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Biofiltration of cyclo-bio fluidized sand bed in recirculating aquaculture system

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A lab-scale cyclobio fluidized sand biofilter was designed to study biofiltration in recirculating aquaculture systems. First, the biofiltration start was studied separately in fresh water and seawater recirculating aquaculture systems. Second, the influence of different operation conditions on water treatment were studied by natural membrane-forming, including three bed expansions (50%, 75% and 100%) and four carbon nitrogen ratios (0, 0.5, 1 and 2). A synthetic substrate solution was continuously fed into the tanks after measuring of water quality every time. The results showed that the total ammonia-nitrogen concentration was decreased, fluctuating lightly in later period. The nitrite-nitrogen concentration was in a shape of clock, increasing quickly first and keeping the maximum for days then decreasing quickly, fluctuating lightly in later period. Not only ammonia-nitrogen and nitrite-nitrogen concentrations, but also the stability of water quality should be as the criteria of completion judgement of biofiltration start. In these conditions, biofiltration start of cyclobio fluidized biofilter were 47 days in fresh water system and 60 days in seawater system. Besides, we found that the cyclobio fluidized biofilter had little help in removing phosphorous, maybe because dissolved oxygen was always more than 6 mg/L in system. The nitrate-nitrogen concentration was increased on the whole. However, high nitrite-nitrogen concentration may harm fish health. To avoid that, there were two control methods: exchanging some new water to system every day, or adding denitrification equipment to recirculating aquaculture systems. Meanwhile, the results of operation conditions showed that the maximum load of system was separately 2.5, 3.0 and 3.5 mg/L with different bed expansions 50%, 75% and 100%. And the removal efficiency of total ammonia-nitrogen increased and the nitrite-nitrogen concentration decreased with the enhancement of bed expansion. The efficiency of ammonia-nitrogen was the highest and the load of system was the largest under 100% bed expansion in this study, while the volumetric total ammonia nitrogen conversion rate was 881 g/(m3·d). Besides, inhibition of organic on nitrification was observed. The ammonia-nitrogen, nitrite-nitrogen and COD concentrations were increased with the enhancement of ratios of carbon and nitrogen. Especially, water quality went bad obviously when ratios of carbon and nitrogen was more than 2.0. The ammonia-nitrogen and nitrite-nitrogen even reached to lethal or medial lethal concentrations of some fishes. The possibility was that heterotrophic microorganisms breed quickly with the enhancement of ratios of carbon and nitrogen and autotrophic nitrifying bacteria was embedding and died absenting of oxygen. This research can provide a reference for starting, operation and management of cyclobio fluidized biofilters in production. ©, 2015, Chinese Society of Agricultural Engineering. All right reserved.
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31 3 Vol.31 No.3
2015 2 Transactions of the Chinese Society of Agricultural Engineering Feb. 2015 249
循环水养殖旋转式生物流化床生物过滤功能
柳 瑶 1,2,宋协法 1,雷霁霖 2,彭 磊 1,黄志涛 1,刘宝良 2
1. 中国海洋大学水产学院,青岛 266003 2. 中国水产科学研究院黄海水产研究所,青岛 266071
要:生物过滤是循环水养殖水处理的关键,生物过滤功能启动以及操作条件直接影响到生物过滤的效果。该文以实
验室规模旋转式生物流化床为研究对象,采用自然挂膜法研究海水和淡水生物过滤功能的启动;设置了 3个膨胀率 50%
75%100%4C/N00.51.02.0,研究其对旋转式生物流化床处理养殖污水效率的影响。结果表明:1)以氨氮
和亚硝态氮浓度降低并稳定为判断标准,淡水和海水系统旋转式生物流化床生物过滤功能启动完成分别需要 47 60 d
2)污水处理效率随膨胀率增大而提高,该研究膨胀率为 100%时处理效率最高,总氨氮转换率高达 881 g/(m3·d)3C/N
增大,抑制生物膜的硝化功能,污水处理效果变差,C/N 大于 2.0 时污水处理效果显著变差。该研究可为旋转式生物流化
床在应用过程中生物过滤功能的启动和日常操作管理提供技术指导
关键词:水产养殖;生物过滤;海水;旋转式生物流化床;生物过滤功能启动;膨胀率;C/N
doi10.3969/j.issn.1002-6819.2015.03.033
中图分类号:S951 文献标志码:A 文章编号:1002-6819(2015)-03-0249-06
瑶,宋协法,雷霁霖,. 循环水养殖旋转式生物流化床生物过滤功能[J]. 农业工程学报,2015,31(3):249-254.
Liu Yao, Song Xiefa, Lei Jilin, et al. Biofiltration of cyclo-bio fluidized sand bed in recirculating aquaculture system[J].
Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2015, 31(3): 249254. (in Chinese
with English abstract)
0 引 言
生物过滤是循环水养殖水处理的关键环节。生物过
滤器的选择对系统建造成本、空间利用率以及水质好坏
影响较大。目前,生物过滤器类型较多,生物流化床氨
氮去除效率高(50%90%[1-2]、占地面积小[3-4]、无需
反冲洗,但运行能耗高、操作管理难度较大。旋转式生
物流化床(cyclo-bio fluidizd sand biofiltersCB FSB)结
构更先进,通过改变进水机制进一步降低了运行能耗。
CB FSB 首先由 Timmons [4]在国际会议上提出;
Summerfelt[5]阐述了该结构的运行机制、滤料选择以及日
常维护;Davidson [6]比较 3种商业化规格 CB FSB 去除
高密度养殖废水中的碳质生化需氧量(5-day
carbonaceous biochemical oxygen demandcBOD5)、
氨氮(total ammonia nitrogenTAN)、磷、总悬浮固体
total suspended solidsTSS)以及大肠菌的效果,以及
控制床层膨胀的 2种方法:虹吸法和生物膜剪切法。张
海耿等[7]研究了石英砂粒径和初始床层高度对 CB FSB
能的影响,并采用回归拟合方法得出临界流化速度的数
学模型。柳瑶等[8-9]采用数值模拟方法研究了 CB FSB
流化状态、最小流化速度以及流速与膨胀率的关系。上
收稿日期:2014-11-26 修订日期:2015-01-12
基金项目:十二五国家科技支撑项目(2011BAD13B04
作者简介:柳 瑶,女(汉族),山东青岛人,博士,主要从事水产养殖工
程研究。青岛 中国海洋大学水产学院,266003
Emailliuyaosdau@163.com
※通信作者:宋协法,男(汉族),山东威海人,博士,教授,主要从事渔
业设施工程研究。青岛 中国海洋大学水产学院,266003
Emailyuchuan@ouc.edu.cn
述研究大多是关于 CB FSB 的运行机理以及应用效果的研
究,关于该装置操作和管理的研究较少,如生物过滤功能
的启动、系统稳定性、操作条件,尤其是膨胀率等流化床
特有的重要参数。针对上述问题,本文分别研究了淡水和
海水系统中 CB FSB 的生物过滤功能的启动过程,并重点
分析了膨胀率和 C/N CB FSB 处理污水效果的影响,
CB FSB 在生产实践中的应用提供理论和技术支撑。
1 试验材料与方法
1.1 模拟养殖污水处理系统
实验室规模 CB FSB 处理模拟养殖污水系统由养殖池、
水泵、生物过滤器、沉淀池及加热棒组成(图 1)。其中
CB FSB 尺寸如下:床体高度 134 cm、床体直径 19 cm、进
水管直径 2 cm出水管直径 10 cm布水腔底部直径 29 cm
1 养殖污水处理系统
Fig.1 Schematic of recirculating system to treat aquaculture
wastewater
1.2 试验材料
1.2.1 模拟养殖污水
试验用水为模拟养殖污水:净水+按一定比例混合而
农业工程学报 2015
250
成的底物(表 1[10],设初始氨氮质量浓度为 2 mg/L
淡水、海水净水分别是自来水、青岛近海砂滤海水。
1 模拟养殖污水的配置
Table 1 Composition of substrate nutrients
化学成分 Component 质量 Mass/g
NH4Cl 1377
NaHCO3 3500
MgSO4.7H2O 36
Na2HPO4 159
KH2PO4 153
FeCl3.6H2O 5
1.2.2 石英砂
石英砂经分样筛处理后粒径 0.350.65 mm,密
2 650 kg/m3,在 CB FSB 中填充高度 40 cm,体积约
11.34 L,填充率 31%
1.3 试验设计
试验设计分为 2部分:
1)淡水和海水系统 CB FSB 生物过滤功能的启动
试验条件:水温25±1)℃,pH 7.88.3,溶解
氧(dissolved oxygen)≥6 mg/L。系统启动后,试验前期
3 d 测定氨氮(total ammonia nitrogen, TAN)、亚硝态
氮(NO2-N)、硝态氮(NO3-N)、无机磷(phosphorus)、化
学需氧量(chemical oxygen demandCOD),每天测定
pH 值、溶解氧dissolved oxygenDO)、盐度(salinity,
SAL)、温(temperatureT)。每次取样之后,补平底物
浓度,使氨氮质量浓度维持在2±0.2mg/L试验后期,
每天测定上述水质指标(表 2)。
2)膨胀率和 C/N CB FSB 生物过滤功能的影响
试验共设置 3个膨胀率:50%75%100%。分别
判断系统在特定膨胀率下所能承受的最大负荷。即逐渐
提高进水氨氮质量浓度至 2.02.53.03.5 mg/L,每 2
水平之间的时间间隔约为 3周,直至出水氨氮和亚硝态
氮浓度短时间内无法迅速降低至安全浓度。
试验共设置 4C/N,即 00.51.0 2.0。设
率为 100%进水氨氮质量浓度 3.5 mg/L蔗糖C12H22O11
为碳源。系统初始 C/N 0,之后逐渐提高。
1.4 试验方法
水质测定方法见表 2
2 主要分析项目与检测方法
Table 2 Analytical items and methods
水质测定指标
Water quality index 测定方法
Determination method
氨氮
Total ammonia nitrogen 靛酚蓝分光光度法(GB 12763.4-1991
亚硝态氮 NO2-N 萘乙二胺分光光度法(GB 12763.4-1991
硝态氮 NO3-N 锌铬还原法
无机磷 Phosphorus 磷钼蓝分光光度法(GB 12763.4-1991
化学需氧量
Chemical oxygen demand 碱性高锰酸钾法(GB 12763.4-1991
pH pH value Orion 3 star 多功能 pH 计(Thermo electro n
corporation USA
溶解氧 Dissolved oxygen YSI 溶氧仪(YSI incorporation USA)
盐度 Salinity ATAGO 手持盐度计(ATAGO COLTD
Japan
温度 Temperature 水银温度计
2 结果与分析
2.1 CB FSB 生物过滤功能启动
2.1.1 氨氮和亚硝态氮浓度变化
淡水、海水系统 CB FSB 生物过滤功能启动过程氨氮
和亚硝态氮浓度随时间变化分别如图 2ab所示。从图 2
中可以看出,淡水、海水系统变化趋势相似。
2 CB FSB 生物过滤功能启动氨氮、亚硝态氮、无机磷、硝态氮浓度随时间变化
Fig.2 Comparison of fresh water and seawater about effluent concentration of NH4+-N, NO2--N, P, NO3-N duaring forming process of
biofiltration in cyclobio fluidized sand biofilters
首先,氨氮浓度整体呈降低趋势,并分别在第 17
30 天,氨氮质量浓度迅速降低到 0.05 mg/L 以下。说明
系统的生物膜中亚硝化细菌数量迅速增多,推测该细菌
处于对数增长期。但是在第 2143 天,氨氮浓度出现
3 瑶等:循环水养殖旋转式生物流化床生物过滤功能
251
明显波动,最高达到 0.6 mg/L。可能与微生物的生长周
期有关,推测早期亚硝化细菌死亡脱落。最终分别在 35
60 d 以后,氨氮浓度维持在较低状态下,持续监测 10 d
左右,无明显波动。说明亚硝化细菌已经适应新环境、
迅速繁殖并进入稳定期。表明:淡水、海水系统分别运
行到第 3560 天,CB FSB 将氨氮转化为亚硝态氮的功
能趋于稳定。
亚硝态氮浓度总体呈钟形结构:先积累升高,后迅
速降低。在第 10 天左右,亚硝态氮质量浓度迅速升高,
淡水与海水系统最高值分别约为 2535 mg/L。说明硝
化细菌数量少于亚硝化细菌,原因是硝化细菌的生长速
度低于亚硝化细菌[12]尤其是 2种细菌对底物存在竞争
关系时。最高值持续约 10 d,分别在第 2639 天迅速
降低。说明硝化细菌数量迅速升高。淡水和海水系统分
别在第 3745 天亚硝态氮浓度明显波动,最高值达到 2
3 mg/L最终分别在 4760 d 时逐步稳定,持续监测 10 d
左右,无明显波动。说明硝化细菌已经适应新环境、迅
速繁殖并处于稳定期。表明:淡水、海水系统分别运行
到第 4760 天,CB FSB 将亚硝态氮转化为硝态氮的功
能稳定。
本研究以系统转化氨氮和亚硝态氮的能力为生物过
滤功能启动完成的判断标准,采用自然挂膜法,淡水、
海水系统 CB FSB 生物过滤功能启动完成分别需要 47
60 d
2.1.2 无机磷浓度变化
淡水、海水系统 CB FSB 生物过滤功能启动过程无机
磷浓度随时间变化如图 2c 所示。进水无机磷质量浓度维
持在(0.4±0.05mg/L。从图中可以看出,启动前期无
机磷保持一定去除率,出水质量浓度维持在 0.3 mg/L
右;尤其是在第 1322 天时,无机磷质量浓度分别降低
0.160.14 mg/L。原因是启动前期微生物快速繁殖,
磷作为微生物合成自身物质的必需底物需要从外界吸
收。1937 天以后,无机磷质量浓度在 0.4 mg/L 上下
波动,说明 CB FSB 无明显的生物除磷作用。推测原因为:
生物除磷通过聚磷菌在厌氧条件下释磷和好氧(或缺氧)
条件下超量吸磷交替进行完成的,而本系统 DO 始终大于
6 mg/L缺少厌氧环境。因此 CB FSB 无法发挥生物除磷
功能。
2.1.3 硝态氮浓度变化
淡水、海水系统 CB FSB 物过滤功能启动过程硝态
氮浓度随时间变化如图 2d 所示。从图中可以看出:硝态
氮浓度总体呈上升趋势。试验前期,硝态氮浓度增长缓
慢,说明硝化细菌数量很少;约 10 d 以后,淡海水系统
硝态氮浓度虽有一些波动,但整体都呈现快速增长趋势,
说明硝化细菌快速增长。虽然硝态氮致死浓度很高,长
时间积累仍会影响养殖鱼类健康生长,可通过 2种措施
调控:1)每天更换一定的新水;2)在系统中增加反硝
化装备,但会增加运行和建造成本,并且要完全实现封
闭循环式养殖,反硝化装备和技术也是亟待突破的瓶颈
之一。
2.2 膨胀率和 C/N CB FSB 生物过滤功能的影响
生物过滤器处理养殖污水的效果受多种因素影响。
膨胀率是生物流化床特有的参数,决定生物滤料间的碰
撞几率和摩擦程度,影响生物膜的附着、脱落与再生。
微生物种群之间竞争激烈,C/N 对种群结构影响重大。
因此,本文分别研究膨胀率和 C/N CB FSB 生物过滤
功能的影响。
2.2.1 膨胀率对 CB FSB 生物过滤功能的影响
试验结果表明:3个膨胀率下系统的最大负荷依次为
2.53.03.5 mg/L,同时该负荷CB FSB 处理养殖污
水效果如表 3所示。
3 不同膨胀率抗冲击负荷能力最强时 CB FSB 的污水处理
效果的比较
Table 3 Comparison of effect of wastewater treatment in CB FSB
with biggest anti-shock loading capability among different bed
expansions
膨胀率
Bed
expansion/
%
水流
流量
Flow
rate/
(L·min-1)
总氨氮
转换率
Volumetric
TAN
conversion
rate/
(g·m-3·d-1)
氨氮质
量浓度
TAN mass
concentration/
(mg·L-1)
亚硝态氮质量
浓度
Nitrite
nitrogen mass
concentration/
(mg·L-1)
无机磷质
量浓度
Phosphorous
mass
concentration/
(mg·L-1)
50 22.77 629 0.0183 0.0451 0.0432
75 34.29 755 0.0158 0.0293 0.0445
100 45.81 881 0.0179 0.0158 0.0418
由表 3可以看出:随着膨胀率提高,CB FSB 的总氨
氮转换率(volumetric TAN conversion ratesVTR)逐渐
升高。出水氨氮和无机磷浓度无明显规律性变化,而亚
硝态氮浓度显著降低。说明膨胀率增大,CB FSB 处理养
殖污水效率升高,系统抗冲击负荷能力增强。
2.2.2 C/N CB FSB 生物过滤功能的影响
由表 4可以看出,氨氮、亚硝态氮浓度以及 COD
C/N 增大逐渐升高,无机磷浓度无明显规律,而氨氮去除
率呈下降趋势。说明 C/N 增大对 CB FSB 生物过滤功能
有抑制作用,尤其是 C/N 达到 2时出水氨氮和亚硝态氮
浓度显著增高,甚至已经达到敏感鱼类的致死或半致死
浓度。可能的原因是:生物过滤器中化能自养菌和异养
菌共存,随着 C/N 增大,异养菌快速繁殖,硝化细菌被
埋在生物膜内层,很难接触到基质和 O2而导致大量死亡
和脱落,使系统转化氨氮的能力降低。同时,有机物浓
度也超出系统负荷,从而导致出水 COD 升高。
4 C/N 对模拟养殖污水处理效果的比较
Table 4 Comparison of effect of wastewater treatment in CB FSB
at different C/N
C/N
氨氮去
除率
TAN
remove
rate/%
氨氮质
量浓度
TAN
mass
concentration/
(mg·L-1)
亚硝态氮
质量浓度
Nitrite nitrogen
mass
concentration/
(mg·L-1)
无机磷
质量浓度
Phosphorous
mass
concentration/
(mg·L-1)
化学需氧量
Chemical
oxygen
demand/
(mg·L-1)
0 99.5 0.0179 0.0158 0.0418 0
0.5 98 0.0692 0.0176 0.0392 4.516
1.0 98.1 0.0665 0.0556 0.0386 5.729
2.0 93 0.245 0.142 0.0445 6.348
农业工程学报 2015
252
3 讨 论
3.1 CB FSB 生物过滤功能启动
生物过滤功能启动过程需要一定的时间,如果没有
完成启动则会导致系统水质不稳定,甚至可能导致养殖
生产失败,而启动完成后继续空转,也导致水电、人力
的浪费。因此,准确判断生物过滤功能启动的完成与否
对养殖成功和生产成本影响较大。目前,国内外对此也
并无统一标准。山形阳一[13]指出亚硝态氮充分氧化、生
物过滤器发挥高效净化能力时,可判生物过滤功能启动
完成。齐巨龙等[14]指出亚硝态氮浓度首次迅速降低后增
加氨氮浓度,亚硝态氮浓度出现镜面 S”型曲线,以第 2
拐点作为启动完成的判断标志。上述两作者仅选择亚硝
态氮浓度为判断依据,其原因可能是氨氮氧化为硝酸盐
2步,亚硝态氮是第 2步反应的底物,且亚硝化细菌
的生长速度高于硝化细菌。Bower Turner[15]、徐元勤
[16]、刘艳 [17]等认为氨氮质量浓度小于 0.05 mg/L、亚
硝态氮质量浓度小于 0.01 mg/L 时,生物过滤器中硝化作
用已经建立。另外,国内生产实践中系统启动时加入较
高浓度底物,运转 30 d 左右,氨氮浓度降低到较低水平
时便直接判断该系统生物过滤功能已经稳定。在此设计
条件下,生物过滤功能即使一直维持在较低水平,氨氮
浓度也会持续降低。本研究结果表明,启动过程应最大
限度的模拟实际养殖水况,每次测定后补平底物浓度。
判断标准应具备两点:1同时以氨氮和亚硝态氮浓度为
判断指标;2)二者达到稳定状态并无明显波动。据此得
到淡海水系统 CB FSB 生物过滤功能启动完成分别需要
47 60 d 的结论。国内外学者关于生物过滤功能达到
态所需时间不一致。有研究指出,生物过滤功能达到稳
态,淡水系统需要 1420 d[18-20];海水系统需要 40
80d[21-22]刘艳红等[17]在研究海水闭合循环系统生物滤器
微生物特性时,系统稳定约需 9周。John Davidson [6]
研究用于高密度养殖污水处理的生物流化床的稳态建立
需要 8周。Summerfelt [5]在研究生物流化床中不同滤
粒径对去除率的影响时,系统运行 15 周形成硝化细菌生
物膜。Zhu and Chen [22-23]研究碳氮比对氨氮去除效果的
影响时指出,3种类型的序批式生物过滤器需要 5周达到
稳态。本研究中淡海水系统 CB FSB 生物过滤功能达到稳
态分别需要 78.5 周,与 John Davidson [6]、刘艳红
[17]研究的启动时间较接近。
此外,在相同试验条件下,得出淡水、海水系统建
立稳态的时间差异约为 2周。可能原因是:1盐分对氨
氧化菌和亚硝酸盐氧化菌有显著的抑制作用;2硝化细
菌能承受渗透压90%来自盐度)的范围相当广,在淡水
和海水中都有相应的种属。
3.2 膨胀率和 C/N CB FSB 生物过滤功能的影响
膨胀率是生物流化床过滤器特有的重要操作参数,
涉及到基质传递效率、水力停留时间、水力剪切力、滤
料碰撞几率和摩擦力等。膨胀率过大,滤料易流失、能
耗增加;膨胀率过小,则滤料摩擦大,生物膜难以附着,
污水处理效率低。然而,目前关于生物流化床膨胀率的
研究较少。本研究指出 CB FSB 最佳膨胀率为 100%,但
是膨胀率曲线无拐点。原因为:控制床层膨胀高度,可
减少滤料流失,初始膨胀高度的设置一般控制在较低范
围内。生物膜附着可导致滤料颗粒密度变小,床层急剧
膨胀。如初始膨胀率为 50%~80%,挂膜后可升高到
200%300%[5],目前国外常采用虹吸法和生物膜剪切法
[6]控制床层膨胀。此外,不同膨胀率下出水氨氮无明显差
别,而出水亚硝态氮差别较明显。原因可能是每次调整
膨胀率,微生物群落结构就会做出相应调整,亚硝酸细
菌的生长速率大于硝酸细菌[24],造成亚硝酸盐积累。
生物膜种群之间竞争激烈,C/N 是影响微生物群落组
成的主要因素之一。本研究结果表明:C/N 增大,抑制硝
化作用,且抑制效果随 C/N 的增大而增强。与 Zhu
Songming [23]的结论趋势相似,即微生物异养作用抑制
了硝化作用,C/N1.0抑制效果随 C/N 增大而减弱。
Ling Jian [25]的结论存在差异,即当 C/N 0提高
0.53种生物过滤器硝化速率都降低;当 C/N 0.5
提高到 2.0,填充珠子的生物过滤器(bead filter)继续
降低,填充石英砂的生物过滤器(sand filter)和填充生
物立方体的过滤器(bio-cube filter)无显著变化。宋奔
[26]指出:C/N12,会破坏系统中生物膜的结构和功
能,导致硝化功能异常。可见众多研究者得出的具体数
值均有一定差异,这可能与进水浓度、生物过滤器类型、
接入系统的方式等有关,但是 C/N 增大会抑制硝化作用
的结论是相同的。
4 结 论
1CB FSB 生物过滤功能的启动,采用自然挂膜法,
以氨氮和亚硝态氮浓度降低并稳定为判断标准,淡水和
海水系统完成启动分别需要 47 60 d
2)本研究中膨胀率为 100%时污水处理效率最高,
总氨氮转换率高达 881 g/(m3·d)
3C/N 增大对生物膜的硝化功能有抑制作用,污水
处理效果变差。C/N 大于 2.0污水处理效果明显下降。
本文对 CB FSB 生物过滤功能启动和操作条件做了
较深入的研究,还可在后续工作中展开微生物群落分析
以及生产放大试验,CB FSB 的应用提供理论参考和技
术支撑。
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农业工程学报 2015
254
Biofiltration of cyclo-bio fluidized sand bed in recirculating
aquaculture system
Liu Yao1,2, Song Xiefa1, Lei Jilin2, Peng Lei1, Huang Zhitao1, Liu Baoliang2
(1. College of Fisheries, Ocean University of China, Qingdao 266003, China; 2. Yellow Sea Fisheries Research Institute, China Academy
of Fishery Sciences, Qingdao 266071, China)
Abstract: A lab-scale cyclobio fluidized sand biofilter was designed to study biofiltration in recirculating aquaculture
systems. First, the biofiltration start was studied separately in fresh water and seawater recirculating aquaculture systems.
Second, the influence of different operation conditions on water treatment were studied by natural membrane-forming,
including three bed expansions (50%, 75% and 100%) and four carbon nitrogen ratios (0, 0.5, 1 and 2). A synthetic
substrate solution was continuously fed into the tanks after measuring of water quality every time. The results showed
that the total ammonia-nitrogen concentration was decreased, fluctuating lightly in later period. The nitrite-nitrogen
concentration was in a shape of clock, increasing quickly first and keeping the maximum for days then decreasing
quickly, fluctuating lightly in later period. Not only ammonia-nitrogen and nitrite-nitrogen concentrations, but also the
stability of water quality should be as the criteria of completion judgement of biofiltration start. In these conditions,
biofiltration start of cyclobio fluidized biofilter were 47 days in fresh water system and 60 days in seawater system.
Besides, we found that the cyclobio fluidized biofilter had little help in removing phosphorous, maybe because dissolved
oxygen was always more than 6 mg/L in system. The nitrate-nitrogen concentration was increased on the whole.
However, high nitrite-nitrogen concentration may harm fish health. To avoid that, there were two control methods:
exchanging some new water to system every day, or adding denitrification equipment to recirculating aquaculture
systems. Meanwhile, the results of operation conditions showed that the maximum load of system was separately 2.5, 3.0
and 3.5 mg/L with different bed expansions 50%, 75% and 100%. And the removal efficiency of total ammonia-nitrogen
increased and the nitrite-nitrogen concentration decreased with the enhancement of bed expansion. The efficiency of
ammonia-nitrogen was the highest and the load of system was the largest under 100% bed expansion in this study, while
the volumetric total ammonia nitrogen conversion rate was 881g/(m3·d). Besides, inhibition of organic on nitrification
was observed. The ammonia-nitrogen, nitrite-nitrogen and COD concentrations were increased with the enhancement of
ratios of carbon and nitrogen. Especially, water quality went bad obviously when ratios of carbon and nitrogen was more
than 2.0. The ammonia-nitrogen and nitrite-nitrogen even reached to lethal or medial lethal concentrations of some fishes.
The possibility was that heterotrophic microorganisms breed quickly with the enhancement of ratios of carbon and
nitrogen and autotrophic nitrifying bacteria was embedding and died absenting of oxygen. This research can provide a
reference for starting, operation and management of cyclobio fluidized biofilters in production.
Key words: aquaculture; biofiltration; seawater; cyclo-bio fluidized sand beds; starting; bed expansion; C/N
... The Eulerian model was selected as the multiphase flow model, the RNG k-model was selected as the turbulence model, the Syamlal-O'Brien correlation was selected to define granular kinetic viscosity, and Gidaspow All levels were operated at the same superficial velocity of 2.71 cm/s. was selected as the drag force model (Liu et al., 2015). All terms of the governing equations for unsteady state were discretized using the first-order upwind differencing scheme. ...
... Under different bed expansions (50%, 75% and 100%) with C/N = 0, VTR in the best combination CB FSB was 629, 755, and 881 g m −3 day −1 , especially (Liu et al., 2015). Under four levels of C/N (0, 0.5, 1.0 and 2.0) with bed expansion = 100%, the TAN removal rates decreased from 99% to 93% operating with inlet TAN concentration 3.5 mg/L and the water quality of outflow deteriorated significantly with C/N = 2. VTR was quite high and the quality of treated wastewater was good (TAN concentration <0.25 mg/L, NO 2 N < 0.15 mg/L). ...
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To improve the removal efficiency for dissolved wastes within CycloBio (CB) fluidized sand biofilters (FSBs) in recirculating aquaculture systems, we investigated their structural design and optimization using computational fluid dynamics (CFD) modeling tools, an orthogonal test method, and experimental verification. Results showed that the effects of structural parameters on bed expansion from large to small were: cone height, cone diameter and slot width. The best combination was: cone height 60mm, cone diameter 165mm, and slot width 1.0mm. The solid phase was well distributed not only in the radial direction, but also in the axial direction in the optimized CB FSB. The bed expansion (40%-120%) was increased about 13%. Energy savings were 21%-28% at the same bed expansion. When the optimized CB FSB was used to treat synthetic aquaculture wastewater, with three bed expansions and four levels of C/N, total ammonia nitrogen removal rate expressed per unit of expanded bed volume was high, from 629 to 881gm-3day-1. All results indicated that the structure of the optimized CB FSB was more reasonable and that the combination of CFD simulation and the orthogonal test method could be successfully applied to structural optimization.
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The conditioning period or time required to establish nitrification in new seawater culture systems was reduced substantially or eliminated after seeding with various media from established seawater aquariums. The relative effectiveness of the seed media was: 10% wet filtrant > 5% wet filtrant > 20% seawater > 10% dry filtrant. The introduction of commercial additives containing nitrifying bacteria or of filtrant from an established freshwater culture system did not accelerate the nitrification sequence in new seawater aquariums.
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Although, it has been recognized that the existence of organic matter in a recirculating system tends to reduce the nitrification efficiency of biofilters, quantitative information is still lacking. In this study, the effect of sucrose carbon on the nitrification rate of biofilters was evaluated under steady-state conditions using a reactor series experimental system. The experiential solution with a carbon/nitrogen ratio of C/N=1.0 or 2.0 resulted in approximately a 70% reduction of total ammonia nitrogen removal rate as compared with a solution that has a similar nitrogen level, but without carbon (C/N=0). The data showed that the nitrification rate decreased with an increase in the organic concentration, but the impact became less pronounced when the carbon concentration became sufficiently high. The results show the benefits of removing organic matter for improving nitrification in recirculating systems.
Article
A mathematical model was developed for the biological-nitrification process. The model assumed two consecutive oxidation steps occurring under a substrate-inhibiting condition. The mathematical model was calibrated using data obtained from batch experiments performed on the contents of five chemostats operated to steady-state on a feed containing 1,000 mg/L of ammonia-nitrogen. In the batch experiments, initial ammonia concentrations ranging from 100 to 1,000 mg-N/L were used. Time-varying concentrations of ammonia and nitrite were collected until the oxidation of these constituents was complete. Parameter sets that optimized the fit on the mathematical model to the experimental data were obtained by nonlinear-regression analyses. The oxidation of ammonia to nitrite was well represented by the Haldane-inhibition model. The Haldane-inhibition model did not satisfactorily describe the oxidation of nitrite to nitrate. It was observed that the simultaneous presence of both nitrite and ammonia led to the inhibition of nitrite oxidation. Modification of the model to consider a revised inhibition mechanism that accounted for the observed behavior was quite successful for the interpretation of the nitrite-oxidation data.
Article
A conventional laboratory scale annular reactor was employed to investigate the growth dynamics of nitrifying biofilm. A dense and thin nitrifying biofilm was developed in the reactor. It was found that the feed concentration (So) has a significant effect on the performance of the nitrifying biofilm reactor. It was demonstrated that the biological constants are strongly dependent on So. The same is true for the volumetric removal rate of substrate (kov), which shows that the process always depends on the reaction. The results indicated that thinner biofilms ranging from 15 to 20μm have a higher specific nitrification rate, that is, the biological reaction of ammonium nitrogen probably occurs at the biofilm‐liquid interface. It is preferable to use thin biofilm for an attached culture. Meanwhile, it was shown that in this system high nitrification capacities could be reached.. It was expected to have promising possibilities to develop a new biological process specialized in wastewater nitrification.
Article
Water recirculating systems for fish culture are potentially desirable for conserving water and reducing heating requirements, maximizing production of fish under water and space limitations, minimizing effluent problems, and maintaining better control over environmental factors. A semiclosed recirculating-water system for intensive culture of rainbow trout Oncorhynchus mykiss is described. The system used self-cleaning, rectangular, cross-flow rearing tanks (water volume, 9 m each), multistage oxygenators, microscreen filters, and a sidestreamed, fluidized-bed biological filter. Rainbow trout were reared under continuous culture conditions, with periodic stocking and periodic selective harvesting. Makeup water entered at 47.3 L/min, producing a newwater turnover time of 9.2 h. Steady-state and maximum fish biomass densities and loading rates were estimated to be 66.0 and 74.6 kg/m and 2.50 and 2.83 kg·L·min, respectively. Steady-state gross productivity was estimated to be 6,257 kg/year (120 kg/week). Overall food conversion (feed fed/fish weight gained) was 1.33. The system performed satisfactorily and provided data for refining future designs. Subsequent modifications of equipment and operating procedures may have made the system economically viable under some pricing scenarios.
Article
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.