Removing solubles dissolved in water is tough but not impossible. What if you could remove salt from sea water by just dosing a chemical into a tank of sea water or even into the ocean itself!
Removing Nutrients, Nitrogen and Phosphorus that dissolve into water is as difficult as removing dissolved salt. Along with CO2, nutrients are the main inputs for photosynthesis. Promoting photosynthesis in water lets the photosynthetic organisms consume nutrients and CO2 and convert them into carbohydrates, proteins, lipids and so on. This produces huge amounts of oxygen. All the oxygen in the atmosphere has been produced by photosynthesis and only by photosynthesis, there is no other process that produces oxygen. Thus the C in CO2 is converted into organic carbon compounds with the help of N & P and O2 is released into the atmosphere.
Photosynthetic organisms are primary producers i.e., organisms that convert inorganic chemicals into organic compounds. While on land grass, plants and trees are the primary producers, in water micro-algae and grasses are the primary producers and are the food for zooplankton, crustaceans, fish and whales.
If algae in general are good, why are algal blooms bad?
All algae are not equal. The fact is that Cyanobacteria or Blue Green Algae are not consumed by zooplankton and most of the other aqueous species. These can be consumed and digested only by a few fishes like Carp and Tilapia.
Diatom Algae are the last group of algae to have evolved about 200 million years ago, much later than Cyanobacteria about 3,500 mya and Green Algae about 1,700 mya. However, Diatoms are estimated to account for about 50% of all primary production in waterways, lakes and oceans. Diatoms have a silica shell unlike other algae which have a cellulose cell wall. Construction of the silica shell is estimated to consume much less energy than the cellulose cell wall. The silica shell is also transparent and allows more light to pass through, so diatoms can continue photosynthesis even when less light is available such as on a cloudy day or at greater depths. Diatoms are also easier to digest and hence are the main food for newly hatched fish and shrimp. Zooplankton and small fish cannot digest the cellulose cell walls of Cyanobacteria and thus Cyanobacteria does not support the biodiversity of a lake. Diatoms are the main food for Zooplankton and small fish that have very simple digestive systems.
The main reason why Diatoms improve water quality and why other algae spoil the water quality is that diatoms do not accumulate in the water, since they are consumed by zooplankton, small fish, crustaceans, etc. Cyanobacteria is not consumed by most fish, so it remains in the water and dies and decomposes. The accumulation and subsequent decomposition reduces the dissolved oxygen level of the water and in extreme cases, may cause a mass fish kill due to low dissolved oxygen.
CO2 in air, nutrients, Nitrogen and Phosphorus in water are regarded as pollutants and huge amounts are being spent or proposed to be spent to remove these from air and water. We must question this fundamental assumption that CO2, N and P are pollutants. After all if these are inputs for photosynthesis and why can’t we use them to grow something useful? If these ‘pollutants’ can be used to grow something useful we can benefit from them.
The total amount of CO2 released into air due to anthropogenic activity is estimated to be about 10 billion tonnes of Carbon per year. Precise estimates of total N and P released into waterways is not available but may be about 100 million tonnes of N and 30 million tonnes of P per year. The N and P can be used to capture huge amounts of CO2.
If diatoms are grown using the N and P, they would be consumed by fish and help increase fish biomass in lakes and oceans. Thus the CO2 gets converted into fish biomass.
In oceans, Whales have declined drastically over the past 100 years. The number of blue whales declined to 275 in 1960s from a peak level of 275,000. After whaling was banned in 1960s the numbers recovered to about 5,000 now. Restoring the Blue Whales back to 275,000 would require huge amounts of Krill, since this is the main food for whales and Krill feed on Diatoms.
In lakes too fish catch has declined in all polluted urban lakes such as Hussainsagar in Hyderabad and also in many rivers, such as the Ganga and Yamuna. The Ganga River Dolphin is on the endangered fish list. Growing Diatoms in lakes and rivers is the first step to restoring fish, since diatoms provide the food and oxygen required by the fish.
Sewage in India is not being treated properly and most of it is released into lakes and rivers and this causes unwanted algae and weeds like Water Hyacinth to bloom and these cause the water quality to deteriorate and fish to die off. The average nutrient level of one person’s urine is about 5 grams of N and 1 gram of P. Thus, the 130 Crore people of India produce about 6,500 tonnes of N and 1,300 tonnes of P per day. This is about two million tonnes of N per year. This may be compared to the seven million tonnes of Urea manufactured in India, N content of Urea is 46%, so this is three million tonnes of N. This is because all the N in our urine is from the food that we consume and this is obtained from the manure and fertilizers used by farmers to grow the crops we consume.
Government of India gives a subsidy of about `75,000 crores per year on fertilizers to encourage farmers to use more Urea, Super Phosphate, etc. to grow more crops to feed the increasing population. People consume the food grown and excrete nutrients and the government spends more money to ‘treat’ the sewage. Would it not be better to use the nutrients in sewage to grow food?
The nutrients excreted by people are in the urine, this is a liquid, flush toilets are the most common type of toilets, so why can’t the nutrients be collected in ponds and used to grow fish. EcoSan solutions to collect urine and use it as fertilizer in agriculture are being promoted, but manual handling of large amounts of urine would be a problem, especially when we are struggling to abolish manual scavenging.
The Swatch Bharat Abhiyan seeks to construct millions of toilets. This would result in collection of the urine and treatment of sewage using septic tanks or other means of sewage treatment. The solids in the sewage is collected in the septic tanks or STPs as sludge and the water with a lot of nutrients flows out. Thus most of the nutrients are wasted. What if the nutrients in the treated sewage can be sent to fish ponds to grow fish? The treated water from the ponds can be used to keep the toilets clean. Water availability is a key problem in the maintenance of flush toilets. This problem would be solved if the water is recycled efficiently. Increase in fish availability would greatly help improve nutrition levels in slums and villages. If the income from sale of fish can help pay for the cost of maintenance of the toilets, then this can be an excellent ‘waste to wealth’ model. If the nutrients in sewage are removed, lakes, rivers and oceans will not be polluted.
Fertilizers and manure used in agriculture and animal dung from dairy farms, poultry farms, etc., too flow into lakes, rivers and oceans and these too cause eutrophication. Growing Diatom Algae in the lakes, etc., is the best solution to remove the nutrients and keep them clean.
How to grow Diatom Algae and prevent Cyanobacteria from growing in tanks, ponds, lakes, etc.? Nualgi can respond to this. Nualgi is a nano-silica based micro-nutrient mix. It is to be poured into the water with nutrients and the native Diatoms in the water consume it and grow rapidly. Since Nualgi contains Silica and Diatoms require silica, only Diatoms consume it and other algae do not. This is an ingenious solution to grow the most useful type of algae in large waterbodies.
Nualgi is a chemical that can be poured into any lake, river or ocean to grow Diatoms to consume and remove nutrients and CO2 from the water.Bhaskar MV,
MD, Kadambari Consultants Pvt Ltd