Optimization Of Nitrification In A₂N Wastewater Treatment Process

As for the continuous-flow two-sludge system with nitrogen and phosphorusremoval simultaneously, the treatment performance of nitrification unit affected thenitrogen and phosphorus removal efficiency directly and obviously. Preliminaryresearches showed that the A₂N/BAF with BAF asnitrification unit obtained fairlywell treatment performance, while it had its own limitation that head loss of BAFwas high and frequent backwashing was required, which was not suitable for thetechnology promotion of A₂N/BAF as well as the reformation of traditional A²/Oand other processed had been built. Since BAF was in high efficiency for substratesremoval and head loss of contact oxidation tank was quite low and backwashing wasneedless consequently, so this thesis aimed to explore a newly nitrificationtechnology with high efficiency and less running resistance, and experiments onselection and modification of fiber filler, treatment performance of BAF with fiberfiller as well as the application in A²/O were conducted in this study.Experiments on selection and modification on PET （polyethylene terephthalatefiber）, polypropylene, composite materials showed that the biofilm formation timeforthose three kinds of materials were10,11,12days, respectively. Nitrificationefficiencies after7h were57.7%,40.7%,28.9%with the initial concentration ofammonia was31.0mg/L, and PET obtained the best nitrification rate. Nitrificationrates after9h were69.3%,78.6%,87.3%for unmodified, ozone/hydrogen modifiedand alkali reduction, respectively, and ammonia removal was the highest after alkalireduction modification. Result of SEM showed that surface cracks and ravines of themodified after alkali reduction were benefit for sludge attachment and growth.Next, selection on type of nitrification column was carried out. PET after alkalireductionmodification was cut intofragment with5mm in diameter, and then wasfilled in the form of fixed bed and fluidized bed. Results showed that thenitrification efficiency was86%for fixed bed, which was higher than fluidized bedby21.2%; nitrification efficiency of fixed bed with HRT of1.5h was15%higherthan ordinary contact oxidation tankwith HRT of6h, and was comparable to BAFwith HRT of1.5h.The advantage of nitrification performance of fixed bed BAF with fiber filledwas obvious, and the BAF was called as Fiber filler BAF （FFBAF） and theefficiency was researched elaborately. Results showed that start time of FFBAF wasonly14days. Under the condition that gas to water ratio of4:1, HRT of1.5h andaverage concentration in influent of34.3mg/L,ammonia concentration in effluent was5.43mg/L on average, corresponding to the removal efficiency of84.2%, whichwas comparable to BAF with porcelain granule as fillers of87.7%.Comparative study between FFBAF and ceramsite BAF showed that impact ofhydraulic loading and temperature on FFBAF was less than ceramsite BAF.Averagenitrification rates were all above than88%of the two BAFs when CODconcentration in influent was low, and nitrification rate of FFBAF was lessthanceramsite BAF by6.5%when with high COD in influent. Head loss of FFBAFwas remained at10cm or so after operation for20days. Backwash cycle wasextended to20days or even longer, as for backwashing, airbleed for40s was enough,which was simple and water saving, moreover, recovery after backwashing wasfaster than ceramsite BAF by30min.Based on the excellent performance of FFBAF, application in the modifiedA²/O process was carried out for a period of20days. Results showed thatnitrification efficiency of FFBAF was about69.6%, which was slightly lower thanceramsite BAFunder the same conditions. Effluent COD was ranged between18mg/L and67mg/L with an average of42mg/L, corresponding to the removal rateof82.0%. In addition, TP in effluent was reduced to0.11¹.76mg/L and averaged at0.78mg/L. In a word, operation performance of the system was fairly well with asimple reformation. However, more researches wererequired to be conducted forfurther promotion and application.