Recovering heat, saving space: Grease trap integrated heat recovery

By Jan Spriet

Wastewater from (commercial) kitchen drains can reach temperatures up to 55°C, consequently, they have a significant amount of embedded energy (that you paid for), that is currently being flushed down the drain. In commercial kitchens the installation of a pre-treatment system, to remove Fat, Oil & Grease (FOG) from the wastewater is mandatory, to avoid fatberg formation. In commercial kitchens, this pre-treatment is performed by a grease interceptor or grease trap. In the proposed prototype, this grease interceptor is used as a wastewater holding reservoir, avoiding temporal mismatches, and a heat exchanger is integrated into this grease interceptor. The heat recovered from the grease trap reduces the energy and fuel consumption of the kitchen’s traditional heating system. Integrating heat recovery in the grease trap would not only reduce the space requirements of heat recovery systems, and reduce their installation costs. It would also aid in the removal of FOG from the kitchen wastewater. In this article, we describe the operation of our prototype.

Figure 1. The working principle, in a nutshell.

Our previous research showed a technical heat recovery potential of 1.4 TWh (388 000 tons of carbon emissions) in the food and hospitality sector in the UK, each year, using currently available heat exchangers. However, it also showed that this potential was limited by temporal mismatches between supply and demand, a required vertical drop in the drain of 2m, and showed that these heat exchangers are not cost-effective for smaller kitchens. The idea of the developed prototype was to address these three bottlenecks. The solution was found by integrating heat recovery into grease interceptors. These grease interceptors are already a mandatory piece of equipment, this would thus not require additional space, and have a limited effect on costs.

Figure 2a. The grease trap with prototype DWHR device

Figure 2b. Picture of the prototype DWHR device

This prototype was tested in steady state conditions in the lab, using heated clean water to simulate the kitchen’s wastewater. This showed an effectiveness between 23% and 55%, and a recovered heat ranging between 600W and 1.8kW. It also reduced the temperature in the grease trap from around 41.5°C in normal conditions to 36.5°C at its lowest point

Figure 3. Heat recovery prototype in the lab set-up

The prototype is deemed profitable for kitchens with a consumption of more than 100 l/day, when complementing electric heating and 300-350 l/day when complementing traditional boilers (fuel oil, natural gas or bio-mass). Applying this prototype in the food and hospitality sectors results in over 150 000 food outlets, where installing the prototype is the most profitable solution. These outlets equate to 2348.52 GWH of heat recovery each year, the equivalent of 69 000 tons of greenhouse gas emissions.

The reduced temperature is expected to improve FOG removal efficiency, which in turn would increase the required emptying frequency of the grease interceptor, as more FOG would be collected. Collecting more FOG has the advantage that, when the removed FOG is treated in anaerobic digesters, additional bio-gas can be recovered.

Changing river water quality under a worst-case climate change scenario: Implications for drinking water supply

By Richard Dallison

Water service providers in the UK face a vast array of challenges when it comes to planning their future operations and services; the impact of climate change on the quality of water arriving at drinking water treatment plants (DWTPs) is just one of these. Changes in water quality are induced by a variety of factors, when considering non-point source inputs. Large or prolonged rainfall events, for example, can lead to greater washing of pollutants from the land in to rivers. Additionally, large streamflow events provide rivers with greater stream-power, enabling more erosion of river banks and the movement of larger particles. Very low streamflow events can also cause spikes in water quality issues, as there is less water available to dilute any pollutants. Therefore, any changes in future climate, and subsequent alterations in streamflow regime could have far reaching consequences in terms of water quality, this in turn could cause problems at DWTPs if they are unprepared for any such changes.

Using the Soil and Water Assessment Tool (SWAT) hydrological model, we have projected and analysed future (2021-2080) streamflows and water quality under a worst case scenario of future emissions, that being representative concentration pathway 8.5, as laid out by the Intergovernmental Panel on Climate Change. To account for uncertainty in future modelling, an ensemble of 12 regionally downscaled models derived from the Met Office Hadley Centre Global Environmental model (HadGEM3), and supplied by UK Climate Projections 2018, have been used as the future climate inputs to SWAT. Five catchments have been studied, the Clwyd and Conwy in north Wales; the Dyfi in mid Wales; and the Teifi and Tywi in south Wales; these systems represent a variety of catchment characteristics in terms of land use, soil types, underlying geology and topography. We have investigated annual and seasonal average changes for four water quality aspects, suspended sediment (SS); total phosphorous (TP); total nitrogen (TN); and dissolved oxygen (DO). Mann Kendall trend analysis was performed on the model outputs, in order to detect any statistically significant trends.

Figure 1. Study area and catchments showing streams larger than third order as defined by Strahler method.

Previous work by the Dŵr Uisce project has shown that extreme streamflow events will become more frequent in the future, with winter and spring seeing more very large events, and summer and autumn seeing much lower streamflows. This is reflected in the water quality outputs, with increases in SS loads seen in winter and spring in four of the five catchments each. At annual average level, SS loads are increasing significantly (p <0.01) in all catchments except the Tywi, were a non-significant increase is seen. TP and TN display broadly similar trends, with concentrations increasing in all seasons, in all catchments except the Dyfi, where a decline is shown in winter, spring and annually on average. Summer concentrations of TP and TN in particular show a statistically significant increase in all catchments (except TP in the Tywi). DO levels show the most variation, although a decline is seen in all catchments in summer. The Teifi catchment is the most divergent, with a statistically significant increase in winter and spring DO levels, compared to declines seen in all other catchments for winter.

Figure 2. Overview of the direction and significance of annual and seasonal average trends in projected future (2021 – 2080) water quality concentrations, as detected by Mann Kendall trend analysis, based on the average of all 12 RCM model outputs.

Given the trends seen in river water quality, it is clear that for the vast majority of the time in the future, water quality will be worse than it is currently. This is an issue that needs to be managed at DWTPs in particular, to ensure that current operating systems, procedures, and technologies will be able to cope with more contaminated water in the future. This adaptation need comes hand-in-hand with the need to also ensure future water security, especially in summer and autumn, when lower precipitation and streamflows, as well as higher temperatures, are projected for Wales. It is clear that the projected changes in climate will have a large impact on catchments in Wales, this will have a significant knock-on impact on a variety of aspects of drinking water supply. Work is therefore needed now to plan and mitigate against these potential changes in order to maintain continued high-quality supplies in to the future.

Eco-code posters in English, Welsh and Gaelic languages

Szu-Hsin Wu

Previously, we have designed an English language version of eco-code poster which shares many water-saving tips. The poster was firstly published on our website and social media and posted across campus in both hard copies and digital format.

Due to the COVID19 pandemic, over the past months, we have all been adjusting our routines and behaviours to slow down the spread of the coronavirus. During the period, we also experienced water shortages in Ireland. We had only 25% of normal rainfall in April and decreased 5% of normal rainfall for May. We thought the sharing of these water-saving tips could also remind everyone making a small effort to collectively create a positive impact on our environment. To further promote these water-saving tips, we converted the poster into a Gaelic language version. These tips circulated to the mailing list of the Sustainability Network at Trinity College Dublin and were well received on many social media such as Twitter, Facebook and Instagram.

Following a positive response from social media, we also designed a Welsh language version of the eco-code poster. Now, these water-saving tips are communicated in three languages.

What’s the best way to use distillery by-products?

By Isabel Schestak

Cattles in Scotland, photographed by Isabel Schestak

By-product use from malt distilleries has a long tradition in Scotland, where it has probably been fed to cattle and sheep for more than 500 years (Crawshaw, 2001). Recently though, a shift from feed to bioenergy use has been observed, as incentives by the UK and Scottish government for renewable energy technologies have been taken up by the distillery sector (Bell et al., 2019). Though energetic use of by-products brings benefits for a distillery’s carbon footprint, from a water use perspective, also feed use might deserve recognition as environmentally favourable, when the protein rich by-products replace imported feed such as soybean meal. This has been shown already for greenhouse gas emissions, but not been looked at from a water perspective yet.

To find out which by-product use option performs best in terms of water use and to which extend it can improve the water footprint of spirits, we applied a recently developed methodology to the operations of a Scottish distillery. The method called AWARE (Available water remaining) does not only take into account the volume of water consumed for a process or product, but also the water availability or scarcity in the geographical area where the consumption takes place (Boulay et al., 2018). Water consumed in an arid region therefore is weighted stronger than that in a fairly water abundant area such as the UK. It is therefore not just a water, but a water scarcity footprint.

We looked at different scenarios for using spent grains and pot ale: 1) direct use as cattle feed in its fresh form and replacing a mix of imported soybean meal and domestic barley, 2) processing them first to dried distillers grains, thus producing a better conserving and more flexible to use feed before also replacing soy and barley, 3) processing to dried distillers grains but only replacing pure soy protein as feed and 4) anaerobic digestion to biogas, with subsequent combustion of the biogas to electricity and heat, and using the leftover digestate as fertiliser i.e. in total replacing grid electricity, heating fuel and fertilisers.

In the feed scenarios, both soy and barley were replaced in order to substitute an equal amount of protein and metabolisable energy found in the by-products.

First results showed that the water scarcity footprint of whiskey can be reduced by about 20% by using the by-products as either direct cattle feed (scenario 1) or generating biogas (scenario 4). Thus, there is no clear benefit for the use of by-products for renewable energy purposes, in contrast to the suggested reduction of GHG emissions through the government incentivised bioenergy option. The water savings are partially “invisible”, indirect savings though, achieved outside the distillery or even abroad and therefore do not directly improve a distillery’s footprint.

Similar observations have been made by Leinonen et al. (2018), who conducted an assessment on greenhouse gas emissions from different by-product use scenarios from single malt whiskey: in terms of percentage reduction of burdens through by-product use, higher reductions were achieved when by-products were used as feed in form of dried distiller’s grains, replacing soybean and barley feed (40%) than through biogas production and digestate application (27%). Again, these were partially indirect savings connected to land use change for the cultivation of soy abroad.

The study will be expanded to include other water footprint methods and data from further distilleries to enhance the reliability of the results. But already now we may question the environmental benefit from incentivising biogas production from distillery by-products.

References:
Bell, J., Farquhar, J., Mcdowell, M., 2019. Distillery by-products , livestock feed and bio-energy use in Scotland, Sruc.
Boulay, A.M., Bare, J., Benini, L., Berger, M., Lathuillière, M.J., Manzardo, A., Margni, M., Motoshita, M., Núñez, M., Pastor, A.V., Ridoutt, B., Oki, T., Worbe, S., Pfister, S., 2018. The WULCA consensus characterization model for water scarcity footprints: assessing impacts of water consumption based on available water remaining (AWARE). Int. J. Life Cycle Assess. 23, 368–378. https://doi.org/10.1007/s11367-017-1333-8
Crawshaw, R., 2001. Co‐product feeds: animal feeds from the food and drinks industries, 1st ed. Nottingham University Press, Nottingham.
Leinonen, I., MacLeod, M., Bell, J., 2018. Effects of alternative uses of distillery by-products on the greenhouse gas emissions of Scottish malt whisky production: A system expansion approach. Sustain. 10. https://doi.org/10.3390/su10051473

Testing explanatory factors and proxy variables in economic and energy efficiency benchmarking

By Nathan Walker

Evaluating efficiency has many advantages to companies, such as enabling assessment of explanatory factors however, the process of doing so is not always easy. Sometimes missing data leads whoever is conducting the research to utilise proxy variables, which replace the ideal choices.

The explanatory factors* analysed in the study were: leakage, per capita consumption, number of sources, proportion of water through size 5-8 water treatment plants (the largest 50%) and average pumping head height. Leakage and number of abstraction sources were concurrent in their negative effect and significance across both the energy and economic assessments. These results were expected to an extent since for leakage the more water that is lost, the more water needs abstracting, treating and delivering, which all require energy and money. Although diversifying abstraction sources can be a positive attribute for companies to make their supply more resilient, it appears as though this is at the expense of a significantly increased energy consumption owing to more pumping being required through a larger network of piping. Average pumping head height displayed a significant negative effect for energy, whereas the variable proportion of water passing through the largest four treatment works was deemed to have a significant negative effect on economic efficiency. These exogenous factors, therefore, need to be corrected for in future benchmarking activities and have the potential to inform water companies about factors to prioritise in order to improve efficiency.

The proxies that were tested were population served for drinking water and length of water mains, which replaced the output volume of drinking water produced and the input of CAPEX, respectively. These were chosen as they are frequently used as proxies in the academic literature. We found that the proxy population served for drinking water can adequately replace the volume of water produced as an input variable (Figure 1) in efficiency benchmarking when leakage and per capita consumption ranges are minimal since companies stayed at the same rank and explanatory factors displayed the same significance. Conversely, length of water mains performed poorly when replacing CAPEX as an economic input (Figure 2), implying companies were on average 12.6% more efficient, resulting in 10 companies changing their rank compared to the original variable and causing some explanatory variables to differ in direction of influence and significance. Further research is recommended on the energy and economic efficiency of WoCs and WaSCs, considering a wide range of exogenous variables and careful selection of (proxy) indicators.

Figure 1. The energy efficiency results with the primary set of variables, and a volume of water produced proxy (population served for drinking water). WoCs are featured as triangles and WaSCs are displayed as circles. 1 Is the optimum efficiency rank and everything above that is classed as the degree to which companies are inefficient.

Figure 2. The economic efficiency results with the primary set of economic variables, and a capital expenditure (CAPEX) proxy (kilometres of water mains network). WoCs are featured as triangles and WaSCs are displayed as circles. 1 Is the optimum efficiency rank and everything above that is classed as the degree to which companies are inefficient.

The full research with more details on the background, methodology and discussion is available here: https://doi.org/10.1016/j.jenvman.2020.110810

*Only explanatory factor results that showed significant results are discussed here.

Free Sustainability Webinars

What a strange time of the year? Usually, it is time our researchers travel to conferences and meetings to get inspiration and exchange ideas and knowledge. It is also the time we work closely with various stakeholders, including practitioners, academics and policymakers. We are used to face-to-face interaction, discuss emerging problems and come up with potential solutions. This year, we all are facing the challenges of Covid-19 pandemic and staying at home. We start to miss the inspiration, idea exchange and aha moment when we learn new things.

However, this is not a moment which stops us developing a more sustainable environment. Dŵr Uisce is planning to run a series of sustainability webinars. Visit our Twitter @Dwr_Uisce (https://twitter.com/Dwr_Uisce/status/1277517115143204864?s=20) and tell us which webinars you are interested in.

Learning in action: Generating actionable knowledge with stakeholders

Szu-Hsin Wu

In the Dŵr Uisce project, it is part of our innovative culture to working with stakeholders on co-designing, co-developing and co-implement green innovation which mitigate impacts on the environment.

In collaboration with National Trust (UK) and National Federation of Group Water Scheme, Dŵr Uisce researcher and stakeholders have installed micro-hydropower energy recovery system at two demonstration sites: Tŷ Mawr Wybrnant  and Blackstairs Group Water Scheme. The process of achieving green innovation has never been easy and straightforward. We encountered numbers of unknown problems and challenges. Without our valuable stakeholders being patience and continuously engaged in the collaboration process, we could not have achieved what we have today. Various forms of actionable knowledge were generated and accumulated from the process. For example, engineering researchers learned insights from realizing the system design in a controlled setting. Researchers from the management discipline also learned how to communicate innovation performance and commercialise the technology to stakeholders and a wider audience. All stakeholders obtained the codified processed experience from designing in the system, communicating with stakeholders and installing the system that can be used for the next cycle of green innovation.

Generating and accumulating new actionable knowledge was through intuiting, interpreting, integrating and institutionalizing. Through intuiting, engineers identified patterns, possibilities, similarities and differences between the two sites. Through interpreting the results of feasibility studies, we selected suitable energy recovery possibilities within specific domains or environments. Through integrating the knowledge, both the academic researchers and the practitioners developed a shared understanding of the objectives, engineering choices and criteria for evaluation and installed the system. This integration took place through direct interaction among group members in order to attain coherence. The Dŵr Uisce team then institutionalised the learning from Blackstairs Group Water Scheme demon site and leveraged it for Tŷ Mawr Wybrnant site and consolidating the learning for further application.

We know that innovation is rarely a linear process and rarely stop at a point of time. We work continuously and closely with stakeholders on innovation. And in the near future, we hope to share more insights from implementing our Wastewater Heat Recovery Systems at other demonstration sites.  

Summer is here! Dŵr Uisce newsletter

Future might seem to be a bit of uncertain to you, lately. We look into future with you in our Summer Edition Newsletter. Check our newsletter here to learn what we have been doing.

Stay at home! (but conserve water and energy where you can)

by John Gallagher

Over the past several weeks, we have all been adjusting to working from home and limiting our movements to occasional outings for grocery shopping or medical appointments. This has been a challenge for everyone, but collectively the positive impact has helped manage this pandemic and the spread of COVID-19.

For many, the focus of daily activities have been within the four walls of our homes, and if we are lucky extending that to the garden and out for short walks (obeying guidelines at all times). So has this change in lifestyle impacted on our consumption of water and energy in our homes? And should we pay more attention to using these resources wisely at this time. 

More time at home means more use of water and energy, and early figures suggest that domestic energy and water consumption have increased since the 'stay-at-home' measures have been implemented. We are using water and energy at a rate that is reflective of our typical weekend consumption. 

Increased water and energy consumption at home translated higher bills for us as consumers. Therefore, ways to save and conserve is in our control more so than ever (and it impacts on our pocket). At Dwr Uisce, we aim to share ways we feel that can support water savings, and in doing so you have win-wins through saving energy too! We wish to share those tips with you all - in English, as Gaeilge - these are simple ideas in which we can all do our part. 

SaveWater - Eco-code poster in Gaelic

As we enter the summer months, and following a rather dry period in Spring, our water resources are depleting and by taking note of our suggested tips, we can be responsible with our water and do our part for conserving and saving. 

Stay safe, stay well, and use water and energy wisely whilst staying at home!

Simple ways you can take climate action at home

By Aisha Bello-Dambatta

Climate change is happening, and many of us have already directly felt some of its impacts. It has increased the likelihood, frequency, and intensity of extreme events like we have, for example, observed in recent extreme temperatures in the UK and deadly heatwaves, floods, and fires in the Amazon rainforest and Australian bushfires last year.

This is just the beginning. Although the causes of climate change are well understood and climate model projections are continuing to match our observations, the UN reports that global GHG emissions continue to rise despite ambitious global commitments and actions to reduce emissions (e.g. Paris Agreement, UN Sustainable Development Goals, several climate and ecological emergency declarations). Global CO2 emissions have risen by 4% since the adoption of the Paris Agreement in 2015 and the latest WMO report on the state of the global climate confirms December 2019 to be the second warmest year on record, 2015-2019 to be the warmest five years on record, and 2010-2019 to be the warmest decade on record.

However, even if we were to meet all global emissions targets today, we will still experience some level of climate change because of the warming that has already happened. We therefore need a way to, at minimum, reduce the impacts of this inevitable climate change. This can be done in two ways: mitigation to reduce the amount of emissions and the drivers of climate change; and learnig to adapt to the change that is already in the system to minimise impacts.

One way to reduce emissions is through water use efficiency – in our homes, at work, and at leisure. The water industry is energy intensive and on average between 2 – 3% of the world’s energy use is used to treat water to potable quality, deliver it to consumers, and to process and dispose of wastewater. In the UK, for example, around 2% of total energy use is used by water companies. However, this represents only around 11% of actual water-related energy use, with around 89% of water-related energy use attributed to water demand, particularly for hot water use and space heating. This constitutes around 95% of household water-related energy use. Hot water heating alone accounts for around 20% of the average household energy bill. Given this obvious link between water use and energy use, reducing the water for demand, especially in hot water use, can significantly reduce water-related energy use and associated emissions and costs.

So, what can we do to help mitigate the impacts of climate change? There are many simple actions (examples, below) we can take in our homes to reduce our emissions and carbon footprint. Many of these interventions are easy to implement and have zero or very low-cost with short paybacks.

SaveWater eco-code poster

Think of your energy supply and use

You can reduce your overall environmental footprint by switching to a renewable energy supplier or installing renewable or low-carbon technology like solar PV, biomass boiler, or even the Micro-Hydro Power (MHP) and Drain Water Heat Recovery (DWHR) pilot installations in the Dŵr Uisce project, depending on your personal needs. Most renewables no longer have a price premium, and even the most expensive have much improved payback periods. Depending on where you live, energy grants and rebates may be available to help cover costs, and you could get money for generating electricity.

Install a water meter

Metering is a prerequisite for understanding your water consumption. It provides a means of measuring and monitoring your consumption over time and has the potential to generate significant reductions in water use and cost savings. Smart water meters that take hourly readings for more detailed consumption information are also available. In the UK, most water companies will install a water meter for free for their household customers and some even have online water usage calculators to help you model and understand how much you can save by having a meter installed.

Fix leaks immediately  

You may have a leak if your water bill or meter reading is unusually high. Leaks can develop along your supply pipework or in internal pipework or fittings. You are responsible for not only internal leakage, but also all leakage along the supply pipe (from property boundary to your water meter) and any underground pipes. Some water companies may fix external leakage for free, so check with your water supplier first if you notice any external leakage.

Also check that your water fittings like loos, taps, and showers are not leaking. A leaky loo can waste up to 400 litres of water a day! A dripping hot tap with one drip per second wastes four litres of water per day, and the worse it gets, the more water and energy is wasted.

Think about your bath and shower water use

Even as average per capita water use has fallen, some households, even efficient ones use more hot water for bathing that we previously have. This is largely because our bathing habits and lifestyles have changed. Although we are having fewer baths, recent trends in power showers and mains pressure systems mean some showers can use as much or even more water than a bath. Water saver showers that typically work at flow rates of between 4 – 9 litres per minute can give the effect of a power shower at a lower flow rate. Some showers can be made efficient by retrofitting them with simple aerators or flow restrictors. Many water companies provide households with free retrofits for water using fittings to help reduce water and energy use. Check on your water company’s website for more information about what is available and how you can apply for free retrofit devices.   

Remember to not leave taps running

The best of us sometimes forget to leave the tap running whilst brushing our teeth, washing our hands, cleaning dishes, or washing vegetables. A hot running tap uses at least 6 litres of water per minute and wastes energy. Remember to switch the tap off when not needed and to use bowls where necessary, for example, for dishwashing or washing vegetables. Some of this water, for example, water used for washing vegetables can be reused to water gardens and indoor plants.  

Use water and energy efficient white goods efficiently

Consider water and energy efficient washing machines and dishwashers when it is time to replace old ones. The water and energy performance of white goods have improved considerably in the past decades and efficient appliances no longer have a price premium. Dishwashers are not as resource intensive as people think and can actually be more efficient than handwashing. Washing a 12-place setting crockery by hand can use about 40 litres of hot water, for example. It is important to note however, that even the most efficient appliance is only as efficient as how it is used. So appliances need to be run at full loads and on the most efficient setting. Check to see if there are rebates for efficient white goods before you shop!