Jawaharlal Nehru Technological University Hyderabad B.Tech IV WATER QUALITY MANAGEMENT Previous Question Paper (March - 2021 - R16)

Suspended solids (SS) represent the portion of total solids retained by a filter, typically glass fiber, and are a critical indicator of water pollution. The determination of suspended solids is performed gravimetrically. A well-mixed sample is filtered through a standard glass fiber filter disk. The residue retained on the filter is dried to a constant weight at 103°C to 105°C. The increase in weight of the filter represents the total suspended solids. The concentration is calculated as follows:

Where A is the weight of the filter plus dried residue (mg) and B is the weight of the filter (mg).

Chemical Oxygen Demand (COD) measures the equivalent amount of oxygen required to chemically oxidize organic matter in water using a strong oxidizing agent under acidic conditions. It is a rapid test compared to BOD. The standard method involves refluxing the sample with a known excess of potassium dichromate (K₂Cr₂O₇) in the presence of sulfuric acid (H₂SO₄) and a silver sulfate catalyst.

The determination steps are:

1. A known volume of the sample is placed in a reflux flask with a measured amount of standard potassium dichromate solution and concentrated sulfuric acid containing silver sulfate.
2. The mixture is refluxed for two hours, allowing the dichromate to oxidize the organic compounds.
3. After cooling, the excess unreacted dichromate is determined by titration with standard ferrous ammonium sulfate (FAS) using ferroin indicator.
4. A blank titration is performed using distilled water instead of the sample to determine the exact concentration of the dichromate.

The COD is calculated based on the difference between the volume of FAS used for the blank and the sample:

Where M_FAS is the molarity of the ferrous ammonium sulfate solution. The result provides an estimate of both biodegradable and non-biodegradable organic matter present in the water sample.

Nonpoint source (NPS) pollution refers to water pollution that does not originate from a single, identifiable source such as a pipe or a specific industrial discharge point. Instead, it results from diffuse land-based activities where rainfall or snowmelt moves over the ground, picking up natural and human-made pollutants and depositing them into rivers, lakes, wetlands, and groundwater.

The primary causes of NPS pollution include:

• Agricultural Runoff: Excess fertilizers, pesticides, and herbicides from croplands, along with sediment from soil erosion and bacteria from livestock waste, are washed into water bodies during rain events.
• Urban Runoff: Impervious surfaces like roads, parking lots, and rooftops prevent water infiltration, causing rapid runoff that carries oils, grease, heavy metals, trash, and road salts directly into storm drains and local waters.
• Construction Activities: Land clearing and earthmoving increase soil erosion, leading to high sediment loads that increase turbidity and smother aquatic habitats.
• Atmospheric Deposition: Pollutants emitted into the air from industrial or vehicular sources can settle onto land surfaces and subsequently be washed into water bodies by precipitation.
• Hydromodification: Alterations to stream channels and flow patterns can increase bank erosion and degradation of water quality.

Effective control measures focus on Best Management Practices (BMPs) to reduce pollutant loading at the source:

• Vegetative Buffers: Planting riparian buffers (strips of vegetation) along water bodies traps sediment, absorbs nutrients, and filters runoff before it reaches the water.
• Conservation Tillage: Agricultural practices that minimize soil disturbance reduce erosion and the transport of sediment-bound pollutants.
• Stormwater Management: Utilizing permeable pavements, rain gardens, and detention basins in urban areas helps infiltrate runoff, reducing the volume and velocity of water entering drainage systems.
• Nutrient Management: Implementing precise application rates for fertilizers based on soil testing reduces the surplus nutrients available for runoff.
• Erosion and Sediment Control: Using silt fences, sediment basins, and temporary seeding at construction sites prevents soil loss during development.