Dr Karki and Dr. Gautam

Since the first few questions were asked on 3rd of April (the first day of the discussion) on material flows, and after 3 weeks...I find that I still dont have the full information on the material flows for solids and liquids.

Take for example the information related on the material flow of solids. We know that the material flow of solids determines the engineering design of the system as it determines the size of the digester you need to build and the size of the compost pits. I presume you have done this. Yet, you use the future tense in your responses which gives me the feeling that you never did determine the material flow of solids and that you just used a blind model from Bangladesh.

In your paper, you wrote:
>The community latrine was put for common use with effect from
>15 March 1998........(cut)......
>From 285 latrine visitors, about 115 kg of human excreta is available
>per day as raw materials for feeding the biodigester
>(0.4 kg of faeces per person).

On April 13th, you responded:
>....when first pit is completely filled in with slurry and vegetable
materials,
>it is left for about 3 months for decomposing and drying.Then, the same
>process would be continued in the second pit.
>.....(cut).....
>The daily output of the digested faecal material (solid) is expected to be
>about 50 kg/day. With the daily addition of 400 kg. of dried vegetable
>materials, about 100 metric tons of the matured compost is expected to be
>produced per annum for use  as organic fertilizer.

On 20 April, you provided the following information for the liquid flow:
>About 180 litre of water is added daily to the digester. Furthermore, some
>liquid (not all) is added from the urine which can roughly be about 50
>litre . Thus, the total daily input of the liquid would be around 230
>litre/day.  When mixed with vegetable materials, about 50% liquid effluent
>will be absorbed by the dried plant materials used for composting.

On 20 April, you provided the following information for the solid flow:
>Let us calculate the whole thing as follows:
>
>Production of slurry/effluent per day = 80 kg day
>Addition of vegetable materials         = 400 kg/day
>Total materials for composting per day = 80 kg + 400 kg = 480 kg/day
>Total quantity of materials (slurry & vegetable materials) for composting
>per year = 175 Metric ton
>Assuming that about 40 percent volume will be reduced when the compost
>will get matured, roughly 100 metric tons of the matured compost will be
>available for use as fertilizer. Out of this amount of  fertilizer, the
watchman
>uses only a small fraction, say about 10% and 90% is supposed to be
>distributed to the farming community for fertilizing their soils.

1) >Production of slurry/effluent per day = 80 kg day
I presume this is the solids (not the effluent or slurry)

but on 13 April, you quoted the figure as:
>The daily output of the digested faecal material (solid) is expected to be
>about 50 kg/day.

Whatever the number maybe, I presume that these numbers are just estimated.
Q: have the actual weighting of the wet weight of separated solids being made ?

Q: since 15 March 1998, how many times have the compost pit being emptied ?
Q: how many m3 of compost is available in the 18 m3 compost pit each time ?

if you have only 2 compost pits, and if the materials are left for about 3 months for decomposing and drying,  it means that the other compost pit (18 m3) that is in use must to accept 3 months of effluent from the digester. If  250 litres effluent and 400 kg of plant biomass are used per day, then

250 litres effluent X 90 days = 22,500 litres.
400 kg plant material X 90 days = 36,000 kg

Q: can these materials be accomodated over the 3 months in one compost pit?

You wrote:
>about 50% liquid effluent
>will be absorbed by the dried plant materials used for composting.

Q: what happened to the oter 50 % of the digested slurry ?

On 20 April you wrote regarding water consumption:
>Assuming that on an average 300 people visit the latrine every day
>and they use 0.5 litre water for anal cleaning, it would amount to 150
>litre of water per day. However, some amount of additional water is
>required for the general cleaning of the latrine which is estimated to be
>about 30 litres. Thus, about 180 litre of water is added daily to the
>digester.
>
>About 250 litre of effluent (slurry) is expected to be produced per
>day from the digester.

if the water consumption is 150 litres, then urine would be 70 litres (or
an average of 233 ml per person).

Q: what is the hydraulic retention time for the digester then ?

regards
jacky