Research Progress on Application of Ipomoea aquatica Floating Bed in Eutrophication Water

Research progresses on growth characteristics,application effect and optimization technology of I. aquatica floating bed were reviewed;its application problems in eutrophication water were discussed,and its application prospect was forecasted.

Influence of Organic and Inorganic Fertilizers on Floating Bed Cultivation of Okra and Cucumber during Summer Season in Southern Part of Bangladesh

Some trails were carried out with a view to evaluate the performances of organic and inorganic fertilizers on growth and yield of okra (Abelmoschus esculentus L.) and cucumber (Cucumis sativus L.) in floating bed cultivation applying water hyacinth in 2014 and 2015 at Gopalpur union under Tungipara upazila of Gopalganj district in Bangladesh. The single factor experiment was conducted following Randomized Complete Block Design (RCBD) involving four treatments with three replications viz. T1: control (without organic and inorganic fertilizer), T2: cow dung, T3: recommended dose of NPK and T4: 50% cow dung + 50% recommended dose of NPK. Different growth parameters in respect of okra grown in 2014 and 2015, the longest plant height (171.73 cm and 164.03 cm), maximum number of branches (5.67 and 5.67) and leaves (60.33 and 69.67) were found in the treatment T3. Regarding yield parameters, significantly higher number of fruits plant-1, fruit length (cm), fruit diameter (cm), individual fruit weight (g), fruits weight plant-1 (g) and yield (t·ha-1) were 24.00 & 23.33, 16.61 & 16.59 cm, 6.01 & 6.17 cm, 23.47 & 24.74 g, 617.33 & 660.33 g, 13.01 & 13.21 t·ha-1 obtained respectively grown in 2014 and 2015 by applying the treatment T3 were identically similar with those in receiving the treatment T4. The lowest output was recorded in control in both seasons for all the cases. Similar trend of growth and yield were also observed during the cultivation of cucumber under the same treatment conditions in both the seasons. Results revealed that there was no identical differences in growth and yield attributes in between the treatments T3 and T4, where as the production cost was subjected to lower in T4 compare to T3. However, from the economic point of view, the treatment T4 i.e. application of 50% cow dung + 50% recommended dose of NPK fertilizers in floating bed cultivation was exposed to be more feasible and suitable as cost effective for the growth and yield of okra and cucumber in the experimental area.

Nutrient concentration variations during Oenanthe javanica growth and decay in the ecological floating bed system

The ecological floating bed system is a natural alternative to technical methods of wastewater treatment and involves complex processes induced by plants or microorganisms in the wastewater. This study aimed to identify nutrient concentration variations during Oenanthe javanica （Blume） DC growth and decay in the ecological floating bed system. Results showed that the third-order polynomial equation was suitable to describe pollutant concentration changes, showing that the effect of O. javanica ecological floating bed system on polluted water could be divided into the purification phase and decay phase. During the purification phase, nutrient concentrations rapidly decreased because O. javanica influenced water microbial communities and water physical parameters （i.e., dissolved oxygen, pH, and temperature）, and had a direct uptake of nutrients. However, during the decay phase, nitrogen and phosphorus concentrations in the plant tissues decreased, and these lost nutrients ultimately transferred to water and led to water quality deterioration. Results also showed that the uptake and storage of O. javanica in nutrients were temporary and the plant served only as media of the nutrients removed from the water. Under these circumstances, harvesting was an appropriate intervention to improve the treatment efficiency of O. javanica ecological floating bed system.

A restoration-promoting integrated floating bed and its experimental performance in eutrophication remediation

Numerous studies on eutrophication remediation have mainly focused on purifying water first, then restoring submerged macrophytes. A restoration-promoting integrated floating bed （RPIFB） was designed to combine the processes of water purification and macrophyte restoration simultaneously. Two outdoor experiments were conducted to evaluate the ecological functions of the RP1FB. Trial 1 was conducted to compare the eutrophication purification among floating bed, gradual-submerging bed （GSB） and RPIFB technologies. The results illustrated that RPIFB has the best purification capacity. Removal efficiencies of RPIFB for TN, TP,NH4＋-N, NO3-N, CODcr, Chlorophyll-a and turbidity were 74.45%, 98.31%, 74.71%, 88.81%, 71.42%, 90.17% and 85%, respectively. In trial 2, influences of depth of GSB and photic area in RPIFB on biota were investigated. When the depth of GSB decreased and the photic area of RPIFB grew, the height of Potamogeton crispus Linn. increased, but the biomass of Canna indica Linn. was reduced. The mortalities of Misgurnus anguillicaudatus and Bellamya aeruginosa in each group were all less than 7%. All results indicated that when the RPIFB was embedded into the eutrophic water, the regime shift from phytoplankton-dominated to macrophyte-dominated state could be promoted. Thus, the RPIFB is a promising remediation technology for eutrophication and submerged macrophyte restoration.

Influence of artificial ecological floating beds on river hydraulic characteristics

The artificial ecological floating bed is widely used in rivers and lakes to repair and purify polluted water. However, the water flow pattern and the water level distribution are significantly changed by the floating beds, and the influence on the water flow is different from that of aquatic plants. In this paper, based on the continuous porous media model, a moveable two-layer combination model is built to describe the floating bed. The influences of the floating beds on the water flow characteristics are studied by numerical simulations and experiments using an experimental water channel. The variations of the water level distribution are discussed under conditions of different flow velocities（ v= 0.1 m/s, 0.2 m/s, 0.30 m/s, 0.4 m/s）, floating bed coverage rates（20%, 40%, 60%） and arrangement positions away from the channel wall（ D= 0 m, 0.1 m, 0.2 m）. The results indicate that the flow velocity increases under the floating beds, and the water level rises significantly under high flow velocity conditions in the upstream region and the floating bed region. In addition, the average rising water level value（ARWLV） increases significantly with the increase of the floating bed coverage rate, and the arrangement position of floating beds in the river can also greatly influence the water level distribution under a high-flow velocity condition（v ？0.2 m /s）.

Coupling of the flow field and the purification efficiency in root system region of ecological floating bed under different hydrodynamic conditions

The artificial ecological floating bed is a commonly adopted in situ treatment technique for repairing and purifying polluted water. The plant root system of the floating bed is the primary region to absorb and degrade the pollutant of water. Its inner flow field characteristics and the interactive water quantity with the surrounding water greatly impact the purification efficiency of the floating bed. In this paper, the particle image velocimetry （PIV） technology and the boundary velocity direct extraction method are used to study the velocity distribution of the root system region by numerical simulations and experiments in an experimental water channel. A pollution removal rate （PRR） evaluation model is built to calculate the PRR by coupling with the flow velocity field of the root system region. The variations of the total pollutant removal rate （TPRR） are discussed for different center distances （L =0.30 m, 0.45 m, 0.60 m）, flow velocities （v= 0.007 m/s, 0.015 m/s, 0.025 m/s, 0.040 m/s, 0.055 m/s, 0.070 m/s） and root system porosities （P = 54.73%, 68.33%, 79.17%）. The results indicate that the position arrangement of the floating beds influences the TPRR significantly, and the distance should be limited in a reasonable range for a high purification efficiency. Moreover, the root systems with higher porosity （P = 68.33%, 79.17%） have higher TPRR value than a lower porosity root system （P = 54.73%） within a certain flow velocity range, and the higher porosity root system has less fluctuation of the TPRR value than a lower porosity situation within a wide flow velocity range. Furthermore, under the same center distance condition, the lower flow velocity condition brings about a significantly higher TPRR value than the higher flow velocity situation.