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1.
Intensive recirculating aquaculture relies on biofilters to sustain satisfactory water quality in the system. Fluidized bed and immobilized cell technologies were used to remove ammonia from the water and maintain fish health. A high‐rate nitrifying fluidized bed biofilter combined with valveless filter was designed for use in a recirculation aquaculture system (RAS). The suspended solids produced during fish culture could automatically be removed using a valveless filter. Natural porosity with fitting proportion, steady fluidization and expanding rate was chosen as the fluidized carrier. The technology of bacterial separation and cultivation was used. The immobilized Rhodopseudomonas palustris (R. palustris) produced through a biotechnologically embedding medium is suitable for fish and could help prevent diseases. Nitrification was promoted through the selective rearing of nitrobacteria in a fluidized bed biofilter. Water quality was improved using fluidized bed biofilter and immobilized R. palustris in the RAS. In addition, the proposed system was able to reduce costs. Maximum fish load was 45 ± 3 kg m?3 in the closed recirculating water fish culture system, and water use was reduced by 80–90%. The total ammonia nitrogen removal rate of the technology was 80–95%, and nitrite N removal rate was above 80%.  相似文献   

2.
Florfenicol (Aquaflor®) is the only U.S. Food and Drug Administration (FDA) approved drug for treating diseased fish reared in recirculating aquaculture systems (RAS). Treating diseased fish in RAS is challenging because of the potential to damage nitrifying bacteria in the biofilters. Impaired nitrification can lead to concentrations of ammonia and nitrite that compromise fish welfare. The objective of this study was to determine the effects of a FDA‐approved parasiticide and fungicide, Parasite‐S® (formalin), on biofilter nitrification. Stable biofilters were exposed once to 0, 9.25, 18.5, 37, or 55.5 mg/L formaldehyde. Total ammonia nitrogen (TAN) and nitrite nitrogen were monitored daily before and throughout the study to quantify biofilter function. Formaldehyde concentrations ≥37 mg/L increased TAN and nitrite nitrogen concentrations, and nitrification did not recover to pre‐exposure concentrations up to 8 day postexposure. On the basis of those results, a second trial was conducted. Stable biofilters were exposed once or on four consecutive days to 9.25 or 18.5 mg/L formaldehyde. Biofilters repeatedly exposed to formaldehyde showed signs of impairment and had variable recovery relative to single exposures. Results of this study may help identify formaldehyde concentrations that can be safely applied to RAS when treating diseased fish.  相似文献   

3.
In recirculating aquaculture systems (RAS), the crucial step of eliminating toxic N compounds like ammonia and nitrite is mediated via nitrifying microorganisms and takes place in biofilters. In this study, analyses of microorganisms colonizing biocarriers of nine moving-bed biofilters of three different RAS operated with freshwater, brackish or marine process water uncovered site specific communities. Illumina-based amplicon sequencing of the V4-region of the 16S rRNA gene revealed a high microbial diversity with 1000–2500 species-level operational taxonomic units (OTUs) in all biofilters with the highest diversity in the brackish RAS. Proteobacteria, Bacteriodetes, Plantomycetes, Chloroflexi and Nitrospirae represented the most abundant phyla. 76 out of 674 known genera occurred in all nine biofilters and were defined as core-taxa, including nitrifying bacteria (Nitrosomonas and Nitrospira) as well as members of the (heterotrophic) genera Planctomyces, Blastopirellula, Nannocystis and Lewinella. Nitrifying communities composed of different, closely related and so far uncultured members of Nitrosomonas and Nitrospira were identified, strongly indicating that several potentially novel ammonia and nitrite oxidizing species are present in RAS biofilters. Relatives of known comammox Nitrospira were detected in the brackish biofilters, revealing 94–99 % identity of the 16S rRNA gene sequence to Ns. inopinata. Salinity tolerance tests with biocarriers derived from biofilters of the three distinct RAS showed an unexpected broad physiological flexibility with regard to salinity. Nitrification performance of freshwater nitrifiers was drastically reduced with increasing salinity and nearly completely inhibited at 15 PSU, while the brackish and marine nitrifiers showed a high resistance and maintained nitrification activity in a broad range of salt concentrations. This data can help to improve the nitrification process in RAS with changing salinity of the process water.  相似文献   

4.
From an environmental point of view, hydrogen peroxide (HP) has beneficial attributes compared with other disinfectants in terms of its ready degradation and neutral by‐products. The rapid degradation of HP can, however, cause difficulties with regard to safe and efficient water treatment when applied in different systems. In this study, we investigated the degradation kinetics of HP in biofilters from water recirculating aquaculture systems (RAS). The potential effect of HP on the nitrification process in the biofilters was also examined. Biofilter elements from two different pilot‐scale RAS were exposed to various HP treatments in batch experiments, and the HP concentration was found to follow an exponential decay. The biofilter ammonia and nitrite oxidation processes showed quick recuperation after exposure to a single dose of HP up to 30 mg L?1. An average HP concentration of 10–13 mg L?1 maintained over 3 h had a moderate inhibitory effect on the biofilter elements from one of the RAS with relatively high organic loading, while the nitrification was severely inhibited in the pilot‐scale biofilters from the other RAS with a relatively low organic loading. A pilot‐scale RAS, equipped with two biofilter units, both a moving‐bed (Biomedia) and a fixed‐bed (BIO‐BLOK®) biofilter, was subjected to an average HP concentration of ～12 mg L?1 for 3 h. The ammonium‐ and nitrite‐degrading efficiencies of both the Biomedia and the BIO‐BLOK® filters were drastically reduced. The filters had not reverted to pre‐HP exposure efficiency after 24 h, suggesting a possible long‐term impact on the biofilters.  相似文献   

5.
The aim of this study was to evaluate variability of nitrifying bacterial community in the biofilm and in the water of a recirculating aquaculture systems (RAS) in a tilapia farming in order to determine if nitrification process is dependent, or not, of nitrifying bacteria abundance. Biofilm and water samples were collected periodically for 30 days and analysed with the fluorescent in situ hybridization (FISH) technique, used to quantify ammonia‐oxidizing bacteria (AOB) and nitrite‐oxidizing bacteria (NOB). Ammonia presented the peak in the first week, while the nitrite's maximum was recorded in the second week. Nitrate increased steadily, indicating nitrification activity. Total bacterial abundance in biofilm increased continuously, while in water, it did not change significantly. In the biofilm, number of AOB was high at beginning, decreased after few days and increased again following augment of ammonia. Number of NOB also showed an increase in abundance in biofilm following the increment of nitrite and nitrate. In water, AOB and NOB did not show major variability. Relative abundance of nitrifying bacteria represented more than 30% of total bacteria in biofilm at beginning of the experiment. Their contribution decreased to >3% in last days. It indicates that nitrifying bacteria are biofilm colonizers, and that their activity seems to be directly related to the concentration of nitrogen compounds. However, contribution of nitrifying bacteria did not vary much along the time. We may conclude that the biofilm‐nitrifying bacteria plays major role in nitrification process in RAS and that the activity of these organisms is dependent of their abundance in response to the concentration of nitrogen compounds.  相似文献   

6.
In biofloc technology (BFT) rearing systems, nitrogen compounds, specially ammonia and nitrite, have to be controlled by microbial pathways, mainly through the activity of heterotrophic and chemoautotrophic bacteria. The objective of this work was to assess different water preparation strategies (heterotrophic, chemoautotrophic and mature) in BFT system for nursery of Pacific white shrimp (Litopenaeus vannamei). A 35-day study was conducted with post-larvae shrimp (0.08 g) stocked in twelve 300 L tanks at a stocking density of 2000 shrimp m−3. The water preparation strategies for shrimp rearing that were evaluated in this study included: i) Heterotrophic treatment, where the water received sugar as a carbon source; ii) Chemoautotroph treatment, where ammonium and nitrite salts were added to the water; and iii) Mature treatment, which was created by the addition of a significant amount of water containing mature biofloc from another established BFT system. In both mature and chemoautotrophic treatments, the nitrification process was able to keep toxic nitrogen compounds (ammonia and nitrite) at low levels without the addition of carbohydrates. In contrast, heterotrophic system showed peaks of ammonia and nitrite during the rearing cycle, and the level of these compounds were found to be higher in this treatment (relative to the mature and chemoautotrophic treatments). The chemoautotrophic system exhibited a lower abundance of bacteria from the family Vibrionaceae in the beginning of the experiment compared to the heterotrophic and mature treatments. The combination of low Vibrionaceae abundance and good water quality resulted in improved growth performance in this treatment. These findings demonstrate the importance of manipulating the environment of BFT systems to induce an enrichment of nitrifying bacteria before stocking shrimp. We have also found that the addition of a carbon source to BFT systems is necessary only in emergency situations, when ammonia spikes need to be controlled.  相似文献   

7.
循环海水养殖系统硝化滤器中氨氧化微生物分析   总被引：2，自引：0，他引：2  
研究循环水养殖硝化滤器载体上附着生物膜的微生物群落结构可以为提高其处理速率和效率,并为特异性工程菌构建提供依据。采用改良的AFLP方法分析了循环水养殖硝化滤器载体上附着的氨氧化细菌16S rRNA基因和氨单加氧酶amoA基因片段及其系统发育情况。结果表明:分析16S rRNA基因得到的序列片段比分析amoA基因片段得到了更多信息,准确度较高,可作为分析循环水养殖硝化滤器氨氧化菌群组成的有效方法。克隆测序所得序列与网上公布数据比对,可见存在于循环水养殖硝化滤器载体上的氨氧化细菌与Nitrosomonas cryotolerans、Nitrosomonas oligotropha、Nitrosospira tenuis、Nitrosomonas marina相似度达100%,与Nitrosomonas aestuarii相似度为87%。大部分属于亚硝化单胞菌属(Nitrosomonas),仅少数序列属于亚硝化螺菌属(Nitrosospira)。采用16S rRNA基因和amoA片段分析方法得到的附着于封闭循环海水养殖硝化滤器载体上的氨氧化细菌主要为变形菌(Proteobacteria)的β-亚类的亚硝化单胞菌属(Nitrosomonas)和少量的亚硝化螺菌属(Nitrosospira)氨氧化细菌,以及一定数量的γ-亚类氨氧化细菌。  相似文献   

8.
The nitrification process is a widely used biological approach responsible for ammonia and nitrite removal in recirculating aquaculture system (RAS) biofilters. Given this pivotal role, the influence of different water quality parameter on nitrification efficiency is important information for RAS operations. One influencing parameter is salinity, and salinity fluctuations in freshwater RAS biofilters are reported to affect the nitrifying bacteria. This study investigated the effects of abrupt increase in salinity in freshwater RAS on substrate-dependent (1’-order) as well as substrate independent (0’-order) nitrification rates. A 100% inhibition was found for surface specific removal (STR) of total ammonia nitrogen (TAN) and surface specific nitrite removal (SNR) when salinity was abruptly increased to 25‰ and above. A fast turnover (i.e. steep decline in [NH4-N+] and [NO2-N−]) were observed at lower salinities (≤10‰), while limited/no degradation of either ammonia or nitrite was seen at salinities above 25‰. At low substrate loading (1’-order process), removal rate constants (k1a) of 0.22 and 0.23 m d-1 were observed for ammonia and nitrite degradation, respectively, declining to 0.01 m d-1when adding marine RAS water increasing the salinity to 15‰. Similar observations followed at high nutrient loadings (0’-order process) with STR and SNR of 0.10 and 0.12 g N m-2 d-1, respectively, declining to 0.01 g N m-2 d-1 at 15‰. When salinities of 25‰ and 35‰ were applied, neither TAN nor nitrite degradation was seen. The results thus demonstrate a pronounced effect of salinity changes when freshwater RAS biofilters are subjected to fast/abrupt changes in salinity. RAS facility operators should be aware of such potential effects and take relevant precautions.  相似文献   

9.
Hydrogen peroxide (H2O2) treatment is an alternative for disinfection in aquaculture, which may be advantageous as it dissociates and disinfects while increasing water oxygen concentration. Yet, accurate dosing remains undeveloped in Recirculating Aquaculture Systems (RAS). Dosage requirements can depend on organic burden, stocking density, feeding frequency, salinity, temperature and biofilter performance. The present case study investigated the dual effect of H2O2 application for oxygen enrichment and disinfection when continuously applied to a RAS rearing European seabass. H2O2 addition equivalent to 2.4 and 15.8 H2O2 mg L−1 were applied for 4 h per day in three 5-days experiments. H2O2 was injected at the inlet of protein skimmer and/or the rearing tanks in or without combination with traditional disinfection methods. Water microbial load and oxygen saturation were determined, along with stress markers glucose and cortisol in blood plasma of fish. Doses of 15.8 mg L−1 H2O2 steadily increased oxygen levels in holding tank water from ∼50 % to over 100 % saturation while reducing microbial load (from 604.4 CFU ml−1 in the rearing tanks before dosing to 159.8 CFU ml−1 after application), achieving suitable conditions for commercial fish densities in RAS. The doses used had negligible impact on biofilter performance and did not affect the fish in terms of stress. Overall results indicate H2O2 is effective for disinfection and oxygenation of RAS systems when applied at appropriate dosage and we recommend the protein skimmer as the safest position in order to protect the bacterial community of the biofilters and the reared fish.  相似文献   

10.
Competition between heterotrophic and nitrifying bacteria is of major practical importance in aquaculture biofilter design and operation. This competition must be understood to minimize the negative impact of heterotrophic bacteria on an aquaculture system. On the other hand, the heterotrophic population is suspected of having a positive effect against pathogenic bacteria. Little information is available on the bacterial communities present within aquaculture systems, except for nitrifying bacteria, but a combination of traditional aquacultural engineering research methods and novel microbiological techniques offers new opportunities for the study of these communities.

The heterotrophic bacterial population activity and the nitrification efficiency of a submerged biological filter were studied for an influent TAN concentration of 2 mg/l and varying C/N ratios. The TAN removal rate was found to be 30% lower at a C/N ratio of 0.5 than at a C/N ratio of 0. For higher C/N ratios the reduction in nitrification efficiency was 50% while the attached bacterial abundance was doubled. Moreover, results confirm that abundance of sheared and attached bacteria are correlated. It is not known to what extent biofilter configuration might influence the relationship between heterotrophic and nitrifying bacteria, and further work will be carried out with moving bed and fluidized filters. A better understanding of the role of the heterotrophic bacteria in RAS will help to optimize any positive “biocontrol” effect and to minimize the microbial degradation of rearing water and the reduction of nitrification rates.  相似文献   


11.
The microbial changes occurring in the upper 1 cm of the solid sediment surface in intensively fed and aerated fish ponds located in northern Israel were examined. The bacterial groups enumerated included: total aerobes, total anaerobes, sulfate and iron reducing bacteria, ammonia and nitrite oxidizing bacteria, acid forming bacteria, and denitrifying bacteria. With the exception of the nitrifying bacteria, large microbial populations were observed in the pond sediment even prior to fish stocking. All the different groups enumerated displayed a rapid change in number during the first 2–8 days following fish stocking, and a subsequent approach toward a steady state. Since both microbial and chemical steady states were approached within a relatively short period of time, it does not appear that these components of the sediment are related to the inhibition of fish growth occurring 50–70 days after fish stocking. While the practice of pond draining and air drying the sediment does oxidize some of the accumulated organic material, it does not appear to affect the resident microbial flora significantly to an extent that could decrease the rate of reestablishment of the microbial community. Therefore, upon establishment of anaerobic conditions a large microbiological community is present capable of mediating the chemical reduction of SO42? to H2S, or other transformations resulting in products which contribute to fish growth inhibition commonly observed in such intensively stocked and fed fish ponds.  相似文献   

12.
The growing popularity of the aquarium trade is greatly increasing the demand for many ornamental fish. While shipping technology has made the worldwide transportation of ornamental fish possible, a significant portion of the fish caught for the aquarium trade perish in transport before being sold to hobbyists. One of the major causes of fish death in transport is ammonia building up to toxic levels in the shipping bags. In order to solve this problem, we investigated the effectiveness of using nitrifying consortia in reducing the ammonia build‐up in marine fish bags during transport. A pre‐activated nitrifying consortium was effective in safely maintaining low ammonia levels during a three‐day experiment. We found that both ammonium chloride and urea can activate nitrifying consortia. Activation of nitrifiers by urea is not only novel but also beneficial due to being less harmful to fish in comparison with ammonia. We also discovered that unexpectedly one nitrifying consortium examined mainly contained ammonia‐oxidizing archaea. The confirmation of the concept of the use of activated nitrifying consortia and the usefulness of nitrifying archaea for fish transportation may be beneficial for the fish trading and aquaculture.  相似文献   

13.
The aim of this study was to compare two rearing systems for freshwater prawn Macrobrachium rosenbergii: one with use of a recirculating aquaculture system with biofilters (RAS) and another with use of microbial flocs (F). Thirty postlarvae of freshwater prawn with an initial average weight of 0.13 ± 0.05 g were randomly stocked in six experimental units with 0.20 m² and volume of 50 L. The experiment lasted thirty days. Dissolved oxygen, temperature and pH were monitored daily; ammonia concentration was determined three times per week; nitrite concentration, alkalinity and hardness were measured weekly. For the formation of microbial floc, molasses was used to keep the ammonia concentrations within safe levels for prawn farming. The variables of water quality remained within the suitable range for the production of the species, except for ammonia concentrations at the F treatment, which exceeded the safe levels. At the end of the experiment, the following parameters were evaluated: survival, specific growth rate, weight gain and feed conversion rate. Differences were found only in feed conversion rate with better values on RAS treatment. The microorganisms present in the RAS and F treatment were also evaluated. The densities of rotifers, amoebas and total bacteria were higher at the F treatment although the same organisms were found at the RAS treatment. The results of this study showed the possibility of rearing M. rosenbergii in biofloc system technology.  相似文献   

14.
本文通过在循环水养殖系统中添加不同浓度的臭氧,研究其对循环水养殖系统生物膜活性及其净化效能的影响.结果显示,当氧化还原电位(ORP)小于450 mV时,氨氮的去除率随着臭氧浓度升高而升高,最高去除率达39.9％,亚硝酸盐氮的平均去除率为28.2％,生物膜菌群的平均存活率为88.1％,生物膜对养殖水体氨氮和亚硝酸盐氮的处理效果良好;当氧化还原电位为500 mV时,经过臭氧24 h处理,氨氮和亚硝酸盐氮的去除率分别由36.5％、28.1％降到12.2％、8.4％,而臭氧4h处理后,生物膜对氨氮和亚硝酸盐氮的去除率分别由47.5％、32.1％降到5.0％、3.3％,水处理效果明显下降,生物膜菌群存活率由88.1％降到31.5％.由此可见臭氧添加浓度对生物膜及净化效能有重大影响.综合试验结果和分析评估,建议封闭循环水养殖系统的臭氧添加量以控制生物滤池内的氧化还原电位低于400 mV为宜,可保证循环水系统的安全性和经济性.  相似文献   

15.
Peracetic acid (PAA) is a powerful disinfectant with a wide spectrum of antimicrobial activity. PAA and hydrogen peroxide (HP) degrade easily to oxygen and water and have potential to replace formalin in aquaculture applications to control fish pathogens, for example the ectoparasite, Ichthyophthirius multifiliis.We studied water phase PAA and HP decay in three aquaculture situations, i) batch experiments with two types of system waters, ii) PAA decay at different fish densities, and iii) degradation of PAA in submerged biofilters of recirculating aquaculture systems (RAS). Furthermore, effect of PAA on the nitrification activity and the composition of the nitrifying population were investigated.PAA and HP decay showed first order kinetics. High dosage PAA/HP in water with low COD inhibited HP removal, which was not observed in water having a higher COD content. PAA decay was significantly related to fish stocking density, with half life constants for PAA of 4.6 and 1.7 h at 12 and 63 kg m− 3, respectively.PAA application to RAS biofilter showed rapid exponentially decay with half life constants of less than 1 h, three to five times faster than the water phase decay rates.Biofilter surface specific PAA removal rates ranged from 4.6 to 13.9 mg PAA m− 2 h− 1 and was positively correlated to the nominal dosage. Low PAA additions (1.0 mg L− 1) caused only minor impaired nitrification, in contrast to PAA application of 2.0 and 3.0 mg L− 1, where nitrite levels were significantly increased over a prolonged period, albeit without fish mortality. The dominant ammonium oxidizer was Nitrosomonas oligotropha and the dominant nitrite oxidizer was Nitrospira. Based on the present findings and other recent results from field and in vitro studies, application perspectives of PAA are discussed.  相似文献   

16.
The effect of water velocity on nitrification rates in fixed bed biofilters was investigated in three freshwater pilot scale RAS with rainbow trout. Removal of total ammonia nitrogen (TAN) and nitrite-nitrogen were assessed by NH4Cl spikes and tested at four different water velocities in the biofilters (1.4, 5.4, 10.8 and 16.2 m h−1) under identical conditions. Water velocities below 10.8 m h−1 significantly reduced TAN- and nitrite removal rates. The surface specific TAN removal rates correlated with the TAN concentrations at the water velocities 10.8 and 16.2 m h−1, and the first order surface removal rate constant was estimated at 0.45 m h−1. However, no correlations between TAN removal and TAN concentrations were found at the lowest velocities. Up to five-fold elevated nitrite levels were found in the RAS when biofilters were operated at 1.4 m h−1 compared to the trials at other water velocities, substantiating the significant effect of water velocity on both nitrification processes. The importance of biofilter hydraulics documented in this pilot scale RAS probably have implications for design and operation in larger scale RAS.  相似文献   

17.
宋志文  徐敏  温少鹏  吴蕾 《河北渔业》2007,(11):29-31,60
研究自制硝化细菌制剂对水族箱水质的净化效果,试验结果表明:硝化细菌制剂对水族箱水质具有明显的净化效果,实验组水族箱水质氨氮、亚硝氮、COD等指标明显低于对照组。投加硝化细菌制剂后,水族箱内氨氧化细菌、亚硝酸盐氧化细菌可在短时间内形成优势,使氨氮、亚硝氮维持在较低浓度水平;在不投加菌剂的情况下,氨氧化细菌虽然可在一定时间内形成优势,使氨氮浓度降低,但由于亚硝酸氧化细菌生长缓慢,水族箱中亚硝酸积累问题严重。  相似文献   

18.
To achieve water reuse in recirculating aquaculture systems, intermittent nitrification and denitrification processes using internal fibrous media was proposed. A pre-acclimated Biocord biofilter, with an initial nitrification rate of 17.1 ± 12.4 mg total ammonia nitrogen-N/m2/d was applied in a marine whiteleg shrimp (Litopenaeus vannamei) culture tank. Throughout the experiment, the aerobic nitrification activity of the biofilter was sufficient to control the ammonia and nitrite levels below 0.2 mg-N/L with an accumulation of nitrate up to 50 mg-N/L. The remaining nitrate was successfully removed after shrimp harvest with the same biofilter through anoxic denitrification in conjunction with a methanol supplement at a chemical oxygen demand: nitrate-N ratio of 5:1. With complete nitrogen removal, the water was re-aerated and the next crop of shrimp culture was initiated. In this study, a two-crop shrimp cultivation was performed in sequence in the same tank without water exchange. The microbial diversity was monitored using high-throughput sequencing on Illumina MiSeq, which demonstrated that Proteobacteria (45.3 %), Chloroflexi (18.4 %), and Bacteroidetes (17.1 %) were the most abundant phyla. With an emphasis on nitrogen removal, the family Nitrosomonadaceae and Nitrospiraceae were the dominant nitrifying bacteria during the aerobic nitrification, while a high relative abundance of the Methylophaga and Methylotenera genera was observed under the anoxic condition.  相似文献   

19.
While biofilters are widely used to metabolize ammonia and other metabolic waste products in recirculating aquaculture systems, their microbial communities are not thoroughly characterized. While inroads have been made characterizing microbial communities within single biofilters, replicated comparisons across biofilters and facilities have been lacking. We hypothesized that microbial communities might differ among filter types and facilities. We characterized and compared the bacterial communities of nine nitrification biofilters in five commercial recirculating marine aquaculture operations by amplifying and sequencing the 16S rRNA gene using the Illumina-MiSeq DNA sequencing platform. Our results demonstrated the usefulness of the approach for elucidating bacterial community structure in aquaculture biofilters; among almost 249,000 usable DNA sequence reads—a mean of 27,663 for each biofilter—we detected a mean of 682 operational taxonomic units. Higher species diversity was observed in the submerged biofilters at farms 3 and 4 (HF_SB1, HF_SB2, HF_SB3, MB_SB1, MB_SB2, and MB_SB3), and a bead filter at farm 2 (XYF-MBBR) than in a bead filter at farm 1 (DF_MBBR) and a fluidized sand filter at farm 5 (TY_FSF). At the phylum level, Proteobacteria were the most frequently observed taxa (representing 36–50 % of reads in the overall data set for a given filter); other frequently observed phyla were Bacteroidetes (13–34 %), Chloroflexi (2–23 %), Nitrospirae (1–7 %), Planctomycetes (1–4 %), and Actinobacteria (2–5 %). However, in fluidized sand filters, after Proteobacteria, the subdominant phyla were Bacteroidetes (19 %), Nitrospirae (17 %), and Planctomycetes (11 %). At the genus level, the nitrite-oxidizing genus Nitrospira was frequently observed in sand filter TY_FSF (16.4 %), bead filter DF_MBBR (7.6 %), submerged biofilter MB_SB1 (7 %), and bead filter XHF_MBBR (7.36), and less frequently in submerged biofilters HF_SB3 (1.94), HF_SB2 (1.77 %), and HF_SB1 (1.63 %), and bead filters MB_SB2 (0.8 %) and MB_SB1 (0.2 %). Observations of the ammonia-oxidizing genus Nitrosomonas varied widely within and among filter types, ranging from 0.06 % in submerged bed filter HF_SB3 to 2.82 % in bead filter DF_MBBR. Principal components and cluster analyses classified the bacterial communities in the nine biofilters into groups corresponding to the respective recirculating marine aquaculture operations and the associated filter types.  相似文献   

20.
Laboratory data and information from the literature were used to develop an equation that models ammonia removal by submerged biofilters. The equation is based on the half-order/zero-order kinetics model and fixed biofilm nitrification, which indicates that the nitrification rate is a linear function of the ammonia concentration at ammonia concentrations <2.0 mg/l. Input data for the equation include easily gathered information of flow rate, biofilter size, maximum permissible ammonia level, biofilter influent and biofilter effluent ammonia concentrations, temperature, and ammonia production rate. The equation can be used to determine the carrying capacity of the submerged biofilters, to estimate biofilter sizes needed to support various fish loads, and to investigate the effects of changes in biofilter system parameters on carrying capacity. Comparisons of the predicted and actual carrying capacities of several experimental biofilters indicated that the equation accurately predicted carrying capacity under most conditions. Studies of the sensitivity of the equation to changes in system parameters demonstrated that flow rate limits biofilter performance and suggested an approach for determining cost-effective flow rates for biofilter operation.  相似文献   

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