| Eutrophication caused by nutrient elements such as nitrogen and phosphorus have brought out serious threat to human health and economic development and greatly reduced the value of utilization of water resources. Therefore, nitrogen and phosphorus removal from wastewater has already attracted widespread attention. Biological phosphorus removal is a kind of high efficient and energy saving technology since it can reduce reagent consumption and pollution. However, the serious imbalance between carbon, nitrogen and phosphorus in the influent of the wastewater treatment plant, especially the shortage of carbon source, makes it difficult to realize the simultaneous nitrogen and phosphorus removal. At present, effluent phosphorus concentration in most sewage plant is difficult to meet the level A requirements in "urban sewage treatment plant pollutant discharge standard"(GB18918-2002). Therefore, the requirement of developing novel technology to remove nitrogen and phosphorus from wastewater has been more and more imminent.According to the theory of denitrifying phosphorus removal, a novel process composed of two alternate aeration biofilters with slag compound material media for synthetic domestic wastewater treatment was carried out. The efficiency and mechanism of phosphorus and nitrogen removal were investigated by changing alternating aeration mode to make the system environment for developing the population of PAOs and DPB. At the same time, the biofilm microbial community diversity and similarity were analyzed by PCR-DGGE and sequencing technology. After that, the phylogenetic tree construction and microbial community succession analysis were carried out as well as the influence of different types of electron acceptors on population evolutionary branch was also investigated, to provide novel ideas and reference for developing of denitrifying phosphorus removal.Results showed that after successfully starting up of the two stage biofilter in alternate anaerobic/aerobic environment using composite inoculation film-forming method for several stable operation period, the average COD removal rate was 86.2%, ammonia nitrogen removal rate was about 96%. While phosphorus removal rate was stable at 64.3%, this stable operation system had excellent ability of carbon and ammonia oxidation, and also had a wellcapability of phosphorus removal.The performance of two stage biofilter by alternate anoxic/aerobic environment with different electron receptors( NO2- and NO3-) were promising, whereas the COD removal rate was 84.3% and 88.8%, ammonia nitrogen removal rate was 93.9% and 94.6% as well as the phosphorus removal rate was 71.61% and 82.55%, respectively. The system had excellent ability of carbon and ammonia oxidation, but its phosphorus removal capability increased obviously.The optimal HRT of one filter was 2 hours while alternative aeration time was 36 h and aeration ceasing time was 12 h. The most appropriate pH value range for DPB was between 7.5 and 8.0. The best concentration was 300mg/L when soluble starch was used as carbon source. Both nitrite and nitrate could be electron receptors to remove phosphorus with optimal concentrations of 20mg/L and 25mg/L, respectively. The denitrifying phosphorus removal by nitrate was higher than that of nitrite. And the different electron acceptor consumption and phosphorus accumulating volume showed well linear relationship.Biological analysis showed that the system presented a complete biophase under two kinds of operation mode, Prokaryotic microorganisms such as staphylococcus aurous,Bacillus, and protozoan and metazoan coexisted in the system. The crystallization of SEM-EDS energy spectrum analysis showed that the product was mainly HAP crystal. Filter crystal surface in No1 and No2 may be accompanied by a certain amount of calcium carbonate crystal, while the surface of the filter media in No3 and No4 may be associated with potassium magnesium phosphate crystal. There were two main ways for to remove phosphorus, phosphorus uptake in the aerobic section by PAO and crystallizing phosphorus removal. Anoxic/aerobic alternate filters could also remove phosphorus by DPB in anoxic stage.Biofilm samples diversity analysis and spectra of DGGE cluster analysis of inoculated sludge, anaerobic/aerobic alternate stable system and anoxic/aerobic alternate stable system showed that microbial communities were in high abundance, and performed an obvious law of succession. The dominant populations were mainly Proteobacteria(including Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, and Epsilonproteobacteria); Bacteroidetes(containing Sphingobacteriia, Flavobacteriia, Bacteroidia, Cytophagia); Nitrospirae(Nitrospirales); Actinobacteria(Actinobacteridae);Chloroflexi(Chloroflexia); among above bacteria, the Proteobacteria and Bacteroidetes were in the majority which accounting for 85% in the total flora species.The dominant denitrifying phosphorus removal populations were Pseudomonas SP, Pseudomonas putida, Propionivibrio SP, Propionivibrio dicarboxylicus, Rhodocyclaceae bacterium, Dechloromonas SP, Filomicrobium sp. These bacteria belongs to Rhodocyclaceae, Pseudomonadaceae and Hyphomicrobiaceae, these three classes of bacteria belongs to Proteobacteria(Betaproteobacteria), Proteobacteria(Gammaproteobacteria) and Proteobacteria(Alphaproteobacteria) respectively, they all belong to Proteobacteria phylum, but lies in different evolutionary branch.The dominant AOB and NOB population in different systems were mainly composed of Nitrosomonadaceae bacterium Nitrosomonas SP and ammonia-oxidizing bacterium; While Nitrosomonadaceae bacterium and ammonia-oxidizing bacterium accounted for the most majority. Through the alternating shock environment, AOB and NOB diversity decreased significantly.After a long time running, the process performed a stable and promising performance of nitrogen and phosphorus removal simultaneously, and got a novel approach to provide reference for nitrogen and phosphorus removal technology. |
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