Wastewater Engineering: Primary, Secondary, Tertiary Treatment, Aerobic/Anaerobic Stabilization Ponds & Zero Liquid Discharge (ZLD)

• Sanitary Landfilling Practice:
• An engineered municipal solid waste disposal technique involving compaction of refuse in thin layers and daily covering with impermeable inert earth/soil.
• Properly managed, compacted, and sealed sanitary landfill cells prevent open decomposition odors and foul gas emissions at the surface while being highly cost-effective and economical. (Correct answer: Option 3)

• Water Supply Cycle Steps: Following raw water abstraction (intake from surface reservoirs or groundwater aquifers), the extracted water must immediately undergo Treatment (coagulation, flocculation, sedimentation, filtration, and disinfection) before entering the distribution network.
• Process Sequence: Abstraction $\rightarrow$ Treatment $\rightarrow$ Storage & Transmission $\rightarrow$ Consumer Supply $\rightarrow$ Wastewater Collection $\rightarrow$ Wastewater Treatment $\rightarrow$ Safe Environmental Discharge.

Correct option: (2) Treatment

• Empirical Turbidity-TSS Relationship: For well-settled secondary effluents from biological wastewater treatment plants (such as activated sludge processes), Total Suspended Solids (TSS) correlates linearly with turbidity via the standard empirical formula:

• Operational Utility: This established ratio enables wastewater plant operators to rapidly estimate suspended solid loadings in real time using continuous turbidity meter readings without waiting for gravimetric oven-drying tests.

Correct option: (1) TSS = (2.3) x Turbidity

• High-Rate Solid Contact Clarifier (HRSCC): When wastewater contains high concentrations of Total Suspended Solids (TSS) and turbidity, an HRSCC is employed. It integrates rapid chemical mixing, internal sludge recirculation, flocculation, and high-rate upflow clarification in a single compact unit.
• Comparison with Filtration: Media filters (such as pressure sand or granular activated carbon filters) would rapidly blind, clog, and require excessive backwashing if subjected to high TSS influent without preliminary high-rate clarification.

Correct option: (2) High rate solid contact clarifier