A “classic” publication on sludge treatment is: US EPA Sludge Treatment and Disposal, 1979, 1152pp, and is available at:
yosemite.epa.gov/water/owrccatalog.nsf/9...07248af!OpenDocument

European Environment Agency also has an interesting publication on sludge treatment. The publication is titled: Sludge Treatment and Disposal - Management Approaches and Experiences. The publication is available at: www.eea.europa.eu/publications/GH-10-97-106-EN-C/download

Quite often, in developing countries, the industrial wastewater goes into the municipal sewer system. There is, therefore, a mix of wastewaters – municipal and industrial. Sludge produced, as a result, is biological sludge and chemical sludge. This may not be the case in developed countries.

While, large land requirements for sludge treatment (sludge lagoons and sludge drying beds) can be met in the rural and peri-urban areas of developing countries, urban areas present a difficult scenario.


F H Mughal

Dear Choudhury
My first reaction is - why lime is used in the first tank? It will definitely reduce or eliminate pathogens from septage depending on the pH raised of septage. Once it is made bacteria free, the question is how supernatant will be treated through any biological treatment system because it will have same pH. Further, cost of lime for 200 cum septage per day will be too high. It also mentions that disinfection of treated effluent will be done before disposal.
You are right that BOD of supernatant will be more than 1000 ppm. Septage is hudrophilic in nature. Therefore, it may take long time to get clear supernatant. Activated sludge process may not work for such high BOD with intermittent loading rate.BOD of final effluent may not meet the norms of discharge.
regards
Pawan

Following a recent directive of the Govt. of India, septage management systems has been initiated in different cities of India. In this connection, recently I came across a proposal for treatment of Septage for a small mountainous city, Kohima in North Eastern India. The proposal is for a separate treatment plant for septage comprising a collection tank with lime dosing arrangement, grit chamber and a holding tank with dosing system followed by gravity thickener with sludge dewatering system. The supernatant from the thickener and sludge dewatering system receives secondary treatment in typical activated sludge process comprising aeration tank and secondary clarifier and disinfection before disposal


The capacity of the septage treatment plant has been considered 200 m3/d. But the number of collection vehicles is only 19, each of capacity 3 m3.

Even for a capacity of 200 m3, is this kind of conventional activated sludge type of treatment for the supernatant very effective ? The supernatant is expected to have a BOD5 in the range of 1000- 1500 mg/l. I feel the cesspool tankers will empty at different times in the day and even with a holding tannk maitiaining a steady flow for 16-20 hours will be tough. Typical activated sludge system may not respond well to intermittent flow with high BOD load.


Just another question, what if the supernatant from the gravity thickener is treated in a ABR (Anerobic baffled Reactor) followed by sand filters

This is my first post in this community. Looking forward to get enlightened.

Hi Elisabeth,
Many thanks for the assistance. I was not sure if I needed to seek approval from the BMG Foundation before release of the document.

Cheers,
Peter

The study that Peter Ho mentioned in his post above (9 July, 9:55) resulted in a document that you can download here from the SuSanA library:
susana.org/lang-en/library?view=ccbktypeitem&type=2&id=1670

Ho, P. Y. C., Teh, T. H., Zakaria, M. Y., Lean, C. L., Tan, S. H., Sasidharan, V. (2011). Landscape analysis and business model assessment in faecal sludge management: extraction and transportation model in Malaysia - Final report. Consultancy report by ERE Consulting Group in collaboration with INDAH Water Konsortium (IWK) commissioned by Bill & Melinda Gates Foundation, Seattle, USA.

Regards,
Elisabeth

Hi Chris,
The bags are made of geosynthetic material not unlike those used in landfill construction. Trails on the material type is best done to determine the appropriate pore size for the bag.
The bags are used once and after sufficient drying out (between 20-30% solids), the whole bag can be disposed or cut and sludge removed for disposal or possibly composting.
No, the bags are not made of biodegradable fibres but is a useful consideration for future trials.

Hi Christoph,
a) The sludge was that from on-site sanitation systems (OSS) such as septic tanks and pour flush systems. In a way these are partly stabilised due to the period over which they accumulate in the systems. Yes, I believe the inner part of the bag will be anaerobic but odour was not an issue from the bag.
b) Overall operational cost using the bag was estimated to be reduced by some 37% and this included disposal cost to a landfill.
c) Sludge collected by vacuum trucks was directly pumped from the truck into an acceptance hose connected to the bag. The bags are porous of geosynthetic material and the normal pressure during pumping is not an issue.

Hi Christoph, Pawan, Chris,
A bit of introduction. I am an environmental consultant with interest in waste management solutions especially in septage sludge and animal waste. I was involved in a project involving 5 Asian countries sponsored by the Bill & Melinda Gates Foundation some 3 years ago on faecal sludge management (susana.org/lang-en/library?view=ccbktypeitem&type=2&id=1670). The study was undertaken in collaboration with IWK, the national sewerage services company responsible for sewerage operation and maintenance. One aspect which we examined was a relatively low cost and easy method for reception and treatment of sludge generated from on-site treatment systems in rural areas. The purpose was to find an alternative to centralised mechanical facilities to improve truck performance and increase revenue. Geobags installed in smaller sewage treatment plants at strategic locations improved overall truck performance by reducing truck travel distances and improved truck turn around. The increase in revenue enhanced the viability of operators (especially smaller ones) engaged in FSM. Compared to traditional centralised treatment and disposal methods, operational cost could be reduced by as much as 37% using Geobags.

Peter

In practice, the option of sludge drying beds which are located sufficiently far from the residential area, but with some treatment of the filtrate either by a sand filter or reed bed, is an acceptable option at low cost. Sludge lagoons may also be considered, although these may be costly to empty when they are eventually full. The environmentally friendly options described by Canaday and others are desirable, but you must then ensure that you have an on-going and reliable maintenance programme associated with it. The 3 year emptying cycle of septic tanks is about right - provided the septic tanks have been correctly sized. For some larger families more frequent emptying may be required (if not there may be carry-over into their sub-surface drain and ultimately block the soil pores).

Dear Peter,

These cloth bags also seem like an interesting option.
Please give us more info on the type of cloth they are made of.
Are they never emptied and used again?
If they are used only once, are they ever made of biodegradable fibers?

Please tell us more about yourself and your work. It seems you have great experience.

Best wishes,
Chris Canaday

Dear Upasana,

Welcome to the Forum. Please tell us more about yourself and the conditions in your city.

There are a number of good options for treating sludge in this excellent compendium from EAWAG:
www.eawag.ch/forschung/sandec/publikatio...ompendium_e/index_EN

It seems that a number of technologies could be applied in series:
(1) UASB (Upflow Anaerobic Sludge Blanket) and/or ABR (Anaerobic Baffled Reactor) to get as much of the solids out of the water and convert theses solids into biogas for some productive use.
(2) The clarified yet still contaminated water could go through Vegetated Sand Filters (such as Subsurface Vertical-flow Artificial Wetlands). Final effluent can be used for irrigation or industrial uses.
(3) Excess sludge periodically removed from #1 could go into Vegetated Drying Beds planted with grass that will produce adventitious roots into the new sludge, thus helping to oxygenate it, plus the grass will physically block movement of wind to control smell and transport of dust. These would have a layer of sand in the bottom and a network of drainpipes to send excess water to #2. When these fill to near the level of their dikes, they can be rested for a prudent amount of time, excavated to the layer of sand, and the soil removed can be used in agriculture, reforestation, or landscaping. Grass can be harvested from both #2 and #3 to feed cattle and other animals.

Sludge could go directly to #3, but I think it is worthwhile to extract biogas in #1 to generate this energetic resource and to reduce Greenhouse Gas Emissions.

(It would be excellent if a percentage of the population could adopt Urine-diverting Dry Toilets, UDDTs, and thus avoid producing so much septage.)

Best wishes,
Chris Canaday

Dear Peter

May like to give details of the cost of such bag and process of filling. Disposal of such bags is itself another problem. Land filling does not appear a practical solution. Similarly composting of such large size bag ( even after pulverization) is not a easy job.
You may like to highlight on these issues based on your experience.

Regards

Pawan