Thursday 14th March
On Thursday I was working in the WaterAid office, and in the afternoon presented the project to our colleagues there.
It was good to share the project with others, particularly as we now have a growing team working on the project. We have a new project officer, and a lady working on some of the social aspects of the project. Along with Suman and Opel, that now makes four in WAB.
It was also useful as Mamun and Dipok from Practical Action joined us, and we discussed several further design developments:
Rubbish Net: Unlike our previous sludge from Phase 1, this sludge was full of detritus, bits of plastic and general rubbish. It wasn't obvious when they collected the sludge, but as it settles in the drying beds, the rubbish is floating to the top. We talked about pouring the sludge into the beds through a coarse net to capture the rubbish, which can then be dumped in a pit on-site to degrade safely. This may also mean we do not need a splash plate, but we shall see.
Lightweight Roof: With all the additional framing, the roof is now found to be too heavy, and a more lightweight design is to be explored. Mamun has spoken with some of the local CNG drivers, and the polythene they use for their windshields is thought to be good - tough and won't rip. So, amusingly, seeing as this was something we suggested way back in the beginning, it looks like we might end up with a poly-tunnel after all!
Scaling and sizing: We have sought to develop a modular design that can be scaled up to suit demand. The beds themselves will be relatively easy to scale, but now we have the reedbed element, we will need to be careful it doesn't get too large. However, I am not convinced that we really understand what volume of water is draining out of the sludge - reedbeds are based on an average daily flow - and as we have an exponentially dropping flow over time, we used the worst-case first 24hrs. However, as the reedbed works with a plug-flow, I am now wondering whether we could have used a smaller version, and taken the total expected volume, and divided it by the number of days...The issue then being, what proportion of water drains out and what is evaporated. perhaps next time, we will focus more on moisture content, and measure the initial moisture content more accurately, along with the total volume drained.
Sludge temperature: As our initial question was around which roof generated the most heat underneath, we have been measuring air temperature over the sludge, rather than the actual sludge temperature. We have been assuming that air temperature is a useful proxy. However, it would be good to now understand more about the actual sludge temperature relative to the air temperature. Practical Action said they had some sensors they could use, so we might try this for the second half of the test, and definitely for Phase 3.
Volumes of sludge: The team working in Khulna are keen to bring the drying beds to their town, but before we can do that, it was suggested that they need to get a better idea of what volumes of sludge they will need to be treating, and how often.
Soil testing: We need to get the now composted material from Phase 1 tested, and arrange for the material from this Phase 2 to be tested too.
So, still more work to do before we get to a final design, but each time we run the test we are learning more, and gaining experience, so I do not think any of our efforts will have been wasted.
On Thursday I was working in the WaterAid office, and in the afternoon presented the project to our colleagues there.
It was good to share the project with others, particularly as we now have a growing team working on the project. We have a new project officer, and a lady working on some of the social aspects of the project. Along with Suman and Opel, that now makes four in WAB.
It was also useful as Mamun and Dipok from Practical Action joined us, and we discussed several further design developments:
Rubbish Net: Unlike our previous sludge from Phase 1, this sludge was full of detritus, bits of plastic and general rubbish. It wasn't obvious when they collected the sludge, but as it settles in the drying beds, the rubbish is floating to the top. We talked about pouring the sludge into the beds through a coarse net to capture the rubbish, which can then be dumped in a pit on-site to degrade safely. This may also mean we do not need a splash plate, but we shall see.
Lightweight Roof: With all the additional framing, the roof is now found to be too heavy, and a more lightweight design is to be explored. Mamun has spoken with some of the local CNG drivers, and the polythene they use for their windshields is thought to be good - tough and won't rip. So, amusingly, seeing as this was something we suggested way back in the beginning, it looks like we might end up with a poly-tunnel after all!
Scaling and sizing: We have sought to develop a modular design that can be scaled up to suit demand. The beds themselves will be relatively easy to scale, but now we have the reedbed element, we will need to be careful it doesn't get too large. However, I am not convinced that we really understand what volume of water is draining out of the sludge - reedbeds are based on an average daily flow - and as we have an exponentially dropping flow over time, we used the worst-case first 24hrs. However, as the reedbed works with a plug-flow, I am now wondering whether we could have used a smaller version, and taken the total expected volume, and divided it by the number of days...The issue then being, what proportion of water drains out and what is evaporated. perhaps next time, we will focus more on moisture content, and measure the initial moisture content more accurately, along with the total volume drained.
Sludge temperature: As our initial question was around which roof generated the most heat underneath, we have been measuring air temperature over the sludge, rather than the actual sludge temperature. We have been assuming that air temperature is a useful proxy. However, it would be good to now understand more about the actual sludge temperature relative to the air temperature. Practical Action said they had some sensors they could use, so we might try this for the second half of the test, and definitely for Phase 3.
Volumes of sludge: The team working in Khulna are keen to bring the drying beds to their town, but before we can do that, it was suggested that they need to get a better idea of what volumes of sludge they will need to be treating, and how often.
Soil testing: We need to get the now composted material from Phase 1 tested, and arrange for the material from this Phase 2 to be tested too.
So, still more work to do before we get to a final design, but each time we run the test we are learning more, and gaining experience, so I do not think any of our efforts will have been wasted.
Intriguing that the polytunnel may still be!
ReplyDeleteRe the rubbish - does it all seem to be of a sort that will degrade, and is safe? We usually find that latrines contain anything from plastic containing sanitary pads to bottles to needles and other medical waste. Would be interested to know what the local SWM practice is and whether you could link up to get rid of the rubbish.
Good work and thanks for posting :)
Good point - I'll check about the SWM - it's not something we've spent a lot of time on!
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