Over the last 12-months, Hoyle Tanner has been working on a comprehensive wastewater treatment facility upgrade design at the Bartlett Bay WWTF (BBWWTF) in South Burlington, Vermont. Our client, the City of South Burlington, adopted an ambitious Climate Action Plan in October 2022. The new Climate Action Plan includes goals of 80% greenhouse gas emissions reduction and 90% use of renewable energy by 2050 and the City is pursuing a wide variety of infrastructure improvements to reach these goals. Hoyle Tanner’s wastewater design team considered a broad range of alternatives during the study phase which focused on energy efficiency, incorporating several innovative technologies into the final design to assist the City in achieving the objectives laid out in their Climate Action Plan. These nonconventional energy-efficient approaches are detailed below.
1. Effluent Heat Exchange
Effluent Heat Exchange is a process by which heat, or thermal energy, can be extracted from treated wastewater effluent before it is discharged from a WWTF. The thermal energy extracted from treated effluent can then be fed to heat pumps to provide space heating for enclosed structures.
The BBWWTF design will include a new central heating plant in the proposed UV treatment building. The new central heating plant will house heat recovery heat pumps, heat recovery heat exchangers, and distribution pumps. Treated effluent will be drawn from the effluent channel to two heat exchangers, which will extract heat from the treated effluent before returning it to the effluent channel at a lower temperature as part of a heat recovery loop.
The extracted thermal energy will be transferred to the two heat pumps to be used for heating enclosed treatment process structures. A backup gas-fired boiler heating system will be provided as a supplement for the effluent heat exchange system during the coldest weather of the year.
Effluent Heat Exchange is an advancing technology in Europe which has yet to see widespread implementation in the United States, though its use is expanding. It has greater benefit for cold climates where wastewater temperatures can be significantly warmer than ambient air temperatures for much of the year. Given the cold weather in northern Vermont, Hoyle Tanner selected this technology for the BBWWTF upgrade as an energy-saving method to help the City of South Burlington meet their Climate Action Plan objectives for emissions reduction and renewable energy use.
2. Controls Optimization
Supervisory Control and Data Acquisition (SCADA) is a system which provides monitoring and control capabilities for industrial processes and is a standard in modern wastewater treatment facilities. In WWTFs, SCADA provides operators with the ability to remotely monitor and control electronic and mechanical instrumentation and treatment equipment.
SCADA can also be used to store data on wastewater flows, temperatures, solids concentrations, chemical concentrations, and more. In conventional practice, SCADA systems are used to manually change or pre-program settings for instrumentation and treatment equipment based on current influent conditions or typical time-dependent influent cycles. New technologies are allowing increased controls automation through SCADA to improve WWTF treatment performance and energy efficiency.
Flexible Load Management
The BBWWTF design includes a new SCADA system with some of these improved automation capabilities. One such improvement will be the implementation of Flexible Load Management (FLM). FLM is a method for more efficient energy use which involves offsetting power draw needs during peak grid demand hours to times outside of those peaks.
To achieve this, the BBWWTF design includes supercharging dissolved oxygen rates in advance of forecasted peak energy load events before ramping down variable frequency drives (VFDs) on aeration system blowers to reduce their speed and power draw during the peak energy load events. In simpler terms, this means that additional oxygen will be added to the wastewater before power grid demand spikes so that less oxygen needs to be added while the grid demand is high, ensuring that adequate treatment performance can be maintained while reducing power consumption at the treatment facility.
FLM helps to reduce stress on the power grid by reducing peak power demand. Green Mountain Power (GMP), the electric utility in South Burlington, will additionally provide the City with a reduced power rate if FLM is implemented and, since FLM is not yet widespread in these types of applications in New England, a pilot program is available through GMP to provide cost support for implementing FLM into SCADA system design.
FLM implementation at BBWWTF will allow reduced power consumption during peak demand hours to alleviate some stress on the power grid while also reducing the rate the City needs to pay for power at the facility. Spacing out the grid’s power supply needs should assist the City of South Burlington in reaching its Climate Action Plan carbon emissions reduction goal.
Hubgrade Digital Performance Platform
The BBWWTF design will also include implementation of Veolia’s Hubgrade Digital Performance Platform to improve the facility’s ability to automatically respond to dynamic influent conditions.
Veolia is an international company focused on clean water sustainability, including the development of innovative water management technologies. Their Hubgrade platform is an online software tool which will allow real-time optimization of the WWTF treatment processes. The tool utilizes online instrumentation to collect data in real time and then applies analytics and algorithms to continuously benchmark and optimize treatment facility performance. The Hubgrade platform includes features which focus on select unit operations of a plant, resulting in:
- Improved hydraulic capabilities during peak storm events
- Increased biological treatment capacity
- Improved biological phosphorus removal performance
- Reduced chemical needs for phosphorus removal
- Reduced energy consumption for aeration
- Reduced energy consumption for internal nitrate recirculation
The BBWWTF design will specifically implement Hubgrade features which optimize dissolved oxygen saturation and nitrogen removal, treatment system performance during storm events, nitrate recirculation, return-activated sludge (RAS) flow rates, and biological phosphorus treatment enhancements. These improvements will optimize the treatment facility’s chemical and energy consumption requirements while improving its treatment efficiency. The biggest advantage of implementing this platform is using the data monitored in real time, allowing the facility to respond dynamically and automatically to changing influent characteristics, ensuring effective and energy-efficient treatment performance despite rapidly changing conditions.
The controls optimization capabilities of this software tool will assist the City in reaching its Climate Action Plan carbon emissions reduction goals by improving energy efficiency while optimizing its wastewater treatment performance.
3. Active Solar Implementation
New photovoltaic (PV) cells, or solar panels, are included in the BBWWTF design to provide renewable energy directly to the treatment facility and reduce its demand for power from the grid. Hoyle Tanner is incorporating the solar array into our site and building designs while collaborating with a solar power vendor to detail the installation.
Hoyle Tanner’s design engineers are supporting the solar power subconsultant through coordination and layout of buried electrical conduit alignments among the many other buried utilities on site. The design includes large solar installations on the proposed operations and chemical buildings, as well as smaller installations on the proposed headworks and ultraviolet (UV) buildings.
Additional PV cell installations will be considered on top of covered biosolids storage tanks on the site to provide further renewable energy. These installations are expected to provide a total of approximately 7,000 square feet of solar panel coverage capable of producing upwards of 300 kWh per day of renewable energy at the BBWWTF. This represents more than half of the power requirement for the entire facility to function on a typical day.
The solar panel installations at BBWWTF will significantly reduce the facility’s energy costs and greatly assist the City in meeting the renewable energy and emissions reduction objectives outlined in South Burlington’s Climate Action Plan.
Additional energy-efficiency alternatives were considered for the project before ultimately being deemed too costly or marginally effective. These alternatives included (1) alternative facility heating methods with geothermal energy sources or wood pellets and (2) biosolids handling methods such as electronic vehicle (EV) trucks for sludge hauling, sludge thickening to reduce volume, or sludge pumping to a disposal site. These particular alternatives did not provide a meaningful return on investment and did not contribute enough of a reduction in greenhouse gas emissions to justify their implementation.
In addition to improving sustainability and use of renewable energy at the BBWWTF, this project will also improve the facility’s resilience to extreme weather and grid conditions while reducing life-cycle costs and streamlining plant operation.
Hoyle Tanner is very excited to be implementing these innovative technologies into the BBWWTF design and expect that they will assist the City of South Burlington in meeting their carbon emissions reduction and renewable energy use objectives while enhancing treatment performance at BBWWTF and improving water quality in Lake Champlain. Reach out to me if you have any questions about implementing energy-efficient features at your WWTF!
