Impact of farming intensity and water management on nitrogen dynamics in intensive pond culture: a mathematical model applied to Thai commercial shrimp farms

A mathematical model is used to investigate the impact of farming intensity and water management on nitrogen dynamics in the water column of intensive aquaculture ponds. The model describes the input of ammonia, its assimilation by phytoplankton or nitrification, and the loss of nitrogen through sedimentation, volatilization, and discharge. The model is calibrated for two commercial shrimp (Penaeus monodon Fabricius) farms in Thailand. Assimilation by phytoplankton with subsequent sedimentation or discharge is the principal process of ammonia removal. When inputs of ammonia exceed the algal assimilation capacity (carrying capacity), nitrification and volatilization of excess ammonia become significant. Carrying capacity is negatively affected by non-chlorophyll turbidity, and was estimated as 6 t ha^?1 cycle^?1 at a non-chlorophyll extinction of 2.6 m^?1. In ponds managed within their carrying capacity, ammonia concentrations are lowest at no water exchange, reach a maximum at exchange rates between 0.2 and 0.4 day^?1, and decline again at higher rates. When the carrying capacity is exceeded, excess ammonia concentrations decline continuously with increasing water exchange. Average exchange rates used in intensive shrimp farms (up to 0.2 day^?1) reduce phytoplankton abundance and sedimentation within ponds, but not ammonia concentrations. Discharges are high in particulate nitrogen at water exchange rates up to 0.3 day^?1, but contain mainly dissolved nitrogen at higher rates.     

Denitrification in recirculating systems: Theory and applications

Profitability of recirculating systems depends in part on the ability to manage nutrient wastes. Nitrogenous wastes in these systems can be eliminated through nitrifying and denitrifying biofilters. While nitrifying filters are incorporated in most recirculating systems according to well-established protocols, denitrifying filters are still under development. By means of denitrification, oxidized inorganic nitrogen compounds, such as nitrite and nitrate are reduced to elemental nitrogen (N₂). The process is conducted by facultative anaerobic microorganisms with electron donors derived from either organic (heterotrophic denitrification) or inorganic sources (autotrophic denitrification). In recirculating systems and traditional wastewater treatment plants, heterotrophic denitrification often is applied using external electron and carbon donors (e.g. carbohydrates, organic alcohols) or endogenous organic donors originating from the waste. In addition to nitrate removal, denitrifying organisms are associated with other processes relevant to water quality control in aquaculture systems. Denitrification raises the alkalinity and, hence, replenishes some of the inorganic carbon lost through nitrification. Organic carbon discharge from recirculating systems is reduced when endogenous carbon sources originating from the fish waste are used to fuel denitrification. In addition to the carbon cycle, denitrifiers also are associated with sulfur and phosphorus cycles in recirculating systems. Orthophosphate uptake by some denitrifiers takes place in excess of their metabolic requirements and may result in a considerable reduction of orthophosphate from the culture water. Finally, autotrophic denitrifiers may prevent the accumulation of toxic sulfide resulting from sulfate reduction in marine recirculating systems. Information on nitrate removal in recirculating systems is limited to studies with small-scale experimental systems. Packed bed reactors supplemented with external carbon sources are used most widely for nitrate removal in these systems. Although studies on the application of denitrification in freshwater and marine recirculating systems were initiated some thirty years ago, a unifying concept for the design and operation of denitrifying biofilters in recirculating systems is lacking.     

淡水养殖环境中氨氧化微生物的研究进展

随着水产养殖业的快速发展,养殖水体氮素污染日益突出,硝化微生物在水产养殖环境氮循环中具有重要作用。本文主要综述我国淡水养殖环境中硝化微生物的多样性、作用机理、厌氧氨氧化过程和机理等研究进展,并展望今后的研究工作:(1)淡水养殖水域硝化作用和氨氧化微生物的时空分布特征及影响因子;(2)淡水养殖环境氨氧化微生物及其他氮素转化关键微生物的过程与机理;(3)深入研究特定生态系统中如池塘生态系统、氮循环的各个过程,构建相关氮素转化和氮素平衡模型,为完善淡水池塘生态系统氮循环理论、水产养殖环境的氮素污染治理和生态修复提供参考。     

Photosynthetic suspended-growth systems in aquaculture

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.     

水产养殖水体循环利用过程中碱度的变化及调控

水体中的碱度水平能通过改变水体中某些物质的存在形态进而影响养殖对象,也会通过影响养殖水体的自养硝化、异养反硝化和氨氮异养同化过程的效率进而对养殖对象产生影响。本文首先概述了水产养殖水体中碱度的标准,根据水体中微生物学过程、光合作用、呼吸作用对碱度的影响及碱度与pH、CO_2、硬度等水质指标的紧密联系,对循环利用的养殖水体中碱度的变化规律和调控策略进行总结。养殖水循环利用过程中碱度会明显降低,通过补充碱度或者替换新水的方式提高养殖水体中碱度到一定的水平,以满足自养硝化和氨氮的同化过程所消耗的碱度从而实现养殖水体的原位净化。关于养殖用水循环利用过程中碱度的变化机制和规律需开展大量基础的研究,为实现循环利用水体碱度控制和维持循环水高密度养殖系统pH的稳定提供参考。     

Efficiency of biofloc technology in suspended growth reactors treating aquacultural solid under intermittent aeration

Aquacultural solid waste from a recirculation aquaculture system was used as a substrate to produce heterotrophic bacteria in suspended growth reactors. The efficiency of nitrogen recycling under intermittent aeration (IA, 0.5-h aeration/0.5-h non aeration) and continuous aeration (CA) strategy was investigated. The nitrogen dynamics, biochemical composition of biofloc and efficiency of nitrification/denitrification/ammonium assimilation of biofloc were determined. No significant differences were observed in the nitrogen recycling rate, crude protein and polysaccharides contents of biofloc between the IA and CA reactors. The energy used for intermittent aeration was almost one half of that for continuous aeration. IA strategy (0.5-h aeration/0.5-h non aeration) appears to be more effective to produce biofloc in aquaculture solid waste in reactors than CA strategy.     

Taxonomic and functional profiling of nitrifying biofilms in freshwater,brackish and marine RAS biofilters

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.     

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.     

硝化型和光合自养型生物絮团对泥鳅生长、肠道菌群和水体微生物群落结构的影响

为了解硝化型和光合自养型生物絮团对于泥鳅(Misgurnus anguillicaudatus)的养殖效果, 设置清水组(CW 组)、硝化组(BFT 组)和光合自养组(ABFT 组)生物絮团养殖泥鳅 45 d, 比较泥鳅的生长和消化酶活性、两类絮团的营养组成情况, 以及养殖水体和泥鳅肠道微生物的群落结构。结果显示, BFT 组和 ABFT 组的饲料转化率、特定生长率和末均重没有显著性差异(P＞0.05)。与 CW 组相比, 两实验组的饲料转化率显著降低; BFT 组的终末密度与 CW 组相比没有显著性差异(P＞0.05)。与 CW 组相比, BFT 组和 ABFT 组生物絮团可以提供(36.69±1.17)%和 (40.20±1.05)%的粗蛋白; 与 BFT 组相比, ABFT 组的生物絮团粗脂肪含量显著提高(P＜0.05), 并且促进脂肪酸由饱和向不饱和转化。ABFT 的泥鳅胰蛋白酶和脂肪酶的活性显著高于另外两组(P＜0.05)。微生物群落分析表明, 添加藻类对成熟生物絮团 Alpha 多样性指数、群落门水平和属水平没有显著影响。泥鳅摄食生物絮团会导致肠道菌群 sobs 指数显著降低。BFT 组肠道的优势菌群为变形菌门(Proteobacteria)、放线菌门(Actinobacteriota)和绿弯菌门 (Chloroflexi); ABFT 组为变形菌门和蓝藻门(Cyanobacteria)。属水平上, ABFT 组检测到高水平的气单胞菌属 (Aeromonas)。本研究表明, 硝化型和光合自养型生物絮团养殖均适合作为泥鳅绿色健康养殖的新模式。     

Ammonia removal capacity of European natural zeolite tuffs: application to aquaculture waste water

Abstract. The possibility of improving aquaculture water quality using different kinds of zeolites is discussed. Zeolites are aluminosilicates, whose framework structure allows them to exchange cations. Cations have differing affinities for different structures, and in particular ammonia has a great affinity for phillipsite and clinoptilolite structures. These zeolites are already used for ammonia removal from municipal piggery, and aquacultural wastes. In the present paper, ammonia removal from aquacultural water from recirculating systems has been tested, comparing different zeolites under laboratory conditions. Phillipsite and clinoptilolite tuffs were effective in ammonia removal, while chabazitc tuff having a lower content of zeolitic material (50%) and lower affinity for ammonia showed that a lower temperature did not influence ion exchange capacity in any of the zeolites.     

工厂化水产养殖中的增氧技术

工厂化水产养殖密度大、水和土地资源利用率高、水质可净化而污染少,是应用工业化方式进行水产养殖的生产模式。高效合理的增氧方式可有效增加工厂化养殖中设施与设备的效能,提高生产效率,是工厂化水产养殖的关键技术之一。本文针对水产养殖发展的新变化、新特点,论述了国内外增氧装备的结构特点、增氧方式和效果,分析了增氧技术在发展过程中存在的问题,探讨了增氧技术在工厂化水产养殖中的应用方法和创新技术的发展趋势,为进一步提高增氧技术提供参考。     

A quantitative method for detecting ammonia‐oxidizing bacteria in coastal aquaculture systems

There is a need to quantify autotrophic nitrifiers in coastal aquaculture systems for evolving a bioremediation strategy. Autotrophic nitrifiers are extremely slow‐growing organisms, which cannot be detected by traditional methods as they are notoriously difficult to culture. Molecular techniques based on functional genes could be deployed for the detection of nitrifiers. Ammonia monooxygenase (amoA), that catalyses the oxidation of ammonia to hydroxylamine in the rate‐determining step of nitrification is largely unique to ammonia‐oxidizing bacteria (AOB). In the present study, a quantitative real‐time polymerase chain reaction assay targeting amoA was developed to estimate AOB population size in coastal soil, ammonia‐removing bioaugmentors and the solid matrix. To achieve this objective, different set of primers and a dual labelled probe have been designed for SYBR Green and TaqMan real‐time assays. The abundance of AOB ranged from 10⁴ to 10⁶ order of magnitude in the samples. In the present study, biofilm formation of the consortium of nitrifying bacteria onto bagasse has also been quantified. The results demonstrate that the developed method is a rapid and sensitive tool for the quantitative detection of nitrifying bacteria in aquatic and related environment. This helps in making the bioremediation approach for ammonia removal by immobilization of nitrifying bacteria onto the natural substrate.     

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/m~3,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。     

养殖池塘增氧机制与装备性能比较研究

水产养殖过程中,池塘生态系统可分为自成熟期和人工维持期。在养殖容量提高的情况下,养殖生物呼吸需氧量在不断增加,缺氧条件下有机物分解成有害物质,影响养殖生产。维持池塘生态系统稳定的主要工程机制为:通过上下水层交换、平衡营养元素等方法,强化光合作用,提高营养物质转化规模,提升初级生产力;形成生态增氧为主、机械增氧为辅的高效增氧机制。以中国养殖池塘生态系统为研究对象,分析探讨养殖池塘生态机制、水体溶氧理论、增氧机作用机理、不同类型增氧机的机械性能等,提出了大宗淡水鱼混养池塘及几种典型单养池塘增氧机配置方式,从而为池塘养殖系统增氧机的配置提供技术参考。     

Screening and evaluation of polymers as flocculation aids for the treatment of aquacultural effluents

As environmental regulations become more stringent, environmentally sound waste management and disposal are becoming increasingly more important in all aquaculture operations. One of the primary water quality parameters of concern is the suspended solids concentration in the discharged effluent. For example, EPA initially considered the establishment of numerical limitations for only one single pollutant: total suspended solids (TSS). For recirculation systems, the proposed TSS limitations would have applied to solids polishing or secondary solids removal technology. The new rules and regulations from EPA (August 23, 2004) require only qualitative TSS limits, in the form of solids control best management practices (BMP), allowing individual regional and site specific conditions to be addressed by existing state or regional programs through NPDES permits. In recirculation systems, microscreen filters are commonly used to remove the suspended solids from the process water. Further concentration of suspended solids from the backwash water of the microscreen filter could significantly reduce quantity of discharge water. And in some cases, the backwash water from microscreen filters needs to be further concentrated to minimize storage volume during over wintering for land disposal or other final disposal options. In addition, this may be required to meet local, state, and regional discharge water quality. The objective of this research was an initial screening of several commercially available polymers routinely used as coagulation–flocculation aids in the drinking and wastewater treatment industry and determination of their effectiveness for the treatment of aquaculture wastewater. Based on the results of the initial screening, a further evaluation of six polymers was conducted to estimate the optimum polymer dosage for flocculation of aquaculture microscreen effluent and overall solids removal efficiency. Results of these evaluations show TSS removal was close to 99% via settling, with final TSS values ranging from as low as 10–17 mg/L. Although not intended to be used for reactive phosphorus (RP) removal, RP was reduced by 92–95% by removing most of the TSS in the wastewater to approximately 1 mg/L–P. Dosage requirements were fairly uniform, requiring between 15 and 20 mg/L of polymer. Using these dosages, estimated costs range from $4.38 to $13.08 per metric tonne of feed.     

An experimental study on nitrification biofilm performances using a series reactor system

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.     

池塘养殖增氧方式效果比较

为了解微孔增氧对池塘水体能量流动、水质及养殖效益的影响,对2种不同增氧方式下3个河蟹养殖池塘的养殖周期(4—9月份)进行了水质测定,获得了池塘不同水层的水温、溶氧、氨氮、亚硝酸盐及高锰酸钾盐指数数据。结果表明,夏季高温时采用微孔管道增氧能有效降低表层、底层的温差,一定程度上降低底层水温。微孔管道增氧能有效增加水体溶氧,开机90min水体底层溶氧增加速率是普通增氧机的5倍;6—9月份采用微孔增氧的池塘水体较普通增氧,NO2-N低70﹪以上,NH3-N低22.9﹪以上,高锰酸钾盐指数低20﹪以上,取得了较高的经济效益。     

Root nitrification capacity of lettuce plants with application to aquaponics

Aquaculture and hydroponics have experienced significant growth and market presence in recent years. While aquaponics, the combination of fish and plant culture systems, is beginning to experience the same exponential growth and interest that hydroponics did many years ago, very little information is available on sizing and design of these systems. Incorporation of hydroponic plants with recirculating aquaculture systems (RAS) aids in removal of ammonia/ammonium based wastes, thus reducing the need for water discharge to control water quality. Surface only nitrification rates were quantified to be 0.83g/m²/day for inert surfaces and 0.20/m²/day for root surfaces. Direct assimilation of ammonia by the lettuce plants was less than 2% of the total ammonia and ammonium nitrogen (TAN) removed from the culture water, with the remainder being removal by oxidation of TAN into nitrate.     

海水工厂化养殖水处理系统的装备技术研究

工厂化养鱼(尤其是全封闭高密度养殖方式)是依靠工艺和设施装备技术的支撑，运用生态学原理及环境条件控制手段进行科学养殖。本文围绕海水工厂化养殖系统主要工艺环节(去除固体废弃物和水溶性有害物质、消毒、增氧、调温、水质测控)中涉及的装备技术和应用进行讨论。     

Screening and evaluation of polymers as flocculation aids for the treatment of aquacultural effluents

As environmental regulations become more stringent, environmentally sound waste management and disposal are becoming increasingly more important in all aquaculture operations. One of the primary water quality parameters of concern is the suspended solids concentration in the discharged effluent. For example, EPA initially considered the establishment of numerical limitations for only one single pollutant: total suspended solids (TSS). For recirculation systems, the proposed TSS limitations would have applied to solids polishing or secondary solids removal technology. The new rules and regulations from EPA (August 23, 2004) require only qualitative TSS limits, in the form of solids control best management practices (BMP), allowing individual regional and site specific conditions to be addressed by existing state or regional programs through NPDES permits. In recirculation systems, microscreen filters are commonly used to remove the suspended solids from the process water. Further concentration of suspended solids from the backwash water of the microscreen filter could significantly reduce quantity of discharge water. And in some cases, the backwash water from microscreen filters needs to be further concentrated to minimize storage volume during over wintering for land disposal or other final disposal options. In addition, this may be required to meet local, state, and regional discharge water quality. The objective of this research was an initial screening of several commercially available polymers routinely used as coagulation–flocculation aids in the drinking and wastewater treatment industry and determination of their effectiveness for the treatment of aquaculture wastewater. Based on the results of the initial screening, a further evaluation of six polymers was conducted to estimate the optimum polymer dosage for flocculation of aquaculture microscreen effluent and overall solids removal efficiency. Results of these evaluations show TSS removal was close to 99% via settling, with final TSS values ranging from as low as 10–17 mg/L. Although not intended to be used for reactive phosphorus (RP) removal, RP was reduced by 92–95% by removing most of the TSS in the wastewater to approximately 1 mg/L–P. Dosage requirements were fairly uniform, requiring between 15 and 20 mg/L of polymer. Using these dosages, estimated costs range from $4.38 to $13.08 per metric tonne of feed.