About the project

Background

This is an action research project funded by Simavi, to explore options for faecal sludge management (FSM) in the hot and humid conditions of Bangladesh.

What is the problem?

Efforts to improve sanitation in the country have seen the rate of open defecation reduced to only 4.4% in 2010 (from 43% in 2003).  This means than almost all of the population are now using latrines, typically pit latrines, and the pits are filling up.

A recent WaterAid Bangladesh (WAB) study showed that in an absence of any safe emptying, transportation, dumping, treatment and disposal mechanism in the country, most of the contents of these latrines are ending up in open drains and water-bodies, undermining the gains made through increased sanitation coverage.


Poorer groups who dwell in unsafe environments close to these polluted waters suffer most from this, while the risk also remains high for those who practice safe sanitation.

What is the answer?

We need to understand how best to manage this faecal sludge (a polite term for poo slurry) so that rather that being a detriment to the local environment, it can be of use/ benefit. 

In the absence of centralised wastewater systems, on-site or localised solutions are needed. These need to have a low electrical power demand, be simple to operate, easy to understand, scaleable, affordable, practical and safe.  

Surprisingly there has been little work done in this context, and few proven technologies exist.  This project aims to explore this niche and develop a solution.

What are you doing about it?

After some research and design development for a Society of Public Heath Engineers competition, Joanne Beale, Christine Cambrook and myself (at the time all working with Buro Happold) developed an idea using the sun to dry out sludge in what was effectively a miniature greenhouse.  This combined things that had been proven to work (large open sludge drying beds, slow sand filters, greenhouses) but in a new and novel way.  The core idea being that once the sludge is dry/ handle-able it can be composted along with kitchen waste, or used directly in fields as a soil conditioner and will not be an environmental hazard.

This idea is now being developed as a WaterAid project, through close collaboration with Buro Happold engineers and implementation partners, Practical Action.  We are now working together to establish a workable design through research in the field.

Now for the science bit...

At the outset of this project, the main aims of the design were:

• Maximise evaporation of water from sludge
• Minimise odors
• Reduce pathogens
• Minimise cost of sludge treatment
• Minimise materials needed
• Minimise treatment time

The design is currently performing well across all areas, athough we need to improve the consistency of the pathogen
reduction results, if we do not want to rely on composting as a ‘polishing’ step after drying.

We also had some key questions at the beginning:

1. Do we need a filter base?
Yes - we have found that a filter base is an important component of this approach to sludge drying, even in hot conditions.

2. What roofing material works best?
We have found that a clear plastic roof performs best in terms of heat gain and reducing drying times. Its long term and whole-life perofrmance is yet to be adequately assessed however.

3. Does a solar chimney help increase ventilation rates?
This is as yet untested, and may actually prove to add unneccessary complexity to the design.

4. What pathogen reduction is achievable?
We have acheved a 99% reduction after ten days in key indicator pathogens such as E.Coli. More resistant pathogens such as helminths and C. Perfringens are difficult to destroy outright through any technology, and results are so far inconclusive in terms of how effectively solar sludge drying can manage their numbers.

5. How much does ambient temperature and humidity affect the drying rate and pathogen reduction?
Ambient temperature and humidity can have a significant effect on the drying rate, and should be considered as key variables.

6. How long does it take to dry out sludge to a safe, handleable consistency?
The current approach takes 5 to 10 days depending on ambient temperatures.

7. What design minimises odours most effectively?
No significant odours were noticed around the design, although an enclosed roof was thought to perform better.

8. How much does a system cost and what materials are needed?
This will be established once the design has been finalised.

A three -step approach to FSM is becoming apparent.:

Step 1: The sludge is dewatered on a sand filter, and dried as far as possible in approximately 5-10 days

Step 2: Any effluent run-off through the filter is treated in a reedbed adjacent to the drying beds (1m2 per drying bed), before discharging into a local watercourse, or being held in a pond to be used for maintaining the moisture content of the compost.

Step 3: The dried sludge is removed and co-composted with woody organics in a 1:2 ratio for a minimum of 15 days.