Natural filtration has been going on since the dawn of time with water purified through a variety of methods.
These include sand which can filter out particles as small as 25 microns and was used by the Greeks and Romans to remove sediment from pools and bathhouses. Plants are automatic water filters too, adding oxygen and removing carbon dioxide as well as heavy metals and toxins. Charcoal can also filter out particles down to one micron including lead and sulfur oxides.
It was this kind of thinking that inspired projects such as Shanghai’s Sponge City Demonstration Park in the city’s Botanic Garden. The Sponge City concept involves absorbing and cleaning water and making it available for reuse with the aim of tackling issues such as water quality, scarcity and flooding.
The aim was to use natural materials recovered and recycled within the Botanic Garden with specialist firm Star Water called in to add its expertise using its Kalkulus sponge filter design tool that selects the most appropriate proportions of each component to optimise the treatment capability.
The resulting Reactive Filter Media provides a solution that is low maintenance, requires no energy and is of course sustainable.
The technology has also been successfully deployed in a variety of projects in Australia.
These include a stormwater treatment and reuse system at Manly Beach, Sydney where the technology is applied to stormwater capture, treatment and reuse using underground storage modules.
The process involves the removal of suspended solids, nutrients such as nitrogen and phosphorous, metals including copper, lead and zinc as well as pathogens from effluent. The water is then used for the irrigation of public gardens and land such as the city’s Rain Gardens, cutting costs and helping avoid the impact of drought.
In general commercial applications, sustainable filtration is becoming more common than the use of materials such as recycled glass. This provides a limitless supply, is light and can be cost effective for a range of applications.
For example, a community lift station in Southwest Florida was causing problems for local residents due to an unpleasant odor coming from the unventilated wet-well.
Specialist firm Evoqua was called in and identified high levels of hydrogen sulfide.
Evoqua’s Whisper Biofilter was installed as it uses natural biological processes to remove odors. In this instance it was combined with a new packing material, Bioglas media, manufactured from recycled glass. This was implemented in both the upper and lower beds to serve as growth sites for the sulfide oxidizing bacteria.
The system was set up to exchange air in the wet-well six times per hour to achieve a 99% sulfide removal in three weeks effectively removing the odor for the local community.
Recycled glass filters have also been proven to be more effective for avoiding clogging than traditional sand filters in wastewater treatment plants even with high solids loading.
Dryden Aqua operates a £5 million plant at Bonnyrigg, Midlothian, Scotland which has been designed to recycle glass and create a subsequent filtration system capable of removing pollutants from water.
The facility can process a quarter of Scotland’s recycled glass and will use mainly green cullet to create a system that can filter drinking or swimming pool water, treat industrial wastewater and provide a solution for ecological issues associated with other filtration media.
Recycled glass filters are also more beneficial for leisure applications such as swimming pools proving superior to traditional sand or cartridge filtration. They have been proven to last up to 10 years while cartridge filters need to be replaced every three years and sand media only lasts a maximum of five years.
Glass filter media can remove particles as small as five microns keeping pool water healthier and clearer while sand and cartridge filters are limited to particles of no lower than 10 microns. This also means fewer chemicals are required for cleaning while glass filters are naturally more resistant to bacteria and require less backwashing, providing another environmental benefit.
Ultimately design can play a major part in the sustainability of filters. An operator ideally wants optimal performance combined with reliability and longevity to deliver the best return on investment.
For example, Amafilter’s Cricketfilter filter element is shaped like a cricket bat providing a 40% greater filtration area while it has a lifespan of up to 30 years and the filter cloths can last far longer than conventional materials.
It was put in place at a gelatine plant where a horizontal pressure filter leaf system had previously required frequent changes of the filter leaves resulting in longer man hours, high maintenance and material costs as well as safety concerns due to frequent manual interventions.
As Cricketfilter is an automated system with lower filter turnover rates, the customer was able to cut down on manpower and run a cleaner, safer and more profitable operation.
Sustainability can also come from the ability to recycle materials. As with any form of waste, used filters can be damaging to the environment which has led to the opening of a specific recycling facility in Nottinghamshire, UK.
Operated by recycling and resource recovery specialist, Enva, the £2.5 million facility can process more than 10,000 tonnes of oil filters and oily rags a year collected from workshops and the automotive and industrial sectors across the UK.
Oil filters are first shredded before passing through multiple recycling technologies including two centrifuges to recover the waste oil which then undergoes further treatment at an oil treatment facility also located on the site.
Magnets and eddy current separators extract ferrous and non-ferrous metals and plastics are also separated. The remaining solid material ends up as an oily cardboard fluff which is used in the production of a sustainable waste derived fuel for energy intensive industries.
Sustainability is more than a slogan
Filter media are one of the short-lived components of any filter system. Depending on the application, they can be replaced weekly, often with inexpensive disposables. In the short term, disposable filter elements are inexpensive to procure. HETA’s filter housings are designed with a service life of up to 30 years, thus resulting in high long-term costs and a high waste disposal effort. The goal was and is to satisfy needs by preserving the natural regenerative capacity of the systems involved. A filter cartridge as a screwed design with a replaceable filter sock, whose supporting structure can permanently withstand a certain amount of resource use without being damaged. Heiko Hensel, managing director of PACO Group’s HETA Verfahrenstechnik GmbH, says: “Sustainability is not just a slogan, but will, idea and implementation.”