The correct option is (c) 1 and 3 only.
Explanation
Septic Tanks are decentralized, onsite mechanisms for the primary treatment and disposal of domestic sewage, relying on sedimentation and anaerobic decomposition.
- Statement 1 is Correct: Septic tanks are a recognized low-cost onsite sewage disposal system. They are extensively used in rural areas, small communities, and urban fringes where the construction of a centralized sewerage network is economically or geographically unfeasible.
- Statement 2 is Incorrect: Septic tanks are not prohibited in residential clusters. They are a standard provision under the National Building Code of India for areas lacking municipal sewerage connectivity. However, they must adhere to specific design and maintenance standards to prevent groundwater contamination.
- Statement 3 is Correct: Septic tanks function independently of the main city sewerage system. They treat wastewater at the source (onsite) rather than transporting it through a network of pipes to a centralized Sewage Treatment Plant (STP). The treated effluent is typically discharged into a soak pit or dispersion trench.
Key Takeaway: Septic tanks are onsite sanitation systems that treat sewage locally through anaerobic processes, serving as an alternative to centralized municipal sewer networks in unconnected areas.