Comparative adsorption evaluation of biochars from paper mill sludge with commercial activated carbon for the removal of fish anaesthetics from water in Recirculating Aquaculture Systems

Tricaine methanesulfonate (MS-222), benzocaine and 2-phenoxyethanol (2-PE) are widely used in intensive aquaculture systems to control stress during handling and confinement operations. This work aimed to study the adsorptive removal of these anaesthetics from water, comparing two waste-based adsorbents produced by pyrolysis of paper mill sludge with a commercial activated carbon. The use of commercial activated carbon resulted in maximum adsorption capacities of 631, 435 and 289 mg g^⿿1 for MS-222, benzocaine and 2-PE, respectively (obtained by the fitting of Langmuir-Freundlich model), which are between 4 and 8 times higher than those determined for the alternative adsorbents. Even so, the obtained results point to the promissory utilization of these waste-based adsorbents in Recirculating Aquaculture Systems, as an integrated way of managing such residues and treatment of aquaculture waters contaminated with anaesthetics.     

聚己内酯添加量对淡水养殖水体硝酸盐氮处理效果的影响

以可生物降解聚合物(Biological degradable polymers,BDPs)为有机碳源进行异养反硝化可以避免多次添加碳源、碳源不足或过量等问题。聚己内酯(Polycaprolactone,PCL)已被证明能够作为水产养殖用水异养反硝化的有机碳源。研究了聚己内酯添加量对水产养殖用水硝酸盐氮去除效率的影响。在进水硝酸盐氮(NO_3~--N)负荷为0.1 g/(L·d)条件下,200 m L水体中分别加入5 g、10 g、15 g、20 g、25 g和30 g的PCL颗粒进行反硝化,各组的NO_3~--N去除效率没有明显差异;出水中溶解有机碳的质量浓度随着PCL添加量的增加而增加;5 g组的PCL利用率明显高于其他组。结果显示:试验条件下,PCL添加量的增加并不会必然增加NO_3~--N的去除效率,反而会造成出水中溶解有机碳的增加;添加5 g PCL为最适添加量。     

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.     

Water reuse in closed hydroponic systems: Comparison of GAC adsorption,ion exchange and ozonation processes to treat recycled nutrient solution

In this study, the removal of root exudates from recycled nutrient solution (RNS) in hydroponic systems was investigated by using alternative advanced treatment processes. In particular, the performance of adsorption on granular activated carbon (GAC adsorption), ion exchange (using Amberlite IRA96) and ozonation was evaluated. The characterization of a RNS from a lettuce hydroponic company showed the occurrence of several organic acids including benzoic, maleic, palmitic, stearic, phthalic, succinic, acrylic, adipic, myristic, mannonic, oleic, arachidic and acetic acid. Furthermore, benzoic, acrylic, myristic and palmitic acid were detected even after the RNS treatment by GAC adsorption, ion exchange or ozonation. Further experiments were performed to evaluate the removal efficiency of root exudates from RNS by the selected treatment processes. For this purpose benzoic acid (BA), which is a potent growth inhibitor, was selected as target compound. Benzoic acid occurring at 23 μg/L in the RNS was completely removed by GAC adsorption, ion exchange or ozonation process. In addition, GAC adsorption was the most efficient technique for organic matter removal. Indeed, the COD removal efficiency was 74%, 67% and 22% for GAC adsorption, ozonation and ion exchange treatments, respectively. The results from UV–vis absorbance measurements corroborated the best performance of activated carbon in organic compounds removal from RNS. For instance, the absorbance removal at 280 nm reached 82%, 51% and 27% after GAC adsorption, ozonation and ion exchange treatments, respectively.     

Controlling of geosmin and 2‐methylisoborneol induced off‐flavours in recirculating aquaculture system farmed fish—A review

Recirculating aquaculture system (RAS) is an increasingly popular alternative to open aquaculture production systems. However, off‐flavours and odours can accumulate in the fish flesh from the circulating water and decrease the fish meat quality. Off‐flavours are typically caused by geosmin (GSM) and 2‐methylisoborneol (MIB) that are lipophilic compounds formed as secondary by‐products of bacterial metabolism. Even though GSM and MIB are not toxic, they often are disliked by consumers, and both have very low human sensory detection limits. Multiple methods have been suggested to remove or decrease GSM and MIB in fish, including ozonation, advanced oxidation processes (AOP)s and adsorption removal from water using activated carbon and/or zeolites. So far, purging with fresh water is the only efficient method available to remove the off‐flavours. There are multiple analytical methods available for the extraction and separation of GSM and MIB from fish flesh and water. This review discusses the current knowledge of GSM and MIB formation, the challenges faced by RAS farms due to these compounds and process solutions available for their removal.     

The type of activated carbon determines how much dissolved organic carbon is removed from artificial seawater

Four granular activated carbons (GACs) made of different materials were tested for removal of dissolved organic carbon (DOC) from artificial seawater of a recirculated aquarium. After 70 days in a continuous flow experiment, comparative removal data (grams of GAC required to remove 1 g of DOC) were coconut shell (491), hardwood (84·4), anthracite (837) and bone char (383), indicating the superior performance of hardwood. Scanning electron microscopy showed that microbial colonization of a sample material (hardwood) was slight and occurred exclusively at the surface. Biological enhancement of GAC was considered to be unimportant as a mechanism for DOC removal.     

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.     

不同有机碳源及C/N对生物滤池净化效果的影响

利用生物滤池模拟装置,以实际养殖废水为处理对象,探讨了4种常见有机碳源(葡萄糖、乙醇、红糖和淀粉)及不同碳氮比对有机物去除、硝化反应和异养反硝化作用等生物滤池主要净化过程的影响.碳源初选结果显示,同种碳源下,当C/N从0升高至6过程中,生物滤池对TAN(总氨氮)的去除率呈先升高后降低趋势;当C/N较小时,各组对NO2--N的去除率差异性不显著(P＞0.05),随着C/N继续升高,NO2-N去除率则显著降低(P＜0.05);乙醇组除外,其他3组随着C/N升高,CODMn去除率先迅速增大然后趋于稳定;各组NO3-N和TN去除率呈先升高后降低趋势,且变化显著(P＜0.05),当C/N=4时,分别达到最高值.碳源复选结果显示,在C/N=4条件下,分别添加有机碳源(乙醇、淀粉、红糖和葡萄糖)的4组对TAN、NO3--N、TN和CODM的去除率显著高于对照组(P＜0.05);而对照组NO2--N的去除率最高,达到93.59％;添加乙醇,生物滤池对水体中TAN、NO2-N、NO3-N和TN的去除效果优于其他3种碳源.研究表明,当C/N=4时,乙醇作为外加碳源能很好地提高生物滤池的净化效率.     

碳源添加方式对循环水养殖系统中微生物悬浮生长反应器水处理的影响

采用中试规模的循环水养殖系统,对比研究碳源连续添加的微生物悬浮生长反应器(SGR-Con)和碳源分次添加反应器(SGR-Sev)的水处理效果。典型反应周期内的溶解性有机碳浓度变化,SGR-Con反应区处于较高的稳定水平,SGR-Sev在反应周期的第0小时至碳源瞬时添加时快速上升至SGR-Con的水平,并且在反应周期的第4小时以后降至较低的稳定水平。实验期间,SGR-Sev反应区和沉淀区的溶解氧含量分别显著高于SGRCon的反应区和沉淀区;2个反应器的反应区pH无显著差异,沉淀区pH在2个反应器之间亦无显著差异。碳源分次添加的方式显著提高了反应器的脱氮效果,SGR-Sev对硝氮和总氮的去除率、出水碱度分别可达63.91%±14.31%、64.07%±12.11%和(278.18±80.33)mg/L。相较于SGR-Con,SGR-Sev的出水总氨氮和亚硝氮浓度较高。反应器采用碳源分次添加的方式可使絮团具有良好的沉降性能。研究表明,微生物悬浮生长反应器宜采用碳源分次添加的方式。     

The nutrient footprint of a submerged‐cage offshore aquaculture facility located in the tropical Caribbean

The effect of effluent generated by a commercially scaled offshore (~13 km) finfish aquaculture facility in the tropical Caribbean on the water column and benthic nutrients and chlorophyll‐a is described. Water column samples were collected up‐ and downstream of the site at various times between 2012 and 2018. Typically, no significant difference in dissolved oxygen, chlorophyll‐a, particulate organic carbon, particulate organic nitrogen, nitrate + nitrite, and total dissolved nitrogen concentration was observed in the water column between the up‐ versus downstream samples. Similarly, sediment samples were collected at various times between 2012 and 2018. Samples were collected at up‐ versus downstream locations and analyzed for benthic carbon, nitrogen, and chlorophyll‐a content. Some of the collected data demonstrates a trend toward sediment enrichment within the vicinity of the farm. These data are of interest to stakeholders concerned with the expansion of offshore aquaculture in the United States and other countries. To our knowledge, this is the first report of its kind from a commercially scaled aquaculture facility utilizing offshore submersible‐cage technologies.     

内陆渔业生态系统的碳循环特征及碳汇机制

渔业是水体生态系统中惟一可控的有效增汇产业, 碳汇渔业是水体生态系统中惟一的“碳汇产业”。为了更好地把握内陆渔业生态系统碳循环及碳汇机制的特征, 目前的重点研究应包括内陆渔业水域生态环境(包括自然水域和池塘)中碳循环的规律, 碳赋存形态的归转, 各类水产品生物对碳汇的贡献途径和份额以及相应的计量体系和评价模型等; 同时, 希望合理地估算及测定内陆渔业水体、水–气界面间CO2通量, 把握内陆渔业水域生态系统碳源/碳汇的动态, 进而构建内陆渔业水域生态系统的环境碳/生物碳/碳通量时空变化的信息库。     

Effect of shrimp farming organic waste on food availability for deposit feeder crabs in a mangrove estuary, based on stable isotope analysis

We have investigated the impact of shrimp farming waste on benthic invertebrates in a mangrove estuary in southern Thailand. Stable carbon and nitrogen isotope analyses were used to assess the contribution of aquaculture feed as a nutrient source for benthic invertebrates (fiddler crabs Uca annulipes, U. bengali, and U. forcipata) and to compare the organic origin of sediments in tributaries with and without a shrimp farm. The isotopic contributions of shrimp feed to crabs varied between the tributaries: in the tributary with the farm, the crabs had higher contributions from shrimp feed, whereas there was only a small contribution from aquaculture feed in crabs from the reference tributary. In contrast, the contribution of shrimp feed to the sediment did not differ between the tributaries, the contributions to sediments from aquaculture feed were, in general, quite low. Based on these results, we suggest that, in mangrove estuaries, changes in the food sources of several surface feeder invertebrates would be an effective indicator of the possibility that aquaculture waste was affecting the benthic ecosystem.     

A novel approach to denitrification processes in a zero-discharge recirculating system for small-scale urban aquaculture

This paper presents an innovative process to solve the nitrate build-up problem in recirculating aquaculture systems (RAS). The novel aspects of the process lie in a denitrification bioreactor system that uses solid cotton wool as the primary carbon source and a unique degassing chamber. In the latter, the water is physically stripped of dissolved gaseous O₂ (by means of a Venturi vacuum tube), and the subsequent denitrification becomes more efficient due to elimination of the problems of oxygen inhibition of denitrification and aerobic consumption of cotton wool. The cotton wool medium also serves as a physical barrier that traps organic particles, which, in turn, act as an additional carbon source for denitrification. Operation in the proposed system gives an extremely low C/N ratio of 0.82 g of cotton wool/g of nitrate N, which contributes to a significant reduction of biofilter volume. The additional advantage of using solid cotton wool as the carbon source is that it does not release organic residuals into the liquid to be recycled. Operation of the system over a long period consistently produced effluents with low nitrate levels (below 10 mg N/l), and there was only a very small need to replace system water. The overall treatment scheme, also incorporating an aerobic nitrification biofilter and a granular filtration device, produced water of excellent quality, i.e., with near-zero levels of nitrite and ammonia, a sufficiently high pH for aquaculture, and low turbidity. The proposed system thus provides a solution for sustainable small-scale, urban aquaculture operation with a very high recovery of water (over 99%) and minimal waste disposal.     

Organic and inorganic carbon levels in recycled seawater during the culture of tropical prawns Penaeus sp.

Suspended particles and dissolved organic carbon in laboratory recirculation systems were broadly categorised by size filtration and ultraviolet absorption. Their concentrations in recycled seawater increased during the culture of tropical prawns with increase in feeding rate and also with a ‘load’ factor calculated to take account of the volume of water used to culture a known biomass of prawns. In systems operated without periodic water renewal the proportion of organic matter in filterable material and the integrated ultraviolet absorbance (Σ A 250–330 nm) of filtrate increased with time. The increasing absorbance observed, particularly in the higher wavelengths (Σ A 290–330 nm), indicated the accumulation of metabolically derived organic material that was resistant to microbial degradation. Mean numbers of bacteria varied immensely from 7 to 25 000 × 10³ ml^?1 but were lower in foamed than unfoamed systems.The relation between the concentration of dissolved inorganic carbon (a measure of carbonate alkalinity) and pH in the systems varied according to the type of media in the biological filter and the method used to control pH. Results closest to natural seawater were obtained in systems containing filters with limestone media periodically dosed with sodium hydroxide solution. Higher levels of inorganic carbon for a given pH above pH 7·9 were, however, noted when sodium hydroxide was used with plastic media filters, a feature beneficial to heavily loaded systems.     

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.     

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.     

The composition of readily available carbon sources produced by fermentation of fish faeces is affected by dietary protein:energy ratios

Fish solid waste (faeces) produced in recirculated aquaculture systems (RAS) might be used for on-farm, single-sludge denitrification if transformed into soluble organic carbon substances. The current study investigated the effect of feeding diets with increasing protein to energy ratios (P:E_15, 17, 19, 21 and 23 g/MJ) to rainbow trout (Oncorhynchus mykiss) on the production of volatile fatty acids (VFAs) and ethanol during 7 days fermentation of the produced fish faeces. The total yields of VFAs and ethanol obtained (expressed as chemical oxygen demand (COD)) ranged between 0.21–0.24 gCOD/gTCOD, showing no differences between treatments. However, the type and quantities of individual VFAs and ethanol changed according to the dietary treatment. Lower P:E ratio diets resulted in higher production of butyric acid and ethanol, whereas higher P:E ratio diets resulted in an increased production of acetic and valeric acid. Changing the diet composition thus affects the composition of readily available carbon that can be derived from the faeces. This can be applied to enhance on-farm single sludge denitrification and reduce the need for adding external carbon sources such as e.g. methanol.     

海水养殖尾水人工湿地处理系统及其脱氮过程研究进展和展望

利用人工湿地处理海水养殖尾水具有很大的应用前景,其中,脱氮是人工湿地的主要任务之一。基质上栽培的植物和附着的微生物参与的氮循环是人工湿地生物脱氮的主要路径,植物和多种氮代谢菌群在人工湿地内部相互协同与制约,构成了一个复杂的氮代谢网络。海水养殖尾水的高盐度和低碳氮比(C/N)又决定了此类人工湿地独特的处理环境和生物脱氮机制。同时,人工湿地的供氧模式、水力负荷(HRT)、水力停留时间(HLR)等水力条件参数对脱氮效能也有很大影响,对这些指标进行调控和优化,可以提高湿地的整体脱氮性能。本文从海水人工湿地的构建、基质的选取、耐盐植物的筛选、氮循环相关微生物以及运行参数调控四个方面,对近年来海水养殖尾水人工湿地生物脱氮方面的研究进展进行了综述和展望,以期为深入理解海水人工湿地脱氮机制和优化运行方式提供参考。     

Waste management in recirculating aquaculture system through bacteria dissimilation and plant assimilation

Wastewater management and disposal in aquaculture is becoming increasingly important due to stringent water regulations regarding waste discharges into natural water systems. Recirculation aquaculture is one of the technologies designed to reduce waste discharge through the nitrification process. However, nitrification results in nitrate accumulation which is normally reduced by dilution through water exchange. Water exchange is only possible with sufficient water. Although nitrification is a conventional process, it has limitations because the autotrophic bacteria require long start-up and multiplication periods. The nitrifiers require high levels of oxygen with relatively higher aeration costs. Moreover, the bacteria are sensitive to rapid changes in pH, temperature, and flow rate. Denitrification can be a solution to the limitations of nitrification since denitrifiers are most abundant in the natural environment and have higher growth rates than nitrifiers. In addition, the process reduces energy costs since there is no need for aeration, water consumption is also reduced drastically since water exchange is minimized. Organic loading can be reduced when fish waste is utilized as a carbon source. An alternative process to manage aquaculture wastes is through anaerobic ammonium oxidation (anammox), where ammonia and nitrite are converted into nitrogen gas. Anammox can efficiently reduce ammonia and nitrites from culture water, but it has not received wide application in aquaculture. Aquaculture wastewater contains nutrients which are essential for plant growth. The plants maintain good water quality by absorbing the dissolved nutrients. Denitrification, anammox, and nutrient uptake by plants are feasible strategies to reduce wastes from aquaculture effluents.     

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。