Source: YouTube - Introduction Wastewater energy production and emissions
Introduction by Hans Aalderink on Wastewater energy production and emissions.
Emile Cornelissen provide the plenary keynote after the lunch for the subtheme Reuse, Recycle and Recover.
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 CO2 footprint of Houtrust with 50%, where 1,9 million m3 biomethane and 2.000 ton of CO2 will yearly be delivered to the society.
Source: Helsen, O. 2021. The upgrade of a dated WWTP into a future proof sustainable energy hub. Wastewater, energy production and emissions, Clean Water & Ecosystem Restoration. AIWW 2021
Installing water reuse technologies is a more and more accepted tool to increase the water life time at the production site and reduce the risk and impact of the upcoming water crisis. Utilising/valorising the maximal capacity of installed assets requires a next level of operational excellence by learning the interactions of different installed processes, associated data trending and actions to be taken.
A good example is the advanced water reuse plant of a leading European meat processor. They started 11 year ago with one slaughter line and gradually expanded with 2 slaughter lines and a rendering facility. The wastewater treatment plant (WWTP) was gradually expanded to 10.500 m3/d capacity treating to facilitate the increased wastewater towards river water discharge quality. The process water production however, based on groundwater extraction and treatment, was not able to meet the growing demand. Increasing draught periods were stressing the quality and quantity of their boreholes resulting in forced reducing in slaughterhouse capacity. To anticipate on this thread, they implemented a Sewage Treatment Effluent Reuse Facility of 4.000 m3/d producing certified drinking water quality for process applications which went into operation in 2019.
Since the start of reuse operation in 2019 the plant output have been increase gradually over the two years (see table below). Key success for this increase can be categorized in increased application knowledge of the integrated WWTP-REUSE system and changed operational and maintenance mindset.
In the period before start of the reuse facility, the WWTP operational approach was focused optimizing performance and OPEX while maintaining river discharge quality. Operators had developed their plant application knowledge, perfectly been able to anticipate on incidents, offsets and season.
After starting up the reuse plant, it however turned out that some of these traditional reactions did had a counter effect on the reuse performance and capacity. Some correlations could quite quickly been identified where others influencing parameters did require serious investigation upstream into the WWTP to understand and anticipate.
Since the hydraulic capacity of the reuse facility is directly linked to the availability of both the quality and the quantity of WWTP effluent, maintenance to the existing WWTP became more important. This has shown accountability to the speed of response on reactive maintenance as well as timing of scheduled maintenance.
To follow the rhythm of the slaughterhouse operation (5 to 6 days slaughtering and 1 to 2 days weekend) scheduled maintenance for the reuse facility had to be moved to the weekend days to maximise water reclamation when water was needed. This was requiring a more long term planning of cleanings and maintenance to increase uptime during the slaughterhouse production.
With an operation, support and monitoring contract in place, local water reuse experts are working in close cooperation on daily basis supporting local client operations team with data monitoring, trouble shooting and plant optimization. This ongoing growth in application knowledge is maximising the plant output capacities, both to water reclamation and river discharge, while operational expenses are continuously optimized.
Source: Wolbrink, T. 2021. Increased water REUSE plant output due to operational excellence. Wastewater, energy production and emissions, Clean Water & Ecosystem Restoration. AIWW 2021
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.
Source: Jen, C. Y. 2021. Fat recovery from industrial wastewater for on-site biofuel production to reduce CO2 emissions. Wastewater, energy production and emissions, Clean Water & Ecosystem Restoration. AIWW 2021
Source: YouTube - Fat recovery
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.
Source: Schmuck, S. 2021. Impacts of gray emissions from typical urban drainage system structures. Wastewater, energy production and emissions. AIWW 2021.