Extrction Of Proteins From Excess Activated Sludge By Composite Enzymatic Hydrolysis

In recent years,with the construction of a large number of urban sewage treatment plants andurban sewage treatment facilities,China has built the sewage treatment plant whose capacity ofsewage treatment is nearly80million m3/d,which effectively curb the pollution of waterbodies.But At the same time,the sewage treatment bring a large quantity of sludge.According tostatistics,the annual production of dry sludge in China increased to11.2milliontons.Furthermore,the treatment of excess sludge is reported as high as20%-45%of the total costof sewage treatment pant.Therefore,through the cost analysis,the sludge has become the limitingfactor directly affect the normal operation of the sewage treatment plant.For such a huge amountof sludge,the final disposal is harmless and resources treatment.It is not only turning the sludgeinto treasure,but also an effective mean to reduce the cost of sludge disposal and an effective wayof sludge disposal and resource combination.According to reports,the crude protein content in the excess sludge is known to account forbetween30%and60%of the weight of dry sludge. For these rich resources of protein,someresearchers have used methods to extract the sludge protein,such as physical,chemical and soon,but composite enzymatic extraction of sludge protein has been reported rarely.In this study, thedigested and dry excess sludge of a sewage treatment plant in Qingpu district of Shanghai wasused as the main raw material.On the basis of extraction of proteins from excess activated sludgeby single enzymatic hydrolysis,selected three enzymes which have higher extraction rate andconstitute three groups of composite enzymes.Extract proteins from excess activated sludge by thethree groups of composite enzymes with their optimum condition.Selected a group of the highestrates of protein.Then extracted proteins from excess activated sludge by this group of compositeenzymatic and studied the best conditions for extraction of proteins from excess activated sludgeby composite enzymatic hydrolysis and finally,through the combination of different pretreatmentsand metal ions, studied the effect of pretreatment and metal ions for extraction of proteins fromexcess activated sludge by composite enzymatic hydrolysis, laid the foundation for improvingenzymatic extraction of excess sludge protein as well as the utilization of excess sludge in thefuture.The main conclusions of the experiments were as follows:(1)The pH and moisture content of the excess sludge were6.8and82.7%.On the basis ofextraction of proteins from excess activated sludge by single enzymatic hydrolysis,selected threeenzymes which have higher extraction rate and constitute three groups of compositeenzymes.Extracted proteins from excess activated sludge by the three groups of compositeenzymes with their optimum condition.The result of measurement using Kjeldahl methodindicated that composite enzymes which composed by alcalase and nematolyt,among others,werethe best composite enzymes and this composite enzymes combined with single factor experimentshowed that the optimal hydrolysis conditions：enzyme ratio (alcalase：nematolyt) is1:12,pH is7.0,temperature is55℃,enzyme dosage is5%,reaction time is4h,liquid-solid ratio is4:1,underwhich the extraction rate of77.16%was achieved.(2)Three sludge pretreatment method-ultrasonic, microwave, hot water solution combinedwith the composite enzymes which composed by alcalase and nematolyt,by changing the single factor experimental conditions to determine the highest protein extraction rate of the threedifferent pretreatment combined with the composite enzymes.The results showed that:In thecontext of the same energy,The composite enzymes combined with Ultrasonic pretreatment got thehighest protein extraction rate and the optimal hydrolysis conditions were that Ultrasonic acousticenergy density1.2w/ml,Ultrasonic time70min,enzyme ratio (alcalase： nematolyt)1:12,pH7.0,temperature55℃,enzyme dosage5%,reaction time4h,liquid-solid ratio4:1,under which theextraction rate of77.16%was achieved.It is clearly superior to the single extraction withcomposite enzymatic hydrolysis.Metal elements including harmful heavy metals contained inproteins were detected as well,which showed the concentrations of them did not exceed the limitsof national hygienic standard for feeds.So,it was concluded that extraction of proteins from excessactivated sludge by ultrasound combined with composite enzymatic hydrolysis was security.(3) In order to investigate the effect of metal ions on extraction of proteins from excessactivated sludge by ultrasound combined with composite enzymatic hydrolysis, a laboratoryexperiment was set up and enzyme activity and protein extraction rate were measured to exploretheir relationship with the added metal ions. The results showed that the monovalent metal ionsNa+and K+had little impact on enzyme activity and protein extraction rate.Different divalentmetal ions had different influence on enzyme activity and protein extraction rate. Among alkalineearth metal ions, Mg2+could promote the reaction while Ca2+inhibited the reaction. The metal ionsin transition Mn2+could improve the enzyme activity and protein extraction rate while the otherions Ni2+、Cu2+、Zn2+would weaken the enzyme activity and protein extraction rate.Heavy metalions Pb2+and Cd2+would both inhibited the reaction. When the concentration of Mg2+was1mmol/L, its activation on the reaction was greatest. The descending orders of metal ions whichinhibited the reaction were as follows: Cd2+> Cu2+> Zn2+> Pb2+> Ni2+> Ca2+.