Solutions for reducing septicity in pumped sewer rising mains?

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As sewage is moved to treatment centres via pumped systems there is a risk of waste water becoming septic, causing odour and damage to downstream assets due to Hydrogen Sulphide emissions.

Anglian Water has many hundreds of sites where chemical dosing is used to control septicity in rising mains with long retention periods, which involves transporting large quantities of chemicals to diverse sites. Every year we build many more sites in this way.

We are looking for an innovative solution to reduce septicity in pumping mains, ideally we are looking for a method which does not involve chemical dosing.

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14 Answers

  1. The use of Bio-filtration to convert the H2S to a low percent H2SO4 and breakdown other gases such as VOC's and Mercaptains is a process that has been very successful in recent years. We use the Bio-trickling Filter for Bio-filtration that uses a tank with media that has microbial growth to break down the H2S with a pH of 1.87 to 2.25 at the bottom up to a 6-7 pH at the top of the tank. This is a very short explanation, a more detailed explanation is available at www.ecoverdetechnologies.com

     

  3. Use a clean water header tank

    Unless there is some particularly active trade effluent in the sewage the reason for septicity is due to the time stoed. Assuming the rising main has been sized correctly then this can generally only be due to a combination of the length of the main and the rate of inflow to the pumping station being low. In 1996 I built a pumping station that only operated as a backup during periods of high flow. Therefore after operation the main would remain full of effluent. As we were on a WwTW we installed a drip feed from the final effluent ring main which would cause the station to pump twice a day. This has been very successful and they have not had any septicity.

    On some recent first time rural sewerage projects where we were putting in pumping stations to pump the flow from small communities to WwTWs in adjacent communities we installed a header filled tank which would dill slowly with potable water and then discharge into the wet well and effectively flush the main twice a day

    1 Comment

    1. As per the comment to Phillip Johnston - We ​have explored ​the water flush ​system but the ​water shortages ​within our area ​mean the volume ​required is too ​great.​
      Thanks for your contribution

  4. Reducing septicity in rising mains

    If you have any simple rising mains, rather than ones with more complex vertical profiles, you might try using a compressor to add air to the main. It also keeps the main clean but there can be a problem at the receiving end as the unused nitrogen has to escape to atmosphere.

    1 Comment

  5. They contain more than 8% for beneficial bacteria. The action of these micro organisms is to eliminate the organic matter in the wastewater. a large part from the defecation and the other part comes from the food preparation. If allowed time for micro organisms to do their job of removing organic matter, in a supportive environment are biological, organic matter disappears between 12 and 15 days. the output liquid contains over 94% organic fertilizer water to vegetated biodiversity that will purify the soil of the urinary pollution. A groundwater sampling economy, reduction of pollution of natural water environments, increased development of biodiversity vegetated reducing soil erosion, a huge financial cost reduction of inefficient management of wastewater. More than 45 million tons of faeces are produced on our planet that current technology turns into Millins 45 tons of excrement mud, a real poison for the environment.

    1 Comment

    1. Thanks for your note. The specific problem we're addressing here is the transfer of sewage to the works for treatment where anaerobic conditions can occur in the course of a period of hours, rather than the days you refer to.

  6. Guy McGowen

    Adding the Archaea species to these stations  will eliminate all odors, reduce the affluent into dissolved bio nutrients, increased oxygen content, and elimination of all pathogens. less bio solids to transport, less to be treated, elimination of chemicals and their transport to offsite locations.  Elimination of chlorine at treatment station if desired.  30 year old technology I know. But you did ask how.

     

    1 Comment

    1. Thank you.
      We have investigated biological solutions in the past and found that they struggle with the variable nature of network conditions. For this to be implemented the solution would have to address this variability.

  7. Mixing and aeration are the two that come to mind. Anything that can be done to eliminate the retention time (sometimes lower float setting etc.) may also help. The chemical route involves iron salt (precipitates sulfide), calcium nitrate, hydrogen peroxide, potassium permanganate, and chlorine as other options. In some countries chlorine may not be favorable due to disinfection byproduct concerns.

    1 Comment

  8. A potential solution came out of the CCTV Survey of serage network we had carried out in 1997. We found that none of the RCC sewers showed any signs of crown corrosion despite being more than 40 years old at the time. The Reson: The city supply was based on ground water which was rich in nitrates. Hence a potential solution is to add ~50 mg/l as Nitrate nitrogen in the pump sump. The aerobes which are very quick multiplying, can also use NO3 as electron acceptors and keep septicity at bay. This has been successfully tried at a small SPS as well, with good results and elimination of odors

    1 Comment

  9. Septicity in pumping mains

    Hi Nilam. If you have water treatment works using iron based coagulants then these can be used to help overcome septicity. Typically the coagulants will be taken from DAF plants and considered a waste sludge to be disposed of. They still have good sequestering potential and can help keep H2S problems down. In fact there are probably many situations where WTW discharge to sewer and companies are unaware of this beneficial effect. You could take the ferric coagulant and discharge it to the network at suitable positions. Worth a try and although it might not eliminate the problem it might help and also find a sustainable beneficial use for the coagulant. 

    Steve

    1 Comment

    1. As per response to John Cook,
      Alternative ​additive ​chemicals could ​offer a benefit,​ but we are ​ideally looking ​for an ​alternative to ​chemical use.​
      Thanks for your comments.

  10. Randall -as you may be aware Singapore is the only nation to convert waste water to potable standards. They claim 98% of the total waster water effluent purified. If there is any other country/region where recycling on a large scale together with energy generation is being done, all of us in this forum would be eager to know about it. Www.refurbindia.com

  11. @Nilam, I have heard about products such as bio-enzyme blends which are supposed to inhibit anaerobes. However, these additives (we're back to a chemical) are proprietary, and I have found it virtually impossible to obtain any objective, non-anecdotal evidence of efficacy. But in theory, there could be catalysts that make it difficult for anaerobes to thrive. Another option, but we're still looking at chemical addition, is to increase the pH using something such as MgOH. That would certainly help control formation.

    1 Comment

  12. One option is to totally eliminate the waste water by converting it into distilled water- easily used for a variety of purposes, including treatment to make it totally safely potable. Equipment is available that will convert sanitary waste water into distilled water while also producing electricity. Systems are available as small as 2500 liters per day input, 2900 LPD output and 30 kW to as large as 211,000/240,000 LPD modules and 2 MW which can be paralleled for higher output if needed.

    1 Comment

  13. pumped sewer septicity

    As we know septicity is a question of time and is due to natural process, so we can limitate it but not avoid it.

    few advices :

    - volume of suction tank should be the minimum according to technical needs;

    - use mixer and flush valves in this tank;

    - bottom of sewerage as smooth as possible and without step or discontinuity;

    - in rising pipe avoid change of slope that create vertical elbow;

    - pipe diameter and pumps flow rate aiming to have a correct minimum velocity.

    If retention time is too long than you'll need chemical dosing compatible to the final WTP 

     

    1 Comment

  14. Septicity

    In Ireland the requirement is to exchange the sewage in the line every 5 hours to avoid septicity. We have had to look at a number of options, dosing usually is not an option as the sewage is going to a municipal plant and will kill all round it. Other options are to pre-treat on site and pump effluent, use a water flush system, for smaller applications use grinder pumps to allow for reduction in pipe size and holding volume in the line.

    1 Comment

    1. Thank you for your comment
      Anglian Water has explored pre treatment as an options but due to the 5000+ pumping stations pre-treatment on site is rarely an option. We have explored the water flush system but the water shortages within our area mean the volume required is too great.