Optimization Experiment Research Into Dewatering Process Of Oil Refining Wastewater Sludge

Sludge from oil refining wastewater contained the sediment of separationtank, scum of air-flotation tank and residual activated sludge. Its nature wasspecial, components were complex and emulsification degree was high. Itbrought great difficulty in sludge treatment. So it need to improve sludgedewatering ability in order to lay the good foundation for recycling of sludge.In this paper, using oil refining wastewater sludge from a refinery in thenorthwest as the sample, acidification oxidation and conditioning was used tooptimize the sludge dehydration process on high viscosity and high oil contentsludge, and the chemical conditioning was used to optimize the sludgedehydration process on conventional and low oil content sludge. By optimizingthe influence factors of sludge dewatering, the optimum process conditions ofsludge dewatering were determined. And on this basis,5L and50L amplificationtest of sludge dewatering were done. Specific conclusions were as follows:(1) The optimum process conditions of acidification oxidation andconditioning on the high viscosity and high oil content sludge were as follows:the pH of system was4, the temperature of reaction was35℃, the dosage ofH2O2was2.0g·L-1, m(H2+2O2):m(Fe)=4, the time of reaction was60min, thedosage of CaO was7.0g·L-1, the time of dewatering was5min and theseparation factor was1558. After processing, the water content and oil content ofthe mud cake were respectively71.0%~75.0%and under2%, the specificresistance of the sludge was about0.31×108s2·g-1. The optimum processconditions of chemical conditioning into the conventional and low oil contentsludge were as follows: the the concentration of CPAM was0.3%, the dosage ofCPAM was45mg·L-1, the time of dewatering was5min, the separation factorwas1558. After processing, the water content and oil content of the mud cakewere respectively88.0%～91.0%and2%~4%, the specific resistance of thesludge was about3.9×108s2·g-1. The water content of the mud cake was72.0%~78.0%after natural drying for24h. (2) The results of multi-factor orthogonal test on impacting dehydrationperformance of sludge were as follows: when using the methods of acidificationoxidation and conditioning to deal with the high viscosity and high oil contentsludge, the order of impacting factors on mud cake water content from big tosmall were the system pH, the reaction temperature, the H2O2dosage, thereaction time, m(H2O2):m(Fe2+) and the CaO dosage. The order of impactingfactors on SRF from big to small were the system pH, m(H2+2O2):m(Fe), theH2O2dosage, the reaction time, the CaO dosage and the reaction temperature.(3) The results of indicators content analysis on the sludge centrifugalsupernatant were as follows: for the high viscosity and high oil content sludge,within a certain range, the content of SS, COD, oil and turbidity in sludgecentrifugal supernatant were decreased with the increase of the H2O2dosage.When reaction time was60min, the content of centrifugal supernatant were lessthan those of30min. For the conventional and low oil content sludge, the contentof SS, COD, oil and turbidity in sludge centrifugal supernatant were reduced andthen rose with the increase of the CPAM dosage. And the centrifugal supernatantcontent under the high molecular weight are smaller than those of low molecularweight.(4) The results of amplification test on5L and50L of sludge dewateringwere as follows: when the high viscosity and high oil content sludge wereprocessed by removing oil and reducing viscosity and centrifuging, the watercontent and oil content of the mud cake were respectively72.0%~79.0%andunder2%. SRF was about0.38×108s2·g-1. The centrifugal separations werebasically clear. The COD dosage was under450mg·L-1, The SS dosage wasunder150mg·L-1, the oil content was under500mg·L-1and the turbidity wasunder100NTU. When the conventional and low oil content sludge wereprocessed by chemical conditioning and centrifuging, the water content and oilcontent of the mud cake were respectively89%~94%and2%~4%. SRF wasabout4.0×108s2·g-1. The water content of the mud cake was73.0%~80.0%afternatural drying for24h. The centrifugal separation were basically clear. The CODdosage was under450mg·L-1, The SS dosage was under80mg·L-1, the oilcontent was under150mg·L-1and the turbidity was under80NTU.(5) The results of morphology changes on the high viscosity and high oil content sludge were as follows: the particles structure of untreated sludge werecompact, sturdy, and more scattered distribution. After process of chemicalremoving oil and reducing viscosity and conditioning, the sludge particlesstructure become loose, formating better permeability and porous mesh-likeskeletal structure, thus improving the sludge compressibility and dehydrationproperty.