Bluebloqs as a circular water solution

Abstract

Urban water management is faced with upcoming challenges due to climate change, the deterioration of existing infrastructures and the depletion of water sources. Climate change brings about more intense rainfall events and longer periods of drought. On top of that, the deterioration of the piped network urges for investments in the existing system, to ensure that the provision of water services can be maintained. Furthermore, the depletion of water sources is raising awareness regarding the value of freshwater which gives rise to the re­use of water flows that have up to now often been considered as nuisance rather than viable resource. Examples of these flows are the wastewater and the stormwater flow.

The existing centralised infrastructure consists of three reliable systems. The first system supplies high­quality water, the second drains out stormwater and the third one discharges wastewater. These three systems operate separately from each other and follow a linear approach to
water management. In recent years, circular water management has become more prevalent. Instead of following a linear approach in the three separate systems, the re­use of water flows as viable sources are applied more often. New, often local, solutions can be designed to effectively complement existing systems in maintaining the high provision of water services that societies have consistently been using over the past decade. This circular approach can ensure that current water requirement levels can be met sustainably by the improved urban water systems.

By dealing with the upcoming challenges of high­intensity rainfall and long periods of drought– which both have a high spatial variability – local solutions are able to support the centralised infrastructure. This is done by both mitigating the pluvial flood risk, as well as by providing a high ­quality water source. An arguably ideal solution which addresses both the pluvial flood risk and also provides a high­quality water source, is the Bluebloqs system. The Bluebloqs system can help mitigate pluvial flood risk by the attenuation of flow, the result of implementing an attenuation tank in the stormwater drainage system. Also, the Bluebloqs system is able to filter and store this stormwater to provide a high­quality water source during water­scarce seasons.

Whether the Bluebloqs system is a viable solution which addresses both the mitigation of the pluvial flood risk as well as the provision of water challenge, is investigated in this research. The Bluebloqs system is a circular water solution that makes use of an attenuation tank, a bio­filter and an aquifer storage and recovery (ASR) system. The attenuation tank is physically connected to the drainage system and it consequently decreases the risk of surcharged pipes in the drainage network. From the attenuation tank, the water is pumped towards the bio­filter, where pollutants from the water are removed and the water is filtered to such an extent that it can be infiltrated into the aquifer. In the aquifer, the water is stored to overcome seasonal variations in
water availability. The Bluebloqs system has the objective to supply water in the dry season, even though its source is stormwater, which enters the system during the wet season. This research has analysed the performance of the Bluebloqs system for different dimensions and operations.

Within this thesis, a framework has been built that presents the performance of the Bluebloqssystem. This framework consists of three groups; the interactions with centralised infrastructure, the water quality indicators and the impact of the Bluebloqs system on its environment. These three have their own distinct performance indicators, which characterise the effectiveness of the Bluebloqs system in providing a specific water service. The group of the framework dealing with the interactions with the centralised infrastructure uses performance indicators for the volume of water lost in overflow events, and volume of water supplied through the Bluebloqs system as high­ quality water source to the end­user. The indicators for the other groups characterise the Bluebloqs system differently. Each group within the framework projects the performance of the Bluebloqs system for other interest groups. For example, the indicators regarding the impact of the Bluebloqs system on its environment are of interest to municipalities thinking about implementing the system.

The behaviour of the Bluebloqs system has been modelled. This model presents the physical processes taking place within the Bluebloqs system. The output of the model are the performance indicators of the framework. By running the model under different input parameters, the performance of the modelled Bluebloqs system is tested on the three groups of the framework.

The outcome of testing the model on the framework has shown that the Bluebloqs system can be improved. One of the suggested improvements is to work with feed cycles for the bio­filter. These feed cycles consist of the periodic saturation of the bio­filter. Once the bio­filter is saturated, the flow from the attenuation tank towards the bio­filter is interrupted, to let the water gradually filter through the bio­filter.
By applying feed cycles, the bio­filter is better capable of removing pollutants from the water. However, periodically interrupting the water flow from the attenuation tank towards the bio­filter negatively impacts the effective storage capacity of the attenuation tank. When having more feed cycles in a day, these interruptions last for a shorter period of time. Depending on the desired performance of the system, which is based on the performance indicators, these feed cycles should be aligned with the capacity of the attenuation tank and the discharge of the pump for the flow between the attenuation tank and the bio­filter.
Fitting the feed cycles to the seasonality of rainfall patterns can further increase the performance of the system in mitigating flood risks. Applying predictive control when overflow events occur is an additional control option that minimises the environmental impact of the system. Finally, the performance of the Bluebloqs system can be presented based on all the performance indicators included in the framework, and the model can be used to adjust the system dimensioning and operations to present the consequences of adjustments to the desired performance of the Bluebloqs system.

The frameworks’ performance indicators can be used to understand the Bluebloqs ideal configuration to deliver a specific desired performance. The desired performance of the system determines the dimensions and operations of the system. Co­designing the Bluebloqs system is thus crucial to its delivered performance.

In conclusion, the framework and model can be used to present the Bluebloqs system for different scenarios. The framework can generate a comprehensive overview of what can be expected of the Bluebloqs system when implementing it in a specific project site, in comparison to other solutions that may be considered, such as green roofs or storage tanks. Also, its use as circular solution being complementary to existing urban water infrastructure can be presented by the framework and model output. This will help in the transition of urban water systems in dealing with the upcoming challenges related to climate change, the deterioration of the piped infrastructure and the depletion of water sources.