Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

Hi Alex,

I agree that simple is good, where possible. In this case, because my suggestion is for a retrofit rather than a new system, a small amount of electrical energy is required for modifying the existing system to an aerobic environment (in this case using recirculation).

My criticism of the BORDA anaerobic DEWATS is multiple-fold:
  • Septic sludge generation (disposal issues)
  • Large capacity required per user (cost)
  • Methane and nitrous oxide generation (if not utilised. If utilised, this might justify the capital investment in capacity)
  • Relatively poor treatment efficiency (overcapacity problem)
  • Poor level of treatment, requiring further tertiary treatment.
Unlike a VW Beetle which is a very effective transportation machine, a cynic might suggest that the BORDA DEWATS is really is only a sedimentation device... rather than a treatment system. More like a VW beetle without tyres.

Lets focus on design considerations for experimentally converting an anaerobic DEWATS into an aerobic vermifilter treatment plant. This doesn't require design manuals and guidelines, but simply the motivation to test options at a pilot scale. The concept behind vermifiltration (or trickling filters/biofilters) is very simple. A tank is constructed with an inlet at the top and an outlet at the bottom. It is filled with media. Wastewater flows in the top, through the media and out the bottom, in the process removing oxygen demand, suspended solids, and dissolved organics, while also aerating the wastewater. The design considerations are capacity and flow. A starting point for developing systems for Kabul conditions could be my suggestion for a 1 m3 capacity vermifilter and 20w fountain pump (i.e. high flow low head) for the BORDA demonstration unit. You have test results under the current configuration, so results could then be compared to determine the retrofit's effectiveness.

sludge recirculation + aeration for the anaerobic modules seem to be much more feasible and easier to implement.

Sludge recirculation + aeration continues with the status quo, that of scaling down centralised systems. The problem is economies of scale, i.e. cost per person. You'll also need a 200w aerator and 1000 watt panel for a plant the size of the BORDA demonstration unit. Then, how do you propose to implement sludge recirculation? Periodic sludge removal to vermifilter could use a portable sludge pump shared amongst 100's of DEWATS.

I have offered three simple designs for testing in Kabul, firstly one for onsite disposal of domestic blackwater. Flush and forget, safe subsurface disposal, with removal of humus every 5 years (figure 1). Then, if incorporating greywater and scaling up, aerobic treatment can be achieved with a simple design requiring no energy input and surface irrigation (figure 2). As a retrofit to the anaerobic DEWATS I have suggested that recirculation + aeration can be achieved with solar energy (figure 3). I'm still puzzled about the energy issue though... looking at the fountain above, is this (1) pump operated, or (2) is this fountain well below the outlet of the DEWATS? If (2), the cascade fountain could be replaced with a passive vermifilter for much higher level of treatment. If (1), the pump would be far more effectively used recirculating the wastewater through a vermifilter.

Don't get the point of your rule of thumb

Rule of thumb: if the effluent still smells then you haven't fixed the problem, so move on and try something else.

Because there has been so little information provided on what is wrong apart from "does not work properly", my assumption is that working capacity is exceeded in cooler months and the effluent is not treated adequately. Effluent that is not properly treated tends to smell sulphurous. If there is actually no problem then we're all wasting our time here. If the issue is only one of groundwater pollution then lets focus on what happens at the other end of the DEWATS:
Is all the treated effluent from BORDA DEWATS in Kabul disposed of to surface? If disposed to subsurface irrigation, is that because it is not treated sufficiently for surface disposal? Are all DEWATS outlets connected to some form of properly engineered soakage fields? Is sufficient land available or are some dewats connected to soak pits? Alex, I'm horrified that you would suggest that one can avoid smell by diluting with rain/greywater... what happens then to this water?

cheers
Dean

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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

Dear Dean,

Please find my comments to your points above:

-Septic sludge generation (disposal issues)
Sludge generation of anaerobic systems is much lower then in aerobic ones. Please tell me more about the accumulation rates, handling of the vermifilter compost. As Kabul has no sewer system, people desludge their blocked soakpit to the storm water drains. DEWATS is not only a treatment device but also sort of a collection device, since anerobic treatment is not happening anymore at the storm water channels and blocking them, resulting in flooding of streets etc. Current sludge of bigger DEWATS is treated at the central wastewater treatment plant in Kabul. But an adequate service value chain is not fully set up in AFG...,work being done.
-Large capacity required per user (cost)
Yes, DEWATS on a household level is expensive, thats way rather bigger systems are implemented in Kabul tackling the big polluters. And once again please consider the life cycle costs, do not limit yourself on the initial investemnt of 1 single pilot intervention implemented at an office...
-Methane and nitrous oxide generation (if not utilised. If utilised, this might justify the capital investment in capacity)
Methane production is an issue, the use of biogas should be promoted
-Relatively poor treatment efficiency (overcapacity problem)
I disagree. You can reach very good treatment efficiencies. See the example above. Constraints are of course available space and budget. Please do not forget that even in Europe you will find examples where a primary wastewater treatment for remote communities for example is still in place

I gave you the contact of our R&D focal point. Please be in touch with him and provide conceptual design guidelines for him...your couple of lines are too vague. Once we have concrete implementation and operation guidelines we can go ahead and identify a suitable project location. We are also willing to make the investemnt that is needed.
As the DEWATS system at our office is working very well and is nicely integrated into our compound, I doubt the the colleagues will implement the vermifilter there... What filter material is required? is that locally available? Material of the tank? Any modifications needed? will the system be overground or underground? Looking forward to get things started and share the results, but proper guidance from your side to the team is crucial.

Regarding your other point,
You mentioned that DEWATS is only a sedimentation device - that is not correct. DEWATS has more treatment modules than only a septic tanks (amongs planted gravel filter, oxidation ponds etc.). Looking solely at the anaerobic modules, they can be considered as a solid retention device, yes.

Regarding the DEWATS effluent:
We have all kinds of disposal systems, infiltration fields, soak wells, french drains and of course using the water for irrigation purposes. And yes, we mix part of the rain water with our treated wastewater and use it for the irrigation of our vegetable garden, trees and grass fields of our office yard...

I assume the statement that was previously made "DEWATS does not work in winter times" was probably a bit excessive,...also no further deatails and info were provided here. So to sum it up: Yes, efficiency of anaerobic DEWATS modules goes down during cold climate, but the efficiency drop can partly be compensated through the use of planted gravel filters and one should consider current framework conditions of the context in Afghanistan (e.g. energy crises, sanitation sector still developing, limited capacities, civil war scenario and many more)

Cheers,
Alex
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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

Hi Alex,
thanks for your positive response. I sympathise with the situation in Afghanistan and I'm only too happy to share my ideas and experience in hope of making a difference.

At a domestic scale I have been practicing removal of sludge (sediment) from septic tank to vermifilter. The volume is reduced multiplefold (5 - 10 x) with the result being black humus that has a loamy texture with no smell. This can be handled and spread around as mulch under trees etc. You can use the same vermifilter for recirculation and sludge processing, so a useful reactor. Sludge processing should take about 2 months from addition to decomposition, depending on volume and temperature. A thicker layer will take longer to reduce. Do you have data on sludge production volumes for your units? The vermifilter should be wider if processing sludge and taller if processing wastewater only. This is because with increased surface area the layer of sludge will be thinner and so process faster, whereas with wastewater the retention time (i.e. contact with the media) is more important. Your design would trade these two off and most likely be a similar height as width. Multiple drippers/tricklers would distribute recirculating wastewater evenly over the surface of the media in the reactor.

I am not familiar with your construction materials and methods, so can only offer some design guidelines at this stage.

I'd estimate that conservative vermifilter capacity for recirculation would need to be 100 litres per person. I'd limit sludge addition to no more than 10cm depth of dewatered solids at one time.

The outlet at the bottom of the reactor must be above the inlet of the ABR, and connected to this. Thus if your DEWATS inlet is at ground level, the vermifilter would have to be over-ground.

The reactor does not need to be water sealed because it does not fill with water. There must be adequate ventilation in the reactor but in your case it would also need to be well insulated. Ideally there is an air cavity between the filtration medium and the wall of the reactor, to improve ventilation, along with air vents at the bottom and top. The top needs to be able to be removed to access and remove humus. I'm just not sure what construction materials you have access to but would be interested in providing feedback on your design ideas.

What kind of coarse organic materials are available ion Kabul? I imagine woodchips or tree bark would not be available as inexpensive filtration media?

Would be a remarkable to see decentralised systems transform Kabul by safeguarding groundwater quality, but also greening the city by using the nutrient rich wastewater and humus to grow crops and trees that would not otherwise survive in such a low rainfall environment.

cheers
Dean

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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

Hi Everyone;

Just out of curiosity, why not consider using a decentralized solution with a centralized network and treatment plant. We have been building these in canada since 1999. here in India our first at a tribal village in Gujarat was commissioned in early 2016 and has been working perfectly since then. From the trail above, I suspect we solve most of the problems identified.

Have a look at our website www.clearford.com and if anyone wants additional information, do have a look at the attached documents - a project writeup and the latest test results. Water supply at the village is 70 LPCD.

Sanjay

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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

Hi Sanjay

Nice project, especially the community-based approach. A few quick questions:

The Clearford system presented, how is it different from a normal solid-free sewer system with a septic tank (justifying the trademark)? The document even states that the single-chamber solid retention tank produces "significantly less sludge" than a regular (two-chamber) septic tank - how is that achieved?
What is the CAMUS SBT treatment exactly (a wetland?), and what are those enzymes it needs to run?
The document mentions potential flooding in the monsoon season. How did you solve this with the retention tank - it seems only to rise up to ground level?
Did you reach ODF status in the village in the end?

And finally, how do you see scalability in a dense urban context as Kabul and how would you address the challenges discussed in this thread (cold winter, sludge disposal, GHG emissions, costs, space requirements) especially, when talking about more than individual household/toilet level?

Cheers
/Jan

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Trinity College Dublin & University of Limerick
Email: jan.knappe(at)tcd.ie, Twitter: @JanKnappe

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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

The opportunity I see is in greening Kabul productively, using water originally pumped from under the ground, adding nutrients to it from human effluent, then actually using it productively, either for irrigating amenity plantings ...or better productive tree crops ...or even better food crops. If this could be done safely and at low cost right down to the household scale then why centralise? The only motivation for putting pipes in the ground would be cost saving, but networks of pipes are costly. The BORDA people have done okay with reducing costs in their decentralised system, but in my view this could be so easily improved, further reducing installation costs AND improving the effluent quality to be able to safely discharge to the soil surface for irrigation purposes. Currently the system only appears to achieve water quality suitable for subsurface discharge.

Unfortunately a paradigm shift is required, which tends to hold up innovation. My favourite quote: "Paradigms fall slowly, from the weight of repeated failure". Vermifiltration offers high levels of treatment and at low cost... win win.

The water resource is in short supply. The wastewater needs to be properly disposed of so it doesn't contaminate the water table, something very easily achieved in such a low rainfall area using surface irrigation, turning a problem into a resource. However, BOD and suspended solids need to be reduced to do this safely. Plant filters are one way. Vermifilters are another.

Jan, CAMUS looks like the Vision Earthcare brand of Soil Biotechnology (SBT) bioreactors that use vermifiltration and plants to purify primary treated wastewater.

Basically a proprietary culture of soil, earthworms, bacteria and special additives. Starts with a septic tank, then to the bioreactor, with rubble in the bottom as drainage layer, then proprietary rock material, special additives and soil as the filter layers. Plants are grown over the top of the SBT beds on soil bunds and wastewater is trickled on top.

There is nothing proprietary about the SBT apart from specific materials that are used, such as minerals and bacterial cultures. Check out their patent,
US Patent No: 6890438 " Process for treatment of organic wastes"
www.google.com/patents/US6890438

Interesting that on their facebook page, the company marketing these CAMUS SBT's, Vision Earthcare, are trying to monopolise their method of vermifiltration with their "patented Soil Bio Technology and Vermifiltration concept." They claim that "Vermifiltration looks like an unauthorized implementation of Soil Bio Technology (SBT) / Constructed Soil Filter (CSF) which has been developed at IIT Bombay by Prof H.S Shankar's group at Chemical Engineering IIT Bombay."

From what I can make out, what they have patented appears to only be very specific, their proprietary bacterial culture and minerals. They use rock powder (novel) and soil media (not novel). They make a special bacterial culture (novel). They use earthworms (not novel) and plants (not novel). They use trademarks and acronyms and proprietary names (novel). Seen it all before.

cheers
Dean

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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

Hi all,
Very nice discussion going on here….

@ Dear Dean: in reference to your vermi-digester toilet post, I would like to know your idea about using it in some informal areas in Kabul.

Almost 70 percent of the city is informal and the whole city relies on groundwater. Many households use shallow wells, although many wells have no water and those neighborhoods are supplied by private companies & public corporation using deep wells.
In 2015 I had a household survey in two informal neighborhoods in Kabul; both areas were upgraded and their dry vault latrines were improved by the government. By now most of the households shifted to water-based technologies mostly deep soak pit. I had household survey and almost all the households want water-based system.
I wandering if we can offer a proper technology (and sanitation chain) to avoid groundwater pollution & satisfy the locals. Dry toilets still could be suitable for some parts of Kabul, but not in densely areas (270 people per sq. km) which is difficult to close the nutrient loop.
Could you (anybody else engaged in this discussion) provide me more information about vermi-digester toilet (simple or double)? And what do you think about its suitability in Kabul informal areas? Or any other technology proper for this kind of context?
If you need more information, please let me know.

Cheers,
Hussain

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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

Hi Hussain,

I assume soak pits are dug deep so that they take longer to fill up? Of course this increases the risk of contaminating the water table, not a good thing when so many rely on groundwater.

Are most toilets out-houses or are flush toilets installed in the house with a wastewater pipe to the soak pit? How much water is used per flush - are the toilets conventional flush? What happens to the greywater from households with deep soak pits?

There is general information on vermidigester toilets on wikipedia and I'm happy to answer any specific questions you have. The key advantage is that the solid waste is reduced to 1/10th of its original volume. In my diagram on page 1 I showed a very shallow soakaway (not deeper than 500mm) to avoid contaminating the water table, and the digester (1m3 capacity) is insulated from extreme cold by soil. The design is suitable for low flush toilets if the toilet is directly above the digester. There are a range of low flush toilets available including squatting. The waste can contain toilet paper but the worms don't mind if it doesn't. The key is that some water must be used in the flush to dilute the urine. A double chamber digester allows for hygenic removal of humus by allowing a rest period for complete decomposition, but this is not necessary. One can expect 5 years service before having to remove humus, it is good to make it easy to do this in your design.

I assume that compost worms are available because Green Organic Agriculture Company is practicing worm composting in Kabul.

cheers
Dean

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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

Hi Dean,

You right; soak pits are so deep, and takes long time to fill up…can say in some cases 10 years or even more. But with some modification to protect the groundwater (like introducing vermi-digester toilets) locals would still enjoy flush toilets if they have enough water:
In terms of water the whole city has problem, and I think Kabul should as soon as possible start using surface water surrounding the city and we have enough surface water, although some difficulties to manage it but still providing water to Kabul City should be considered a national project.
Link below is JICA Report. There is a contingency plan for Kabul water supply which I think should be seriously now considered:
http://open_jicareport.jica.go.jp/pdf/12058566_01.pdf

But for the aforementioned site and similar contexts, I think if people want to have water-based toilets, they should forget their shallow wells: most of the shallow wells don’t have water already. There are private companies (government cannot cover the whole Kabul soon and I think private sector should be engaged also) digging deep wells & providing water to the households: government monitoring should be established.
I think avoiding groundwater pollution and also access to enough water are two main factors which should be considered here. Of course any suggested solution should consider different components of environmental sanitation and the whole sanitation chain.
For flushing, If possible people can use even greywater which is now directly discharged into streets or drainage channels.
I am attaching here the household survey report; might be helpful.

@Water-based toilets are mostly pour flush toilets in the yards. In terms of compost worms, I think it is not a big deal: can be produced or already available.


Cheers,
Hussain

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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

Hi Hussain,

centralised systems discharge to waterways, which in my view is not a sustainable solution. However, once a city gets too built up there is no hope for decentralised systems. To be successful and sustainable there needs to be vegetation to irrigate with treated wastewater, which means available land. Once a city gets too built up there is no land left to revegetate. There is so much concrete in Kabul! How much of the land area is covered in concrete? From the pictures it looks like maybe 50% of the land is not covered by roofs and concrete?

Decentralised systems can be built at lower cost than centralised systems now that the vermifilter is available. However, treating the wastewater is one thing, disposing of it is another. Recycling nutrients back into plant growth is the natural cycle which mankind seems to have broken, with the rationale being one of hygiene. Vegetation supplies valuable products, such as fuelwood, food and even wood chips for the digesters! My interest is in producing wastewater that is safe to use for surface irrigation of useful crops. However, there is a cost to doing this right, for example using discharge pipes with drippers to ensure dispersal and avoid concentration. Surface irrigation is much cheaper than subsurface soakage though.

Thanks for the background to the situation in Kabul, especially your survey. I have copied some gems here:

Greywater

Greywater as an important part of household wastewater is mainly discharged into the drainage channels or street without treatment.

In cultural point of view exposure to greywater is not a major problem and people comparing to black water discharge it freely into drainage. Greywater is a mixture of kitchen, laundry and bath wastewater which makes it difficult to use for irrigation or other purposes. Due to high volume and pollution risk of greywater, any sanitation management plan should consider greywater as well.

Greywater is a mixture of kitchen, laundry and bath wastewater which makes it difficult to use for irrigation or other purposes. Due to high volume and pollution risk of greywater, any sanitation management plan should consider greywater as well.


Blackwater

The material which is used for the construction of a dry (traditional toilet) are bricks, concrete and in old houses mud, but usually all are strong enough and in a good condition in terms of robustness. Dry toilets in most cases are not lined, but constructed above the ground to prevent groundwater pollution. They have a pipe which diverts urine and anal cleansing water to the street while dry feces is collected later for agricultural purposes; containments have a door which opens in the street: when a dry toilet is full the collector has access to it from the street.

most households are not willing to use dry (traditional) toilets. That could be the main reason behind switching to water-based system. According to the Figure 25, they are not interested in composting toilet as well: dealing and exposure to black water and fecal sludge is prohibited culturally and it is also considered a low profile practice.

I can understand cultural aversion to dealing with fecal sludge, but what about humus (black earth with no smell) that was once feces?

the percentage of households using water-bases system is increasing; almost all of the water-based systems are flush toilets connected to a soak pit which is getting popular

Households with same family members who use septic and holding tank need to empty their facilities in average around six months too; usually septic and holding tanks don’t have any infiltration into ground.



Usually households cannot afford to have a proper septic tank; they construct flush toilets connected to a soak pit which cost around $200 while a holding tank or a septic tank could cost 10 times more. In terms of operation and maintenance, a soak pit should be emptied each two or three years while a regular septic, holding tank or traditional toilets get emptied more.

usually septic and holding tanks don’t have any infiltration into ground. As discussed earlier households who are using flush toilets are mostly relied on soak pit which is cheaper than septic tanks and more convenient comparing to dry toilets.




One of these concrete rings plus a lid could be used as is for constructing a simple vermifilter toilet. What would these cost in Kabul?

cheers
Dean

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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

Hi Dean,

Topography and mountains divide the city into several zones, and one huge centralized system cannot cover the whole city.

According to the current plan, the only semi-centralized treatment plant will be extended as one of treatment plants in Kabul and its effluent will be discharged into the river; there will be no use for the treated WW near the treatment plant.

-Difficult to say how much concrete (but 50 percent is a good estimation). There are many unpaved roads and neighborhoods, but government and private sector use too much concrete for pavement & construction. This trend has already decreased infiltration capacity and caused flooding.

Humus: dry toilets have been used in Kabul and other cities for a long time and collected night soil have always applied on agricultural lands: So there is no problem to use it. Produced sludge in Kabul WWTP is also sold to the farmers around. The constraints are low demand, rapid urbanization and finally failure of the traditional sanitation system which is not applicable anymore specially for inner-city areas.

Cost of a concrete ring and its lid: around 50 USD. Simple vermi filter is a good idea but still I am thinking of groundwater pollution & required water for flushing. About that produced greywater is much more comparing to blackwater: any potential solution should find a way for greywater management as well. Let’s say if at the end we need to build a communal plant (for example) in a neighborhood to treat the greywater, why not using it for both blackwater and greywater? What if we use Passive Vermifilter/Biodigester (Figure 3 in your last posts) which means high amount of treated used water for infiltration or gardening (where possible)?

Cheers,
Hussain

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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

Hi Hussain,

there will still be those pushing for a series of centralised systems around the city which discharge to waterways... the bigger the plant, the more likely to discharge to waterways. Household level is best, the fewer networks of sewer pipes the better. Communal is okay, provided the sewer network is minimal... There just needs to be unpaved soil to discharge to.

Groundwater pollution can be eliminated with simple vermifilter toilet, provided the drainage field is wider rather than deeper. The key is always dispersal not concentration. I see the simple vermifilter toilet as applicable for households too poor to treat their greywater and who otherwise would build a deep soak pit. The cost is lower than a soak pit and the system does not pollute groundwater. Win win! Add another win, that nobody needs to deal with fecal sludge any more. Also, low flush toilets isolate the user from what goes on underneath and only use 500 ml water. In Africa the handwash water is being used to fill the bowl for the next flush to further conserve water use.


The SaTo pan, a squatting pour flush latrine using 500 ml water per flush.

Turning septic tanks into holding tanks is a negative step. The soakage field is integral with a functional septic tank. You can't have one without the other... certainly no point in having one without the other anyway...

The main problem with septic tanks is that because the leach fields are subsurface, these are expensive to set up properly in order to properly match soil infiltration and discharge volumes.

If proper secondary treatment can be achieved, a new world of surface irrigation opens up. So easy in a dry climate...

On a household scale, vermifiltration offers opportunities for both greywater and blackwater treatment. Either passive (if there is the opportunity to use gravity) or active (e.g. solar panel operated).

Once treated, surface irrigation is easy, provided a pump with floatswitch is available:





Pressure compensating dripperline, 2.1 litre per hour drippers @ 60cm spacings ($1 per metre).

Low pressure effluent distribution (LPED)/dose loading systems can also be used if required to be passive.

cheers
Dean

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