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Cyanotoxins Have Met Their Match

In the summer of 2014, the threat of algal blooms made national headlines courtesy of an outbreak in Toledo, OH. Although it has been a wastewater treatment concern for years, the public reaction to the news has put nutrient removal at the top of mind for utilities across the country.

Following suit, the market has been flooded with cyanotoxin combatants. To help sift through the options, Water Online spoke with Andy McClure, Product/Marketing Manager at Jacobi Carbons, Inc. (Columbus, OH) about complying with algae regulations, how to find the ideal nutrient removal method for a given plant, and what we can learn from Australia.

What causes cyanobacteria formation in surface waters?This is a complex question. Cyanobacteria are naturally present in surface waters and have been around for millions of years. They become a problem when certain water conditions cause them to multiply to the point that visible blooms appear in surface water supplies. These conditions include the right mix of temperature, agricultural runoff of nutrients such as phosphate, and other conditions. Typically, late summer is the time of year when these conditions occur.

What are the adverse health effects associated with algal bloom?Note that it’s not the algae itself that is toxic, but the cyanotoxins metabolized within the algal cell that are harmful. And actually, the so-called “blue-green algae”

are not really algae, but single-cell bacteria that form into large mats or colonies that impart the characteristic blue-green color.

The toxins within the cyanobacteria (blue-green algae) are released into the water during the lysis (disruption) of the cells, which occurs via natural death of the algal cells, by water treatment processes such as chemical oxidation or by mechanical means (friction from the cells rubbing together). There are several cyanotoxin compounds that have been linked to liver disease (hepatotoxins), nervous system disorders (neurotoxins), and skin problems (dermatotoxins).

Do you think Toledo’s water shutdown in the summer of 2014 significantly raised awareness about the danger of cyanotoxins among the nation’s water utilities?Absolutely. While the issue of cyanotoxins is not new and has been building for some time, the event of 2014, with an impact on a major metropolitan area and the water supplies of hundreds of thousands of people, definitely thrust this issue into national news. In particular, the water utilities in the state of Ohio have been monitoring the occurrence and appearance of cyanotoxins in fresh water reservoirs, and the U.S. EPA has

Image Credit: NASA

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been working with various states besides Ohio to use satellite imaging to observe the appearance of blue-green algae in fresh water reservoirs since at least 2010. What happened in Toledo, drawing water from the western Lake Erie basin (fed by the Maumee River), has been monitored for years, but the conditions in 2014 were ideal for a rapid bloom to create the crisis in a very short time.

Since then, has the water treatment industry invested more heavily in treatment solutions?Yes, there have been efforts to quickly identify potential solutions and a number of papers have been published on the subject in the past year. Some utilities have adopted short-term measures such as increasing their dosage of powdered activated carbon (PAC) on a seasonal basis, while more permanent solutions are investigated.

What regulations have been implemented as a result of that shutdown? What requirements do they impose on water treatment in addition to the requirements that already exist?Some regulations were in place prior to the recent algal bloom issues. The World Health Organization released a provisional drinking water guideline for microcystin-LR (one of the most common cyanotoxins) in 1998. The EPA does not have a national standard yet, but did issue some health advisory levels in May 2015, and added 10 cyanotoxins to the proposed UCMR4 in December 2015.

Certain states have adopted guidelines and drinking water thresholds. In Ohio, they have established limits for four cyanotoxins. The Ohio EPA is proposing that all surface water utilities in the state monitor for cyanotoxins, to get a better idea of the scope of the problem.

What are some ways that treatment plants are handling algal bloom?One of the other techniques for handling algal toxins that has been studied is ozonation. It is a very effective method and I expect many utilities will seriously consider it. It’s possible that PAC or GAC

will complement ozone and be used as a polish step. The biggest drawback of ozone is the potential for bromate formation, but that will only be a worry if bromide is present in the water supply. As an adjunct to ozonation there is also the use of a biologically active carbon bed (granular), where good or non-toxic bacteria will grow on the activated carbon as a support and digest the organic byproducts created from ozonation.

Another method is to physically filter out the algal cells before they lyse and release the cyanotoxins. Existing processes like coagulation/sedimentation/filtration, membranes, and dissolved air flotation can remove the cells. As long as they don’t lyse, these techniques can be effective.

If the cells lyse and cyanotoxins are present, other oxidation methods besides ozone can be looked at, including potassium permanganate and chlorination. Reverse osmosis will work too, but it’s really expensive and probably would only make sense to handle other issues in conjunction with the toxins.

If the cyanotoxins have not lysed, use of potassium permanganate (widely used by many water utilities to oxidize unwanted

organics in raw water) is actually discouraged, as that can actually increase the amount of cyantoxins released by rupturing cells.

So the whole treatment scheme has to be both intelligent and based on the actual operation and situation of individual water treatment plants.

What makes activated carbon a particularly effective solution for cyanobacteria treatment?Since cyanotoxins are organic compounds, they can be removed via adsorption onto activated carbon, if the cell structure is ruptured and cyanotoxins are released in the water treatment process. Note that there are dozens of individual compounds that fall under the umbrella of “cyanotoxins” and some will adsorb more strongly than others. There is data on some cyanotoxin compounds, but not all of them to my knowledge. However, in general, they can be removed using activated carbon, which has a high surface area and pore structure that is well suited toward the adsorption of organic compounds. In some cases, municipalities already use activated carbon, whether in powdered or granular form, and thus are familiar with its uses and capabilities.

From Ohio EPA presentation in September 2015 at the Ohio AWWA conference

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It’s also important to note that there are various types of carbon out there, with different pore structures and other properties. Much of the work to date on cyanotoxins has focused on wood-based powdered activated carbon (PAC), and the meso- and macroporous nature of this type of carbon is a good fit for surface water supplies. Certain proprietary blended PACs, with a mix of micro-, meso-, and macropores, find good application when a wide mix of cyanotoxins, from lower to higher molecular weight compounds, are present.

What are the main differences between PAC and granular activated carbon (GAC)? How can they be utilized most effectively to combat cyanotoxins?PAC is especially useful for algal blooms which can form cyanotoxins on a temporary seasonal basis. PAC can be temporarily added (or its dosage increased) until after the bloom has passed. GAC forms a better “failsafe” option as it remains online at all times, but utilities need to be aware that some of GAC’s capacity can be partially exhausted by background organics in the

water, which may impact its capacity for cyanotoxins when needed. In some cases, utilities will likely consider keeping their GAC online while adding PAC up front as a temporary measure if required.

What do you see in the near future for algal bloom treatment?The development of performance data on various technologies, including activated carbon, will continue and I expect there will be some effort at the regulatory level to tie to prevention of the blooms in the first place (i.e., regulations around agricultural runoff to reduce phosphates in peak season). Like many water treatment issues, there will be no one single solution to the problem.

This has been a problem for water treatment plants in tropical and semi-tropical locations for many years. It is an extremely critical problem in Australia, for instance, and much of what we apply now in the U.S. is from lessons learned there. There has been a close cooperation for years between the American Water Works Association Research Foundation (AWWA RF) and the same body in Australia on this very issue.