Hi npopat,
thanks for your reply, this provides some clarity on the situation, but also more questions...

Is the intention to terminate the use of drainage channels as open sewers? I'm wondering if a compromise could be to instead intercept and digest solids at the boundary of each household? That is, the drains could form part of an aerobic "treatment" system... hardly ideal but the investment required for conveyance might best be diverted into basic hygiene measures like limiting the food source for flies and rodents?

Just as a follow-up to my earlier comment: gravity is not only useful for water based systems, but can also be utilized for ropeways to transport fecal sludge (and other goods).

See this interesting technical guideline on how such basic gravity run ropeways can be constructed:
answers.practicalaction.org/our-resource...ravity-goods-ropeway

Dean,

Thank you for your inputs on the discussion. Pl find my specific response against each in Red.

With hilly terrain gravity can be used to advantage for treatment systems requiring no energy input. I would suggest that the key sustainability objective is to avoid direct discharge of wastewater into waterways, and the other key sanitation objective would be to avoid direct community contact with the wastewater. All at low cost of course...

Hilly Terrain and gravity is an opportunity for designing waste water carriers but is equally challenging in implementation due to density of settlement and difficulty in connecting each household waste outlet to single carrier system.

Open drains are not viable going forward because rainfall will inundate the system they discharge into. Rocky terrain would be problematic for constructing pipework, but smaller pipes mean lower costs and buried pipes might not always be necessary. Pipes will be necessary to convey wastewater from highly populated areas because if directly discharged the capacity of the soil matrix will not be sufficient to avoid contaminating groundwater.

I assume there is a water supply for domestic greywater and blackwater generation. Can I assume a community preference for flush toilets?--Yes community prefers flush toilets.

What is the geography below the settlement? Less hilly land with more soil, used for agriculture? Does the soil get less rocky down the slope? Is the land densely settled all the way down to the waterway with no opportunity to discharge treated wastewater to land?

The terrain is extremely rocky, difficult to excavate and with minimum absorption capacity. The settlement is densly populated on this hill/mountain which has open drains which disposes in the natural drains leading to water bodies..

Pl find some pictures of the settlement

The issue with septic tanks as primary treatment is that sludge needs to be dealt with. With vermifiltration the product is humus, so meets npopat's criteria of "sustainability" by requiring no further treatment for use as a soil conditioner.

A "rock filter" could also be a vermifilter, because without worms the bacterial slime will build up and slough off, requiring further treatment stages. Worms maintain the biofilm by grazing it and converting this to humus. I prefer an organic substrate such as bark or biochar rather than crushed rocks because the buildup can be removed and used directly as a soil conditioner. However, if crushed rock is more available then that would be suitable as a substrate.

A wetland should only be used if the treated effluent is then discharged to a waterway, and therefore the nitrates need to be removed. A more sustainable solution would treat the nitrates and phosphates as a resource and retain these within the water for irrigating productive plants. Vermifiltration offers a solution that retains the plant nutrients in the water, reducing BOD and pathogens sufficiently to meet regulations, then the wastewater is used for surface irrigation of crops. If good treatment levels are achieved (capacity is matched to influent level), food crops could also be irrigated.

cheers
Dean

I do not understand the exact situation of the hilly regions, but it reminds me of my application of rorck filte system which was applied to hilly areas without any supports from electrical and mechanical equipments. The basic idea include a combination of septic tank + rockfilter + wetland system.
Unlike trickling filter, no primay and final settling tanks are furnshed in this system. The septic tank works as primary and sludge treatment facility and the wetland works as a final settling tank as well as as final polishing unit as attached article. The rock filter is single pass flow and nitrification may not be possbile. The wetland must be designd to remove nitrogen as well as phosphorus removal.

Euiso Choi
Director of innovative water center (iWc), NPIC
Phnom Penh Cambodia

npopat,

With hilly terrain gravity can be used to advantage for treatment systems requiring no energy input. I would suggest that the key sustainability objective is to avoid direct discharge of wastewater into waterways, and the other key sanitation objective would be to avoid direct community contact with the wastewater. All at low cost of course...

Open drains are not viable going forward because rainfall will inundate the system they discharge into. Rocky terrain would be problematic for constructing pipework, but smaller pipes mean lower costs and buried pipes might not always be necessary. Pipes will be necessary to convey wastewater from highly populated areas because if directly discharged the capacity of the soil matrix will not be sufficient to avoid contaminating groundwater.

I assume there is a water supply for domestic greywater and blackwater generation. Can I assume a community preference for flush toilets?

What is the geography below the settlement? Less hilly land with more soil, used for agriculture? Does the soil get less rocky down the slope? Is the land densely settled all the way down to the waterway with no opportunity to discharge treated wastewater to land?

cheers
Dean

Hi naresh0597,
what I am trying to explain is that claims are not the same as independently verified findings. In promoting your product you are directly comparing performance of your "biodigester" with the conventional septic tank. This may arouse suspicion on the objectivity of the comparison.

Only by undertaking an independent scientific investigation, using exactly the same influent quantity and quality, and measuring the effluent across a sufficient sample size and over time, can you objectively compare two treatment systems. I could claim that snake oil is twice as effective at treating arthritis than green lipped mussel extract. That claim is meaningless because I do not also consider the effect of dose. Then, even if I "proved" the efficacy with my own data and used that in my marketing media, I cannot expect to be taken seriously by a community that wants the truth. I'm not saying the biodigester is no better than a septic tank, I just want to see good evidence of its effectiveness.

cheers
Dean

Please have a look at the attachment wherein the test results of the effluent discharged by our Bio-DIgester Systems is tabulated.

It would be interesting to read your comments / observations on these test results.

Keep in mind that npopat requires a system for a dense settlement on a hilly area. The biodigester is only a primary treatment system, so could be used as an alternative to the primary vermifilter, but simplified sewers and a semi-centralised secondary treatment system would still be required, preferably using only gravity and with land disposal of the treated wastewater outside of the dense settlement. I doubt the household-scale biodigester would be cheaper than a primary vermifilter per person, but this is an option, along with the current septic tanks for removing the solids so that low-cost simplified sewers can be used.

This biodigester can only be claimed to be more efficient than a septic tank for primary treatment. Thats all. This means that the capacity is smaller for the same level of treatment, or that treatment is better for the same capacity. Nothing more. Claims that both capacity is reduced AND treatment is improved are misleading. It's one or the other, not both... i.e. does a biodigester at one third of the capacity of a septic tank give the same treatment level?

This design may be an improvement from the standard septic tank, in that the compartments are smaller and there are three within each tank instead of two. The "poly grass matting" dividing each compartment would provide better bacterial attachment sites than a concrete wall, but this is still just an anaerobic "septic tank" for primary treatment. In series they become a "dewats". Capacity is required because anaerobic treatment has efficiency limitations, that is it isn't fast compared with aerobic.

The claim is that one cubic metre capacity biodigester is sufficient for basic primary treatment for 6-10 people, one third of the capacity of a septic tank. Show me the independant study published in a reputable journal with data showing that capacity reduction factor, benchmarked against the conventional septic tank with identical influent flows. If this system achieves a genuine cost reduction over the conventional septic tank and achieved the same treatment levels then I'd be the first to agree that the "bacterial reservoir" design is a step forward.

However, claims that no sludge removal is required are absurd. Sludge is inevitable in anaerobic systems.

I do like the biogas outlet in this design, which offers the option to harvest and use the methane, unlike conventional dewats.

The special bacterial culture... well just another income stream for the business. There is no doubt that belief is a very powerful marketing tool.

There are many inaccuracies presented on the website which invite scepticism. Sorry, but septic tanks are not aerobic. Ringworm or tinea is not a type of intestinal worm infection. The list goes on... this is a sales/marketing website, not one presenting objective facts.

cheers

Dean

We beg to differ.....Bio-Digester Systems and Septic Tanks are completely different in design and construction. If we were to go by your logic then adding the proprietary additives in septic tank should work....the fact is they do not work and are washed out within a matter of few days ...which means the design and construction of Bio-Digester Systems is completely different from Septic Tanks.

More details are available on our website www.biodigester.in

Please also find attached our technical brochure for your information.

"Biodigester" tanks are just septic tanks with proprietary additives. Stay away from snake oil. Also stay away from anaerobic systems that do not harvest the methane and that require fecal sludge removal/management.

Another solution, rather than separating greywater systems from container-based systems for fecal waste, is primary vermifiltration at the household level for both blackwater and greywater (to remove and digest the solids), connected to simplified sewers that transport solid-free primary treated wastewater to semi-centralised vermifiltration units for secondary treatment and safe land-based disposal.

cheers
Dean

Consider using Bio-Digester Systems...more details on our website www.biodigester.in