The latest surveys conducted by the Saigon Water Supply Company (Sawaco) show that the indexes for COD, ammonia, bacteria content, suspended solids of raw water sources from the Saigon and Dong Nai rivers all have increased dramatically and shown abnormal signs. The problem is that Saigon and Dong Nai rivers are the main sources of water supply for millions of people.
The pollution alarmingly serious
It is now the middle of the rainy season; therefore, the temporary saltwater infiltration does not exist at this moment. However, the serious pollution of raw water sources has put water plants on the tenterhooks. Sawaco has pointed out that all the indexes for COD, ammonia, bacteria content, suspended solids of the Saigon River, which provides hundreds of thousands of cubic meters of raw water to the Tan Hiep water plant in the last two years have increased.
The allowed COD index is no higher than 10 mg/l, but the COD concentration has always been nearly the alarming level since 2008, while it exceeds the allowed level at many different moments during a year. Regarding the suspended solids which can be defined based on the muddiness of river water; the index is changeable regularly and sometimes exceeds the allowed level of 20 mg/l.
The biggest worry is that the ammonia index tends to increase recently with the current concentration higher by 5-10 times than the allowed level (0.1 mg/l). The index sometimes reaches 1 mg/l, or 10 times higher than the allowed level.
Similarly, the raw water from the Dong Nai river which provides one million cubic meters of water to Thu Duc, BOO Thu Duc and BOT Binh An water plants, has also been alarmingly polluted. The content of microorganism has exceeded the standard level by 2-4 times, while the ammonia has been increasing rapidly, and has exceeded the allowed level by 4-16 times.
The content of organic matter has also increased very rapidly, and though the index remains within the safety line, it always nearly hits the ceiling level. The increasing organic matter content in water will badly affect the process of reducing iron and manganese in water. And if the ammonia content in water is overly high, this will create the dangerous compounds if the treatment process has problems.
Polluted water needs more chemicals for treatment
Representatives from water supply plants said that since the beginning of 2011, the raw water sometimes got seriously polluted, which forced water plants to stop supplying water for several hours, during which the raw water was mixed with the stored water in the tanks to ease the pollution.
The only solution to treat the seriously polluted water now, besides the above said solution of dissolving water from different sources, is to treat water with more chemicals.
Vo Quang Triet, Director of the Tan Hiep Water Plant, said that the volume of chemicals needed for water treatment has increased. For example, the content of lime to neutralize water has increased by 3.49 g/m3, while the levels of alum used to treat turbidity has increased by 0.18 g/m3, PAC levels up to 0.95 g/m3 and sediment content chlorine used to treat pollution has increased by 0.93 g/m3.
As a water plant has to treat 300,000 m3 of water a day, the additional volume of chemicals it needs would be very big. The Tan Hiep water plant has sent a document to Sawaco, asking for the adjustment of the allowed expenses, because it has to pay 1.8 billion dong additionally to treat water.
Meanwhile, SAWACO has sent a report to the HCM City authorities, informing that the pollution on the Saigon and Dong Nai River has become serious, which has exceeded the capability of the water treatment technologies utilized at the water plants. The company has asked the city authorities to instruct relevant branches to carry out the action plans to ease the pollution on the rivers.