Hydraulic Installation for Water Aeration

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Journal of Mechanics Engineering and Automation 3 (2013) 141-145

DAVID

PUBLISHING

Hydraulic Installation for Water Aeration Adrian Ciocanea, Sanda Budea and Andrei Dragomirescu Department of Hydraulics, Hydraulic Machinery and Environmental Engineering, University Politehnica of Bucharest, Bucharest 060402, Romania Received: January 21, 2013 / Accepted: February 26, 2013 / Published: March 25, 2013. Abstract: This paper presents some problems related to water quality and the condition of lakes in Romania, as well as methods for improving the quantity of oxygen dissolved in water. A method for water aeration and the installation used to implement it are described and the associated advantages regarding the reduction in the level of eutrophication are highlighted. The hydraulic installation for improving the quality of water from lakes, basins, reservoirs or slow flowing rivers was designed and tested in our hydraulics laboratory during a research project. It is floatable, environmentally friendly, and energetically autonomous, being powered by photovoltaic panels, which together with rechargeable batteries can assure a continuous operation. This installation could also be used in early stages of wastewater treatment. Experimental results regarding the performance curves of the hydraulic installation are also presented. Key words: Eutrophication, water aeration, GPS (global position system) monitoring.

1. Introduction The objectives of the research presented in this paper are manifold: to analyze water quality in lakes, to analyze methods for improving water quality in order to highlight the most environmentally friendly aeration processes, to design and manufacture an energetically autonomous hydraulic installation for water aeration, and to carry out laboratory tests of the installation. Water resources are the subject of increasing anthropogenic pollution from industrial or domestic sources. There are over 80,000 known natural chemicals obtained by industrial processes that can create billions of effects by combining them. Water quality, determined by analyzing the organoleptic, physical, chemical, biologic and bacteriological characteristics, may degrade due to different types of pollution: with fertilizers, bacterial, or chemical

Adrian Ciocanea, Ph.D., assistant professor, research field: hydraulic machinery and environmental engineering. Andrei Dragomirescu, Ph.D., assistant professor, research field: hydraulic machinery. Corresponding author: Sanda Budea, Ph.D., lecturer, research field: hydraulic machinery and environmental engineering. E-mail: [email protected].

asphyxiation. The forms of pollution may occur separately or together, the most frequent case. One such case is that of eutrophication, a natural evaluative process that can be enhanced by human intervention. When the metabolic chain breaks in closed water basins, bottom accumulation deposits representing secondary source of biogenic elements appear. Enrichment of water by nutrients, mainly nitrogen and phosphorus, leads to flourishing algae, excessive growth of aquatic macrophytes, a high turbidity, lack of oxygen in bottom waters of lakes and, in some cases, induces a disagreeable smell and taste of the water. Once the eutrophication has occurred, either from natural or artificial causes, water quality declines from ultraoligotrofic, oligotrophic and mesotrophic basin, to eutrophic and hipereutrofic. The environmental element to quantify the degree of eutrophication of a lake is the algal biomass, an eco-physiological indicator directly dependent on the lake condition. Blue-green algae, also known as the cianophite, or cianoprocariote cyanobacteria algae, is most common in lake water. In order to preserve water quality, relevant parameters

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Hydraulic Installation for Water Aeration

must be monitored. The main physico-chemical and biological analyzes currently made are related to: indicators of oxygen (O2 dissolved, CCO-Mn, CCO-Cr, CBO 5), indicators of the nutrients regime (ammonium, nitrites, nitrates, phosphates), plankton biocenosis (phytoplankton, zooplankton), physico-chemical and bacteriological aids (pH, CO2, alkalinity, Mn, Fe, total coliforms bacilli, etc.). These indicators may take values within certain limits, depending on which lakes fall under three categories: oligotrophic lakes, mesotrophic lakes or eutrophic lakes. The surface of the lakes in Romania, including also anthropogenic lakes, is estimated at 2,600 km2, which is about 11% of the country area. During the years, the qualities of many lakes in Bucharest and surrounding areas as well as the quality of the ground water were monitored. These waters are polluted with nutrients and it was found that many of the monitored lakes (Snagov Lake, Morii Lake, the lake in Carol Park, the lake in Tineretului Park, etc.) have serious problems due to high concentrations of nitrogen and phosphorus and large quantities of sulfur. After this introduction, regarding water quality and parameters that must be monitored, with an emphasis on the importance of dissolved oxygen and the condition of lakes in Romania, the paper is organized as follows: Section 2 discuses the aeration process and methods to improve water quality; section 3 presents the hydraulic installation for water aeration designed in the frame of a research project; section 4 presents performance curves of the installation, which were obtained experimentally and section 5 presents conclusions and suggests future work.

2. Process of Aeration and Methods to Improve Water Quality The aeration of a lake is required usually in the summer, when the exchange of water and matter between hipolimnion and epilimnion comes to a standstill. During this period, phosphorus, nitrogen and their

complex nutrient compounds that cause reactions in the aquifer environment, foster the development of blue-green algae in lakes that have a low N/P ratio. An increase in temperature coupled with an excess in nutrients can lead to a bloom in algal and plant growth, resulting in an increase in the concentration of dissolved oxygen. Later, when the algae decompose, the level of dissolved oxygen decreases. The relationship between water temperature and O2 concentration is inversely proportional. Taking into account that aquatic life is significantly influenced by stratification and by the inversion of water layers (turnover phenomenon), the methods used to improve water quality should maintain as much as possible the stability of the aquifer’s natural environment. From this point of view, global motion induced by the installation which is presented in this paper prevents phosphorus and nitrogen from becoming a source for blue-green algae bloom, which creates toxic conditions for aquatic life. By submerging the installation, a water mixing can be obtained, which allows the nutrients enter in the food chain of the lake, so that phosphorus and nitrogen levels are no longer a problem, thus the lake becomes a productive one. Biodiversity is reinvigorated, the water clears up, the level of dissolved oxygen increases, the pH value decreases as well as that of chlorophyll. Regarding the rate of fish growth, this can be approx. 15-20 times higher than before commissioning the aeration installation. Different methods for reducing the eutrophication of lakes and improving water quality are available: chemical methods (precipitation of nutrients, dredging of the anoxic sludge from the lake bottom or its inactivation); biological methods (mowing and removal of algal vegetation and even of fish, application of toxic substances, such as herbicide, algaecides, pesticides, direct manipulation of the food chain and ecological balance through the introduction of allochthonous species, etc.) and methods based on mechanical aeration.


In case of mechanical methods, studies in this field [1-7] show that refreshing the water surface can improves up to 7 times the transfer of gas into and out of the water, compared to the case when the water surface is motionless. Thus, a better oxygen absorption and elimination of methane or ammonia occurs. This paper presents two versions of a mechanical installation for water aeration: one with an axial runner, the other with two cross-flow runners. The latter version is the subject of a patent request (OSIM A00706/8.10.2012) [8]. The aeration methods—mechanical mixing, oxygen injection, air injection are closer to the natural biochemical processes, without having negative and uncontrollable effects on aquatic ecosystems. Aeration can be done by means of pneumatic oxygenation equipment with porous diffusers, mechanical aeration equipment which ensures a continuous recirculation of a quantity of water (aeration brushes, mechanical surface aerators with slow impeller and axial runner, etc.), and mixed equipment [9-12]. The installation proposed in this paper fulfills in good conditions the hipolimnetic aeration requiring. It keeps stratification, so that water temperature at the hipolimnion level does not rise significantly. It increases the oxygen level in the hipolimnion while decreases the levels of iron, manganese, hydrogen sulfide, and methane. It does not affect significantly the zooplankton populations and change the level of chlorophyll. It allows an increase in fish population in cold waters. This paper analyzes the performance of the proposed hydrodynamic hipolimnetic aeration installation, of which main feature is a continuous operation adapted to the aquatic ecosystem in which the installation is placed.

3. Hydraulic Installation for Water Aeration The proposed installation for water aeration is floatable, mobile, and energetically autonomous. Two designs of the installation are presented in Fig. 1. In the first design, the essential hydraulic elements are two

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Fig. 1 Designs of the hydraulic installation for water aeration. Left: with two cross-flow runners. Right: with one axial runner.

cross-flow runners. The runners are modified to operate at lower rotational speeds in order not to disturb the balance between the layers of the aquatic micro system, with the condition of providing exogenous

water

oxygen

(atmospheric

oxygen

2

dissolved to 50 mg oxygen/day/m ). A second design of the installation, having an axial runner [13], was also tested. The cross-flow runners of the first design are immersed into the deep water layers, from where they draw the water. The required hydraulic head is of about 5-20 mm water column. Since the water velocity at the intakes should be reduced so that the balance of the aquatic micro-system is not disturbed, the flow rate of the runners is relatively low. As a result, the installation has low power consumption: less than 100 W considering also the overall efficiency. With such a small energy requirement, the power can be successfully supplied from renewable sources, more specifically from photovoltaic panels. The installation is realized so that when water from the deeper layers is re-circulated, the degree of turbulent mixing of the water surface is minimized. The water that flows directly through the installation induces in the vicinity a secondary flow. The flow rate of this secondary flow is roughly 2-2.5 times larger than the flow rate of the direct flow. The installation was designed and manufactured at the Renewable Energy Laboratory of the Department of Hydraulics, Hydraulic Machinery and Environmental Engineering at University Politehnica

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Fig. 2 Lake condition before and after commissioning the installation.

of Bucharest. The design with an axial impeller having a diameter of 350 mm was tested in order to determine the total energy balance required for sizing the photovoltaic panels used for power supply. Fig. 2 illustrates the lake condition before and after commissioning the installation.

4. Experimental Results The hydraulic machine is driven through a gear box at low rotational speed by a brushless DC electric motor. The runner has a speed in the range of 60-70 rpm. The motor has a rated power of 112 W and is powered by rechargeable batteries which are in turn recharged by photovoltaic panels mounted on board. During normal operation, the flow rate is within 250-300 l/min. The installation is electronically controlled, so that the rotation speed of the electric motor is constant and the batteries are protected from overload. Also, the operation of the installation is monitored by GPS, the system sending SMS reports on

relevant parameters, such as rotation speed, battery status, etc. The photovoltaic panels and the rechargeable batteries were chosen so that it is be possible to store energy in batteries in order to ensure its continuous operation around the clock during the summer. For the second design, several axial runners, both with three and with two blades, and with different pitch angles were designed, manufactured, and tested. Preliminary tests were carried out first with air and then with water, in a tank with variable level. The water flow rate, Q, was determined based on the readings from a current-meter. The head, H, was determined by reading the water rise above the runner using markings on the discharge diffuser. The performance curves obtained—H(Q), P(Q), and P(n) are presented in Fig. 3. The experimental results show that the required power supply is less than 70 W at a speed of 70 rpm and a water rate flow of 270 l/min. The hydraulic installation for water aeration presented in this paper will be tested again in situ on a pond formed on a branch of Pipera River, north of Bucharest. The aim is to verify the efficiency in real operating conditions for a full cycle of one year. The subsequent analysis of the installation efficiency will confirm to what degree the beneficial effects on the aquifer environment can be achieved. It is expected that the level of dissolved oxygen in the hipolimnion will increase, while maintaining as much as possible the water stratification and temperature. At the same time,

Fig. 3 Performance curves of the hydraulic machine with axial impeller.


the levels of iron, manganese, hydrogen sulfide and methane are expected to decrease. The zooplankton populations and the chlorophyll should remain unaffected, while the fish population should increase.

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5. Conclusions

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The paper presents a hydraulic installation for water aeration designed, manufactured and tested under laboratory conditions in the Department of Hydraulics, Hydraulic Machinery and Environmental Engineering, University Politechnica of Bucharest. Preliminary results allowed the selection of an impeller which is the most appropriate in terms of hydraulic parameters and energy consumption. These operating characteristics allowed, on the one hand, to select photovoltaic panels and rechargeable batteries that power the electric motor and, on the other hand, to determine the re-circulated water volume and, therefore, to estimate the aerated water surface. Future experiments that will be carried out in situ will be dedicated especially to investigations of the influence on the aquifer environment, monitoring especially the pH level, the concentration of dissolved oxygen, and the concentration of phosphorus and nitrogen.

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[7]

[8]

[9]

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Acknowledgments This work was funded through contract No. 119 CI/2012 in the frame of the national research program “Innovation Checks” supervised by UEFISCDI.

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