Leaching of plastics used in closed aquaculture systems

Toxic dioctyl phthalate plasticizer leaches from new plastics used in closed aquaculture systems. Closed systems employing new plastics probably should be flushed for about 10 days with warm fresh water before they are put into use.     

活性污泥降解水中邻苯二甲酸酯类的研究

用液质联用测定了活性污泥对7种邻苯二甲酸酯（PAEs）的降解能力。结果显示,PAEs的降解过程可用一级动力学方程描述,随着分子量和初始质量浓度的增加,其降解速率常数减小,活性污泥对混合体系PAEs的降解能力优于降解单一种类PAEs,温度和pH能直接影响降解性能,其最优水平组合为温度36,7℃,pH7．6。     

Engineering investigation of design procedures for closed containment marine aquaculture systems

The objective of this paper is to investigate potential design procedures for rigid, closed containment aquaculture systems deployed in the marine environment. In this context, closed containment is a term used to describe a range of aquaculture technologies that attempt to restrict and control interactions between farmed fish and the external aquatic environment, with the goal of minimizing impacts. The containment units are often closely spaced and moored to the seafloor bottom. The geographical area of interest is the Straits of Georgia, British Columbia in Canada.In this study, the design configurations of multiple closed containment systems are investigated. The design procedures include examining: (1) local environmental conditions, (2) drag forces on multiple containment units, (3) wave loading, (4) undamped heave motions, (5) mooring gear components and (6) material stresses on a rigid containment structure. Operational and other design considerations are also discussed. Preliminary findings indicate that wave forces could be substantial. In addition, little is known about how containment units, which are closely spaced, will respond individually or as a farm when subjected to surface waves.     

循环水养殖系统中的固体悬浮物去除技术

循环水养殖系统(Recirculating aquaculture systems,RAS)中固体悬浮物(Suspended solids,SS)的去除效果直接影响到鱼类生长、生物净化效果、系统配置和运行成本等诸多重要因子。根据固体悬浮物产生、物理特性和分布规律,结合颗粒悬浮物去除工艺特点,对去除技术进行系统研究分析。固体悬浮物源自饲料,密度一般为1.05~1.19 g/cm3,运用重力分离、过滤和泡沫分离等工艺通过预处理、粗过滤和精处理三道工艺步骤,可分别去除不同直径的颗粒物质,在达到合理含量的前提下,获得低能耗、低成本和系统稳定运行的综合效果。固体悬浮物的去除符合目标明确、排出及时和区别对待三原则,去除工艺注重相关技术的优化集成。     

Engineering investigation of design procedures for closed containment marine aquaculture systems

The objective of this paper is to investigate potential design procedures for rigid, closed containment aquaculture systems deployed in the marine environment. In this context, closed containment is a term used to describe a range of aquaculture technologies that attempt to restrict and control interactions between farmed fish and the external aquatic environment, with the goal of minimizing impacts. The containment units are often closely spaced and moored to the seafloor bottom. The geographical area of interest is the Straits of Georgia, British Columbia in Canada.In this study, the design configurations of multiple closed containment systems are investigated. The design procedures include examining: (1) local environmental conditions, (2) drag forces on multiple containment units, (3) wave loading, (4) undamped heave motions, (5) mooring gear components and (6) material stresses on a rigid containment structure. Operational and other design considerations are also discussed. Preliminary findings indicate that wave forces could be substantial. In addition, little is known about how containment units, which are closely spaced, will respond individually or as a farm when subjected to surface waves.     

Ammonia removal in selected aquaculture water reuse biofilters

Four fixed-film biological filters (rotating biological contactor, biodrum, trickling filter, and a submerged anaerobic filter) were tested for the removal of ammonia using a simulated warmwater fish and invertebrate culture water supply. Filter design may be determined based on the results of ammonia removal efficiency over a wide range of hydraulic loads. The rotating biological contactor (RBC) provided the best ammonia removal (over 90%) up to about 0·06 m³ m^?2 day^?1 (1·2 gpd ft^?2). The biodrum removed over 80% of the ammonia to a hydraulic load of 0·05 m³ m^?2 day^?1 (0·9 gpd ft^?2). The trickling filter removed 50% of the ammonia at a hydraulic loading of 0·012 m³ m^?2 day^?1 (0·3 gpd ft^?2).     

生物—电氧化法去除海水养殖循环水污染物

为提高海水养殖循环水处理效率,降低处理成本,本研究采用曝气生物滤器与电化学阳极氧化组合工艺,考察了不同阳极电势、进水氨氮和亚硝酸盐浓度下系统对氨氮及亚硝酸盐等污染物的去除效果,研究了微生物与工作电极之间的相互作用,并分析了电化学反应能耗。在水力停留时间为45 min、1.4 V阳极电压、进水氨氮和亚硝酸盐浓度分别为4.5和1.3 mg/L条件下,生物—电氧化法对氨氮去除率达88.8%,高出对照组7.6%,出水氨氮和亚硝酸盐浓度分别为0.5和0.9 mg/L,COD去除率为88.2%,高出对照组19.4%,平均能耗0.040 kWh/m³,电极表面微生物生长对阳极电氧化过程有促进作用,微生物功能预测显示实验组硝化功能占比为0.03%,对照组为0.07%。研究表明,生物—电氧化法对海水养殖循环水的污染物有良好的去除效果,具有一定的发展应用潜力。     

Nitrate removal effectiveness of fluidized sulfur-based autotrophic denitrification biofilters for recirculating aquaculture systems

There is a need to develop practical methods to reduce nitrate–nitrogen loads from recirculating aquaculture systems to facilitate increased food protein production simultaneously with attainment of water quality goals. The most common wastewater denitrification treatment systems utilize methanol-fueled heterotrophs, but sulfur-based autotrophic denitrification may allow a shift away from potentially expensive carbon sources. The objective of this work was to assess the nitrate-reduction potential of fluidized sulfur-based biofilters for treatment of aquaculture wastewater. Three fluidized biofilters (height 3.9 m, diameter 0.31 m; operational volume 0.206 m³) were filled with sulfur particles (0.30 mm effective particle size; static bed depth approximately 0.9 m) and operated in triplicate mode (Phase I: 37–39% expansion; 3.2–3.3 min hydraulic retention time; 860–888 L/(m² min) hydraulic loading rate) and independently to achieve a range of hydraulic retention times (Phase II: 42–13% expansion; 3.2–4.8 min hydraulic retention time). During Phase I, despite only removing 1.57 ± 0.15 and 1.82 ± 0.32 mg NO₃–N/L each pass through the biofilter, removal rates were the highest reported for sulfur-based denitrification systems (0.71 ± 0.07 and 0.80 ± 0.15 g N removed/(L bioreactor-d)). Lower than expected sulfate production and alkalinity consumption indicated some of the nitrate removal was due to heterotrophic denitrification, and thus denitrification was mixotrophic. Microbial analysis indicated the presence of Thiobacillus denitrificans, a widely known autotrophic denitrifier, in addition to several heterotrophic denitrifiers. Phase II showed that longer retention times tended to result in more nitrate removal and sulfate production, but increasing the retention time through flow rate manipulation may create fluidization challenges for these sulfur particles.     

应用生物脱氮新技术处理循环养殖废水的研究

由于氨氮的传统去除在工艺运行上有多方面的局限性,寻求低价可靠的生物完全脱氮工艺,成为循环水养殖系统中亟待突破的关键技术,近年来迅速发展的一些生物脱氮新技术为解决这一难题提供了新的思路。综述了循环养殖废水脱氮研究现状及生物脱氮新技术,指出了将脱氮新技术应用于养殖废水处理具有的多方面的优点及存在的一些有待于研究解决的问题。     

Calculation of pH in fresh and sea water aquaculture systems

A procedure for the calculation of pH in fresh and salt waters has been developed. The method is based on a fourth-order polynomial relationship between hydrogen ion concentration and other (conservative) water quality parameters. The method avoids trial and error estimations and results in a direct calculation procedure that can be implemented in models developed in various modeling environments, such as spreadsheets, conventional programming languages (BASIC, C, FORTRAN, PASCAL, etc.) or specialized modeling languages (Extend^™, Stella^™).

The method developed is based on the solution of the full alkalinity-pH equation. Because of the need for simplification of the equations to yield explicitly solvable polynomial equations, the accuracy of the solutions depends on the simplification made and varies with water properties. Three simplifications are tested based on a second-, a third-and a fourth-order polynomial equation for hydrogen ion concentrations. the equations have been tested for salinities ranging from 0 to 35‰ (fresh to sea water), for temperatures ranging from 0 to 35°C, for total carbonate carbon concentrations of 0·1 and 5·0 mmol/liter, and for total ammonia nitrogen concentrations of 0 and 10 mg/liter. Approximations are most accurate in waters of high total carbonate carbon and low ammonia concentrations, where the fourth-order approximation yields results that are within 0.05 pH units for the full range of pH values tested (5–10).     

Alum residuals as a low technology for phosphorus removal from aquaculture processing water

Aquaculture process waters are often scrutinized for loading phosphorus discharges into surface water. With the growing regulatory control of discharge from aquaculture process industries, it has become very important to address low cost and effective technological solution for aquaculture facilities. This study aims to investigate the effectiveness of alum residuals, which were generated during drinking water treatment for adsorption of phosphorus from aquaculture process water. Alum residuals were dried using an oven at 105 °C for 24 h. Particle size (d₆₀) was similar to conventional adsorbent, granular activated carbon. Bench scale experiments (batch and fixed bed column tests) were conducted using oven dried alum residuals. Fixed bed column tests also looked at the effect of influent pH on the effectiveness of oven dried alum residuals. Experimental results observed phosphorus removal of 94–99% using an alum residuals concentration of 4–16 g/L. Freundlich adsorption isotherm was effective in explaining partitioning among solid and liquid phases. Oven dried alum residuals were a better adsorbent for orthophosphate phosphorus than total phosphorus. Effluent pH levels for both batch and fixed bed column tests were within range of 6–9 for most of the samples tested and therefore, suitable for surface water disposal. There were no effects of pH observed on the breakthrough pore volume processed during fixed bed column test. There was aluminum leaching from oven dried alum residuals, however, not high enough to cause toxicity for aquatic species if disposed in surface water. Oven dried alum residuals were also able to adsorb organic matter from aquaculture process water. The effluent BOD₅ was below 30 mg/L for most of the samples with an exception of a few samples where BOD₅ was beyond the limit for surface water disposal guidelines. The results indicated that oven dried alum residuals have potential to provide a technological solution for small aquaculture facilities.     

循环水养殖系统生物挂膜的消氨效果及影响因素分析

针对工厂化循环水养殖系统,利用海水中的自然净化微生物挂膜,挂膜成功后,形成了很好的硝化作用,进行不同水温、进水氨氮浓度和水力停留时间(HRT)影响因素实验。结果表明,相同的进水氨氮浓度,随着水温的升高,不同水温之间氨氮浓度变化差异显著(P0.05)。在28℃水温时,经过生物膜120 h的净化处理,进水氨氮浓度降低到最低;随着进水氨氮浓度和HRT的增大,氨氮去除率及特殊去除率也不断的增大,但在同一进水氨氮浓度下,氨氮特殊去除率随着水力停留时间的延长反而降低。     

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.     

A design study on the optimal water refreshment rate in recirculating aquaculture systems

Refreshment (make-up) water is used in recirculating aquaculture systems (RAS) mainly to purge off-flavors, to add alkalinity and sometimes for temperature control. Alternatively, alkalinity may be added by means of a chemical base and heat may be supplied by a heating system. The objective of this study is to show how the optimal (minimizing cost) mix of the three controls: water, base and heat, can be found for given temperatures and water prices.The optimal solution varies over the temperature space and also depends on the price of water. For conditions at Eilat, Israel (on the Red Sea), using supplementary heating to maintain a constant temperature may become prohibitively expensive. If heating is given up, the remaining choice is between the supply of alkalinity via the refreshment water and adding a base. The supply of alkalinity with the water requires 2.0 m³[water]/kg[feed], much more than the minimum refreshment rate required to purge off-flavors, which is thought to be 0.3 m³[water]/kg[feed]. If the price of water is more than 0.03 USD/m³, the use of sodium bicarbonate for alkalinity control is justified.     

硝化细菌浓度及滤料对养殖水中氨氮处理效果的影响

分别研究了不同硝化细菌浓度(0、20、60、120 mL/100 L)和不同微生物滤料(珊瑚石、锅炉煤渣、牡蛎壳)对养殖水中氨氮处理效果的影响。结果显示,添加硝化细菌后,水体中的氨氮浓度呈现下降趋势,在8～12 h出现极低值后,开始上升,但上升速度较慢;随着水体中硝化细菌添加量的增加,水体中的氨氮浓度下降速度加快;水体中亚硝酸氮浓度呈现先上升后下降的趋势,并在4～6 h出现极高值,然后迅速下降,且硝化细菌添加量越高,下降速度越快。硝化细菌对以珊瑚石和锅炉煤渣为滤料的养殖水体中氨氮和亚硝酸氮的处理效果显著优于牡蛎壳,但珊瑚石和锅炉煤渣之间无显著差异。综合试验结果,应急水质处理时,硝化细菌菌剂的添加量以一次60 mL/100 L(或以活菌计数为1.2×109个/100 L)、间隔24 h添加1次为宜;经过脱硫筛选之后的锅炉煤渣可以作为循环水养殖用滤料。     

克氏螯虾的生物学和生态养殖模式

生物絮凝技术可以通过在养殖水体中调节碳氮比而维持良好水质,促进养殖品种健康生长,产生的生物蛋白可实现蛋白的多级利用,节约经济成本。实验从摄食环境(曝气、无曝气、水草)、摄食时间以及生物絮凝质量浓度等角度,探讨了克氏原螯虾 (Procambarus clarkii) 幼虾摄食絮凝的适宜条件。结果显示,絮凝质量浓度为500~600 mg·L^–1可满足幼虾的摄食需求,并在摄食4 h之后幼虾肠道达饱和状态。相同摄食时间,絮凝曝气组幼虾摄食量最大,显著高于水草组(P<0.05),但与无曝气组差异不显著(P>0.05),比较幼虾肠道的充塞度,可见曝气组在摄食4 h后肠道食糜较多,肠道更为饱满,优于其他各组。综合生物絮凝培养条件、水化指标以及幼虾的摄食情况,认为生物絮凝技术应用到克氏原螯虾的养殖具有可行性。     

Nitrogen removal techniques in aquaculture for a sustainable production

As the aquaculture industry intensively develops, its environmental impact increases. Discharges from aquaculture deteriorate the receiving environment and the need for fishmeal and fish oil for fish feed production increases. Rotating biological contactors, trickling filters, bead filters and fluidized sand biofilters are conventionally used in intensive aquaculture systems to remove nitrogen from culture water. Besides these conventional water treatment systems, there are other possible modi operandi to recycle aquaculture water and simultaneously produce fish feed. These double-purpose techniques are the periphyton treatment technique, which is applicable to extensive systems, and the proteinaceous bio-flocs technology, which can be used in extensive as well as in intensive systems. In addition to maintenance of good water quality, both techniques provide an inexpensive feed source and a higher efficiency of nutrient conversion of feed. The bio-flocs technology has the advantage over the other techniques that it is relatively inexpensive; this makes it an economically viable approach for sustainable aquaculture.     

Performance evaluation of four different methods for circulating water in commercial-scale,split-pond aquaculture systems

Split-pond aquaculture systems are being implemented by United States (US) catfish farmers as a way to improve production performance. The split-pond consists of a fish-culture basin that is connected to a waste-treatment lagoon by two water conveyance structures. Water is circulated between the two basins with high-volume pumps (water circulators) and many different units are being used on commercial farms. In this study circulator performance was evaluated with four different circulating systems. Rotational speeds ranged from 0.5 to 3.5 rpm for a twin, slow rotating paddlewheel; 12.5 to 56.5 rpm for a paddlewheel aerator; 60 to 240 rpm for a high-speed screw pump; and 150 to 600 rpm for an axial-flow pump. Water flow rates ranged from 8.6 to 77.6 m³/min and increased with increasing rotational speed. Power input varied directly with flow rate and ranged from 0.24 to 13.43 kW for all four circulators. Water discharge per unit power input (i.e., efficiency) ranged from 3.5 to 70.9 m³ min⁻¹ kW⁻¹ for the circulators tested. In general, efficiency decreased as water flow rate increased. Initial investment cost for each circulator and complete circulating system ranged from US $5850 to $22,900, and $15,335 to $78,660, respectively. The least expensive circulator to operate was the twin, slow-rotating paddlewheel, followed by the paddlewheel aerator, high-speed screw pump, and axial-flow pump. Our results show that four different circulating systems can be effectively installed and used to circulate water in split-ponds. However, water flow rate, rotational speed, required power input, efficiency, initial investment cost, and operational expense varied greatly among the systems tested. Long term studies are underway to better define the relationship between water flow rate and fish production in split-ponds. That information will help identify the water circulating system most appropriate for split-pond aquaculture.     

生态浮岛植物在富营养化养殖水体中去磷途径的初步分析

植物修复富营养化养殖水体过程中磷(P)的去除途径主要包括植物吸收、植物根系吸附、底泥吸附和还原状态下的磷挥发。为了深入探讨植物修复去磷机理,阐明植物修复富营养化养殖水体过程中磷的去向问题,分别以夏秋季(高温)和冬春季(低温)的高效除磷植物大漂和冬牧70组成的生态浮岛为研究对象,通过研究模拟条件下的富营养养殖水体生态修复系统,研究不同温度季节下生态浮岛植物在富营养养殖水体中各去磷途径对水体总磷(TP)去除量的贡献率大小。结果表明:经过20 d处理后,生态浮岛植物大漂和冬牧70对富营养化养殖水体中总磷的去除效率都较高 ,均达50%以上;在生态浮岛植物修复富营养养殖水体过程中最主要的磷去除途径都为植物吸收作用和底泥吸附作用,分别占水体中总磷去除量的23%~58%和27%~51%;其次是植物根系吸附作用,占水体中总磷去除量的13%~28%;贡献率最低的是还原状态下的磷挥发,一般低于1.5%,几乎可忽略不计。     

Reciprocating biofilter for water reuse in aquaculture

The reciprocating biofilter is automatically dewatered at regular and frequent intervals, in contrast to the conventional upflow submerged biofilter which is continually inundated. Reciprocating biofilters were compared with submerged biofilters in terms of ability to maintain water quality in small-scale fish holding units. In the first trial the reciprocating filter systems averaged 35% more fish in terms of numbers, 59% more fish in terms of weight, and a 45% greater feeding rate. In the second trial the reciprocating filter systems averaged 29% more fish in terms of numbers, 33% more fish in terms of weight, and a 29% greater feeding rate. Superior performance of the reciprocating filters appeared to be the results of resistance to clogging and improved aeration of the filter substrate.