Ask An Expert 31010

State your "Ask an Expert" question
I have a problem with ammonia violations at some of my small (less than 7,500 gallons/day) extended aeration package wwtp’s that I contract operate. These plants are designed to remove an influent ammonia level in the range of 25 mg/l. However, after testing the influents at some of these small plants, I have found the influent levels to be in excess of 100 mg/l.

 
I have been in this business for 30 years, so I have extensive experience in operating WWTP's and clearly understand the nitrogen cycle and also how finicky nitrifiers can be in a WWTP. My personnel opinion on this issue is the problem lies in the design limitations of a package WWTP. I realize that nitrifiers are bacteria that prefer a place to grow vs. being free swimmers like other bacteria's, however you’re simply limited in a package plant as to what you can do. I believe the EPA is partially to blame in this situation for not recognizing the fact that new standards requiring low flow toilets, etc... be installed on new installations; however the EPA green book standards continue to use outdated information in the design of the systems. I also have a personnel pet peeve when it comes to putting a septic tank in front of an aerobic package plant as well, which is the standard operating practice in the State of Ohio since the bacteria from these "Trash Traps” (or more like septic tanks) in my opinion cause many problems in a package plant as well.
 
I am really looking for someone that has extensive background in the operation of package plants especially when it comes to schools, factories and other site specific situations which specifically bring there own set of unique circumstances to the operations of a package plant. I also believe that most of these types of installations that I have reference that as a rule the occupants simply do not use the restroom for the #2 business as much as they do the #1 business, thus the problem is compounded because of this. Maybe someone out there who operates ODOT rest areas could be of assistance. Also as a side note, I realize that nitrifiers need a source of alkalinity and for most of these systems we have 150 to 200 mg/l of alkalinity in the effluent. We have had some success of feeding sodium bicarbonate in some cases but not all. Any assistance or guidance would be greatly appreciated.

May OWEA share this question and answer with our membership/readership?
Yes
 
If you answered YES to the above question, would you like your name/facility to remain anonymous?
No


I would prefer communication via
Cell Phone, Email, Office Phone, Fax


Provide your contact method information - phone, fax, and/or cell numbers. Include your facility/organization name and address if you wish
Lonnie Mcghee
President, MTWSi
2230 James Road
Bellville, Ohio 44813
Phone/fax (419) 886-4716
Cell: (419) 565-8975
e-mail: mtwsi@aol.com

What is your position/area of expertise?
President/Owner, 30 years operators experience


Answer #1
Lonnie, I would like to refer you for assistance from my Ohio EPA DSW Technical Assistance Group who have previously done a lot of work advising ODOT with compliance problems at their small Rest Stop package plants. these small plants have very high ammonia-urine rich slightly acidic influents. I believe they worked to add chemical addition to buffer the pH to allow the nitrifiers to get back in their happy zone.

Ohio EPA Keith Kroeger  614-863-8778  614-863-8778 Keith.Kroeger@epa.state.oh.us


Keith Riley, Assistant Chief
Ohio EPA NE District Office
2110 E. Aurora Road
Twinsburg, Ohio 44087
330-963-1111
fax 330-487-0769
keith.riley@epa.state.oh.us
Answer #2

I think that Keith summarized this pretty well. I agree with his suggestion to run this question by the OEPA, DSW, TAG. I will add a few
comments:

 

  1) Both TKN and ammonia should be measured to see how much nitrogen is in organic form.

 

 

 2) pH < 7 SU hinder the maximum rate of substrate conversion for nitrification. The idea pH would be about 7.8 to 8.5 SU, and below 6.5 SU, the nitrogen greately slows or stops. Also, nitrifiers are temperature sensitive. The theta value, if I recall, is about 1.06.
Operators at some small plants have resorted to covering tanks in winter.

 

3) Nitrifiers are strict autotrophs, which require a highly oxic environment both inside the floc and in bulk liquid. The maximum rate for substrate conversion occurs at DO > 3.0 mg/l. DO greater than 4 mg/l adds little and wastes energy. Also, being strict autotrophs, nitrifiers lack the ability to store food for subsequent conversion, which means that they have to "eat what they see" at the time. This is unlike hetrotrophs, which have a storage feature - which is why contact stabilization works to convert CBOD5. As a result, temporal variations in concentration will cause substrate bleed through and effluent violations.

 

4) These factors point to the need to have a well sized bioreactor system, with adequate DO, provisions to add a source of alkalinity, and a great need for load equalization througout the day. I think that load equalization and possible bleed through during peak periods may be a factor.

 

5) Also, there is a possibility that short circuiting may be occurring.
Baffling in small systems can help provide a system that resembles mixed cells in series.

 

6) Alkalinity in the final effluent needs to be above 100 mg/l CaCO3 to avoid pH suppression.

 

7) I agree that having a trash trap ahead of a package plant is a great source of unknowns and should not be done if possible. It adds too much variability. The dilemma is finding very small screens that can work in very low flow environments. However, as a former OEPA employee, I saw more "dead" communitors than "live" ones.

 

8) One final word: Please make sure that there is enough carbon available in the wastestream to complete the denitrification process.

 

While soda ash will help balance pH, there is a possibility that there is not enough carbon to complete the nitrification process at certain times of the day.

 

In thinking further, effort should be made to inventory cleaning agents as they may behave as toxicants if introduced in inappropriate mass loadings.

 

Nitrifiers are sensitive and can be hurt easily.

 

Good Luck,

Dale E. Kocarek, PE, BCEE
President Elect, OWEA
 
 
 
 
Have an answer you would like to submit?  Email to info@ohiowea.org
 
 
 
Disclaimer: Responses to “Ask an Expert” questions represent opinions of the individual writers and shall not be construed to be those of the Ohio Water Environment Association or its officers. The Ohio Water Environment Association does not authenticate or endorse any opinion, position, or recommendation delivered or received via this process as technically accurate, appropriate, or suitable for implementation at any facility. Accordingly, the Ohio Water Environment Association shall not be held liable by any party for any information, opinion, or recommendation disclosed via the “Ask an Expert” process.
 


This section under construction.