Indiana imposes a hard limit on phosphorus. Can you meet it?

Sep 30, 2020
water testing

Does your operation discharge wastewater to a publicly-owned treatment works (POTW) in Indiana? If so, be prepared for a letter. A letter that could cost you if you aren’t prepared. Your operation will need to meet stringent new limits on nutrients, phosphorus in particular.

These limits are being imposed as part of a regional response to the excessive loads of nutrients impacting local waterways and ultimately being delivered to the Gulf of Mexico. So, how does the phosphorus discharged from POTWs in Indiana impact the waters of the Gulf? Phosphorus plays a key role in developing hypoxia, an area of ocean with critically low dissolved oxygen.

Hypoxia in the Gulf of Mexico

Hypoxia occurs in aquatic ecosystems when the oxygen concentration in the water drops to less than 2 mg/L. At this concentration, free-swimming organisms will flee and/or avoid the area. At 1 mg/L, oxygen-dependent organisms die.

Although hypoxic zones occur naturally in aquatic ecosystems, their number and extent has increased dramatically due to human activities. A large hypoxic zone was identified in the Gulf of Mexico in 1972. Its development every summer has been chronicled in the years since. It has become the second-largest hypoxic zone in the world after one in the Baltic Sea.

The primary driver of hypoxia in coastal waters is eutrophication, an excess of nutrients fueling massive primary production.


The nutrients nitrogen and phosphorus are essential for plant growth on land as well as in aquatic ecosystems. However, human activities have increased the supply of nutrients to waterways to the point that natural systems can’t cope. The primary sources of nutrients to waterways are:

  • agricultural runoff,
  • wastewater treatment effluents, and
  • the combustion of fossil fuels.

Nutrients in waterways encourage algal growth. In a balanced system, zooplankton grazes on the algae and constrain their growth. When nutrient supply exceeds the system’s ability to assimilate them, algal blooms result. Algal blooms choke out light to the water column and clog fish gills. Some types of algae produce toxins that kill fish and impact human health. When the algal die and fall to the bottom, microorganisms decompose them, using up dissolved oxygen in the process.

Nutrient-based hypoxia formation

The process of eutrophication alone does not result in the formation of a hypoxic zone. Hypoxia requires stratification – layering – of the water column. Stratification in the Gulf of Mexico begins with less dense freshwater flowing out of rivers and over the colder, denser, saltier seawater. Stratification isolates the bottom layer from the surface layer and cuts off the normal resupply of oxygen from the atmosphere.

The warm, nutrient-rich top layer encourages excessive algal growth, blooms. As the algae die, they fall to the bottom where microorganisms start the decomposition process. Decomposition consumes the oxygen in the water, leading to hypoxia.

Hypoxic zone in the Gulf of Mexico

History and extent

First observed in 1992, the size of the hypoxic zone fluctuates from year to year due to climate and weather variations. The development of the hypoxic zone is seasonal. It begins to develop as spring brings increased river inputs from snowmelt and rain upstream.

In 2017 NOAA measured the hypoxic zone in the Gulf of Mexico at 8,776 square miles (approx. 23,000 km2), an area about the size of New Jersey. It is the largest measured since dead zone mapping began in 1985.

Impacts of hypoxia

In addition to the obvious environmental impacts of a ‘dead’ zone, there are economic and community impacts as well. Hypoxia can damage important commercial fisheries in the Gulf of Mexico over the long term as food webs become disrupted, and organisms at all trophic levels are impacted. Fish, shrimp, crabs, zooplankton, and other important fish prey are significantly less abundant in bottom waters in a hypoxic zone.

Algal blooms impact tourism by restricting coastal boating, fishing, swimming, and other water recreation. NOAA, in 2014, estimated that the hypoxic zone in the Gulf of Mexico caused a loss of $82 million to the fisheries and tourism industries.

Taskforce and action plan

As the extent of the hypoxic zone increased year by year, stakeholders began seeking ways to reduce its size and severity. A task force was assembled to start the process.

The Mississippi River/Gulf of Mexico Watershed Nutrient Task Force

Established in 1997, the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force (Hypoxia Task Force or HTF) is a federal, state, and tribal partnership seeking to gain a better understanding of the causes and effects of the northern Gulf of Mexico hypoxic zone. The task force was established to coordinate activities to reduce the size, severity, and duration of the hypoxic zone and lessen its impacts.  

The Hypoxia Task Force is made up of representatives from federal agencies and the 12 states within the Mississippi/Atchafalaya River Basin (MARB). HTF members include:

  • five federal agencies:
    • the United States Environmental Protection Agency or U.S. EPA,
    • the United States Department of Agriculture,
    • National Oceanic and Atmospheric Administration (NOAA),
    • the United States Department of the Interior, and
    • the United States Army Corps of Engineers;
  • 12 states: Arkansas, Illinois, Indiana, Iowa, Kentucky, Louisiana, Minnesota, Mississippi, Missouri, Ohio, Tennessee, and Wisconsin; and
  • a representative from the National Tribal Water Council.

In 2001 the HTF set the goal of reducing the areal extent of the Gulf of Mexico hypoxic zone to less than 5,000 square kilometers by 2015. To reach that goal, the HTF estimated that loads of total nitrogen and phosphorus delivered to the Gulf of Mexico must be reduced by 45%. That goal was reassessed in 2008 and the target date to reduce the extent of the hypoxic zone was extended until 2035.

Action Plan

Releasing the first federal action plan in 2001, the HTF reassessed and updated the plan for reducing nutrient loads to the Gulf of Mexico in 2008. The action plan is based around states committing to strategies that forward the goals of the task force. Federal agencies are committed to supporting states in the prioritization of watersheds through monitoring and modeling.

A key action in the plan is for member states to develop and implement a nutrient reduction strategy for waterways that are part of the MARB. In support of the development of state strategies, in 2011, the USEPA released a memo that outlined eight recommended elements of a state framework for managing nitrogen and phosphorus pollution.

An important element of a nutrient reduction strategy is to apply limits on point source permits for municipal and industrial wastewater treatment facilities that contribute to significant nutrient loadings in targeted/priority watersheds.

Indiana’s Response to Phosphorus Concerns

While developing its nutrient reduction strategy, Indiana implemented a non-rule policy (NRP) in 2014 that requires POTWs that discharge more than 1 MGD of effluent to meet a monthly average of 1.0 mg/L TP. It also requires monitoring of TN to be included on permits. As each POTWs permit comes up for review, the new limits and monitoring requirements are included.

Indiana published its Indiana State Nutrient Reduction Strategy in 2018. The strategy represents the state’s commitment to reducing nutrient runoff into Indiana’s waterways from both point and non-point sources.

Section 6 of the strategy discusses managing point source discharges from POTWs by employing optimization techniques and by analyzing their current operation and maintenance processes to seek better nutrient removal. A key optimization technique is pre-treatment of industrial inputs to the treatment works to remove or reduce concentrations of contaminants like phosphorus before they hit the treatment plant.

A best practice management principle for managers of POTWs that must meet the 1.0 mg/L P is to impose a limit on industrial users as point source inputs to the treatment plant. Industrial users may end up paying significant fees for over-strength discharges to the sewer.

Discharge permit renewals for industrial users in Indiana

The increased focus on nutrients in POTWs effluent means increased interest in industrial wastewater. It is far easier for a POTW manager to require industrial users to reduce the inputs of nutrients to the plant than it is to optimize nutrient removal through the sewage treatment process.

In Indiana, when discharge permits come up for renewal, a hard limit on phosphorus will be imposed. Are you ready? Depending on the composition of your wastewater, phosphorus can be tricky to remove. You need a solution specifically tailored to your operation, your wastewater. MacDermid Envio has been designing wastewater treatment systems for nearly 50 years.

It starts with sampling and analyzing your wastewater or process water. MacDermid Envio then formulates the most efficient and cost-effective solution for your needs, including proprietary wastewater chemicals uniquely adapted to the specific processes and the treatment systems they deploy.

MacDermid Envio Solutions backs their systems with our customizable EnvioCARE Service Program that allows you to select from a range of wastewater and environmental systems support options, ensuring continued environmental compliance. 

MacDermid Envio takes a holistic approach to building-integrated systems with a focus on keeping clients in compliance with the lowest possible operating costs. If you are facing changing discharge limits on nutrients, contact MacDermid Envio today.