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As the world is faced with rapid global urbanisation, climate change and increasing water scarcity, we are in the midst of a paradigm shift in the way we manage water. Cities all over the world are devising more holistic adaptation and mitigation strategies to deal with increasing populations, a changing climate and evolving regulatory requirements. 
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Vejle Spildevand A/S implements advanced dosing control as an efficient mitigation solution
 
To manage operations more efficiently, the water utility Vejle Spildevand A/S centralised its wastewater treatment. However, this resulted in increased and severe hydrogen sulphide (H2S) production in the sewer network, leading to negative consequences such as odour problems, sewer system degradation and health and safety concerns for workers and the public. By implementing automated chemical dosing, Vejle Spildevand A/S is now able to adequately deal with H2S-related issues, streamline operations and contribute to positive environmental outcomes.
 
Challenge
 
Sewer network length, transport time of wastewater and industry types in the catchment were identified as the main causes for H2S formation. H2S can have numerous negative consequences:

Odour issues: H2S has a characteristic unpleasant smell which can spread to nearby areas, affecting residents, businesses and public spaces
Degradation of the sewer: H2S is a corrosive gas that can react with metal components, leading to the degradation of pipes, manholes and other infrastructure, resulting in leaks, failures and costly maintenance
Health and safety concerns: H2S is toxic and poses health and safety risks. At low concentrations, H2S can cause respiratory irritation, headaches and other health issues. At higher concentrations, it can cause unconsciousness and is highly explosive.

 
To mitigate H2S issues, Vejle Spildevand A/S originally implemented chemical dosing in selected pumping stations and manually up- or down-regulated dosing at irregular intervals. This approach resulted in time-consuming manual regulation and over- or under-dosing, as wastewater composition can vary significantly over time.
 
Solution
 
Vejle Spildevand A/S desired an automated solution for efficient regulation of chemical dosing for H2S management. Preferably, a cost-efficient solution which could be integrated into their existing management platform. They found the answer in DHI.
 
Data from the H2S sensors were integrated into DIMS.CORE, DHI’s data repository and real-time data management platform. Together with existing data from pumping stations, the sensor data provide real-time information on H2S concentrations in selected parts of the sewer network. This is instrumental for understanding the dynamics of H2S formation and regulating chemical dosing. Next, DHI developed and customised the controller logic in the sewer network to dynamically adjust dosing rates based on hydraulic retention time and the H2S concentrations measured upstream.
 
This solution integrated data from sensors, pumping stations and the customised controller logic into the utility’s DIMS.CORE management system. This enabled Vejle Spildevand A/S to optimise chemical dosing strategies and suppress H2S with efficient chemical use. The combination of real-time data and customised controller logic empowers Vejle Spildevand A/S to make automated proactive decisions, and the system responds promptly to changing conditions while minimising the impact of H2S-related problems. 
 
Vejle Spildevand A/S uses DIMS.CORE for numerous other operations, including aeration control, sludge recirculation control and quantification of combined sewer overflows (CSO). Furthermore, DIMS.CORE is used for data collection and transfer to applications such as ‘Badevandsudsigten’ and ‘PULS’. Incorporating the advanced H2S controller in DIMS.CORE was a more efficient solution as compared to implementing a new system.

New DHI report supports solutions to minimise PFAS and other harmful substances from spreading to water environments 
 
PFAS, or per- and polyfluoroalkyl substances, are widely used, long-lasting chemicals. They are also called forever chemicals because they break down very slowly over time. PFAS have been found in water, air, fish and soil at locations across the globe. In recent years, scientific studies have shown that PFAS is linked to harmful effects on both the environment and human health. Consequently, there is increasing public and political concern about the spread of PFAS and other environmentally harmful substances, not least into groundwater and water environments.
 
Denmark’s largest wastewater utility BIOFOS asked DHI to trace the sources of PFAS and other environmentally harmful substances in the catchment area of 15 municipalities in the Greater Copenhagen area together with the 15 catchment municipalities. The investigation found that two waste management companies were the sources behind 40% of the PFOS (perfluorooctane sulfonic acid, part of PFAS) found at one wastewater treatment plant.
 
 
Challenge
 
There are thousands of PFAS chemicals, and they are ubiquitous in consumer, commercial and industrial products. As they break down very slowly, these so-called forever chemicals accumulate in the environment. In recent years, scientific studies have shown that PFAS is linked to harmful effects on both the environment and human health. Consequently, there is increasing public and political concern about the spread of PFAS and other environmentally harmful substances, not least into groundwater and water environments, and wastewater utilities are faced with strict environmental requirements for discharges of PFOS and PFAS. However, it can be challenging to know where to start and how to limit the spread of these harmful substances most efficiently.
 
Wastewater utilities are actively investigating how to ensure that PFAS is not disseminated to water environments through their treatment plants, but it is both complex and costly to remove PFAS at the wastewater treatment plants in diluted streams. It is therefore more cost-efficient and effective to minimise the spread of PFAS directly at the source in the concentrated stream.
 
BIOFOS had found that the concentration of 15 environmentally harmful substances was higher than what is allowed in the European and Danish environmental quality standards in the outflow from the utility’s three wastewater treatment plants in the region. In 2020, BIOFOS consequently wanted to map their existing knowledge and data on these environmentally harmful substances, which included PFAS. The procedure was a so-called dry source tracing in the catchment municipalities. The procedure is called dry, because it consists of collecting existing data, in this case information from the 15 catchment municipalities on companies in the region and control data. The conclusion was that there was a lack of more in-depth knowledge about several of the environmentally harmful substances identified in the wastewater, including PFAS and tin.
 
Solution
 
BIOFOS therefore decided to initiate a more comprehensive source tracing investigation with the support from DHI’s experts. This time, the procedure was wet source tracing in which samples are collected. The overall purpose of the investigation was to gather more information about the sources of the environmentally harmful substances as an initial step in reducing the discharge of these substances into the wastewater.
 
Samples were taken from 30 companies in nine selected industries in the catchment of BIOFOS’ three wastewater treatment plants. The selected industries were: waste deposit sites, waste management companies, asphalt production, industrial laundry, laboratories, car wash facilities, train/bus/lorry wash facilities, fire drill sites, contaminated groundwater remediation and construction dewatering.
 
For the sampling, DHI experts used passive samplers, SorbiCeller™. This method allows for a time and cost-efficient sampling over long time periods, which results in more longitudinally representative values than what is possible with the conventional short-term measurements.
 
The following analysis parameters were included in the source tracing programme:
 

Six metals: lead, cobalt, copper, mercury, tin, zinc
Bisphenol A
DEHP
15 PAH: Naphthalen, Acenaphthen, Acenaphthylen, Fluoren, Phenanthren, Anthracen, Fluoranthen, Pyren, Benzo(a)anthracen, Chrysen/Triphenylen, Benzo(b+j+k)fluoranthene, Benzo(a)pyren, Indeno(1,2,3-cd)pyren, Dibenz(a,h)anthracen, Benzo(g,h,i)perylen
12 PFAS: PFBA, PFBS, PFPeA, PFHxA, PFHxS, PFHpA, PFOA, PFOS, 6:2 FTS, PFOSA, PFNA, PFDA

 
The investigation found that two waste management companies were the sources of about 40% of the PFOS discharged into one of BIOFOS’ wastewater treatment plants. Waste management companies are in general the largest sources of PFAS and a number of other environmentally harmful substances in the three wastewater treatment plants in the Greater Copenhagen Region.
 
Results
 
The investigation launched by BIOFOS and the 15 catchment municipalities has provided these municipalities with a tool for identifying the major sources of PFAS contamination in their municipality. They now also have a data-based foundation for dialogues with the waste management companies.
 
Because PFAS is a so-called forever chemical and widely used in consumer products, waste management sites will likely continue to be major sources of PFAS dissemination in the future, irrespective of any ban on future use of the chemical. The sooner the sources of PFAS are identified, the sooner action can be taken to limit the spread of these environmentally harmful substances. At least one of the waste deposit sites in question is currently looking into testing PFAS purification methods.
 

Identification of major sources of PFAS discharge to wastewater treatment plants
Basis for dialogue with waste management companies on reducing discharge of PFAS and other environmentally harmful substances
Improved basis for stronger protection of water environments in the long term


A digital twin of the wastewater utility in Gothenburg and surrounding municipalities is helping to future-proof the region and make the most efficient use of existing infrastructure
 
Gothenburg has a vision of becoming the best city in the world when it rains. And this vision makes perfect sense as Gothenburg is one of the rainiest cities in Sweden. Add to that a growing population, an ageing infrastructure and increasingly extreme weather patterns due to climate change, and the city’s water utilities have their work cut out for them to protect both the city and the surrounding environment.
 
Challenge
 
Heavy rainfall causes large loading variations to the Gothenburg region’s central treatment facility, the Rya water resource recovery facility (WRRF). Approximately 25% of the sewers in the City of Gothenburg are combined, which increases the risk of floods as stormwater and wastewater are transported in the same system. It also increases the risk of untreated wastewater being discharged into the surrounding ecosystem.
Furthermore, changing climate conditions combined with a growing population add further pressure to Gothenburg’s ageing infrastructure and make operations more complicated.
 
The main priority for Gryaab is to protect the citizens of Gothenburg from floods and to protect the ecosystems in the waterways and basins in the region from polluted wastewater. To do so, Gryaab has to ensure optimal management of the water flowing in and out of the city. They needed to find a more future-proof way to efficiently manage issues related to combined sewer overflows (CSOs) and to reduce storm weather impact on the WRRF. The traditional approach relied heavily on operator experience and judgement.
 
However, the Rya WRRF is only manned in the daytime on regular working days, and standby personnel operate the facilities from home the rest of the time. This puts a natural limit to the hours of monitoring and the amount of information which could be processed. It also leaves room for manual errors. Especially when high flows are expected, it is important for the operators to have as much information as possible so that they can make the right decisions and avoid critical situations, which could have negative impacts on the city and the environment.
 
The main challenges for Gryaab were:
 

Minimising the impact of flow variations in extreme weather
Improving the attenuation of inflow to the Rya WRRF as much as possible to reduce pressure on the system
Improving water quality in receiving water bodiesControlling where the CSOs occur to minimise environmental impact

 
Solution
 
Gryaab has a history of using innovative and digital solutions to support them in managing the region’s wastewater infrastructure, and they quickly saw the potential in having a digital twin of the entire system to improve overview and management.
 
A digital twin is basically a dynamic digital representation in real-time of a physical object or a process, such as the Gothenburg region’s tunnel system and catchment. A digital twin can be compared to the co-pilot on a plane, and it uses analytics and predictive modelling to validate decisions and to automate time-consuming and manual technical or operational processes.By implementing the Future City Flow (FCF) digital twin, Gryaab could get real-time information about events in the tunnels as well as accurate predictions of potential issues and peak pressure on the system as the FCF digital twin also incorporates weather forecasts in the modelling.
 
The project included:
 

Building detailed hydrological and hydrodynamic models of the tunnel system with detailed simulation of the 250 km2 catchmentIncorporation of all controllable devices (e.g. gates, pumps) in the digital twin real-time control system
Development of Forecast-on-Demand features with the option of adjusting pre-suggested strategies and analysing historical events for training purposes
Development of an operational strategy to mitigate the risk of urban flooding

 
With the FCF digital twin, Gryaab can act early, and staff can make decisions based on comprehensive, real-time data and prognosis. They also use the digital twin for training in various scenarios so that the staff is better prepared for future critical situations and for making better, informed decisions. In short, the FCF digital twin is used for gaining better real-time control and for finding ways to improve the operation of the tunnel system, both today and in the future.

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