Design of High Turbidity Raw Water: Technical Analysis of Mekong River Water Treatment Project in Vientiane, Laos
Chen Shichu, Liang Jiawen, Cui Hechuan, Huang Jingchun, Wu Mengmeng, Chen Yongquan
（Foshan Hongjun Water Treatment Equipment Co., Ltd）
Summary
This article takes the high turbidity raw water of the Mekong River in Vientiane, Laos as the research object. In response to the water quality characteristics of sudden increase in turbidity during the rainy season (up to several thousand NTU), a set of prefabricated integrated water purification processes with a daily treatment capacity of 20000 tons was designed and implemented. The system adopts a four stage combination process of hydraulic circulation clarification tank, grid flocculation, inclined tube sedimentation, and gravity type valve free filter, which has strong resistance to impact loads and can adapt to severe fluctuations in turbidity. By optimizing key technologies such as flocculation structure, inclined tube settling, and automatic backwashing, the effluent turbidity is stably controlled at ≤ 0.5 NTU, which is better than the drinking water standards of the World Health Organization and Laos. This process combines the advantages of high efficiency, energy saving, and modularity, providing a scalable technical solution for drinking water treatment in high turbidity river areas in Southeast Asia.
Keywords
High turbidity water treatment; Mekong; Hydraulic circulation clarification tank; Grid flocculation; Inclined tube sedimentation; Valve free filter tank; Laos Water Supply Project; Drinking water treatment process
Project Background
Vientiane, Laos is located in the Mekong River Basin. During the rainy season (May to October), rainfall is concentrated, and the river carries a large amount of sediment and suspended solids. The turbidity of the raw water can suddenly increase to over 1000 NTU or even thousands of NTU in a short period of time, posing a great challenge to the stability and water quality safety of the water supply system. To meet the daily demand of 20000 tons of drinking water for a water plant in the Vientiane region, we have designed and built a set of integrated water treatment equipment for high turbidity raw water. This article focuses on the process design ideas and technical characteristics for high turbidity raw water in the Mekong River.
Raw water characteristics and design challenges
High turbidity fluctuation: During the rainy season, the turbidity of the Mekong River changes dramatically, requiring the design of a pre-treatment system with strong shock load resistance.
1. High sediment content: Suspended solids are mainly fine sediment particles with poor settling characteristics, requiring enhanced coagulation and sedimentation efficiency.
2. Seasonal water quality differences: There is a significant difference in water quality between the dry and rainy seasons, requiring the process to have flexible adjustment capabilities.
Core process design
In response to the characteristics of high turbidity raw water in the Mekong River, we adopt the following four stage treatment process to ensure stable and compliant effluent (turbidity ≤ 1 NTU):
1. Efficient hydraulic circulation clarification tank (pre settling tank)
Function: As a preprocessing core unit, it achieves rapid sedimentation of high concentration sediment through hydraulic circulation.
Design features:
Adopting a conical bottom structure combined with a sludge concentration zone to achieve continuous discharge of sediment.
Built in guide tube and flocculation zone, utilizing the kinetic energy of raw water to form circulating flocculation, reducing the dosage of chemicals.
The surface load rate is designed to be 6.0 m ³/(m ² · h) to adapt to turbidity fluctuations.
2. Grid flocculation tank
Function: Generate micro vortices through multi-level grids, enhance the collision efficiency of colloidal particles, and form dense alum flowers.。
Design features：
Adopting stainless steel mesh modules, with graded settings (large holes in the front section and small holes in the end section), gradually increasing the flocculation strength.
The flocculation time is 13 minutes, and the GT value is controlled within the range of 10 ⁴~10 ⁵ to meet the flocculation needs of high turbidity water.
Combined with polyacrylamide (PAM) coagulant aid, the sedimentation rate of alum is increased.
3. Inclined tube settling tank
Function: Utilizing shallow pool theory to improve sedimentation efficiency and efficiently separate suspended solids after flocculation.
Design features：
By using honeycomb inclined tube packing (with an inclination angle of 60 ° and a diameter of 50mm), the effective settlement area is increased to 5 times that of traditional horizontal flow tanks.
The surface load is designed to be 6 m ³/(m ² · h), and the effluent turbidity can be controlled below 5 NTU.
Equipped with an automatic scraper to achieve continuous cleaning of sludge.
4. Gravity valveless filter
Function: Final filtration guarantee, no valve control required, relying on hydraulic automatic backwashing.
Design features：
Using homogeneous filter material (0.5-1.5 quartz sand) to intercept fine suspended solids.
The filtration speed is 6-8 m/h, and the backwash is automatically triggered by the siphon system to ensure filtration stability.
The effluent turbidity is stable at ≤ 0.5 NTU, which is better than the WHO drinking water standard.
Innovative Design and Technological Highlights
1.Anti impact load capacity：
The combination design of hydraulic circulation clarification tank and grid flocculation tank can treat raw water with turbidity up to 3000 NTU without the need for a pre regulating tank.
2.Energy saving and automation：
Gravity flow design (no valve filter+inclined tube sedimentation) reduces pumping energy consumption.
The PLC system monitors turbidity and pressure in real-time, automatically adjusts the dosing of chemicals (PAC/PAM) and backwash cycle.
3.Adaptive design：
The modular structure facilitates expansion and maintenance, and adapts to the local technical conditions in Laos.
During the rainy season, the pre settling tank and coagulant reinforcement mode will be activated, while during the dry season, some units can be skipped to save energy consumption.
Conclusion
This project successfully solved the treatment problem of high turbidity raw water in the rainy season of the Mekong River through a four stage combination process of hydraulic circulation clarification tank, grid flocculation, inclined tube sedimentation, and valve free filtration. The design takes into account efficiency, stability, and operating costs, providing a scalable technological paradigm for drinking water treatment in high turbidity river areas in Southeast Asia. At present, the system is running stably and the effluent quality meets the national drinking water standards of Laos (NSDW 2020), providing reliable water supply guarantee for the Vientiane region.
Author: [Chen Shichu/Foshan Hongjun Water Treatment Equipment Co., Ltd.]
Position: Chief Engineer
Project location: Vientiane, Laos
Project scale: 20000 tons/day
Keywords: high turbidity water treatment, Mekong River, hydraulic circulation clarification tank, valve free filter, Laos water supply project
