Decarbonisation Technology - August 2024 Issue

Biogas

Existing sludge tanks

Existing dewatering

Class A biosolids

Mesophilic digesters

Dryer 90% solids

Thickening

Class A biological hydrolysis

Figure 1 UAJA treatment flowsheet featuring Class A digestion

change with the completion of the University Area Joint Authority (UAJA) biosolids upgrade, a project that will mark the first North American installation of BH technology. The UAJA, located in State College, Pennsylvania, operates the Spring Creek Pollution Control Facility. This facility is situated on the boundary of Benner Township and College Township in Centre County, Pennsylvania, and provides wastewater treatment, solids handling, and water reuse services to the Centre Region. It also includes an existing composting process that converts sludge and wood chips into a Class A biosolids compost product, which is sold nationally. This composting operation meets the US EPA’s Biosolids Rules and Regulations as a Process to Further Reduce Pathogens (PFRP). Additionally, the sewage sludge processed here meets vector attraction reduction (VAR) requirements, qualifying it as Class A biosolids. Operational since 1993, the original composting facility was nearing the end of its useful life, prompting UAJA to enlist engineering consulting firm RETTEW to design an upgraded solution. UAJA evaluated a multitude of options, narrowing these down to two viable alternatives: expanding the existing composting facility or replacing it with a comprehensive treatment system featuring BH, AD, and sludge drying. RETTEW conducted an economic analysis of both options, evaluating the relative capital and operating costs over the next 25 years. Those calculations are shown in Table 1 . RETTEW’s economic analysis included several assumptions such as costs of natural gas of $7/MMBTU, electricity costs of $0.075 per KWHr, RNG revenue, inclusive of environmental attributes such as RINs, of $15/MMBTU, Class A biosolids revenue of $10/ton, and tipping

fees of $35.00/ton of waste. Based on the clear technical advantages and especially the projected economic 25-year cost benefit of BH, AD, and sludge drying, UAJA selected the second alternative to address its long-term handling and disposal of wastewater treatment plant biosolids. treatment system is displayed in Figure 1 . The Class A digestion sequence features Veolia’s Enhanced Biological Hydrolysis (EBH) system and two anaerobic digesters (see Figure 2 ). The EBH system employs multi-stage hydrolysis at both mesophilic and thermophilic temperatures and incorporates six reactor vessels, all with a nominal volume of 33,500 gallons and Process design The flowsheet for UAJA’s multi-phased designed to operate anaerobically. By isolating and optimising the hydrolysis and acid-forming stages of digestion, volatile fatty acid (VFA) conversion and pathogen destruction are

Figure 2 Example of Veolia’s Enhanced Biological Hydrolysis (EBH) system ( Photo courtesy of Veolia)