A Murky Future

The end of the semester is coming up, and as I draw my blog to a close, I suppose it is fitting to discuss the cutting-edge of water treatment techniques in Singapore.

Innovation in Water Singapore is a yearly publication by PUB that highlights research and developments in water treatment technology that I would recommend you check out!

The 2018 and 2019 issues both featured algal blooming as a subject of concern and for good reason. Even without considering excessive nutrient loading from industries, a warming urban environment (Roth & Chow, 2012) still makes freshwater bodies an inviting place for algae to proliferate (Lai, Chua, Chan, 2018). One of our national taps source water from these water bodies; and the presence of algal blooms clog up NEWater’s signature reverse osmosis (RO) membranes, adding to RO’s already high energy usage and membrane maintenance (Ooi et al., 2019). I don’t think murky green waterways littered with dead fish (Ooi et al., 2019) would be very appealing, wouldn’t you agree?

In our discussions of eutrophication, treatment measures for algal blooms mostly revolved around reductions in nutrient loading. Alternatively, the 2018 issue showcased ultrasonic disinfection, where a pilot study was conducted on the Serangoon Reservoir (Lai et al., 2018). Its principle of operation is the exciting part: where cavitation bubbles form and implode, creating an environment where water decomposes and forms biocidal hydroxyl radicals that eliminate algal cells (Joyce, Wu, & Mason, 2010).

Operating like a floating fish tank filter, closed water systems like a catchment could conceivably be protected from algal blooms (Lai et al, 2018). Conversely, it would be a lost cause in open waters where desalination plants draw seawater from. Ultimately, the best solution lies in managing the growth factors of algae: nutrients and warmth. That would mean dealing with warming seas, urban heating, and anthropogenic nutrient inputs: each is a tall order in their own right.

Concerning last week’s post, PUB’s 2017 issue indicates that they already dabbled into Membrane Contactor technology! If you have not read last week’s post, Membrane Contactors are one of many liquid-phase extraction technologies, which also encompasses RO. In particular, Membrane Contactors offer opportunities for resource recovery: in this case, the recovery of methane from anaerobic bioreactors (Wang, Bae, 2017). Unlike VOC recovery which features a liquid extractor, either the property of pressure gradient force on gases is exploited by using a vacuum, or carrier gas(es) with high affinity for biogas are utilized.

This adds on to Ryan’s comment about political will for the implementation of such technologies in Singapore. The realisation hit me that there is a strong political will for the implementation of novel and critical technologies in wastewater treatment; just not in the places that need it the most! If this project tenure was awarded to point-source emitters of high-VOC wastewaters, widespread industrial adoption of wastewater resource-recovery and treatment technologies could have begun years ago!

Could the 2017 ECOSWM fire have been avoided with PUB’s research involvement? Source: https://www.channelnewsasia.com/news/singapore/tuas-plant-fire-eco-special-waste-management-fined-mom-11848164

While it is invigorating to know that such technological advancements are taking place, the reach of Singapore’s political will is not yet enough to provide holistic solutions to our water problems. We already have the research, now its time to implement them where they are needed.

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Joyce, E. M., Wu, X., & Mason, T. J. (2010). Effect of ultrasonic frequency and power on algae suspensions. Journal of Environmental Science and Health – Part A Toxic/Hazardous Substances and Environmental Engineeringhttps://doi.org/10.1080/10934521003709065

Lai C. L., Chua C. Y. , Chan W. S. (2018). Managing microalgae growth with ultra-low frequency technology. Innovation in Water Singapore, Vol 10, 27. Retrieved from https://www.pub.gov.sg/Documents/Innovation_in_Water_Singapore_Vol10.pdf

Ooi S. K., Babovic V., Navarro L. M., Yim S. S. P., Wang M. Y. | NUS; Xia L. J., Gao R. M., Sim M., Mahadevan A. | PUB;

Tay S. H. X. | H2i (formerly NUS) (2019). An algal proliferation prediction system for Singapore’s coastal waters. Innovation in Water SingaporeVol 11, 40. Retrieved from https://www.pub.gov.sg/Documents/Issue%2011_Innovation%20in%20Water,%20Singapore_Full%20PDF.pdf

Roth, M., & Chow, W. T. L. (2012). A historical review and assessment of urban heat island research in Singapore. Singapore Journal of Tropical Geography. https://doi.org/10.1111/sjtg.12003

Wang R., Bae T. H., Y. Zhang (2017). Maximising biogas recovery for used water treatment. Innovation in Water SingaporeVol 9, 27. Retrieved from https://www.pub.gov.sg/Documents/PUB_InnovationinWater_Issue9.pdf

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The Fiery Underbelly of Singapore

From mutant superbugs to foul-smelling but helpful microbes, this week’s post will cover a truly blistering affair right in our own backyards that you might not have heard of!

Singapore’s water management policies and clean water supply seem to indicate that our water situation is fine and dandy. However, you might be surprised to learn that the unsafe release of toxic or volatile organic compounds (VOCs) into Singapore’s wastewater streams are a recurring and unfortunately common occurrence if these news articles[1][2][3] are any indication.

Among the offenders are licensed toxic industrial waste collectors (TIWCs) like NSL Oilchem and Cramoil that handle almost any hazardous waste under the sun, or at least they are supposed to. But before we point any fingers, consider this analogy: you are given a stew and told that you must extract every last drop of water out of it using your household equipment without burning or damaging any of the ingredients, or face a fine. Now imagine that some of the ingredients cannot be removed and can spontaneously combust!

This is the predicament that many TIWCs are in: dealing with highly varied liquors of various VOCs from industries. Many of these VOCs like alcohols, phenols and polyaromatic hydrocarbons seem impervious to municipal wastewater treatment technologies (Paxéus, 1996), requiring specialised equipment that these TIWCs have. Even so, once TIWCs have isolated highly concentrated liquors of VOCs from industrial wastewater, they have to find ways to store a highly flammable and varied VOC mixture with poor industrial reusability before disposal by incineration.

That is just an accident waiting to happen! Case and point, the 2017 ECO Special Waste Management fire was caused by mishandling of extracted hexane and dimethyl benzene (Xylenes) from industrial wastewater[4].

2017 ECO Special Waste Management facility on fire. (Photo by Mohamad Danial) Source: https://www.straitstimes.com/singapore/cause-of-tuas-plant-blaze-under-investigation

Instead, if we shift the onus of VOC wastewater to the point-source emitters: the industries in Singapore, this essentially kills two birds with one stone! Industries can recover isolated volatile reagents from their own wastewater and immediately reuse them without risky storage and handling; there is less wastewater sludge ash we have to landfill.

Burnt liquid hexane storage tanks, illustrating the risks of storage and handling VOCs. (Photo by Ministry of Manpower) Source: https://www.channelnewsasia.com/news/singapore/tuas-plant-fire-eco-special-waste-management-fined-mom-11848164

The proverbial silver bullet technology is a Membrane Contactor. It utilises liquid extraction principles (Anil Kumar Pabby, Syed S.H. Rizvi, 2015; B.W. Reed, M.J. Semmens, 1995) where a liquid extractant designed to have a high affinity to the desired product (VOC) draws the chemical away from wastewater through a porous hydrophobic membrane by diffusion. The extracted product can then be isolated from the designer extractant, and both the extractant and the product can be reused.

Sounds too good to be true? Industrial-grade membrane contactors are already on the market, like 3M’s Liqui-CelTM range here:

There are even cases industrial applications for the recovery of industrial reagents from wastewater (Anil Kumar Pabby, Syed S.H. Rizvi, 2015)! If KoSa Netherlands BV can find economic viability with such a system, I believe industries in Singapore should follow their lead. All it takes is for industries and the government to get their minds off maximum profits and economic growth, and think a little more of safety and environmental sustainability.

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Anil Kumar Pabby, Syed S.H. Rizvi, A. M. S. R. (2015). Handbook of Membrane Separations Chemical, Pharmaceutical, Food, and Biotechnological Applications (Second Edi). Taylor & Francis. ISBN 9781466555563

B.W. Reed, M.J. Semmens, E. L. C. (1995). Membrane Contactors. In S. A. S. R.D. Noble (Ed.), Membrane Separations Technology: Principles and Applications (pp. 467–496). Elsevier. ISBN 9780444816337

Paxéus, N. (1996). Organic pollutants in the effluents of large wastewater treatment plants in Sweden. Water Research. https://doi.org/10.1016/0043-1354(95)00278-2

[1] PUB media release on Cramoil repeat offence in 2018 for discharging hazardous VOCs – http://www.nas.gov.sg/archivesonline/data/pdfdoc/20180425010/PUB%20ISSUES%20STOP%20ORDER%20ON%20CRAMOIL%20SINGAPORE%20PTE%20LTD_press%20release%2025%20Apr%202018.pdf

[2] 38 firms charged with releasing dangerous substances and VOC in 2019 – https://www.straitstimes.com/singapore/health/illegal-discharge-into-sewers-38-firms-punished

[3] 5 firms charged with releasing prohibited VOC and heavy metals in 2018 – https://www.straitstimes.com/singapore/five-firms-fined-for-illegally-discharging-waste-into-public-sewers

[4] https://www.channelnewsasia.com/news/singapore/tuas-plant-fire-eco-special-waste-management-fined-mom-11848164

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