Sewage Issue Primer

Apart from the varied insights around user behavior that the Potty Project research afforded us, we have learned that sewage and water service provisioning are also key factors ensuring the prolonged operation of facilities.

We decided early on that our designs needed to use a ‘septic tank’. This stemmed from the challenges affecting cities similar to our pilot locations in regards to sewerage access: Bhubaneswar has only a limited system while Cuttack lacks one altogether. The common practice in these instances is to couple an independent waste storage tank with a supporting bore well, for water requirements.

We observed a number of reasons for toilet facility failure due to sewage issues:

1. Lack of adequate capacity planning: In many toilets requiring on-site storage and evacuation, capacities weren’t planned appropriately. Inadequate frequency of vacuum truck evacuation caused systems to break down as the tanks flooded with excess waste water.

2. Inappropriate technology or lack of training to maintain technology: In many cases, we observed toilets being designed to use ‘septic tanks’, which is usually inappropriate for the scale at which community toilets are running. Additionally, the delicate ecology of septic tanks need to be maintained, a fact that is oftentimes not clearly understood. Chemicals such as bleach often kill microbes in the tank essential for proper operation. This practice thus turns septic tanks into sewage holding tanks.

What are the solutions not available to us?
Two technologies unavailable to us as we design and build these sanitation facilities are:
1. A connected sewerage system: Bhubaneswar and Cuttack are currently putting in place comprehensive ‘City Sanitation Plans’ which will install a highly connected system of sewers in the coming years. This means we must design the Project Sammaan facilities so they can be retrofitted to the sewerage system once it’s in place.
2. On-site treatment: Existing technologies for on-site treatment of waste (such as comprehensive DEWATS and constructed wetlands) are capital and space intensive. The Project’s limited funding-per-facility mandate to facilitate future replication, and scalability, precludes their use.

What solutions are available to us?
There are currently four possible solutions available to us. However, before getting into that, let’s review two critical components of waste management that impact our design:
1. Types of waste water
+ grey water: waste water from activities like laundry, bathing and hand-washing.
+ black water: associated with water that contains fecal matter and urine, usually that which has been used for flushing and anal cleansing.
+ fecal sludge: heaviest solid particles in tanks where black water is permitted to settle.

2. ‘Honeysuckers’
This term is synonymous with ‘vacuum trucks’. In India, these vacuum pump-equipped trucks withdraw black water and fecal sludge from sewage holding and septic tanks for homes lacking sewerage line connections.

The term ‘honeysuckers’ comes from Africa where these trucks were rechristened to give them a positive spin as the waste was being used quite effectively as fertilizer.

And now the solutions:
1. Soak Pits
Also known as a soakaway or leach pit, this is a covered, porous-walled chamber that allows water to slowly bleed into the ground, leaving behind a solid effluent that requires excavation, though at a lower frequency than the other options. This system is not recommended for places with a high water table due to the danger of groundwater contamination.

2. Sewage holding tank without grey water separation
A tank where all effluents are disposed of in the same space. This requires frequent emptying with contents disposed of in a soak pit away from city residents since there is no on-site treatment. Waste can also be taken to sewage treatment plants. Facilities of this type currently do not exist, though they are part of both Bhubaneswar and Cuttack’s City Sanitation Plans for the future.

3. Sewage holding tank with grey water going to open drains
Similar to the previous option, except grey water is disposed of into nearby open drains to facilitate a lower frequency of tank emptying. An important thing to note: grey water requires treatment prior to being dumped in open drains.

4. Septic Tank
This solution has separation of all three effluents: grey water is disposed of in open drains, solid matter settles in the tank, and black water is regularly evacuated and disposed of. ‘Desludging’, the removal of settled fecal sludge, is also required but at less frequent intervals (determined by tank size).

These are very simplified explanations. You can read more about sanitation systems and technologies in this enlightening document produced by EAWAG and WSSCC.

Next Steps
We are currently bringing in an expert to work with our team on two levels:
At the broadest level, the expert will put in place a strategy document which will be vetted by the government, to provide requisite sign-offs on the adopted system.This process will ensure buy-in on the sewage strategy from the government who will be taking on the responsibility for several aspects of service provisioning post-construction.
Collaborate with Anagram Architects to design site-specific capacities and systems.