A Failing Panacea

From radioactive sea monsters to mutant superbugs. This week, I’ll be discussing antibiotic-resistant viruses and their relationship with wastewater treatment!

Antibiotic compounds have flooded and permeated into every nook and cranny of our society. They are commercially utilized for livestock and aquaculture to prevent diseases outbreaks; applied to crops to improve disease resistance and increase yields; and even prescribed by clinics and hospitals(Kümmerer, 2009) for minor ailments like giving candy to children during Halloween!

Antibiotic introduction into the natural environment come from both non-point sources (surface run-off, groundwater permeation etc.) and this post’s primary focus: point source from wastewater treatment plants(WWTP) and direct discharge(Kümmerer, 2009). However, the real danger does not arise from the antibiotics released itself, but what happens when bacteria and viruses present and utilized in biochemical treatment in WWTPs receive a sublethal dose of antibiotics(Manaia et al., 2018).

That’s right! For the same reason your doctor tells you to finish the prescribed dose of antibiotics, a non-lethal dose of antibiotics combined with bioreactor conditions that boost bacterial growth hosts a favourable environment for bacteria with antibiotic-resistant genes(ARG) to outcompete their regular counterparts(Manaia et al., 2018).

Potential for ARG and ARB to develop in PUB’s wastewater treatment system. Source: https://www.pub.gov.sg/PublishingImages/PUB_29_UsedWaterConventionalTreatment%20PA-01.png

To make things worse, many bioreactors (like in PUB’s municipal WWTPs) recycles portions of bacterial sludge from previous batches, exposing the antibiotic-resistant bacteria(ARB) to a wide variety of other antibiotics(Manaia et al., 2018). These fluctuating conditions preferentially select bacteria and viruses with ARG that resist a wide variety of antibiotics(Manaia et al., 2018), similar to Dr Rick Pott’s Variability Selection hypothesis.

If you’ve read A Clearer Picture, you might be wondering: since the wastewater ends up being disinfected before being discharged, why worry? While most ARB are vulnerable to disinfection, some studies show that ARG go through WWTPs largely untouched where they may be transferred to other cells in the natural environment(Yuan, Guo, & Yang, 2015); some ARB can even go into dormancy only to be reactivated once out of the disinfection tank(Manaia et al., 2018). Of course, antibiotics also make it out of the treatment process(Kümmerer, 2009), which makes it easier for bacteria in natural ecosystems to evolve into ARBs.

The consequences of this inadequacy are all around us. Wei et al. (2018) found significant amounts of ARG in bioreactor bacteria in Chinese WWTPs; Hatosy & Martiny (2015) found known and undiscovered ARG in coastal waters of California and Hawaii; and to top it all off, two separate studies found ARBs in bottlenose dolphins, harbour seals and harbour porpoises ((Schaefer et al., 2019), and this preliminary study conducted in Puget Sound).

A Harbour Porpoise, one of the hosts of ARB found in a preliminary study. Harbour Porpoise ©Niki Clear. Source: https://www.wildlifetrusts.org/wildlife-explorer/marine/marine-mammals-and-sea-turtles/harbour-porpoise

All that is left for a potentially apocalyptic outbreak is for the ARG to incorporate itself in a human vector or pathogen(like E. Coli) or god forbid, an influenza virus with multiple ARGs that resists all kinds of antibiotics, a superbug(Manaia, 2017).

Possible Pathways for ARG and ARB to make their way from natural systems into human and livestock. Source: (Manaia et al., 2017)

If it isn’t clear enough already, excessive antibiotic use not the way forward. With ARG all over our biosphere, it’s just a matter of time before a superbug pandemic matching the scale of the black plague starts. Antibiotic substitutes like Yan Yang et al.’s polymer could be our salvation. Until then, go organic, eat fewer products that use antibiotics(like meat and dairy); and please, finish your antibiotic dose. Doctor’s orders!

Next week, I’ll be looking at the ways to deal with antibiotics and pharmaceuticals right at the source, so stay tuned!

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Hatosy, S. M., & Martiny, A. C. (2015). The ocean as a global reservoir of antibiotic resistance genes. Applied and Environmental Microbiology. https://doi.org/10.1128/AEM.00736-15

Kümmerer, K. (2009). Antibiotics in the aquatic environment – A review – Part I. Chemosphere. https://doi.org/10.1016/j.chemosphere.2008.11.086

Manaia, C. M. (2017). Assessing the Risk of Antibiotic Resistance Transmission from the Environment to Humans: Non-Direct Proportionality between Abundance and Risk. Trends in Microbiology. https://doi.org/10.1016/j.tim.2016.11.014

Manaia, C. M., Rocha, J., Scaccia, N., Marano, R., Radu, E., Biancullo, F., … Nunes, O. C. (2018). Antibiotic resistance in wastewater treatment plants: Tackling the black box. Environment International. https://doi.org/10.1016/j.envint.2018.03.044

Schaefer, A. M., Bossart, G. D., Harrington, T., Fair, P. A., McCarthy, P. J., & Reif, J. S. (2019). Temporal Changes in Antibiotic Resistance Among Bacteria Isolated from Common Bottlenose Dolphins (Tursiops truncatus) in the Indian River Lagoon, Florida, 2003-2015. Aquatic Mammals, 45(5), 533–542. https://doi.org/10.1578/AM.45.5.2019.533

Wei, Z., Feng, K., Li, S., Zhang, Y., Chen, H., Yin, H., … Deng, Y. (2018). Exploring abundance, diversity and variation of a widespread antibiotic resistance gene in wastewater treatment plants. Environment International. https://doi.org/10.1016/j.envint.2018.05.009

Yuan, Q. Bin, Guo, M. T., & Yang, J. (2015). Fate of antibiotic resistant bacteria and genes during wastewater chlorination: Implication for antibiotic resistance control. PLoS ONE. https://doi.org/10.1371/journal.pone.0119403

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60,000Bq/L… Not Great, Not Terrible

Wow, this just popped out of the blue. Japan’s environmental minister stated in a press release that Tokyo Electric Power(TEPco) will have to dump Fukushima nuclear powerplant’s radioactive wastewater into the ocean for dilution as it runs out of storage space (one of the many articles). Well doesn’t that sound like the plot to 2014’s Godzilla!

Irradiated sea monsters aside, there are serious controversies and environmental implications of this decision. The Korean government and Japanese fishermen are quite understandably vocal about their concerns with this decision (McCurry, 2019). Meanwhile, Osaka offers to dump radioactive wastewater into Osaka bay as long as it only contains tritium and is environmentally safe (Johnston, 2019).

What’s the big issue with dumping radioactive wastewater? Radionuclides! Specifically, Caesium-134(134Cs), Caesium-137(137Cs), Strontium-90(90Sr), and Tritium(3H), the most prevalent nuclear fallout products at Fukushima now(TEPco, 2019). These radionuclides emit high-energy particles when they decay, which literally tears up DNA upon contact. This causes cells to reproduce into defunct and cancerous cells or even cell death(S. Dingwall, C.E. Mills, N. Phan, K. Taylor, 2011; Starr; Taggart; Evers; Starr, 2019).
Water treatment at Fukushima Daiichi nuclear plant involves treating the water used to cool the damaged fuel rods in Reactors 1, 2, and 3. The main processes are:

  1. Ion-exchange modules (Kurion/Sarry) that exchange strontium and caesium ions for less harmful ones.
  2. Reverse osmosis (RO) that recycles clean water into the reactor core and concentrates remaining brine
  3. Adsorption of remaining caesium, strontium and other (heavy) metals onto various substrates

“Multi-nuclide removal equipment” for process 3. Source: https://www7.tepco.co.jp/wp-content/uploads/hd03-02-03-001-m120625_01-e.pdf

Now you might have noticed that there is a radionuclide I listed earlier that is missing from the treatment process above. That’s right, it’s tritium! Being an isotope of hydrogen, it is incorporated into a H2O molecule as HTO, and passes seamlessly through all of the processes above just like plain old water. Yet, HTO is as dangerous as any radionuclide when tritium decays. What’s worse, TEPco has 800,000m3 of tritiated water sitting around with no feasible isotopic separation method (METI, 2016).

Fortunately, tritium ionizing radiation possesses very little energy and is unable to pass through physical environments or even the layer of dead skin on your epidermis. Contamination is therefore primarily through ingestion or inhalation of tritiated molecules. Dingwall et al. (2011) referred to Brooks et al. (1976) that found that mice could receive 37,000,000 Bq/L of tritiated water without damaging their DNA and causing adverse health effects.

The Tritiated Water Task Force of TEPco estimates a tritiated water concentration of 0.3 to 3.3million Bq/L as of March 2016. They plan to dilute the tritiated water with seawater until concentration levels are 60,000Bq/L before discharge. They also estimate this concentration to drop by 3 orders of magnitude 100km away from the point of discharge (ie.a maximum of 60 Bq/L). To provide perspective, this exceeds most standards of tritium in drinking water.


With all the bad press surrounding Japan, we need to recognise that environments close to the source of discharge face potentially unknown effects of concentrated tritiated water (IRSN, 2012); as well as acknowledge what they have accomplished to reduce impacts as much as they have. Less fear-mongering, more research!


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Brooks, A. L., Carsten, A. L., Mead, D. K., Retherford, J. C., & Crain, C. R. (1976). The Effect of Continuous Intake of Tritiated Water (HTO) on the Liver Chromosomes of Mice. Radiation Research. https://doi.org/10.2307/3574329

Cecie Starr; Ralph Taggart; Christine Evers; Lisa Starr. (2019). Biology: The Unity and Diversity of Life, 15th Edition. Retrieved from https://www.cengage.com/c/biology-the-unity-and-diversity-of-life-15e-starr/

Dingwall, S., Mills, C. E., Phan, N., Taylor, K., & Boreham, D. R. (2011). Human health and the biological effects of tritium in drinking water: Prudent policy through science – Addressing the ODWAC new recommendation. Dose-Response. https://doi.org/10.2203/dose-response.10-048.Boreham

E. Johnston (2019). Osaka mayor Ichiro Matsui offers to take in tainted Fukushima water and dump it into Osaka Bay. Japan Times. https://www.japantimes.co.jp/news/2019/09/17/national/osaka-mayor-offers-take-tainted-fukushima-water-dump-osaka-bay/#.XYMScCgzZEY

IRSN (2012) Radionuclide sheet: Tritium and the environment. Institut de radioprotection et de sûreté nucléaire. https://www.irsn.fr/EN/Research/publications-documentation/radionuclides-sheets/environment/Pages/Tritium-environment.aspx

J. McCurry (2019). Fukushima: Japan will have to dump radioactive water into Pacific, minister says. The Guardian. https://www.theguardian.com/environment/2019/sep/10/fukushima-japan-will-have-to-dump-radioactive-water-into-pacific-minister-says

METI (2016).Tritiated Water Task Force Report, June 2016. Ministry of Economy, Trade and Industry https://www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/20160915_01a.pdf


Radionuclide concentrations around reactor sites(pardon my underlining skills)
Source for Table: https://www4.tepco.co.jp/decommission/data/analysis/pdf_csv/2019/3q/2tb-east_19091301-j.pdf
Source for sampling sites around the reactors: https://www4.tepco.co.jp/en/nu/fukushima-np/f1/smp/form_pdf/2tb-east_form-e.pdf


A Clearer Picture

Since my last post dealt with the importance of water treatment in Singapore, I think it’ll be quite fitting to make this one about the process of water treatment. PUB actually has rather well designed and concise infographics that introduces their water treatment system (check this and this out for more information). Therefore I’ll add on some details they may have missed out on, and also tap on my personal knowledge of the treatment techniques used by Toxic Industrial Waste Collectors (TIWCs) in Singapore from my internship.

Let’s try a little exercise! Head to Google Maps and look up satellite images of PUB’s water reclamation plant in Singapore. What caught your eye?

Was it these structures? I sure hope so! These are the core part of most water treatment plants, the bioreactors and clarifiers for settling bacteria aggregates after biochemical treatment.

These are like giant beer barrels; except instead of yeast, the bacteria cultures used are designed to digest and break down a wide variety of polysaccharides, lipids, and other pollutants.

They are the workhorse of any water treatment facility and help cut BOD and COD of wastewater down to safe levels for human use. The other processes of a water treatment plant revolve around the welfare and performance of these little guys.

The bacteria require high surface area access to pollutants, but high TSS and settleable solids just get in their way. Therefore, plants incorporate filter screens to remove large settleable solids and chemical coagulation and clarification of TSS.

Bar screen for filtering large settleable solids. Source: https://aosts.com/types-wastewater-screening/

Saline wastewater reducing the productivity of bioreactor? (Linaric et al., 2013) Then pass the wastewater through a distillation set up to reduce TDS through evaporation!

A multiple-effect(stage) Distillation set up for lowering TDS Source: https://gemina.es/files/catalogue/pdf/18_Evaporadores_ING.pdf

Heavy metals slowing down the growth of bacteria? (Cabrero et al., 1998) One of our TIWCs implemented an Electric Coagulator that precipitates charged aqueous metal ions as solid metal particles out for filtration without the use of chemicals!

Refractory non-biodegradable VOC and SVOC like tetrahydrofuran slowing down or even sterilising bioreactors? (Yao et al., 2012) Actually, that’s one of the headaches plaguing water treatment in Singapore at the moment! Fortunately, novel technologies are being experimented and pilot tested by PUB and a few TIWCs. I’ll be covering this in a later post.

After the bioreactors have done their job, its time to add final touches to the water. This depends on what the water is being used for. Domestic and industrial potable use calls for pH balancing and sterilisation. Specialised industries that need ultra-pure water go to NEWater, where our crème de la crème of water treatment technologies resides.

Every step along the way is filled with its own intricacies and face their own set of problems that probably deserve articles of their own. Plenty of research is being done along every step, and novel technologies are being thrown around left and right. However, a healthy dose of scepticism due to economic feasibility, performance, and stringent policies blocks the path of innovation. Let’s hope it does not come down to environmental degradation and human death to get things moving.

Satellite Images of Kranji(Top) and Jurong(Bottom) Water Reclamation Plant. Source: Google maps

Close-up of a clarifier for settling bacteria aggregates after biological treatment. Source: https://www.pub.gov.sg/usedwater/treatment/usedwatertreatmentprocess

Aerated Activated Sludge Tank. Source: https://www.watertechonline.com/sludge-treatment-efficiency/

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Cabrero, A., Fernandez, S., Mirada, F., & Garcia, J. (1998). Effects of copper and zinc on the activated sludge bacteria growth kinetics. Water Research. https://doi.org/10.1016/S0043-1354(97)00366-7

Linaric, M., Markic, M., & Sipos, L. (2013). High salinity wastewater treatment. Water Science and Technology. https://doi.org/10.2166/wst.2013.376

Yao, Y., Lu, Z., Min, H., Gao, H., & Zhu, F. (2012). The effect of tetrahydrofuran on the enzymatic activity and microbial community in activated sludge from a sequencing batch reactor. Ecotoxicology, 21(1), 56–65. https://doi.org/10.1007/s10646-011-0765-3

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