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West Lafayette’s water resource recovery facility (WRRF) in Indiana, USA, partnered with DHI to assess technology and reduce carbon footprint by 50% before 2025 while achieving better effluent quality. DHI developed a dedicated plan to optimise WRRF operation and validated it by using WEST software for detailed biokinetic process modelling and simulation. The proposed solution for real-time control, digester optimisation and biological phosphorus removal is set to achieve a 60% energy neutral operation.

Challenge

West Lafayette’s WRRF committed to minimise their city’s impact on climate change by reducing carbon footprint by 50% before 2025 and continuously improve the quality of effluent discharged into the Wabash River. Improvements were to be implemented with minimal modifications to existing infrastructure.


Solution

DHI developed an optimisation plan following a systemwide approach to evaluate current operation of the WRRF. Through the use of DHI’s simulation software WEST, plant process modelling was completed in order to develop and test real-time control strategies for aeration in a virtual environment. Additionally, operational modifications for anaerobic digester optimisation showed the potential to double the power harvested from biogas.

Results

Improved effluent quality

< 10mg/L Total Nitrogen
< 5mg/L Total Phosphorus

Improved efficiency

60% energy neutral operation achievable

Annual savings

Estimated $ 293,000


‘DHI has provided West Lafayette with a roadmap to our goals. Our vision of being energy neutral while still maintaining excellent effluent seems achievable now.’

Dave Henderson
Utility Directory, Water Resource Recovery Facility
City of West Lafayette, IN


The full story

Challenge

Rethinking traditional WRRF operation to achieve an ambitious goal
In 2017, the city’s mayor of West Lafayette, Indiana, initiated a climate action plan to reduce the city’s carbon footprint, with focus on one of the highest contributors – wastewater treatment. As part of the plan, the goal set for West Lafayette WRRF is to achieve 50% reduction in carbon footprint by 2025. This challenged the WRRF to rethink and convert the traditional ways of working in order to operate carbon neutral processes while being consistently below permitted limits.

To achieve this vision, the WRRF has focused on optimisation of the current operational strategy with minimal modifications to existing plant infrastructure. A new operating strategy was required to achieve stability in effluent quality with the potential to convert the treatment process for near-future modification to Total Nitrogen (TN) discharge limits.


Solution

Performance assessment and development of a multi-target optimisation plan
DHI performed a comprehensive evaluation of current operation of the WRRF in order to identify the potential for improved efficiency. Potential solutions were tested in a virtual environment using DHI’s WEST software for biological process simulation to quantify the effects and benefits of new operational strategies and process configurations. An optimisation plan was subsequently developed, whereby priority actions were identified.

The provided solution identified the following actions:


  • Nutrient-based aeration control
    Implementation of turbo-blower speed control using a direct ammonia-based controller to reduce the specific energy and total energy required for aeration.

  • Biological phosphorus removal
    Conversion of a waste activated sludge (WAS) storage tank into a side-stream fermenter for return activated sludge (RAS).

  • Anaerobic digester and biogas harvesting optimisation
    Use real-time controls and timers to create a steady-state environment for VSS destruction and optimise digester heat and energy balance.

  • Carbon footprint analysis
    DHI developed a carbon footprint calculator for West Lafayette to monitor and track improvements to holistic greenhouse gas emissions in terms of CO2 equivalents.

Figure 1. Blowers for aeration of activated sludge tanks at West Lafayette WRRF. © DHI


Results

The preferred solution resulted in significant effluent quality and energy performance improvements for the WRRF.

Improved effluent quality
Simulation results demonstrated the potential to convert existing nitrifying processes into either simultaneous nitrification-denitrification or an MLE-type of process for TN removal. With side-stream fermentation of return sludge, it is feasible to operate within permitted and expected nutrient limits for all projected loadings:


< 10 mg/L effluent TN concentrations
< 0.5 mg/L effluent TP concentrations


Reduction in chemical dosing
As a result of the implementation of biological phosphorus removal, almost complete abatement (99%) of chemical dosing of precipitation is expected.

Increased energy efficiency
The implementation of nutrient-based aeration control with high-efficiency aeration equipment will generate a 49% reduction in aeration energy requirements. This is equivalent to 22% reduction of the power consumption of the entire WRRF. The solution, combined with the optimisation of biogas recovery from anaerobic digestion, will result in 60% energy neutrality, including a 99% reduction in natural gas reliance for digester heating.

Major yearly savings
Overall, the implementation of the optimisation plan will yield annual savings of $293,000. DHI and West Lafayette are now working to identify low-cost implementation options to fit with the city’s budget for process improvements and carbon footprint reduction fund sources.


About the client

The city of West Lafayette WRRF is subject to variable loading caused by seasonal population changes from Purdue University student housing. Among the most densely populated cities in the US, West Lafayette is home to over 30,000 permanent residents. The West Lafayette WRRF treats 7-9 MGD depending on the season for discharge into the Wabash River. The city’s mayor has, as part of the original Paris agreement, initiated a plan to reduce the city’s carbon footprint with focus on wastewater treatment.


Software used


WEST - The state-of-the-art software for efficient dynamic modelling of wastewater treatment plants and virtual testing of a wide range of control strategies.


DIMS CORE - The software platform has been proposed as a method for implementing real-time control, data assimilation, automated anomaly detection, and automated reporting for process monitoring and optimisation.

Case story - Highlights flyer

Achieving 50% carbon footprint reduction by 2025

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