无机碳源对生物絮团降氮及沉降性能的影响

利用异位生物絮团反应器,分别在有机碳源存在(第Ⅰ阶段,持续21 d)和有机碳源缺失(第Ⅱ阶段,持续21 d)阶段,比较研究了无机碳源(NaHCO_3)浓度为0.0 (对照组),0.5,1.0和1.5 g/L的模拟养殖废水对反应器生物絮团降氮及沉降性能的影响。结果显示,第Ⅰ阶段对照组出水氨氮浓度显著高于其他处理组,但总体上呈先下降后稳定的趋势,各组亚硝态氮和硝态氮均有少量积累;生物絮团生物量及沉降速度对照组显著低于处理组,处理组之间差异不显著。第Ⅱ阶段各组出水的氨氮、亚硝态氮浓度无显著差异,对照组硝态氮浓度高于各处理组,氨氮浓度迅速下降;此阶段生物絮团的生物量、沉降速度有所下降,NaHCO_3浓度为1.0 g/L处理组表现出较好的沉降效果;粒径分布也趋向均匀。整个实验阶段,不同浓度无机碳源处理条件下,氨氮的去除效率均达到97.8%以上,亚硝态氮无显著积累,处理组生物絮团沉降速度和生物量显著高于对照组。研究表明,添加无机碳源可提高生物絮团降氮性能,增强其沉降速度;移除有机碳源后,生物絮团反应器可维持氨氮去除能力,但引起硝态氮积累,生物絮团生物量减少;有机碳源缺失时,无机碳源(≥0.5 g/L)有助于生物絮团反应器保持其氨氮去除能力。     

墨瑞鳕循环水养殖系统中不同生物膜反应器水处理效率及微生物群落对比分析

固定床生物膜反应器(fixed-bed biofilm bioreactor, FBBR)和移动床生物膜反应器(moving- bed biofilm reactor, MBBR)在养殖水体氨氮(NH4+-N)和亚硝酸氮(NO2–-N)污染控制中已有较为广泛的研究，然而相关研究大多是在实验室完成的，目前尚缺乏实际生产的循环水养殖系统(recirculating aquaculture system, RAS)中FBBR和MBBR水体净化效能的对比研究。因此，本研究将FBBR (弹性毛刷滤料)和MBBR (PVC多孔环滤料)并联接入实际生产的墨瑞鳕(Macculochella peeli) RAS中，实现二者的同步连续运行(35 d)，考察了其出水水质变化和微生物群落结构。出水水质变化表明，FBBR和MBBR中氨氧化能力的形成快于亚硝氮氧化能力，硝化能力渐趋成熟，可以有效控制养殖水体中的NH4+-N和NO2–-N浓度，但会导致养殖水体中硝酸氮(NO3–-N)积累和pH下降；单因素方差分析表明，FBBR出水中NH4+-N、NO2–-N、NO3–-N浓度和pH与MBBR出水无显著差异，两反应器的硝化效率相似。FBBR和MBBR在微生物群落上的相同点在于：优势菌门为变形菌门(Proteobacteria) (相对丰度分别为69.42%和86.92%)，优势菌纲为γ-变形菌纲(γ-Proteobacteria) (40.71%和63.36%)和α-变形菌纲(α-Proteobacteria) (26.58%和21.74%)，优势菌属为不动杆菌属(Acinetobacter) (27.50%和53.29%)；硝化菌由亚硝化单胞菌属(Nitrosomonas)和硝化螺菌属(Nitrospira)构成；硝化螺菌属的相对丰度远高于亚硝化单胞菌属，两反应器中可能存在完全氨氧化菌。两反应器在微生物群落上的不同点在于FBBR微生物群落的丰富度和多样性以及硝化菌的相对丰度均高于MBBR。本研究可以为RAS养殖水体净化提供技术支撑，助推循环水养殖模式的推广应用。     

添加不同碳源对零换水养殖系统中团头鲂鱼种生长、肠道生化指标和水质的影响

为探究添加不同碳源物质所形成的生物絮团对团头鲂鱼种生长、消化酶以及抗氧化酶活性的影响,设计5个不同碳源物质的添加组[淀粉组、葡萄糖组、蔗糖组、甜蜜素组和复合碳源组(葡萄糖∶淀粉=1∶1)],其中淀粉组为对照组,每个碳源添加组设置3个重复。每个水泥池投放团头鲂鱼种20尾,初始体质量为(36.74±0.82)g,实验期为8周。结果发现:(1)形成的生物絮团可以有效地调节水质,降低水体中的氨氮和亚硝酸盐氮水平;(2)与对照组相比,葡萄糖组团头鲂鱼种的鱼体末质量显著提高23.1%,增重率显著提高39.4%,特定生长率也显著提高23.6%,饲料系数显著降低28.1%,但存活率并没有显著差异;(3)肠道组织光镜观察表明,团头鲂鱼种肠道单层柱状上皮附近存在未消化的生物絮团;(4)添加不同碳源形成的生物絮团对团头鲂鱼种体成分没有显著的影响;(5)复合碳源组的肠道总蛋白酶的活性(3.64±0.53)U/mg显著高于对照组275.3%,淀粉酶活性显著高于对照组(淀粉组)289.2%、葡萄糖组166.7%和蔗糖组860%;(6)葡萄糖组的团头鲂超氧化物歧化酶(SOD)活性为(238.67±13.63)U/mg,显著高于对照组的SOD活性72.5%,葡萄糖组团头鲂的过氧化氢酶(CAT)酶活性为(192.31±17.06)U/mg,显著高于对照组的CAT活性40.4%,与对照组的丙二醛(MDA)水平相比,葡萄糖组、蔗糖组、甜蜜素组和复合碳源组分别显著降低了69.0%、59.7%、38%.0和48.8%。研究表明,水体中添加葡萄糖为碳源能显著提高团头鲂鱼种的生长性能和抗氧化水平,并有效改善水质。     

循环水养殖罗非鱼氮收支及对水质影响的初步研究

为提供实际生产理论依据,改良系统水处理工艺,开展循环水养殖系统中吉富罗非鱼氮收支和对水质情况的初步研究。起始养殖密度8 kg/m3,投饲率2%,系统循环量1 m3/h,总水量0.8 m3。试验期间溶解氧大于6 mg/L,pH 7.0～7.2,水温23～25℃。每周监测水质2～3次,监测指标包括氨氮、亚硝酸盐氮、硝酸盐氮,每2周检测1次水中总氮。用凯氏定氮法测定实验前后饲料、试验鱼体、粪便、悬浮颗粒的氮含量。结果显示,摄食氮有50.00±1.50%转化为生长氮,32.61±1.38%转化为排泄氮,17.39±4.0%转化为粪氮;58%的粪氮为悬浮颗粒物,42%为可沉淀颗粒物。     

水产养殖过程中为何要定期使用“增效葡萄糖”？

养殖池塘水体中可溶性的糖在养殖过程中是随着养殖周期的延长而逐渐减少的,并持续维持在一个较低的水平上。糖是池塘水体中微生物生长所必需的碳源物质,因为水体中碳源物质的缺乏使得水体营养物中的碳氮比例不平衡,大多数的微生物不能正常生长。所以有的养殖户长期大量使用微生     

微生物悬浮生长水处理系统在工厂化水产养殖中的应用研究进展

微生物悬浮生长是水产养殖重要的水处理方式之一,是指进行水处理的微生物悬浮式地生长在水体中。回顾了微生物悬浮生长水处理在工厂化水产养殖中的应用历程,总结其应用进展。通过文献分析,生物絮团原位养殖技术的养殖动物和水处理微生物生长在同一空间,是当前微生物悬浮生长被广泛应用的主要形式,具有调控水质和提供饵料等优点,但是仍有悬浮颗粒物质量浓度过高等缺点;为此,养殖动物和水处理微生物在空间上是分开的异位反应器被用于污染物的处理和循环水养殖系统(RAS)的核心水处理装置。研究认为,异位反应器用作RAS的核心水处理装置可以简化RAS的装备组成,资源化地处理多种污染物,下一步仍需不断优化其工艺,研究氮磷以外的物质在养殖用水长期重复使用过程中的积累和流动规律。     

基于珊瑚骨基质的凡纳滨对虾内循环养殖系统的构建与运行效果

采用珊瑚骨作为生物膜载体,利用海水素配制人工海水,构建盐度为15‰(海水)和5‰(淡水)的两个凡纳滨对虾内循环养殖系统,通过添加硝化细菌菌剂和氮源,分别用8 d和13 d建立硝化功能。按照500尾/m~3密度投入虾苗后,海水系统和淡水系统分别运行97 d和83 d。在运行期间淡水和海水系统养殖水体氨氮浓度始终维持在较低水平,平均浓度分别为(0.015±0.008) mg/L和(0.014±0.008) mg/L;在海水系统运行前60 d,亚硝氮浓度维持在较低水平,在60～90 d,亚硝氮浓度呈缓慢上升趋势,在90 d后,海水系统亚硝氮浓度开始快速增加,最终达到3.43 mg/L;淡水系统在运行前40 d亚硝氮浓度维持在较低水平,40 d后开始小幅上升,运行至70 d后,亚硝氮浓度开始快速增加,最终达到0.52 mg/L。最终海水系统和淡水系统凡纳滨对虾存活率分别为51.5%和48.5%。     

碳源和氮源加富对脆江蓠生长及生化组分的影响

在实验室条件下研究了碳源(添加CO2)和氮源(添加Na NO3)加富对大型海藻脆江蓠(Gracilaria chouae)生长及其生化组成的影响。设置碳源加富(800μL/L CO2)和对照(400μL/L CO2)2个碳源处理组,氮源加富(100μmol/L、300μmol/L和500μmol/L 3NO?-N)和对照(10μmol/L3NO?-N)4个氮源处理组,每个处理3个重复。实验共进行10 d,测定不同处理组藻体的生长及可溶性总糖(SS)、可溶性蛋白质(SP)、藻红蛋白(PE)、叶绿素a(Chla)、总碳(TC)和总氮(TN)含量的变化。结果表明,碳源和氮源加富都会促进脆江蓠的生长,在800μL/L CO2和100μmol/L 3NO?-N处理组,脆江蓠的瞬时生长率(SGR)最大(11.70%/d);高浓度CO2会降低藻体SP、PE和Chla的含量,但提高了SS的含量;随着硝态氮浓度的增大,PE和SP含量逐渐增加,而SS含量逐渐降低,Chla含量没有明显变化。藻体的TN含量随着硝态氮浓度的增加而逐渐提高,而TC和C/N比值则呈现逐渐降低的趋势,并且藻体的TN和TC含量呈现出显著的负相关关系(P0.05)。本实验证实添加碳、氮会引起脆江蓠生长和生化组成的变化,但其能耐受较高的CO2浓度和氮浓度。     

溶解碳源与固体碳源对对虾生物絮团养殖系统的影响

为探讨溶解碳源与固体碳源在凡纳滨对虾(Litopenaeus vannamei)生物絮团养殖过程中的影响，设置5个不同碳源搭配组、花生壳粉组、红糖组、花生壳粉∶红糖(1∶1)组、花生壳粉∶红糖(2∶1)组以及花生壳粉∶红糖(1∶2)组，分别进行为期40 d的南美白对虾养殖试验，每4 d进行一次水质监测，试验结束时对对虾肝胰腺取样进行谷胱甘肽-S转移酶活性测定并且将抽滤滤膜进行高通量测序分析，探究不同类型碳源且不同搭配比例对生物絮团养殖系统内水质、对虾生长性能、微生物多样性及其群落结构的作用。结果显示：在水质调控方面，花生壳粉∶红糖(2∶1)组的氨氮在整个试验周期始终维持在较低水平，氨氮峰值仅为(2.43±0.45)mg/L,而氨氮峰值最大的花生壳粉组高达(9.80±0.35)mg/L;亚硝酸盐氮在对照组中呈上升趋势，在生物絮团组浓度呈先上升后下降趋势，花生壳粉∶红糖(2∶1)组的浓度变化拐点要比其他处理组提前；在硝酸盐氮水平，除对照组外其余生物絮团组都呈上升趋势，花生壳粉∶红糖(2∶1)组在试验结束时硝酸盐氮质量浓度高达(17.84±1.20)mg/L;在微生物群落分析中，副球菌属是属...     

钝顶螺旋藻在养虾废水中的生长研究

研究了钝顶螺旋藻(Spirulina platensis)在养虾废水中的生长情况。结果表明,钝顶螺旋藻不能直接在该养殖废水中生长,但在废水中添加5%比例的Zarrouk培养液后,钝顶螺旋藻能在其中较好地生长。通过正交试验获得了钝顶螺旋藻在含5%Zarrouk培养液的废水中的生长最佳条件:pH=8,初始密度A560为0.3,光强2500lx。在该条件下,钝顶螺旋藻对废水中的氮、磷均有较好的清除效果,氨氮、硝态氮、亚硝态氮和活性磷的清除率分别达到64.5%、41.9%、67.1%和43.9%。     

深凹壳型香港牡蛎选育群体生长性状的遗传参数估计

为了培育壳型和生长性状优良的深凹壳型香港牡蛎新品系,以广东台山镇海湾野生香港牡蛎天然采苗的2龄养殖群体为基础群体,以壳型指数D为指标,按照10%留种率和1.755选择强度,利用截头法进行深凹壳型香港牡蛎的群体选育;分析了幼虫期、中间培养期、养成后期的选择反应、遗传获得和现实遗传力等遗传参数。结果发现,选择组的壳高和壳型指数D均大于对照组,遗传参数估算值随着个体的增大而增加。幼虫期,壳高的平均选择反应、平均遗传获得、平均现实遗传力分别为0.363±0.167、1.678%±0.416%、0.207±0.095,中间培养期分别0.639±0.115、7.618%±2.666%、0.364±0.065,养成后期分别为0.668±0.179、8.861%±3.072%、0.381±0.102。养成后期,壳型指数D的平均选择反应、平均遗传获得、平均现实遗传力分别为0.748±0.066、9.090%±0.565%、0.426±0.038。研究结果为培育深凹壳型、生长性能良好的香港牡蛎优良品种提供了实验依据和理论基础。     

The efficiency and condition of oysters and macroalgae used as biological filters of shrimp pond effluent

Current shrimp pond management practices generally result in elevated concentrations of nutrients, suspended solids, bacteria and phytoplankton compared with the influent water. Concerns about adverse environmental impacts caused by discharging pond effluent directly into adjacent waterways have prompted the search for cost‐effective methods of effluent treatment. One potential method of effluent treatment is the use of ponds or raceways stocked with plants or animals that act as natural biofilters by removing waste nutrients. In addition to improving effluent water quality prior to discharge, the use of natural biofilters provides a method for capturing otherwise wasted nutrients. This study examined the potential of the native oyster, Saccostrea commercialis (Iredale and Roughley) and macroalgae, Gracilaria edulis (Gmelin) Silva to improve effluent water quality from a commercial Penaeus japonicus (Bate) shrimp farm. A system of raceways was constructed to permit recirculation of the effluent through the oysters to maximize the filtration of bacteria, phytoplankton and total suspended solids. A series of experiments was conducted to test the ability of oysters and macroalgae to improve effluent water quality in a flow‐through system compared with a recirculating system. In the flow‐through system, oysters reduced the concentration of bacteria to 35% of the initial concentration, chlorophyll a to 39%, total particulates (2.28–35.2 µm) to 29%, total nitrogen to 66% and total phosphorus to 56%. Under the recirculating flow regime, the ability of the oysters to improve water quality was significantly enhanced. After four circuits, total bacterial numbers were reduced to 12%, chlorophyll a to 4%, and total suspended solids to 16%. Efforts to increase biofiltration by adding additional layers of oyster trays and macroalgae‐filled mesh bags resulted in fouling of the lower layers causing the death of oysters and senescence of macroalgae. Supplementary laboratory experiments were designed to examine the effects of high effluent concentrations of suspended particulates on the growth and condition of oysters and macroalgae. The results demonstrated that high concentrations of particulates inhibited growth and reduced the condition of oysters and macroalgae. Allowing the effluent to settle before biofiltration improved growth and reduced signs of stress in the oysters and macroalgae. A settling time of 6 h reduced particulates to a level that prevented fouling of the oysters and macroalgae.     

Activated sludge denitrification in marine recirculating aquaculture system effluent using external and internal carbon sources

Stringent environmental legislation in Europe, especially in the Baltic Sea area, limits the discharge of nutrients to natural water bodies, limiting the aquaculture production in the region. Therefore, cost-efficient end-of-pipe treatment technologies to reduce nitrogen (N) discharge are required for the sustainable growth of marine land-based RAS. The following study examined the potential of fed batch reactors (FBR) in treating saline RAS effluents, aiming to define optimal operational conditions and evaluate the activated sludge denitrification capacity using external (acetate, propionate and ethanol) and internal carbon sources (RAS fish organic waste (FOW) and RAS fermented fish organic waste (FFOW)). The results show that between the evaluated operation cycle times (2, 4, and 6 h), the highest nitrate/nitrite removal rate was achieved at an operation cycle time of 2 h (corresponding to a hydraulic retention time of 2.5 h) when acetate was used as a carbon source. The specific denitrification rates were 98.7 ± 3.4 mg NO₃⁻-N/(h g biomass) and 93.2 ± 13.6 mg NO_x⁻-N/(h g biomass), with a resulting volumetric denitrification capacity of 1.20 kg NO₃⁻-N/(m³ reactor d). The usage of external and internal carbon sources at an operation cycle time of 4 h demonstrated that acetate had the highest nitrate removal rate (57.6 ± 6.6 mg N/(h g biomass)), followed by propionate (37.5 ± 6.3 mg NO₃⁻-N/(h g biomass)), ethanol (25.5 ± 6.0 mg NO₃⁻-N/(h g biomass)) and internal carbon sources (7.7 ± 1.6–14.1 ± 2.2 mg NO₃⁻-N/(h g biomass)). No TAN (Total Ammonia Nitrogen) or PO₄^3- accumulation was observed in the effluent when using the external carbon sources, while 0.9 ± 0.5 mg TAN/L and 3.9 ± 1.5 mg PO₄^3--P/L was found in the effluent when using the FOW, and 8.1±0.7 mg TAN/L and 7.3 ± 0.9 mg PO₄^3--P/L when using FFOW. Average sulfide concentrations varied between 0.002 and 0.008 mg S^2-/L when using the acetate, propionate and FOW, while using ethanol resulted in the accumulation of sulfide (0.26 ± 0.17 mg S^2-/L). Altogether, it was demonstrated that FBR has a great potential for end-of-pipe denitrification in marine land-based RAS, with a reliable operation and a reduced reactor volume as compared to the other available technologies. Using acetate, the required reactor volume is less than half of what is needed for other evaluated carbon sources, due to the higher denitrification rate achieved. Additionally, combined use of both internal and external carbon sources would further reduce the operational carbon cost.     

Settling velocity distribution of bioflocules generated with different carbon sources during the rearing of the river shrimp Cryphiops caementarius with biofloc technology

Controlling the concentration of bioflocs is one of the main concerns in aquaculture systems with Biofloc Technology (BFT). Biofloc accumulation deteriorates the water quality and can negatively affect the production rates of the farmed river shrimp. This study describes and characterizes the settling velocity distribution of bioflocs generated with the addition of two carbon sources (molasses and chancaca) when applying the BFT for the rearing of the river shrimp Cryphiops caementarius. This study revealed that bioflocs generated with different carbon sources have different settling velocity curves. Regarding the mass fraction settling velocities, there were significant differences (P < 0.05) for mean solids fraction at similar withdrawn times between molasses and chancaca. The average settling velocities for bioflocs were 0.1044 ± 0.1224 cm s⁻¹ for molasses and 0.1131 ± 0.1225 cm s⁻¹ for chancaca. Therefore, a settling device operating with a given overflow rate will more efficiently remove bioflocs generated with chancaca than with molasses. The settling velocity curves obtained in this research contain valuable information to select appropriate devices for bioflocs and suspended solids removal in aquaculture systems with BFT.     

Suspended Solids from Baitfish Pond Effluents in Drainage Ditches

Effluents from aquaculture facilities vary between species and among production systems. Drainage ditches commonly convey effluents from central Arkansas baitfish ponds. Ditches could potentially reduce suspended solids prior to effluent release into receiving streams through settling. We characterized suspended solids in effluents from baitfish ponds and evaluated changes in suspended solids in drainage ditches. We also characterized drainage ditches based on width, depth, slope, and percent vegetation cover. Average (± SD) total suspended solids (TSS) at the point of discharge was 52 (± 41) mg/L, while volatile suspended solids (VSS) averaged 22 (± 23) mg/L. Screening effluents did little to alter their composition. Approximately 76% of TSS were less than 5 μm. There were no significant changes in effluent solids along drainage ditches 100 m from the point of discharge and no significant correlations between ditch characteristics and changes in either TSS or VSS. Existing ditches are quite variable and are not necessarily effective in removing solids present in baitfish effluents. Screening and use of ditches as settling basins seem impractical for effluent treatment given the characteristics of solids in baitfish effluents.     

Treatment of hatchery wastewater by a sequencing batch reactor process

After settling pretreatment, the primary sludge wastewaters from a fish hatchery were treated in three five-litre bench-scale sequencing batch reactors. The sequencing batch reactors were operated concurrently under the same operating conditions. A cycle of 24 hours was adopted during the course of this study. Two different temperature regimes (22°C and 10°C) were employed, and a range of initial BOD₅ concentrations was treated. The results showed the occurrence of very high reductions in BOD₅ and COD concentrations, and very high removal of ammonia---nitrogen and suspended solids. The average five-day BOD₅ reduction was 98% for high influent concentrations, while the reduction for lower influent concentrations was 95%. The average five-day BOD₅ concentration for the effluents was less than 100 mg litre⁻¹. Nitrification was pronounced after 40 days of reactor operation. Denitrification occurred when the reactors were fed wastewaters with high BOD₅ concentrations, although it was not observed with low influent BOD₅ concentrations or at low temperatures (10°C). The overall treatment efficiency remained very high when the reactors were operated under a low temperature regime (10°C).     

Directly counted bacteria in a trout farm and its effluent

Abstract. Directly counted bacteria increased in abundance in water passing through a trout farm in north-east England and were not removed by a settling lagoon. Total bacteria in the effluent were such that they might potentially bring about immediate increase in the bacterioplankton populations of recipient rivers. Directly counted bacteria increased cumulatively through rows of well-stocked fish ponds arranged in series, thus all ponds contributed to the increase in suspended bacteria. In contrast, bacterial numbers varied irregularly through rows of low-density stocked and fallow ponds. The increase in bacteria in well-stocked ponds was greatest shortly after the daily feeding time.     

Water quality and sludge characterization at raceway-system trout farms

Studies were conducted to characterize raceway water quality, effluent water quality, and waste solids within three, raceway-type trout farms. No significant differences were found in effluent water quality between the three farms during 7 months of monitoring. Average effluent quality over the course of the day was not found to be impaired. However, effluent quality was found to change significantly during times of feeding and harvesting. In a concrete/earthen-lined farm, normalized total suspended solids (TSS) concentrations were as high as 115 and 63 mg/l during harvesting and feeding events, respectively. Total Kjeldahl nitrogen (TKN) and ortho-phosphate (OP) also increased with higher TSS loads. The majority of particles (by weight) measured in effluent samples at all three farms were evenly divided between the smallest range (1.5–30 μm) and the largest (>210 μm). For settled sludge samples, the majority of the particles were in the size range of 1.5–30 μm. Particle size in the raceway was positively correlated with fish size during feeding events, but this correlation dissipated during the 4-h period after feeding. The accumulation and characteristics of sludge in a sediment trap were also monitored over a 22-day period.     

The start-up and saline adaptation of mesophilic anaerobic sequencing batch reactor treating sludge from recirculating aquaculture systems

Treatment of sludge from aquaculture is a matter of special importance and there is a need for salt-tolerant biological wastewater treatment to coincide with the development of brackish/marine aquaculture. The aims of the current study were to determine the ability of anaerobic sequencing batch reactor (ASBR) to anaerobically digest sludge from fresh-water recirculating aquaculture systems and the ability of adaptation to low saline conditions. The mesophilic ASBR were evaluated with loading rates between 0.12 and 0.41 g chemical oxygen demand (COD)/day at a 20-day hydraulic retention time (HRT) for start-up and with organic loading rates (OLR) of 0.39–0.41 g COD/L day at a 20-day HRT for saline adaptation. The average removal rate of total chemical oxygen demand (TCOD), total suspended solids (TSS) and volatile suspended solids (VSS) of the ASBR were above 97%, 96% and 91% during the stabilization period of the experimental reactors. The average daily gas production of ASBR was between 0.013 and 0.022 L/g TCOD from day 118. A sludge-mass reduction of up to 94 ± 2.3%, TCOD reduction of 44 ± 13% and VSS/SS of 39–70% were demonstrated for the reactor performance during the gas production period. However, the process of gas production was obviously inhibited, presumably by salt, and unstable due to the dissolved COD (DCOD), total ammonium nitrogen (TAN) and alkalinity of the effluents of the experimental reactors and TSS and sludge volume index (SVI) observed within the reactors. The daily gas production was observed to decrease during the saline adaptation period and stopped when the salinity of the effluents was higher than 8.7 ppt until the end of the experiment.     

Sydney rock oyster, Saccostrea commercialis (Iredale & Roughley), filtration of shrimp farm effluent: the effects on water quality

Shrimp pond effluent water can contain higher concentrations of dissolved nutrients and suspended particulates than the influent water. Consequently, there are concerns about adverse environmental impacts on coastal waters caused by eutrophication and increased turbidity. One potential method of improving effluent water quality prior to discharge or recirculation is to use bivalves to filter the effluent. In this study, we examined the effects of the Sydney rock oyster, Saccostrea commercialis (Iredale & Roughley), on the water quality of shrimp pond effluent. Effluent from a shrimp farm stocked with Penaeus japonicus (Bate) was pumped directly into 34-L tanks stocked with different densities of oysters. Combinations of live and dead oysters were used to test the effects of three different densities of live oysters (24, 16 and 8 live oysters per tank). The concentrations of total suspended solids, the proportion of organic and inorganic matter, total nitrogen, total phosphorous, chlorophyll a and the total number of bacteria in the pond effluent water were determined before and after filtration by oysters. The oysters significantly reduced the concentration of all the parameters examined, with the highest oyster density having the greatest effect. Shrimp pond effluent contained a higher proportion of inorganic matter (72%) than organic matter (28%). The organic component appeared to be mainly detritus, with chlorophyll a comprising only a minor proportion. Filtration by the high density of oysters reduced the effluent total suspended solids to 49% of the initial level, the bacterial numbers to 58%, total nitrogen to 80% and total phosphorous to 67%. The combined effects of settlement and oyster filtration reduced the concentration of chlorophyll a to 8% of the initial effluent value.