PROTECTING OUR DRINKING WATER
We need to plan ahead to deal with water treatment plant failures due to contamination and other unforeseen circumstances, writes
THE recent ammonia contamination at the Simpang Renggam Water Treatment Plant has many people up in arms, yet again. The ammoniacal nitrogen (NH3-N) level at the Sungai Benut intake was 13mg/L and levels were purported to be higher upstream.
The primary source appeared to be leachate, which originated from a landfill. Leachate from landfills are well documented to contain high levels of organics, ammonia and heavy metals.
Ammoniacal nitrogen in leachate is known to hover between 1,000 and 3,000mg/L. Legally, prior to discharging effluent into a river, the ammoniacal nitrogen has to be treated to reduce it to around 5mg/L as per the Environmental Quality (Control of Pollution from Solid Waste Transfer Station and Landfill) Regulations 2009.
Think about that. To lower the level from 1,000mg/L to 5mg/L, the wastewater treatment plant has to achieve at least a 200-fold reduction. This is possible from an engineering point of view, but the consequences of failure are gruesome.
And, in the case of structural failure (the bund is said to have “broken”, compounding the leachate contamination at Simpang Renggam) the effects can be most disconcerting.
Water contaminated with large amounts of ammonia not only emits a pungent odour, but can also react with chlorine (used as a disinfectant at the drinking water treatment plant) to produce chloramines. This reaction reduces the “potency” of disinfection to ward off bacteria (eg. E. coli) in water supplied to our homes.
Besides ammonia, leachate also has high levels of organics which can react with chlorine to produce trihalomethanes such as chloroform. In themselves, these substances are also harmful if ingested. Leachate also contains heavy metals such as lead (Pb), arsenic (As) and mercury (Hg).
Unfortunately, this is not the first time a wastewater treatment failure has occurred. There have been many incidences where drinking water treatment plants had to be shut down temporarily due to the failure of wastewater treatment plants located upstream.
The fact of the matter is there is no guarantee a wastewater treatment facility will function as intended — meeting limits as per the regulations, 24 hours a day, 365 days a year. Perhaps it is time we planned ahead for such failures and other unforeseen circumstances.
There are several ways to do this. The first option is to prevent the discharge of effluent, including treated effluent, into stretches of river that are upstream of water intake points.
While upstream development cannot be avoided in certain cases, the discharge can be channelled downstream, hence bypassing water intake points. Effluent-specific drains, pipes and outfalls can be constructed to channel treated or untreated effluent downstream or away from water intake points. To ensure that downstream river stretches are protected, the effluent load must be kept under control.
The second option is to have a buffer prior to release into rivers. The current practice is to release effluent directly into a river or drain after it has undergone treatment. Perhaps its time to rethink this practice.
Prior to discharge, it may be desirable to release the effluent into a holding pond that can act as a final buffer before it enters waterways. This holding pond not only functions as a buffer, but also provides an added layer of treatment.
Certain vegetation, which absorb pollutants (including ammonia, nitrate, phosphorous and heavy metals), can be grown in the pond to clean the water further. This technique is known as phytoremediation.
At larger scales, the effluent can be discharged into a constructed wetland, which works in a similar way.
Sometimes, the quality of water that has been put through phytoremediation is so good it can be recycled and reused for other, purposes; reducing or even avoiding the need for discharge altogether.
If the water treatment system fails, a holding pond or constructed wetland can provide added response time for corrective measures to be taken. In other words, the contamination would occur in the holding pond or constructed wetland before it goes into the river. This would give wastewater treatment plant operators time to seal off the discharge and stop untreated effluent from entering the river. However, not all failures can be remedied through these methods.
Sometimes, as in the case of Sungai Benut, where the bund broke and leachate entered the river, those measures would not work because the problem was due to structural failure.
Under such circumstances, a final resort would be to install online systems that monitor the water quality of the river in realtime. This data is relayed to plant managers and authorities.
The online stations have to be installed at locations that allow sufficient response time for treatment plants to shutdown if contamination is detected.
To avoid supply disruption, treatment plants need to ensure that there are sufficient water reserves throughout the shutdown period. This can be achieved via other strategies such as off-site storage.
In short, we need to expect the unexpected and prepare how to deal with them. Public health and safety are at stake.
The fact of the matter is there is no guarantee a wastewater treatment facility will function as intended — meeting limits as per the regulations, 24 hours a day, 365 days a year.