Settling velocity characterization of aquacultural solids

A top-loading settling column is described and used to characterize the settling properties of the solids in the discharge water from a commercial rainbow trout production facility. Mass-based and phosphorus-based settling curves are presented. The median settling velocity on a mass-basis for the settleable solids was 1.7 cm s⁻¹. The median settling velocity for the settleable phosphorus was 1.15 cm s⁻¹. Manually stripping fecal material from rainbow trout resulted in settleable solids with a median settling velocity of 0.7 cm s⁻¹. Examination of the settling velocity curves show that halving the overflow rate (OFR) from 2 to 1 cm s⁻¹ changes the removal efficiency from 0.61 to 0.73, an increase of about 20%. Halving the OFR again to 0.5 cm s⁻¹ increases the removal efficiency to 0.81, an improvement of about 11%. Settling characteristics of aquacultural solids will vary from facility to facility. The methods described in this paper can be used to perform a similar type of analysis at other aquacultural sites, which may be growing other species under different management regimes.     

牙鲆养殖循环系统中固体废物的去除研究

对自行设计的牙鲆Paralichthys olivaceus循环养殖系统采用斜板式沉淀槽、水力旋流器、泡沫分离器去除固体颗粒物的效果进行了研究。结果表明:该系统实际运行过程中,养殖槽的固体颗粒物含量小于10 mg/L;对养殖水中总悬浮固体颗粒物的去除能力,沉淀槽最强,去除量(干重,下同)为(11.3±3.5)g/d,占69.2%,水力旋流器为(4.8±1.0)g/d,占29.5%,泡沫分离器为(0.2±0.1)g/d,占1.3%;对难沉降颗粒物的去除能力,泡沫分离器较强,去除量为(4.2±1.1)g/d,占53.1%,其中挥发性悬浮固体占93.2%,沉淀槽为(3.6±0.7)g/d,占44.8%,水力旋流器为(0.2±0.0)g/d,占2.1%;牙鲆摄食饲料所产生的固体废物量(干重)约为245.8 g/kg。     

不同含固率和接种比对尾菜厌氧消化的影响

文章通过尾菜中温批式厌氧消化实验,研究不同含固率(4%,8%)和接种比(RI/S=0.8,1.0,1.2)对尾菜厌氧消化产气特性的影响。结果表明,累计甲烷产量随含固率的提高而增加,随接种比的提高而降低,在含固率为8%,接种比为0.8时,累计甲烷产量最大,达到253.81 mL·g^-1VS。含固率一定时,接种比越高,越有利于缩短厌氧消化周期,但会降低累计甲烷产量;接种比一定时,含固率越高,产甲烷延滞期越长,累计甲烷产量越高。厌氧消化第9天各处理组均开始出现不同程度的丙酸积累现象,含固率为8%,接种比为0.8时,丙酸浓度最高可达1981.522 mg·L^-1。含固率越低,接种比越高,越有利于丙酸降解。厌氧消化第33天时,各处理组丙酸全部被转化利用。     

不同品种嫩果椰水主要品质性状、矿质元素含量分析

以海南4个主栽椰子品种为试材,研究不同品种嫩果椰水基本性状间及椰水中的矿质元素(K、Ca、Na、Mg、Fe、Mn、Cu、Zn)含量间的差异。结果表明,嫩果椰子水的pH平均值为5.50～5.58;可溶性固形物含量为5.60%～7.75%;测定的8种矿质营养元素中,K含量最高,达355.93mg/kg,Na为32.70mg/kg,Ca为6.36mg/kg,Mn为2.67mg/kg。各品种间存在显著和极显著差异。3个矮种椰子品种均具有各自特点,均可作为嫩果椰子品种发展,可根据不同特色矮种椰子的观赏价值、生态价值、经济价值和营养价值,规模栽培矮种椰子,发展海南热带旅游观光农业。     

Settling velocity and particle size bioengineering parameters gathered from solids generated by wild-caught premature punctuated snake-eels (Ophichthus remiger) reared in a marine prototype recirculating aquaculture system

This research reveals the applied engineering basis for determining the particle size and settling velocity distributions of solids generated while rearing wild-caught premature punctuated snake-eels (Ophichthus remiger) in a prototype recirculating aquacultural system. Settled solids were sampled from the bottom of the rearing tanks, and suspended solids were sampled before filtration within the drum filter and analyzed to characterize their settling velocity and particle size properties. These particle properties are considered bioengineering parameters since they will provide biological information to improve engineering solutions for RAS solids removal processes. The average settling velocity for the settleable solids in the rearing tanks was 2.89 ± 0.02 cm s⁻¹, and the average particle size ranged between 7.32 ± 3.41 and 19.44 ± 8.58 mm. Suspended solids within the drum filters before filtration had an average settling velocity of 0.35 ± 0.11 cm s⁻¹ and it was found that 69.93 % of the particles size was greater than 200 μm, 15.40 % were within the range of 120 μm and 90 μm sizes, and 6.53 % were between 70 μm and 40 μm sizes. The particle physical properties, settling curves, and particle sizes curves obtained from this experience represent valuable information to be used to improve engineering design of solids handling mechanisms, especially in marine land-based systems, and in this case, applied for rearing wild-caught punctuated snake-eels. The present investigation constitutes an advance in the knowledge of applied engineering to the design of a marine aquaculture fattening operation targeted to feed up wild-caught premature punctuated snake-eels to the point of sale or trade.     

The use of clarifiers to remove and control the total suspended solids in large-scale ponds for production of Litopenaeus vannamei in a biofloc system

High concentrations of total suspended solids (TSS) need to be controlled, as they can affect shrimp production due to the excess of particles in the water column. Water renewal and clarification are alternatives used to reduce TSS. In order to determine the better method of TSS control, we carried out a study using water renewals and clarification on a commercial scale with nine ponds (600 m² each) in an intensive biofloc system. A total of 87 shrimp m⁻² were stocked in each unit divided into three treatments: R (water renewal), C1 (one clarifier) and C2 (two clarifiers in series). Each treatment had three replicates, and the experiment lasted 105 days. There were no significant differences (p > 0.05) in the parameters of water quality and zootechnical performance. Significant differences (p < 0.05) were observed in the performance of clarifiers (time of operation, TSS removal rate and total solids removed) and in the efficiency of water use and effluent generation. All treatments maintained controlled TSS levels, although C2 showed a better removal efficiency than C1, with percentages rates of 71.2 and 47.9%, respectively. This difference resulted in a 160-hour reduction in the total operating time in C2. Compared to the R treatment, the percentages of water saved in C1 and C2 were 50.7 and 51.3% higher, respectively, and the percentages of effluent generated in C1 and C2 were 97 and 96% lower, respectively. The use of clarifiers helps to control TSS concentrations in large-scale. In addition, they reduce both the amount of water used for renewals and the effluent discharges into the environment, thereby increasing biosafety in the biofloc system.     

Effect of Growth Season and Slow-Release Fertilizers on Quality Characteristics of Tomatoes

This study discusses the effect of growth season and fertilization on quality characteristics of tomatoes. In a pot experiment, established in an unheated glasshouse, tomatoes were grown in two widely differing soils during two different seasons (winter and summer). Conventional fertilizers, applied in two doses, and corresponding slow-release fertilizers, applied in a single dose, were used. Summer fruits contained greater lycopene content and had a more reddish coloration than those harvested by the end of winter. Slow-release fertilizers further increased lycopene content compared to the conventional fertilizers. The widely different electrical conductivities between the two soils had no effect on the lycopene content. Fertilization contributed to an increase of soluble solid content (Brix) in fruits, but there was no difference among fertilizers used. Similarly, there was no significant response of pulp pH to growth season or fertilizer treatments.     

Harvesting and postharvest handling practices and characteristics of Uapaca kirkiana (Muell. Arg.) fruits: a survey of roadside markets in Malawi

Uapaca kirkiana (Muell. Arg.), a highly valued indigenous fruit species, is being domesticated to increase its utilization in southern Africa. Vendors, who were also the fruit gatherers, that were selling U. kirkiana fruits at roadside markets in Dedza, Malawi, were interviewed on four occasions during the marketing season (October 2003–January 2004) and fruit samples were concurrently sampled from each vendor. Information was obtained on when and how the fruits had been harvested and handled. Timing of fruit harvest was based on experience, aided by indicators such as occurrence of first heavy rains, natural abscission, size and color changes. Harvesting by knocking down unripe fruits from trees was practiced throughout the␣season, but naturally abscised fruits were also gathered in December and January. Fruits harvested when mature but unripe required incubation in soil, plain and woven plastic bags or clay-pots. The incubation method changed and the duration of incubation decreased between October (3–4 days) and January (≤2 days). Fruit samples were evaluated for damage, color and soluble solids concentration (SSC). Fruit SSC and color lightness/brightness (L*) increased from 10.1 to 16.4% (P<0.01) and from 45.7 to 50.5 units, (P<0.01), respectively. Higher SSC values were generally associated (R ²=0.68, P<0.001) with increasing pulp color intensity. Cracking, at 48%, constituted the most common form of damage in sampled fruits. On average, fruits were saleable for only 3–4 days, this being attributed to inherent fruit characteristics combined with immaturity at harvest, and damage during harvesting and storage in hot dry conditions. Lack of appropriate harvesting and handling techniques were associated with fruit darkening, drying, rotting and other postharvest problems.     

Assessing the Role of a Limestone Quarry as Sediment Source in a Developing Tropical Catchment

Impact assessments on river systems of the combined effect of bed and suspended sediment loads from quarries are difficult to find. In this study, bed and suspended loads were measured to determine the impact of a 20‐ha limestone quarry on the river system of its 5,000‐ha steep, diverse land use/land cover but mostly forested catchment. A network of hydrologic and sediment monitoring instruments was deployed over the catchment during two separate study periods when sediment loadings were measured from captured storms. Results showed that the quarry stood to make a disproportionately large contribution to the catchment's estimated 2·1 Mg ha⁻¹ yr⁻¹ suspended sediment load. Large storm events contributed most of the loadings with five events supplying 92% of total loadings at the outlet. A paired method approach to compare suspended sediment loads between two subcatchments showed that during eight storm events, the quarry yielded between 2 and 49·2 Mg ha⁻¹ per event, whereas the forest never yielded more than 0·1 Mg ha⁻¹. Furthermore, the contribution of sediments from the quarry to bed load was more than 75% at a section located 1·2 km downstream. Future management activities to reduce sediment and bed loads, not only from this catchment but also from all others with similar land use/land covers, should focus on improving quarry operations. Copyright © 2014 John Wiley & Sons, Ltd.