| It was a new technology in wastewater treatment that fluidized-pellet-bedbioreactor(FPB) which could integrate the sludge granulation and pellet solid/liquidseparation in one reactor. By providing appropriate biological environment such asoxygen, the microbe were enrichment, and then the contaminants could be removedeffectively on the physical-biochemical effects. On the earlier research, it was provedthat the FPB could not remove particular or colloidal contaminants efficiently, but alsocould remove high percentage of soluble COD, nitrogen and phosphorus. And on thecondition of HRT1-2h, the removal of contaminants in FPB was more effective thanCEPT. As one type of short-process treatment, the prospect of popularization andapplication of FPB ischeerful. In order to reveal synergic physical-biochemical effectsof soluble contaminants, a small-scale FPB system with simulated wastewater wasestablished, on the research of the removal of soluble contaminants, physical andbiochemical property of pellets, and influence of coagulant on microbe in FPB. Resultsand findings in the study were including the perspectives as:(1) Removal of soluble contaminants in FPBOn the condition of laboratory, a small-scale FPB system was established and along-term operation was carried out. The operational conditions in FPB weredetermined as: PAC dosage50mg/L, PAM dosage3mg/L, upflow velocity1mm/s,mechanical stirring speed ω25rpm, HRT in aerated tank2h, and the blanketheight110cm～130cm; the parameters in aerated tank were determined as: SS0.82g/L,DO8mg/L and recycled0.5L sludge to aerated tank in every2hours. Under the aboveconditions, the removal efficiency for soluble COD, nitrogen and total phosphorus was85%,34%and46%. The removal of soluble contaminants was including coagulation, adsorption andbiodegradation. The removal of soluble COD in different mechanisms was estimated aspreaeration46%,coagulation6%, adsorption8%, biodegradation22%, undegradematerial22%; the removal of soluble nitrogen in different mechanisms was evaluated aspreaeration9%,coagulation5%, adsorption10%, biodegradation11%, undegradematerial65%; the removal of soluble phosphorus in different mechanisms was estimated aspreaeration27%,coagulation1%, adsorption3%, biodegradation17%, undegradematerial52%. The preaeration fulfilled in the aerated tank was the biodegradation of solublecontaminants which were adsorbed in the recycle sludge. For soluble contaminantsadsorbed in the pellets, it was equivalent to extending aeration which was also the partof bio-degradation. Therefore, the removal of soluble COD, nitrogen and phosphoruswith biodegradation was68%,20%and44%, suggesting that biodegradation couldremove soluble contaminants effectively.(2) Physical and biochemical property of pellets in FPBThe formation process of pellets, the morphological characteristics and sizedistribution of the pellets in the reactor were examined, and the following results couldbe obtained: the pellets in the reactor were sphere and their sized decreased along theheight of reactor, namely, the average sizes of pellets which were described as d50fromthe bottom, middle and upper of the reactor were2.84,2.22,1.92mm. It was found thatthe effective density of pellets slightly decreased with the increasing diameter. Theeffective density was in the range of0.006-0.013g/cm3, which was much higher than theactivated sludge and was showing the compact structure.As the analysis of the biochemical property of pellets, DO was continuouslyconsumed from8mg/L in the bottom to1.7mg/L on the top of the reactor, obviously,mainly consumed in the bottom. The MLSS in the reactor decreased along the height ofreactor which was much higher than the activated sludge. It was found that the biomassin the reactor was in the magnitude of108, which was close to the activated sludge. Thebiomass in the bottom of the reactor was highest as a result of the plenty of substrateand sufficient DO, and the biomass in the reactor decreased along the height of reactor.(3) Microbial community distribution in the pellets of FPBAs the identification of nitrosobacteria and nitrobactor using FISH, it could be judged that the percentages of AOB/DAPI and NOB/DAPI from10cm,50cm,90cm inthe reactor were3.4%,3.9%,2.5%and1.8%,1.8%,1.4%respectively. There wasslightly changed along the height of reactor in the distribution of nitrosobacteria andnitrobactor. The percentages of AOB/DAPI and NOB/DAPI in the pellets of FPB wereclose to the activated sludge.It was shown from DGGE profile that the bacteria in FPB are abundant. Thebacteria structure in different position of FPB were slightly changed, and the amount ofbacteria such as Actinobacillus declined sharply in the aerated tank, but the anotherbacteria were stable which were Actinobacillus, Arcobacter sp., Epsilon proteobacteriaand Beta proteobacteri. It was revealed that the bacteria could be adapted to thevariation of contaminants and DO, and the operation of FPB could be stable.AOB and NOB from FPB pellets were purified in3months in order to improve thenitrogen removal. It was found that Nitrosospira sp., nitrobacter sp., pseudomonas sp.and pseudomonas aeruginosa could be identified from the enriched solution usingPCR-DGGE. Pseudomonas sp. could be revealed that was co-existence with NOB,which was denitrifying bacteria.(4) Influence of coagulant on microbe in FPBIt was found that the influence of the coagulant was dominated in FPB on thebacterial community of sludge by comparing a set of SBR reactors with the samecondition of PAC and PAM addition. It was indicated that the addition of PAC and PAMcould not have obvious influence on nitrifying bacteria by means of biomass analysisand FISH technology. The removal efficiency of TP was increased significantly withPAC addition, and COD removal was improved with the addition of PAC and PAM.Howerver, there was no obvious improvement of nitrogen removal in the same reactors.(5) Stabilization of FPB with two alternate stagesIt was revealed that the mechanism of soluble contaminants removal and thestabilization of pellets in FPB with two alternate stages. The size of pellets decreaseddue to the lessening PAC and PAM; on the converse, the sizes of pellets were increased.After two stages alternating repeatedly, it was shown that the pellets got into the cycleof“broken-grown-broken-grown”, and the effective density of the pellets did not changeobviously, indicating the pellets possessed a dense structure on this operation. It was revealed from the experimental that the pellets had very good dynamic stability. Due tothe FPB with two stages and extending HRT, the removal efficiency of solublecontaminants could be enhanced. |
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