Initial results and reflections

We have all learnt a lot so far, and the current reflections on the design and the approach are:

1.  Lifting the roofs - We should add handles to the short edge of each of the roofs to enable easier lifting and removal.  They could even be hinged and propped in future iterations.
2. Delivery process - We need to think about how to safely unload and pour in sludge from barrels/ containers on a pick-up truck.  There was only one major slippage when we were watching, but it resulted in a 150L container falling about half a metre and splashing many of the sweepers – one even got some in their eye.  Luckily we had a tubewell on site and amongst all the resultant shouting and arguments, they could all wash before recommencing work.
3. Treating and controlling the effluent runoff – particularly when the sludge is first poured into the beds, a significant amount of water drains through the beds and into the soakaway.  Should we control this flow, and only allow it to drain at a certain rate to try and enable treatment of the effluent as it passes through the bed, or should we build an accompanying reedbed to capture and treat it?
4. Defining ‘sludge’ – this is a tricky substance to define, and our first batch, delivered by vacutug was only the wastewater component of a septic tank’s contents.  The next was mixed sludge and wastewater, and the last I think we got somewhere near what we were expecting.
5. Increasing temperatures - our first few days of results show temperatures topping out in the high 30's for the plastic roofed beds - we'd need to hit 50+ for 5 days for pathogen reduction. We'll have to wait for the results from the lab to see what kind of die off we will achieve here.  

Oh and by the way, I'm now comparatively famous in Faridpur...

The Sludge settles

Wednesday 28th November

This morning we convened again at Practical Action’s offices:

Practical Action's Faridpur Office

I was shown a photo in the paper of the landowner giving over the rental agreement to the Major for this project (the municipality are paying the rent for the site), and told that my picture would be in there tomorrow! I dread to think which photo they'll use!

We then went to the site via a hardware shop / workshop that had welded us up a rake.

After lashing it to a bamboo shaft, we proceeded to rake over each bed in turn, taking the roof off and mixing the contents of each bed. This took about an hour in total. 

I made some qualitative observations, rather than taking moisture sensor readings.  All the beds were now much more pastey-soupy (I told you we were lacking adjectives) with thicker material at the end where the sludge had been initially poured in.  When we were taking the samples, it was much more stratified, with a foamy scum on top, a watery mid layer and a thick paste on the bottom.

Once we'd done raking, the weather station was repositioned, as there were concerns that it was being shielded by the trees.

New position for the weather station

View across the site

The Morning after the night before

Tuesday 27th November

In the morning we went back to site and surveyed the situation.  The tanks now had had the following volumes of sludge put into them:

1 – Filter bed with metal roof: 580L

2 – Filter bed with plastic roof: 510L

3 – Filter bed with thatch roof: 560L

4 – Flat bed with metal roof: 490L

5 – Flat bed with plastic roof: 490L

6 – Flat bed with thatch roof: 490L

The reason for the differences is the assortment of containers the material was delivered in.

We took the roofs off while I prepared the sampling materials.  We had screw top plastic jars, plastic spoons, and gloves.  I labelled up each of the jars and set them out on the sides of each of the tanks.  Suman and I put some plastic gloves on, and started spooning in the sludge into each jar.  The spoons were discarded after use and Opel collected them all in a rubbish bag.  At this point the smell really wasn’t too bad, it was more a revulsion at the collecting part!  The sampling process took about an hour.

Me at the laboratory desk preparing the sampling equipment

Setting out the jars - three samples were taken from each bed

Hopefully this will be enough to test

Taking a sample from the drainage pipe

 We wiped down all the jars with antiseptic wipes just to clean off any traces of spills or splashes, and packed them with ice in a coolbox and bag, making sure they would remain upright for the journey into Dhaka.

Packing the samples on ice to take to Dhaka

Before the roofs went back on, I scurried around with my laptop, and downloaded information from the sensors.  I also tried to use the moisture sensor I’d brought, but the batteries had run down, and we had to get some replacements from town.  I wasn’t very convinced by the readings I got – one bed may have been clearly more liquidy than another, but the sensor was saying that it had a lower VWC (volumetric water content).  I suspect this may be because they are all >85% moisture and it’s confusing the sensor.  Once they dry out a bit, I’ll re-try.

I spent the remainder of the afternoon creating some pretty graphs of the initial results and trying to send a few emails on the rather limited internet connection here.

Sludge, Round Two

Monday 26th November - WARNING, THIS POST CONTAINS IMAGES OF AN EXPLICIT NATURE, NOT TO BE VIEWED WHEN CONSUMING FOOD!

We inspect the site, and discover only a very thin layer of sludge remaining in the tanks – the influent must have been >90% water, the bulk of which has now drained out through the filters.

A view into the plastic roofed tank - basically a thin film of sludge on the sand

Condensation on the roof

We had lots more discussions about where to get ‘better’ sludge, as in thicker sludge, and how to get it to site, given that the vacutug cannot remove the thicker material.  We inspect the various containers available at Practical Action, and more are bought from the market to enable the volume required to be collected.

300L square plastic tank

70L plastic barrels

Practical Action's backyard/ treasure trove, if you like that sort of thing

From some initial qualitative observations - putting my hand underneath each roof - the metal roof is very much cooler than I had been expecting, and so we paint it black to see if this will improve things.

Painting the shiny metal roof black

We retire to town for dinner, while Practical Action staff make the final arrangements with the sweepers (those who actually do the dirty work of sludge collecting) and wait for the evening and our next delivery of sludge.  We return to site at around 9pm to see our first delivery of the thicker sludge.

The first container from Batch 2 - Mmm thick sludge

The first container is indeed much more what I was expecting…and this is where the one of the problems with talking about sludge comes…the lack of appropriate adjectives!  This first load was kind of a thick soup/ McDonalds milkshake kind of consistency.  Unfortunately the next container was much more runny, and as each container was emptied into the beds, it was obvious that it would be difficult to ensure each bed received the same input material.  Ah well, we will do what we can. 

Once this batch had been delivered, we returned to town to have dinner (!) before joining the sweepers in the bus station to oversee collection of some ‘better’ sludge (there was some discussion amongst them of where to find the ‘good stuff’. 

Watching them work highlighted the dangers of this kind of job – there was no PPE (personal protective equipment) and a significant risk of splashes and slips.  They had absolutely no qualms about handling the dirty buckets and loading containers onto the lorry.

This batch was emptied into the flat beds, and again was a soupy consistency.

  In order to make at least the volumes consistent, we left then to do one final delivery and put the roofs back on, and retired to the hotel around midnight.

Incense being burnt to mask any odours

Still draining...

The Sludge hits the bed(s)...

Sunday 25th November, part 2

With the town distracted by the parades associated with the religious holiday, we were out emptying the septic tank of a local school…

Parade in the town centre

We have a little generator on site powering lights for the night-work

The roofs are off, awaiting the first sludge delivery

The vacutug arrives, pulled by a tractor

The hose is connected to the back…

And finally our first sight (and smell) of the long waited-for sludge…

Except it’s not very sludgy…and is a lot like wastewater!  We decide to just use the filter beds for this lot, as this isn’t the consistency that we were designing for, and if we put it in the flat beds, we will just have smelly puddles. 

 It seems the vacutug is best for removing the liquid portion of the septic tanks contents, and cannot remove the solid/ sludge part.  A learning point – clear definitions of ‘sludge’ are needed when setting up/ operating FSM designs/ projects.

Animated discussions about sludge

There then follows lots of deliberations about the sludge issue – whether the septic tanks will have the right stuff in, if not, where to get it from, how to remove it, how to transport it, who to do it, how much we need…

Meanwhile, the filters start draining out the excess water – slightly clearer than what went in! 

Drained effluent from the three filter beds

One of the beds had some wiggling travellers in....

Maggots

  

Night falls, and we retire for the evening, and plan to reconvene at Practical Action’s offices in the morning to plan our next steps.

Final preparations

Sunday 25th November

After another 5hr drive from Dhaka, we arrived at the site and admired our new sign:

We've also now got some gateposts being built and the beginning of some fencing:

Peeling off the formwork

Chopsticks for giants

We inspected the site and saw the finishing touches being made to the soakaway.  This is where any water draining out of the three beds with sand filters in will end up.

Detail of the soakaway - inlets from each bed and an overflow into a nearby ditch

 As ever the labourers had come prepared:

The labourers lunches - probably better than a meal-deal from Boots!

Tools, lunch and materials and transport.

Next I set up the weather station, much to the interest and intrigue of the others:

Putting it all together

Attaching it to a long bamboo pole

That should keep it out of reach of curious hands...

Then we attached the temperature sensors (ibuttons from Maxim) to the underside of each of the roofs, hanging down about 6inches.  

After lunch we started putting the filters together.  Firstly any stray leaves were removed from the beds:

Detail of the drainage holes in the drainage pipe at the base of the filter beds

The materials being prepared and brought from the next-door field (where the sand had been being washed) onto the site:

The lines we’d put into the cement plaster worked really well at letting the labourers know how high to fill each bed, and to make sure it was level.

The coarse layer goes in

The middle level gravel was sieved to get rid of all (most of) the dust in it – we were fighting against daylight here – the labourers stopped at 4pm, so we had an elite team of 3 or 4 doing the work after then.

At some point after 5, some more labourers turned up and the sand layers went in quite quickly.  The sand was thrown onto the sieve and raked over with a piece of wood, and the pebbles/ detritus discarded to one side.

Sieving the sand layers into the filter beds

Finally, we were done and scurried back to town for dinner and another layer of clothing – it gets cold when the sun goes down!