Hi Dean!

Does it mean that vemifiltration reduces BOD mainly through suspended solids reduction while leaving total NPK levels still high enough?

In this case it looks more like a primary treatment stage for me even with pathogene reduction.

Best wishes,
Bogdan

Hi Kris, the worms don't need solids in the wastewater at all, indeed their preference is to graze the biofilm (bacterial slime) that grows on the media. All that is required is water with a high BOD... which is what is provided. The (aerobic) media provides a huge surface area for the biofilm to grow on and the water is rich in dissolved and suspended organics, which is what I'm removing with the biofilm-coated media. The part that the worms play is in maintaining the biofilm on the media surface by grazing it, then converting it into stable (biologically inert) humus. The humus in turn, along with the worms, maintain the porosity of the media. So what I end up with is wastewater with a low BOD and low pathogen levels and low suspended solids, but that remains rich in plant nutrients.

Bogdan, thanks for your post and yes, you are right - I need to confirm that the nitrogen is retained through the process by testing the primary and secondary effluents. Unlike other sewage treatment processes that are designed to remove N into the atmosphere as ammonia gas (so the water can be discharged into water bodies... lakes, the sea etc), vermifiltration retains the N and is therefore my technology of choice for a sustainable future where crops can be irrigated with what can only be described as "liquid plant food". I haven't actually tested the water from this unit for plant nutrients because I've seen the impressive growth response in the plants, but I will do that and report the results!

cheers
Dean

Hi Dean!

Thank you very much for sharing! This is such a great compact system!

Would be very much interested to see what is the effluent quality in the last removal tank compared with effluent from the primary digester. Could you test it somehow at least for total N?
Best wishes,
Bogdan

Looks interesting. But where do the worms come into play and is there still sufficient food for them after the primary vermifilter and the settling tanks? It seems to me that it might work just as well without them?

This system uses a vermidigester for primary treatment (removal & digestion of solids), then secondary treatment using vermifilters as described here. The system accepts all household waterwater including toilet, kitchen and bathroom. Treated wastewater is discharged to soil surface using dripper lines.

Not including labour the cost for the secondary system is between $200 and $300 depending on how much the barrels cost. This system is for a household of 3-5 people, and is scalable by adding more modules in series. The intention is to produce effluent of a quality suitable for food crops.

The primary vermi-digester uses two large fruit baskets but is not the focus of this topic:


This design is for a site where there is little or no fall and therefore this simple gravity system cannot be used:


Here it is:


and a diagram of the same design:


Please note that this is made entirely from reused 40 gallon plastic drums and other accessible materials that allow construction in any country. In this case because the house had electricity, an electric pump with float switch ($80) was installed in the pumpout drum. This discharges to drippers in the garden and where fall allows could be replaced with a dosage siphon (e.g. Flout ).

This system also uses 5 watt recirculation pumps ($10) that "feed" the vermifilters continuously. Where electricity is not available very small solar panels would drive the pumps. I have found these recirculation pumps to be very reliable:


The secondary vermifilters are constructed using plastic mesh, shadecloth, plastic pipe and cable ties:


I use bark or woodchip media, but other options with similar porosity are available. The drums have small holes drilled in them for ventilation.

Recirculated water is dropped on to a half-round "splasher" from about 30 cm above, which distributes the water evenly on the surface of the media:


This is a very simple and low cost system for treating domestic wastewater. Maintenance is minimal and treatment level can be adapted for the required application.

Dean