Urban areas: technologies for cleaning and waste collection
The means used for urban cleaning have evolved a great deal, both in terms of the machines used to clean the streets, pavements, squares and yards, and in the systems for sorting urban waste
The cleaning work carried out by the city council covers the collection of rubbish left on the ground and also the cleaning of areas dirtied by various causes. On the subject of litter, the results of a survey carried out in France by AVPU (Association des Villes pour la Propreté Urbaine) on litter found on the ground during the year in some sixty participating cities, totalling 20,000 sites, are very interesting. On a standardised 2.5 metre wide by 2.5 kilometre long road, the following were detected: paper and food packaging every 160 metres; cigarette butts every 266 metres; animal droppings every 1000 metres; pieces of glass every 1330 metres. The quantity of such waste is mainly related to the civic education of citizens, but also to the presence of specific collection containers along the route.
The vehicles used for cleaning operations are mainly street suction sweepers and road washers. There are both models with a driver on the ground, mainly for internal areas of buildings and small external areas, and models with a driver on board. The propulsion is provided by internal combustion engines, petrol or diesel, and also increasingly by electric motors powered by lithium ion batteries.
Street suction sweepers with driver on board
The components of a street suction sweeper with driver on board are:
– rotating brushes on a vertical axis (frontal, lateral and ventral), whose function is to collect and convey waste towards the suction inlet;
– suction fan which, by creating an air vacuum, lifts the material into the collection container and also sucks up the raised dust. The suction intensity can be adjusted from the driver's seat. There can also be a manual suction hose for targeted interventions to collect material not reached by the brushes;
– collection container, which can be lifted and tipped for unloading, and whose capacity varies from 1-2 to 6 m3 or more depending on the type of machine. High capacities are found in road sweepers (they are road-legal), which are able to reach high speeds (60-70 km/h) in order not to impede car traffic;
– filter to retain dust and reduce the emission of fine dust;
– water circuit (tank, pump and nozzles), not always present, to moisten the ground, collect dust and reduce brush abrasion. A hand lance is often present for targeted washing operations;
– supporting frame that can be either articulated or rigid. The former allows high manoeuvrability of the machine, making it suitable for work in restricted areas with trees, street furniture, etc.
The brushes, depending on the operating conditions, must have fibres of a different nature. On "fragile" surfaces, such as pedestrian and cycle paths, car parks, valuable paving, etc., the sweeping action must not be too impacting and the fibres, which must have a certain flexibility, are made of polypropylene, polyester or nylon material. When the cleaning action must be "energetic", brushes with steel fibres or brushes with a mixed composition (steel and plastic) are used. The duration varies from 30 to 50 working hours. The height of the suction nozzle can be adjusted, allowing it to overcome steps such as kerbstones. When reversing, the nozzle lifts automatically to prevent damage from obstacles. An optional camera for the suction nozzle enables more precise work. The integrated four-wheel steering system, when fitted, provides high manoeuvrability and a very small turning radius. The sweeping width varies depending on the model and equipment (number of brushes), and is approximately between 1 metre and over 3.5 metres, with motor power from 20-25 kW.
Multifunctional suction sweeper models are available, which are also road-legal and can be fitted with grass-cutting equipment and snowploughs. In recent years there has been a growing popularity of all-electric models, which are less polluting and less noisy, and can operate continuously for more than 10 hours. These are very manoeuvrable machines, with a sweeping width of 1-2 metres, a collection container of around 1 m3 and power in the order of 15 kW.
Road washer with driver on board
These machines provide not only high-pressure washing but also the sanitation of urban areas. These trucks are powered by a petrol or diesel engine and are equipped with a water tank, a high-pressure pump (35-60 bar), an adjustable nozzle bar and a hand lance to reach less accessible areas. The washing width is 2-3.5 metres.
Fully electric models are also produced, powered by lithium-ion batteries, equipped with a 1500-2500 litre water tank, with pivoting nozzle bars capable of covering a washing width of up to 3.5 metres.
Separate collection for recycling
Separate waste collection in Italy is growing, even though there are large disparities between regions and, within regions, between municipalities. ISPRA data for 2019 show that the amount of urban waste collected nationwide reached 30 million tonnes, equal to about 500 kg per inhabitant per year. However, there are large variations, ranging from 663 kg in Emilia Romagna to 354 kg in Basilicata. Although the quantity of waste from the north is the highest (14.4 million tonnes compared to 6.6 in the centre and 9.0 in the south), it is the north that has a higher percentage of separate waste collection than the national average of 61.3% (18 million tonnes). At national level, 29% of the waste collected is sent to material recovery plants, 21% to biological treatment, 21% to landfills and 18% to incinerators. The remaining 11% has various destinations. Within the next 15 years Italy will have to halve its landfilling from the current 21% to 10%. This means that the whole chain, from separate collection to treatment plants, will have to improve.
The growth and improvement of separate waste collection is linked, on the one hand, to the behaviour of citizens, who must commit themselves to reducing the amount of waste per capita and to separating it correctly, and, on the other hand, to the improvement of the systems for collection and delivery to treatment plants. The waste collection systems are basically represented by the collection containers and the type of trucks and motor vehicles deployed by the public administration to collect and transport waste.
Containers
The evolution of containers plays an important role in improving the organisation and efficiency of waste collection systems. Classic bins and containers of different colours mounted on wheels are still very common, but new forms of container are increasingly being used. The solutions on the market fall into three categories:
– surface containers, including classic bins and square-shaped bins with and without wheels. The evolution is towards models with different levels of technological content. They are generally made of thermoplastic material, with capacities ranging from a few dozen to a few hundred litres, and up to 1-2.5 m3 for the most high-tech, crane-operated ones. They can be placed anywhere and do not require any type of foundation. They are sometimes camouflaged with differently coloured coatings;
– basement containers, for which two thirds of the volume is below street level. There are different solutions in steel and polyethylene, with a circular or square base and different volumes, from 0.6 to 5 m3;
– underground containers, they have an above-ground loading tower, configured to accommodate the different waste fractions. There are several versions. Underground bins of 0.5-1 m3 with suction pump collection of the contents. Bell-shaped, with a prefabricated concrete tank with 3-5 m3 bins placed inside. They are removed by a crane. When the bins are placed on a hydraulic platform, this acts as a lift and rises up to street level.
The latter two types have the advantage of reducing land occupation and are more widely used in tourist resorts, historical areas and areas of urban value. In order to reduce the impact of each type of solution (surface, basement and underground containers), ecological islands are created through structures that are in harmony with the environment. The most common are still the surface containers for which, as for basement and underground containers, we are moving towards increasingly smart solutions. Artificial intelligence technologies, IoT (Internet of Things) sensors and RFID systems are being installed in these containers, allowing not only geolocation but also the monitoring and measurement of certain quantities such as weight, volume, temperature and humidity of the mass placed inside. These measurements reach a waste sorting and coordination centre, which processes them and can then organise the collection in a rational manner. In order to personalise waste delivery, the citizen is given a personal smart card which is placed on the display on the container. This recognises the person and allows them to deposit their waste, distinguishing between undifferentiated waste, organic waste, glass and cans, plastic and paper.
Loading, transport and unloading
The operation of loading, transporting and unloading waste is carried out by means of waste collection lorries, on which a fixed container is fitted with a compacting shovel and a system for lifting/turning bins and containers. A schematic distinction can be made between lorries:
– two- or three-axle heavy-duty compactors with capacities of 12-14 tonnes, with automatic rear or side loading and also top loading;
– Lightweight, rear-loading compactors with a load capacity of less than 12 tonnes.
Automatic side-loading of skips is preferred because it is very quick and takes up less road space. An advanced system for emptying high volume skips is the use of geo-referenced lorries equipped with a crane. The crane picks up the skip, lifts it over the lorry's body and the bottom of the skip opens, allowing rapid gravity discharge. The skip is then placed back in position. The whole process requires the presence of the driver and takes just over a minute. Fully electric versions of compactors are also produced for a load volume of 1.5-3.0 m3 and a hydraulic tipping system.
