It’s becoming a trial and error process as WWTP submit plans to the DNR regarding efforts to reduce the level of phosphorous. For example, two Wisconsin counties need to tweak their current plans:
Melrose and Taylor officials will rework their sewer optimization plans and resubmit to the Wisconsin Department of Resources — a move many municipalities in the state have had to make in the wake of new regulations.
“This being new, we’re expecting these things. We expect to be working through this process with the facilities,” said Mike Vollrath, a DNR regional wastewater supervisor. “We’re getting more and more used to that ourselves.
“We’re on a learning curve with the facilities and communities.”
New phosphorus rules came into effect in 2010 after the federal-level Environmental Protection Agency pushed states to adopt more water-quality standards.
Turns out, such an effort by WWTPs has become the norm.
Over the better part of the past four decades, secondary wastewater treatment has been the norm with only a small fraction of facilities having to meet more advanced standards. However, remaining water quality concerns are making nutrient standards common place, and over the next few years advanced wastewater treatment for phosphorus and/or nitrogen nutrient removal will become the norm.
For freshwater discharges, phosphorus is typically the nutrient of concern, while for discharges that impact marine environments or groundwater, nitrogen is the nutrient of concern. In freshwater environments, phosphorus is often the limiting factor for algae growth and can have significant impact on water clarity and oxygen levels. Where these water quality concerns exist, phosphorus standards are being imposed. Standards may range from 1 mg/l down to less than 0.1 mg/l depending on the receiving water quality limitations.
Testing for phosphorous isn’t without controversy – leaving some officials doubting the new levels are obtainable.
Officials also previously have expressed concern that the new phosphorus limits are unattainable and could require new, costly plants to meet the standards.
Melrose public works superintendent Ray Knudtson said he believes the additional testing will happen in the spring, and the engineer is still in the midst of working on the new plan.
He also said some groups are working to lobby the state to slow down the implementation of the new limits to ease the impact on municipalities.
It is, however, an effort that municipalities and the DNR are working together for a common solution.
Vollrath said the DNR hopes to work with municipalities and plants to develop compliance solutions that are affordable.
“Some of the limits are very low, but with these new phosphorus rules we have we do have some alternative compliance options available,” he said. “We’re feeling we have provided some alternatives to them that are significantly lower in cost to achieve or implement.
“That’s our hopes at this time.”
The most common method to reduce phosphorous is the use of chemicals.
The most common way to convert soluble phosphorus to an insoluble form is to chemically precipitate it with a metal salt, such as alum or ferric chloride. There are a number of factors that need to be considered in selecting the best chemical or combination of chemicals, the points of addition, and the appropriate dosage of chemicals. Chemical precipitation of phosphorus is well proven and easy to install and control. With this approach, it is relatively easy to convert the majority of the phosphorus to an insoluble form.
However, the lower the phosphorus limits,the higher the chemical dose required. The downsides of chemically removing phosphorus include chemical costs, increased sludge production, and the difficulty of sludge dewatering. Chemical precipitation to low levels can be difficult if there is an unusual fraction of recalcitrant phosphorus. Accordingly, it is very important to understand the forms of phosphorus in the waste stream, particularly if you have to achieve very low levels.
Regardless of its methodology, reducing phosphorous levels is the rule. Hopefully, as time and technology progress, inexpensive solutions will become available leaving both state and local officials all on the same page.[subscribe2]