Removal Of Ammonia By Upward-flow Biological Zeolite-activated Carbon Filter Under Low Temperature Condition

Bio-filtration was widely employed as an efficient and low cost method in removing biodegradable dissolved organic carbon(BDOC)and ammonia in water.However,biofiltration drawn fierce resistance in the northern part of China because of the lower biological activity under low temperature conditions(<5 ?).Compared with heterotrophic bacteria,nitrifying bacteria grew more slowly with longer generations within low temperature period,had longer recovered period after filter backwashing,at the same time,it can be covered by heterotrophic bacteria and deprived of substrate,DO,other nutrient element.These made the removal efficiency of ammonia by the biofilters even worse.Although the representative ammonia removal method of zeolite adsorption would not be affected by temperature,zeolite adsorption has the following disadvantages,such as limited capacity,complicated operation,needs of periodical regeneration,high maintenance cost.So research of physiochemical-biochemical coupling system to remove ammonia will be of more value.This dissertation,aiming at the precedent-control of ammonia in drinking water at low temperature,study a novel combined process of catalytic ozonation and up-flow multi-layers bio-filter(UMBF)for unstable and high levels of ammonia and organic matter pollution at pilot-scale and full-scale experiments.Results showed that the catalytic ozonation-UMBF had a more powerful buffering action and a very effective removal of ammonia.When the influent ammonia concentration was less than 1.5 mg/L,ammonia concentration in the effluent was lower than 0.01 mg/L.As the influent ammonia concentration rose to 2.75 mg/L,ammonia in the effluent was lower than 0.2 mg/L.When the influent ammonia concentration rose to 3.5 mg/L rapidly,ammonia in the effluent would gradually rise to 0.6 mg/L~0.65 mg/L at about 4 h~5 h later.After the influent ammonia concentration decreased abruptly,ammonia in the effluent would keep the same concentration for about 4 h and then would decline gradually.Additionally,UMBF presented longer backwashing period at nearly all the lower temperature period without any blocking,so the biofilter is more suitable for handling high ammonia polluted water.Mechanism of inorganic nitrogen transfer and transformation in UMBF at low temperature period was discussed.The author deemed that bio-oxidation in UMBF at low temperature conditions(2?~4?)was an important way for the removal of ammonia and nitrite,and nitrification mechanism became stronger and stronger along with the higher ammonia concentration.Most of ammonia in the influent was removed at the biozeolite layer and the bottom of the biological activated carbon(BAC)layer,nitrite was accumulated rapidly at the bottom and middle part of the BAC layer,then was controlled at the middle and upper part of the BAC layer,the optimum layers arrangement for ammonia and nitrite control would change accompanied with the influent ammonia concentration.In addition,the author also found that the inorganic nitrogen in the middle and upper part of BAC layers in the UMBF was not balanced in mass,especially with high ammonia loading and high nitrite concentration.So the author concluded that there was short-cut nitrification and denitrification in the partial area of the bio-filter.Microbial community response mechanisms in UMBF was detected by using high-throughput sequencing.Results indicated that ammonia oxidizing microbes and ?-proteobacteria were the dominant microorganism besides Alpha-proteobacteria in the biozeolite layer,and Alpha-proteobacteria and nitrite oxidizing microbes were mainly riched next to the zeolite layer.So ammonia was removed firstly by ammonia oxidizing microbes with the competitive edge to DO and nutrient elements.The results also revealed that a more uniform microbial community distribution in the whole bio-filter and the carrier in the UMBF was made the best use.Physiochemical mechanisms for the effects of media in the UMBF on ammonia absorption was investigated.Results showed that for treating Huai river water for a period of 3 years,biozeolite still had an obviously adsorption-desorption property for ammonia in water,yet the biozeolite had a different adsorption process from new zeolite.Freundlich isotherm is the better-suitable model for the sorption of ammonia onto biozeolite,while the Langmuir isotherm is the most-suitable isotherm for zeolite.The adsorbing capacity of biozeolite decreased by around one-third after running for 3 years,but the desorbing rate was increased.Co-existing cation,pH,and biochemical effect will all affect zeolite and biozeolite adsorption-desorption property of ammonia in water.The author found that both the presence of lower valence and high concentrations of cation,under pH<5 or pH >10,and the presence of biofilm will benefit zeolite and biozeolite desorption performance.So the biozeolite adsorption-desorption rate of ammonia in water could be accelerated by adding just enough cation etc.and provided a more stable ammonia concentration for microbes at relatively lower influent ammonia concentration.At the same time,the adsorption capacity was in situ regenerated rapidly.In this dissertation,it was found that UMBF combined with catalytic ozonation could remove ammonia and organics effectively at the period of heavy/micro-pollution,ammonia removal mechanism in the UMBF under low temperature was disclosed,the proliferation and response mechanism of nitrifying bacteria under low temperature with high ammonia loading was validated,this would be of significance and provide theoretical foundation for solving ammonia pollution problem of drinking water at low temperature period.Although the cost was increased somehow,it could achieve better effluent quality and ensure normal water quality.Therefore,the combined process is practical and meaningful of application in cold areas.