Treatability of wastewaters from totally chlorine-free bleaching

Wastewaters from totally chlorine-free (TCF) bleaching were compared with wastewaters from chlorine-gas (CG) bleaching and elemental-chlorine-free (ECF) bleaching. Activated-sludge treatment of TCF wastewaters reduced COD by 55-65%, compared with 35-45% for wastewaters containing chlorine compounds. Chemical flocculation of biologically treated TCF wastewaters with aluminum sulfate resulted in 85% total removal of COD. TCF wastewaters were very light in color, in contrast to wastewaters from CG bleaching. Combined biological and flocculation treatments of TCF wastewaters reduced phosphorus by 97-99%. Nitrogen in TCF wastewaters was high because of the presence of EDTA (ethylenediamine tetraacetic acid). Activated-sludge treatment did not remove EDTA, but addition of aluminum sulfate to treated wastewaters reduced EDTA by 65%. Residual peroxide in TCF wastewaters made them highly toxic, although biological treatment removed this toxicity. Treated TCF wastewaters had higher levels of heavy metals and nonprocess elements than CG and ECF wastewaters. Changing the composition of the wastewaters had little effect on the operation of the activated-sludge treatment system.