Phosphates are essential nutrients for animals and plants. They are commonly used in artificial fertilizers, phosphate-based detergents and are a by product of sewage treatment.
Although they make up a valuable part of the eco-system, too many phosphates in our waters can cause problems and disrupt the delicate balance of animal and plant life.
Phosphates end up in our water as run-off from agricultural sites and as part of the organic waste generated by sewage and industrial waste. Although plants need it to survive, too much speeds up eutrophication (which reduces the levels of dissolved oxygen in the water due to an increase in mineral levels).
While certain levels of eutrophication happen naturally (such as lakes developing levels of sediment), there has been an increase in levels due to human behaviour and this is having a detrimental impact on rivers, lakes and coastal areas.
Excessive phosphorous in water can lead to algal blooms, green ‘clouds’ of algae. Although these aren’t dangerous in themselves, as bacteria break down dead algae, they consume oxygen. This can create ‘dead spots’ in the water where aquatic life can’t survive due to a lack of oxygen. These algal blooms are a problem across the world, including the Lake District in England, Llyn Padarn in Wales and Forfar Loch in Scotland, which have all had to cancel water sport and swimming events due to high levels of algae in the water.
The repercussions don’t end there. Water contaminated with high levels of phosphates can be harmful to animals and humans.
How can phosphates be removed from water?
Now that there is more awareness of the impact phosphates can have on our water, more is being done to reduce it. Phosphate levels in fertilizers are being managed, and there are more checks to reduce the amount of run-off from agricultural sites and sewage treatment works.
Standards for phosphorus in UK rivers and lakes were introduced under the Water Framework Directive in 2009 and the river standards were updated in 2015. Natural England has produced ‘nutrient neutrality’ guidance for developers and farmers to calculate their levels of phosphate production, and mitigation, where there could be an effect on some of our most sensitive freshwaters.
Once phosphates have reached the water system, various methods have been employed to reduce the levels to varying degrees of success. One common method is to add chemicals such as ferric sulphate to sewage, for example, to reduce phosphate levels at the beginning of any processing. However, it is anticipated that the cost of these chemicals will rise in the future and they can also lead to an increase in iron levels, which itself may need to be addressed, making it less viable as a long-term option.
Another option is sand filtration. This still relies on adding chemicals to waste water as it enters a sewage treatment plant, but it’s then passed through vertical sand filters which can easily remove the phosphates.
Some water treatment plants use particular types of bacteria which can absorb up to 20% of their own mass in phosphates, and which are then removed from the sludge.
Is there an alternative?
These methods come with their own financial and ecological issues, and many are only suitable for use in contained areas such as water treatment plants; they don’t address the issue of agricultural run-off or other sources of excess phosphates.
One tested and developing method is the use of constructed wetlands. This is essentially a man-made reed bed which takes advantage of the natural processes to break down organic matter in the waste water.
The base of the wetland is covered with liner, which is then filled with gravel and planted with reeds (normally common river reeds). Water flows from the site and through the reed bed, where bacteria which live among the reed roots and gravel digest the phosphate.
This low-cost option is environmentally friendly and simply uses devices already at work in nature, rather than introducing further potentially harmful chemicals, while being equally as effective.
The reed beds can take many forms depending on the landscape and what kind of water needs to be treated, including vertical flow, Forced Bed Aeration™ and sludge treatment reed beds, but horizontal flow reed beds are most commonly used.
As an added benefit, the reeds themselves can have other uses – they can be turned into musical instruments, used for food, made into mats, or used as nesting tubes for solitary bees.
The future of phosphates
While the production of phosphates through the use of fertilizers and waste water treatment is now closely monitored, the volume of phosphates entering our waters will remain a problem.
Chemical and mechanical solutions have helped in the short term, but create their own issues in terms of cost, extra chemical production, and complexity of the systems.
Constructed wetlands seem to answer many of these problems – once in place, they are self-generating, using natural systems to remove phosphates from water without damaging the surrounding environment and while creating a more diverse ecological landscape.
Other mitigation may include new woodland planting, or removing land out of agricultural production to create new wildlife habitat. Natural England requires some planning applications to achieve ‘nutrient neutrality’ through the implementation of ecological mitigation.
If you require nutrient neutrality calculations or phosphate removal options for your planning application or farm use, get in touch with us on 01225 459564 or email firstname.lastname@example.org
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