NPDES effluent guidelines: Industrial wastewater discharge

In short

  • To comply with the stringent NPDES effluent guidelines, it is vital to understand the mechanisms and interactions that affect the balance in the aquatic ecosystems
  • The NPDES effluent guidelines aims to control water pollution by regulating point sources that discharge pollutants to surface waters
  • To ensure safe quality of water, we need to consider the concentration of total suspended solids (TSS)
  • Huge cyanobacterial blooms can block sunlight from the water,  release toxins, and increase the TSS concentration

The National Pollutant Discharge Elimination System (NPDES) requires power plants in the U.S. to control their levels of harmful pollutants released in surface waters according to the specific effluent limitations.

In this article, we will explain the correlation between different pollutants and  the health of the water ecosystem, as well as their effects on the quality of water. We will discuss the major factors and risks including the water temperature and chemistry, concentration of total suspended solids, dissolved oxygen levels, pH, turbidity, and algal growth.

This knowledge can help improve the wastewater management of hydroelectric, thermal, and nuclear power plants to ensure compliance with the official pollutant limitation guidelines, standards, and NPDES permit requirements.

Electric power plants and water pollution

The NPDES effluent guidelines aims to control water pollution by regulating point sources that discharge pollutants to surface waters. Electric power plants generate significant amounts of contaminants that can have devastating effects on the water bodies and their inhabitants. For example, steam electric power plants produce the greatest amount of toxic pollutants discharged to surface waters by industrial activities.

Many of these pollutants, once in the environment, remain there for many years. This creates severe health risks for people including cancer and lowered IQ among children. They are also dangerous for the environment, causing deformities and reproductive harm among fish and wildlife. The low-income communities and minorities living in proximity to electric power plants are the most at risk from consuming the water and fish contaminated by industrial discharges.

NPDES effluent guidelines and permits

The wastewater discharge to water bodies and municipal sewage treatment systems is regulated by national standards. The requirements cover the treatment process and pollutant control technologies. The Clean Water Act (CWA) requests companies to protect public health and the environment from any harmful pollutants in water including toxic metals and nutrients. The National Pollutant Discharge Elimination System (NPDES) sets up effluent limitations to control harmful pollutants entering the surface water. EPA issues specific effluent limit guidelines for different industrial categories. The NPDES permits establish technology-based effluent limits to protect the water quality standard. Strengthening the pollutant limitation guidelines and standards (ELGs) for the steam electric power generating industry must become a priority to protect our waters and communities.

In the Final Rule, EPA establishes the first national limits for the steam electric power generating industry. It specifies the amount of toxic metals and harmful pollutants that steam plants are allowed to discharge as wastewater. The rule aims to reduce the allowed discharge of toxic metals, nutrients, and other pollutants by 1.4 billion pounds per year. It also reduces the volume of annual water withdrawal by 57 billion gallons. The resulting social costs are estimated at $480 million with monetized benefits between $451 to $566 million.

Water contamination

An increase in water turbidity often indicates potential pollution and poor water quality. Pathogens and pollutants like dissolved metals tend to attach to suspended particles in the water. Contamination with industrial nutrients like nitrates and phosphorus, pesticides, and heavy metals (e.g. mercury, lead) can be dangerous and toxic to aquatic life. Additionally, excessive nutrients stimulate the development of harmful algal blooms.

Organic materials from industrial effluent and decaying organic matter support more bacteria, protozoa, and viruses in the water. When the organic suspended solids decompose, they reduce the level of dissolved oxygen, damaging the entire ecosystem.

Suspended solids and algal growth

To ensure safe quality of water, we need to consider the concentration of total suspended solids (TSS) – any particles larger than 2 microns drifting or floating in the water column. Either from sand, sediment, and silt, or from algae and other plankton.

When the aquatic animals, plants, and algae die and decompose, they release small organic particles into the water column, increasing the TSS concentration. Chemical precipitation also contributes to the increase in suspended solids. The TSS content is a crucial factor for assessing the water clarity. With more solids, the water becomes less clear.

Changes in water chemistry

Suspended solids tend to absorb more solar radiation, heating up the water. High levels of  TSS  increase the water temperature, so the concentration of the dissolved oxygen (DO) becomes critically low. Higher water temperature triggers stratification, when upper layers of water don’t mix with the lower layers. Then, there is not enough oxygen for microorganisms in the lower layers to survive.

Algae and water quality

Algae are photosynthesizing organisms that can live in freshwater or saltwater. They vary in size – from tiny phytoplankton forms to giant sea kelp forests. All forms of algae consume nutrients from the water, increasing the level of dissolved oxygen through photosynthesis. Yet, when they die, microbes decompose their organic material in the water. This process can decrease the dissolved oxygen to critical levels.

Seaweed and kelp typically grow rooted to the seafloor. But phytoplankton and other micro-algae also live at the water’s surface or spread through the water column. Cyanobacteria, also known as blue-green algae, use special floating mechanisms to stay near the surface. Huge cyanobacterial blooms can block sunlight from the water,  release toxins, and increase the TSS concentration. If rooted vegetation or attached streambed-mat forms of algae become detached, their mass also adds to suspended solids.  This happens when they die, or if they are removed from the floor by force.

Algal blooms can be extremely dangerous to water ecosystems. When an excessive amount of algae grows quickly across the surface of a water body, it can create a massive bloom. An influx of nutrients like nitrogen and phosphorus from agricultural runoff or decomposition can trigger an algal bloom.

The impacts of climate change resulting in more extreme heat and warmer water temperatures also provoke excessive algal growth. Harmful algal blooms endanger public health and ecosystems, as they release toxins and deplete the oxygen in the water.

How to control algal blooms

Complying with the national standards and regulations for water quality requires a holistic scientific approach. The impacts of industrial wastewater on the water systems can be devastating, but there are novel technologies available to rescue the water ecosystems from long-term destruction.

Algal growth can happen naturally, often during warmer seasons. Yet, excessive growth can indicate high levels of nutrient pollution. Different algae control methods are available, but each of them has certain restrictions, which must be carefully considered before use.

Real-time monitoring of water parameters allows us to predict and prevent harmful algal blooms. Turbidity monitoring tools can determine whether the increase in suspended solids and algae is natural, or due to industrial pollution. The Ultrasonic Algae Control method is one of the safest and eco-friendly technologies, used to improve the water quality around the world for many years.

Ultrasound is highly effective for green and blue-green algae control, and harmless to fish and plants.