Effects of calcined aluminum salts on the advanced dewatering and solidification/stabilization of sewage sludge

The high moisture content （80%） in the sewage dewatered sludge is the main obstacle to disposal and recycling. A chemical dewatering and stabilization/solidification （S/S） alternative for the sludge was developed, using calcined aluminum salts （AS） as solidifier, and CaCl 2 , Na 2 SO 4 and CaSO 4 as accelerators, to enhance the mechanical compressibility making the landfill operation possible. The properties of the resultant matrixes were determined in terms of moisture contents, unconfined compressive strength, products of hydration, and toxicity characteristics. The results showed that AS exhibited a moderate pozzolanic activity, and the mortar AS 0 obtained with 5% AS and 10% CaSO 4 of AS by weight presented a moisture contents below 50%–60% and a compressive strength of （51.32 ± 2.9） kPa after 5–7 days of curing time, meeting the minimum requirement for sanitary landfill. The use of CaSO 4 obviously improved the S/S performance, causing higher strength level. X-ray diffraction, scanning electron microscopy and thermogravimetry- differential scanning calorimetry investigations revealed that a large amount of hydrates （viz., gismondine and CaCO 3 ） were present in solidified sludge, leading to the depletion of evaporable water and the enhancement of the strength. In addition, the toxicity characteristic leaching procedure （TCLP） and horizontal vibration （HJ 557-2009） leaching test were conducted to evaluate their environmental compatibility. It was found that the solidified products conformed to the toxicity characteristic criteria in China and could be safely disposed of in a sanitary landfill.

Enhanced dewatering characteristics of waste activated sludge with Fenton pretreatment： effectiveness and statistical optimization

In this work, the enhanced dewaterabing characteristics of waste activated sludge using Fenton pretreatment was investigated in terms of effectiveness and statistical optimization. Response surface method （RSM） and central composite design （CCD） were applied to evaluate and optimize the effectiveness of important operational parameters, i.e., H202 concentrations, Fe2＋ concentrations and initial pH values. A significant quadratic polynomial model was obtained （R2= 0.9189） with capillary suction time （CST） reduction efficiency as the response. Numerical optimization based on desirability function was carried out. The optimum values for H202, Fe2, and initial pH were found to be 178 mg-g-1 VSS （volatile suspended solids）, 211mg.gI VSS and 3.8, respectively, at which CST reduction efficiency of 98.25% could be achieved. This complied well with those predicted by the established polynomial model. The results indicate that Fenton pretreatment is an effective technique for advanced waste activated sludge dewatering. The enhancement of sludge dewaterability by Fenton＇s reagent lies in the migration of sludge bound water due to the disintegration of sludge flocs and microbial cells lysis.