Removal of Microcystins by Phototrophic Biofilms. A Microcosm Study (6 pp)

Background, Aims and Scope Microcystins (MCs) are a family of natural toxins produced by cyanobacteria (blue-green algae). As a result of eutrophication, massive cyanobacterial blooms occur more frequently and MCs represent important contaminants of freshwater ecosystems. Bacterial biodegradation is considered a main mechanism for MC breakdown in environmental conditions. While existing studies were mostly focused on MC biodegradation by planktonic bacteria, our experiments examined the fate and kinetics of MC degradation in river-originated phototrophic biofilms and investigated factors influencing the rate of MC removal. Methods The fate of dissolved MCs was studied in laboratory microcosms with different composition (containing water only, water with phytoplankton and/or phototrophic biofilms). Biofilms originated from river ecosystem were pre-incubated under various conditions (with/without presence of cyanobacterial biomass or model organic substrates: glucose and protein - casein). Changes in MC concentration (0-14 days) in water columns were measured by HPLC DAD after external additions of purified MCs (160 μg L-1, MC-LR and MC YR), and halftimes (t1/2) of MC removal were estimated. Results and Discussion The slow degradation of MC was revealed in tap water (t1/2 ~ 14 days) and river water without cyanobacteria (t1/2 ~ 8 days). Enhanced removal occurred in the presence of natural planktonic cyanobacteria (t1/2 ~ 44 h), most probably due to microorganisms associated with the biomass of cyanobacterial bloom. More rapid MC elimination occurred in the variants containing phototrophic biofilms, and was particularly pronounced at those biofilms pre-cultivated in the presence of cyanobacterial blooms (t1/2 ~ 20 h). Much slower removal was observed in the variants simulating possible substrate-dependent induction of microorganism metabolism (biofilms pre-incubated with glucose: t1/2 ~ 35 h, and casein: t1/2 ~ 80 h). After termination of experiments, total amounts of MCs accumulated in the biofilms were below 5% of the initial toxin level revealing significant biodegradation processes. Conclusion The microcosm studies contributed to understanding of the environmental fate of MCs and revealed a rapid biodegradation by phototrophic biofilms. The rate of MC elimination depends on history of biofilm community, previous contact with cyanobacteria seems to be a selective factor improving the biodegradation potential. Recommendation and Outlook Our results experimentally showed a positive role of biofilms in MC elimination during water treatment processes such as bank filtration or slow sand filtration, and could eventually serve for further research of biofilm-based technological applications for MCs removal in small-scale drinking water treatment facilities.     

生物膜微环境和传质现象研究进展

生物膜法污水处理工艺对污染物的降解去除主要依赖活性生物膜,研究生物膜的结构和传质特性是揭示反应机理和提高反应器处理效率的重要手段.综述了近年来国外在生物膜微环境和微观传质过程中的研究进展,包括对生物膜微观结构的解析、膜内不同菌系的分布特征及其功能以及生物膜的传质现象和数学模型.在此基础上,提出了生物膜研究领域今后应开展的研究方向.     

生物流化床法处理废水的研究与应用进展

介绍了国内外应用生物流化床法处理废水的研究及技术进展，着重阐述了好氧流化床与厌氧流化床的发展,概况，并介绍了几种新型生物流化反应器，指出了今后进一步研究与应用生物流化床的前景与努力方向。     

pH对藻类生物膜脱氮除磷的影响研究

在室温(25±2)℃和4 000 lx的连续光照条件下,分别以斜生栅藻、水华鱼腥藻为实验藻种,附着固定于立体弹性载体上形成藻类生物膜,研究不同p H对2种藻类膜生长状况及脱氮除磷能力及方式的影响。结果表明:斜生栅藻和水华鱼腥藻藻类膜生长最适p H均为9;2种藻类膜分别在p H为8和9时EPS产量、磷去除率最大,EPS产量分别为48.50×10-2,48.22×10-2g/m2,磷去除率分别为95.24%和94.71%;p H为10时,2种藻类膜对氨氮有最大去除率,分别为98.96%、97.93%;藻类膜对磷的去除在p H≤7时以同化吸收为主,当p H>7时同化吸收与化学沉淀共同作用;藻类膜对氨氮的去除在p H<8时以同化吸收为主,当p H≥8时同化吸收与化学挥发共同作用。     

Effect of the C:N:P ratio on the denitrifying dephosphatation in a sequencing batch biofilm reactor (SBBR)

A series of investigations were conducted using sequencing batch biofilm reactor(SBBR) to explore the influence of C:N:P ratio on biological dephosphatation including the denitrifying dephosphatation and the denitrification process.Biomass in the reactor occurred mainly in the form of a biofilm attached to completely submerged disks.Acetic acid was used as the source of organic carbon.C:N:P ratios have had a significant effect on the profiles of phosphate release and phosphate uptake and nitrogen removal.The highest rates of phosphate release and phosphate uptake were recorded at the C:N:P ratio of 140:70:7.The C:N ratio of 2.5:1 ensured complete denitrification.The highest rate of denitrification was achieved at the C:N:P ratio of 140:35:7.The increase of nitrogen load caused an increase in phosphates removal until a ratio C:N:P of 140:140:7.Bacteria of the biofilm exposed to alternate conditions of mixing and aeration exhibited enhanced intracellular accumulation of polyphosphates.Also,the structure of the biofilm encouraged anaerobic–aerobic as well as anoxic–anaerobic and absolutely anaerobic conditions in a SBBR.These heterogeneous conditions in the presence of nitrates may be a significant factor determining the promotion of denitrifying polyphosphate accumulating organism(DNPAO) development.     

管材对供水管网生物膜微生物种群多样性的影响

研究了3种管材(灰口铸铁管、镀锌管和不锈钢复合管)对管网生物膜微生物种群多样性的影响.采用R2A平板培养计数可培养细菌、荧光定量PCR计数细菌总数、流式细胞法确定活菌比例、扫描电镜观察生物膜形态,高通量测序研究管段生物膜微生物种群多样性.研究结果表明:灰口铸铁管可培养菌数和细菌总数都最高,其次是镀锌管,不锈钢复合管可培养菌数和细菌总数都最少,但活菌比例方面镀锌管活菌比例高于灰口铸铁管和不锈钢复合管.扫描电镜结果与可培养菌数及细菌总数结果一致,即灰口铸铁管细菌量最高,不同管材管壁生物膜细菌形态皆以球菌和杆菌为主,并无显著差异.微生物种群多样性结果显示:灰口铸铁管生物膜种群多样性最高,镀锌管生物膜种群多样性相对较为单一,不锈钢复合管生物膜种群多样性最低.饮用水管网生物膜种群以变形菌门为主,各管道变形菌门都高达90%以上,不同管材生物膜细菌群落组成有很大差异.本研究结果对今后饮用水供水管段材料的选取具有指导性意义.     

跌水曝气生物滤池的挂膜与启动研究

为实现污水的无能耗处理,根据"跌水曝气式生物滤塔"专利设计制作了5层跌水曝气生物滤池,对其在生活污水处理过程中的自然挂膜过程进行研究,分析了挂膜过程中生物相的变化及对COD、NH4+-N的去除效果。试验结果表明:COD的去除主要集中在滤池的中上部(第1、2、3滤料层),而对NH4+-N的去除主要集中在中下部(第4、5滤料层)。当COD的去除率稳定在61.5%左右,NH4+-N的去除率稳定在56%以上,且滤料中的生物相趋于稳定时,标志着反应器挂膜已完成,历时约21 d。     

氢基质自养微生物还原降解水中对氯硝基苯的研究

将中空纤维膜微孔曝气和生物膜工艺结合设计出一种新型的水处理工艺——氢基质生物膜反应器(MBfR),其中,中空纤维膜为自养微生物的生长载体,还可作为扩散装置使氢气均匀扩散至生物膜中.同时,对氢基质自养微生物还原降解水中对氯硝基苯(p-CNB)的可行性、还原机理和去除效果进行了研究,并分析了共存的硝酸盐(NO3--N)和硫酸盐(SO24-)对p-CNB还原产生的影响.结果表明,MBfR生物膜中氢自养微生物能有效利用氢气为电子供体生物转化p-CNB,其中,p-CNB经硝基还原生成对氯苯胺(p-CAN),p-CAN再通过还原脱氯生成低毒的终产物苯胺(AN).经过长期运行,MBfR对进水500μg·L-1和2000μg·L-1的p-CNB具有稳定高效的生物降解性能,p-CNB去除率和去除通量最高达到96.9%和0.056g·m-·2d-1.通过投加NO3--N和SO42-发现,p-CNB还原速率随NO3--N和SO42-浓度升高而降低,表明p-CNB还原受到NO3--N和SO24-的抑制.NO3--N和SO24-对p-CNB还原产生的抑制主要与对电子供体(氢气)的强烈竞争和还原产物对脱氯微生物的毒性有关.电子通量分析进一步表明,反硝化或SO24-还原消耗更多的电子,当氢气利用率受限制时将对p-CNB还原产生强烈的电子供体竞争性抑制.     

厌氧-缺氧下反硝化除磷对低碳污水的处理性能研究

采用厌氧-缺氧条件运行的序批式移动床生物膜反应器,考察了NO3--N进水浓度及其投加方式对低碳废水(COD=200mg/L)反硝化除磷的影响.经驯化后,反硝化聚磷菌(DPB)在总聚磷菌的份额从15.7%增长到71.3%,富集了DPB.NO3--N的浓度对处理有较大影响.在NO3--N为30mg/L(即C/N=6.7:1)时,COD、PO43--P和NO3--N的去除率分别为97.8%、82.0%和81.2%,实现低碳污水的高效处理.NO3--N较低或较高浓度(20mg/L和40mg/L)时,缺氧段吸磷不充分,PHB由厌氧开始时的2.2mg/g左右分别积累至5.1mg/g和3.5mg/g,影响下一周期磷的释放.1次投加、2次投加和连续流加NO3--N,除对缺氧初期的反硝化吸磷速率有影响外,对反硝化除磷的效率影响不明显.     

SBBR挂膜前活性污泥培养与驯化的研究

在序批式生物膜反应器（SBBR）挂膜前驯化活性污泥对养猪场废水进行生物降解实验。结果表明,在驯化期结束时,COD和NH₃-N的去除率分别达到85%和74%。对驯化过程中出现的污泥膨胀、上浮、泡沫等异常现象进行了分析,并提出了相应的解决措施。