I am currently doing some research to quantify mass flows (N, P, H2O and TS as an indicator for organics and energy) in a broad range of sanitation system options considering novel technologies. The LaDePa is one of these novel technologies.
there are some information from my conversation with Rein Buisman, the owner of the company who manufactures Ladepa plants (PSS Technologies) and Santiago Septien from the Unviersity of KZN that might be interesting for others:

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Under the typical operating conditions, the faecal sludge is fed into the LaDePa at a mass flowrate of 1000 kg per hour, from which approximately 150 kg/h of detritus are removed prior to the drying zone. Therefore, approximately 850 kg/hour of sludge at a moisture content of 75 -80% are dried up to a moisture content of 15-20%, leading to a mass flowrate of 300 kg/h of dried sludge. I have attached into this email a document with the technical details of the operation of the LaDePa.

According to my investigations in a laboratory-scale prototype, the nutrient and ash content are not affected during the process, which suggests that the LaDePa process only affects the moisture content of the solid by leading to its evaporation (which is the objective of the LaDePa), but does not influence the composition of the dried material. I had an oral presentation in the WEDC conference about this investigation.

At 80-85% moisture content (typical initial value of the faecal sludge from VIP latrines in Durban), the sludge contains considerable amounts of water (4 – 5.7 0.2/g of water per g of dry solid). However, when the sludge is dried up to 20-25%, the moisture in the material is very low (~0.3 g of moisture per g of dry solid). At this dryness level, the moisture should be quite bounded to the material, so it is hardly available for transfer to the environment. So, I think that the moisture in the sludge won’t have an effect in the growth of crops if the dried pellets are used in agriculture. However, I am not at all,a specialist in agriculture so I suggest to seek for a second opinion. I have added Dr. Alfred Odindo in the Cc list. He is a partner of our research group, specialist in agriculture, who has already performed agriculture trials of the LaDePa pellets. So you can contact him for all your questions regarding the use of pellets in agriculture.

The pellets have great potential to be used as a biofuel (calorific value of 17 MJ/kg, similar to the value of wood), but this option has not be considered by the municipality so far.

the inputs of the LaDePa are transported stabilized sludge with trash;
the outputs of the LaDePa are trash (for landfill) and dried faecal sludge pellets (agricultural product);
not all the moisture from the sludge is lost in the air (there is still remaining around 0.2-0.25 g of water inside 1 g of sludge);

Ladepa in extruded form evaporates 3.0 -3.2 litres of water /kWatt hr input at 20 % solids
The new improvements will save 25-30 % on electricity

We discharge at 80 % solids when the product is basically dry .

That is better than any technology available on the market
And more affordable than anything available on the market .
It is simple and unskilled operators can run it .

Using ECO add-on the Ladepa technology is totally self-sustainable .
More than that it produces a High Carbon organic fertiliser.

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Based on these information, I have defined the LaDePa as follows for my model:

Inputs	Outputs
transported sludge, transported stabilized sludge, transported pithumus, trash	trash (for landfill), dried faecal sludge pellets (agricultural product or biofuel)
OR	AND

Transfer coefficients

total phosphorus (TP):	1% to the air, 99% to pellets, with an uncertainty range of 10%
total nitrogen (TN):	1% to the air, 99% to pellets, with an uncertainty range of 10%
water (H2O):	77.5% to air, 22.5% to pellets, with an uncertainty range of 10%
total solids (TS):	1% to the air, 99% to pellets, with an uncertainty range of 10%

I also quantified some appropriateness attributes of the technology including energy requirements, water requirements, operation and maintenance requirements, design and construction skills requirements, etc. I am not posting all the details here, but please feel free to contact me if you are interested in my definitions...

Cheers, Dorothee

hello eThekwini, hi Dave,

as indicated in my post of May I would like to know how the LaDePa is going during its normal operations with advantages and disadvantages.

It also looks to me that the machine is only operated sporadically because the pits are emptied in one go every few years? Like they fill up over 5 years and then there is a contract to empty them over the course of two years, is that correct? In between the machine is not being used?

If so, would it not be more economical to have a smaller machine, operate it (almost) continuously while also the emptying process is ongoing without break?

ciao
Hajo

Thanks for this clarification on the solid waste issue, John.


Meanwhile, I received another update about the situation with the LaDePa plant in Durban. This one came from Rein Buisman, the owner of the company who manufactures Ladepa plants (PSS Technologies):

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We received the order in November 2015 for the lease of 3 Ladepa plants .

We have been battling to get finance , because we are a small company.
And No commercial Bank wants to finance any project for a Municipality in South Africa .

And we now after 17 months due diligence finally have the loan approval , but with lots of conditions .
So I am still not sure when we get the funds ( Eur 800,000) to build the 3 plants

Our agent in Finland is more successful in that they get Government assistance
The first Ladepa is to go into the WWTW in the town of Puumela

The test work they have done on the 600 mm wide small production unit is extremely promising in that they managed to cut the power consumption in half.

Tomorrow I am in Durban , as DEM wants the Tongaat machine modified and re –commissioned

Rein Buisman
Director
PSS Technologies (Pty) Ltd
www.parsep.co.za/index.html

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Thanks for this update Rein!
We hold our breath to see how this drama unfolds! Upscaling is so much harder than it seems at first, even with a technology that seems to make so much sense such as this one.

Regards,
Elisabeth

Hi Elisabeth,
Considering that the garbage was mixed in with fecal sludge, the was concern was for anyone coming into contact with the detritus once separated. (Some countries do not secure dump/landfill sites and informal workers scavenging would come into contact with potentially dangerous pathogens.)
In July I had the chance to meet Teddy Gounden (e Thekwini Municipality) at the AGUASAN workshop on Circular Economy in Switzerland. He said that waste sites are secured--reducing the chance of detritus coming into contact with people. We agreed that this should be a requirement for any city considering LaDePa technology.
Best regards
John

Just a little update on the LaDePa machine in Durban:

I have been told that "there has been a delay in procurement for various reasons but that we should be on track in September".

Regards,
Elisabeth

Dear Hajo,

Good questions! I would also like to know about an update.
Just letting you know that I've e-mailed some people in the background in May. So far no luck. I was told by Santiago Septien that the main responsible for the LaDePa plant is Dave Wilson. I've just sent him another e-mail now. So I hope we'll soon hear something either from Dave or from someone else from Durban.

John: as far as I know the garbage that was separated out just goes to landfill. What kind of special treatment would you have in mind or why? Are you thinking of incineration?

Regards,
Elisabeth

This has been an interesting and inspiring project/post to follow!
About the step where the solid garbage/detritus is separated from the fecal sludge (before the sludge is processed into pellets): What happens to the detritus separated out in the screw conveyor? Does it receive special treatment or go to a special landfill? I was concerned about those who work in informal sector waste recycling.

Thank you
John Brogan
Terre des hommes

Hi all,
hello eThekwini!

it's almost two years that I posted under this thread and nothing has happened since then... how comes? I still believe that the LaDePa can be a useful tool in peri-urban FSM (OSS sanitation chains) and therefore I like to know what the current status is of its use in eThekwini.

Is there anybody in eThekwini who is willing and has the time to give us on this forum an overview of the current use of the LaDePa? What are technical, organisational and financial successes and shortcomings of its daily operation over the last two years out of the perspective of eThekwini?

It was reported in 2015 that eThekwini is about to tender a further management contract for the emptying of the 35,000 pit latrines and the possible lease of 3 more LaDePas to treat the FS from those pit latrines. Can you report on the progress of that activity?

Looking forward to hear from eThekwini,
ciao Hajo

Dear Rein (PSS),
dear John (eThekwini),

you have been pressured by Elisabeth to answer all my questions and when you do, I do not even acknowledge your efforts. SORRY! for that and thank you very much for your comprehensive replies. They had not been forgotten: the alert by SuSanA Forum has been resting in my Intray since May. And I hope very much that once I will be able to make good use of your valuable information.

As we try to promote sanitation governance and activities in Moshi/Tanzania, we face a bunch of problems:

1. sanitation has low priority with politicians, administrators and customers alike;
2. although about 60% of the peri-/urban population depend on pit latrines in Moshi;
3. no formal service chains exist for empying those pits;
4. also because emptying of pits is a hazardous job from pits which are not made and not meant to be emptied;
5. building as well as O&M of household latrines in Tanzania is defined as 'private business' by GoT and no donor/financier/business will put money into developing service chains,... not yet .

Although I am quite convinced that the LaDePa is a good answer to the processing of faecal sludge from pits, we first need to find ways to empty pits regularly at large scale to justfy the installation of such machine.

I hope we will some day have reason to come back to you for more information and how to lease/procure a LaDePa...

ciao Hajo

Dear everyone,

I attach here the poster presented during the Conference FSM3, which presents the results obtained in a laboratory-scale LaDePa machine from the Pollution Research Group of the University of KwaZulu-Natal,in Durban, South Africa. These results include: drying kinetics and faecal sludge composition as a function of the MIR emitter intensity; the pasteurization extent concerning Ascaris eggs, as a function of the MIR emitter intensity; the thermal properties (calorific value), chemical composition (P,K) of the the dried sludge in order to evaluate its potential use as a fertilizer or biofuel.

Kindly,
Santiago

Hi Hajo

Sorry about the delay in my response. I was very nervous about answering some of the questions as there are a number of students doing post graduate work very closely aligned to the answers to some of the question that were asked and I did not want to publish things that they were about to publish. So I just needed to clear with them first. There was also a minor issue that I am still chasing deadlines. So please accept my apologies.

1) Emptying pits free of charge every 5 years (or whatever) is beyond the finance and the sanitation policy in Tanzania. But people are used to pay for the emptying, thus an improved service will be appreciated and hopefully paid.

This is a comment more than a question and I have no experience in Tanzania so cannot comment further, except to say that Ladepa is not financially self-sustaining. By this I mean that the income from the sale of the product does not cover the cost of the operation of the machine, let alone the cost of emptying the pits. The Ladepa has a positive balance in the case of eThekwini and most of the cities in South Africa, because the alternative legal disposal method is to a hazardous land fill site. There are very few of these in the country and the cost of transport and disposal to landfill, consequently makes the Ladepa viable.

2) You say EWS owns one LADEPA and leases three more. In your Hanoi presentation you quoted the price of a 2000 m3/year plant at 6.5 million ZAR (about 550,000 USD). Is that still valid about? 2000 m3 stands for 2000 m3 sludge input into LADEPA? How many kg is that?

3) Since lease and maintenance by PSS would be not possible for Tanzania (or?) we would have to find other ways for maintenance. Also in Moshi neither municipality nor utility would be able to maintain the plant.

These two questions are best answered by PSSH, who I asked to make comment on but have not followed up to see if it was done. However the maintenance in general is not difficult, but certain spares would need to be held in stock in Tanzania. If there are a few Ladepas then the cost of holding stock can be shared, which is one of the reason that we chose to lease from PSSH, so that they would be responsible for holding the stock which cost they can off -set if they get more customers.

4) You are lucky in SA that you can tender out a management contract for pit emptying and LADEPA operation. In Tanzania we probably will have to consider an additional capacity development plan for such contractor. But that should not be an obstacle. I guess PSS would also provide O&M training?

The operation of the ladepa Plant is very simple for anyone with an aptitude for operating mechanical plant. PSSH is going to provide training for our pit emptying management contractor.

5) You differentiate 'wet' and 'dry' pits. Do you envisage problems that some pits may be too dry to be pumped, but at the same time still too wet to go into the LADEPA. Do you have figures to judge which sludge can still be pumped, and what maximum moisture content is acceptable for the LADEPA process?

6) The previous question is also of interest because we had discussed to moisture/dilute the sludge to make it 'pumpable' which may then prohibit its LADEPA processing.

Here in eThekwini we generally have a very strong binary system, in that the VIP sludge is either "wet" or "dry". The "dry" sludge is stiff enough to form "spaghetti" on extrusion through the ports in the barrel of the screw conveyor. These spaghettis form an open voided matrix when it falls onto the belt. These voids allow the air to pass through the pile; this is the deciding factor as to whether it can be treated through a Ladepa Plant. (Wet sludge forms a "cow pat" that does not hold up in a form with voids when it falls onto the belt).

As far as the moisture contents are concerned we generally operate on visual triggers as to whether an open voided matrix will be achieved, and because of the clear distinction between wet and dry sludge it is generally clear which sludge can be treated by the Ladepa and which cannot. Whether a sludge is too dry or not is a far more difficult question and is generally based on what you are prepared to live with.

If the sludge is too dry, there is not a good separation between the detritus and the sludge and the dryer the sludge the more sludge passes through the barrel of the extruder with the detritus, hence my remark about what you are prepared to live with. We have only found the phenomenon of sludge being too dry, on sludge that has been left in the open and has air-dried to a degree. Sludge coming out of the pits and then directly into the machine does not seem to have this problem.

Chris Buckley and his team are busy with a report to our Water Research Commission on trying to determine the moisture content relative to the rheology of the sludge, so I will wait until that is published before commenting on the moisture content. But again based on my experience of the behaviour of wastewater sludge I would guess that the lower solids limit of what can be treated through a Ladepa would be about 22% solids.

As far as pumping is concerned that is an open question and it depends on what sort of pumps are being used. I have seen peristaltic pumps pumping 16% solids waste activated sludge, thickened in a centrifuge with a heavy dose of polyelectrolyte. The problem though is getting the sludge into the pump, because it is well into the sticky phase by then. From Ladepa perspective, as a general rule, if you are able to pump then it is probably too wet for Ladepa.

With regards to the clear distinction between wet and dry sludge, Lungi Zuma and Chris Buckley pointed out is that they have found two different types of "wet" VIPs, the "crust-liquid-settled solids" type and a type where the "liquid" forms pockets or lenses within the more dense sludge.

I have untested hypothesis as to why there is distinct separation between "wet" and "dry" pits based on the mass balance and movement of the liquid into and out of pit. (For simplification of explanation, we can exclude the liquid lost through evaporation). The rate that water leaves the pit is governed by the product of the transmission rate through the wetted surface, and the area of the wetted surface. (This implies that the transmission rate through the surface is rate limiting as opposed to the rate through the soil being rate limiting).

If one considers the situation of water flowing into an empty pit, there is an automatic system of adjustment in that if the water is flowing into the pit faster than the rate that it is currently flowing out of the pit, the level of water in the pit will rise. This will increase the wetted surface area until such time that the product of the surface area and the rate of transmission through the wetted surface matches the inflow rate, (and vice versa, if there is a net loss of moisture).

If we now consider the same inflow rate but in the case where a pit is filled with sludge to a level above that of the level that the water would have risen to in the equilibrium state. In this situation there is more wetted surface area than the inflow rate requires, that is, there is potentially a net outflow of water from the pit or a net drying effect. Now the rate limiting factor is the rate that the water can be transmitted to the wetted surface. In most pits a "conical" top surface forms which moves the water to the sides of the pit. The water will then flow down the path of least resistance between the sludge and pit side, the soil and the sludge.

In most cases, I suspect that the line of most resistance is sludge and consequently the rate at which water ingresses into the sludge is far lower than it will move away from the interface. The time scale between wetting incidents and the relative rate of transmission of water into soil compared to the rate the water moves into the sludge is such that we land up with a "dry" sludge.

"Wet" pits occur when the rate of inflow is greater than the outflow, and this occurs when either there is very low permeability in the soil or the pit walls are blinded or when excessive amounts of water are being added to the pit (when people are bathing in the toilets and discharging wastewater into the pit).

Theoretically, one could find a situation where the sludge layer is exactly equal to the level that the water would rise to if the pit was in equilibrium, in which case the sludge may be somewhere in between "wet" and "dry", but the chances of obtaining this situation is remote particularly at the stage when people come to empty the pits.

7) Who is going to market the pellets, EWS or contractor? Do you have a possible sales price / market value from your previous production?

At the moment we are not marketing the product, we are giving it to our parks department who are passing it on to their community gardens section, we sometimes get a gratuity from the parks department as it reduces their fertiliser costs. However, this is an interesting questions with many facets which we, the Engineering profession, are unable to answer. The accountants do not want sludge as it is a liability to them, however the moment this sludge is converted to a marketable product it becomes an asset to them. In terms of the Municipal Finance Management Act, the disposal of Municipal assets need to be done by public tender. However the question is who does the asset belong to? Does it belong to the Municipality who paid for its conversion, the community who produced the sludge or the owner of the technology that converts the waste into the asset? PSSH have a vested interest in how the product is marketed as this affects their Ladepa machine market. Fortunately it is not my problem.

I think this answers the question as best I can.

Regards John

Hi Hajo,

I lost my computer through an encrypting virus and with it somehow also the SuSanA mails and contacts.

I am getting back on track.

We build Ladepa plants although to date we have spent much of our time developing and testing the technology.

The Ladepa (Latrine Dehydration and Pasteurization) can accept sludges from between 16 – 35 % solids. If less than 16 % the extrusions become too wet and clog the belt and “wet” extrusions reform into a wet “pudding” which does not allow air through and so prevent the sludge from drying.

If too dry the extruder may have problems extruding.

The art is to form a layer of extrusions which allow air to pass between the extrusions to remove evaporated water.



We build Ladepa plants to requirements.

If you could give me an idea of volumes or kilograms then I can make a proposal (for sludge we generally work on 1 litre = 1 kilogram).

The Ladepa has standard belt widths 250 – 600 – 950- 1400 – 1900 – 2500 – 3000 mm.
We build in any length with multiples of arrays. No need to operate all arrays. You use as required and switch off some arrays when there is less product.

If the sludge is very wet I would suggest to place the sludge for a period in paddock until the consistency is better 25 – 30 % solids is ideal, and allows better belt loading.

Generally you can work on 3.0 – 3.5 litre of water evaporation/ kWatt hr. This way you can determine on how many kWatt/hr you need and we can then also size a Ladepa plant.

If you are paid for emptying latrines and you get an off take for the dried product then generally the operation pays for itself on a double shift and a profit on a 24/7 operation.
As for maintenance, we have dryers in operation in the DRC, Angola, Kazakhstan and very remote areas.

Maintenance is very simple and only requires a semi-skilled employee.

The wear items are the extruder flight and housing – extrusion head. Life ± 1 – 2 years, depending on the presence of detritus and abrasive sands/glass etc.

The belt life is 3- 5 years, balance is pulleys and bearings.


Power can be through a Genset and/or network. In future probably direct gas to MIR as well.

I trust I have answered most questions.

Regards
REIN BUISMAN
Director
Particle Separation Systems Holding (Pty) Ltd