Water quality in Bangkok city, Thailand
Bangkok is the capital city of Thailand, covering a surface area of 1,569 km2. Bangkok's highly urbanized landscape is home to roughly 11 million people, making it a dynamic metropolis in 2024.
Bangkok, similar to other large cities, grapples with several challenges in managing its surface water resources. The city's rapid urbanization has resulted in considerable pollution of its rivers and canals. Industrial effluents, untreated domestic sewage, and solid waste disposal are primary contributors to the deteriorating water quality. At present, canal water pollution is very severe as the canals still act as sewers for the direct discharge of wastewater in most areas of Bangkok, even though there is already a requirement for large buildings to treat wastewater, and houses must have at least septic tanks. However, other wastewaters are discharged without treatment to the public sewers, which drain into the canals. The main wastewater treatment system of Bangkok consists of 8 plants. Covering a total area of 191.60 km2, it can treat 1,112,000 m3/day (actual wastewater treatment volume is 879,536 m3/day in 2023). Approximately 58% of the effluent is discharged untreated into the canals and rivers (Pollution Control Department, 2022).
Furthermore, flooding constitutes another critical concern, particularly during the rainy season when the city's drainage infrastructure struggles to accommodate the excessive water volume (Polprasert 2007). The rapid urbanization in Bangkok has led to increased vulnerability to flooding due to the replacement of agricultural and retention areas with commercial and residential development. This has resulted in the drainage and flood protection systems reaching their capacity (Roachanakanan, 2013; Sintusingha, 2006). Bangkok experiences major and minor flood events regularly. The 2011 Flooding was the most devastating flood event in Thailand in the last 10 years, causing significant damage and loss of life. The city's vulnerability to flooding is due to its low-lying terrain, run-offs from the north, seasonal heavy rainfall, tidal bores and soil subsidence.
The major waterway in Bangkok, the lower Chao Phraya River, a crucial water source for Bangkok, suffers from high pollution levels. Contaminants include heavy metals, industrial waste, and untreated sewage. The evaluation of the water quality index (WQI) in the lower Chao Phraya River, which included dissolved oxygen (DO), organic matter (BOD), total coliform bacteria (TCB), fecal coliform bacteria (FCB), and ammonia in nitrogen units (NH3-N), was used to calculate the WQI at each station. The lowest to highest scores ranged from 24.41 to 60.41 points, with an average of 42 points indicating that water quality was deteriorating. The water quality trend assessment for the lower Chao Phraya River during the previous six years (2017-2022) indicates deterioration and stability (Pollution Control Department, 2022). It is thought that both the amount of pollution load causes this water pollution situation from the river basin through the canal and the flow and tidal conditions of the Chao Phraya River.
Fig. The Chao Phraya River
While traditional pollutants like organic matter and heavy metals have been long-standing concerns, there are presently emerging pollutants that are seriously endangering the ecosystem of the Chao Phraya River and the general public's health, including:
The occurrence of antibiotic pollutants in water resources is a growing concern worldwide, and Bangkok is no exception. Detected antibiotics in effluent from hospital WWTPs in Bangkok ranging between 1.50 - 13,166 ng/L (Sinthuchai et al., 2016). In effluent from WWTPs in Bangkok, concentrations of antibiotics 0.7 - 1,720 ng/L. Antibiotic concentrations at the four sampling locations in the Chao Phraya River ranged between <1 and 1100 ng/L (Tewari et al., 2013). Similarly, antibiotics were detected in effluent from WWTPs in Bangkok and downstream water samples from Bangkok concentrations ranging between 0 - 2,940 and 2.8 - 13,600 ng/L, respectively (Li et al., 2012). To reduce this problem, waste management improvements and effective treatment processes at wastewater facilities and farms are necessary to reduce the levels of antibiotic pollutants entering the environment.
Microplastics (MPs) have become a pervasive global environmental issue, affecting ecosystems worldwide, from the deepest oceans to remote mountain regions and even the air we breathe. Their widespread distribution and persistence have raised significant concerns about their long-term environmental and health impacts. The Chao Phraya River has been facing increasing microplastic pollution. These tiny plastic particles, often smaller than 5 millimeters, pose a significant threat to the river's ecosystem and the health of aquatic organisms. The average abundance in all water samples ranged from 0.54 ± 0.05 to 1.07 ± 0.28 items/L (Jendanklang et al., 2023). The MPs concentration is in urban and estuary zones of 80 ± 60 items/m3 and 48 ± 8 items/m3, respectively (Babel et al., 2022). The lower Chao Praya River average concentration of MPs is 21 ± 16 items/m3 (Ounjai et al., 2022) and 80 ± 65 items/m3 (Ta et al., 2020). Microplastics with morphologies of fragments and fibers were mainly found in the rivers. Polypropylene and polyethylene items were the most abundant of all collected samples. The high concentration of microplastics in the Chao Phraya River stems from its urban and industrial surroundings, which contribute significantly to plastic pollution through waste mismanagement and runoff from surrounding areas. This pollution threatens the aquatic ecosystem and human health, as microplastics are eventually transported into the Gulf of Thailand and the broader marine environment.
Persistent organic pollutants (POPs) are toxic chemicals that adversely affect human health and the environment around the world. Because they can be transported by wind and water, most POPs generated in one country can and do affect people and wildlife far from where they are used and released. Studies from the 1980s and 1990s often reported relatively high levels of POPs in the Chao Phraya River. These findings were consistent with the widespread use of POPs as a pesticide during that period (Onodera et al., 1986; Tabucanon et al., 1992; Boonyatumanond et al., 1996; Boonyatumanond et al., 1997). Over time, due to regulations and reduced use, concentrations have likely decreased. However, the persistence of aldrin in the environment means it may still be present in detectable quantities.
To the best of our knowledge, cyanotoxin concentrations in Bangkok's water bodies, including the Chao Phraya River and its canals, have not yet been investigated. It was a concern given the potential for their presence in polluted waterways. Cyanotoxins are toxic compounds produced by certain types of cyanobacteria, commonly known as blue-green algae. These toxins can have severe impacts on water quality and public health. It can vary significantly based on environmental conditions and pollution levels. The presence of cyanotoxins is a recognized issue with potential risks to public health and ecosystems. Continued monitoring, improved pollution control measures, and public awareness are essential to managing and mitigating the impacts of cyanotoxins in Bangkok.
In conclusion, water quality is a critical issue in Bangkok, with pollution from various sources deteriorating surface water. While progress has been made in improving sanitation and hygiene, more long-term measures are needed to address the country's root causes of water pollution. Although there is limited long-term data on water quality in Bangkok, studies suggest that pollution levels have increased in recent decades. This is mostly caused by population growth, industrial activity, and inadequate wastewater treatment facilities.
The Bangkok Metropolitan Administration (BMA) has undertaken various projects aimed at improving the water quality in the city's rivers and canals. Efforts include better wastewater treatment, stricter regulations on industrial waste, and initiatives to raise public awareness about environmental preservation. The government, civil society, and other stakeholders must collaborate to develop long-term solutions.
References
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