The project is located in Italy and the project team is able to treat the 90 % of the average annual rainfall using some systems in series. The water comes from the roofs and all the hardscape in the site area (there is also vegetation where water is considered 100 % treated). The water coming from impervious surfaces flows through the drainage basin and then is collected in a sedimentation tank; after that it flows through some filters and then goes to the sewage systems. According to table 2 Reference Guide LEED NC v3 (page 104) I assumed that the sedimentation tank has an average TSS removal of 15% (oil grit separator).
Question 1) I don't know which is the average TSS removal for the drainage basin and for the filters. Do you have any suggestion ?
Question 2) Is there any comparative table where I can find the correlation between the filter mesh and the average TSS removal ?
Question 3) Once I have all the average TSS removal percentages (for each system), how can I count them together? I don't think a solution is to sum the TSS removal percetages for each system...
Thanks
Amy Rider
Sustainability ManagerKEMA Services
161 thumbs up
August 25, 2010 - 1:59 pm
1. Drainage basins don't typically remove TSS by themselves. For the filters you'll need to confirm the TSS removal rates with the manufacturer and get documentation from them showing the infield performance data.
2. I don't know of any table that correlates filter mesh with TSS removal rates. I think there a lot of factors that come into play outside of just the mesh size. Again the best bet is to contact the manufacturers as they generally conduct their own tests.
3. You describe a train of treatment devices. Here is the approach we recommend:
TSS x (1- % removal efficiency) = A
A x (1- % removal efficiency) = B
B x (1- % removal efficiency) = C ...
A is the TSS remaining after that BMP. B is the TSS remaining after that BMP plus the measure that achieved A, and so on...
One item of note, although the table on page 104 of the Reference Guide states that an oil/grit separator removes 15% of the TSS on average, you should confirm this again (sorry for being so repetitious) with the design and manufacturer. Remember that the Ref. Guide also defines TSS as those particles too small or light to be removed via gravity settling.