Plastics Separation from Stormwater

[MES2022]

Hello, I am working on a project for a plastics and vinyl recycling facility where they are undergoing a major expansion to their facilities. They grind up pvc piping, vinyl siding, etc. into a powder and resell the powder back to the piping and siding manufacturers. Some of the grindings are pretty fine while others are more coarse, with the final product similar to the consistency and size of sugar while others are the size of "beans" you might find in a bean bag chair. There are also coarse grindings that would be like the size of landscaping mulch. These grindings find their way into the storm sewer and I'm trying to determine the best way to separate them out before entering detention basins. My thought was to try to use sandfilter vaults. These would force water through the sand to filter out the grindings before the basins. For maintenance and cleaning of the vault, I would have a valve I could close, flood the vault with water which would allow the material collected to float, vac it out with a vacuum truck, and then open the valve back up. Just wondered if anyone else had any experience with something like this?

 

[1503-44]

I would have thought that plastics are seperable by density difference, although many plastics have a SG near 1, many do not, some being lighter, others heavier. If tou run them through a settling basin, you'll get some sinking to the bottom, others floating up, net the ones that do neither.

https://plasticranger.com/density-of-plastics/

A black swan to a turkey is a white swan to the butcher ... and to Boeing.

 

[TigerGuy]

Storm box that allows the solids to settle, and prevents the oils from continuing downstream?

 

[TugboatEng]

The problem is the fine particles. While they may be slightly positively or negatively buoyant their size is simply too small to generate enough force to get them to move. They will persist in suspension.

Have you considered a centrifuge? They are expensive to purchase but can filter at very high flow rates which reduces the costs related to tankage. A split bowl centrifuge with sludge discharge capabilities will be necessary if there is a large volume of plastic in the water stream.

 

[bimr]

If you are concerned about storm water drains, most people are using catch basin inserts (sock). There are a number of companies that make these. They are installed just below the grate and are replaced as needed.

Look on pages 12-13 of the attachment.

These inserts are widely used on the west coast where the stormwater regulations are strictly enforced. On the west coast, there are NPDES limits on stormwater discharge. If you can't meet the discharge standards for the stormwater discharge, most people install the inserts. The inserts are capable of meeting the strictest stormwater standards.

These inserts will be much more cost-effective than a sand filter vault.

 

[MES2022]

Thank you for the responses everyone. We have been considering the centrifuge style separators as well. I don't think the inserts would be used, they have been trying those already and they seem to spend more time than they want to maintaining them. What they really need to consider is their production and housekeeping approaches. They have mobile grinders that they use outside and grind products at random places throughout their outside facilities. So a mess gets made one place and then moves to another location and make another mess instead of trying to contain all the exterior work they do to one location. This would give them a concentrated place to apply an operation and maintenance program/practice. They do try to clean things up but obviously they aren't getting everything.

 

[bimr]

that they use outside and grind products at random places throughout their outside facilities.

You are describing something that is no longer an accepted industrial practice. Rather than trying to clean up after the fact, you should tell your client that these activities should be done under a roof to prevent stormwater from carrying away the mess.

Otherwise, if the facility is allowing these materials to run off with the stormwater, the facility must immediately apply for an industrial stormwater general permit.

These stormwater regulations have been in force for some time, but in most of the states, there is no money allocated for enforcement.

While you aren't in Minnesota, the Minnesota Industrial Stormwater Best Management Practices Guidebook can be used as a guide. Ohio may have something similar.

Link

If the facility is undergoing a major expansion to their facilities, it should be designed properly to eliminate the stormwater contamination.

 

[dhengr]

MES2022:
Let’s see if we’ve got this right..., The client is too inept and/or too lazy to clean up the mess they make at each small grinding site on the property, besides that, it costs too much and takes too long and ties up their best people; then, they don’t like maintaining any separation system in the storm sewer system either, which might be fairly economical and practical, but take some attention during rain storms. So their solution is a more expensive filtration system which requires significant maintenance although it might be somewhat automated. Why not some sort of a self cleaning screening system in the main sewer line? Why not something akin to the construction site erosion control fencing, around each of the small grinding sites until they are cleaned up after use? How can this fencing system be made reusable, and somewhat automated in its installation and pick-up? Could 300'x300' sites be laid out, in a two row checkerboard fashion, so several lengths of fence would serve sites on both sides of the fence at the same time? Otherwise, they might make a big contribution to their church, those people are generally in charge of miracles.

 

[bimr]

dhengr:
Enjoyed reading your post, but as I outlined above, the uncovered outdoor industrial activity is no longer an accepted practice and is a violation of the stormwater regulations. If you have an industrial activity outdoors where contaminants will runoff with stormwater, the industrial activity area should be under a roof to prevent stormwater from contacting the material. Especially for a new facility.

When the clean water regulations were developed years ago it was thought that end of sewer pipe wastewater treatment was adequate to improve water quality. After those regulations were in force, it was noticed that there is a substantial amount of pollution associated with stormwater. That is the reason that the stormwater regulations were imposed decades ago.

 

[FacEngrPE]

The permitting authority may be the state state or the EPA. More information at this link:
National Pollutant Discharge Elimination System (NPDES) Stormwater Discharges from Industrial Activities
Understanding the firm's permit is a necessary part of creating an appropriate design.

 

[FacEngrPE]

Ohio allows the use of "BMP's for this purpose Link to Ohio DEQ stormwater site.. Sand filters are specifically listed.

Virginia BMP clearing house indicates hydrodynamic BMP's can remove 20% of total phosphorous. For lighter than water plastic, you would need to ask the manufacturer.

The Virginia BMP clearing house also has an entry for approved filters "FILTERING DEVICES AWARDED 50% TP REMOVAL EFFICIENCY"

You would need to discuss with your sites permit writer if either of these would be accepted for your use case. I think putting the operation indoors is a really good idea. It may be possible to improve product quality with an indoor process.