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1.
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   

2.
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   

3.
Total ammonia nitrogen (TAN) concentration is often a key limiting water quality parameter in intensive aquaculture systems. Removing ammonia through biological filtration is thus the first objective in recirculating aquaculture system design. In this study, the performance characteristics of a steady-state nitrification biofilm were explored using a series of reactors. Four nitrification kinetics parameters were estimated using the data collected from the experimental system, including minimum TAN concentration, half saturation constant, maximum TAN removal rate and maximum specific bacterial growth rate. Experimental data showed that a minimum TAN concentration was needed to support a steady-state nitrification biofilm. For the temperature of 27.2°C, the mean minimum TAN concentration was 0.07 mg/l. For a single substrate-limiting factor, the relationship between TAN removal rate (R) and TAN concentration (S) was represented by an empirical equation [R=1859(S−0.07)/(S+1.93)]. The characteristics of nitrite oxidation were also demonstrated by the experiment system. The results of this study will help to better understand the characteristics of nitrification biofilters applied in recirculating aquaculture systems.  相似文献   

4.
A laboratory-scale recirculating aquaculture system for fluidised bed biofilter evaluation was engineered. The design included all components found in typical full-scale commercial production systems. The system included two identical units each with oxygenation, UV treatment, cooling, biofiltration and a particulates separation device. Water from the two systems was mixed in a degassing unit. A 1 month test period after biofilter maturation revealed stable concentrations of total ammonia nitrogen (TAN), nitrite and nitrate within the system. Mean nitrification rate was 0.27 and 0.21 g TAN m−2 day−1. Oxygen consumption in the biofilters ranged between 56 and 64% due to nitrifying activity. Mass balances on nitrogen indicated that 48%, added via the feed, was converted to nitrate within the system, with 6% of the added nitrogen being found in the sludge. The remaining 43% was either used during fish growth, left the system, as organic nitrogenous compounds (or unidentified nitrogenous compounds), via the outlet, or was lost to the atmosphere. At least 61% of the nitrate produced was generated by the biofilters. The system proved to be an exceptional set-up for evaluation of the performance of fluidised bed biofilters, allowing both pre- and post-filter measurements of various water quality criteria.  相似文献   

5.
Design and management of conventional fluidized-sand biofilters   总被引:2,自引:0,他引:2  
Fluidized-sand beds are an efficient, relatively compact, and cost-competitive technology for removing dissolved wastes from recirculating aquaculture systems, especially in relatively cool or coldwater applications that require maintaining consistently low levels of ammonia and nitrite. This paper describes several types of flow injection mechanisms used in commercial fluidized-sand biofilters and provides criteria for design of flow distribution mechanisms at the bottom of the fluidized bed. This paper also summarizes the most critical aspects of sand selection, as well as methods for calculating or experimentally measuring fluidization velocities and pressure drop for a given filter sand size distribution. Estimates of nitrification rate, ammonia removal efficiency, carbon dioxide production, and oxygen consumption across fluidized-sand biofilters are also provided for various conditions. Fluidized-sand biofilter operational and management practices are also described.  相似文献   

6.
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   

7.
Factors such as limitations in water quality and quantity, cost of land, limitations on water discharges, environmental impacts and diseases, are driving the aquaculture industry toward more intensive practices. This will force producers to adopt environmentally friendlier technologies. Recirculating systems, with a biofilter as the most prominent characteristic, treat internally the water contaminated with dissolved organics and ammonia and reduce the amount of water use and discharge from aquaculture operations. This paper reviews the implications of the changing use of recirculating aquaculture systems (RAS) on biofiltration research for freshwater and marine operations. Demand for cost effective biofilters will increase with the expansion of recirculating systems, both as a complement and replacement of traditional ponds. For freshwater aquaculture, emphasis should be placed in cost competitiveness, low head operations, intensification of ponds with RAS biofiltration and the evaluation of suspended growth systems. In the marine systems, an increase in demand of oligotrophic and ultraoligotrophic systems is expected, particularly in the nursery systems. Sizing and cost efficiency of biofilters for nursery operations should be addressed. Problems in marine biofilter acclimation appear to justify the development of new acclimation procedures. Biosecurity concerns, land cost and storm threats will drive nursery systems inland, where saltwater supply and disposal will force an increased water reuse. Denitrification strategies will need to be redefined and optimized for the marine nursery environment.  相似文献   

8.
Photosynthetic suspended-growth systems in aquaculture   总被引:3,自引:0,他引:3  
Standardized evaluation and rating of biofilters for aquaculture should be assessed in the context of the economic efficiency of ecological services (waste assimilation, nutrient recycling, and internal food production) provided by earthen ponds, and the availability and cost of land, water, and electrical energy resources required to support particular classes of production systems. In photosynthetic suspended-growth systems, water quality control is achieved by a combination of natural and mechanical processes. Natural processes include photosynthesis of oxygen, algal nutrient uptake, coupled nitrification–denitrification, and organic matter oxidation; mechanical processes include aeration and water circulation. Ammonia is controlled by a combination of phytoplankton uptake, nitrification, and immobilization by bacteria. Unlike biofilters for recirculating aquaculture systems, unit processes are combined and are an integral part of the culture unit. The important design and operational considerations for photosynthetic suspended-growth systems include temperature effects, aeration and mixing, quantity and quality of loaded organic matter, and fish water quality tolerance limits. The principle advantages of photosynthetic suspended-growth systems are lower capital costs relative to other recirculating aquaculture systems and increased control over stock management relative to conventional static ponds. The main disadvantage is the relatively low degree of control over water quality and phytoplankton density, metabolism, and community composition relative to other recirculating aquaculture systems. Examples of photosynthetic suspended-growth systems include semi-intensive ponds, intensively aerated outdoor lined ponds, combined intensive–extensive ponds, partitioned aquaculture systems, greenwater tanks, greenwater tanks with solids removal, and greenwater recirculating aquaculture systems.  相似文献   

9.
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   

10.
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   

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