Celine Shen
As “Water and sanitation” is one of the UN sustainable development goals, one can infer the importance of this ubiquitous liquid and the severeness of its scarcity. According to current statistics, although water makes up for 70% of the Earth’s surface, a measly 1% of the water is accessible and reaches the standard to be consumed.
Impacts of water pollution
A third of the human population is affected by water scarcity, whose major cause is water pollution. In areas where consumable water is unavailable, habitants suffer thirst as well as hunger due to the lack of water fit for agricultural purposes; the living areas are usually unsanitary, which provides an ideal environment for diseases to spread easily, untreated water can also cause water-borne illnesses. As a result, draughty areas are nearly always impoverished, therefore, increasing the difficulty for them the develop a system to treat the polluted water.
Moreover, water pollution make devastating impacts on animals, especially aquatic organisms. On a global average 80% of wastewater is discharged into large bodies of water without being subjected to proper treatment. Domestic, agricultural and industrial wastewater are the major sources of water pollutants (in fact sewage wastewater makes up for 80% of water pollutants!).
Wastewater usually show high levels of chemical oxygen demand (COD) when being tested, this is an indicative measure of the amount of oxygen in milligrams that 1 litre of wastewater would consume due to bacterial action or the oxidation of inorganic chemicals. Due to this oxygen shortage, smaller aquatic creatures would be killed, which in turn would affect the food sources of larger marine animals. Wastewater also contains high amounts of toxic metals and nutrients (eg. nitrogen and phosphorus); mercury for example affects the reproduction functions of animals, whereas an excess of nutrients can lead to excessive plant growth, an overgrowth of toxic algae in water bodies can poison fish, once again affecting the food sources of larger marine animals. Under a shortage for food, the animals would either die from hunger or migrate in search for food. Nonetheless, the animals would usually fail to adapt to new environmental conditions.
Simple Ways to conserve water
Strategies to conserve water can be sorted into three categories:
-Improving water management
-Avoiding further pollution to our resources
-Waste prevention
There is a wide array of ways we can better conserve our precious water resources, if we all implement a few, a difference surely will be made. Some examples are as follows:
-Switch to water-saving bathroom installations:
If you are moving in to a new home or reconstructing your current lodging, choose water-saving bathroom instalments (shower heads, taps, toilets) over regular ones. If this is not your case, simply purchase flow restricters.
-Swimming pool covers helps prevent evaporation of pool water, therefore decreasing the number of times needed to refill the pool with water.
-Check for toilet leaks
-Leave a plastic bottle in your toilet
-Do not leave water running when washing, rather, fill the sink with a suitable amount of water.
-Use the dishwasher/washing machine when it is fully loaded.
-Reduce shower time
-Rain catching
Collect water straight from the clouds using available containers, reuse it when appropriate (rain water does not reach drinking standard).
-Shower buckets
Make it habit to leave a bucket in with you during showers. This way, some unused water that usually run off to the sewage can be collected to be used for other purposes such as plant watering or dish washing.
-Purchase unprocessed foods instead of processed ones
Processed foods have much larger water foot prints than natural foods such as meats, vegetables and legumes. This is because that water is frequently used in industrial processes like that of cooling, cleaning, maintaining pressure, diluting etc. This change in life style will not only help to save water but it will also benefit your own health! :)
To find out more about the ways we can conserve water you can visit this website (https://www.earthreminder.com/ways-to-conserve-water/) or do more research on your own. :)
Why is wastewater discharge an issue in Shanghai?+ more ways to improve the current situation
1. Large wastewater production
For the special case of Shanghai, the city has been consistently producing overwhelming amounts of wastewater in the past decade exceeding all other cities in China as shown in the chart(fig 1). Though Shanghai produces the most wastewater (2.3x10^9 m^3 annually), it is ranked the 7th nationally in terms of treatment efficiency.
From the two graphs above, a disproportion can be seen between the resident usage and wastewater production; as the total percentage of water consumption for sanitary purposes (Urban public water supply. Residents supply & Agricultural water) only make up for 32.8%, however, the sanitary sewage consists of 72% of the total wastewater produced in Shanghai, hence the importance of recycling water and reducing wastewater production in homes.
Industries (especially those which manufacture glass, steel, cotton textiles, pulp and paper) can reuse the wastewater for certain purposes, this can bring about economic as well as environmental benefits:
-Manufacturers can isolate certain chemicals using technologies such that of high-tech membranes rather than purchasing raw chemicals.
-After adequate treatment (of relatively mediocre standards) the treated water can be used for the following and more:
-irrigation
-As process water for power plants, refineries, mills and factories
-Concrete mixing
-Dust control
2. Low wastewater treatment plant (WWTP) standards
In 2016, a mere 4% of the WWTPs (more information about the general water treatment process can be found below) constructed in Shanghai are capable of meeting the national standards to be qualified as top tier treatment plants. It is not an easy task to improve on this issue. They are expensive to operate continuously, and large amounts of material are required for construction, overall the costs is dependent on 2 factors:
-The amount of water needed to be processed in a day.
-The quality of the wastewater.
As previously mentioned, Shanghai’s production of wastewater is immense. I cannot make a direct judgement on the quality of the wastewater produced in Shanghai for that I have not found any statistics. Nonetheless, according to the Shanghai water quality report, most of the surface water in Shanghai are designated class 3-5, a poor quality is indicated, thus it can be inferred that the wastewater is heavily polluted. Considering the water conditions, Shanghai needs to invest more in the construction and operation of WWTPs than other metropolises.
The financial impact of our needs can be mitigated by new wastewater treatment technologies developed by engineers that are both more efficient and more cost-effective. In fact, the discovery on new technologies might just as well be the key to solving this problem.
3. Geographical disadvantage
As Shanghai is located in the lowers-stream region of the Yangtze river, wastewater from upper stream cities gets collected in Shanghai. Shanghai is a flat city as well, implying that the waste from other cities will remain in Shanghai for extended periods of time. As a result, WWTPs in Shanghai need to treat not only the wastewater produced in Shanghai, but also the waste produced by upstream cities, increasing their work loads.
Wastewater Treatment (This sectional is optional for you to read if you are not interested in the science behind wastewater treatment)
Since pollutants are abundantly present in wastewater, wastewater is treated very differently before it’s discharged compared to fresh, untreated water.
Wastewater is first collected from sewers and pumping stations, its treatment is split into three stages:
Primary treatment: physical treatment aimed at insoluble materials
Screening: Wastewater would first flow through a metal screen which removes all of the larger solid objects in order to prevent damage being done to the treatment plant.
Grit chamber: In the grit chamber, the sand and grit present in wastewater would settle at the bottom of the chamber.
Sedimentation tank: As the water flows more slowly in the sedimentation tank, suspended solids left in the water sink to the bottom forming sludge, which is then collected by pumping and is then repurposed as fertilisers.
Secondary treatment: biological treatment to remove soluble organic substances
Trickling filter: Primary effluent is sprayed continuously on a thick bed of stones. As the water trickles down, bacteria latch on to the stones and multiply. With sufficient oxygen supply, the microbes are used to then absorb the soluble organic substances thus lowering the biological oxygen demand.
The aeration tank and the secondary clarifying together forms the activated sludge treatment system. The sludge from the primary treatment section is circulated to the secondary clarifying to be mixed with the wastewater which then flows to the aeration tank. In the aeration tank, air is injected into the mixture providing oxygen. With enough oxygen, bacteria thrive to form a suspension of biological solids which is called activated sludge. Usually, the water stayed in the aeration tank for around 6 hours giving the microorganisms enough time to reduce the BOD level even further. After that, the water flows back to the secondary clarifying to be separated with the sludge.
3. Tertiary treatment (optional): to further purify effluent for more vulnerable bodies of receiving water.
Effluent polishing: The secondary effluent is filtered using granular media filters (which is water we use for drinking water) in order to remove more of the suspended solids and BOD present.
Plant nutrient removal: Phosphates are removed by chemical precipitation. Nitrogen in the form of ammonia and nitrates are removed by a process called nitrification-denitrification, during which ammonia is converted into nitrates using microorganisms, then the nitrates are converted into nitrogen gas through bacterial action.
Why did I write this article?
My original intention was to inform the general public about this environmental concern and to evoke changes in our behaviours. After further consideration, I think that a published letter should be written to Shanghainese authorities to remind them of this issue and to hold them accountable.
A letter to Shanghainese authoritiesA letter to responsible authorities on wastewater treatment and recycling
To whom it may concern,
I am a high school student currently residing in the city of Shanghai. As I have recently gained insights on the current environmental issues caused by the discharge of wastewater, I sought to write this letter as a reminder to the authorities responsible for positive changes on the behalf of all those who support the idea of sustainable development. I wish that this letter would also convey the message that the matter is regarded as a serious one not only by the government, but also the citizens of every age range.
Shanghai is a rapidly developing metropolis, it stands out from other growing cities because of its environmental-awareness. This is shown by the previous projects that the Shanghainese authorities have successfully executed, such as the recycling program which was established in 2019. Nonetheless, before researching about Shanghai’s water quality, I was not at all aware of this immense issue. With the severe consequences of excessive wastewater discharge and water pollution in mind, I wish to urge you to increase the public’s awareness and knowledge on the subject of water conservation by using the media, raising the priorities of projects which involve WWTP constructions, and lastly, to encourage research on more efficient methods by which wastewater can be treated.
With my voice, I published this article in order to give the general public some ideas on the ways in which we can change our water management behaviours to be more environmental friendly and to warn them of the impacts which water pollution can bring about to our planet and also to our healthy well-beings. Despite the fact my platform is certainly far smaller than what is necessary to reach enough people and cause a significant change in our behaviours, I still wish to contribute to finding the solution of our current problem to the greatest extent possible.
For further information on wastewater pollution and it's treatment, please refer to the my article.
Please take time to consider my suggestions,
Kind regards,
Celine Shen
Please fill in the following surveys (one of which is for general readers, and the other is for those who work in industries or in relation with wastewater treatment):
