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
Multiple-effect distillation columns Source: https://www.indiamart.com/proddetail/distillation-column-21227565788.html
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.
Gallery
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/
References
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