Study On The Influence Mechanism Of Precipitated Calcium Carbonate On Sludge Dewatering Process

Pulp and paper mill sludge is a byproduct of papermaking wastewater treatment,which has huge yield and high moisture content.Sludge dewatering is not only an important step of sludge reduction,but also a prerequisite for subsequent disposal and resource utilization.In this paper,precipitated calcium carbonate（PCC）was used as the research object to study the influence mechanism of PCC content on the dewatering performance of simulated paper sludge.On this basis,the synergistic mechanism of PCC,chemical conditioner FeCl₃ and fiber on simulated paper sludge dewatering process was studied.Firstly,the influence mechanism of PCC content on sludge dewatering was studied.The results showed that PCC could improve the dewatering performance of sludge.With the increase of PCC content（≤444 mg/g DS）,moisture content,effective moisture content,specific resistance of filtration（SRF）,net sludge solids yield（Y_N）and sludge compressibility all decreased.When the content of PCC exceeded 444 mg/g DS,the further improvement of sludge dewatering performance was negligible when the content of PCC continued to increase.The effect mechanism of PCC on sludge dewatering can be explained by Ca²⁺bridging to reduce blinding and PCC rigidity enhancement（i.e.PCC rigid structure）to reduce compressibility.Secondly,the effect of PCC/FeCl₃ conditioning on sludge dewatering performance was studied.The results showed that compared with the addition of PCC or FeCl₃ alone,the moisture content,effective moisture content,SRF,Y_N sludge compressibility and Zeta potential（absolute value）were further reduced after PCC/FeCl₃ conditioning,and the size of sludge floc was increased,indicating that PCC/FeCl₃ could further improve the sludge dewatering performance by synergy mechanism.Thirdly,the effect of PCC/fiber conditioning on sludge dewatering performance was studied.Through the analysis of sludge cake moisture content,SRF and sludge compressibility and other performance parameters,it can be seen that the combined conditioning of PCC and fiber can further improve sludge dewatering performance compared with the addition of PCC or fiber alone,that is,PCC and fiber have synergistic dewatering effect on the sludge dewaterability.The synergistic effect is related to fiber skeleton and PCC rigidity enhancement.Finally,the effects of fiber,PCC and FeCl₃ on sludge dehydration were studied.The analysis of SRF,moisture content and sludge compressibility showed that fiber/PCC/FeCl₃had synergistic conditioning effect.This synergy mechanism can be explained by FeCl₃bridging,Lewis acid properties of FeCl₃,fiber skeleton and PCC rigidity enhancement.