Achieving Permit Levels of Indicators

[Burton & Cherstin Sparks]

Dean,

In order to discharge to the surface as greywater I need to show that fecal coliforms have been reduced to <=200cfu/100mL.  This website suggests using the number of stages to achieve whatever level is required, and that at least a secondary if not tertiary recirculating vermifilter is generally enough.  Would you recommend just suggesting that performance  varies based on actual HLR, HRT, temperature, media, influent levels, etc., so testing should be used?  My understanding is that 1-3-log reduction in pathogens has been reported in scientific literature for a primary vermifilter.  I'm not sure what performance is anticipated for subsequent stages where you indicate that height has more influence than surface area as with primary vermifilters.

Burton

[Dean Satchell]

Hi Burton,

my primary vermifilters aren't designed to significantly reduce pathogens or remove biological oxygen demand (BOD), all they are required to do is remove (and digest) the solids from the wastewater flow. That is why they are wide rather than tall, the solids build up and spread out on the surface and the worms digest them from underneath. If the primary digester has a deep media there is a risk that the media will impede the flow and drown the worms. A shallow media depth (and coarse media) will drain well, which supports the worms in digesting the solids. Of course that shallow primary digester could be stacked directly above a vermifilter that has deep media for secondary treatment, but there should be a cavity between them so that drainage cannot be impeded in the primary digester.

The deeper the media, the more treatment you get, simply because there is more contact time for the aerobic bacteria that is attached to the media to remove pathogens and oxygen demand. That is why I design secondary treatment vermifilters deep rather than wide. Importantly, you should note that the narrow basket + cavity design allows for the full depth of media to remain aerobic. If the vermifilter is deep AND wide the aerobic zone will only be 30-40 cm deep, so defeats the purpose of the deep media. 

By putting secondary vermifilters in series you achieve greater levels of treatment. They are not expensive to construct and my suggestion is to use more of them rather than fewer of them, especially if you are proving the quality of the treated wastewater via testing. It's easier to build them into the system rather than retrofit them later. My suggestion is a minimum of two recirculating secondary treatment vermifilters in series. 

Cheers

Dean

[Burton & Cherstin Sparks]

Dean, thanks for the input!  Here's what I submitted, which was approved, in case it helps anyone:

Fecal coliform (FC) reduction from other primary vermifilters used in this type of application has been documented in the range of 1-3Log10 as shown in the table below, with the 10 field trials in India reporting 1.7x103 ± 6.02x102 cfu/100mL, or less than 1 Log10 away from the greywater requirement of 200 cfu/100mL required in DEQ Chapter 25 section 17.  Since the pathogen reduction in a vermifilter is due to the oxidation and decomposition process of microorganisms and earthworms, temperature can have an effect[i].   An Indian study showed that the trend of FC removal ranged from 2.5 to 3.7 Log10 over a temperature range of 15-35C (59-95°F), reaching a maximum  of 1.4x103 MPN/100mL over winter with medium strength synthetic wastewater[ii].  Since greywater is typically warm, processing it in the same system as the blackwater in this design will help keep the temperature up in our cold winters.  Given the above, it is anticipated that a primary vermifilter followed by 2 secondary recirculating vermifilters will be sufficient to reliably achieve 200 cfu/100mL.  If needed, additional stages will be added.

[i] Arora, S., Rajpal, A., Bhargava, R., Pruthi, V., Bhatia, A., Kazmi, A.A., 2014b. Antibacterial and enzymatic activity of
microbial community during wastewater treatment by pilot scale vermifiltration system. Bioresour. Technol. 166, 132-141.
[ii] Arora, Sudipti & Kazmi, A.A.. (2015). The effect of seasonal temperature on pathogen removal efficacy of vermifilter for wastewater treatment. Water Research. 74C. 10.1016/j.watres.2015.02.001.
[iii] Furlong, Claire & Templeton, M. & Gibson, W.. (2014). Processing of human faeces by wet vermifiltration for improved on-site sanitation. Journal of Water, Sanitation and Hygiene for Development. 4. 231. 10.2166/washdev.2014.107.
[iv] Furlong, Claire & Patankar, Rohit & Thakar, Gouri. (2015). The development of an onsite sanitation system based on vermifiltration: the ‘tiger toilet’. Journal of Water, Sanitation and Hygiene for Development. 10.2166/washdev.2015.167.
[v] Furlong, Claire & Patankar, Rohit & Thakar, Gouri. (2015). The development of an onsite sanitation system based on vermifiltration: the ‘tiger toilet’. Journal of Water, Sanitation and Hygiene for Development. 10.2166/washdev.2015.167.
[vi] Furlong, Claire & Patankar, Rohit & Thakar, Gouri. (2015). The development of an onsite sanitation system based on vermifiltration: the ‘tiger toilet’. Journal of Water, Sanitation and Hygiene for Development. 10.2166/washdev.2015.167.

[Dean Satchell]

Hi Burton, glad your system was approved. How is your design progressing? Would be great if you could share some details with the group.

Cheers

Dean