Sludge is the residual solid, semisolid, or slurry material produced as a by-product of wastewater treatment processes. This sludge needs to be treated and disposed- off, in many countries as hazardous waste. In the ZDHC WWG 2,0, all kinds of sludge generated from primary, secondary and tertiary wastewater treatment processes, as well as fly ash generated from onsite incineration and any residues generated from ZLD treatments are covered under the definition of Sludge. Screen and Grit waste from primary treatment, scum or greasy waste, cleaning chemicals used for drum washing, machines and floors, and print paste waste is EXCLUDED from the scope of Sludge As per the SAP, if there are different types of sludge generated in a facility, a composite sample of these various sludge samples can be collected and tested as per the WWG 2,0 guidelines.
Sludge generated from industrial processes is hazardous in nature as it can contain:
- Organic MRSL substances that have the propensity to settle down/ partition into the sludge during WW treatment processes. Hence, AP/APEOs Chlorotoluenes and PAHs are included in WWG 2,0 test parameters for sludge
- Metals from dyes, pigments, cotton and piping systems
- Pathogens that can harm the environment and human health