Modelling undertaken to inform the sizing of the proposed Energy Recovery Facility
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 (NLWA) 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. 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 old facility with an Energy Recovery Facility (ERF) which will enable NLWA to continue to treat all of the non-recyclable waste delivered by the seven boroughs in a responsible manner. For the difference between an EfW and an ERF.
2. What waste will we need to deal with over the likely life of a new plant?
In 2012/13 the north London borough 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 produced in north London in 2012/13.
The proposed tonnage capacity of the new ERF is 700,000 tonnes. This sizing of the ERF 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 north London is likely to produce over one million tonnes of waste from homes and businesses for collection by the seven boroughs.
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 facility (up to 2051) and 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 seven north London 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 NLWA waste model predicted London’s future household waste arisings up to 2051 based on the above factors. The resulting growth rate over this period was applied to current household waste arisings for the seven north London 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 Business Waste and Recycling Rates
Data on future business waste arisings were 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. Only a proportion of the total business waste produced in north London is collected by the boroughs. Within the model this proportion was applied to the predicted future tonnages of total business waste. In 2012/13 that proportion was around 10% decreasing from 16% in 2009/10. The overall proportion was assumed to increase to approximately 20% by 2018/19 and was held constant for the remainder of the study period. Beyond the modelled period (2036) the growth in waste was assumed to remain constant up to 2050/51.
The same growth rate as the household recycling was applied to the business waste arisings to predict future tonnages of business recycling. 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 includes 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 NLWA 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 NLWA 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 strongly correlate 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 (Draft Further Updates to the London Plan – published in January 2014). 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).