by Malcolm Bates
It would be good to report that the rest of the world’s highway sweeper manufacturers had woken up to the challenge of dust filtration posed by a tightening of PM10 legislation after 2010 – it is after all, just a few years away.
At Dulevo’s recent international press conference in Italy to discuss the dangers of dust particles exhausted from highway sweepers, the world’s technical press were keen to learn about the detrimental effect fine dust particles have on human health. The company used WMW’s September 2007 article as part of the press pack to help explain the issues.
Since my last visit to the Dulevo plant near Parma, Italy, the company has grown to become not only the largest manufacturer of sweeping machines in Italy, but (it claims) the third largest manufacturer in Europe. A recent extension to the new 20,000 m2 production facilities is now completed and up-and-running, while the workforce has grown to 200. Dulevo has been part of the Lampogas Group – now one of the largest suppliers of LPG and industrial gases in Southern Europe – since 1992. Today, the Group has an annual turnover of €850 million – €53 million of that generated by Dulevo.
While Dulevo is, to date, primarily known for small sweepers and scrubber driers for in-plant operations and its larger purpose-built ‘mechanical’ highway sweepers, that perception is due to change as both compact ‘precinct’ and larger truck-mounted vacuum sweepers are also now part of the product range – the latter as a result of E S Zetta (the company used to market Bucher Schorling machines in Italy), which is now building truck-mounted units for Dulevo. This development was formally announced at the recent Samoter exhibition in the Spring.
So, have the other sweeper manufacturers woken up to the challenges posed by dust emissions from sweeping machines? And how high on the priority list for new machines needed after 2010, should the potential customer put ‘dust emissions’?
Confusion
Clearly, ‘filtration’ cannot be considered as a stand-alone topic – it doesn’t, for example, make a badly performing sweeper into a better one that should be purchased over and above more efficient machines. But the team led by Professor Giulio Ceccarelli – the leading academic in the team that first looked into dust emissions at Pisa University – is clearly concerned that, unlike other topics relating to emissions – such as exhaust gases and noise, for example – the whole topic of dust particles and the technology needed to contain them within the sweeping machine is quite literally being ‘swept under the carpet’, and not discussed openly by manufacturers. So far, only Dulevo and Faun Viatec in Germany have made research available to customers and list high-efficiency dust filtration as a production option. Part of the reason for this, he suggests, is the confusion over what ‘PM10’ actually means. The other reason could be that fitting anti-dust filtration systems – especially onto vacuum machines – is both a technically complex and expensive procedure.
So what does it mean? PM10 is the title of original testing procedures that originated some years ago in the USA; the overall name given to European-based aspirations for a method of measuring air quality in the context of dust particles, as well as the specific size of a certain proportion of the dust particles such legislation seeks to reduce. And already, the lack of a single, specific meaning has been used as a smokescreen (or perhaps, more precisely, a dust screen) by certain manufacturers who have yet to start developing the new strategy necessary to filter the dust that is exhausted from sweeping machines while they work.
The key factor here is that even with a single definition of PM10 – that is the size of dust particle and the minimum air quality standards that the residents of a modern city should expect – the whole issue gets far more complicated when scientists talk of PM7.5, PM5 and even PM 2.5 and below. Because unlike a comparison between, say, vehicle exhaust emissions – where Euro-4 and Euro-5 has obviously helped diesel engines emit less of the same basic chemicals than a Euro-2 or Euro-3 unit – with dust particles, the degree of filtration becomes much more difficult as the particles get smaller.
After all, PM10 particles are just 10 microns across (a typical human hair measures 50 microns in diameter) and anything smaller is invisible to the human eye. Yet the smaller the particles, the further they manage to get into the human respiratory system and the more harm they can do to human health.
An air quality issue
In this respect, Professor Ceccarelli outlined a couple of little-known facts. Firstly, dust particles are far from smooth-surfaced – their surface area can be equated to a heavily-cratered sponge. Secondly, dust particles should be seen in the context of increasingly poor overall air quality. And even asbestos – known to be injurious to human health for many decades and now widely thought of as a banned substance – is still widely found in air quality measurements.
While the production of asbestos has indeed been banned by many countries, Professor Ceccarelli suggests that a continuing trend towards accepting imports from developing markets has brought with it the need to be even more vigilant. ‘All the vehicles on our city streets will emit a quantity of dust particles,’ he explains. ‘It comes from brake pads, tyres and many other sources.’ But the key consideration for the future, he asserts, is that the vehicles and machines used by city authorities to clean up the environment, should make a positive contribution, not a negative one. And in that context, it could be argued that ‘re-circulating’ harmful dust particles by passing them through a sweeping machine and exhausting them right back into the atmosphere is probably more harmful to human health than not trying to pick them up in the first place. Which is not the sort of message our industry wants to hear.
In recent years, attempts have been made to reduce air pollution in city streets by introducing physical limits to traffic – indeed, the author recalls the attempts made to reduce traffic congestion by the Government in Lagos, Nigeria, as far back as the 1970s, by the simple expedient of banning all cars with ‘odd’ numbers on their registration plates one day and ‘even’ numbers the next. The reasoning was, it would reduce traffic congestion by 50% – but of course it didn’t. Many of the people who could afford to travel into the city by car (travelling by public transport in Nigeria wasn’t for the faint-hearted), could afford to buy a second car with a suitable plate. And it could be argued that even more sophisticated systems will achieve little more than increasing the tax burden on inner city businesses, which will in turn be passed on in increased prices – without solving the core problem. To put this argument in context, while diesel and petrol exhaust emission standards have made great strides in the past 30 years, the dust particles exhausted from a vacuum highway sweeper have, to date, largely remained the same.
But just as this issue isn’t a simple ‘mechanical sweepers versus vacuum sweepers’ issue, nor is it just about vehicle emissions. The research undertaken by Pisa University in conjunction with the Studio Alfa test laboratory (also based in Italy), has also identified the effect city centre street design has in causing – or preventing – dust clouds in city streets. Indeed, when analysed, a significant proportion of the dust particles contain cement dust and potentially harmful fibres from sources other than vehicles.
The recent Dulevo conference also heard that any form of machine-based sweeping system – whether mechanical or vacuum – was likely to reduce harmful dust emissions by over 25% when compared with manual sweeping methods. That fact alone should also start a debate concerning the health and safety of the operatives that cities employ to help keep the environment clean for the rest of us and will come as a shock to those who suggest that ‘manual’ sweeping has benefits in downtown areas.
There are also those who still see air-conditioned cabs on sweeping machines as a ‘luxury’, even though aircon is a standard feature on all but the cheapest passenger cars, these days. In fact, not only is it an essential safety aid in reducing misted windows in wet weather, it also helps keep the driver alert – but it seems we should now consider adding ‘and helps prevent respiratory illness’ to the list of advantages of aircon as well. It must be the case that the health and safety of operatives working in precinct and highway sweeping every day is looked at in more detail in future.
Adding filters
So can current designs of vacuum sweeper be produced with suitable dust filtration systems to meet the demand for lower emissions? At present, all machines currently produced by the world’s leading suppliers are claimed to meet EU PM10 standards. That’s no real surprise, as the manufacturers were closely involved with setting the criteria and realistically, it would hardly be worth any national government introducing air quality standards that were higher than the levels that could be reached by machines currently in production. But, as Professor Ceccarelli explains, things get tougher after 2010 when the number of days in which air quality can exceed agreed targets drops considerably. Even on current levels, he explains, there are weeks in which traffic is banned from certain Northern Italian cities at least one day a week.
It is of course arguable how much difference highway and precinct sweepers can make to the air quality of an entire city, but the argument here is what happens to dust particles when they are picked up by a sweeper – no one can argue it makes ecological sense to eject them back into the same atmosphere. To prevent that, more advanced filtration systems are the only solution and are already on the agenda of many leading cities where tourism and ‘image’ are a major part of the local economy. Germany-based manufacturer Faun Viajet has already got truck-mounted vacuum sweepers in service with high efficiency filter packs, but managing director Helmut Schmeh confirms this can add a further 20% to the price of each unit.
Part of the problem is that vacuum sweepers work by a high throughput of air through the fan, while mechanical sweepers only use a smaller fan to draw dust from the brushes up into the machine – on mechanical sweepers, the actual material is collected by the mechanical action of the brushes sweeping the debris onto a vertical conveyor that deposits it into the hopper. Does this mean that in the face of growing awareness over the harm that fine dust particles cause, all the cities in the world will move from predominantly vacuum machines as is the case today, to mechanical ones? Obviously, you’d be forgiven for assuming that Dulevo managing director Vincenzo Geddes da Felicaia would like to think so, but in fact, Dulevo now offers both vacuum and mechanical sweeping solutions in its product range, so avoids the charge that it is using the ‘dust debate’ entirely to it’s own advantage.
There is another factor to consider: as we originally reported in Waste Management World, even though Dulevo is based in Italy – a country known above all else for its style – the ergonomics, the styling and the product design of the current range of ‘5000’ mechanical machines is still some way behind the vacuum machines produced by other competitors. And while the smaller 200 ‘Quattro’ is also behind current design thinking, the overall concept of the machine makes it an ideal contender for inner-city precinct sweeping. All it needs is a ‘face-lift’, a high speed transit mode and lockable four wheel steering-mode. Significantly, Dulevo has already demonstrated that it can produce a better cabin and driver environment with its purpose-built ‘850 Mini’ and ‘Commando’ vacuum machines, but the wider issue has to come back to the availability of dust filtration. And this is currently where the mechanical machines score.
Enhanced filter pack available
Dulevo had already offered both a standard and ‘enhanced’ filter pack option for its mechanical sweepers prior to reaching agreement with the US-based Gore Corporation. The recent press conference heard that the initial discussions and agreement to offer the Gore filter membrane as a standard production fitting has already resulted in orders far exceeding expectations at Dulevo.
The Gore brand is best known as a material used in breathable waterproof jackets, but the same membrane formula is also widely used in industry, healthcare, military and automotive applications. In fact, it’s even used in the production of ‘mechanical’ human replacement hearts! Gore filters are already widely used in the cement industry and in waste incinerator plants. The key advantage of a Gore filter membrane is that all the particles are held outside the filter – dust particles are caught on the membrane surface and therefore cannot clog the actual filter as is the case with conventional filter designs. How efficient is this membrane? An efficiency capable of catching ‘99% of all dust down to 0.3 microns’ was mentioned in the presentation and a Gore filter-equipped Dulevo 5000 sweeper with a transparent rear hopper door was used to demonstrate how effective the filter system was in operation – and how quickly a Gore filter could be ‘shaken’ to clean the filter surface – without any dust emissions.
So what happens next? Technicians from the independent Reggio Emilia-based Studio Alfa test laboratory have devised an 8.9 km test route to ‘take in all aspects of a modern city,’ according to Dr Ivan Panini in charge of the testing, to provide a firm basis for more research. It’s clear this is only the start of the story – for example, other manufacturers are yet to agree on a common operational test procedure. But according to Vincenzo Geddes da Felicaia, ‘We have arrived at our first objective, but Dulevo will continue to go further.’
Waste Management World will be looking further into all aspects of dust filtration on sweeping machines as well, looking at new developments as they happen, trying new machines as they reach the market. And above all, trying to get a clearer picture of the whole dust emissions issue.
Malcolm Bates is Transport Correspondent of Waste Management World
e-mail: wmw@pennwell.com
