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Using model-based process optimisation and advanced control strategies to minimise infrastructure changes
Aarhus Water, the managing water utility in the city of Aarhus, Denmark, has planned a capacity expansion of Viby wastewater treatment plant (WWTP) with minimum investments in new infrastructure. DHI partnered with other consultants and technology providers to identify a cost-efficient solution that relies on optimisation of existing processes. Interventions to achieve increased capacity were identified by using DHI’s modelling software, WEST. The proposed solution is now implemented in full-scale operation at the WWTP with considerable improvements in operational stability.
Aarhus Water has planned to increase the capacity of Viby WWTP in order to ensure stable and efficient treatment performance. Due to the WWTP’s expected short lifetime (10–15 years), a cost-efficient capacity expansion should be achieved with minimum infrastructure interventions.
In partnership with NIRAS A/S, TechRas Miljø ApS and EssDe GmbH, DHI provided a solution relying on the optimisation of existing processes to achieve the desired increased capacity while minimising capital expenditures. A new optimal operational strategy was identified and tested using WEST. The strategy involved conversion of existing tanks and implementation of real-time control combined with innovative granular sludge technology.
achieved through process optimisation and minimum infrastructure changes
under high influent loading conditions
in implementation of the capacity expansion
Flemming B. MøllerProject ManagerAarhus Water
Insufficient capacity at Viby WWTPAarhus Water has been facing several challenges in the operation of Viby WWTP. The WWTP (90,000 PE) has experienced sub-optimal nitrogen removal performance and solids handling, resulting from insufficient biological treatment capacity and hydraulic capacity under heavy rain events. The impact of insufficient capacity is expected to deteriorate due to forecasts of increased loading in the coming years.
Looking for cost-efficient solutions while considering short WWTP lifetimeTo ensure stable performance, Aarhus Water has planned a 33% capacity expansion of Viby WWTP from 90,000 PE to 120,000 PE. Operation with increased capacity is expected to continue for the next 10–15 years when a shutdown of Viby WWTP and other WWTPs in Aarhus is planned, at which time the entire urban area will be served by a single, centralised WWTP.
Therefore, the short lifetime of Viby WWTP calls for cost-efficient solutions to be implemented, and the required expansion should be achieved by optimising existing processes and avoiding infrastructure investments with high capital expenditures.
DHI partnered with NIRAS A/S, TechRas Miljø ApS and EssDe GmbH to provide a solution for the desired capacity increase of Viby WWTP through revamping and optimisation of existing processes. The solution minimised interventions for new infrastructure and ensured the cost efficiency required by the client.
Using process expertise to identify interventionsA number of options for increasing the WWTP capacity were considered, namely:
Using process modelling for time-efficient evaluation of alternativesThe combination of different options resulted in 22 possible WWTP configurations that were simulated using WEST. The performance of each configuration was evaluated under typical and extreme conditions (dry and wet weather, low temperature). Key performance indicators such as effluent quality, energy consumption and chemical usage were used to compare the different configurations and identify optimal operation.
Identifying a new operational strategyThe optimal WWTP configuration that would enable achieving the desired increased capacity was identified and included (Figure 1):
Improved treatment performance Model simulations of Viby WWTP operation with optimised process configuration showed significant improvements when compared to both current operation and other configurations tested, particularly:
Up to 47% reduction in effluent taxes was estimated to be achievable through the optimised operation, leaving considerable room to overcome costs for chemical usage and equipment installation.
Full-scale application of new operational strategyAt the end of 2019, the new operational strategy was implemented in Viby WWTP. A comparison of the treatment performance before (March 2019) and after the capacity expansion (March 2020) is presented in Figure 2. Despite significantly higher influent flow, the reported measurements indicate similar, if not improved, effluent nitrate and ammonia levels in 2020. Specifically, more efficient denitrification was achieved by implementing the advanced control strategy and increasing sludge retention in the system, as shown by improved settling characteristics (Figure 3).
Overall, the proposed solution for capacity expansion has provided tangible improvements in the performance and operational stability of Viby WWTP while proving to be cost-efficient and reducing the need of preliminary full-scale testing.
Aarhus Water (Aarhus Vand A/S) is the managing water utility in Aarhus, Denmark’s second largest city. The company is the local water supplier, storm- and wastewater service provider, and responsible for managing 10 wastewater treatment plants that receive 35 million m3 of wastewater per year.
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 deployed in the implementation of real-time control, data assimilation, automated anomaly detection, and automated reporting for process monitoring and optimisation.
Cost-efficient capacity expansion of Viby wastewater treatment plant
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