Microscreen effects on water quality in replicated recirculating aquaculture systems

This study investigated the effects of three microscreen mesh sizes (100, 60 and 20 μm) on water quality and rainbow trout (Oncorhynchus mykiss) performance compared to a control group without microscreens, in triplicated recirculating aquaculture systems (RAS). Operational conditions were kept constant during a 6-week period where the microscreens were manually rinsed three times a day. The effects of microscreen cleaning frequency and nitrification performance were subsequently assessed.Compared to the control group, microscreens removed particles, reduced particulate organic matter, and increased β-values. Particulate parameters reached steady-state in all treatment groups having microscreens at the end of the trial. The time to reach equilibrium seemingly increased with increasing mesh size but the three treatment groups (100, 60 and 20 μm) did not significantly differ at the end of the trial. Increased backwashing frequency over a 24-h period had no further significant effects on the parameters measured. The results demonstrated the role and importance of a microscreen, and showed that mesh size, within the range tested, is less important at long operations under constant conditions.Fish performed similarly in all treatments. Preliminary screening of trout gills did not reveal any pathological changes related to microscreen filtration and the resulting water quality. Biofilter performance was also unaffected, with 0′-order nitrification rates (k_0a) being equivalent for all twelve systems (0.148 ± 0.022 g N m⁻² d⁻¹).Mechanisms for RAS equilibrium establishment, within and between systems with different mesh sizes, are discussed.     

牡丹江水质监测与评价

我们于1993－1995年对牡丹江进行了污染源监测，沿江不同江段设采样点采样进行水质分析，本根据数理统计的方法，结合水质参数各自对水环境质量的影响，采用半集均方差模式对该江进行污染现状评价，其 结果：WQI值为10．285，该江已污染。     

Waste and particle management in a commercial, partially recirculating trout farm

The present case study, deals with a recently built aquaculture facility using 80–120 L s⁻¹ spring water for trout production. The farm consists of six raceways, discharging in a common outflow channel, leading to a drum filter equipped with 80 μm gauze. About 120 L s⁻¹ of the microscreen effluent is pumped back in the inflow channel of the six raceways. The remaining effluent is oxygenated with pure oxygen in gravity oxygenation units and led to two U-shaped raceways. The farm effluent is finally filtered by a drum filter with 63 μm mesh size. The microscreen backwash sludge is treated in a cone settler, where the sediments are extracted for agricultural manure application. The sedimentation supernatant is further led in a sub surface flow (SSF) constructed wetland prior to discharge.Due to the advanced effluent treatment within the farm, the total farm effect on the receiving effluent is kept to a minimum. The nutrient increase produced by the farm is only 0.03 mg L⁻¹ total phosphorous (TP), 1.09 mg L⁻¹ biological oxygen demand (BOD₅) and, 0.57 mg L⁻¹ total suspended solids (TSS) in the brook. Especially the incorporation of an intermediate microscreen prior to water recirculation, prevents leaching of dissolved nutrients from particulate matter, as large particles are effectively and as fast as possible removed from the water flow.At the pumping station, needed for water recirculation, the particle size distribution (PSD) was monitored with the previous microscreen in use and by-passed. When the screen was by-passed a significant crushing effect on PSD through pumping action was found. Through the removal of large particles, the crushing effect of the pumping station on the particles is prevented, as revealed by particle size distribution (PSD) measurement. Thus, leaching of dissolved nutrients is prevented twice.In consequence, the farm configuration can be recommended as an effective possibility for intensive trout production at sites with a small freshwater source and stringent effluent thresholds, even with the unexpected low treatment efficiencies measured for the microscreens. Both drum filters showed relative low treatment efficiencies of 33–53% for total suspended solids, respectively, while an efficiency of 70% should be expected from the measured PSD. With this impact, the farm still emitted a low nutrient amount, especially due to the highly effective offline microscreen backwash sludge treatment, where the SSF wetland efficiently reduced dissolved and particulate nutrients as nitrite (NO₂-N), nitrate (NO₃-N) and TSS. Thus this SSF wetland application might be suitable as a denitrification step in a closed recirculating trout farm.     

The power law in particle size analysis for aquacultural facilities

Fine particles tend to accumulate in recirculating aquacultural facilities, which can lead to serious fish health problems. The literature indicated that in many particle systems, the particle size distribution may be accurately represented by a two-parameter, hyperbolic power-law function, dN/dl=Al^−β.

The purpose of this paper is to investigate whether this observation holds for aquacultural facilities. Particle size distribution data from four research establishments were examined, using 14 data sets, comprising 11 aquacultural systems, and covering three species of salmonids and one of striped bass. In the data examined, the exponent, β, varied from 2.9 to 4.6, with one sample reaching as high as 6.3. Correlation coefficients varied from 0.998 to 0.975. Larger exponents, indicating a greater number of fine particles, appear to dominate recirculating aquaculture systems.

The results strongly suggest that a hyperbolic distribution is valid for aquaculture systems. The usefulness in this technique is that once a worker has established the exponent from the distribution of particle sizes at any given point in his facility, an estimate of particulate contributions by size to the total particle number, surface area and volume/mass concentration can be obtained.     

流清河湾扇贝养殖区夏季附着生物特征研究

2007年6~9月,利用悬挂不同网目的试网方法,对夏季青岛流清河湾栉孔扇贝筏式养殖区附着生物的种类、数量及其垂直分布特征进行了研究。结果显示,流清河湾附着生物群落的优势种在6月份为麦秆虫和钩虾,7月份以后贻贝成为优势种。附着生物湿重随挂网时间延长而增加,8月份增长最快,特定增长率最高可达8.77%/d,主要是由于优势种贻贝的快速生长。玻璃海鞘等海鞘类在流清河湾较少出现。附着生物的数量受网目和水深的影响,总体上随水深的增加而下降,较小网目上附着生物量较大。贻贝为群落优势种是流清河湾夏季附着生物数量较高的主要原因。     

海水工厂化养鱼多点在线水质监测系统的研究

对海水工厂化养鱼水质监测系统进行了研究,开发出一种多点在线水质监测系统,该系统集多路数据采集、测量、转换、计算、储存、显示、打印、报警等功能于一体,可同时在线监测6个不同监测点的水质情况;对每一个监测点,可同时监测其溶解氧、温度、电导率、pH、氧化还原电位、盐度等6个参数。     

Design and management of conventional fluidized-sand biofilters

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.     

不同管理方式对参池颗粒物质沉降作用及沉积物的影响

为探究不同管理方式对刺参养殖池塘(简称参池)沉降颗粒物及相关底泥、水体指标的影响,分别测定9 口参池(分为养水机、自然纳潮、微孔曝气3组参池,每组3个重复)颗粒物质在四季的平均沉降量和水平空间分布情况,底泥有机质含量和弧菌(Vibrio)总数,水体营养盐含量、浮游植物生物量和净初级生产力.结果显示,自然纳潮和微孔曝气池...     

进水流速对圆形循环水养殖池流场特性影响的数值模拟

通过对工厂化循环水养殖进水流速的智能调控,可降低饵料残留,避免水质恶化.为此,本研究采用数值模拟方法探究了进水流速对工厂化循环水养殖池流场特性的影响,并基于该研究设计出一套确定进水流速调控的实验方法.首先,通过对比Standard k-ε、RNG k-ε和Realizable k-ε3种湍流模型及多种壁面函数的仿真效果,确定RNGk-ε模型和标准壁面函数作为仿真配置.同时,针对多相流模型,对欧拉多相流模型和DPM离散相模型进行对比,为提高计算准确性选用DPM离散相模型,并基于上述模型进行网格无关性验证、制定网格划分方案.其次,以大菱鲆(Scophthalmus maximus)养殖为例,模拟不同进水流速下养殖池流场、排污和水温调节的效果.最后,针对仿真结果提出进水流速调控方案.结果显示,日常采用1.0 m/s的进水流速,可有效提高适宜流速区面积并控制水处理成本;投饵前,采用0.2 m/s的进水流速可以解决循环水养殖中存在的饵料浪费问题;进食结束后,采用1.2 m/s的进水流速可快速排出残饵避免水质恶化;水温异常时,采用15℃的水、以1.2 m/s的进水流速注水230 s,可使20 ℃的水下降到正常水平,精准化控制水温.采用本研究提出的方法,可针对不同养殖生物和养殖环境设计进水流速智能调控策略,可用于解决循环水养殖过程中饵料浪费、水质变差和水温异常等问题.     

Coldwater RAS in an Arctic charr farm in Northern Norway

Use of coldwater recirculating aquaculture systems (RAS) are still very rare in Norway, and only two farms are producing Arctic charr. This project took place in one of these commercial Arctic charr farms; Villmarksfisk AS in Bardu, Northern Norway.The farm gets its make-up water from ground water that holds 5 °C year around. Temperature in the rearing water varies between 7.5 °C (“low”) to 12 °C (“high”) through the year. The biological filter in the RAS seems to work stable at both “low” and “high” temperatures, including after incidents when feeding has been stopped for a day and started on top again the day after. Such an extreme change in loading was measured as a 70% increase in TAN concentration, with only minor changes in nitrite levels recorded. The biofilter also kept the nitrite stable and low in spite of diurnal variation in TAN excretion at normal feeding regimes (every day in three periods at day-time).The farming concept is to stock the farm with wild caught juvenile fish for on-growing to market size fish (0.75–1.00 kg). A drop in growth rate during early autumn has been a main concern for the farm. This may reflect a seasonal shift in growth potential, sometimes referred to as “autumn depression”. Interestingly, there is little sign of seasonal changes in the growth of hatchery-produced fish tested in the farm. Sampling of water quality through the seasons in tanks holding fish undergoing such growth depressions indicate that TAN excretion is much higher per kg feed used in the wintertime than in the springtime. This observation corresponds with the lack of weight gain during wintertime despite that the fish is feeding. Thus, feed conversion calculations indicate that feed utilization also varies with season reaching its nadir during this period.Both challenges concerning RAS in cold water and strongly reduced growth in autumn and winter time, have been investigated from 2005 to 2007 in a project financed by the Norwegian research council and the partners in the agricultural framework agreement.     

Heavy metal and waste metabolite accumulation and their potential effect on rainbow trout performance in a replicated water reuse system operated at low or high system flushing rates

A six-month trial was conducted to compare the effects of high and low make-up water flushing rates on rainbow trout performance and water quality in replicated water reuse aquaculture systems (WRAS). Six identical 9.5 m³ WRAS, containing a single 5.3 m³ tank and operated at a total recirculating flow of 380 L/min were stocked with 1000 rainbow trout each (133 ± 1 g). Three WRAS were operated at high flushing rates (2.6% of total flow) and three were operated at low flushing rates (0.26% of total flow), providing system hydraulic retention times of 0.67 and 6.7 days, respectively. During a one-week period when fish were at maximum feeding (i.e., mean feed loadings of 0.53 and 5.3 kg/m³ make-up water flow high and low make-up conditions, respectively) and maximum densities (80 kg/m³), water samples were collected across all unit processes. All typical water quality parameters measured at the culture tank outlet during this week were significantly different between treatments, except for dissolved oxygen, carbon dioxide, and temperature, which were controlled. Within the low exchange WRAS, total suspended solids (TSS), carbonaceous biochemical oxygen demand, total ammonia nitrogen, un-ionized ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, dissolved organic carbon, particle counts, true color, and total heterotrophic plate counts were significantly greater, whereas UV transmittance (%) and alkalinity were significantly reduced. Of these parameters, TSS, fine particles, and heterotrophic bacteria counts were the only parameters of concern within the low exchange WRAS. The potential impacts of each water quality constituent are discussed. Element analysis indicated that concentrations of nine metals were significantly greater within the low exchange WRAS. The highest metal concentrations measured at low exchange were within safe recommended limits, with the exception of copper (0.037–0.056 mg/L), which could have reached chronically toxic levels. Although cumulative mortality was relatively low for all WRAS, a linear trend between copper concentration and mortality was evident. The highest mortality, which occurred within a low exchange WRAS, coincided with the highest copper (0.056 mg/L); and the lowest mortality, which occurred within a high exchange WRAS, coincided with non-detectable copper levels. A comparison of survival between treatments bordered significance, 99.5 ± 0.1 and 98.9 ± 0.4% for the high and low exchange WRAS, respectively. There was no significant difference in rainbow trout weight at the conclusion of the study, i.e., approximately one year post-hatch: 1401 ± 23 and 1366 ± 33 g for the high and low exchange WRAS, respectively. There were no differences in thermal growth coefficients or feed conversion ratios between the high and low exchange treatments. Rainbow trout condition factor was significantly greater within the low exchange WRAS.     

剑湖摇蚊幼虫的空间分布与水质评价

通过研究云南剑湖摇蚊幼虫的种类组成和空间分布,结合水质生物学评价指数,分析其群落结构特征并评价水质现状,旨在为该湖泊水生态系统健康评价和发展渔业生产提供基础数据。于2011年1月、4月、6月和10月分冬、春、夏、秋4个季节在剑湖设定11个采样点,进行摇蚊幼虫群落调查。结果表明,摇蚊幼虫共检出13种,隶属3亚科、6属,优势种为中华摇蚊(Chironomus sinicus)、溪流摇蚊(Chironomus riparius)、花纹前突摇蚊(Procladius choreus)和多足摇蚊(Polypedilum spp.);其中中华摇蚊为全湖性分布,其分布平均水深为162 cm,前突摇蚊属种类分布的平均水深最大,其它种类为局部性分布。摇蚊幼虫的平均密度冬季最高,为858.091个/m~2,夏季最低,为154.182个/m~2;冬季生物量最高,为15.741 g/m~2,其它3季均处在较低水平,其中秋季最低,仅1.245 g/m~2。根据水质生物学评价指数,目前剑湖的水质等级为中-重污染,已达富营养化水平;同时给出了剑湖水环境治理和控制建议。     

鱼类粒径谱研究进展

文章根据2015、2017和2018年3次底拖网渔业资源调查数据,构建了大亚湾夏季鱼类生物量粒径谱,并比较分析了这3个时期夏季鱼类生物量粒径谱特征参数差异性。结果表明,大亚湾夏季鱼类生物量粒径谱存在明显的年际和空间变化,3个时期Sheldon型生物量粒径谱呈“单峰”型,粒径范围以2015和2018年最大 (−1~9),2017年次之 (−1~8);优势种组成由2015年以黄鳍马面鲀 (Thamnaconus hypargyreus)、短吻鲾 (Leiognathus brevirostris) 和细条天竺鲷 (Apogon lineatus) 为主演变为2017、2018年以短吻鲾、黄斑蓝子鱼 (Siganus oramin) 等粒径级小的鱼类为主。标准化生物量粒径谱曲率年际变化上以2015年最大,2018年次之,2017年最小;空间分布上,沿岸海域以2015年最大,2017年最小;湾中部海域以2018年最大,2017年最小;湾口海域以2018年最大,2017年最小。数量-生物量比较 (Abundance-biomass comparison, ABC) 曲线表明,大亚湾夏季鱼类群落处于严重干扰状态。大亚湾夏季鱼类生物量粒径谱特征存在明显的年际差异与鱼类自身生活习性、补充比率、栖息环境及人类活动干扰有关,尤其是捕捞因素。

     

藻类在养殖水体中的作用

目前国内外开展了藻类对污水净化的研究.国外利用某些藻类治理水体富营养化的研究取得一定进展[1-2],如日本科学家经过广泛的调查发现水网藻的繁殖能力比形成水华的蓝、绿藻更强,在其生长过程中可以大量吸收水体中的N和P,使N、P含量恢复至正常水平.     

沙颍河周口市段水质的生物学监测及评价

对沙颍河周口段水质进行检测,包括微生物学检测、叶绿素a测定等,结合理化检测对其水质做出初步评价。结果表明大闸上游段水质为β中污带,贫营养型;胜利桥段水质为α-中污带,中营养型;地区医院段水质为多污带,属富营养型。