Case Study: A Residential Septic System Affected by Home Hemodialysis

Case Study: A Residential Septic System Affected by Home Hemodialysis

The University of Minnesota Onsite Sewage Treatment Program assessed a residential septic system in Minnesota owned by a patient undergoing home hemodialysis treatment for kidney failure to evaluate the wastewater being generated by the household and determine whether the composition of this wastewater has the potential to affect the function of the septic system.

A site assessment and sampling for general wastewater constituents was done and showed higher-than-normal concentrations of total suspended solids at 142 mg/L, total Kjeldahl nitrogen at 132 mg/L and biochemical oxygen demand at 198 mg/L. Chloride and sodium were also found to be at higher-than-normal levels: 1,250 mg/L and 742 mg/L, respectively. However, it is suggested that more data must be collected on this subject to observe any trends and further this research. 


The two wastewater streams produced by home hemodialysis are reverse osmosis reject water and a post-dialysis effluent called dialysate. In this system, the two streams are combined at the output point. Fresh dialysis solution has a high concentration of sodium and chloride, and because of this, the dialysate dialysis solution is also high in sodium and chloride. If a patient is discharging this waste to his or her septic system, these high concentrations have the potential to negatively affect the function of the system. The reverse osmosis water is not harmful to a septic system because it is considered clean. The only concern would be that, depending on a patient’s treatment plan and schedule, a septic system may not be designed for the additional flow.

Many patients plumb their dialyzer directly into their home plumbing. Wastewater is usually discarded directly into the toilet and flushed. There is no published documentation about this issue but the general recommendation by septic professionals is that hemodialysis patients who are living in residences served by soil-based wastewater treatment systems should be separately capturing the dialysate solution and discharging it into a belowground rock pit to ensure there is no extra strain on the system.

Site information

The homeowners involved in this project volunteered their septic system for assessment and testing. There is a 1,500-gallon septic tank from which the wastewater flows via gravity to rock trenches. The system is sized appropriately for the number of bedrooms and soil conditions. There is a demand-based water softener. It was estimated that the septic tank was last cleaned in early April 2018.

The homeowner's hemodialyzer is plumbed directly into the toilet.
The homeowner's hemodialyzer is plumbed directly into the toilet.

The dialysis patient living in the home began home hemodialysis in May 2018. He undergoes hemodialysis about five times per week with a treatment time of approximately three hours per treatment. Thirty liters (8 gallons) of dialysate are used per treatment. The hemodialysis machine gets cleaned about two or three times per month. The homeowner uses 120 milliliters (0.03 gallons) bleach water solution to clean the plastic dialysis lines. This particular dialysis machine is plumbed into the home’s water supply and discharges into the toilet.

Results and Discussion

Septic system

Using a sludge judge to measure, the depth of the water in the septic tank was about 48 inches and there was about 8 inches of sludge on the bottom of the tank and minimal scum. The inspection caps in the drainfield were removed from all visible inspection pipes and were all observed to be dry.


Wastewater Parameters of Septic Tank Effluent at Hemodialysis Site
Wastewater Parameters of Septic Tank Effluent at Hemodialysis Site

Total Kjeldahl nitrogen is the combination of organic nitrogen, ammonia and ammonium nitrogen. The primary source of nitrogen in septic system wastewater is urine. The other sources of nitrogen are digested and undigested food and commercial cleaners. TKN concentrations at this site were 132 mg/L, which is high for typical domestic wastewater that averages 40-100 mg/L.

Biochemical oxygen demand is the amount of dissolved oxygen consumed by microorganisms that are breaking down organic matter in wastewater. This was measured in the study because it is an indicator of waste strength. Typical strength for domestic wastewater in a septic tank is 140-200 mg/L of BOD. BOD concentrations were above expected at 198 mg/L with two people residing in the home and a 1,500-gallon septic tank. This could be a result of higher levels of glucose due to the dialysate entering the system, but it is not high enough to be of concern.

Total suspended solids are a measure of the solids that remain in the wastewater after settling has occurred in the septic tank. TSS is also a measure of waste strength. Typical TSS for residential septic tank effluent is 50-100 mg/L. TSS concentrations were high for this site at 142 mg/L, particularly with two people residing in the home and a 1,500-gallon septic tank.

Fecal coliform
Fecal coliform bacteria are indicator bacteria common to the digestive systems of warm-blooded mammals. This analysis was performed to determine the overall bacterial count in the wastewater. The fecal coliform concentrations were reported from this sampling event as too numerous to count. This indicates the laboratory did not sufficiently dilute the wastewater prior to analysis, but the bacteria count is still noted to be numerous.

Sodium and chloride
Sodium concentrations at this site were 742 mg/L and chloride concentrations were 1,250 mg/L; both are higher than normal. These high concentrations could be caused by the composition of the dialysate solution and the water softener.

Total phosphorus
Phosphorus in wastewater comes from feces, detergents and other household cleaning supplies. Total phosphorus concentrations at this site were 7.3 mg/L.


As a result of the higher than normal TKN concentrations, it is recommended that the homeowner not dispose of any undigested food into the system, evaluate all cleaners and remove those that contain ammonia or nitrogen. It could also be helpful, because of the higher than normal levels of BOD and TSS, to evaluate if there are any sources of organic material that can be reduced, such as a garbage disposal. Over time, if the levels stay high, it could plug up the soil treatment area. It would also be helpful, in order to reduce TSS, to add an effluent screen on the outlet of the septic tank. 

High sodium and chloride concentrations can affect the function of the septic system by potentially killing or changing the organisms that the system needs to function properly. The septic system can also be negatively affected by these high levels because they could potentially foster organism overgrowth either in the tank or downstream. To help minimize the potential effect of the water softener, it is recommended to have it adjusted to regenerate less frequently, not run the discharge to the septic system or discontinue use.

The general recommendation for home hemodialysis patients is to not discharge post-dialyzer effluent to the septic system because the high saline content of the fluid could affect proper wastewater treatment. For this specific site, there were no signs of impact in the drainfield, but with continued use, it is possible. Due to the elevated wastewater constituents resulting from this sampling event, more sampling is needed to determine if these results are consistent. 

For a full version of the research report please see

About the author
Sara Heger, Ph.D., is an engineer, researcher and instructor in the Onsite Sewage Treatment Program in the Water Resources Center at the University of Minnesota. She presents at many local and national training events regarding the design, installation and management of septic systems and related research. Heger is education chair of the Minnesota Onsite Wastewater Association and the National Onsite Wastewater Recycling Association, and she serves on the NSF International Committee on Wastewater Treatment Systems. Ask Heger questions about septic system maintenance and operation by sending an email to


Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.