In part one of our series on condensate management, we covered what condensate is and where it comes from. In this second part, we'll address how to dispose of it responsibly, and how to do it in a cost effective manner. To answer these questions, it's important to examine the laws governing wastewater discharge.

There are three basic methods for discharging condensate: 

1. Let it flow into groundwater/stormwater.
2. Store it in containers for pickup by a waste disposal company.
3. Direct it to a sanitary sewer for treatment at a wastewater plant.

Method 1 is common, but can be illegal in most places in the US, and is undesirable due to the stringent permitting and compliance requirements. Method 2 is expensive and logistically cumbersome.

Method 3 entails separating the water from the oil and other contaminants to the point that the water may be safely introduced to municipal (or onsite) wastewater treatment processing. This offers the best combination of cost efficiency, convenience and environmental compliance. We will focus on this method in more detail.

Discharging condensate into a sanitary sewer requires the operator of the compressed air system to be familiar with national, state, and local laws. The Federal Clean Water Act mandates that water cannot pose hazards to bodies of water. Wastewater treatment plants process the community’s wastewater before it is discharged into the environment, ensuring compliance with EPA regulations on discharges into surface waters. To meet these national standards, local treatment plants set limits on incoming contaminants to ensure they can meet the EPA guidelines. State and local governments may set their limits even stricter than Federal requirements.

For operators of compressed air systems, meeting these requirements is generally not difficult. Oil/water separators and condensate filters that collect and process condensate are readily available and are designed to comply with even the most stringent regulations. However, it's crucial to understand the specific requirements of your locality, which can be obtained by contacting the local wastewater treatment plant or visiting their website. Even if your discharge complies with regulations, a permit may still be required depending on your location and circumstances.

The primary contaminant of concern in condensate is oil, so determining the oil content is essential. This can vary depending on the compressor type and operating conditions. Lubricated piston units have high oil carry over and yield much higher concentrations of compressor oil in the condensate than fluid injected screw types. The oil carryover from a fluid injected screw compressor varies by design but is generally about 3 ppm by weight. This oil then enters the compressed air system and can be filtered out using high-efficiency coalescing filters, which remove nearly all the oil from the air. However, this oil mixes with the water collected in tanks, dryers, and filters–creating an oily water mixture that can exceed 400 mg/l in concentration. Such high oil concentrations are likely to surpass local requirements, regardless of the discharge method, and need to be treated before discharging.

Oil free screw compressors might make it seem that the condensate wouldn’t be oily, but it’s common for these compressors to have dirty condensate also. This is because hydrocarbon vapors might be in the air around the compressor, and then get ingested and concentrated in the compression process. It’s still best practice to treat the condensate from an oil free compressor system to ensure the condensate discharge is clean and within requirements.

This is where the type of condensate treatment becomes important. There are three main methods of oil/water separation:

• Gravity systems
• Filter media systems
• Evaporation systems

These have different maintenance requirements and costs, and their effectiveness may be influenced by the compressor fluid chemistry.

Gravity systems use the difference in density between oil and water to separate the two. Oil, being less dense, rises to the top of the mixture, similar to how oil separates from vinegar in a salad dressing. The top layer of oil can then skimmed off, leaving mostly water in the bottom layer for disposal. However, the effectiveness of this method depends on the oil's demulsibility—how well it separates from water. If the oil doesn’t separate well, the oil content in the effluent may still be high and above regulatory requirements. Gravity systems are less commonly used now because they require adjustment, can overflow and are not as reliable as new filtration media systems.

The final type of condensate treatment system is the evaporative system, which uses electric heaters to boil off the water, leaving only the oil behind. This method nearly eliminates the need for water discharge, as the water is released as vapor. Some systems even condense the water back into a liquid for disposal, resulting in a very clean, high-quality condensate with minimal oil traces. Its main drawbacks are the high energy costs associated with boiling water and it still requires handling of the oily remains. Due to these factors, evaporation systems are not widely used but can be effective for remote compressed air systems not accessible to any wastewater systems.

Now that we've covered the reasons and methods for condensate treatment, the next blog post will discuss how to transport the condensate from the air system to its final discharge point.

• Read part one: Introduction to condensate management
• Condensate disposal products by Kaeser 
• Contact one of our air system specialists for assistance with a project