Written evidence submitted by Emerson UK Ltd T/A InSinkErator [PNZ 019]

About InSinkErator

InSinkErator is a leading manufacturer of kitchen sink appliances, including in-sink food waste disposers (FWDs). It is a division of Emerson Electric Co, a global technology and engineering company, which serves industrial, commercial and consumer markets. Registered as Emerson UK Ltd the company operates its EMEA headquarters from Watford, Herts.   Food waste disposers are small appliances that fit under the kitchen sink and grind food waste to minute particles that flush easily through the waste pipe to wastewater treatment. Here increasingly biogas, vital soil nutrients and fresh water are recovered.

InSinkErator has been engaged with domestic food waste management since 1928 when the company founder invented the first food waste disposer. The company welcomes the opportunity to contribute to the Committee’s inquiry into achieving ‘Net Zero’ specifically in relation to the waste management section of the inquiry and the role innovation in domestic food waste management can play.

Local Government Path To Net Zero – Waste Management

Introduction

There is a global movement to reduce food waste and where reduction is not possible, to make better use of food waste through resource recovery.  Since 2009, kerbside collection of food waste has been the preferred choice of the UK government and the devolved authorities, although inadequate thought seems to have been dedicated to complementary methods that can be deployed to improve recovery rates.

Kerbside collection of separated household food waste is seen as the single solution, with the collected material recycled through composting or anaerobic digestion for energy generation. However, this approach requires behaviour change by the public to separate, store, and set out food waste as well as significant cost for local authorities to maintain weekly collections, particularly where participation rates are low. A Government response dated March 2020[1], reported that just 35% of local authorities in England managed to collect segregated food waste on a weekly basis.

Experience in the most environmentally aware nations such as Sweden demonstrates that the performance of kerbside collection of domestic food waste plateaus in densely populated urban areas and alternatives must be sought. In 2017, having reached 47% kerbside collection rates[2], to achieve higher recovery values from food waste Helsingborg, Sweden, incorporated plans for alternative collection systems in their new urban development H+[3]. The first phases of this model of eco-housing, already occupied, include food waste disposers in all homes.

Separation of food waste is a particular problem in high-rise flats and similar high-density housing due to lack of space and concerns about contamination, odour and hygiene. These problems are compounded by households that either will not or are cannot (for physical or other reasons) take  food waste caddies to collection points.

Another potential solution for resource recovery from food waste is to discharge it into the wastewater collection system, after processing with food waste disposers that grind the material into small particles.  Progressively, wastewater treatment is focused on recovery processes to  ensure zero waste. While this food waste disposal option is commonplace in many parts of the world, it has limited uptake in Europe due to past concerns about plumbing and sewer blockages. In 2010-12 the concern over blockages was a consistent argument deployed by water companies in the UK against the wider use of food waste disposers. However, recent research studies have now shown that blockage from ground food waste poses a minimal risk and that food waste disposers are a recommended option for resource recovery, particularly for multi-occupancy or high-rise buildings.

Management of food waste in high-rise buildings

Separation of organic food waste requires behaviour change in household residents and additional waste handling equipment (e.g. organic waste containers).  Resistance to waste separation projects includes objections to the effort required, odours, hygiene, and contamination related to waste containers as well as interruptions in collections due to issues such as work force disruption due to disputes, weather or unexpected events like the COVID pandemic.  These problems are exacerbated in high-rise buildings due to lack of storage space (both within each unit but also centrally), distaste of communal waste bins, and lack of social cohesion among residents1,[4].  Many cities have realised that high-rise buildings will be the most difficult aspect of their food waste reduction efforts; for example, in the Netherlands it is estimated that high-rise buildings contribute only 1.5% to the national waste separation figures2.

Kitchen food waste disposers offer an alternative for organic food waste disposal with many appealing features for high-rise buildings including reduced odour, lack of additional containers, and convenience.  They are particularly valuable to address those householders unwilling or unable to participate in separate kerbside collection of food waste.

In addition, many local authorities may face challenges that necessitate the use of several options to meet their waste management obligations. The January 2020 study by Resource London entitled ‘Making Recycling Work for People in Flats’[5] is a good example of the unresolved challenges presented.  The study carried out across 12 London local authorities looked at how to improve the poor levels of recycling from London estates, particularly as it is forecast that 46% of London residents will live in flats by 2030. Despite a highly engaged programme of education, improved signage and bin location, the initiative still only managed to improve food waste collection by 3% (from 10.7% to 13.9%) even though this waste stream accounted for 28% of all waste from the flats in the survey.

Latest Research

Minimal Potential for Drainage Piping or Sewer Blockages from Food Waste Disposers

A detailed study of food waste disposer impact was completed in late 2020 by KWR Watercycle Research in the Netherlands in collaboration with a number of Dutch municipal authorities, water companies, and industry partners[6].  This study was particularly focused on the application of kitchen sink food waste disposers in high-rise flats, a dwelling type which has been shown to have minimal uptake rates of food waste separation for kerbside collection and thus may require a different type of food waste management solution.   The drainage piping configurations in high-rise buildings are significantly different to those found in detached or semi-detached houses, with long vertical runs of pipe between floors and often more sharp bends.

Using a custom-constructed pipe test rig to simulate drainage pipe design in high-rise buildings, the study investigated the potential for particle accumulation and pipe blockage for 16 different pipe configurations, 17 individual ground foods or food mixtures, and water flow rates during grinding.  These experiments showed that if in-building plumbing is built according to Dutch building requirements for slope and number of bends, there is no drainage pipe blockage impact from food waste disposers.  Even drainage pipe configurations with horizontal runs, which would not conform to building standards but exist in practice, showed no long-term blockage problems since any temporary accumulation of particles was flushed clean by subsequent water use at the sink or dishwasher.

The KWR findings support the results of more recent research in a study by the University of Sheffield funded by EPSRC and including field work in Upper Rissington, Gloucestershire[7], to verify results.  This study tested 18 different food types ranging from common fruit and vegetables to egg shells and fish.  Unlike many previous studies which tested only a few particle sizes, this project developed and applied a robust method to characterise particles across a continuous range of sizes from 0.06 to 8.0 mm.  Importantly, this study also measured settling velocities for each particle type, which are important in determining whether the particles will remain entrained in the flow or will settle out of flow, possibly leading to accumulation.  The mean size of the ground particles ranged from 0.58mm to 2.70mm. 

Rice, pasta, and egg shell were found to be the food types with the highest likelihood of particle deposition in the sewer.  However, the density of rice and pasta particles was such that they would easily be entrained into the flow under typical dry weather flow conditions.  While egg shells produced more dense particles than other food waste, the egg shell particles were found to be less likely to deposit than sand, which is a common component of sediment in sewers, and would likely be mobilised during peaks of normal sewer usage such as during morning high water use times.  Given that egg shells typically make up less than 1% of food waste mass, this study confirms that the accumulation of such particles to the extent of blockage in sewer networks is not likely to occur.  The water company serving Upper Rissington (Albion Water), where food waste disposers were installed in a newly constructed estate, has also confirmed that they have not experienced any sewer blockages. 

An open access tool has also been developed as part of this work to estimate the particle characteristics and behaviour from different food mixes (DOI 10.5281/zenodo.3697303).

Fats, oils and greases (FOG) from domestic and commercial premises continue to be a problem for sewer blockages, made worse by flushing of wet wipes.  UK water companies have invested in a number of campaigns to educate the public on this issue.  Food waste disposers are not recommended for disposal of fat alone. This aspect is highlighted in the product instructions and would need to be emphasised as part of training and education about food waste disposal. The KWR study found that a moderate amount of fat within a mix of other food waste, as would be representative of a typical meal, did not cause excess blockage of the drainage pipe.

Boost to Energy Recovery from Addition of Food Waste to Wastewater Anaerobic Digestion

The emerging body of evidence is that the carbon contributed from food waste in the sewers is recoverable as additional energy from anaerobic digestion at the wastewater treatment works.  Estimates of the energy boost from food waste vary from a worst case of 14% to a best case of 70% or more[8], depending on the specific food waste and local sewage composition. 

An important question is whether the food waste particles remain suspended, and therefore require treatment in the liquid treatment process at a wastewater treatment works, or settle out of the water flow, thereby being removed at the primary settling stage and sent directly to sludge treatment via anaerobic digestion.  The KWR study comprehensively calculated that 67% of the carbon associated with the food waste stays in particulate form and would be removed during primary settling4.  This result means that roughly two thirds of the carbon associated with food waste can be converted into energy, which is a significant recovery rate.  Although the presence of the food waste particles will increase the sludge volume requiring treatment, estimates of the extent of the increase vary widely6 and are dependent on the food waste and sewage composition in the local area.  Despite this increase in sludge handling requirements, the energy recovery boost is a positive benefit that cannot be overlooked.

Food Waste can Contribute Valuable Carbon to Wastewater Treatment

While carbon from food waste in particulate form will primarily be sent directly to digestion, the remaining portion of carbon and other nutrients will require treatment in the liquid wastewater treatment processes.  This impact has been an active topic of research and the KWR study further emphasises the potential benefits of including food waste in the wastewater stream.  The small increases in carbon load (depending on local uptake levels, food waste characteristics, and sewage composition) will impact treatment costs but also may have beneficial effects by altering the nutrient ratios towards a more favourable composition for biological treatment4.  Many wastewater treatment works with dilute sewage need to add carbon to optimise biological treatment and food waste could therefore minimise this requirement.

How FWDs can Support a Circular Economy

The KWR study included a life-cycle carbon impact calculation to better understand the impact of food waste disposers using the latest advances in life cycle inventory databases.  The conclusions of this study were that for a municipality that already has a food separation and kerbside collection programme, continuing with kerbside collection is slightly favoured over installation of food waste disposers.  This result contradicts earlier research that found the food waste disposer scenario to have a greater carbon impact[9]. The KWR study found that the carbon impact of the food waste disposer scenario is heavily influenced by the mix of electricity sources so locations with green energy sources will have a more favourable life cycle carbon performance. In the UK where renewables now provide more than 40% (40.2% in the period from July to September 2020, for example[10]) of primary electricity generation the result could be even more positive.   Reductions in the water consumption required to operate the food waste disposer were also noted in this study compared to previous ones.

Importantly, for high-rise buildings where the alternative scenario is to send food waste to landfill, the carbon impact of food waste disposers to the sewer network is significantly lower and contamination of the dry recyclable streams will be minimised.

The view of wastewater as a problem to be treated rather than as a resource with plentiful of carbon, nutrients, reusable water, and energy is rapidly changing.  Current wastewater treatment practices require significant inputs of chemicals and energy to convert dissolved carbon to carbon dioxide (which is clearly undesirable from a climate perspective), dissolved nitrogen to nitrogen gas, and dissolved phosphorus to solid form/biomass.  As the paradigm of wastewater treatment shifts to better align with circular economy principles, a variety of beneficial uses for recovered resources from wastewater are emerging.  For example, reactor-based production of microbially-produced protein can be done using nitrogen feedstocks derived from wastewater to produce animal feed and plant-based human food products (e.g., Quorn)[11].  Ammonia, which is naturally found as one form of nitrogen in wastewater, is seen as a cost-effective and highly feasible carrier of hydrogen to support a hydrogen economy[12].  These circular economy benefits from wastewater, along with increased energy recovery through anaerobic digestion, would all be enhanced by the addition of carbon and nutrients from food waste disposers to the sewer while also mitigating the significant impacts of food waste itself.

Blackwater and Greywater Capture in the Circular Economy

Sweden and the Netherlands have researched and instigated a number of projects which aim to maximise the recovery of food waste, greywater, blackwater and fresh water from new residential homes. This has been achieved by installing two or three pipe disposal systems in new homes which capture and co-mingle black water from toilets and food waste from the sink to be sent to a local AD plant that aims to provide power to the surrounding area, while all other wastewater is directed to other recovery and recycling systems. While these systems, of which Helsingborg + in Sweden is an outstanding example, aim to maximise organic waste and water recovery from homes for AD and nutrients, they also limit the need for road transport collection, along with the associated congestion and carbon emissions. While the plumbing infrastructure of these systems is both initially more complex and expensive, the performance over time fits more closely into a ‘net zero model’.

Conclusion

This submission seeks to draw to the attention of the Committee the limitations of current UK kerbside food waste collection systems in progressing towards ‘net zero’, especially in relation to high rise properties in urban areas and uses recent academic research from the UK, Sweden and the Netherlands to call for a more flexible approach to food waste recovery management. Such an approach has been shown to increase the capture of household organic waste in Sweden and the Netherlands and improve the amount of renewable energy that can be recovered along with fertilizer and water. These techniques are especially appropriate for high rise or multi-occupancy properties in urban areas and the advantages can be further enhanced as an increasing proportion of renewable energy becomes available through the national grid.

April 2021