Efficacy of Chitosan as a Coagulant Aid to Alum Precipitation of Congo Red In Wastewater

The use of chitosan prepared from prawn shells as coagulant aid for congo red (CR) dye removal from wastewater was investigated in this study. Characterisation of the prepared chitosan samples showed characteristics similar to commercially available ones. The coagulation – flocculation experiment was carried out using the jar test procedure. Both chitosan and alum were used separately for the dye precipitation and then combined together. The usage of alum alone showed no precipitating effect on the CR dye molecule, while chitosan was able to considerably reduce the concentration of the dye in solution. When chitosan was used as a coagulant aid in the alum precipitation, the amount (%) of dye removed increased greatly. Optimization of the process via study of effect of pH and flocculation time at optimum alum – chitosan combination indicated that pH 4-5 and settling time of 40 min were suitable conditions for maximum decolourisation of CR dye wastewater with about 98% efficiency. Moreover, study of settling characteristics of the sludge produced from the alum-chitosan synergy was better than that produced from either of them alone. Also, occurrence of redispersion and restabilization of the precipitate was not encountered.