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Working with the scientists and researchers at the University of Brighton has been an eye-opening experience for our dedicated AHPs recycling project team here at Medisort. For those who are only just hearing about this project, we are currently carrying out extensive research and experimentation into finding the best way to recycle nappies and other absorbent hygiene products (AHPs) on a larger, commercially viable scale.

We have been growing and developing Medisort for the last 10 years, working with NHS trusts, private practices and adult care patients to collect, sort and dispose of a wide range of healthcare waste. A number of our staff within Medisort have worked in this sector for decades. 

Partnering with the University of Brighton on our latest project gives it the best possible chance to succeed. We understand the industry from a commercial sense, and they understand the science. For this blog post, you will hear from our PHD student, Chibi, who works on this project from our office in Littlehampton and in her University of Brighton lab. She explains what the microbiology challenges are of finding a cost-effective method of disinfecting offensive waste to make it suitable for recycling. 

Microbes: They are everywhere

It is well known that humans are hosts to various microscopic organisms (aka microorganisms or microbes). These microbes are all around us – coexisting on/in us, our pets and our diverse environments. They include bacteria, fungi, viruses, and protozoa. While some microbes are pathogenic (i.e. disease-causing), others are non-pathogenic but still have the potential to cause diseases if given the opportunity. 

In other words, the latter group is not considered harmful unless the host organism has a weakened immunity, or if certain microbial’ strains end up in the wrong location within the host – a typical example of this is Escherichia coli (E.coli) bacteria which normally live harmlessly within our intestines. 

Unfortunately, some E.coli strains go rogue and migrate to our urinary tracts, causing bladder or kidney infections. Other bacteria are relatively friendlier, like the Lactobacillus acidophilus species that are often found in probiotic dairy products. 

For those interested in this, more information is available from open-access research papers like Robino et al. (2014) and Wiles et al. (2008). 

Microbes are small but ‘clever’

Certain microbes can exist in vegetative (i.e. actively growing and reproducing) or dormant phases. The latter phase is like a self-defense mechanism to protect certain microbes from unfavourable environments. This is accomplished by forming spores which can survive unfavourable conditions for extensive periods. For instance, while several non-spore-forming bacteria can be inactivated with disinfectants, high-temperature treatments such as steam sterilisation are required for spore-forming bacteria (Rutala et al. 2008; Maamari et al. 2016). 

But non spore-forming microbes can also have their own clever forms of self-defence too. E.coli, for instance, are non-spore-forming bacteria that are capable of protecting themselves in plant leaf crevices using surface appendages, such as hair-like pili and whip-like flagella when exposed to antibacterial agents (Saldaña et al. 2011). Other studies have shown that E.coli can form biofilms to protect themselves from chlorine-based disinfectants (LeChevallier et al. 1984).

Killing microbial foes: Disinfection vs. Sterilisation

We’ve established that microbes can be friends or foes to us host organisms depending on the prevailing circumstances. To render our environments and materials safe for use, there is therefore a need to rid ourselves of harmful or potentially harmful microbes. Disinfection and sterilisation are the two decontamination routes used for achieving this.  However, as we’ve seen earlier, microbes are incredibly capable of protecting themselves from unfavourable conditions, moreso for spore-forming microbes. 

A great deal of research has been done to identify the most effective ways of destroying harmful microbes present in a wide array of environments. Steam sterilisation is capable of destroying all microbial organisms including spores but the process .can be energy-intensive. Disinfection is capable of destroying most vegetative microbes and perhaps also spores (depending on the level of disinfection).

Ideally, disinfectants should be fast-acting, able to inactivate a wide range of microbes, soluble and stable in water, economical, environmentally friendly, and compatible with detergents, soaps, and other routinely-used chemicals (Rutala et al. 2008). 

In reality, however, no one disinfectant can meet all these requirements. There are limitations as to the nature of the material being disinfected, or the formation of harmful by-products.

Killing microbes: A waste management perspective

When deciding on the appropriate level of commercial-scale waste decontamination, a number of factors need to be considered, including the nature of waste, microorganism type and density, environmental impact, and of course, cost. These factors are especially important when considering waste recycling options.

All wastes that are currently being generated in Europe are classified by industry and/or process using a standardised waste classification system referred to as the European Waste Catalogue (EWC). The EWC is essentially a book, with each chapter describing waste generated from a particular industry or process. 

By legislation, offensive human wastes, which are categorised under the EWC code of 18 01 04, require less stringent handling protocols than hazardous wastes. However, the pathogenic potential of the former category implies that any recycling benefits are dependent on adequate decontamination protocols and appropriate end uses. 

An example is Quaternary Ammonium Compounds (QACs or QUATs), which are normally suitable for ridding surfaces of some types fungi and vegetative bacteria. However, QACs don’t do very well in the presence of organic matter and cotton-based materials, and since offensive human wastes tend to contain over 75% of cellulose-based disposable nappies and incontinence pads, using QACs is not a viable solution. 

Other potentially viable chemical disinfection methods include the use of peroxides or chlorine compounds. Medisort Ltd is in partnership with the University of Brighton to find commercially viable waste decontamination processes for offensive human wastes. This is an important for changing public perceptions of this waste stream.

Thus far, we are making progress – our small-scale absorbent waste decontamination trials suggest that chemical disinfection is capable of destroying E.coil, S.aureus, and a number of other unwanted microbes. We look forward to scaling up similar decontamination trials but collaboration is key. 

If you’re interested in getting involved with this project, email ask@medisort.co.uk

References

LeChevallier, M.W., Hassenauer, T.S., Camper, A.K., McFeters, G.A., (1984). Disinfection of bacteria attached to granular activated carbon. Applied and Environmental Microbiology. 48(5), 918-923. 

Maamari, O., Mouffak, L., Kamel, R., Brandam, C., Lteif, R., Salameh, D. (2016). Comparison of steam sterilisation conditions efficiency in the treatment of Infectious Health Care Waste. Waste Management. 49, 462-468. doi: 10.1016/j.wasman.2016.01.014

Robino, L., Scavone, P., Araujo, L., Algorta, G., Zunino, P., Pirez, M.C., Vignoli, R. (2014). Intracellular bacteria in the pathogenesis of Escherichia coli Urinary Tract Infection in children. Clinical Infectious Diseases. 59(11), 158-164. doi: 10.1093/cid/ciu634

Rutala, W.A., Weber, D.J., HICPAC. (2008). Guideline for disinfection and sterilization in healthcare facilities, 

[Online]. Available at: https://www.cdc.gov/infectioncontrol/pdf/guidelines/disinfection-guidelines.pdf (accessed 16 August 2018).

Saldaña Z., Sánchez, E., Xicohténcati-Cortes, J., Puente, J.L., Girón, J.A. (2011). Surface structures involved in plant stomata and leaf colonisation by Shiga-toxigenic E.coli. Frontiers in Microbiology. 2(119), 1-9. doi: 10.3389/fmicb.2011.00119

Wiles, T.J., Kulesus, R.R., Mulvey, M.A. (2008). Origins and virulence mechanisms of uropathogenic Esherichia coli. Experimental and Molecular Pathology. 85(1), 11-19. doi: 10.1016/j.yexmp.2008.03.007