WASTEWATER IN AGRICULTURE - Exploring The Use Of Wastewater In Agriculture - Once seen as a problem to be disposed of, municipal liquid waste is now being eyed as an option for addressing water scarcity. With food demand and water scarcity on the uptick, it's time to stop treating wastewater like garbage and instead manage it as a resource that can be used to grow crops and help address water scarcity in agriculture. Properly managed, wastewater can be used safely to support crop production — directly through irrigation or indirectly by recharging aquifers — but doing so requires diligent management of health risks through adequate treatment or appropriate use. Although more detailed data on the practice is lacking, we can say that, globally, only a small proportion of treated wastewater is being used for agriculture, most of it municipal wastewater. But increasing numbers of countries — Egypt, Jordan,, Mexico, Spain and the United States, for example — have been exploring the possibilities as they wrestle with mounting water scarcity. The reuse of wastewater for irrigation has been most successful near cities, where it is widely available and usually free-of-charge or at low cost, and where there is a market for agricultural produce, including non-food crops. But the practice can be used in rural areas as well. The important thing is that wastewater be managed adequately and safely used in a way that is appropriate to local conditions, he adds.

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Wastewater In Agriculture

Exploring The Use Of Wastewater In Agriculture

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Untreated wastewater often contains microbes and pathogens, chemical pollution, antibiotic residues, and other threats to the health of farmers, food chain workers, and consumers — and it also poses environmental concerns. A number of technologies and approaches exist that are being utilized around the globe to treat, manage, and use wastewater in agriculture, many of them specific to the local natural resource base, the farming systems in which they are being used, and the crops that are being produced.

wateronline.com

 

Once seen as a problem to be disposed of, municipal liquid waste is now being eyed as an option for addressing water scarcity

With food demand and water scarcity on the uptick, it's time to stop treating wastewater like garbage and instead manage it as a resource that can be used to grow crops and help address water scarcity in agriculture.

Properly managed, wastewater can be used safely to support crop production — directly through irrigation or indirectly by recharging aquifers — but doing so requires diligent management of health risks through adequate treatment or appropriate use.

How countries are approaching this challenge and the latest trends in the use of wastewater in agriculture production will be the focus of discussions by a group of experts taking place today in Berlin during the annual Global Forum for Food and Agriculture (19-21 January).

The event has been convened by FAO along with the United Nations University, Institute for Water, Environment and Health (UNU-INWEH), the UN's Educational, Scientific and Cultural Organization and the Leibniz Research Alliance Food and Nutrition.

"Although more detailed data on the practice is lacking, we can say that, globally, only a small proportion of treated wastewater is being used for agriculture, most of it municipal wastewater. But increasing numbers of countries — Egypt, Jordan,, Mexico, Spain and the United States, for example — have been exploring the possibilities as they wrestle with mounting water scarcity," says Marlos De Souza, a senior officer with FAO's Land and Water Division.

"So far, the reuse of wastewater for irrigation has been most successful near cities, where it is widely available and usually free-of-charge or at low cost, and where there is a market for agricultural produce, including non-food crops. But the practice can be used in rural areas as well — indeed it has long been employed by many smallholder farmers," notes De Souza.

The important thing is that wastewater be managed adequately and safely used in a way that is appropriate to local conditions, he adds.

An alternative source of a critical resource

Water is of course fundamental for food production, and the intensifying scarcity of this important natural resource — likely to be more intense in a context of climate change — has very significant implications for humanity's ability to feed itself.

Globally, population growth and economic expansion are placing increasing pressure on freshwater resources, with the overall rate of groundwater withdrawals steadily increasingly by 1 percent per year since the 1980s.

And those pressures are now increasingly being exacerbated by climate change.

Already, agriculture accounts for 70 percent of global freshwater withdrawals — with demand for food estimated to grow by at least 50 percent by 2050, agriculture's water needs are poised to expand.

Yet demand from cities and by industries is on the rise as well.

Greater use of non-conventional, alternative sources of water — including the urban effluent and farm-runoff — can help mitigate this competition, if properly treated.

In addition to helping cope with water scarcity, wastewater often has a high nutrient load, making it a good fertilizer.

"When safely used and managed to avoid health and environmental risks, wastewater can be converted from a burden to an asset," De Souza says.

Managing risks

Untreated wastewater often contains microbes and pathogens, chemical pollution, antibiotic residues, and other threats to the health of farmers, food chain workers, and consumers — and it also poses environmental concerns.

A number of technologies and approaches exist that are being utilized around the globe to treat, manage, and use wastewater in agriculture, many of them specific to the local natural resource base, the farming systems in which they are being used, and the crops that are being produced.

In Egypt, for example, where water supplies are limited and wastewater tends to be highly contaminated, constructed wetlands are proving to be a promising, economically viable approach to treatment.

In Egypt and also in Tunisia wastewater is being widely used in agroforestry projects, supporting both wood production as well as anti-desertification efforts.

In Central Mexico, municipal wastewater has long been used to irrigate crops.

In the past, ecological processes helped reduce health risks.

More recently, crop restrictions — some crops can be safely grown with the wastewater, while others cannot — and the installation of water treatment facilities have been added to the system.

In Jordan, reclaimed water represents an impressive 25 percent of all total water use in the country.

In the United States, treatment and managed aquifer recharge is a common practice, especially in the West.

Beyond helping tackle the problem of water scarcity, reducing environmental contamination, and supporting food production, infrastructure and management systems for reclaiming, treating, and re-using wastewater can be job creators, according to De Souza.

The Global Forum for Food and Agriculture, organized by the German Federal Ministry for Food and Agriculture (BMEL) takes place every year, bringing together high-level decision makers, technical experts, researchers and farmers to discuss pressing issues affecting agriculture worldwide.

The Forum's theme this year is "Agriculture and Water - Key to Feeding the World." An organizing partner of the event, FAO is taking the lead on a number of events at the Forum.

Kevin Westerling has served as the editor of Water Online, the Internet's premier source for water and wastewater solutions, since 2008. Kevin's education includes a bachelor's degree in English Literature, a minor in Journalism, and certification as a Web Content Developer. He can be reached at editor@wateronline.com.

https://www.wateronline.com/doc/exploring-the-use-wastewater-agriculture-0001

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SCHISTOSOMIASIS AND PESTICIDES - Pesticides speed the spread of deadly waterborne pathogens - Widespread use of pesticides and other agrochemicals can speed the transmission of the debilitating disease schistosomiasis, while also upsetting the ecological balances in aquatic environments that prevent infections, finds a new study led by researchers at the University of California, Berkeley. Schistosomiasis, also known as snail fever, is caused by parasitic worms that develop and multiply inside freshwater snails and is transmitted through contact with contaminated water. The infection, which can trigger lifelong liver and kidney damage, affects hundreds of millions of people every year and is second only to malaria among parasitic diseases, in terms of its global impact on human health. The study, published in the journal Lancet Planetary Health, found that agrochemicals can increase the transmission of the schistosome worm in myriad ways: by directly affecting the survival of the waterborne parasite itself, by decimating aquatic predators that feed on the snails that carry the parasite and by altering the composition of algae in the water, which is a major food source for snails. The findings come as the connections between environment and infectious disease have been laid bare by the COVID-19 pandemic, which is caused by an emerging pathogen thought to be linked to wildlife.

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Schistosomiasis And Pesticides

Pesticides speed the spread of deadly waterborne pathogens

by University of California - Berkeley

A man waters his crops near Lampsar, a community about 12 miles  from the city of Saint Louis
 in the lower Senegal River Basin in West Africa. A new study led by researchers at the
University of California, Berkeley finds that use of some agricultural pesticides can speed
 the transmission of the debilitating disease schistosomiasis, while also upsetting the
ecological balances in aquatic environments that prevent infections.

Widespread use of pesticides and other agrochemicals can speed the transmission of the debilitating disease schistosomiasis, while also upsetting the ecological balances in aquatic environments that prevent infections, finds a new study led by researchers at the University of California, Berkeley.

Schistosomiasis, also known as snail fever, is caused by parasitic worms that develop and multiply inside freshwater snails and is transmitted through contact with contaminated water.

The infection, which can trigger lifelong liver and kidney damage, affects hundreds of millions of people every year and is second only to malaria among parasitic diseases, in terms of its global impact on human health.

The study, published in the journal Lancet Planetary Health, found that agrochemicals can increase the transmission of the schistosome worm in myriad ways: by directly affecting the survival of the waterborne parasite itself, by decimating aquatic predators that feed on the snails that carry the parasite and by altering the composition of algae in the water, which provides a major food source for snails.

"We know that dam construction and irrigation expansion increase schistosomiasis transmission in low-income settings by disrupting freshwater ecosystems," said UC Berkeley's Christopher Hoover, a doctoral student in environmental health sciences and lead author of the study.

"We were shocked by the strength of evidence we found also linking agrochemical pollution to the amplification of schistosomiasis transmission."

The findings come as the connections between environment and infectious disease have been laid bare by the COVID-19 pandemic, which is caused by an emerging pathogen thought to be linked to wildlife.

"Environmental pollutants can increase our exposure and susceptibility to infectious diseases," said Justin Remais, chair of the Division of Environmental Health Sciences at the UC Berkeley School of Public Health and senior author of the study.

"From dioxins decreasing resistance to influenza virus, to air pollutants increasing COVID-19 mortality, to arsenic impacting lower respiratory tract and enteric infections — research has shown that reducing pollution is an important way to protect populations from infectious diseases."

After combing through nearly 1,000 studies gathered in a systematic literature review, the research team identified 144 experiments that provided data connecting agrochemical concentrations to components of the schistosome life cycle.

They then incorporated these data into a mathematical model that captures the transmission dynamics of the parasite.

The model simulates concentrations of common agrochemicals following their application to agricultural fields and estimates the resulting impacts on infections in the nearby human population.

The researchers found that even low concentrations of common pesticides — including atrazine, glyphosate and chlorpyrifos — can increase rates of transmission and interfere with efforts to control schistosomiasis.

Agrochemical amplification of parasite transmission was not inconsequential.

In the study communities in the Senegal River Basin in West Africa, the excess burden of disease attributable to agrochemical pollution was on par with disease caused by lead exposure, high sodium diets and low physical activity.

"We need to develop policies that protect public health by limiting the amplification of schistosomiasis transmission by agrochemical pollution," Hoover said.

"More than 90% of schistosomiasis cases occur in areas of sub-Saharan Africa, where agrochemical use is expanding. If we can devise ways to maintain the agricultural benefits of these chemicals, while limiting their overuse in schistosomiasis-endemic areas, we could prevent additional harm to public health within communities that already experience a high and unacceptable burden of disease."

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DROWNING MACHINE - THE DANGERS OF LOW HEAD DAMS - A low head dam, sometimes simply called a weir, is a small structure that impounds a small amount of water and spans the width of river or stream. Usually made from concrete, the purpose of a low head dams is to raise the water level upstream on a river. This can assist with navigation of the channel by boats, create a drop for generating hydropower, and for water supply and irrigation. Low head dams almost always have subcritical flow upstream. The flow is deep, slow, and tranquil as it makes its way to the dam. But as the flow passes over the weir, it picks up speed and becomes supercritical. When this supercritical flow transitions back to subcritical flow in the slower moving water downstream, it creates a hydraulic jump. These could pose a threat to those using the waterway for recreation. Any location with fast moving water and high turbulence can be dangerous to swimmers or kayakers, but the location of this hydraulic jump can turn a manageable risk into an almost surefire way to drown.

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 Drowning Machine : 

The Dangers of Low Head Dams

Grady Hillhouse

Practical Engineering

Dams serve a wide variety of purposes from hydropower to flood control to storage of water for municipal and industrials uses.

But when a dam’s useful purpose fades away, the structure itself still remains.

Dams come in all shapes and sizes, but contrary to what you might think, the most dangerous dams are often the smallest.

A low head dam, sometimes simply called a weir, is a small structure that impounds a small amount of water and spans the width of river or stream.

Usually made from concrete, the purpose of a low head dams is to raise the water level upstream on a river.

This can assist with navigation of the channel by boats, create a drop for generating hydropower, and make water available at intakes for water supply and irrigation.

Thousands of these structures have been constructed over the years to take advantage of natural watercourses and rivers.

The heyday of low head dam construction was actually in the 1800s when mills and factories often relied on waterpower to drive grinding wheels and other equipment.

This was at a time when moving water was the most consistent source of power available in large quantities before widespread adoption of electricity.

Most of these old mills and factories are long gone, and the ones that still survive certainly don’t depend on water for power anymore.

That means many property owners are forced to maintain these old structures that no longer have any practical use.

Or more commonly and much worse, these dams are abandoned by their owner and gradually fall into disrepair.

In the U.S., dam safety regulations focus primarily on the possibility of a dam breaching and causing a flood wave downstream.

But, because low head dams are relatively short, a breach poses minimal danger, so most states don’t keep track of these small structures.

And, especially if they’ve been abandoned, it can be difficult to enforce maintenance requirements on the owners.

But, even though they pose little danger in the event of a breach, low head dams create a public safety issue that has caused more fatalities in the U.S. than all dam failures in the past 20 years.

To understand why, we first need to know a little bit about open channel hydraulics.

If you haven’t seen my video about hydraulic jumps, I’ll summarize it here. Go back and check out that video if you want to learn more.

Open channel flow - that’s flow not confined within a pipe - has a very important property related to its velocity that governs its behavior.

Slow, tranquil flowing water is called subcritical because waves propagate faster than the flow velocity.

Fast moving water is supercritical because waves move slower than the flow velocity.

Any time a supercritical flow encounters subcritical flow, an interesting phenomenon called a hydraulic jump is formed.

Low head dams almost always have subcritical flow upstream. The flow is deep, slow, and tranquil as it makes its way to the dam.

But as the flow passes over the weir, it picks up speed and becomes supercritical. When this supercritical flow transitions back to subcritical flow in the slower moving water downstream, it creates a hydraulic jump as you can see here in my model flume.

It’s easy to see why these types of structures could pose a threat to those using the waterway for recreation.

Any location with fast moving water and high turbulence can be dangerous to swimmers or kayakers, but the location of this hydraulic jump can turn a manageable risk into an almost surefire way to drown.

The depth of the flow downstream of a dam is called the tailwater, and it controls the location of the hydraulic jump.

In my model, I can adjust the elevation of the tailwater by adding or removing these stoplogs.

When tailwater is low, the hydraulic jump forms away from the dam. This is a fully developed jump that follows the traditional shape and flow patterns.

If I send down this piece of wood as a kayaker surrogate, it experiences some turbulence as it passes over the weir and through the jump but, it doesn’t have much trouble escaping downstream.

But, as the tailwater rises the jump moves closer and closer to the dam. Eventually if the tailwater is high enough, the hydraulic jump will reach the dam.

This condition is called a submerged or drowned jump. It may look fairly innocuous, but this is when things get dangerous.

Let’s send down our kayaker surrogate to see why. A submerged hydraulic jump creates an area of recirculation immediately downstream of the dam sometimes called a “keeper” for obvious reasons.

The jet of the hydraulic jump surfaces downstream causing a boil point. Sometimes this is easy to see and sometimes it’s not.

Either way, objects or people can will only be able to escape a submerged hydraulic jump if they are able to get beyond this boil point.

And, any rescuers who approach a submerged jump from downstream run the risk of being drawing into the hydraulic themselves.

The recirculating currents that trap recreators is dangerous enough on its own but there are other factors contributing to the danger at low head dams.

These currents also trap large debris between the strong hydraulic forces and the hard concrete surface of the dam which can batter someone trapped in the keeper.

The water is often cold, increasing the potential for hypothermia and further disorientation.

The turbulence of the hydraulic jump entrains a lot of air, reducing the buoyancy of a swimmer. And, low head dams often span the entire width of the river, meaning there is no still water nearby that can be used as a safe haven.

This is exactly why the low head dam is called the perfect drowning machine. All these factors added together create a situation that’s almost impossible to survive.

There are a lot of ways to mitigate this issue. The simplest option is just to keep people away from these structures.

Some states require that exclusion zones be established to make sure that kayakers safely portage dams instead of trying to run them.

Good signage and buoys as warnings can sometimes be enough to keep people safe. Another option is to modify the structure to reduce the potential for recirculating currents.

Researchers have proposed various retrofits to existing dams to improve flow conditions when tailwater is high. Of course, the most obvious (but also most expensive) way to address the issue is to remove these dams altogether.

In many cases they are no longer serving an important role, and removing dams can help restore ecosystems and improve connectivity for aquatic species in addition to removing a hazard.

If you’re swimming or paddling on a river with a low head dam, don’t underestimate the danger of these powerful hydraulic forces.

Different flow conditions on the river can dramatically change the behaviour of the hydraulic jump, as we saw, so be careful. Thank you for watching and let me know what you think!

https://youtu.be/GVDpqphHhAE

Hey, I’m Grady Hillhouse and this is Practical Engineering! I am a husband, a professional civil engineer, and educational video producer in San Antonio, Texas.

Randall Munroe said, "You can look at practically any part of anything manmade around you and think, 'Some engineer was frustrated while designing this.' It's a little human connection." My goal for Practical Engineering is simple: to increase exposure and interest in the field of engineering.

Of course, as a civil engineer, much of my content is geared towards infrastructure and the stories behind the humanmade world we live in. I like to help people make a connection between themselves and their constructed environment. In order for people to care about infrastructure, they need to be interested in the engineering behind it and see people who are passionate about finding innovative ways to meet humanity’s basic needs. I really believe this and it’s important to me. I hope that my videos are helpful to you and encourage you to take opportunities to be an advocate for civil engineering.

https://practical.engineering/blog/2019/3/16/drowning-machine-the-dangers-of-low-head-dams