Study On The Effect Of Near-anode Sludge Modification With Calcium Oxide On Electro-dewatering Performance

The efficiency of common sludge electro-dewatering(EDW)is restrained by the following issues:1,the near-anode sludge dries out quickly,causing a rapid increase in electrical resistance;2,the pH at anode decreases by the accumulation of H+ from the electrolysis of moisture,resulting in a decrease in Zeta potential(?).In order to improve this situation,in this study,calcium oxide(CaO)was used for near-anode sludge modification to increase its pH and electrical conductivity.The impacts of the dosage of CaO and the thickness of modified sludge on the dewatering efficiency,reduction effect,economic benefit and other aspects of sludge EDW were analized,and then the optimal CaO dosage and modified sludge thickness were obtained.On this basis,the effects of constant voltage mode and constant current mode on the performance of EDW were further explored,so as to optimize the experiment.The main conclusions of this study are as follows:(1)Near-anode sludge modification with CaO weighing 3%-5%mass of raw sludge(mu(RS))improved the filtrate rate and moisture content decreasing rate,so the time to obtain target moisture content(60%)was shortened from the blank group's(no CaO added)1060 s to 910 s-590 s.After EDW,the final moisture content of sludge was 54.5%-44.3%,below the blank group's 57.9%.When 3%-5%mu(RS)of CaO was added,the effect of sludge EDW was improved.However,the energy consumption(ERW)increased from the blank group's 0.157 kW·h/kg H2O to 0.233 kW·h/kg H2O—0.271 kW·h/kg H2O.Economically and energetically,the experiment with 4%mu(RS)of CaO added for near-anode modification was the optimal condition in this research,due to its second smallest KSiEDW(9.6 kW·h2/(kg DS)2),the best sludge reduction effect(67.2%),lower final moisture content(46.2%),less time(640 s)to obtain target moisture content,and moderate CaO dosage(4%).(2)Adding 4%mu(RS)of CaO to modify 4 mm-6 mm of near-anode sludge improved the filtrate rate and moisture content decreasing rate,so the time to obtain target moisture content was shortened from the blank group's(0 mm of modified sludge)1060 s to 880 s-620 s.After EDW,the final moisture content of sludge was 54.4%-46.8%,below the blank group's 57.9%.When 4%mu(RS)of CaO was added to modify 4 mm-6 mm of near-anode sludge,the effect of sludge EDW was improved.However,the energy consumption(ERW)increased from the blank group's 0.157 kW·h/kg H2O to 0.212 kW·h/kg H2O-0.275 kW·h/kg H2O.Economically and energetically,the optimal modified sludge thickness was 6 mm in this research,due to its smallest KsiEDW(10.3 kW-h2/(kg DS)2),the best sludge reduction effect(67.5%),lowest final moisture content(46.8%),and least time(620 s)to obtain target moisture content(3)Under the constant voltage mode at 35 V,the sludge EDW can obtain target moisture content faster,and obtain lower final moisture content.In this condition,it took only 420 s to obtain the target moisture content,and finally the moisture content of sludge was reduced to 39.3%.Under the constant current mode at 2.0 A,the sludge EDW can obtain target moisture content faster with less energy consumption.At this time,the time and energy consumption(ERW)to obtain the target moisture content were only 760 s and 0.167 kW·h/kg H2O,respectively.