The Effect Of Hydrothermal Method Combined With Advanced Oxidation Technology On The Deep Dewatering Performance Of Sludge And Its Mechanism

Sludge treatment has been a major problem in China's environmental management in recent years.More and more attention has been paid to sludge treatment,and related policies have been introduced to regulate the requirements for sludge treatment and disposal.The main problem that restrict sludge treatment is the difficulty of sludge dewatering.Sludge pretreatment is one of the most effective solutions to improve sludge dewawterability.In this paper,the sludge samples were taken from a sewage treatment plant in Maanshan,and a combination method of hydrothermal treatment and advanced oxidation technology was used to improve sludge dewaterability.Two advanced oxidation technologies were selected,i.e.,Fe SO₄/Ca?Cl O?₂ and Na₂S₂O₈/CuFe₂O₄.Effects of hydrothermal conditions,amount of oxidant,and addition ratio on the dewatering performance of sludge were analyzed.Moreover,the moisture distribution of sludge and the degradation mechanism of EPS were also studied to explore the inherent mechanism and factors that influence the sludge dewatering performance.Hydrothermal treatment combined with advanced oxidation pretreatment experiments were conduced.The results showed that hydrothermal method is the most important factor for improving sludge dewatering performance,and advanced oxidation technology played an auxiliary role.Hydrothermal treatment promotes the generation of active free radicals,and the oxidant acts as a hard spot.The synergy between the two methods promotes improved sludge dewatering performance.For Fe SO₄/Ca?Cl O?₂combined hydrothermal pretreatment method,sludge dewatereability reached the optimal value when the hydrothermal temperature is 180°C,the molar ratio of Fe SO₄/Ca?Cl O?₂ is 1.25,and the amount of Ca?Cl O?₂ added is 0.04g/g-DS.The sludge filtration performance is increased by about 98%,the dewatering rate is increased by about 62.02%,and the water content of the sludge mechanical dewatering cake is reduced to 51.72%.Na₂S₂O₈ and CuFe₂O₄ was treated as oxidant and catalyst in the Na₂S₂O₈/CuFe₂O₄combined hydrothermal pretreatment method.In this experiment,the prepared magnetic composite material?CuFe₂O₄?was used to catalytically activate the oxidant?Na₂S₂O₈?,and promote the generation of active radicals.The recovery rate of CuFe₂O₄was about 50%.Sludge dewatereability reached the optimal value when the hydrothermal temperature is 150?,the mass ratio of Na₂S₂O₈/CuFe₂O₄ is 2:1,and the added amount of Na₂S₂O₈ is 0.08mmol/g-VSS.The sludge filtration performance is improved by about 51.43%.Simultaneously,the dewatering rate increased by 58.62%,and the moisture content of the sludge mechanical dewatering cake was reduced to51.57%.The results showed that the optimal hydrothermal reaction temperature was decreased to a lower level by the addition of oxidant.The moisture distribution and the functional groups of sludge changed after hydrothermal oxidation reaction.It could be concluded that EPS degraded after sludge pretreatment.The content of hydrophilic groups?C-O and C=O?decreased,and the content of hydrophobic groups?C-C/C-H?increased,which prohibited the binding between water and sludge.The surface bound water was reduced and the interstitial water and free water were increased,which makes the water in sludge easier to be mechanically removed and thus improved the dewatering performance of the sludge.According to quantum chemical calculations,the oxygen-containing functional groups in EPS have a high surface reactivity,and it is easy to adsorb water molecules and form hydrogen bonds,causing the high hydrophilicity and high water content of the sludge.Based on the calculation results of BDE and bond order analysis,the break order of the oxygen-containing functional groups in sludge was obtained,i.e.,the carboxyl C-O Bonds of in Dextran,Cellulose and Poly-gamma-glutamic acid>the C–C bond in Poly-L-lysine>the C–C bond in Poly-gamma-glutamate.Based on the above results and the actual sludge treatment process,a hydrothermal mechanical dewatering process was designed.The energy balance in the system was calculated.The results showed that the main energy consumption in the hydrothermal mechanical dewatering process is consumed by the hydrothermal reaction.Compared to the traditional thermal drying process,it was found that the energy consumption required to remove the same moisture for the hydrothermal mechanical dewatering process is only 32.24%of the energy consumption for thermal drying.