| The sludge deep dewatering is a common problem in current papermakingindustry. Due to the increase of the paper mills production, a great number ofsludge with high water content will be produced in the process of papermaking.Improving the dewatering properties of the sludge will not only make the sludgedisposal process easy, but also relieve the environmental problems. The spendingof sludge disposal in the pulp and paper mill has up to about50%of the effluenttreatment costs. Applying more effective pre-conditioning methods andcombining with more efficient mechanical dewatering device to reduce the finalmoisture content of the sludge and achieve sludge utilization can benefit to theenergy-saving and environmentally friendly income.The effect of sludge settlement performance, dehydration rate, transmittanceof the filtrate and its final cake moisture content on dewatering properties ofsludge were evaluated by adding different types of inorganic flocculants,different types, different molecular weights and different ionic organicflocculants polyacrylamide and different types of surfactants into the sludge.The results showed that when the dosage of inorganic flocculants was15ml(1.0g/L) FeCl3,20ml (5.0g/L) Al2(SO4)3and20ml (4.0g/L) PAC to the conditionsludge respectively, the moisture content was still more than80%. The final cakemoisture content reduced to74.90%,13.50%lower than not used while usingCPAM with the ionic degree5%, the molecular weight6million and dosage2.76%.When the cationic surfactant CTAB and anionic surfactant SDBS wasadded into the sludge, it had a positive on the settelement performance anddehydration rate of the sludge; the dosage of CTAB was0.10:1, the final cakemoisture content reached72.59%, which decreased by15.81%compared with theblank sample. It was also found that the temperature and pH in the mud system had a certain impact on the performance of the sludge through the single factorand orthogonal experiments. When CTAB and sludge system temperature was at15℃, sludge dewatering ratewas better than other temperatures. When the pHwas5, the settling properties of sludge became better than others. When thedosage of SDBS was0.06:1, the sludge system temperature at20°C and pH wasslight acid, sludge dewatering rate of the final cake moisture content decreased to71.29%. It was found based on analyzing each factor of the experiments, thedosage of CTAB or SDBS had a better effect on the final cake moisture contentthan other factors such as temperature and pH.When the surfactants and organic flocculants were used together, thesequence of first surfactant and then cationic organic flocculants could improvethe settling properties. When the amount of CPAM was1.40%and CTAB was0.05:1, the moisture content decreased to68.72%, which decreased by19.82%compared with the blank sample; when the amount of CPAM was1.0%andSDBS was0.03:1, the final moisture content would decrease to70.76%,whichdecreased by17.64%compared with the blank sample. These showed that CTABcombined with CPAM could enhance the performance of the sludge dewatering.Finally, through the economic accounting, we could know that when usedCPAM alone, the costs was the lowest. While the performance of the sludgedewatering was very well when the CTAB and SDBS respectively combinedwith CPAM to treat the sludge, it cost the most. It could seen by SEM after thetreatment of surfactant that the sludge flock was specially destroyed, the numberof complete and clear spherical flock decreased and the proportion of fineparticles increased, as well as part of sludge surface had became networkstructure.While the sludge particles by CPAM treatment became the larger flockbecause of the effect of the bridging the macromolecular chain. Surfactants onthe performance of the sludge dewatering were mainly depended on the effect ofthe dispersion and volatilization as well as its macromolecular chain could alsoplay a role of adsorption and bridge of the sludge flocks. |
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