The Main Source of Protein: Fish

Fish is one of the main source of protein. Bangladesh is one of the leading fish producing country among the world. Most of the cases, cultivator follows traditional methods for fish farming. They uses chemical as a growth promoter or for emergency situation which has various side effects. So with the increasing demand for fish production as a source of food, the knowledge of fish cultivation system should increase. Fish farming contains various problems specially Dissolve Oxygen (DO) problem. These problems can be eliminated by using Aeration. In our thesis, we tried to show how to do intensive fish farming by aeration process in both on grid and off grid aria. We found that if it is possible to maintain necessary Do level in the water, fish production rate will increase. In our project we did an experiment to estimate increase in DO level if water is spread in pond. Aeration is not only increase oxygen level, but also eliminates several harmful elements like ammonia gas. As the molecular mass of ammonia less than the molecular mass of atmosphere, aeration process helps to dissipate the ammonia gas. We have found that it is possible to increase fish production up to 200% to 600% than the conventional method. In our work, we have derived the formula to estimate dissolve oxygen and energy required to pump water for aeration in fish pond.From the view of climate change impact, Bangladesh is one of the most unsecure countries.

Situation will further enhanced due to unplanned and excessive dependency on fossils fuel. In our country renewable energy currently contributes only 2.89 percent of the total electricity generation. Among all the forms of renewable energy sources, solar energy has the shining prospect in our country. Government has already taken a target to increase renewable energy generation capacity to 2829.68 MW by 2021. In our country until now solar PV is being used only in light, fan and rural homes or shops but is not remarkable in industrial scale. But in big aspect we can use it in agricultural sector and hence fish farming Yet fewer using in irrigation and poultry farming but very limited in fish farming. At present formers rely on 266000 electrically power water pumps to irrigate almost 1.7 million hector land and 3 million diesel run pumps to irrigate 8.4 million acres of land by using almost a million tons of fuel. Aeration can be done in different way. By using solar PV it can introduce an economic solution. Rural areas often do not get sufficient power supply and costs of fuel are getting increasingly prohibitive. As the cost of solar panels coming down, in future each village may be able to install solar panels and be able to generate adequate power to irrigate.From the view of climate change impact, Bangladesh is one of the most unsecure countries. Situation will further enhanced due to unplanned and excessive dependency on fossils fuel. In our country renewable energy currently contributes only 2.89 percent of the total electricity generation. Among all the forms of renewable energy sources, solar energy has the shining prospect in our country. Government has already taken a target to increase renewable energy generation capacity to 2829.68 MW by 2021. In our country until now solar PV is being used only in light, fan and rural homes or shops but is not remarkable in industrial scale. But in big aspect we can use it in agricultural sector and hence fish farming Yet fewer using in irrigation and poultry farming but very limited in fish farming. At present formers rely on 266000 electrically power water pumps to irrigate almost 1.7 million hector land and .3 million diesel run pumps to irrigate 8.4 million acres of land by using almost a million tons of fuel. Aeration can be done in different way. By using solar PV it can introduce an economic solution. Rural areas often do not get sufficient power supply and costs of fuel are getting increasingly prohibitive.

As the cost of solar panels coming down, in future each village may be able to install solar panels and be able to generate adequate power to irrigate.Bangladesh is one of the leading fish producing country among the world with a total production of 41.34 MT. Figure shown the last ten years growth (average) of this sector which is almost 5.43% and government is trying to maintain this growth. In Bangladesh around 50% of farmers received experience for fish farming from their neighbor and 33% acquired by formal taking formal training provided by different organization like NGOs, DoF and BFRI. Most of them uses chemicals, artificial wave, recycling of water for their cultivation which is not reliable enough for intensive farming.From the fig: it can be shown that china is the most fish producing country of 79.389(MT) which is almost 38% of total world capita. Our neighbor country India contributes 11% with total production of 22.215(MT). Vietnam shows surprising production of 6.208 MT (3%). Where Bangladesh shares only 2% of world capita. So we have an alluring opportunity to enhance this sector.The process of maintaining or increasing water saturation level in both artificial and natural environment is called Aeration. In this process oxygenated water diverse by the circulation of water around aerator. This method effects thermal and chemical desertification. Amount of water created by this process helps to sustaining high oxygenated transmission efficiency because the new oxygenated water replaced by lower dissolve oxygenated water.We made a set up for our experimental purpose to observe the behavior of oxygen in water. For this experimental purpose we took 100 l of water in a plastic drum. We used a handmade shower to convert water into droplets so that collective surface can increase which will consume more oxygen. We circulated the water from two different heights of 1.2 m and .6 m to determine if the oxygen remains in contact with water whether DO reaches to saturation level (7.5 mg/L) fast or not. To measure the DO in water we used DO meter.

The model of DO water is PDO-519 manufactured by Lutron. While taking the data we also recorded water temperature showed in DO meter. Temperature was almost constant in both cases.In our experiment after every 50 L of water circulation, We recorded DO and list it in table in both cases. We had to circulate the water 2.5 times from height 1.2 meter and 4 times from 0.6 m meter height. From the graph we can see that water circulated from a height of 1.2m (4feet) DO saturated faster than .6m(2feet) height. From this we can calculate that if water remains in contact with more time it will absorb oxygen more and reach a saturation level very fast. From the experiment we can also conclude that oxygen absorption will less when oxygen is near to saturation level.

With the help of this data we designed our system.

To aerate a pond we will spray water in the air so that water droplets can consume oxygen from air with the help of an electric pump which will consume some electric energy. In this chapter we will calculate how much energy is needed to aerate an acre of pond with 1.5m depth. At the end of this chapter we will know how much energy can supply what amount of oxygen.

Size of pond=1 acre with 1.5 meter depth.

With the help of date we have taken from a height of 1.2m previously discussed, we will calculate our energy.

Initial DO level=5.2 mg/L

After pouring 100 L water, DO level increases to 6.7mg/L

DO increased=1.5 mg/L

So total amount of DO increase in 100 L water is=150mg.

So energy requires to increase DO 150 mg is, P=mgh==100*9.81*1.2=1177 J

So, To increase 150 mg DO, energy requires=1177 j

Therefore, 1Kg DO requires=(1177*1000)/(150*10-3)=7.8*106 J.

Discussion:

i. When water pump will be used water will rise up to 1.2m & fall down from same height. So oxygen consumption by water will be doubled.

ii. Water droplet size is much smaller in an aeration pump spray. We assume that water surface will be doubled. So consumption will also doubled

iii. In open air ponds will have DO level varying from5.5-6mg/L.

Upon the discussion we can say that oxygen consumption will be 4times than our experimental data.

As oxygen consumption increases to 4times,so energy requirement will now ¼ .

Therefore, Energy requirement for 1kg of DO is= 7.8*106 /4=1.96*106 J.

DO calculation of Pond:

For fish cultivation, optimum depth is=1.5 m.

Therefore, the volume of water for 1 acre of pond is=4046.85m2*1.5m=6.07*103 m3 =6.07*106L.

On an average Do is available in Pond is=5.7mg/L

Therefore, amount of DO available before aeration in 1 acre of pond at 5.7mg/L

is =6.07*106L*5.7*10-6kg=34.59kg.

If aeration is required up to saturation level (7.5mg/L),amount of DO will be available in 1 acre of pond is=7.5*10-6kg*6.07*106L=45.88 Kg.

So additional DO to be pumped is=45.88-34.59=10.93 kg.

Therefore energy requirement for 10.93 kg of DO is=1.96*106*10.93=21.42*106J.=6 Kwh (1j=3.6*106 Kwh).

Considering the efficiency of water pump 50%, energy requirement is=12kwh.

3.2.2 Size of solar PV, Pump & Inverter for the system

Energy requirement for the system is=12 kw-h for 1 acre of pond with 1.5m depth.

Considering inverter loss, transmission loss, we can only extract 70% of rated power of the panel. To ensure 12 kwh energy we have to supply to system is=17.14 kw-h.

Average sunshine in BD is=4.6kw-h/m2 /day, so panel size would be=3.72 Kwp to meet the desire energy.

For remaining in safe side, we suggest a panel size of=4.5 kwp.

Pump size=3 kw (1.5kw each).

Inverter size=3 kw (1.5 kw each).

Aeration is needed when dissolved oxygen (DO) level is less than 3mg/L in the pond for increasing oxygen level. Mechanical aeration which is used mixture to air and water. As a result oxygen can be absorbed into the water. Some examples are low speed surface aerator, fountains, floating surface aerators, paddlewheel aerators.Paddlewheel aerator most used in the fish pond for increasing oxygen. It used for interacts between air and water to transfer oxygen from the air. Paddle turn on by using electricity forcesA fountain aerator pumps water from water level and interacts between water and air. This process water absorbed oxygen from air. As the water is impelled into the water, it breaks small droplets. Small droplets more oxygen absorbed compared to large droplets because of small droplets have large surface area. Generally fountain aerators are used in large area. Floating surface aerators are similar to fountains, but it is not esthetic appearance compared to fountain aerators. It used for interacts between water and air from 1-2 feet of the water level.

Water is disordered at the water surface by using it. Floating surface aerators are used in small area.The low speed aerator is used for biology aeration. These devices are generated high torque. Low speed aeration used for water purification. Diffused aeration is one of the most aeration system used in pond for maintain DO level. Air is pumping by a tube or pipe and this air is released using diffuser under the water surface. Release oxygen mixture between bottom and top water level using the water column. Normally this system is used at least 6 feet depth in pond.