The algae bloom challenge to drinking water

When we turn on the tap, the water coming out has usually gone through a number of steps to be considered safe for consumption. This of course can depend on where you live in the world. Nonetheless, drinking water suppliers aim to take a raw water source, treat it until safe for consumption, and supply it to customers. Achieving the required quality requires a series of processes that vary according to the initial characteristics of the resource. When surface water is used for drinking water supply, there are a number of challenges that can affect quality such as algal blooms.

Impacts of algal blooms on drinking water

Algal blooms and growth of macrophytes (often invasive species) can be caused by eutrophication due to excessive nutrient inputs from different sources including from agricultural practices, and can be exacerbated during drought conditions and with rising temperatures. These directly affect water quality, transportation, dam operations, but also related activities like hydropower generation and recreation.

One specific hazard to water quality, in fact to whole aquatic ecosystems, are ‘Harmful Algae Blooms’ (HAB). What this term describes is a drastic increase in algae, too much for an ecosystem to handle. You probably have seen this yourself; a greenish or rusty brown pond or channel, with in-transparent water and slimy clumps of algae. These blooms are triggered by an abundance of one or several limiting factors to algae growth: sunlight, carbon dioxide and availability of nutrients (nitrate & phosphorus). Algal blooms can occur in ponds, reservoirs, streams, rivers and oceans; often on a devastating scale. So called ‘ocean dead zones’ or collapsed lake ecosystems frequently make the news (The Guardian [i]).

The problems with such harmful algal blooms are twofold:

During decomposition of algae most dissolved oxygen is used up by bacteria, therefore the majority of living organisms suffocate and die.
Blue-green algae contain cyanotoxins, which can be dangerous for humans and in extreme cases cause death.

What leads to HABs?

During dry periods the concentration of nutrients often increases due to low flows, on the other hand during heavy rainfall events large amounts of sediment are flushed into water systems. Both events become more frequent due to climate change; together with higher temperatures. The use of synthetic fertilizer in agriculture, as well as increased sewage due to population growth and extensive livestock farming are additional risk factors. Environmental conditions which lead to harmful algal blooms are becoming more likely in many parts of the world.

What are the impacts of HABs?

Algal blooms can lead to a number of severe impacts:

‘Dead zones’ destroying aquatic ecosystems at massive scale;
poisoning of fish and sea food;
toxic contamination of surface- and groundwater reserves;
disruption of drink water supply;
death and severe illness of animals and humans; and
loss of livelihoods and economic damage.

Achieving the Sustainable Development Goals (SDGs) including those related to health (SDG 3), clean water & sanitation (SDG 6), and life below water (SDG 14) means that these impacts from algal blooms need to be addressed. Scientists around the world therefore demand more attention for the nitrogen pollution crisis. We must reduce the amount of nitrogen released to the environment. We need more efficient agricultural practices and protection of water systems in order to reduce the risks of HABs. Once an algal bloom occurs, little can be done to stop it. The prevention of HABs is therefore very important.

Water treatment plants face the difficult task to not only reduce turbidity and remove algae and toxins, but doing so in a safe and cost-effective way. Suspended solids interfere with water disinfection because the particles act as shields for pollutants like bacteria.

The following examples illustrate the risks associated with algal blooms in drinking water supply systems:

Lake Erie – Ohio, USA

In 2014 a HAB event in Lake Erie left more than 400.000 people in the city of Toledo without safe water supply for two days. The toxic algae overburdened the local drink water supply utility and made their way into the water supply system. A public allocation of $US 4 million for water treatment chemicals was required to cope with the contamination[ii].

Waco, Texas, USA

Treatment costs for drinking water supply related to algae in Waco, Texas between 2002 and 2012 accumulated to estimated cost of $70.4 million for improving the taste and odour of tap water. Potentially $6.9 million to $10.3 million were lost in revenue during this time (Dunlap et al. 2015).

Auburn, New York, USA

Cyanoalgal toxins are so costly to remove because conventional treatment is usually not sufficient and advanced treatment processes must be implemented. For the city of Auburn’s plant the cost of installing blue-green algae toxin treatments will likely be between $1.5 million and $15 million[iii].

England and Wales:

The annual costs of freshwater eutrophication in England and Wales to be $105-160 million yr-1 (£75.0-114.3 m). Policy response costs for addressing the damage thereby amount to $77 million yr-1 (£54.8 m). These costs account for (among others) reduced value of waterfront dwellings, reduced recreational and amenity value of water bodies, and drinking water treatment costs for removal of algal toxins[iv].

All these examples show the costs and obstacles that water treatment plants face in order to handle HABs. Due to the nature of algae, problems with cyanotoxins generally occur during night, making immediate response often difficult and expensive. It is therefore cheaper for utilities to plan ahead[v].

What are the solutions?

The root cause of the problem is what really needs to be addressed, which is the need to reduce the amount of nitrogen used to produce our food! Only by reducing and controlling the discharge of manure and fertilizer into the environment can we protect ecosystems and reduce the occurrence of harmful algal blooms.

Since this is a necessary, but rather a difficult goal to achieve; we need to develop ways to address the ongoing problem. One way to cope with HABs in drinking water resources is being able to forecast algal bloom events. Using monitoring tools that draw on satellite technology, blooms can be predicted and water treatment plants can prepare accordingly.

The EU-funded SPACE-O project currently develops tools to forecast algal blooms and high turbidity events. These tools are designed for water treatment utilities to forecast water quality in order to take preventive measures or adjust their treatment processes. The root cause still needs to be addressed to sustain the ecosystem which we rely on to provide water. However using such technology can help in tracking impacts of reducing nutrient inputs on the water supply, as improving the operation of water treatment plants, and therefore the safety of our drinking water.

References and resources

Dunlap et al. 2015. A Costly Endeavor: Addressing Algae Problems in a Water Supply, Catherine R. Dunlap; Karen Seligman Sklenar; Laura J. Blake, First published: 1 May 2015

EPA – Harmful Algal Blooms & Drinking Water Treatment (https://www.epa.gov/water-research/harmful-algal-blooms-drinking-water-treatment)

Hans W. Paerl, Valerie J. Paul, 2012. Climate change: Links to global expansion of harmful cyanobacteria, Water Research, Volume 46, Issue 5, Pages 1349-1363, ISSN 0043-1354. (http://www.sciencedirect.com/science/article/pii/S0043135411004386)

J.A. Westrick in H. K. Hudnell 2008, Cyanobacterial Harmful Algal Blooms: State of the Science and Research Needs, Advances in Experimental Medicine and Biology – Volume 619, Springer