Carbon tank backwash pathogen load

My question is to Dr John Agar. I refer to the use of carbon tanks to remove chlorine and chloramines from haemodialysis water to prevent damage to the Reverse Osmosis machine membrane. Can you provide any research material on the measurement of the pathogen load in the carbon tank backwash waters? Because I live in the countryside, I use rain water for my haemodialysis. This means I have to chlorinate it to 1.5ppm of free chlorine before I use it for dialysis. Since I am already chlorinating the water to be used, can I not return the back wash waters from the carbon tanks to my 2,200 litre chlorination tank.
I wish to do this to save water, if possible, since such water is a very precious commodity here in Australia.
Hope you can give this your considered attention.
Kind Regards,
Paul Cruice

Hi Mr. Cruise,
Dr. Agar has retired from the practice of nephrology. I sent your question to water treatment expert Matthew Arduino, MS, DrPH, FSHEA, M(ASCP), Senior Advisor, Environmental Hygiene and Infection Prevention Consultation Team, Office of the Director, Division of Healthcare Quality Promotion, Centers for Disease Control and Prevention. He responded with this:

So, let’s think about carbon tank backwash for a minute. This is assuming they already have depth filtration and some prefilters before the carbon tank. Carbon tanks are a great source nutrients for microbes and provide lots of surface area. So the backwash is going to contain lots of bacteria. It will also contain carbon fines and other particulate matter that get washed out which you wouldn’t want to go directly into your into your chlorination tank without some form of pre-treatment. If they were on a drinking water system, the carbon tank would also be adsorbing other contaminants (organic and inorganic) that may also be in the backwash at higher concentrations then what is in the incoming drinking water (at levels higher than allowable under drinking water regs)

Carbon tanks

Backwash treatment

*Treat the backwash fluid to remove particulate matter (through particulate filters) *
Cartridge filter with pressure gauges pre and post filter (change based on (∆P) have to think about filter size here.
Possibly a Carbon Block filter change based on flow meter (basically like your refrigerator) this is for potential organics and inorganics.

Hope this helps.

Unfortunately, the response does not help at all. It is obvious that Mattthew is not familiar with dialysis situations and certainly my situation which I explained in my question.
So sorry to hear Prof. John Agar is no longer responding to our questions. A great loss.

Actually, Dr. Arduino is quite knowledgeable about dialysis and water safety. He has written several articles on dialysis water that can be found at arduino m dialysis water - Search Results - PubMed.

Dr. Arduino reached out to Dr. Richard (Dick) Ward who has also published articles on water safety. His publications can be found on PubMed at ward ra dialysis water - Search Results - PubMed.

Dr. Arduino shared your question with Dr. Ward and he’s what he wrote about that conversation.

So went over my thoughts about the filtration of backwash with Dick Ward. He thought that the microbial load which could be >106-108 CFU/mL back would overwhelm the amount of chlorine being added…He thought we would also then have to add filtration for the microbes so we are actually building a more complicated water treatment system just to treat the backwash. Some of these filters are made for hospitals some are sold for faucets are advertised for 30 days but their life span varies (breakthroughs occur < 30 days). So we recommend testing if this a remediation during an outbreak in some cases these filters only last 2 weeks.

He thought that this could get a little costly (build out and then filter maintenance replacement of the different filters). also said we would also have to filter include an absolute filter (bacterial filter) because the challenge of bugs would overwhelm the amount of chlorine added to system for drinking water purposes. He thought the costs of such a filtration system would quickly get expensive to maintain. Because of the different filters they would need to change out at different frequencies (some of these are not cheap)

He was thought it would be cheaper and less complicated to either keep the GAC but do not backwash and replace the carbon beds more frequently or change to carbon block filters that do not require back washing and replace when needed. They should talk to their water treatment company.

We agree that Dr. Agar it was a great loss when Dr. Agar retired. However, after decades of caring for thousands of CKD and dialysis patients, we had to accept that he earned his retirement. Before I reached out to Dr. Arduino, I emailed him and his response was that he thought “back-washing the carbon filter is an eco-step too far.” But he suggested I reach out to others.

Thank you Beth for filling in the information for me. It seems the answer to my question really depends on the actual testing of my backwash water for the pathogen load. Dr Arduino seems to say it could be greater than 106-108cfu/ml, however my rain water is 1400cfu/ml (at 36° for 44hrs) to begin with, and this is what is used for my dialysis, but, after chlorinating this water in my separate Dialysis Tank, the cfu/ml count falls to less than 3.
Perhaps no one has actually done pathogen load tests on the backwash water, since that part of my question was not answered.

If you have any amount of iron in the water I would put the carbon in AFTER the softener.
If it is hardness and smell then it could go before the softener.