Since I did do my PhD in cyanobacteria growth and treatment optimization modeling AND work in the water treatment industry, I’m gonna share my theory as to what’s happening here and how to fix it. People are focusing on the painted bottom of the pool increasing residual heat, and while that 1/19
RIP Mark Rothko. You would have loved how the hydrogen peroxide bleach is only turning the Reflecting Pool blue around the perimeter
could contribute to faster algae growth, the real issue is nutrient eutrophication. Given warmth and light (summer), ANY water with enough nutrients will grow algae. Blue-green algae (cyanobacteria) isn’t limited by temperature and light this time of year, it’s limited by nutrient availability 2/19 (typically phosphate, sometimes but rarely nitrogen). So why, all the sudden, would it be really high in nutrients? My guess is they refilled it with city water. Washington DC like most major metropolitan areas, adds orthophosphate to the water for lead corrosion control. It works beautifully 3/19 for this, but orthophosphate is also a bioavailable form of phosphate, aka algae food! Eutrophication, the term used to describe water that is so high in nutrients it causes an explosion of algae growth leading to ecosystem disruption, is defined by water containing more than 0.03 mg/L of 4/19 phosphorus, which is equivalent to 0.09 mg/L of orthophosphate. In order for orthophosphate to reach the ends of a distribution system, water treatment plants typically dose it high enough to carry a residual between 1.0-2.0 mg/L, more than 10-20x the amount needed to cause an algae bloom. 5/19 This pool is 6.9 million gallons. Typically, only a relatively small amount of water is added to top off the pool, so orthophosphate is diluted to levels low enough for typical treatment and natural biology to handle. But because they refilled the entire pool at once, 6/19 they had high phosphate levels and caused this bloom. This theory is consistent with the fact that we ALSO saw an algae bloom in 2012 after it was entirely refilled following repairs and renovations. The bottom was still light colored then, but high nutrients lead to a bloom. 7/19 So, what could be done about it? Actually, the hydrogen peroxide was NOT a bad idea to start with, it was just poorly executed. Peroxide oxidizes cyanobacteria cell membranes and causes them to lyse VERY quickly. But, it also breaks down very fast into water and oxygen, so it has to be spread 8/19 evenly and at a high enough dose to completely kill the algae. Typically you'd want a dose of 10-20 mg/L of H2O2 depending on the bloom density. Since they used 12% H2O2, that would be at least 600-1200 gallons for this pool. I don't know how much they applied, but I doubt it was that much. 9/19 Because they only applied to the edges, and peroxide breaks down before it has time to reach the middle, as we saw it was only effective at the edges. On the bright side anyone who was worried about wildlife rest assured peroxide is one of the safest algaecides you can use since it breaks down 10/19 into water and oxygen. I would have recommend it to start with, but I would have recommended they use a stabilized form (such as sodium carbonate peroxyhydrate) labelled as an algaecide and distributed it evenly across the entire pool. But that's not enough. Even if they apply more and 11/19 manage to kill back the algae, ALL of that phosphate that was bound up inside the algae cells is immediately released BACK into the water. They will see rebound growth within a week or two. So, obviously they need to treat the cause of the problem: the phosphate. 12/19 I have seen interviews and articles claim it's not possible to remove algae to a low enough level to prevent a bloom, but this is simply not true. In fact, this is exactly what I'm working on in research and development at my company. 13/19 Phosphate removal and sequestration is done in wastewater treatment and to manage recreational and drinking water lakes and reservoirs all the time. A water treatment coagulant is all you need to achieve this. These are typically aluminum (or sometimes ferric) based coagulants that are used to 14/19 treat your drinking water before disinfection, and your wastewater before it is released into waterways. While wastewater typically only treats down to around 1.0 mg/L phosphate, lower levels are achievable with the right coagulants. The phosphate will bind to the aluminum ions, precipitate, 15/19 collect into clumps called floccs, and settle to the bottom of the pool. From here, it can be vacuumed into the filters where it can be easily removed with a backwash. So in conclusion, this problem can be solved, and would be solved if they listened to the appropriate scientists. 16/19 And while I am THOROUGHLY enjoying pointing and laughing at this administration's avoidable failures just like the rest of you, I WOULD like to see this problem solved sooner rather than later. Why? Many species of cyanobacteria are capable of producing cyanotoxins, 17/19 which can be fatal if ingested. People, wildlife, pets, all can come in contact with this water. If it contains cyanotoxins such as microcystins, which is more likely than not given it's appearance, and someone's pet dog drinks from it, it could be fatal to that dog. 18/19 A kid splashing in it could get a serious rash. Wildlife swimming in it and drinking from it are also at risk. So as funny as green water for the fourth of july celebrations might seem to you, let's hope these folks get their shit together quickly! 19/19 Also, I will coincidentally be in DC next week presenting at a water treatment conference, so if anyone in the national parks service wants some help with this issue, I'll be around!