Recovery of Spent Liming Liquor Case study: Afrotan Tannery, Sudan

Spent liming liquor is produced from unhairing and liming processes. This study was carried out in Afrotan Tannery, by using the existing liming recovery unit in the tannery. The aim of the study is to determine and to evaluate the efficiency of the method of treatment applied in liming liquor recovery unit. The results showed that the value of pH was 12 and the values of TSS, Cl, NH4 and COD in liming liquor before treatment were 10623, 8511, 498 and 37396 mg/l, respectively. The value of pH is 11.5 and the values of TSS, Cl, NH4, COD and sulphide in liming liquor after treatment were 4321, 7796, 407, 21985 and1602mg/l, respectively. The liming liquor recovery unit receives 300 m3/day of spent liming liquor. 140 m3/day of the quantity is floated and precipitated as sludge. 60 m3/day of this sludge does not enter sludge treatment unit and directly is filled in land contaminating the soil with sulphide. 160 m3/day of the quantity is the treated spent liming liquor which is mixed with fresh makeup basic sodium sulfide and ammonium sulphate and recycled in unhairing and liming processes. The study concludes that it is important to conduct further studies to decrease COD in clear liming liquor and to send all sludge to sludge treatment unit.