Anthony wrote: How can one flare a small quantity of biogas from a non-pressurised, sealed, ABR tank? Some kind of small pressure vessel would surely need to be added-on, with associated O&M complications (e.g. cleaning and removal of condensed water). Any thoughts on this..?

Well maybe there is some new biological treatment option upcoming (currently being researched) that utilizes dissolved methane to denitrify waste water. Sort of dual beneficial

It is based on a recently discovered quite unique bacterium that gets it's oxygen for metabolizing methane from NO3:
www.nature.com/news/2010/100324/full/news.2010.146.html

A potential application for low energy waste-water treatment is already being tested for example:
edepot.wur.nl/246167

I didn't look into it much yet, but it seems like a very interesting line of research for DEWATS systems. What is especially intriguing to me is the fact that these bacteria naturally live in a dense mud-layer, so maybe it is as simple as pumping faecal sludge under such a thick layer to create an anaerobic zone for methane production, which then raises to the top-layer and gets utilized directly by those special bacteria. Some sort of earlier aeration is probably still needed though, to oxidize some of the NH4 to NO3.

Edit: Also interesting: www.b-ware.eu/content/project/publicatie...icrobiology-2012.pdf
Maybe we will soon be constructing "Artificial Peatlands" instead of artificial wetlands

Thanks Florian and Detlef,

I undertook a BORDA-DEWATS consultancy here in Haiti in January 2013, we looked at the feasibility of pre-fab. fibre glass units in country, but this was unfeasible in the short-term. Perhaps this will be an option once DEWATS technologies become more established here.

To summarise your comments; if biogas capture and usage is required, then it is best to have a multi-stage DEWATS plant, with a biogas settler before an ABR. If not, then use an ABR only.
However, the question remains what to do with the biogas from the ABR (there will be some). If it is just vented to the atmosphere then this is an environmental negative (CH4 being more destructive than CO2). How can one flare a small quantity of biogas from a non-pressurised, sealed, ABR tank? Some kind of small pressure vessel would surely need to be added-on, with associated O&M complications (e.g. cleaning and removal of condensed water). Any thoughts on this..?

mfg,
Anthony.

AquaVerde wrote: I am not sure why this proper "multi-stage biogas plant" is only used as a wwtp after a less stable "single tank biogas plant". Florian do you know more about? I am guessing the reason is to simplify the whole DEWATS system and to have after biogas production a simple but stable COD reduction "only".

Yes, I think you're right with your last guess. It's mostly practical considerations I think: A fix-dome digester as first treatment unit is easy to make gas-tight and allows for storage of gas. Also in the first stage, most biogas can be harvested. The ABR afterwards serves for reducing COD in the effluent. If you'd want to capture biogas from all chambers of an ABR, you would need come up with a gas-tight sealing for the entire ABR, and you would need an external gas storage.

Dear Anthony and Florian,

In my opinion the DEWATS of BORDA are two biogas plants one after the other. The ABR by it self is basically a proper but simplified multi-stage biogas plant with permanent hydraulic mixing of substrate with very stable anaerobic phases. Because, in relation to the 4 phases: hydrolysis; fermentation; acetogene; methanogene, been more or less made to "work" separated one after another in each of the 4 ABR-compartments.

This intended separation by compartments creates stability and opportunities to steer via different geometry of cambers, pH's and temperature the whole process. E.g. giving to the first ABR-camber more volume will give more time to the hydrolysis. The following 3 phases will "work" better, See 2012 research from Malaysia: scialert.net/fulltext/?doi=jas.2012.2586.2591

I am not sure why this proper "multi-stage biogas plant" is only used as a wwtp after a less stable "single tank biogas plant". Florian do you know more about? I am guessing the reason is to simplify the whole DEWATS system and to have after biogas production a simple but stable COD reduction "only".

Anthony, as you are "in the field" you can not go for any researches on the ABRs, you need for sure a ready to implement system. I recommend the prefab biogas digester + ABR from BORDA to save time and have more assurances in quality management during construction and operation & maintenance.

All the Best
Detlef

Hi Anthony,

I think with strong wastewater from a school, you can produced biogas, yes. If it makes sense or not depends most of all if there is a use for the biogas. If the use of biogas brings a real benefit, e.g. saving of gas for cooking in the school's kitchen, than this may greatly enhance the acceptance and the care of the wastewater treatment facility.

Technically, you need to put a biogas digester as a first step before the ABR. The first large chamber of the ABR can then be reduced. I have no experience with operating such plants, but I assume that the O&M requirements would not need to be higher than in a classical ABR. Quanities of sludge to be extracted would be even less (mixing biogas digester as first unit), but the biogas piping, storage tanks etc. would probably need some regular checking and repairing.

Best, Florian

Hi Detlef,
I am in touch with BORDA.
Thats a nice informative piece from lesotho - thanks.
Anthony.

Dear Anthony,

I am not a BORDA-Engineer, but based on BORDA`s I design some ABRs adapted for our cold climate for COD reduction only, not for biogas production, using BORDAs Practical Guidebook (detailed manual) by Engineer SASSE (with detailed equations) 28 of 356 pages:
- www.borda-net.org/fileadmin/borda-net/ne..._Guidebook_small.pdf and
- www.borda-net.org/knowledge.html and
- www.borda-net.org/knowledge/biogas-handb...rum-back-issues.html
Important Remark on the older 1998 manual:
!!! Based on practical experiences the absolute maximum up-flow velocity should 1 m/h not any more 2 m/h, inside the reactor cambers!!!

BORDA offers prefab ABRs made from fiberglass, costs +/- 500 EUR/m3

You may contact BORDA in Latin America direct. www.borda-net.org/ I hope you get a response, as they are very busy.

As fare I understand, BORDA is using in very similar school settings around the world for biogas production standard dome shaped digester and treating the biogas effluent by ABR and planted gravel filter for COD reductions only.

Maybe in the meantime the GIZ-biogas review is helpful to you: www.sswm.info/sites/default/files/refere...gas%20sanitation.pdf

Further more you may go through a biogas case study on dome shaped digester with ABRs from Lesotho 2009: www.eawag.ch/forschung/sandec/publikatio.../dl/Mueller_2009.pdf

Good Luck with your plans, I am interested about your upcoming results on the ABRs.

All the Best

Detlef
MSc. Tropical Water Engineering

Dear SuSanA,

Does anyone have experience of DEWATS using ABR (Anaerobic Baffled Reactor) technology for the treatment of strong sewage from schools in the tropics? My project is for a school in Haiti, p.e. = 2,600. The toilet block flush is 'communal', hence the classification of the sewage strength as 'strong'.

If so, what are your experiences with biogas production - was there a useful quantity for the project site? was it put to some use? and did it add much to the operation and maintenance requirements for the ABR?

Many thanks,
Anthony.