Experimental Study On High-efficiency Extraction Of Polymeric Substances From Excess Sludge

Resource recovery is an inevitable direction for future wastewater treatment technologies.Among them,the recovery of valuable elements and substances from excess sludge in wastewater treatment is the focus of future research.In addition to phosphorus resources and chemical energy,the excess sludge contains many polymeric Substances such as extracellular polymeric substances?EPS?.These polymeric substances synthesized by bacteria have unique chemical properties.They can be used such as heavy metal adsorbents,biological flocculants,soil conditioners,thickeners high-value flame retardant materials,even making high-end jewelry.However,limited by the original content in the sludge and the extraction method,the extraction efficiency of EPS is often very low.In this regard,the subject research proposes a surfactant-enhanced ultrasonic extraction method,which aims to increase the EPS extraction efficiency,and at the same time extracts the polymeric substances released by the bacteria cell wall breaking are extracted to expand the application scope of the excess sludge resources.The anionic surfactant sodium dodecyl sulfate?SDS?and cationic surfactant cetyltrimethylammonium bromide?CTAB?were used to enhance the ultrasonic method to extract the polymeric substances in sludge.The optimization experiments of extraction conditions showed that the best extraction situation is the power of 100 W and pulse time of 5 min,the surfactant concentrations of 0.10 g/L.Extraction amounts increased 76.5%and 53.1%for CTAB and SDS,respectively.Organic substances extracted at high surfactant concentration undergo centrifugal sedimentation,resulting in lower extraction efficiency.Surfactant-enhanced ultrasonic method had synergistic effect,which promoted the disintegration of the sludge floc structure and reduce the particle size,superior to the surfactant method and the ultrasonic method alone.The characteristic analyses of the extracted polymeric substances showed that they contained mainly proteins,polysaccharides,nucleic acids?DNA?and inorganic elements.High surfactant concentrations precipitate DNA and acidic polysaccharides,and experimental data showed that DNA content decreases.Surfactant-enhanced ultrasonic method can increase protein content,but the nanometer size of the extracted polymeric substances was smaller.The analyses of Fourier infrared spectroscopy?FTIR?and X-ray photoelectron spectroscopy?XPS?showed that functional group types are similar in the polymeric substances extracted by the two methods,including hydroxyl,carboxyl,and amide groups,however their contents were very different.The O 1 s spectrum peak fitting pointed out that the polymeric substances extracted by surfactants-enhanced ultrasonic method contained more C-OH,while more C=O by ultrasonic method alone.These functional groups concerned with nature of polysaccharide,showed that the polymeric substances extraction by both methods have different properties.Similar to the previous methods,the polymeric substances extracted by the proposed method also has a high adsorption capacity for heavy metal ions.The experimental results showed that the removal rate of Pb²⁺reached 98.5%.Langmuir curve fitting revealed that the adsorption capacity can be comparable to the commercial adsorbent,and therefore,it can be considered as a novel potential biosorbent.FTIR and XPS analysis revealed that the characteristic functional groups such as hydroxyl group,carboxyl group,phosphate group and amide group in the extracted polymeric substance were combined with Pb²⁺through complexation reaction and ion exchange.C=O in the polymeric substances extracted by ultrasonic method alone played an important role in the adsorption,while C-OH played an important role in the polymeric substances extracted by surfactant-enhanced ultrasonic method...