Study On The Effect Of Alkali Pretreatment On Sideflow Enhanced Biological Phosphorus Removal And Phosphorus Recovery Process

The lateral flow enhanced biological phosphorus removal（S2EBPR）process is a new type of enhanced biological phosphorus removal（EBPR）process,which has received widespread attention at home and abroad because it can well alleviate the pressure of insufficient carbon source in the influent water faced by the conventional EBPR process.The S2EBPR+Phosphorus Recovery（S2EBPR+PR）coupling system reduces the phosphorus load of the influent by recovering phosphate(PO₄^3--P)in the supernatant of the lateral flow anaerobic reactor,in line with the concept of sustainable wastewater treatment and recycling.The hydrolytic fermentation and acid production of reflux sludge in the lateral flow anaerobic reactor is the key process of intensive nitrogen and phosphorus removal in the S2EBPR process.Adding alkali pretreatment to the anaerobic fermentation process of lateral sludge can promote acid production in sludge fermentation,strengthen the mainstream phosphorus removal performance,and shorten the anaerobic fermentation time.However,the effects of alkali pretreatment sludge fermentation process on nitrogen and phosphorus removal functional microorganisms,phosphorus removal potential and phosphorus recovery of S2EBPR system and S2EBPR+PR coupling system are unknown.Therefore,this study analyzed the activities of alkali pretreatment under different pH conditions on the release of organic acids and nutrients,extracellular polymer（EPS）components,nitrogen and phosphorus removal functional microorganisms during sludge anaerobic fermentation,and the effects of the changes of acid production and nitrogen and phosphorus removal microorganisms after fermenation after lateral sludge alkali pretreatment on phosphorus removal performance and phosphorus recovery in S2EBPR+PR coupling system were simulated and studied.The main findings are as follows:（1）A fter alkali pretreatment of the anaerobic hydrolysis fermentation process of activated sludge,the soluble chemical oxygen demand（SCOD）of pH=9 and pH=10 groups was 3.07 and 4.8 times higher than that of the group without alkali,respectively;The proportion of acetic acid and propionic acid that are easily utilized by biological denitrification（BNR）and EBPR systems to total volatile fatty acids（TVFAs）increased by 16.7%and 28.36%,respectively;The total amount of protein,polysaccharide and humic acid was 1.63 times and 2.53 times of that of the control group,respectively;The content of PO₄^3--P is 1.08 and 1.35 times higher than that of the non alkali group,respectively.After using the bird droppingstone method for phosphorus recovery,the content of protein and humic acid in soluble microbial products（SMP）significantly decreased,and the phosphorus recovery rates decreased by 13.6%and 30.77%,respectively.（2）Alkali pretreatment can inhibit the activity of functional microorganisms related to nitrogen and phosphorus removal.The specific aerobic phosphorus uptake rate(P_up)of phosphorus accumulating bacteria（PAOs）and denitrification phosphorus accumulating bacteria（DPAOs）decreased by 42.61%and 54.58%respectively after three days of fermentation of alkaline pretreated sludge.After re adding external carbon sources,the P_up of PAOs in the pH=9 and pH=10 groups decreased by 35.66%and 46.58%compared to the non alkali group.The activity of PAOs（measured by phosphorus release to carbon source absorption ratio（P/C））showed little decrease under pH=9 alkaline pretreatment conditions,but decreased by 57.89%under pH=10 conditions.After 3 days of alkaline pretreatment of sludge fermentation,the ammonia oxidation activity of ammonia oxidizing bacteria（AOB）decreased by 32.79%～76.92%,and the nitrite oxidation activity of nitrite oxidizing bacteria（NOB）decreased by 71.72%～89.89%;DNB denitrification activity with internal carbon source as substrate decreased by 37.7%and 82.31%respectively after alkali pretreatment,while DNB denitrification activity with external carbon source as substrate decreased by 17.85%and 81.25%respectively after alkali pretreatment,and the stronger the alkalinity,the higher the degree of decline.（3）Based on the experimental results,it is estimated that under the conditions of S2EBPR system with a side flow ratio of 30%and a side flow residence time(SRT_ss)of 5 days,the maximum carbon source generated by anaerobic fermentation of sludge in the side flow reactor can remove 41.88%of the influent phosphorus load.After pH=9 alkali pretreatment,the additional carbon source generated by the side flow reactor with SRT_ss=1 d and side flow ratio=30%can remove 48.83%of the influent phosphorus load.After pH=10 alkali pretreatment,the side flow reactor with SRT_ss=1 d and side flow ratio=30%can fully meet the phosphorus removal needs of the system.Alkali pretreatment promotes more sludge fermentation within the same time frame,achieving fermentation acid production and enhanced biological phosphorus removal under shorter SRTSS conditions,thereby reducing the footprint of the S2EBPR system side flow reactor.Without alkaline pretreatment,S2EBPR coupled with chemical phosphorus recovery can reduce the phosphorus load of the system,to some extent reducing the demand for biological phosphorus removal,thereby reducing the dependence on sludge fermentation in the side flow reactor.Under the conditions of side flow ratio=5%,SRT_ss=1 d,and recovery ratio=10%in the S2EBPR+PR coupling system,the enhanced phosphorus removal rates for the untreated,pH=9,and pH=10 groups were 2.96 mg P/d,4.51 mg P/d,and 6.86 mg P/d,respectively.The stronger the alkalinity,the higher the contribution of enhanced biological phosphorus removal to the S2EBPR+PR coupling system.The alkaline pretreatment of the S2EBPR+PR coupling system side flow sludge fermentation can simultaneously solve the problems of low carbon source and phosphorus recovery in the influent.