Evaluating the capacity of river to receive wastewater by model MIKE 11

The necessary of study

 Currently, many rivers in Vietnam are facing the degradation in both water quality and quantity, especially in the area with high economic growth. One of the major causes of water pollution is due to discharge wastewater (from sewage drains, medical waste, residentials, industrial areas, livestock, etc...) that untreated or treated but not meet standard into rivers and streams. This lead to increase pollutant concentration in the water sources, such as indicators turbidity, suspended solids, COD, BOD5 has exceeded the permissible limits. In the dry season, some river-section and sub-streams dried up, reducing the ability to dilute pollutants and self-clean of the river. Water pollution impacts on social aspects such as the environment and human’s health.

The Law on Water resources (2012) of Vietnam regulated  some new provisions on water resources management and protection, especially the field of wastewater discharge management. The Article 37 of the Law stated: “The organizations and individuals who discharge waste water into water sources must be granted licenses by competent state agencies (except the small scale  and waste water without  a harmful chemical or radiative matter). One of the basis to grant a license is capacity to receive wastewater of water sources (Decree No. 201/2013/ND-CP, 2013). Therefore, evaluating the capacity of river to receive wastewater is considered as one important task of water resources management and protection. That will provide a basis to help the managers, decision makers in managing, controlling, licensing the wastewater discharge into the river, sanctioning the offending organizations, individuals (who discharge waste water over the receiving capacity of the river) and ensuring socio-economic development.

Introduction of the case study

Thuong river belongs to the Hong – Thai Binh river system, has a length of 157 km, area approximately 6,640 km², flows through the territory of Lang Son, Bac Giang, Hai Duong provinces. In Bac Giang Province, the Thuong river has a length of about 80m, flows through the districts of Lang Giang, Yen The, Tan Yen and Yen Dung and Bac Giang city. The catchment area is about 3.571km² (accounting for 95% of the natural area of the province). The annual average rainfall is only 1527mm, the flow module in only 15 ¸ 20l/s/km², total flow is about 1.93 billion m³.

Figure 1. Map of Thuong river in Bac Giang province

(Source: Centre for Water resources technology, 2014)

The status of waste water discharge and wastewater quality

According to the survey along the Thuong river in Bac Giang province, there are 16 organizations  discharging wastewater directly into the river with average flow of about 2.2 million m³/day. Most of the wastewater discharge into Thuong river are  exceeding the Vietnamese standards. The pollutants are mainly organic matters and micro bacteria., Some waste sources are contaminated by mineral oil. Specific parameters of water quality in the Thuong river  as follows:

- Production wastewater: BOD₅ exceeded 1.9 - 2.4 times, COD 1.4 - 1.8 times, NH4⁺ 9.0 - 26.4 times and Coliform 5.4 - 11.1 times (Compared with QCVN 40:2011/BTNMT).

- Wastewater from the drainage pumping station: BOD₅ exceeded 1.6 to 2.14 times, NH4⁺ 7.0 - 20.3 times and Coliform 4.66 - 9.33 times (Compared with A column of QCVN 14:2008/BTNMT).

- Water from rivers and streams flow enter to Thuong rivers: BOD₅ exceeded 2.5 - 6:25 time, COD 2.44 - 5.1 times, and NH4⁺ 11.2 - 23.2 times (Compared with A column of QCVN 08:2008/BTNMT).

Discharge culvert of Ha Bac Fertilizer Plant	Wastewater Channel of Ha Bac Fertilizer Plant
Chau Xuyen I drainage pumping station	Chau Xuyen II drainage pumping station

Figure 2. Some discharge sources on Thuong river

(Sources: Internet)

Application of model MIKE 11 to evaluate the capacity or Thuong river to receive wastewater

To evaluate the capacity of the river to receive wastewater by using model MIKE 11, the steps are defined as follows:

- Identifying and collecting neccessary data for the model

- Analyzing and defining the purpose of water use in each section of the river

- Running  the hydrology and hydraulic model

- Calculating, simulating water quality process by using MIKE 11

- Calculating the contaminant dispersion process

- Analyzying, assessing the changes in water quality of Thuong river

- Zoning the waste receiving capacity of Thuong river.

- Evaluating the capacity to receive wastewater of Thuong river base on the assessment  scenarios.

Conclusion

The water quality at many points along the Thuong river have been polluted, most of the indicators were exceeded permissible standards several times. If this wastewater sources are discharged regularly, continuously and in long term will make water quality lost the ability to self-clean and heavily contaminated.

MIKE 11 is considered  as a very good  tool for solving the problem of this study. However, the accuracy of the results depends much on the completeness, accuracy and continuity of the collected data, as well as  the calibration, verification of the model carried out by  users.