Rate of filtration of septage through sand filter beds and technology for septage management

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Rate of filtration of septage through sand filter beds and technology for septage management

Dear All
For designing a sand filter bed for septage* management rate of filtration is an important aspect. If any professional has such data on septage management through sand filter beds and other technologies, may kindly inform.
regards
pawan



* Note by moderator (EvM): We have discussed in great length what the definition of the term "septage" is here: forum.susana.org/forum/categories/53-fae...onfusing-terminology
If I understand Pawan right, he meant the entire content of a septic tank when he spoke of "septage".

Pawan Jha
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Re: Rate of filtration of septage through sand filter beds and technology for septage management

Dear Pawan,

The filtration rates, depth of filter bed, effective size and uniformity coefficient of sand, depend on the objectives of filtration that are to be achieved.

On water treatment side, a filtration rate of 0.2 meters/hour will remove the microbial population. This is typical of slow sand filtration. If the filtration rate is increased to 5 cubic meters/sq. meter per hour, only turbidity will be removed. This is typical of rapid sand filtration.

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F H Mughal

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Re: Rate of filtration of septage through sand filter beds and technology for septage management

Dear Mughal and all

Thanks for your quick respond.
Objective of the filtration of septage is to minimize organic loads and use effluent for further treatment for its safe reuse in agriculture purpose and also use of dried solid sludge for agriculture purpose. Filtration rate of septage can’t be increased to 5 cum / m2 per hour through natural sand filtration. It is much slower than water filtration. Septage is hydrophilic in nature. My query is simple and straight. What is filtration rate of septage through natural sand filtration under gravity per square meter of sand filter bed per 24 hours or so?
Those who are involved in septage management through sand filter beds can provide data based on the their practical experience. Any published data on the aspect would be helpful to design such system.

pawan

Pawan Jha
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Re: Rate of filtration of septage through sand filter beds and technology for septage management

Dear Pawan,

the answer is very difficult for sandfilter for wastewater treatment as quality varies very much. Particularly I would not use sand filter as they will clogg always or you have to set up a maintenance cycle (for pealing of the surface).

I use always constructed wetlands. Attached you find the long version of an article from 97 (sorry – very old but still very valid and I use the findings until today almost unchanged)

Platzer, Chr. & Mauch, K. (1997). Soil Clogging in Vertical-flow Reed Beds - Mechanismns, Parameters, Consequences and ..... Solutions?. Wat. Sci. Tech. Vol 35, No. 5. pp 175-181.

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In the published version we had to cut out several general observations due to page limitations but it might be interesting for you the part around figure 1. Therefore I attached the long version which is not nicely corrected and everything perfect – please see the content not the form.

I do vertical flow wetlands (which would be somewhat close to your case) as a rule of thumb with less than 200 mm a day constant load in subtropical conditions. You could as well do 1000 mm in certain moments as the hydraulic capacity normally is not the limitation. Limitation is the pore clogging by biological activity over the time.
As explained in the article, resting periods help to restore hydraulic conductivity – but planted filters I guess not sand filters.

Working about infiltration with sand filters the publications of Bouwer, Rice et al (see literature) might be helpful as well but that is treated wastewater.

Hope that helps
Christoph
P.S. I forgot, pulse loading is absolutly crucial and intervals of rest and load as well

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Re: Rate of filtration of septage through sand filter beds and technology for septage management

Dear Chritoph

Thanks a lot for your inputs with posting a useful paper.
I am preparing a design for a sand filter bed with 200 mm coarse sand and 200 mm loading of septage per day. Bottom design of the filter bed is suitable for creating partial vacuum for high filtration rate. Hope it will solve the daily filtration of loaded septage. For precaution (in case of clogging)there would be up to 10 filter beds to be used in sequence. It will help sun dry of septage. However, it is not clear whether the designed filter bed area will be sufficient for filtration of septage volume taken up to 200 mm.
Filtered effluent will be treated through WSP or contact media anaerobic or aerobic methods for its safe reuse in agriculture.
Use of constructed wetlands for septage is more problematic for its reuse in agriculture purpose. Moreover, settle sludge remains a major problem to handle.
I would like to have any data / report on sand filtration system for septage.
regards

pawan

Pawan Jha
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Re: Rate of filtration of septage through sand filter beds and technology for septage management

Dear Pawan,
I did not get you right I guess.
Let me describe what I understood.
10 beds in parallel with 20 mm of coarse sand for a loading of 200 mm (in total?) per day of raw?? wastewater.
Followed by a WSP (don´t now what is that) or a anaerobic or aerobic filter.
Is that right?
I would do it the other way round in order to avoid clogging.
First a treatment and for helminth eggs in the end the filter beds. In this case these publications might be interesting - they are all older but valid:
BOUWER H.; RICE R.C.; LANCE, J.C. & GILBERT, R.G. (1980). Rapid-infiltration research at Flushing Meadows Projekt, Arizona. Journal Water Pollution Control Federation 52. 2457-2469.
BOUWER, H.; RICE, R. C. & ESCARCEGA, J. C. (1974). High-rate land treatment I: Infiltration and hydraulic aspects of the Flushing Meadows project. Journal Water Pollution Control Federation 52. 834-843.
ELLIS, K.V. & AYDIN, M.E. (1995). Penetration of solids and biological activity into slow sand filters. Water Research. 29. 1333-1341.
GUILLOTEAU, J. A.; LESAVRE, J.; LIENARD, A. & GENTY, P. (1993). Wastewater Treatment Over Sand Columns. in: Proceedings of the 2nd IAWQ Conference on Small Wastewater Treatment Plants. 28 - 30.06.1993, Trondheim. 153-160
GUPTA, R.P.& SWARTZENDRUBER, D. (1962). Septic tank effluent percolation through sands under laboratory conditions. Soil Science Soc. Americ. Proc. 26. 6-10.

best whishes
Christoph
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Re: Rate of filtration of septage through sand filter beds and technology for septage management

Dear Christoph
One filter bed will be designed for total loading of septage for one day. 10 filter beds will be used one after another. It will help Sun dry of solid part on sand filter beds. In case of high rain fall areas more filter beds will require. At present, there is no such data either of rate of filtration rate or Sun drying rate for septage.
Treatment of filtered waste water will be carried out through any technology- WSP ( Waste Stabilisation Pond)or other technologies. That's not a problem.
I'll go through the papers you have mentioned. Thanks for sending such relevant papers.

regards
pawan

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Re: Rate of filtration of septage through sand filter beds and technology for septage management

pkjha wrote: sand filter bed for septage management


Hi Pawan,

In drying beds, sludge is poured onto beds in batch loads. Liquids percolates through the sand bed while the thickened sludge dries on the surface until it is dry enough to be removed (and the beds can be loaded again). In that process, drying takes much longer than the percolation of the liquids. Thus factors for design are not the filtration rate but rather the drying rate of the sludge, which is determined by sludge characteristics and climatic conditions, thus very variable.

For guidance on design of drying beds for septage, I guess you should look for the Sandec sludge book, or american septage management literautre.

Best, Florian

Florian Klingel
Water and Sanitation Specialist at Skat Consulting Ltd.
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Re: Rate of filtration of septage through sand filter beds and technology for septage management

Dear Pawan,

I have not heard of using filter beds for septage treatment. In the wastewater plant that I designed back in 1982 (aerated lagoons) in Karachi, septage was mixed with raw wastewater, and the wastewater flowed through a series of unit treatment system - grit removal chambers, primary sedimentation tanks, aeration units, and secondary sedimentation tanks. The sludge from secondary sedimentation tanks was pumped to the sludge drying beds. The final treated effluent was used for irrigation, and the dried sludge was used as fertilizer and soil conditioner.

The objective that you mention: "Objective of the filtration of septage is to minimize organic loads and use effluent for further treatment for its safe reuse in agriculture purpose and also use of dried solid sludge for agriculture purpose,"
was fully satisfied - BOD and SS removals were more than 90 per cent.

Regards,

F H Mughal

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Re: Rate of filtration of septage through sand filter beds and technology for septage management

Dear Mudghal

Treatment of septage along with waste water in a STP is one option where such Sewage Treatment plants of required capacity are available. Main problem is for the areas where no centralised treatment facility is available - in most of the urban municipalities in developing countries.
For low income areas sand filter beds with or without plantation or constructed wetlands are sustainable.
A recently released book on Faecal Sludge Management by IWA mentions different technologies for FSM. I got proper answers of my queries.
regards
pawan

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Re: Rate of filtration of septage through sand filter beds and technology for septage management

Dear Pawan

The normal practice is to design sludge drying beds on the basis of the total solids loading. EAWAG suggest that the design loading figure should be 100 - 200kg total solids per square metre per year for hot countries, (as compared with 50kg TS/m2.yr for temperate countries. However, they quote actual loading rates of up to 300kg TS/m2.yr measured in some field investigations in West Africa. Books like Metcalf and Eddy and Crites and Tchobanoglous give similar figures. (The EAWAG book should be downloadable from www.sandec.ch/fsm_book . (See post by Linda Strande elsewhere on this forum)

For typical solids concentrations in the septage and assuming perhaps 70% of the sludge is liquid that percolates through the filter, the average filtration rate is likely to be of the order of 2 - 3 metres per year.

The normal recommendation is that the sludge is loaded to am initial depth of 200 - 300mm and the drying period is 10 -15 days. One interesting paper describes experimental work done in Sanaa, Yemen and suggests that shorter drying periods are possible (see iwtc.info/wp-content/uploads/2013/11/99.pdf ) but this is in a dry climate. Rain will certainly increase the drying time required. Most of the drying occurs during the first few days and the time required depends to a large extent on the final solids content required.

I can provide more detail but I think this covers the main points

Hope this helps

Kevin

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Re: Rate of filtration of septage through sand filter beds and technology for septage management

Dear all from my side!

I would agree with Christoph that constructed wetlands are more efficient in removing solids than sand filters (drying beds) at least in terms of area requirements. There is no time lost with dying of the solids, you can consistently load the wetlands, and there is not too much hassle with removing the solids. Pawan, you were arguing that sand beds are more efficient in removing pathogens - what evidence would there be for that claim?

As a little addition to this post: on the pic on the left you see me together with my friend Simon on the edge of an artificial wetland for sludge disposal, located in Adjumani, Uganda. We had (and still have) 3 small basins in parallel, for four truck loads each. I think we have never reached the limit of the capacity of these wetlands.

Kind regards,

H-A

Hanns-Andre Pitot
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