This is a story that ranges from cleaning streets to sustainability. Jump aboard as we uncover the fate of street sweeper waste.
In the bustling streets of cities worldwide, street sweepers play a pivotal role in maintaining cleanliness and public health. However, the journey of the waste they collect is often overlooked.
This article dives into the complex processes involved in the treatment, recycling, and disposal of street sweeper waste, shedding light on the intricacies of urban waste management.
Introduction
Street Sweepings from Cleaning Public Spaces
Street sweepings are the materials collected during street sweeping. They include non-hazardous materials and, on some occasions, hazardous materials: such as
- Inert materials: soil, sediment, sand, and eroded rock from the weathering of bricks, concrete, and asphalt from pavement and structures.
- Vegetation, including leaves, grass cuttings, and woody materials
- Industrial emissions, including atmospheric fallout, oil, and hydrocarbons from vehicles, tyre rubber, etc.
- Litter, frequently including plastics, microplastics, and discarded food.
Surface runoff, wind, vehicle trackouts from construction sites, unpaved roads, and pavement abrasion from vehicular traffic all carry this material.
Key Takeaways: The Future of Street Sweeper Waste Management
Comprehensive Approach to Waste
- Transition from traditional disposal to innovative recycling processes.
- Emphasis on meeting stringent EU regulations to reduce landfill use to below 10% by 2035.
- Do all this cost-effectively by avoiding high landfill tax charges and obtaining a good income from the sales of the resulting construction materials.
Technological Innovations and Case Studies
– By highlighting successful recycling initiatives and providing case studies of successful projects the waste industry will increase the uptake of these advancements in waste processing technology.
Environmental and Economic Benefits
– Efforts contribute to resource conservation, lower waste management fees, and a smaller carbon footprint.
Sustainable Urban Waste Management Practices
– Showcases a shift towards sustainability in managing urban cleanliness and public health challenges.
The Evolving Challenges of Sustainable Street Sweepings Waste Management
At first in the early years of this century, there grew a general pressure for all waste management companies to apply the 3Rs of sustainable waste management, namely:
- reduce waste,
- reuse what cannot be reduced wherever possible, and if not possible
- recycle.
Then, in the noughties (2000 to 2010) came the introduction of the waste hierarchy. That has meant that the waste management industry must also consider “energy extraction” in addition to recycling, when that is not feasible:
- extract the energy bound up in the organic waste before resorting to the final “last resort” option of landfilling.
- whenever possible use the anaerobic digestion process for organic waste energy extraction (not incineration) due to its acknowledged superior benefits in terms of sustainability and carbon emissions reductions.
Next, in 2012, the UK Environment Agency ramped up the requirements by issuing the street sweepings composting ban:
UK Street Sweepings Composting Ban
Following the Environment Agency's regulation against the composting of street leaf sweepings due to high contaminant levels, several UK street sweepings facilities have been opened. These street sweepings waste processing plants not only address the recycling challenges faced by local authorities, but the best of them also ensure 100% recovery of this waste.
But, until now, organizations that were willing to pay the landfill tax and could bear the cost have been able to send their sweepings to their local landfill. But not for much longer in Europe!
Before long, that won't be allowed.
In the next section, we explain the current approach to street sweeping disposal, and after that, we move on to explain the new EU regulation to place a new statutory limit on waste to landfill by 2035.
Current Developments in Minimizing Street Sweeping Waste Sent to Landfill
Street-sweeping waste must be processed and reduced in quantity before disposal, as with all waste. That's not a matter of negotiation.
Landfill capacity is running out in all developed nations, and the public is not about to accept that new landfills be opened.
EU targets have been set to drastically reduce the proportion that can be sent to landfills, and this will hit street waste disposal hard because, until now, a large proportion of street waste has been sent to landfills.
That has been due to the following factors:
- it's a relatively small quantity relative to domestic and commercial waste and the complexity and cost have made treating it a low priority
- the high cost of bringing it to a central location where specialist processing equipment can be located to recycle as much as possible while also separating the inert materials from the organics
- the processing equipment is costly to buy, and the processing technology is one-off, not necessarily well proven to work and still evolving
- the markets for the sale of the products made from this waste have been depressed in value and limited due to a lack of acceptance of the recyclates within government tender specifications. Establishing end-of-waste criteria has been hard to do.
- with comparatively few examples of successful street-sweepings processing facilities, the extent to which Life Cycle Analysis (LCA), when applied to these facilities, will show a net reduction in carbon emissions is unknown.
The result so far has been patchy, with only the largest and most environmentally responsible organisations diverting their street sweepings away from landfill.
But in 2035, all that will change throughout Europe.
In 2035, EU Waste to Landfill will be Capped to No More than 10%
The European Commission's goals for 2035 set a cap at 10% on the proportion of Municipal Solid Waste (MSW) that may be allocated to landfills, and that will finally force street sweepings diversion.
These objectives also aim to drive society toward:
- reduced natural resource usage,
- a decrease in waste management costs and lower rates for home owners, plus
- a smaller carbon footprint for the construction material supply chain.
This is a big challenge, and the only way it will be met is for street sweepings processing capacity to be progressively expanded and the technology to do it improved, starting now.
So, that's what needs to happen.
Let's look at the very real advances that are happening by discussing the recently published case studies, right now:
Street Sweepings Management Case Studies
Introduction and a Summary of Snippets of Street Sweepings Information We Found
a) A study published in September 2023 in Science Direct notes that the average operational cost for street sweeping in Italy is approximately 41 € per ton of litter collected. The inert material derived from this process can be sold, generating about 3 € per tonne of profit.
Such facilities optimize waste recovery from street sweeping, thus diminishing landfill waste and promoting the recycling of waste as a raw material for secondary usage.
b) But street cleaning costs are substantial. For example, in Italy, the operational costs for street sweeping and washing are significant.
In 2014, they accounted for 12.6% of the total MSW management operational costs for one municipality, even though litter only comprised 3%–5% of the total urban waste. The same report estimated the annual per-capita cost of this service at 23.50 euros.
Case Study 1. Treatment of Street Sweeper Waste: The Journey of Street Sweeper Waste to Disposal at SUEZ
Normally, grit, soil, twigs, and other detritus swept from streets by cleaning crews wind up in landfills, but SUEZ's dedicated facilities can convert these materials for profitable purposes.
- Sand
- Aggregates
- Organics.
This is achieved via the following stages:
Separation
Street sweepings are loaded into a reception hopper and fed via a conveyor to the AggMax, a heavy-duty separation machine. This removes stone fragments from the soil and pollutants.
The AggMax (AGGMAX™ SCRUBBING & CLASSIFICATION SYSTEM) combines pre-screening, scrubbing, organics removal, sizing, stockpiling, fines recovery, and filtrate removal on one compact chassis.
The one-of-a-kind paddle design is built to last in even the harshest circumstances.
To ensure maximum equipment longevity in the highly abrasive environment, the specialist company CDE created Xtryl, a high-cast chromium substance.
Washing
Water is added to the AggMax to wash the waste. Organic material and other lightweight wastes are taken from the surface water, filtered, dewatered, and delivered to a composting bay.
Screening aggregate
Large particles of the washed aggregate (greater than 6mm) are dewatered and deposited in a bunker. This aggregate can be reused in road building or mixed with salt and used for gritting roads.
Secondary separation
The remaining material (less than 6mm) is collected and driven by a pump to a variable-concentration hydrocyclone, which separates sand from finer silt.
The sand is emptied onto a dewatering screen before being dumped into a sand bunker. This sand can be used to make concrete, as pipe bedding by utilities, and in other applications.
Silt treatment
The silt (less than 75 microns in size) is pumped straight into an AquaCycle thickener. The fine silt particles cling together when treated with a modest amount of chemical flocculants and coagulants.
The material then rapidly coagulates in the AquaCycle tank, resulting in a thick sludge that settles at the bottom.
Process water overflows from the tank's top into a recycled water storage tank, where it is reused throughout the system.
Sludge
After that, the sludge is squeezed in a device known as a “press” to dewater it, making a “filter cake”. This nutrient-rich clay-like substance can be combined with soils in land restoration efforts.
However, after all that, there remains a small residue of non-recyclable waste, and that is disposed as follows;
Disposal of Non-recyclable Waste
Landfilling and energy from waste, including incineration (combustion) processes
As we have indicated earlier, both landfilling and energy-from-waste processes have negative environmental implications and are subject to strict regulations to minimize their impact.
While landfilling is still a common method of street sweepings waste disposal in the UK, energy from waste (often available for street sweepings at a similar gate-fee price to landfilling) provides a means to reduce the volume of waste.
The higher calorific content may optionally be incinerated to recover energy from waste materials. To dispose of the hazardous content in the ash, the incineration ash is either landfilled or further treated by encapsulation.
Case Study 2. Recycling of Street Sweeper Waste in Bern, Switzerland
The Bern municipality reported in a recent article on their experience of plastics recycling from street waste, the challenges they overcame in recycling street sweeper waste, and their own street-sweeping success story.
Bern City's Street Cleaning Scope and Cost
We have summarised Bern's street cleaning responsibilities in the bullet points below. We have also included the cost information they have provided.
We were unable to find any other comparable cost data published on the costs of street waste and street sweepings from any other source. However, a summary of the quantities and costs of street waste collection in Bern, including financial values in Euros and US dollars, is provided below:
- Bern's public space: 4.1 million square meters.
- Number of city litter boxes: 1,300, emptied up to 10 times daily.
- Street refuse collected in 2013: 3,113 tons.
- Annual cost for street cleaning and waste disposal: CHF 30 million (approximately €28 million or $30 million USD).
- Cleaning cost per resident per year: CHF 200 (around €190 or $200 USD).
For detailed information, please refer to the article on SWI swissinfo.ch.
Case Study 3: Grundon's UK Approach to Road & Street Sweeping Waste
Grundon Waste Management is at the forefront of the UK's waste management industry, renowned for its innovative and sustainable approach to handling waste.
Grundon provides comprehensive services, from recycling and waste collection to the disposal of hazardous materials. Their investment in cutting-edge technology underscores their commitment to reducing environmental impact and promoting the circular economy.
Grundon Waste Management has established a ground-breaking city and rural road sweeper waste recycling facility at Ewelme, in Oxfordshire, that sheds light on the context of local authorities struggling to maintain and improve recycling rates.
This facility, representing a significant waste management investment of £1.3 million, was innovatively designed for the effective treatment and recovery of road sweeper waste. This is assumed to have included road gulley waste collected via gulley washing tankers.
Location and Capacity
Situated at the Ewelme operation in Oxfordshire, the facility is equipped with a substantial processing capability. It can handle approximately 25,000 metric tons of road and city street sweepings annually, equivalent to an impressive rate of about 10 metric tons per hour.
Response to Environment Agency Regulations
The inception of this facility was a direct response to the Environment Agency's (England) regulation against the composting of street leaf sweepings.
The Agency's decision left Grundon with no choice but to build a street sweepings waste recycling facility that complies with all UK good waste management practices.
The Agency was compelled to prohibit composting of street sweepings by the discovery of high levels of contaminants in the compost from city and road sweepings that could pose health risks, in studies conducted on their behalf.
The Environment Agency’s ban on the composting of road sweeping materials has had a significant negative impact on the recycling rates of many local authorities.
However, the Grundon street waste processing facility has emerged as a crucial and sustainable solution, specifically addressing the challenges posed by these new regulations.
Sustainable Waste Recovery at Ewelm, Oxfordshire
The facility reportedly provides an environmentally friendly alternative to the previously used composting process, standing out for its 100% recovery rate of all road-sweeping waste.
This innovative approach is understood not only to adhere to environmental standards but also to enhance the green credentials of both local authority clients and private contractors using similar road-sweeping equipment.
The following sections are based on an article on the Grundon Waste Management website.
Processing of Road Sweeper Waste
Upon arrival at the facility, road sweeper waste is directed to a specialized tipping area, designed to hold approximately 300 tonnes. This stage involves an essential dewatering process where excess water is efficiently drained and syphoned (siphoned – US) into a large storage tank.
This water is stored for treatment and reuse later in the recycling process.
Metal Removal and Material Washing
Subsequently, the waste undergoes a critical cleansing phase. It passes under a large magnet, effectively removing any metal objects like bottle tops or nails.
Following this, the waste enters a log washer equipped with giant teeth, which meticulously scrub and wash the material, ensuring thorough cleaning.
Sorting and Screening Process Stage
During the next stage, a ‘triple screen' system is employed to sort the waste. Smaller particles remain in the water, while larger aggregate materials, ranging from 5mm to 40mm or more, are carefully sorted and stored by size in dedicated bunkers.
Advanced Separation Techniques
The remaining material progresses to the Hydrocyclone, an advanced system analogous to a giant wash and spin cycle. This process effectively separates organic components (such as leaves) and litter from smaller particles like sand and grit (less than 5mm in size). These separated materials are then stored in additional bunkers for further processing.
Water Treatment and Sludge Processing
The final remnants of wastewater are channeled into a water treatment facility. Here, a polymer is introduced to facilitate the separation of clean water from coagulant solids. The resulting sludge undergoes centrifugation, extracting as much water as possible, and forms a filter cake, subsequently utilized in land restoration projects.
Final Stages of Material Handling
In the concluding phase, litter is segregated from organic material. The litter is then transported to an Energy from Waste facility, where it serves as a fuel source for green electricity generation through incineration.
Concurrently, the organic material is prepared for composting to make a compost that is aimed at land restoration projects.
Recycling Outcomes and Market Impact
Thanks to the facility's sophisticated recovery processes, both the sand and larger aggregates achieve “end of waste” status.
This qualification allows these materials to be marketed to the building trade and sand and gravel businesses. The rising demand for recycled products in these sectors is met with these materials, offering a cost-effective alternative to virgin aggregates.
This innovative approach not only contributes to environmental sustainability but also addresses the growing market need for recycled materials.
Enhancing Green Credentials
The facility's commitment to thoroughly reprocess all materials reflects a profound dedication to environmental stewardship. This commitment is pivotal in supporting clients to achieve their recycling and sustainability objectives, thereby contributing significantly to broader environmental conservation efforts.
Case Study 4. Ling Hall Recycling Facility (Veolia Waste)
Veolia's Approach to Recycling Road Sweepings
Veolia Environmental Services stands out as the premier recycling and waste management company in the UK, dedicated to transforming waste into valuable resources.
Through its partnerships with various city councils and waste authorities, Veolia tackles the significant challenge of managing street sweepings, historically destined for landfills.
A Shift Towards Sustainability
Located on a working landfill site, Veolia has an essential need for restoration material and identified its own landfill restoration material needs as a synergistic use.
Starting with that need, the company has pioneered a system that diverts 85% of street sweepings and gully waste from landfills, aligning with stringent restoration criteria and emphasizing environmental and economic benefits.
Implementing Cutting-Edge Technology
After extensive research, Veolia chose CDE as a partner to develop a washing treatment process for transforming waste into landfill restoration materials and recyclable aggregates. The semi-automatic CDE recycling system processes road sweepings and gully waste, incorporating advanced technologies like the AggMax logwasher and EvoWash fine materials classification system to ensure high-quality outputs.
The following is our interpretation of the Veolia system:
Processed Materials Recycled at Ling Hall
The processed gully garbage and road sweepings materials include various aggregates and sand, which are repurposed for onsite construction and landfill remediation. This has the added benefit of significantly reducing their dependency on virgin aggregates.
Their innovative approach not only meets environmental standards but also supports Veolia's commitment to sustainable waste management practices.
The CDE Road Sweepings and Gully Sucker Waste Recycling Process
The CDE recycling system is a semi-automatic plant that handles 50 tph of road sweepings.
The system takes road sweepings and gully garbage. Most of it is dewatered first at the originating site before being sent in bulk by truck to the Ling Hall recycling facility. Wet garbage can also be received and treated, with the water pumped to the facility for treatment.
Now let us follow the journey of sweepings waste:
a) Initial Logwasher Stage
The AggMax ™ logwasher scrubs aggregates to break up clays and remove contaminants from stone. Lightweights and organic material are discharged onto the dewatering screen to remove surplus water, while the aggregate is separated into two washed products and sand is eliminated.
b) Fine Materials Classification (Hydrocyclone) System
Sand and process water are pumped to the EvoWash™ fine materials classification system. The material enters the sump and is pumped to the hydrocyclone to separate wastewater and silt from the sand. The dewatered sand product (12-15% moisture content) is discharged to the stockpile conveyor.
c) Decanter Centrifuge
The decanter centrifuge separates fine solids from water, eliminating hydrocarbons and heavy metals. Clean water is subsequently kept in the AquaStore for recirculation throughout the system, while 50% dry solids are released into a stockpile.
The results
The processed outputs include +20mm aggregate, 20-5mm aggregate, and -5mm sand. The trommel screen processes oversized materials such as rags, twigs, and large stones, while ferrous metals, organics, and polymers are recycled. The decanter filter cake is then utilised for landfill cleanup, while the aggregates and sand are used for on-site building. This minimises the requirement to buy fresh aggregates.
UK Environment Agency Guidance Governing Waste Disposal of Street Sweeping and Gully Emptyings
Cleaning Up Streets and Gullies
Note: The trash code “20 03 03: street cleaning residues” is currently used for all UK gully emptyings and street sweeps that are collected by the waste authority.
Even though both of these waste categories could be dangerous, this is a designation for non-hazardous garbage. The recovery and disposal of these wastes are both governed by regulations.
According to the List of Wastes (LoW) Regulations 2005, a “waste code” is a six-digit code that specifies how a waste item is classified. The LoW Regulations domesticate the wastes included in the European Waste Catalogue (EWC). The terms “LoW code” and “EWC code” are other names for waste codes.
It is not possible to dispose of street sweepings and gully emptyings at an exempt facility or an inert landfill.
Trashes, with a waste code of 20 03 03, must be approved for acceptance by the landfill.
Gully Emptyings Guidance
The EA requires that dewatering be applied for gully emptyings, with the liquid removed following a consent to discharge to sewer.
Heavy metals, other physical pollutants, and a high leachable organic content may be present in the remaining solid wastes, which also have a relatively high water content. Dewatering is not classified as “treatment”.
Only in their recommendations for recovering street sweeps and gully emptyings does the EA address the proper disposal and recovery of solid residue.
Some examples of the more varied and dry elements that make up street sweepings are litter, grit, glass, oils, paper, plastics, and so on. Heavy metals and other pollutants may be present, and their high leachable organic content is another concern.
Conclusion
This article explores the journey of street sweeper waste from urban cleanliness to sustainable management. It highlights the complex processes involved in treating and recycling street sweepings, addressing the challenges posed by environmental regulations and the need for innovative disposal methods.
With the EU setting ambitious targets to reduce landfill waste by 2035, the article showcases various case studies, including successful recycling initiatives and technological advancements in waste processing.
These efforts not only aim to meet regulatory demands but also contribute to resource conservation and a reduced carbon footprint, underscoring a shift towards more sustainable urban waste management practices.
FAQs
Question 1: What percentage of street sweeper waste is recyclable?
Answer 1: The variation in street sweeper waste is so wide that any answer to that would be meaningless. Data analysis of the waste from a city or borough would be needed to meaningfully answer the above question, and the answer would still vary widely between each location and seasonally.
Question 2: How does street sweeper waste management contribute to environmental sustainability?
Answer 2: Street sweeper waste management, when applied in accordance with the waste hierarchy enhances environmental sustainability by reducing landfill waste, recycling materials, lowering greenhouse gas emissions, preventing water pollution, contributing to urban cleanliness and public health, and supporting a circular economy.
Question 3: Are there any incentives for cities to improve their street waste management?
Yes, and these are much wider than simply receiving financial grants from governments keen to encourage tourism. Cities are frequently motivated to improve their street waste management by enlightened self-interest, as evidenced by the advantages clean streets offer in terms of:
- improved community health and environmental quality,
- as well as the growing potential for revenue generation from recycled materials.
These incentives drive sustainable practices and contribute to overall urban development and ecological conservation.
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