Organic waste treatment solutions

Bags, film and bioplastics are separated from MSW’s organic fraction without wrapping around the shafts thanks to HDDS Ecostar technology (Hyper Dynamic Disc Screening). A special flap hooks bags and stringy materials and pushes them forward, keeping them above the screening surface up to the oversize; the free sleeves, independent of the shaft’s rotation, prevent plastics from building up on the shafts. This is exactly where traditional screens stop repeatedly for cleaning, and where HDDS keeps running instead.

On top of this, a second design feature comes into play: as it advances along the screening deck, the material meets a step that produces a sudden vertical drop. Because the organic matter inside the bags is wet, dense and heavy, this drop helps open the bag and release the organic fraction, recovered as undersize while the plastic film continues towards the oversize.

A useful clarification on bioplastics: mechanical screening separates by size and behaviour, not by type of polymer. A still-intact compostable bag (e.g. Mater-Bi) behaves like a conventional one, long and film-like, and is therefore carried to the oversize by the flap in exactly the same way: the screen does not distinguish compostable from conventional, that choice depends on the plant’s process.

A screen upstream of anaerobic digestion or composting is worth installing because it protects everything that comes after it. Incoming organic waste, the organic fraction of municipal solid waste (OFMSW), carries film, bags, straps and inerts that contaminate the substrate and wear down downstream equipment. A screen with DDS Ecostar (Dynamic Disc Screening) technology removes them upstream and delivers a drier material to the secondary shredders, increasing their capacity and reducing their wear.

A shaft that clogs with bags stops the line every shift: with flat-profile discs and the free-sleeve anti-wrapping system, this does not happen. The discs are made of Hardox, the anti-wear steel: no small advantage when the material is abrasive. In a documented comparison on MSW and compost pre-treatment, the Ecostar screen required 60 hours of maintenance per year against the 600 hours of a traditional disc screen.

The choice between DDS and HDDS technology for organic waste depends on how contaminated the incoming material is. DDS Ecostar is the baseline: flat-profile discs that, with a jolting movement, let the fine undersize fall through and move the oversize forward, even on wet material. When the OFMSW comes from MSW and is loaded with bags, film and packaging straps, HDDS Ecostar is the answer, its flap hooking these long materials and carrying them to the oversize.

The rule of thumb is simple: the more filamentous material there is, the more HDDS makes the difference. On cleaner “green” organic waste, DDS is already enough. Both were developed for the same purpose: reduce to the minimum the wrapping and clogging; but at different levels of difficulty.

It depends on the site’s volumes, space and logistics. Hexact Ecostar is the modular stationary screen for structured plants and continuous volumes, with 7.5 kW electric motors and a surface that can be expanded without replacing the machine. Hextra Ecostar is the mobile one — track or hooklift, also available in an electric version — designed for flexibility and for working in a loop with shredders. Nhexa Ecostar is the compact screen for medium-to-low throughputs and tight spaces, easy to handle even on difficult ground or directly at the landfill.

One figure to orient yourself: the Ecostar range reaches up to 200 t/h, but for organic waste the working range is 10–60 t/h, on both dry and wet material.

Better separation of organic waste does improve the quality of the downstream product, and it’s a direct relationship: upstream quality determines downstream quality. Removing plastics and inerts from the OFMSW means sending a cleaner, more homogeneous substrate to digestion or composting, with fewer contaminants in the digestate and in the final compost.

HDDS Ecostar technology makes it possible to obtain an organic fraction free of contaminants, while reducing the share of usable material that would otherwise end up as waste. Fewer inerts in the substrate also mean less abrasion and sedimentation in the later stages.

Organic waste screening yields fractions of 20, 30, 50, 80 and 100 mm, adjustable in real time by ±30% via inverter by varying the speed of the shafts. This lets you calibrate the separation without mechanical downtime, adapting it to the material, to the destination (substrate for digestion or a fraction for composting) and even to the season, when the moisture of the waste changes.

Organic waste can be treated while taking up less space in the plant with Ecostar’s dynamic disc screening technology, which delivers the same production volume as a trommel while halving footprint and energy consumption. The reason is geometric: the disc screen uses the entire screening surface, whereas a trommel separates only in the lower part of the drum and needs far greater lengths.

In a real case, two decommissioned trommels (25 metres in total) were replaced by a single 9-metre dynamic screen, at the same production output. This makes it possible to install screening even in urban plants with limited surface area, or to free up space for other process stages.