What is the Shear strength of that shit you drop in that pit

SYNTHETIC SLUDGE EXPERIMENT

Synthetic sludge is a mixture of top soil and kaolin clay which when mixed with water in appropriate quantities; it emulates the behavior of faecal sludge.

Why use synthetic sludge

It is quite disgusting to use faecal sludge for experiments as many tests need to be carried and it is also difficult to handle faecal sludge in a clean manner without spillage.

Why carry synthetic sludge experiment

In engineering it better to establish the forces you are working against before making any decisions. So in the synthetic sludge experiment we are trying establishing the shear strength of sludge and establish the shear stress range over which a particular pump can perform. The available pumps we have are; the Gulper, Rammer, Nibbler, Modular gulper and the Auger

Methodology

One of the modest ways of establishing uniform composition of sludge is through a slump cone test. The slump cone test also aids figure out the behavior of sludge of different compositions

A slump cone is a cone with a standard bottom diameter of 200 mm and top diameter of 100 mm with a height of 300 mm.

The slump cone experiment involves filling the slump cone with synthetic sludge and measuring the slump.

Figure 1: Measuring components of the synthetic sludge

Figure 2: Mixing the components with a quantified amount of water

A slump cone is placed on a level ground, filled with sludge ensuring that all voids are filled and then the cone gently removed. The collapse of the sludge called slump is measured. The slump is the distance from the initial level of the sludge when in the cone to the point where it collapsed.

Figure 3: The cone of sludge after removing the slump cone

Figure 4: Measuring the slump

Some equations have been modeled which predict the behavior of feacal sludge and these equations also apply to synthetic sludge. Each value of water content corresponds to particular shear strength. A graph of shear strength against water content shows a linear relationship. From this relationship, synthetic sludge with specified shear strength can be mixed since approximate water content can be got from the plot

Table 1 : Plot of shear strength against water content

From the chart the shear strength of sludge at any water content can be established or the water content at a given shear strength can be got.

During this experiment synthetic sludge was taken to contain 85% top soil and 15% Kaolin clay by dry mass and then varying the amounts of water to obtain specific shear strength.

It is at this point that three barrels of synthetic sludge of shear strength 2kpa, 500Pa and 100Pa were mixed for testing the pumping ability of the available pumps

Figure 5: Lowering a barrel containing synthetic sludge with specific shear strength into a pit for testing the available pumps

Figure 6: Testing of the Rammer

Give me a lever long enough, And i will lift a barrel of shit

As a part of the Emptying and Transport sanitation technology stream of development undertaken by Sani-Hub, a method of lifting barrels onto the back of a pickup truck is needed to improve pit emptying operational logistics.

Currently pit emptying entrepreneurs are restricted by logistics costs, because households appear unwilling or unable to pay for more than 3 barrels of sludge to be removed from their pit. At current rates, the removal of 3 barrels of sludge will generate 90,000UGX, however the rental of a pickup truck will cost a minimum of 80,000UGX, and the pickup is required to remain at the site for the whole pit emptying operation.  Therefore the profit margin is not great enough to allow rapid business expansion.

Fabrication of the first prototype 

With the use of a barrel lifting device entrepreneurs will be able to increase their net income by reducing the transport costs per pit, because they will be able to service multiple pits in one area with one pickup truck. The pit emptying entrepreneurs can coordinate between each other and share transport vehicles this will increase their net income by reducing transport cost individually. And if barrels of sludge can be lifted onto a transport vehicle when they are full, this could lead to rapid expansion of the pit emptying services generating more business for the pit emptying entrepreneurs, and mitigate the issue of the pickup having to remain at the pit emptying site all day.

Barrel Lifting Device Prototype One:

The first prototype developed uses the concept of a counterweight through a simple lever system to lift a barrel of sludge. The device can be fully disassembled, so it can be loaded onto the back of a pickup truck, and then fully assembled once on the site where it is needed to lift barrels. 

The image shows the first prototype lifting a 150l barrel
(Of water, the test with poo is still to come)

We aim for 3 pit emptying team’s equipment to be loaded onto the back of a pickup truck consisting of, 6 barrels, 3 gulpers, hand carts and a barrel lifting device. The 3 teams will be dropped at 3 different sites within an area with a gulper, hand cart and 2 barrels. They will empty two barrels worth of sludge and then manoeuvre the full barrels with the use of a handcart to the roadside where the barrel lifting device can be set up and the barrels lifted onto the back of the pickup truck.  This means the rental cost of a pickup truck to be split between the 3 pit emptying teams allowing them to gain more net income from emptying a pit.

The barrel lifting device when disassembled 

We are currently testing the barrel lifting device prototype evaluating its ease of assembly and disassembly, lifting capabilities and usability for the pit emptying operators. It’s evident that the lifting arm of the device is heavy due to the weight in which it has to lift. Additionally, a driver to reverse a pickup underneath the barrel once it is hoisted. Evaluating these challenges will enable us to refine the barrel lifter’s design such that it effectively reduces the logistics costs of a pit emptying operation and allows businesses to scale up.  

Sanitation technologies: Failing to reach the market

Water For People’s business development service, Captiva Africa, whose aim it is to catalyze investment in rural latrine construction through institutions such as FMI’s an SACCO’s, recently provided some valuable information on the challenges for latrine construction businesses. Poor road quality in rural Uganda means accessing some customer’s houses is impossible. To answer this, I developed another flat-pack latrine! Branded as the ‘Easy San’, this construction is made from metal poles, which result in a latrine frame when assembled. Wrapped around this frame, the latrine’s walls and roof are made from a single piece of PVC fabric. Transparent netting on three sides of the fabric provides light and ventilation. It’s assembly requires a low skill level. In fact, here’s a video of Richard and I constructing it in 6 minutes for World Toilet Day 2013: http://www.youtube.com/watch?v=Bsf7wkxADRc&feature=youtu.be. When disassembled, all the components can be carried on the back of a motorcycle taxi as shown below. Locally known as Boda-Bodas, these taxis are renowned for reaching the most remote stretches of Ugandan countryside, thus solving Captiva’s transport issue.

The initial prototype was designed and fabricated in partnership with Tent Deals, located in Kampala. Technically sound and made from modern materials, the technology could be viewed as aspirational to many locals. However, question marks remain over developing a sustainable supply and distribution chain to the rural markets. Materials such as PVC fabric are only available in Kampala, which becomes an issue when considering maintenance needs. Furthermore, previous WFP studies have shown that most households prefer a latrine with solid walls as it provides greater privacy to the user.

These indications have again shown that by developing a technically sound solution, you’ve only solved 20% of the problem. The other 80% is solved through developing business models, supply chains and a route to the market.

However, we haven’t given up on the Easy San yet. As you might have considered, considering its quick, simple assembly, it could be applicable for a disaster or aid relief situation. We are currently in contact with Oxfam, who we hope will show an interest in the technology.

Latrine Rehabilitation Businesses

Pour flush latrines have many benefits over a dry pit latrine. These include a facility that is cleaner and has no smell or flies due to a water seal. A sealed, offset pit not only improves pit access, but also ensures no rubbish can enter the pit, thus allowing the pit to be emptied with ease. A tiled finish on top of the floor slab improves hygiene and cleanliness, resulting in more desirable facility that is currently unavailable in Kampala.

These benefits come at little added cost when compared to a dry pit latrine, however, with access to capital an issue for many potential customers, a cheaper option would be to rehabilitate their existing facility rather than building a new one. What this means is that the existing superstructure and slab remain, however another pit is dug beside the facility, in which waste is delivered from the pour flush system through pipework.

Figure: A full pit latrine before (left) and after (right) the renovation. Note the pour flush system, lined pit, and vertical soak away.

Recent innovations in pit design have also resulted in improved pit performance and life span. Two such innovations will also be used as selling points for a latrine renovation service. The first is to maintain the desired volume of the pit (m³), while increasing its surface area (m²) and therefore aspect ratio. This increases the contact area between the sludge and soil, and thus the flow rate of effluent that can percolate through the soil, which, in theory reduces the pit fill up rate. The second innovation is a vertical soak away - inserted into an augured hole at the base of the pit. The soak away is made from gravel packed PVC pipe, which is scarfed below the base of the pit to allow effluent to leach into the surrounding soil once the pit is almost full. This innovation saves on the cost and space required for constructing a separate soak away, and again increases the life span of the pit.

Figures 2 & 3: Model of the latrine slab before and after the upgrade

The feasibility and acceptability of this renovation is currently being tested in an unplanned settlement in Kampala, locally known as Natete. A local mason named Lawrence has been recruited, and several sites have been identified for testing. The community chairman has also shown enthusiasm for the technology and has promised to promote Lawrence’s new business opportunity, should our testing prove successful.

Several challenges have arisen in testing site one. Because the constrained site is located in a densely populated unplanned area, removing the soil from the freshly dug pit and transporting it out of the neighbourhood has proved costly. Secondly, the business model requires a highly skilled mason due to the technical challenges which can vary from site to site. Testing site number two is located in a flood prone area of Natete, meaning the pit will have to be plastered and arranged differently to prevent faecal matter from escaping into the environment. This will make the renovation more expensive, but hopefully still affordable for the low-income households it aims to benefit.

Update on the Dura-San

By minimising the skill level required for latrine construction, the Dura-San is a complete pour-flush latrine package that allows customers to assemble their product much like a kit of Lego. No longer reliant on the long-exhausted mason led approach to latrine construction, this innovation is comprised of interlocking, pre-cast concrete components, resulting in a quick, simple assembly process in which the final quality is guaranteed. The standardised manufacturing process makes for an attractive investment for entrepreneurs, while customers feel more comfortable purchasing a brand of toilet that is clean, affordable, long lasting, and a stress free investment.

Since constructing the first prototype in October, some final technical issues have been solved and we are now ready to push the Dura San into the urban markets alongside Water For People's business development service providers. The better understand bottlenecks in the construction process,  the Dura San will be built for our 10 tiger toilets.

Without compromising on the fundamental concepts behind this innovation, we've added a pour flush option, which comes at little added cost. A pour flush is water borne, so is much cleaner, as well as being odour and fly free. We've decided to use the system that was testing during our fake poo flushing experiments. We've also added a pitch to the roof to improve its aesthetic appeal, while developing a pre fabricated door and frame with a sub-contractor who works locally to our first latrine making factory in Kampala - TurnKey Industries. Finally, like any innovative new product, branding and communication material is necessary to share the benefits of the Dura San. The following images were created by Josh Bellman - an architect I studied with at Bath University.

Figure 2: Pour Flush System is also mortarless

Figure 3: Close up of the latrine's interlock concrete blocks which provide it's strength

Figure 4: Exploded diagram of the entire latrine

Figure 5: Section