A Week Becomes a Day: New Ideas and O&M Collaboration Leads to the Shortest THP Shutdown on Record

The first North American installation of the Cambi B6 modular THP was installed at the HRSD Atlantic Treatment Plant (ATP) in 2019 and started up in March 2020. The drivers for installing THP at ATP were to achieve Class A biosolids, maximize existing digester capacity, improve final product dewaterability, stackability and minimize storage requirements, in addition to receiving FOG to improve biogas production. Each year, the THP pressure vessels (Pulper, four Reactors and Flash Tank) require inspection, resulting in a planned shutdown of this critical system and requiring storage of liquid and dewatered solids upstream of THP as well as an interruption of feed to the anaerobic digesters downstream of the THP. This has also required temporary hauling of unstabilized pre-dewatered cake, as the liquid storage capacity at ATP is insufficient to store for the typical shutdown duration. At the ATP, as with many THP installations worldwide, there is no redundancy of the single Pulper and Flash Tank on THP train, and therefore it has been critical for the plant to develop and optimize processes to perform the required cleaning, inspection, and maintenance activities while minimizing the shutdown duration and expedite the return to normal operations. Since commissioning, HRSD has conducted four planned 'turnarounds', as well as experienced a handful of unplanned shutdowns that required quick responsiveness for repairs. After each shutdown, the staff have reevaluated performance, documented lessons learned and revised processes to improve the next one. Through this process of refining and updating guidance documents, for the third shutdown in December 2022, ATP had optimized to a 5-day shutdown, from stopping feed to the THP to returning the solids processes to normal operations. While this duration was in line with the most efficient Cambi B6 shutdowns at other installations in the UK and elsewhere abroad, it still required the hauling of unstabilized solids during the shutdown, approximately 15 solids trucks per day. Hauling operations are not only costly, but also increase the instance of odor complaints from the nearby neighborhood and high school adjacent to the WRF. Following the third shutdown, two Maintenance Operators (MO - maintenance staff) identified some innovative ideas that with the potential to shorten the shutdown enough to completely eliminate the need for hauling of unstabilized pre-dewatered cake. These ideas stemmed from their intimate knowledge of the THP equipment and their collaboration with the operators in order to have a comprehensive understanding of the operating requirements of THP and the capabilities and constraints of the solids handling system. The new approach was discussed at length internal to the plant and then further with HRSD leadership, as it was not without risks and the potential for extra costs. With support from all levels of HRSD, the fourth annual THP was conducted in December 2023. Prior to ever shutting down the THP and interrupting operation, maintenance staff worked with operations to sequentially remove reactors and cooling heat exchangers from service, cleaned and inspected them, all while maintaining the THP in service. The intent was to do as much as possible while still processing solids and feeding the digesters. At the same time, operations took the lead on preparing for the shutdown, managing the solids inventory strategically to maximize the available storage volume for the liquid solids upstream of THP. The actual shutdown of the THP lasted just over 24 hours, rather than the previous best practice of five days. HRSD completed the shutdown and cleaned the Pulper and Flash Tank and other critical parts and completed all maintenance activities in one day — which is the shortest outage ever recorded by the many dozen operating Cambi THP facilities. This shutdown did not require any hauling of solids, and was performed by HRSD's own staff, other than the contract high-pressure cleaning services by Jet Blast. By eliminating the need for contract hauling and contractor staff to assist the MOs, HRSD realized a nearly $80,000 savings for the shutdown (Table 1). Through this process collaborating between O&M staff, the ATP has learned that many of the maintenance activities can be completed while service to the plant remains in operation. This paper will focus on the innovative ideas that arose from the collaboration between the ATP O&M staff, without which the no-hauling shutdown would not have been possible. Additionally, this presentation will provide lessons learned from this and prior planned and unplanned shutdowns and the approach taken by ATP to efficiently perform the required tasks while minimizing downtime. This presentation will benefit all WRF personnel, regardless of if THP is a part of the solids handling process. These lessons help ensure that the time for THP downtime, temporary operations and impacts to the rest of the solids handling processes are minimized. Most importantly, other WRFs will benefit from the experiences of the collaborative process conducted by HRSD to bring an idea from MOs to plant and HRSD leadership— when everyone comes to the table with an open mind to reach a common goal. By empowering staff's creativity, WRFs can realize cost and labor saving innovations and at the same time demonstrate the value that everyone brings to the utility.