(Click on a slide to see its full page image; press ESC to return to text)
Freshwater is one of the four pillars on which our civilization rests - the others are food, energy and the climate. Humans have adversely impacted all - in a big way - no wonder the new epoch is called the anthropocene. How long will it last? - Humans will have the control on that too!
I had looked at food in a recent blog. Water is fundamental to our survival - water is a marvel of nature with such unique properties that without these the very existence of life would not be possible. I recommend highly that you look at the Wiki article to feel amazed how this simple molecule can express myriad of such wonderful properties.
To put the subject in context, I shall take a brief historical look before discussing the present situation. Then, I shall detail a few ideas about tackling the water crisis to ensure adequate freshwater supply to all of the world population in 50 years time.
Historical Context: Climate change and water in particular have been linked to the demise of many of the great ancient civilizations. The first of the following two slides provides a summary and the second slide tells a case history of the Indus Valley Civilization (IVC) to demonstrate that these were advanced societies with well thought out and established system of civil engineering, governance etc.
IVC lasted over 6000 years - much longer than the present western civilization. I am sure the quality of life was also very reasonable - and they say that people lived peacefully with no wars.
We note that the populations in these ancient civilizations were relatively small - a few million people - and they always developed in areas where water supply would be plentiful. However, they did not have the means to shift a lot of people over vast distances to escape from natural climate changes and resulting water shortages.
Current Situation: In our technologically advanced societies, we understand the global conditions very well and have good scientific understanding of the Earth's hydrological cycle.
The amount of water in the world is fixed; freshwater is a mere 2.5% of the total. To make matters more difficult, accessible freshwater is only 0.008% of all water. (see slide).
To understand the magnitude of the problem facing the world, we need to look at the way water is used in agriculture to produce food.
Naturally, large populations settled in area that had big promise of rain-fed irrigation - water was plentiful to grow food. Then, we also learnt that irrigation is helped by drawing water from rivers and aquifers (groundwater or fossil water). Even today, 80% of the agriculture production is by rain-fed water. The three main users of freshwater - agriculture, industries and domestics - share the global freshwater supply. 70% of global freshwater is used for irrigation that produces the remaining 20% of the food. This is the biggest call on global freshwater supply and there lies the problem.
Global warming (GW) is an established fact - our Earth is heating - both land and seas. This has many consequences that are well researched and reported. For our context, the main point is that warming of the seas increases evaporation and also disturbs the exchange of energy between the oceans and the air in the atmosphere (remember that water in the oceans absorbs the greatest part of the solar energy that falls on the Earth and this energy is then redistributed through global air and water circulation patterns). Air circulation carries moist air to various parts of the globe and causes rainfall - that is responsible for 80% of food production in the world. GW is predicted to affect the way air circulates with consequences in terms of shifting rain fall patterns. Areas that currently receive large amounts of water may experience droughts; but that is where the populations are and agricultural land produces most of the food. The result will be loss of agricultural yields, famines and mass migration.
A second threat is our dependence on groundwater for irrigation and domestic use. Groundwater is water that is trapped underground in aquifers. Some aquifers are closed and are not replenished by rainwater while others do get topped up by rain. If the withdrawal rate of water from aquifers is greater than replenish rate then total amount of water available will be reduced and is indicated by the increasing depth that pipes must be dug to reach the water levels. The following slide indicates the regions of current water stress:
Climate change will affect many areas by either making them too hot to live and/or by creating drought conditions. This will result in mass migration of populations creating many social, political and financial problems. Resettling of refugees will also require additional strains on the food and water resources.
The above discussion emphasizes the need to be careful how we plan our policies and actions. Future is uncertain and climate change effects must also be taken into account in forming policies. Some common sense steps pop up:
Currently, agriculture uses 70% of the available freshwater. If we can reduce the water usage in agriculture by 20% then domestic water availability will more than double from 10% to 24%. This alone would be enough to supply potable water for 10 billion people. Good agricultural practices like drip irrigation can achieve this but are still not widely used.
Water from aquifers should only be withdrawn at rates that does not reduce the total volumes available - rate of withdrawal must not exceed recharge rate. This will impact on irrigation but must be taken into account as a prudent step.
Coastal areas have desalinated seawater to provide freshwater - desalination is a energy intensive process - and the use of fossil fuels for desalination contributes to global warming. Better technology here will help.
Water is a precious commodity and recycling of waste water is a must. Good progress has been made in the past decades in recycling technologies.
Addressing water scarcity issues: I float a few ideas in the following - with particular emphasis on water desalination processes:
a. Agriculture uses 70% of freshwater: How does one reduce the consumption of water used in agriculture? In my previous blog, I had addressed the question of sustainable food supplies. Switching our diet from animal protein to plant protein will be enormously effective and will eliminate the need to expand arable land, at the same time reducing the water requirements. I had discussed hydroponic farming that uses water (and land) extremely efficiently. 3-D printing of food holds a big promise in terms of reducing waste in food production. Reducing loss of food in storage, transportation and in homes can save up to 15%.
In traditional agriculture, drip-irrigation can save up to 50% water requirements. Drip irrigation has a serendipitous discovery that is worth recounting here:
In the 1930s, a water engineer was visiting his friend in a desert in Israel when he noticed a line of trees with one member that was much taller and more robust looking than the others. He did a little digging, literally, and found that a household water line running along the tree line had sprung a leak in the area of that one tree and was feeding it with a steady drip drip drip of water. The wet area spot on the surface didn't seem like much, but down below was a large onion-shaped area of juicy soil.
b. Drinking Water: While there is much scope of reducing the use of freshwater in agriculture - this can not be the whole solution. Many of the world's coastal areas suffer from lack of drinking water. Sea water contains about 3.5% salt and is not good for human consumption or for agricultural use. Some areas, as in the Middle East, also experience drought conditions regularly. Many urban areas, particularly in developing countries, have poor water supply systems. Currently, more than 1 billion people do not have supply of safe drinking water. The mantra for supplying potable water has to be to minimize waste, collect and recycle all available water.
Rainwater Harvesting has been practiced in semi-arid areas for centuries but has become much more common recently. Some countries require new homes to have adequate rain collection systems. Rainwater is essentially pure water and is suitable for drinking. Rainwater collected in tanks is still quite clean and is suitable for general household purpose and also for irrigation. Rainwater harvesting is an excellent example of harnessing a resource that is essentially cost free, is widely available and is already helping in mitigating water scarcity in semi-arid areas around the world.
Recycling: Recycling water makes sense. An extreme example of recycling water is at the International Space Station (ISS) where 93% of all water is recycled. Treated wastewater from residential buildings and industries can be reused for many useful tasks such as agriculture and landscape irrigation, industrial processes, toilet flushing and also recharging groundwater aquifers. Recycled water can satisfy most water demands, so long as it is adequately treated to ensure water quality appropriate for the use.
Water Desalination has long been used in water-scarce regions to increase drinking water availability. Currently, 11 billion gallons desalinated water is produced globally everyday. Water desalination (WD) not only holds great promise for solving future water scarcity problems but also it is being used for desalting brackish (moderately saline) water and for softening and removal of organics and impurities in groundwater. Unfortunately, the quality of conventional freshwater sources is being degraded by pollution etc and a process to improve general water quality is required. Membrane separation is a cost-effective way to achieve this.
In the words of John F Kennedy: If we could ever competitively, at a cheap rate, get freshwater from seawater...(this) would be in the long-term interests of humanity which could really dwarf any other scientific accomplishment.
WD can be performed either by thermal distillation or by membrane separation. The following two slides are adapted from Banat.
Thermal Distillation: Over 60% of the world's desalted ocean water is produced by boiling seawater to produce water vapour that is then condensed to form freshwater.
Thermal distillation plants produce water with salt concentrations from 5 to 50 parts per million - seawater salt content is 35000 ppm. Thermal distillation is highly energy intensive and so far the energy source has been fossil fuels which is damaging for the environment and the climate. Middle East with about 50% of the global desalination capacity has plenty of cheap oil and there has been little incentive to use renewable energy sources. In fact, it is the drought affected areas that need to desalinate water and these are the areas where solar energy is plentiful. With prices of solar cells plummeting, it is expected that solar renewable energy will replace fossil fuel for thermal distillation. Currently the energy cost is about 13 kWh or one US dollar per cubic meter of thermally desalinated water.
Membrane Separation Processes (MSP):
Nano-filtration (NF); Reverse Osmosis (RO)
Membrane separation processes (MSP) use a membrane - a filter or a semi-permeable membrane - to produce drinking water in a more cost-effective manner than thermal distillation. Water can have impurities that are either suspended (microbes, chemicals, dirt etc.) or dissolved (salt, minerals etc.). These are detailed in the following slide
For desalination where sea salt (NaCl) is dissolved in water at a concentration of 3.5% and is in ionized state, the process used is reverse osmosis (RO). RO was developed in the 1960s and represents a serious breakthrough in desalination technologies. Let me explain this in more detail:
In osmosis, two solutions with different salt concentrations and separated by a semi-permeable (also called partially or selectively permeable) membrane (SMP) have a tendency to make the concentration equal in both parts. This is achieved by the solute molecules (water in our case) passing through the SMP from lower concentration side to higher concentration side. SMP does not allow impurity molecules (salt ions in our case) to pass through - only water molecules can.
In reverse osmosis a change in the direction that salt water naturally seeks is achieved; and water molecules from high concentration (seawater side) move through the membrane to the low concentration side (pure water). This is done by applying high pressure on the seawater side of the system.
The cost of RO desalination is about half of the cost of thermal desalination; energy costs are 30% and membrane replacement costs (a typical lifetime of the membrane is 5 years) 10%. These costs have been coming down - membranes are 5 times cheaper since 1970. In traditional water-short areas the costs of desalted water are already competitive with conventional water sources.
It is hoped that with renewable energy becoming more widely available with improved affordability, water desalination will not only supply sufficient potable water to water-scarce coastal areas but also we shall be able to use brackish (less salted) water, wastewater etc. This will increase the available water pool size. Additionally, recycling of water with membrane technology holds the promise of satisfying domestic residential water requirements.
New technologies are coming up that could make filtration much cheaper and efficient. See
Final Word: I have considered the ways in which sufficient potable water can be made available to 10 billion people in about 50 years time. The technology is there already and in the future, systems will become more efficient with even lower costs. Irrigated agriculture water supply situation requires more widely adopting methods like drip-feeding, hydroponic farming that are well tested but requires better information to be made available to farmers. Switching from animal protein to plant protein will solve the water problem in a big way but this requires a change of culture and habits - these tend to be difficult asks - but one hopes that with good official backing (UN is already promoting the shift) from individual governments, people may be convinced over the next decades to consume more plant proteins.
But then one also has to ask the question - that with plentiful food and water available, why in the world today over one billion people do not have enough to eat and sufficient potable water to drink?
My biggest concern remains climate change. Shifting rainfall patterns can cause havoc for indigenous populations and forced mass migration from such areas can destabilize our already fragile geo-political order. Is it too late to do something substantial to mitigate the effects of climate change?
No comments:
Post a Comment