Evaluation of environmental impact of typical leather chemicals. part ii：biodegradability of organic tanning agents under activated sludge

Abstract： The biodegradability of typical organic tanning agents, including aromatic syntans, aldehydic tanning agents and acrylic tanning agents, were investigated. The results showed that the biodegradation behaviors of these leather chemicals are closely associated with their chemical structures, molecular weights and compositions. Therefore, different organic tanning agents might result in different environmental impacts even though they belong to the same type of tanning agent. The four aromatic syntans tested in experiments exhibited low biodegradability in general. Among them, phenol-based syntan was not biodegradable and phenol-sulphone-based syntan produce a strong inhibitory effect on respiration of activated sludge. Comparatively, naphthalene-based syntan was somewhat easier to be biodegraded than other aromatic syntans. In the cases of aldehydic tanning agents, both formaldehyde and glutaraldehyde were not biodegradable and were toxic to organisms in activated sludge. Thus, they have potential hazardousness to inhibit biodegradation of other organic compounds in wastewater. However, an aliphatic aldehydic tanning agent tested in experiments was biodegradable and showed no toxicity to microorganisms in activated sludge. As for acrylic tanning agents, experimental results indicated that commercial anionic products have no negative effect on biodegradation activity of activated sludge but they themselves were hardly biodegraded. Whereas, cationic acrylic tanning agents have potential to inhibit activated sludge process when presented at a high concentration.