Utilization of fine powder in demolition concrete as recyclable coagulant in removing color from dye-bearing wastewater

Abstract

The fine powders in demolition concretes with Portland cement, high alumina cement or white silicate cement as binders were used as coagulants to treat wastewater containing disperse red S-GR (typical hydrophobic dye) or reactive brilliant blue X-BR (typical hydrophilic dye). The efficiency in removing a color from wastewater was examined at varying contact time, dosage and regeneration cycles. In addition, the coagulation sludge was characterized by thermal analyses and X-ray diffraction technique for recycling. High alumina cement can coagulate both dyes at a relative low dosage of 2–3 g/L, but regeneration performance was poor. The coagulation with white silicate cement reached a color removal of 98 % for disperse red S-GR at a dosage of 6 g/L and 90 % for reactive brilliant blue X-BR at a dosage of 18 g/L. Portland cement showed a rapid coagulation rate and >95 % color removal for both dyes even after seven cycles of coagulation and sludge calcination. The dosage of the coagulant required for active brilliant blue X-BR coagulation (10 g/L) was much higher than that for disperse red S-GR coagulation (2.5 g/L). It is concluded that Portland cement can be used as a recyclable coagulant in the treatment of dye-bearing wastewater.