What this document is
A waste forecasting model was developed to determine the required size of the proposed ERF. The methodology used to forecast the expected future waste tonnages is described. This document also addresses how any uncertainties relating to future recycling performance have been considered within the modelling work.
1. Why do we need to replace the existing Edmonton energy-from-waste facility?
North London Waste Authority is responsible for managing recyclable and non-recyclable (known as residual) waste collected by the seven north London boroughs of Barnet, Camden, Enfield, Hackney, Haringey, Islington, and Waltham Forest (the Constituent Boroughs). Waste which is not set out for recycling is sent to the Energy from Waste (EfW) facility located in Edmonton.
The facility, operating since the early 70s, is approaching the end of its operational life (around 2025) and requires replacement. NLWA proposes to replace the existing facility with an Energy Recovery Facility (ERF) which will enable The Applicant to continue to treat all of the non-recyclable waste delivered by the Constituent Boroughs in a responsible manner. For the difference between an EfW and an ERF see What is EfW.
2. What waste will we need to deal with over the likely life of a new plant?
In 2012/13 the Constituent Boroughs collected around 827,000 tonnes of recyclable and residual waste comprising household waste (679,000 tonnes) and waste produced by businesses (102,000 tonnes). The remainder was made up of a variety of minor waste streams arising from street cleaning, flytipping, construction and demolition, and highways cleaning. In 2012/13 households in north London achieved a re-use, recycling and composting rate of approximately 32%. In the same year the Edmonton EfW facility treated approximately 530,000 tonnes of waste. Overall, almost 600,000 tonnes of residual waste was delivered to the Applicant in north London in 2012/13.
The proposed capacity of the new ERF is 700,000 tonnes and is based on detailed waste modelling used to forecast north London’s waste arisings between 2012/13 and 2050/51. The results of this model indicate that by 2051 the NLWA Area is likely to produce over one million tonnes of waste from homes and businesses for collection by the seven boroughs. Other factors were also used to determine the proposed capacity of 700,000 tonnes. These additional factors are discussed below.
In addition to residual waste collected by the Constituent Boroughs (known as Local Authority Collected (LAC) waste), NLWA is proposing to treat non-LAC waste if less LAC residual waste is produced or recycling rates increase above what is expected.
3. What recycling assumptions have we taken into account when developing the waste forecasting model
A waste forecasting model was developed in order to estimate the amount of waste likely to be produced over the anticipated operational life of the proposed ERF (up to 2051). The Applicant’s waste forecasting model incorporates the following assumptions:
Forecasting Household Waste and Recycling Rates
The data relating to household waste arisings and ‘other’ smaller waste streams (street cleaning, flytipping etc.) is from the Department of Environment Food and Rural Affairs (Defra) official waste database (WasteDataFlow). This database was set up to help local authorities monitor their waste data. Each of the Constituent Boroughs provides data to WasteDataFlow.
A detailed statistical analysis of historic household waste arisings was carried out in order to
identify the factors showing the strongest correlation with waste arisings. The identified factors included: Gross Disposable Household Income (GDHI), a time variable (assumed to represent the cumulative effects of waste prevention and minimisation measures), and a recessionary impact variable to account for the impacts of the economic downturn and subsequent recovery. A comparison against waste projections contained within the London Plan, the spatial strategy for the capital, show that GDHI is a lower growth assumption than the growth rates assumed as part of the London Plan.
The Applicant’s waste model predicts London’s future household waste arisings up to 2051 based on the above factors. The resulting growth rate over this period is applied to current household waste arisings for the Constituent Boroughs which produced an estimate of future waste tonnages.
In this target-led model, three scenarios relating to expected future recycling rates (high, central and low) were applied to the total household waste arisings. The recycling targets selected for household waste are as follows:
- Low Recycling – 40% recycling by 2020/21 and static thereafter;
- Central Recycling – 50% recycling by 2020/21 and remaining static thereafter; and
- High Recycling – 50% recycling by 2020/21, rising to 60% by 2031/32 and remaining static thereafter.
The results provided a range of potential future tonnages of non-recyclable waste available for energy recovery.
Forecasting Commercial Business Waste and Recycling Rates
Data on future commercial business waste arisings was sourced from work completed as part of the draft revision to the London Plan published in January 2014. This study was based on updated employment and business waste data from 2009. At the time these projections were the most up-to-date projections of likely future business waste arisings available at a borough level. Within the London Plan study business waste arisings were predicted up to 2036. Beyond this period, growth in business waste arisings used within the Applicant’s model was assumed to remain constant up to 2050/51.
Only a proportion of the total business waste produced in the NLWA Area is collected by the Constituent Boroughs. Within the Applicant’s model this proportion was applied to the predicted future tonnages of total business waste identified in the London Plan study. In 2012/13 that proportion was around 10% decreasing from 16% in 2009/10. The Applicant’s modelled approach assumed that the proportion of NLWA business waste (10% for 2012/13) increases to approximately 20% by 2018/19. The proportion of business waste was then held constant through to 2050/51 (the final year of the anticipated operational life of the facility).
In order to predict future tonnages of commercial business recycling the same growth rate as for household recycling was applied to the business waste arisings within the Applicants model. For example, if household recycling experiences a 10% increase over 10 years, then the same growth is applied to the business waste. Therefore, as business waste recycling continues to be encouraged and recycling behaviours change, an improvement in household and business waste recycling is assumed. The remaining tonnages of residual waste from business were added to the predicted tonnages of household residual waste.
Forecasting ‘Other’ Waste and Recycling Rates
Waste arisings other than household and business waste are described as ‘other’ waste and include fly-tipped waste; construction and demolition waste; ground clearing waste and highways waste. Other waste represents only a minor proportion of the overall waste arisings and is treated at the existing EfW facility. Owing to the relatively low tonnage when compared to the other major waste streams, the tonnage of other waste was kept constant at 2012/13 levels throughout the modelled period. In addition it was assumed other waste will continue to be treated at the replacement ERF over the modelled period.
The combined outputs of the model indicate that by 2025 the Applicant would need to plan for the management of over 996,000 tonnes of waste from the seven north London boroughs. This figure is expected to increase to more than 1 million tonnes by 2051. Therefore, by 2051 the replacement ERF will be expected to treat between 713,000 (low recycling scenario) and 611,000 (central recycling scenario) of residual waste.
This result is considered by the Applicant to be a robust forecast of the likely tonnage of residual waste requiring treatment by 2051 given the past recycling performance across the boroughs and the expected increase in overall waste arisings. The low and central recycling scenario anticipates a household recycling rate of 40% and 50% by 2021 respectively. This compares well with Europe’s highest performing cities in terms of recycling.
4. How are we managing uncertainties in the waste flow?
The model was developed based on the best data available, a robust analysis of historical trends; and a robust set of assumptions about what will happen to these trends in the future.
The predicted tonnages of household waste are based on a set of factors which have been shown to correlate strongly with waste arisings. The identified factors (GDHI, a time variable accounting for waste prevention measures; and an economic recovery variable) are based on economic and well as social influences and were used to predict future household arisings.
Data for business waste arisings was based on the most up to date waste forecasting model at the time (London Plan - including 2015 Further Alterations). This data was combined with borough level data extracted from WasteDataFlow (the web based system for municipal waste data reporting by UK local authorities to government).
5. In addition to the waste forecast model what other factors are used to inform the capacity of the replacement ERF?
While the waste forecast model was undertaken to help inform the capacity of the facility, waste projections are just one of the important factors which are considered when sizing a facility. Other influencing factors which have also been examined to enable a fully considered approach to sizing include:
- Capacity and risk to the Authority and therefore, the Constituent Boroughs;
- Waste seasonality and operational impact;
- ERF thermal capacity and its effect on associated throughput.
Because of uncertainty over the future treatment capacity within reasonable proximity to the north London along with the gate fees offered by these facilities, the undersizing of a new facility poses a significant risk to the Authority.
A further factor relates to the seasonality of waste arisings and the impact this will have on operations. Waste arisings vary throughout the year with peaks (e.g. Christmas and New Year) and troughs occurring at different times. The facility must have sufficient capacity to process waste within a number of days; for operational, as well as health and safety reasons. Therefore, prolonged stock piling of waste in the bunker is undesirable. The proposed capacity of the ERF bunker is around 7 days. The bunker will not be full at all times but it will provide a greater buffer/capacity to manage both waste deliveries and plant shutdown related disruptions. The bunker size will enable the waste to be mixed thoroughly to create a homogenous fuel.
Another key parameter for the design of the facility is the calorific value (CV) of the waste. The CV refers to the amount of energy which may be released when the waste is combusted. The capacity of the ERF is based on achieving a balance between the mechanical throughput (tonnes) and the thermal capacity or CV. The design of the replacement ERF is such that it will not be possible to increase the throughput of the ERF if the design CV (10 MJ/kg) reduces. On the other hand, if the CV of the fuel increases above the design CV the fuel throughput will be reduced. The design CV is based upon operational experience from the existing EfW.
6. Is the replacement ERF expected to treat waste other than that which is collected by the Constituent Boroughs i.e. non-LAC residual waste?
The waste forecast model estimates that by 2025, under the central recycling scenario, the replacement ERF is expected to have spare capacity of around 127,000 tonnes in 2025/26 reducing to around 89,000 tonnes by 2050/51 (based on a design CV of 10 MJ/kg). This amount will be reduced during periods of peak seasonal demand.
In terms of the risk associated with any potential excess capacity, and changes to CV, these could be mitigated by offering any spare capacity to third party residual waste collectors. In doing so, this could result in a lower overall gate fee because of income from external sales. Such sources of third party residual waste may include:
- NLWA Area non-LAC commercial/industrial waste;
- Other London LAC residual waste; and
- Non-London LAC residual waste and commercial/industrial waste
The Applicant considered the availability of residual commercial/industrial waste within a 50 mile radius of the Edmonton EcoPark. The result was an estimation that currently (on 2014/15 modelled figures) around 565,000 tonnes of residual commercial/industrial waste could be available for disposal at the Edmonton EcoPark.
Should lower than forecast waste arisings occur and/or higher rates of re-use, recycling and composting be achieved, then these other sources of residual waste will be available both from within the NLWA area and beyond to fill any spare capacity in the replacement ERF. In doing so, this will not result in any barrier to continued efforts by the Applicant and the Constituent Boroughs to move the management of LAC residual waste further up the waste hierarchy.
Want to know more?
What is EfW: Eunomia Waste Forecasting Project Report
Interim Need Assessment (AD05.15)
Further Alterations to the London Plan