Conditioning of Oily Sludge with Alum

Sludge dewatering is a process whereby water is removed from sludge so as to reduce its volume and alter its physical state from semisolid to damp solid. This physical change reduces the volume of sludge considerably and therefore the cost of disposal. The degree of reduction of sludge volume or dewatering is a function of the characteristics of sludge and the type of dewatering device. Sludge characteristics such as specific resistance, capillary suction time(CST), filter yield and solid content can be determined in the laboratories. Knowledge of these characteristics with different dosages of sludge conditioners helps in effective dewatering and sludge handling operations.Oil and grease have an affinity for suspended solids. Experiences show that the presence of oil in wastewater results in poor substrate utilization causing less aerobic treatment and subsequently hinder settling and dewatering processes. Sludge samples with different oil contents varying from 1.8% to 8.0% by weight have been examined in the laboratory to find out their specific resistance, capillary suction time and filter yield. Alum was used as a conditioner. Different dosages of alum varying from 2% to 12% by weight were used to determine the optimum chemical dosage for varying oil contents. Buchner funnel apparatus, filter leaf apparatus and capillary suction time test apparatus were used to determine the dewatering characteristics specific resistance, filter yield and capillary suction time respectively.Addition of alum decreases the specific resistances and capillary suction times of oily sludges rapidly upto 4% dosages. Alum dosages beyond 4% only increase the solids content in the sludge cake and increase the sludge volume to be handled. The total suspended solids of filtrate decrease with alum dosage. The correlations between dewatering characteristics were studied. A correlation between CST and specific resistance to filtration was established. CST can be measured easily and quickly in the laboratories. Using the CST and the correlation a quick prediction on dewaterability can be established.