Polyhexamethylene biguanidine used as a new type sewage sludge conditioning agent: Effect on sludge dewaterability and mechanism.

Dewatering is the basic procedure of sludge treatment and disposal, and environmentally friendly and efficient sludge conditioning methods are urgently needed. Polyhexamethylene biguanide (PHMB), a broad-spectrum germicide used in daily life and medicine, was proposed as a sludge conditioning reagent in this paper, and its effect on waste activated sludge (WAS) dewaterability was studied for the first time. Results showed that PHMB can improve sludge dewatering performance, and capillary suction time (CST) and water content (Wc) of dewatered sludge cake was reduced by 78.11% and 13.37% with 100 mg PHMB/g dry sludge (DS). Further investigation revealed that the sludge properties changed pronouncedly after PHMB conditioning, the bound water content decreased from 1.58 g/g DS to 1.29 g/g DS, the particle size (D50) increased from 34.3 µm to 39.2 µm, the zeta potential increased from -20.96 mV to -3.36 mV, and the flowability increased whilst the viscosity decreased. When the dose of PHMB was lower than 50 mg/g DS, it mainly reacted with extracellular polymeric substance (EPS), resulting in a decrease in its content, which was also manifested by the decrease of molecular weights. However, when the dose reached 100 mg/g DS, PHMB would disrupt the cytomembranes of microorganisms and release cellular contents, reflected by a corresponding growth of EPS contents and the intensity of Fourier transform infrared (FTIR) spectrum. And the scanning electron microscope (SEM) images showed that PHMB conditioning made cracks and holes on sludge microstructures. The key mechanism of PHMB improving sludge dewaterability was inferred as "organic molecules disrupting" and "sludge particles flocculating". These findings demonstrate that PHMB is promising to be a novel, effective, and environmentally friendly sludge conditioning reagent.

Insights into the enhancement of waste activated sludge dewaterability using sodium dichloroisocyanurate and dodecyl dimethyl ammonium chloride: Performance, mechanism, and implication.

Sludge dewatering is essential for reduction of sludge volume to cut the cost of transportation and disposal. Combined application of sodium dichloroisocyanurate (DCCNa) and dodecyl dimethyl ammonium chloride (DDAC) was attempted to promote sludge dewatering performance and physicochemical properties for the first time in this work. The results showed that capillary suction time (CST) and moisture content of dewatered sludge cake (Mc) decreased to 15.9 s and 61.54% compared to 144.5 s and 90.39% of raw sludge, respectively, with the addition of optimal dosage of 150 mg DCCNa/g DS and 125 mg DDAC/g DS. The conditioning mechanism of combined treatment was elucidated by investigating the variations of extracellular polymeric substances (EPS) composition, flocs morphological structure, rheological behavior, moisture distribution and Fourier transform infrared (FTIR) of sludge. It could be found that sludge floc cells were decomposed and bound water was released after DCCNa treatment. The bound water content was further decreased with the presence of DDAC. In addition, DDAC not only increased the zeta potential and flowability of sludge, but also reduced the surface tension and interact with oxygen-containing functional groups in sludge. As a result, the sludge dewaterability was significantly improved. Moreover, the calorific value analysis of dewatered sludge cake indicated that combined conditioning of DCCNa and DDAC presented the advantage of incineration disposal.