Design and Inspection of Gross Pollutant Traps

14 May 2018

Before this post starts rifling off data about gross pollutant traps, we need some background. Contextually, it comes down to this, the notion that a primary barrier determines the efficiency of a waterway’s filtration system. Sure, there are material screens at work throughout stormwater drainage systems, but a frontline barrier meets the brunt of any muck-filled assault. Ground filth or litter, what design factors stop this messy invasion?

Workable GPT Design Ideas

In principle, a nominated Gross Pollutant Trap (GPT) solution is expected to function during the worst flooding events. Organic matter, including plastic bottles and metal cans, are flow-hampering obstacles. They’ll quickly choke the system opening, so our solution must somehow keep the water moving. Looking towards a high-flow water corridor, there are several litter-collecting mechanisms available to the discerning technical services engineer. Litter booms stretch across fast-flowing streams. They direct trash to separation chambers where they can be cleared periodically. Weirs and nets carry out similar duties. Then, over at a ground opening, there’s a partially concealed pit. In here, silt baskets and mesh iron grates provide a litter barrier. As the non-biodegradable material drops into this pit, a wet sump scoops up the waste before it chokes the filtration system.

Gross Pollutant Trap Inspections

Any half-capable consulting service can design a litter trap or a grated pit aperture, the kind of site that collects floating rubbish before it enters our waterways. The real design challenge comes from constructing a solution that’s self-sustaining. The elected design has to stop silt, particles that are larger than 5mm, and it also has to prevent those bottles and waste products from travelling any further. Moreover, the filtration system must channel the waste into a collection basket or wet sump pit. As those dirt-clearing containment units fill, the first actionable inspection operation is initiated. Workers remove the baskets, cranes lift heavier sump containers, and the rubbish is dried before it’s compacted and removed. The inspections continue. Is the litter boom failing? What about the silt basket? Is that basket clean and operational?

Although such design and inspection questions may seem tiresome, remember that this is the first line of defence in a wastewater filtration system. Furthermore, a medium-sized city could contain hundreds of these material filtering assets. They care for our rivers, protect wastewater corridors, and keep our waterways clear of infrastructure choking litter dams. Designed to filter large volumes of plastic, paper and other imperishable items, the screening apertures and catchment sites must cope with this messy outpouring without causing an intake choke.

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