Concentrating contaminants: CDE

Concentrating contaminants: CDE

CDE’s Daniel Webber explains how high-pressure filtration and decontamination can increase the resale potential of construction and demolition waste.

The NSW EPA’s new construction and demolition (C&D) waste guidelines, released April 2019, highlight environmental risk via contamination and poor recycling processes as a core concern.

Daniel Webber, CDE’s Regional Manager for Australasia, says the presence of contaminants in the C&D stream is particularly significant, given one of the material’s major resale markets is road base.

“If the material used in road base contains heavy metals or polycyclic-aromatic hydrocarbons, which are known to be carcinogenic, those materials can leach out and penetrate the water table, and once they enter the water table, they can potentially contaminate drinking water,”
Daniel says.

For CDE, an international materials wet processing design and manufacture company, eliminating contaminants in C&D waste is critical to market viability.

“One of the first things we noticed when we first began working with the C&D waste sector was that there are no completely pure C&D sites.

“They all drag contaminated soil in eventually, and when there are no clean sites, there’s no clean materials. CDE quickly learned that this was something we needed to address with our clients.”

A central challenge to addressing the issue, Daniel says, is the variability of C&D contamination regulations across jurisdictions.    

“Conflicting regulations range from waste levy rates, urban development and state planning zones, to contaminant levels and disposal requirements,” he explains.

“We need to be across all the various legislative requirements and, as such, prioritise working in partnership with our clients to achieve that.”

According to Daniel, leachate is a focal point when dealing with C&D. He adds that because of the location of most C&D plants, large tailing ponds are often unfeasible.

“C&D is not like virgin mining or quarrying, which happens in the outer suburbs or the regions. Most construction sites are in metropolitan areas,” he says.

“To minimise transportation costs and therefore maintain resource recovery practicality, a lot of resource recovery also happens in metropolitan areas, meaning operators have to be much more cognisant of the contaminant problem.”

To remove contaminants, CDE facilitates two separate processing methods, both of which can be customised to suit individual client needs. Daniel adds that contaminants include anything from unwanted material such a plaster board and heavy metals, to dangerous chemicals such as PFAS.

“To wash and process contaminated C&D material, CDE designs plants that push contaminants into a tertiary water body for filtration, or alternatively, into sludge for processing via filter press technology,” Daniel says.

“When a client chooses the filter press option, their material is passed through mesh under extremely high pressure to produce a dry filter cake, which is then discharged into a bay below the filter press enclosure.”

Daniel says the filter press method allows CDE-designed plants to salvage 90 per cent of the original feedstock material.

“If a client is running a 200-tonne-per hour plant, with feeds coming through the front end, CDE equipment can concentrate existing contaminants into 20-tonne-per-hour of feed material.

“That means 180 tonnes of material can be repurposed and put straight back into the market as clean construction material.”

Additionally, Daniel says by concentrating contaminants, operators can save on landfill charges and prevent extra investment in waste storage equipment. Effectively removing contaminants also requires high-energy scrubbing and dewatering cyclone systems.

“By introducing CDE technology, plant operators can eliminate the need for settling ponds, reduce the space required to accommodate a washing plant and maximise water recycling.”

CDE’s minimum target, Daniel says, is an 80 per cent recovery rate, designing plants to increase traditionally unusable recycled sand and aggregates for multiple resale applications.

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