Yamuna River Pollution Control Requires Flow Augmentation and Load Reduction

The Delhi section of the Yamuna River is one of the most contaminated in India. Researchers from Delhi Technological University and Jamia Millia Islamia University recently made an attempt with the QUAL2Kw water quality model for measuring the river's assimilation capacity. The research was directed towards pollution control through the simulation of various flow augmentation and pollutant load reduction scenarios. It suggested that only with an ideal combination of enhanced upstream flow and reduced discharge of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) loads from several point sources would such drastic alteration take place.

The study was carried out along the 22-kilometer course between Okhla and Wazirabad, where the Yamuna has 16 major drains of untreated and partially treated effluent. This section, taking the highest percentage of the river's pollution load, is beset with critical dissolved oxygen (DO) deficit, thus rendering it nearly anoxic water body after it has received drains such as Najafgarh, which alone gets about 58% of the total pollutant load.

The QUAL2Kw model divided the stretch into 14 segments considering drain outfalls and physical-chemical characteristics of the river. Calibration and validation was done on the basis of field data of the Delhi Pollution Control Committee (DPCC) for pre-monsoon low-flow conditions. The base case illustrated how existing conditions, including a flow rate of 1 cubic meter per second and raw drain loads, reduced DO levels to zero and raised BOD levels well above safety levels (over 60 mg/L in parts).

The model was then used to generate 41 scenarios distributed across four cases with different flow augmentation and pollutant loads. At all operations, the aim was to achieve Central Pollution Control Board (CPCB) Class C quality water defined as DO ≥ 4 mg/L and BOD ≤ 3 mg/L. In the initial set of scenarios, upstream flow rising from 10 to 120 cumecs while BOD and COD levels held constant at 10 mg/L and 50 mg/L respectively resulted in improving DO but could not maintain BOD under control throughout.

In increasingly more complicated scenarios, increasingly diminishing loads of pollutants were presumed. Case 2 lowered COD to 25 mg/L, and case 3 lowered BOD to 5 mg/L. These changes together with flow augmentation created better performances, with DO and BOD kept closer to the set values. The optimum result was also attained in case 4 with individual reductions of BOD from D1, D11, D12, and D15 to 5 mg/L and the rate of augmentation of upstream flow to 120 cumecs. This design produced values of DO and BOD in the set class.

The research identified that the quality of water here in the river can be good only when upstream flow is increased considerably and point-source pollutant load is reduced systematically. For instance, 80 cumecs of upstream flow gives assimilation for 31.33 tonnes/day of BOD and 142.85 tonnes/day of COD when DO and BOD are in Class C water quality.

As compared to previous studies, which had not thoroughly investigated the role of COD in deoxygenation of water, the present study has introduced it as a new observation of importance in river self-purification. It brings new light to the element that the infrastructure is weak, there is no real-time monitoring system, and strict compliance with the effluent standards provided by the National Green Tribunal (NGT) is essential.

The earlier researches have suggested separately increasing flow or treating plants, but this one deserves to implement both the practices together in order to achieve improvement in water quality in the long term. This one also highlighted that nitrogenous waste, which is normally present in household sewage, might also have some other effects on the amount of oxygen and needs to be addressed by future research on monitoring.

Delhi’s stretch of the Yamuna suffers from very low natural flow due to water diversions at the Wazirabad barrage, compounded by high pollutant loads. Without intervention, this leads to persistent anoxic conditions and failure to meet even the minimum ecological standards.

Since the model can be applied to provide river response through minimum input simulation, it is highly valuable in situations where Indian city river continuous monitoring hardware is on hold. Given a set of probable, realistic conditions, the study can offer administrative personnel a reasonable methodology through which to balance their decision under complicated pollution matters presenting themselves for highly stressed-up river systems.

Source and Credits
Source: Water Science & Technology, Vol 88 No 7 (2023), Authors: Nibedita Verma, Geeta Singh, Naved Ahsan