing energy consumption with aeration upgrades (8% increase) and increasing energy production with food waste co-digestion (16% increase). The plant-wide analysis indicated that the aeration upgrades did not affect effluent quality; however co-digesting food waste at 20% additional organic load caused some minor downstream impacts including reduced dewaterability, fluctuating biogas quality and solids accumulation. A solar dryer was installed to manage the increased biosolids production resulting from co-digestion. The dryer reduced biosolids transportation costs by 30% with minimal increase in total plant energy (below 2%). Payback periods for the co-digestion facility and blower upgrade were 10 and 17 months, respectively. The solar dryer, however, has a payback period of 30 years. Findings from this case study provide practical knowledge of the trade-offs for different strategies commonly employed to improve energy self-sufficiency at WWTPs. The results provide evidence that there is significant incentive for similar plants to improve energy self-sufficiency through co-digestion and aeration upgrades.