Experimental Study On Ozonation Of Wood Cooking Wastewater

Industrial wastewaters generally have characteristics of large discharge,complex composition,high concentration and poor biodegradability.It is necessary to select appropriate water treatment technology for each type of wastewater.Wood cooking wastewater contains a large amount of wood extract,among which lignin and other substances are the main reason for its poor biodegradability.Ozone method with the strong oxidizing potential,the advantages of fast oxidation,being less influenced by temperature and less secondary pollutants,has been widely applied in the industrial wastewater treatment.In this study,experiments on the treatment of wood cooking wastewater were carried out using ozone alone,sponge-iron/ozone,flocculation/ozone combined methods,and a comparative ozonation of sodium lignosulfonate was carried out.Through the changes of COD,TPh?the total phenol?,BOD₅/COD,UV₂₅₄ and UV₅₈₀ during the processes,and referred to the results in the literature,the ozone's effect on the biodegradability of wood cooking wastewater was speculated.This study can provide useful data and theoretical reference for the actual treatment of wood cooking wastewater.The main research results are as follows.?1?Changing ozone flux?20,34,66 and 91 mg/min?,initial pH of wastewater?4.03,6,8,10 and 12?and reaction time?10,20,30,40,50,60 min?,it was found that after 60 min under the conditions of an ozone flux of 66 mg/L and initial pH 4.03,the BOD₅/COD was increased from 0.22 to 0.42.?2?With different initial pH of sodium lignosulfonate?4,8 and 12?and the reaction time,it was found that the removal rate of TPh,sodium lignosulfonate content and COD reached55.64%?82.58%and 35.99%with the reaction time of 10,10 and 60 minutes respectively,under the condition that the initial pH was 4 and the ozone flux was 66 mg/L.These experiments showed that higher COD,TPh removal rate and lower sodium lignosulfonate removal rate were achieved under alkaline conditions?initial pH of 8 and 12?,while under acidic conditions?initial pH of 4?,lower COD and TPh removal rate,higher sodium lignosulfonate removal rate were achieved.Referred to the results in the literature,it is speculated that ozone is more selective for the benzene ring structure in lignin than phenolic hydroxyl groups.The degradation kinetics of sodium lignosulfonate at different concentrations?0.2,0.4,0.6,0.8,and 1.0 g/L?under saturated ozone concentration was explored,it was found that they followed first-order/pseudo-first-order reaction kinetic lines,the reaction rate constants were found between 0.18⁰.19 min^-1.?3?In the ozonation experiments of wood cooking wastewater,under acidic conditions?the initial pH of the wastewater was 4.03 and 6?,the lower COD removal rate,higher BOD₅/COD,higher TPh removal rate and higher UV₂₅₄ removal rate were achieved.Under alkaline conditions?the initial pH of wastewater was 8,10 and 12?,higher COD removal rate,lower BOD₅/COD,lower TPh removal rate and lower UV₂₅₄ removal rate were obtained.It was proposed that alkaline conditions may be suitable to oxidizing the biodegradable substances in the wastewater,and acidic conditions may increase in biodegradability.This may be related to the selectivity of ozone to lignin-based phenols in wastewater.?4?Using polymeric ferric sulfate?PFS?and polyacrylamide?PAM?as flocculant and coagulant respectively,the best flocculation conditions were obtained,for which the initial pH of wastewater was 10,and the dosage of PFS,PAM were 3.0 g/L and 0.75 mg/L.The flocculated effluent's pH was 4.28.The best initial pH of ozonation was selected to be 12.The total COD removal rate was 69.4%.