Wastewater, energy production and emissions

The moderator of this session is: Hans Aalderink (Deltares)

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This session will include the speakers: Oscar Helsen (Delfland), Chih-Yuan Jen (Nijhuis Industries) and Sebastian Schmuck (Urban Water and Waste Management, Faculty of Engineering Sciences Building Sciences, University of Duisburg-Essen)

Take a look at the abstracts below: 

The upgrade of a dated WWTP into a futureproof sustainable energy hub 

Presenting author: Oscar Helsen

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The regional water authority of Delfland, located in the west of The Netherlands, wants to contribute to the global sustainable goals. Therefore it aims to be energy neutral in 2025 and climate neutral in 2050.  
Houtrust, the waste water treatment plant (WWTP) in the city of The Hague, has been developed from a simple mechanical WWTP built in 1967, into a sustainable modern biological WWTP nowadays. Houtrust feels like a tribute to the developments in wastewater treatment; wandering through corridors and various spaces you will come across many different pieces of technology, which shows the development of the past decades. Developments as a result of stricter legislation, of a better understanding of microbiology, and more insight into treatment processes. Or because of social necessity, like adaptations to reach the global sustainable goals. 

After several earlier major renovations, Houtrust has recently undergone a transition towards a sustainable plant. One might think that energy optimization, heat recovery, production of biomethane and CO2 recovery are only feasible in newly built WWTPs. However, this project shows that with smart combinations, new technologies and commitment, older WWTPs can also contribute to energy transition and thus to mitigation of climate change.  

Biomethane 

A biomethane installation purifies biogas acquired from the sludge digestion tanks by means of cooling, activated carbon filters and using a membrane installation so that flows of biomethane gas and CO2 remains. After adding an odorant, the biomethane is fed into the gas grid, to provide in the need of sustainable energy sources.  

However, when biomethane is fed into the gas grid, it is no longer available for the combined heat and power plants (CHPs) of the WWTP. Until recently, these CHPs supplied both power for the treatment process and the heat was used for digestion. Since the CHPs can no longer be used, the heat demand for the digestion of sludge has to be found elsewhere. 

Heat study  

In order to heat the digestion tanks in a sustainable way, a heat study was made, resulting in a package of measures that reduces the heat demand and made the heat supply more sustainable. This is achieved by an optimal cooling and heating balance, and a heat pump. Using redundant heat from the biomethane and CO2 recovery installation, introducing serial digestion and longer fermentation time, and if necessary extracting heat from effluent.  

CO2 

Another important part of the project is the CO2 recovery installation. Because the biomethane installation already separates the methane and CO2, it is relatively easy to liquify the CO2 to make it suitable for supplying to greenhouses in the area. Further quality improvements may even lead to more upcycled use of this green CO2 for example in the drinking water industry or the food and beverage industry. 

In this way WWTP Houtrust has been upgraded into a sustainable energy hub. Delfland has decreased the COfootprint of Houtrust with 50%, where 1,9 million m3 biomethane and 2.000 ton of CO2 will yearly be delivered to the society. 

Fat recovery from industrial wastewater for on-site biofuel production to reduce CO2 emissions

Presenting author: Chih-Yuan Jen

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Industrial wastewaters from the food and beverage sector often contain high calorific compounds which can be valuable to recover and reuse. For example, poultry slaughterhouse wastewater typically contains a high amount of fat. If such fat is recovered, it can be reused for heat production on site or sold as products such as biofuel or co-substrate in digesters. By reusing fat from the wastewater, industries can reduce CO2 emissions and achieve a more sustainable operation.

A fat recovery installation (AECO-FAT) was put into operation in 2020 at one of the largest poultry slaughterhouses in the Netherlands, with a slaughter capacity of around

250.000 chickens per day. The installation consists of a dissolved air flotation (DAF) unit removing solids and fat from the wastewater in the form of sludge without dosing chemicals, followed by the chemical wastewater treatment downstream. The sludge from the chemical-free DAF was then heated via the disconnector system and separated into solids, water and oil fractions in a three-phase decanter (picture 1 and 2). The oil is now used as biofuel in a hot water boiler with a specific liquid fuel burner, delivering heat to the slaughterhouse production process.

Throughout one year the obtained oil quality was measured. The recovered oil was more than 99% pure (Table 1). The higher heating value of 39.1 MJ/kg is around 90% of the energy content of fuel oil, showing the suitability to use the recovered oil as fuel.

Applying the fat recovery installation made the poultry slaughterhouse more sustainable in three ways. Firstly, the fat was recovered as fuel on site, saving gas consumption by 15%. Secondly, the use of chemicals can be reduced in the wastewater treatment system. Finally, the total amount of sludge in the wastewater treatment system was reduced by around 30% thanks to the upfront recovery process.

The fat recovery installation not only reuse a valuable compound from wastewater, but also leads to reduction of environmental impact and CO2 emissions. This innovation shows the potential of recovering fat from food and beverage wastewater, making the industries more sustainable and circular.

Impacts of gray emissions from typical urban drainage system structures

Presenting author: Sebastian Schmuck

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Besides meeting the minimal requirements, normally the decision to build storm water treatment systems and waste water treatment plants are dominated by economic reasons. But solutions for adaptation and mitigation in waste water treatment cause new carbon dioxide equivalent (CO2e) emissions, which could enforce the effect of climate change. To quantify this effect, a carbon footprint of the typical structures of the urban drainage system are calculated. The different structures are calculated, evaluated, and compared regarding CO2-emissions, providing an additional parameter for decision support systems. The focus of the presentation will be the explanation of the calculation of climate-relevant emissions from the construction process.

The parameter CO2e could flank the economic aspects to find the optimum ratio in drainage comfort and flood protection, with minimization of CO2e emissions and economic aspects.

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