Dear Mr. F H Mughal!

I think in this topic we are mostly talking about wastewater produced in rural households.
Regards,
Bogdan

Dear Mr. Bogdan,

You say:

"Maybe it is better to talk about "soil surface treatment" which means the waste water is released above soil horyzon A but possibly below O horyzon."

Is the wastewater, you refer to here, is municipal treated wastewater, or it is untreated industrial wastewater?

Regards,
F H Mughal

Hello evrybody!
There are two very useful points became quite clear to me through the discussion
1) We should differentiate between irrigation and surface discharge for cold climate conditions . While irrigation that provides direct plant needs in water and nutrients may be practiced fot very limited period of the year in cold climate, surface discharge can be implemented for the most of the year (possibly whole year) and system can be designed for it through soil buffering strategies. Maybe it is better to talk about "soil surface treatment" which means the waste water is released above soil horyzon A but possibly below O horyzon en.wikipedia.org/wiki/File:Horizons.gif
2) The term “decentralized sanitation” can probably be only applied to on-site treatment, since whenever we have several users connected to sewer that brings WW to treatment we have some kind of centralization happening . In this latter case it is probably better to talk about “local” or “ small-scale” sanitation or even “community sanitation”.

Best,
Bogdan

Hi Dean!

You are absolutely right about making soil a buffer. That's why I am so interested in biochar modified soils.

Best,

Bogdan

Hi Bogdan,
one important issue with regards to surface irrigation is that although you only have a few months of the year when it is really useful (summer), the rest of the year also provides benefits. Soil has "buffers" such as cation exchange capacity whereby nutrients are held from leaching until the plant roots take them up. Yes, water is not required all the time but storage until it is required might not be economic in most cases. However, the soil still acts as a filter preventing contamination of the water table even in periods where the irrigation is not required. For example here it rains all winter and the soil becomes saturated. The plants don't require the water because transpiration is minimal. Household systems still discharge treated wastewater on to the soil even when it is wet and raining. The idea is that surface discharge is better than trenches for preventing the treated wastewater from reaching water tables even when the soil is saturated because of the soils filtering and buffering capacity. Willows do not use any water at all during winter when we most want the water used. Like any plant, their water requirements are high only in summer when our wastewater is least likely to cause contamination. That is, we rely on soils rather than plants to be the buffer, soil stores the nutrients until when the plants want them. Plants offer a means for recycling the nutrients though, as in removal of crops or animals from the land for human consumption.
cheers
Dean

Dear Roumiana

Thank you for interesting discussion too!
That’s right – I do not want to rely on authorities . I want to rely on communities))))
At the moment it looks for me like broad scale on-site individual waste water treatment with nutrient and water recycling is unrealistic since it may require too much user's involvement, is rather complicated and do not guarantee the quality, safety and pollution preventing. It is also something that is potentially illegal and against regulations in case of mixed flow or even grey water. Maximum what I expect on site is some grey water use for short periods in summer for the trees /shrubs and maybe some urine collection. I wish I am wrong. On the other hand most people probably will gladly connect to sewer on their street if it is offered for reasonable cost and service is provided. Local community small-scale farm integrated waste water treatment probably could provide this opportunity to have minimal level of centralization and at the same economic viability and necessary quality and procedures control as well as real sustainability in terms of recycling.

Thank you for making focus on matching the quantities of waste water produced by households and needed by WWTP! Also how it is related to available water supply on household level. Very important issues! What I think is that small-scale community based waste water treatment opens up possibility for feed back communications between users and WWT plant to ajust or modify activities on both sides. This is something hard to imagine with big centralized WWTP
I do not have precise data on willows water uptake at hand but can try to find. I am sure someone has done these researches in regard of willows in constructed wetlands or energy forests.
I have built recently a cold-climate heavily insulated biochar based vermifilter for a student hostel (24 PE) in Ukraine and experiment now with it. So far it doesn’t look for me like technology suitable for standard individual household for average Ukrainian family. For small scale WWTP, eco-farm or eco- dedicated Ukrainian family –definitely yes though.

Best,

Bogdan

Dear Bogdan,

you have initiated a very interesting discussion and I would like to thank you.

Regarding the size of the plots you have mentioned - it looks that on-site individual solutions will be more economically viable, compared to a centralized sewer, which collects settled wastewater after the septic tanks, because of the length of pipes which will be required to transport it to a wastewater treatment plant.

The issue of water reuse - we have to think of the wastewater system and the reuse system as a whole. In other words, we can reuse as much as we produce. And here comes the issue of inhabitants - how many of them are producing wastewater and how much of it. Are they full time residents or just visiting in summer? The quantity of wastewater produced is directly related to the availability of central water supply. If people are using wells in their own plot, then the consumption might be lower. This information is essential in order to plan your farm. Also, if people reuse gray water directly, this will reduce the amount of black water by ~50% and you may end up with no water for your plants. Considering these points, I would encourage on-site solutions.

The vermifilters suggested by Dean look as an interesting idea, but before you can apply it, a serious amount of research would be needed, in order to be successful in your case.

My impression is that you would not like to relay on local authorities, but the issue of regulations is very important. At the end of the day we would like to implement a system, which is legal and applicable to numerous cases, not just in your own property.

I like your ideas for the reuse of treated wastewater - could you provide information regarding the water requirements of willows?

Best regards,

Roumiana

Hi Dean!
Most of Ukriane can expect 8 month above zero temperatures. Theoretically during this period surface discharge is possible and it can be extended for at least two more month if discharge would go under some insulating mulch layer further enhanced by snow layer on top. The infiltration would depend on soil type (sand or clay), how saturated it is from the rain and humus (organic) content. Some plants will benefit constant wetting with nutrient rich liquid and keep nutrients uptake (willow) for most of the time. Some simply tolerate it and uptake nutrients for limited period during warm season or at certain accumulated degree day while at other time let it all pass through soil or accumulate in it (quince, raspberries). Planting on ridges with discharge in between them into mulch filled depressions would be nice self-regulating approach.
A good strategy will be buffering the soil with biochar or zeolite that will absorb unused nutrients (and water) and later release it to the plants during active vegetation phase on demand. A lot of things would depend on mycorrhiza forming fungi that bond the nutrients and enhance their availability to plants. They play enormous role in cold climate soil nutrient cycles.
Another approach is glass –house growing when irrigation can be kept all-year round given artificial light and heat is provided.
Anyway it is quite possible to design surface discharge system for the most part of the year in Ukrainian climate.
Best,

Bogdan

Hi Phillipe,

I am building domestic scale vermifilters out of low cost recycled materials, with developing countries in mind that most need the technology. The primary vermifilter uses 2x large plastic fruit crates and secondary filters use 2 x plastic 40 gallon (200 litre) drums.


1200 x 1000 x 800 forklift style fruit crate


Twin chamber domestic primary vermifilter

There is no doubt in my mind that secondary treatment could be cost-efficiently scaled to the community level for irrigating a local farm, with primary vermifilters at the household and small diameter pipes to a community facility for secondary/tertiary vermifiltration.

In its simplest form a vermifilter is a drum filled with media such as sawdust, bark or even biochar, with an inlet at the top and an outlet at the bottom. The inflow volume depends on capacity and residence time, which depends on the porosity of the media and media depth. Biofilm develops on the media and the worms graze that biofilm. By passing wastewater through the media with its very large surface area, rapid aerobic treatment takes place, removing BOD and pathogens. Because the worms work the media, porosity is maintained. The key is maintaining an aerobic media, which means ventilation.

Its easy to provide conditions for worms to thrive, the media just needs to drain and ventilation is essential. The worm population quickly adjusts to different quantities of influent and nitrogen is only an issue if no flush water is used. Low flush works fine.

Matching media volume and porosity with the volume of inflow is important in "traditional" vermifiltration. The longer the retention time, the greater the level of treatment but with an increased risk of inflow exceeding outflow. The simplest system uses gravity alone but requires slope away from the dwelling. Variable dosage (increased loadings from bath or washing machine etc.) is allowed for by having sufficient capacity.



My preference is for a relatively coarse media and constant recirculation. I use horizontal flow reactors and a modular design that has the reactors in series with number of reactors determined by number of users.


Secondary recirculation vermifiltration reactors in series

Recirculation is with 5 watt 12 volt pumps and a small solar panel. The total cost of each reactor is about US$80

No need for anaerobic filters or planted gravel filters or polishing ponds as required in DEWATS

N is retained in the wastewater because treatment is fast and aerobic. Anaerobic digestion offers conditions suitable for ammonification and loss of nitrogen to the air. There is plenty of research showing high destruction levels of bacterial/viral pathogens, whereas helminths are retained in the filter medium so are removed from the wastewater.

cheers
Dean

Hi Bogdan, yes, with vermifiltration the outlet is lower than the inlet, i.e. the depth of the media lower. Septic tanks have the outlet at the same height as the inlet, which appears to be set just under the height of the frost line... all one level right through into the leach trench.

The only reason the vermidigester would be built on the surface is that a failsafe overflow can be built in to ensure the water table does not rise and flood the digester. If underground, the sump under the digester can have a float-switch operated pump because the solids are removed, but this would need to be reliable. If it fails, the water table will rise in the vermidigester and drown the worms... unless the leach trench were always above the water table.

To me it's not so much about when irrigation is needed, but when irrigation is not limited by freezing temperatures. Surface discharge removes the risk of groundwater contamination, so I'm wondering how many months a year surface irrigation is possible? How many days in a row can occur where the temperature never gets above freezing?

cheers
Dean

Hi Dean,

You make me (us) very curious about the potential of vermifilters. I have the following questions: (i) it is just a filter: how does it deal with 100 L wastewater per person per day? And how can the pathogens and nutrients be retained?; (ii) what do you do with the effluent? In my understanding, the pathogen removal is rather low; (iii) I think that worm management is more that temperature impact on individuals: the colony has to grow, and be efficient. I see as further risks a two high water-content (or even saturation in case of clogging) and sometimes potentially high nitrogen content.

It would be great if you could send us a drawing of what you exactly have in mind, mentioning the scale of operation.

Cheers,

Philippe

Thanks Dean!
Ukraine is a huge country with highly variable climate and other condtions. High ground water level is very common in many places both for natural and anthropogenic reasons. The water table gets highest level usually in spring after snow melt and in autumn after rains. In some places it drops down a in the middle of the winter , in some places it stays. Very often the water table disappears completely after midsummer and that what makes the wells go dry and people complaining about the water shortages. The frost line depth varies between 50 cm to 1 m although lately due to (probably) climate change the winters become milder ( last December hit the warmest temperature record) and thus frost line is usually higher. Common practise is to have 50 cm of dirt over both septic tank and top of leach trench and mostly it is enough to keep things unfrozen. Sometimes during very cold winters on North of the country infrastructure may freeze on this depth and in such localities pipes and tanks usually buried deeper.
What is noticeable that in places of high ground water one can expect more attempts from people to treat their waste water with septic tanks since it directly affects their and neighbors well water.
Usually in the country the size of plots that belong to dwellings is between 1 000 and 3000 square meters. Most of these plots grow fruit trees , shrubs and vegetables and it is possible to use the secondary treated effluent produced on site for irrigation for 2-3 month during the year. It is what many people already do with the grey water and some of them can even do this with the black water from their septics. However during rainy summers (like the last one) irrigation might not be needed at all.
I can’t argue with the possibility to have a vermidigester at each household for primary treatment before I see robust, low cost, low maintenance, cold climate working example of one
One of the limitations for this technology I would see that most already built houses have the outlet for the waste water underground and vermidigester is probably better to build on surface? This would involve sump and fecal pump (not good at all). Underground vermidigester could be an option? But then we could possible consider modifying septic tanks into vermidigesters? That would be an interesting project!
Still for me the key factor which would makes local closed loop sanitation work is a viable profit generating LOCAL FARM. Not worms, urine separation or pipes, but people having meaningful job where they live, producing good stuff for the other people and not depending on the state to solve their problems.
Best,
Bogdan