STAGE 3 OF 5

Treatment

Effective Fecal sludge management requires safe treatment that enables beneficial reuse of treated by-products. Three major approaches are available: retrofitting existing systems, co-treatment at existing STPs, or establishing new FSTPs.

Approach 1 Retrofitting Approach 2 Co-Treatment at STPs Approach 3 New FSTP

Approach 1

Retrofitting

Retrofitting refers to the upgradation or improvement of existing toilet containment systems such as single pit latrines and septic tank–based toilets. In many rural areas, toilets already exist but are poorly designed or not suitable for safe fecal sludge management. Retrofitting is therefore an important approach to ensure that these existing systems function safely and support proper FSM.

Provisions for retrofitting toilets:

Converting single pit latrines to twin pit, by adding an additional pit
Correcting defective septic tanks (e.g. adding the chamber separation wall, sealing the bottom, etc.)
Improving twin pits (e.g. ensuring functional junction chamber, honeycombing or perforations in pit wall, adequate distance between pits, safe distance from water sources, etc.)
Installation/retrofitting of alternative twin pit diversion mechanisms which are easy and safe to install and use, for example SATO V-trap connection system
Improving technologies and replacing leach-pit latrines with appropriate technologies in challenging geographies such as high-water table, rocky areas, etc. (example bio toilets, composting toilets, raised toilets, etc.)

Challenges:

Un-availability of land at households, acceptance by households, expenses for reconstruction, etc., with this approach

Note: Retrofitting is not suitable as treatment approach in urban areas.

Video: Single Pit to Twin Pit Conversion

Approach 2

Co-Treatment at Existing STPs

Leverage existing wastewater treatment infrastructure for cost-effective treatment of Fecal sludge through integration into under-utilised STPs.

Step 1: Identification of Underutilised STPs

STPs operating below capacity should be shortlisted for co-treatment. A technical checklist must be used to ensure that the STP is suitable for receiving Fecal sludge without compromising treatment efficiency or effluent quality.

STP Assessment Checklist

XLSX

Co-treatment Registration Manual

PDF

State Level Orientation

PPT

Step 2: Clustering of Villages

Villages located within a 15 km road distance from the identified STP will form a cluster for centralized FS collection. This minimizes transportation costs and ensures efficient service delivery.

STP Mapping (Haryana)

IMAGE

Step 3: Quantification of Fecal Sludge

Accurate FS quantification is essential for designing treatment capacity. A triangulation approach is followed, using three complementary methods:

Population Method: Population projections using Arithmetic Progression, Geometric Progression, and Incremental Increase
Volume of OSS Systems Method: Based on septic tank design, number of users, desludging frequency, and standardized sludge accumulation rates
Desludging/Transportation Method: Operational data from desludging vehicles including truck capacity, daily trip frequency, and volume transported

Step 4: Co-treatment Technology Selection

Two primary approaches are commonly adopted for co-treatment:

A. Dilution Method (Direct Addition)

Direct addition of Fecal sludge into the sewage influent of an underutilized STP based on remaining treatment capacity and compatibility with existing wastewater.

Key considerations:

FS is mixed with sewage, diluting solids and organic matter load
Total load must not exceed STP's designed hydraulic and organic capacity
One of the simplest methods, requiring minimal infrastructure modifications
Demands continuous operational monitoring to ensure plant performance remains within acceptable limits

B. Solid-Liquid Separation Method

Extracts solids from Fecal sludge prior to introducing the liquid fraction into the STP. The goal is to achieve a supernatant quality equivalent to domestic sewage.

Suitable dewatering technologies:

Planted Drying Beds (PDB): Utilizes vegetation for enhanced drainage and solid stabilization, ideal for decentralized settings with low-to-medium FS load.

Screw Press: Mechanically dewaters sludge, suitable for larger volumes or where space and operational reliability are concerns.

Approach 3

Establishment of New FSTP

Build new Fecal Sludge Treatment Plants for villages that fall outside the operational clusters of existing co-treatment facilities.

Step 1: Land Identification

A suitable site, with appropriate land size and environmental clearances, should be selected for constructing the FSTP.

Key factors to consider:

Access roads for desludging vehicles
Groundwater level and soil conditions
Distance from habitation (buffer zone compliance)
Environmental clearances and regulatory requirements
Availability of water and electricity connections

Step 2: Cluster Formation

Villages located within a 15 km road distance should be grouped to form a cluster for service coverage. Care should be taken to ensure that these new clusters do not overlap with clusters served by existing co-treatment facilities.

Step 3: Fecal Sludge Quantification

The Fecal sludge load for these clusters should be estimated using the triangulation method, which relies on three complementary approaches:

Population Method: Population projections using standard approaches
Volume of OSS Systems Method: Analysis based on septic tank design and sludge accumulation rates
Transportation Method: Estimates from operational data of desludging vehicles

Step 4: Technology Selection

Based on sludge quantities, land availability, and local conditions, appropriate treatment technologies should be selected:

Sludge Drying Beds (SDB)

Simple, cost-effective technology for dewatering and drying Fecal sludge through natural evaporation and drainage.

Advantages:

Low capital and operational costs
Simple construction and operation
Minimal energy requirements
Suitable for small to medium loads

Planted Drying Beds (PDB)

Enhanced drying beds with vegetation that improves drainage, pathogen reduction, and sludge stabilization.

Advantages:

Better dewatering through plant transpiration
Improved pathogen reduction
Higher quality biosolids output
Aesthetic and environmental benefits

Systematic Coverage

By ensuring systematic coverage of villages through new FSTPs, even those areas outside co-treatment clusters can achieve safe and sustainable Fecal sludge management. This approach ensures no village is left without access to proper treatment facilities.

Resources

Standard Designs & Estimates

EXTERNAL LINK