Understand sampling
Pretreatment is a process where a facility reduces, alters or eliminates pollutants in wastewater discharge prior to release of the water to the CETP. Some of the pretreatment examples include, but are not limited to, pH adjustment, filtration, biological treatment of the wastewater and other physical/chemical processes.
The pretreatment process may or may not generate sludge. The processes below, when installed as a standalone system, cannot be considered as pretreatment:
- Equalisation tank/homogenisation tank (if no chemicals are added in the equalisation tank/homogenisation)
The processes below, when installed as a standalone system, to be considered as pretreatment:
- Grit removal with the mesh size <6mm or ≥ 6mm (the residue collected here should not be classified as sludge).
- Equalisation tank/homogenisation tank (if chemicals are added in the equalisation tank/homogenisation and generate sedimentation, which is collected and disposed of by the facility, then this should be classified as sludge.
Wastewater discharge types and sample locations
There are five ZDHC supplier types under wastewater, listed below:
- Direct discharge
- Indirect discharge with pretreatment (with sludge)
- Indirect discharge with pretreatment (without sludge)
- Indirect discharge without pretreatment
- Zero Liquid Discharge (ZLD)*
*For suppliers to be classified as a Zero Liquid Discharge (ZLD) treatment system they must meet ZDHC’s definition of ZLD.
Additionally, there are three possible sampling locations, listed below:
- Untreated Wastewater (raw wastewater): Wastewater that is collected prior to any treatment.
- Discharged wastewater (effluent): Treated wastewater that is discharged to the environment, or partially treated or untreated wastewater that is discharged to a Central Effluent Treatment Plant (CETP) for further treatment. (This is not applicable to indirect discharge without pretreatment as well as to Zero Liquid Discharge facilities)
- Sludge: The residual solid, semisolid, or slurry material generated as a by-product of wastewater treatment processes, including primary, secondary and tertiary (ZLD) treatments.
Threshold limits for wastewater flow rates
Solution providers are required to conduct wastewater sampling and testing based on a threshold wastewater flow rate of 15 m3/day in the facility. This is because suppliers that discharge less than 15m3 of wastewater per day (for example, screen printing facilities that wash moulds, screens and tools) do not impact the environment in the same way as those that discharge more than or equal to 15m3 of wastewater per day (such as a typical dyehouse or tannery). The threshold wastewater average discharge applies to suppliers irrespective of the supplier’s production type or production processes. The flow rate is calculated as follows:
Sample locations
These tables acknowledge the difference between facilities with direct, indirect, zero liquid discharge and those with an average total industrial wastewater generated, that is equal to or more than 15 m3/day.
Testing Requirements for Suppliers that Generate on Average, Equal To, or More Than 15m3 of Industrial Wastewater per Day
| Test Parameters and sample locations/discharge type | ZDHC MRSL Sample untreated wastewater and test MRSL parameters | ZDHC heavy metals: sample discharged wastewater/effluent | ZDHC conventional parameters and anions sample discharged wastewater/effluent | ZDHC sludge sample sludge and test as per the major sludge disposal pathway |
|---|---|---|---|---|
| Direct | Yes | Yes | Yes | Yes |
| Indirect with pre-treatment (with sludge) | Yes | Yes (b) | No | Yes |
| Indirect with pre-treatment (without sludge) | Yes | Yes (b) | No | No |
| Indirect without pre-treatment | Yes | Yes (b) | No | No |
| Zero Liquid Discharge (ZLD) | Yes | No | Yes |
b= For the facilities with indirect without pretreatment discharge type ZDHC MRSL substances as well as ZDHC heavy metals (arsenic, cadmium, chromium (VI), lead, mercury) as explained in the above table should be sampled and tested only at untreated wastewater as there is no pretreatment involved.
Testing Requirements for Suppliers that Generate less than 15m3 of Industrial Wastewater
| Test Parameters and sample locations/discharge type | ZDHC MRSL (a) sample untreated wastewater and test MRSL parameters | ZDHC heavy metals sample discharged wastewater/effluent | ZDHC conventional parameters and anions sample discharged wastewater/effluent | ZDHC sludge sample sludge and test as per the major sludge disposal pathway |
|---|---|---|---|---|
| Direct | No | Yes | Yes | No |
| Indirect with pre-treatment (with sludge) | No | No | No | No |
| Indirect with pre-treatment (without sludge) | No | No | No | No |
| Indirect without pre-treatment | No | No | No | No |
| Zero Liquid Discharge (ZLD) | No | No | No | No |
a= Excluding ZDHC Heavy Metals
Testing Requirements for MMCF Facilities
Wastewater testing requirements for MMCF facilities do not depend on the volume of wastewater generated. Even if generated wastewater is less than 15m3 per day, all parameters mentioned in the MMCF Guidelines apply to a MMCF facility.
| Test Parameters and sample locations/discharge type | ZDHC Heavy metals sample discharged wastewater/effluent | ZDHC Conventional parameters and anions sample discharged wastewater/effluent | ZDHC Sludge Sample sludge and test as per the major sludge disposal pathway |
|---|---|---|---|
| Direct | Yes | Yes | Yes |
| Indirect with pre-treatment (with sludge) | Yes | No | Yes |
| Indirect with pre-treatment (without sludge) | Yes | No | No |
| Indirect without pre-treatment | Yes | No | No |
| Zero Liquid Discharge (ZLD) | No | No | Yes |