Monitor microfibre discharge in wastewater
Natural and synthetic textile fibres can fragment during wet processing and finishing, then enter the aquatic environment through discharged wastewater. The scientific definition of a microfibre (also referred to as fibre fragmentation) is defined as a synthetic fibre with a diameter of less than ten micrometres.
Total Suspended Solids (TSS)
Suppliers should monitor the Total Suspended Solids (TSS) results and ensure that it meets at least ZDHC Wastewater Foundational Level requirements. If the values of TSS are higher than the Foundational Level, suppliers must undertake a RCA and upload a CAP to the ZDHC Gateway.
Studies by Hohenstein, ZDHC and The Microfibre Consortium (TMC) have established a direct correlation between the Total Suspended Solids (TSS) of discharged effluent and the number of microfibres released from a wet processing facility; as determined by Dynamic Image Analysis (DIA). Thus, the TSS parameter can be used as an indicator or measure of fibre fragmentation and monitoring.
Reducing the TSS in discharged wastewater can directly reduce the level of microfibre discharge in the wastewater stream. These studies clearly indicate that failure to meet foundational limits for TSS potentially results in undesirable levels of release of microfibres into the environment and any non-conformance should be viewed as a very high priority regarding this newly identified environmental threat.
Furthermore, ZDHC stakeholders should be aware that achieving Progressive and, ultimately, Aspirational Levels for TSS will reduce microfibre releases by an average of ~70% and ~94% respectively, compared to an average Foundational Level conformance.
Facilities should consider determining their own microfibre release profile using a Dynamic Image Analysis (DIA) method, after which TSS tests can be used to monitor microfibre releases with a good degree of accuracy.
Microfibre releases in discharged effluent can be effectively minimised by optimising the operation of the clarifiers in an Effluent Treatment Plant (ETP). If operated and maintained efficiently, such measures should meet Foundational Levels and in most instances are capable of meeting Progressive Levels. Additional investments in ultrafiltration, reverse osmosis or MBR (membrane bio reactor) effluent treatment technology can also be explored to ensure conformance to Aspirational Levels.
TSS test results will be reviewed on an ongoing basis and it is anticipated that limits are likely to be revised downwards in future updates.
Click here for a further article on microfibre studies
ETP and microfibres
In a properly functioning ETP, microfibre emissions are settled by gravitation in ETP clarifiers and become part of the sludge. To minimise releases to the environment, it is recommended not to dispose to land applications (Sludge Disposal Pathways F and G).