Improvement of Taihu water quality by the technology of immobilized nitrogen cycle bacteria

Vol.13 No.2NUCLEAR SCIENCE AND TECHNIQUESMay 2002Improvement of Taihu water quality by the technology ofimmobilized nitrogen cycle bacteriaLI Zheng-Kui', PU Pei-Minz, HU Wei-Pin2, HU Chun-Hua2, CHEN Bao Jun?,LI Bo2, CHENG Xiao-Ying2，ZHANG Sheng Zhao2, FAN Yun-Qi2,ZHANG Wei-Dong' , ZHU Jia-Ting'(2 Institrute of Application of Atomic Energy, Jiang8u Academy of Agricultural Sciences.Nanjing 210014;2Nanjing Institute of Geography and Limnology, the Chinese Academy Sciences,Nanjing 210008)AbstractExperimental studies were carried out on the purification of eutroplicTaihu Lake water by dynamnic experiment using immobilized nitrogen cycle bacteria(INCB). The results showed that the eutrophic water of Taihu Lake can be purifiedeffectively as it passes through the experimental reactor into which some immobilizednitrogen cycle bacteria were put. The remnoval fficiencies for Total N (TN), NHT-Nwith immobilized nitrogen cycle bacteria were 72.4% and 85.6%, respectively. It wasfound that the immobilized nitrogen cycle bacteria also have purificatory effect oneutrophic water of Taibu Lake at winter temperature (7°C), and that the removalmeficiencies for Total N (TN), NH; -N were 55.6%，and 58.9%, respectively. Theremoval efficiencies for TN and NHt-N depend on the time the water stays in theexperimental reactor .Keywords Radiation polymerzation, Immobilized nitrogen cycle bacteria, Dynanicexperiment, Taihu Lake water in winterCLC numbers X172, X524A1 INTRODUCTIONTaihu Lake is one of the five famous largest freshwater lakes in China, with an areaof 2338 km2 and a depth of 2-4m. With the social and economic development duringthe last decades, the Taihu Lake has been polluted and become more eutrophic, whichhave influence on the social and economic sustainable development around its areas. Tcontrol the Lake eutrophication, dredging, diluting,1 restoring hydrophyte, and takingbiomanipulation2] and other means have been applied to control and harness these prob-lems. As a new technology, the physico-ecological engineering (PEEN) using physicaland biological methods to remedy and rehabilitate a healthy ecological system ftom thephytoplankton-dominated state in eutrophic lakes can improve local lake water qualityobviously.[3] It is found that bacteria and mutualism of bacteria with hydrophyte haveimportant effect for purifying water. However, the remedial system of hydrophyte is notstrong enough resisting the environmental hazards. Accordingly, making a carrier withSupported by European Union [Contract No. CI1*-CT93-0094 (DG 12 HSMU)], also by the Nocialdevelopment project of Jiangsu Province, China (No.BS99021)Maruscript received date: 2001-12-20中国煤化工MYHCNMHG116NUCLEAR SCIENCE AND TECHNIQUESVol.13suitable pore structure can provide refuge effect for bacteria and developing the technol-ogy of immobilized nitrogen cycle bacteria (INCB)}|)] by physical and microbial methodsfor remedying and rehabilitating the healthy aqua ecosystem in eutrophic lakes has veryimportant theoretic and practical meaning. The key issues of INCB are microbial- basedwith aids of physical means. There are three major techniques of INCB, e.g.. makingcarriers for immobilized nitrogen cycle bacteria, cultivating special nitrogen cycle bac-teria with high efficiency for nitrification-denitrifcation, and improving water quaJlityfrom laboratory to local water with INCB. By using INCB bacteria releasing techniquesin PEEN, four groups of nitrogen cycle bacteria, including ammonifying, nitrobacte-ria, ritrosobacteria and denitrifying bacteria have increased remarkably in the water;oxidation-deoxidization of nitrogen have consolidated; nitrogen have been rernoved moreeffectively from the water and local lake water quality have improved obviously. Thesimilar study has not been found about the improvement of lake water quality, and thispaper supply major biological aspect with INCB toward this goal. Therefore the INCBtechnique provided a new, important, and more effective approach for improving waterquality, controlling eutrophication and resisting the environmental h az ards.2 METHODS2.1 OrganisumFour group of nitrogen cycle Bacteria were obtained from Taihu Lake, includingammonifying, nitrobacteria, nitrosobacteria and denitrifying bacteria. The basic mediumused for the agar slants and the synthetic liquid medium used for the growth of the fourgroups of bacteria was the same as reported previously.15.6] After 2 months of cultivation,the four kinds of nitrogen cycle bacteria were harvested by centrifuge at 4000 r/minfor 10 mins. The wet nitrogen cycle bacteria were obtained and further prepared forimmobilization.2.2 Preparation of porous carriersIn order to grow different sorts of bacteria, various kinds of hydrophilic andhydrophobic glass- forming monomers, 2-Hydroxyethyl acrylate (HEA ), 2-Hydroxyethylmethylacrylate(HEMA) and polyethylene glycol dimethacrylate (nG) -14G, 9G, 4G, 2Gwere used in this work and mixed with distilled water to different concentration. Themixtures were irradiated at -78°C with γ-rays from 60Co source for 10h with a dose rateof 1 kGy/h. The resultant polymer carriers were prepared in small pieces, approximately5-10 mm in diameter and shaken with excess amount of water for 3 days in order to befully swollen. The swollen carriers were sterilized by autoclave at 120°C for 40 mins. Thesterilized carriers were immersed into the nutrient medium for 2 days to be flled withthe nutrient medium.2.3 Preparation of immobilized nitrogen cycle bacteria (INCB )The swollen carriers were added to the mixture of precultured nitrogen cycle bacterinand the nutrient medium. The composition of the nutrient medium used in this workwas the sarmne as said previously.6l After aerobic and anaerobic incubation for 72 h, the中国煤化工MYHCNMHGNo.2LI Zheng- Kui et al: Improvement of Taibu water quality by ...117polymer carrier of immobilized nitrogen cycle bacteria allowed to cultivate in incubator at28土1 °C under gentle rotary shaking. After being cultivated, the immobilized nitrogencycle bacteria (INCB) were prepared.2.4 Experimental systemThis experiment was performed in the device designed by our research group, the :reactor (working volume 91L) with its control and monitoring systems. The eutrophicTaihu Lake water was continuously pumped at a constant rate during all the runs. Thetemperature of the reactor depended on the room temperatures from 14°C to 7°C. The .DO was monitored via the JPB-607 model DO noitor device and the pH in the reactorwas monitored via the PHS-3C pH device.2.5 Analytical methodsTotal N, nitrate, nitrite and aunmonium nitrogen were analyzed according to stan-dard methods of China.7]3 RESULTS AND DISCUSSION3.1 The purifcation eficiency of immobilized nitrogen cycle bacteria for TaihuLake water with dynamic cxperimentAfter the eutrophic Taihu Lake water passcd the reactor, the Total N and NHT-N ofthe water were decreased gradually. It was found that the Total N and NH4+ -N decreased29.1% and 27.8% respectively on the 5th day and decreased 54.2% and 74.1 % respec-tively on the 10th day. After 10d cxperiments, the removal efficiencies of Total N andNH -N tend to stabilize and reached 72.4% and 85 6% respectively. The results showedthat at the beginning the xemoval eficiencies of INCE system for Total N and NH -Nwere relatively lower due to imnobilization, l:cwever after 10 d cxpcriment continuously,the removal efficiencies of INC3 for To:al N i:nd NH4+-N keep steady. The F examineshowed that eutrophic Tailhu L:xke water purified with immobilizcd nitrogen cycle bac-teria (INCB) and that with no INCB trcatment had remarkable difference (p <0.01).Therefore, the INCB could reinove nitrogen from the water and purify eutrophic TaihuLake water eficaciously (Fig.1).3.2 Removal eficiencies for Total N and NH4+-N of eutrophic Taihu Lakewater with INCB in different tempereturesDuring the experimental period, the water temperature changed with the weatherfrom 14°C to 7°C. The result showed that the rernoval efficiencies for Total N and NH4-Nof eutrophic Taihu Lake water using INCB decreased as temperature decreased. Whenthe water temperature descended from 14°C to 7°C, the removal efficiencies for TotalN and NH -N with INCB decreased slowly from 72.4% and 85.6% to 55.6% and 58.9%respectively as shown in Fig.2. After 30 d experiments, the removal eficiencies of TotalN and NHt -N have slightly decreased due to temperature decrease shown in Fig1. Thisshowed that although the change of tempere.ture hnd some effect on the reinoval efficien-中国煤化工MYHCNMHG118NUCLEAR SCIENCE AND TECHNIQUESVul.13cies for Total N and NH4 -N because of the activity of INCB system decreased slightlyunder the low temperature and caused removal efficiencies for Total N and NH -Ndecrease, the INCB has relative higher removal eficiencies for Total N and NH4-N ofeutrophic Taihu Lake water .R 804020o1020304050Experimental days4121C..●.. TN infow-o- TN eiuentwater t(C)..▲●NH4*-N inf一一.NH&*Nefu口TN1 I NH&"-NFig.1 Changes of TN and NH -N duringFig.2 The effect of water temperatures onDynamic experimentthe removal eficiencies for TN and NHT-N4 CONCLUSIONBased on this investigation, INCB plays a significant role in purifying eutrophicTaihu Lake water, especially during autumn and winter. With the temperature dropping,most hydrophytes stop growing and some hydrophytes would die and become the source ofpollution. As a new technology, the INCB using physical and biological methods to purifyeutrophic Taihu Lake water can improve eutrophic Taihu Lake water quality obviouslyby using INCB and the“microecosytem” porous carrier, which provides the bacteriawith favourable ecological environment. With this kind of porous carriers, nitrogen cyclebacteria can improve eutrophic Taihu Lake water through nitrification denitroficationreaction which lead to purify the Taihu Lake water quality.AcknowledgementsThe authors thank Prof. QU Bei shen for assistance in taking electron microphotographsof pore structure of carrier.ReferencesWelch E B, Barbiero R P, Bouchard DL et al. Ecol Eng, 1992. 1:173-1972 Shapiro J, Lamarra V, Lynch M. Biomanipulation: an ecosystem approach to lake restorationin water quality management through biological (Brezonik, DL. AND jl. Fox eds). UniversityPress of Florida, Gainesville, 1975, 85-96; Pu P, Hu W, Yan J et al. Verh Internat Limnol, 1997, 26:756 -759LI Z K, PU P M. Jiangsu J Agr Sci (in Chinese), 2000a, 16(2):115-1175 LIZKPU P M. J Lake Sci (in Chinese), 2000b, 12(2):119-1236 LIZ K, PU P M. Nucl Tech (in Chinese), 2001, 24(8):674-6797 State Bureau for Environmental Protection ed. The analytical methods for water undwastewater (3th edition, in Chinese). Beijing: Chinese Environnental Science Press 1989中国煤化工MYHCNMHG