Effects Of Spent Mushroom Compost Addition On The Nitrogen And Phosphate Removal And Corresponding Mechanisms In SBR

Nitrogen is a vital factor contributing to water eutrophication,which is widespread in lots of locations in the world.In particular,excess discharge of nitrogen from wastewater treatment plants(WWTPs)into receiving waters is a major reason for this issue.Thus,inorder to effectively remove nitrogen,WWTPs have to be upgraded inmany countries.Basically,nitrogen removal in WWTPs is carried out by biological processes where nitrification and denitrification are involved,proper denitrification depends mainly on sufficient organic carbon sources.As such,uncompleted denitrification usually occurs when the influent with a low C/N ratio treated in a WWTP.As the largest producer in the world,Ching generates a huge of spent mushroom composts(SMC)every year,which has exerted a great pressure on the local environment and thus how to effectively reuse SMCs has been a hot topic.Notably,SMCs contain not noly ample organic carbon sources but also a variety of trace elements,both of which are vital factors ensuring that microorganisms could denitrify completely.Accordingly,SMCs were used as extra carbon sources in a sequencing batch reactor(SBR)in the present study to investigate their effects on the removal of nitrogen and phosphous and relevant mechanisms were analyzed,through which we hope to provide a new idea for t"using pollutants to treat pollutants".First of all,the orthogonal experimental was to optimize the conditions of hydrolyzing SMCs and the best pretreatment conditions were as follows:4%diluted sulfuric acid,temperature of 115?,time of 1.5h,and solid:liquid ratio of 1:24.Considering pretreatment cost and environment pollution,the diluted sulfuric acid was reused and results show that it could be reused as high as 5 times.Secondly,SMCs were added to SBR to explore their effects on the removal of nitrogen and phosphorous.It can be found that the removal efficiency(RE)of nitrogen increased from 46.9%before SMC addition to 87.8%after SMC addition,suggesting SMC as an external carbon source has a significant effect on denitrification.In the first stage,no SMC was supplemented and the reactor was operated for 20 days,where the RE of NH4+-N ranged from 42%to 59%with the average RE was 51.8%.But the RE of TN seemed to change more evidently,fluctuating between 28%and 54%with an average RE of 43%.From Day 21 on,the reactor entered the period of SMC addition,consisting of stage 2 fed with PESMC,stage 3 fed with HMSMC and stage 4 fed with TFSMC,and each period lasted for 50 days.In stage 2 when fed with PESMC hydrolasates were added into the SBR,the RE of NH4+-N exceeded 87%except Day 27,the average RE of TN was estimated to be 84.6%.In stage 3,HMSMC was used as external carbon source.It can be seen that NH4+-N RE within this stage was still higher than 80%except for on Day 97(78%)and Day 111(77%),the average RE of TN was estimated to be 81%.In stage 4,external carbon sources were changed to TFSMC,where most of NH4-N REs were higher than 90%,and the average RE of TN was estimated to be 89.4%.In addition,there was no obvious change in both NO2-N and NO3-N.In stage 2,the average influent and effluent COD was 515mg/L and 60mg/L,respectively,with the average RE of COD being 88.3%,while the average influent and effluent TP was 24.7%and 5.6mg/L,respectively,with the average RE of TP being 76.8%.When the external carbon source was changed to HMSMC in stage 3,the RE of COD and TP was 79.3?90.4%and 62.3?79.1%,respectively.In stage 4,the average RE of COD was calculated to be 83.3%under the condition of influent COD ranging from 454?565mg/L,and the average RE of TP was calculated to be 78.3%under the condition of influent TP ranging from 23.1 to 34.7 mg/L.Thus,after SMCs addition,the average RE of COD in different stages was relatively stable(between 83.3%and 88.3%).Subsequently,effects of SMCs on the functional genes and biodiversity in activated sludge were analyzed using qPCR and high-throughput sequencing technology.Results showed that the abundance of norB increased remarkably from 8.5 without SMC to 11.8 with SMC.The abundance of amoA elevated from 12.19 before SMC addition to 12.43 after SMC addition,and nosZ went up from 6.59 to 7.32.These phenomena revealed that SMC contributed to the growth of functional microorganisms and hence further promoted nitrogen removal.On the other hand,regardless of with or without SMC,the abundance of nirS was much higher than that of nirK.In addition,there were 21 families with the relative abundance higher than 1%when SMC was fed,and these families were divided into the following parts:12 familise belong to the phylum of Proteobacteria,5 families belonging to the phylum of Bacteroidetes and 2 families falling into the phylum of Chloroflexi.From these data,the abundance of some families rose obviously,out of which Rhodobacteraceae was reported to be able to denitrify,while Anaerolineaceae could degrade macromolecular organics to provide more available carbon sources for denitrification.Therefore,the increase of these two families could no doubt improve both microbial activity and nitrogen removal.The genera including Citrobacter,Rhizobium and Enterobacter grew strong gradually with the reactor operation proceeding,revealing that the operation conditions benefited these genera growth.Finally,to further explore the status and function of those related microorganisms,the isolation of functional microorganisms was carried out from activated sludge and a strain with heterotrophic nitrification and aerobic denitrification was obtained and identified as Enterobacter asburiae YT.Initial experiments indicated that using sodium citrate as carbon source,temperature 30?,C/N 10 and with a dissolved oxygen of 0.9mg/L.Based on the nitrogen balance analysis,it is found that the ammonia nitrogen removal rate reached 100%within 24h.The nitrogen assimilated into cells is 30.5%,and thus nitrogen losses(in forms of gaseous products)achieved to 58.4%.Moreover,the properties of the crude enzyme indicated that the strain YT can directly convert hydroxylamine to gaseous nitrogen,showing that it might be a new strain with high performance of nitrogen removal and could have a good application value in the field of biological nitrogen removal.Also,these results confirmed that SMCs benefited these microorganisms like YT to improve the SBR efficiency.