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Sewer Disinfection

12/10/2015 11:29 PM

Hi

I want to workout the best possible way for disinfection of sewage effluent.

I was thinking of using 15% Liquid NaOCl.

Effluent Flow rate: +/-50m3/hr

How much of NaOCl do i need to dose per hour.

Residual chlorine need to be 0.2mg/L.

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#1

Re: sewer disinfection

12/10/2015 11:42 PM

No one can tell from your pitifully inadequate information.

No offense intended, but some idea of the makeup of the effluent stream may help.

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#3
In reply to #1

Re: sewer disinfection

12/11/2015 12:02 AM

Thanks for your non constructive suggestion.

I guess anyone who knows about sewage treatment will know what i m talking about.

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#8
In reply to #3

Re: sewer disinfection

12/11/2015 1:00 PM

You're welcome. Glad to help out.

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#2

Re: sewer disinfection

12/10/2015 11:54 PM
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#4
In reply to #2

Re: sewer disinfection

12/11/2015 12:06 AM

thank you

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#5

Re: sewer disinfection

12/11/2015 1:15 AM

If only sewage guy Ed Norton were a CR4 poster, we could clear this up in a New York minute.

Depending on how "dirty" the effluent stream is, it can take more or less treatment chemical (of whatever kind) to maintain sufficient residual chemical. Some fairly easy arithmetic can give the minimum required dose, but you may need to multiply that by some factor, measure the actual residual, and then adjust the dosage rate accordingly.

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#6

Re: Sewer Disinfection

12/11/2015 7:31 AM

"best possible way"

The best way is to compost it.

Instead of adding poisons to try to kill bacteria, feed the bacteria with a little carbon amendment and they will sterilize the effluent and die off after there is nothing left to feed on.

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#12
In reply to #6

Re: Sewer Disinfection

12/12/2015 5:51 AM

Composting is a possibility for sewage sludge, but it's final effluent (nearly all water) that we're talking about here.

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#7

Re: Sewer Disinfection

12/11/2015 9:44 AM

Think "Chloromines"

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#9

Re: Sewer Disinfection

12/11/2015 11:21 PM

why is effluent has a (-) negative rate? In engineering point of view, that means an influent.

It depends how much load you got, a water analysis would be preferably advised to know what and how much there is to treat.

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#10
In reply to #9

Re: Sewer Disinfection

12/12/2015 1:02 AM

thank you Mr small. Actually its the final stage of treatment before discharge to the river. Hence i m saying its effluent. (+/- 50m3/hr) its an estimated flow rate of the effluent.

I guess you are right about water analysis, so we can determine how much is required.

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#11
In reply to #10

Re: Sewer Disinfection

12/12/2015 5:15 AM

If the sewage treatment is adequate, final effluent say 20mg/l BOD, 30 mg/l SS, 5 mg/l NH3, I would design for 5 mg/l dose as available chlorine. If I remember right NaOCl is supplied in solution as 14/15% av chlorine, but you need to check.

Most regs don't allow any free chlorine into the river, in that case you need to consider dechlorination using SO2, most likely in the form of sodium bisulphite for this sort of flow.

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#14
In reply to #11

Re: Sewer Disinfection

12/12/2015 7:25 AM

Thanks. This sounds like the answer I have been looking for. Yes I will be using a 15% av Chlorine in NaOCl solution.

I will use this as my starting base. tanks a lot.

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#15
In reply to #14

Re: Sewer Disinfection

12/12/2015 10:55 AM

Chlorine is toxic to life in larger dose. As possible minimize chemicals spillage on rivers and ocean as well, it damages marine life. Chlorine disinfects- disinfection means killing microbial life which has the same almost components to us and other animals. Chlorine will bleach you out.

In the position that you're in right now, do not decide yet with out the appropriate knowledge on it. Consult a professional who runs an operation or expert in STP.

The basic thing they do in STP is aeration. This is dissolving oxygen in water by mechanical means or by a bubbler. There is no bad effects on it since only oxygen is added by physical mixture (except it need energy for the compressor or bubbler system)

Effluent basically could be classified into

1) Organic

2) Chemical/Oil

3) Mixed

The 3 demands oxygen.

Decomposition of organic waste actually is an aerobic(oxygen based) bacterial decomposition. Putting a Chlorine in it will destroy this active bacteria which decompose the load and it won't solve the problem. The same organic load discharge. USEPA or local authority won't allow that.

The basic process of organic decomposition is

CxHyOz + O2-(--bacterial decomposition)--> H2O+CO2

Disinfection is only done when you have say hazardous waste ex. Hospital waste water or morgue.

Also, disinfection is needed when you plan to reuse the water in the vicinity.

Say you have a 50 cu.m/hr waste water and treat it to result may be say 2% solution. By mass you need approximately 1 cu.m/hr or 1000L/hr NaOCl at Ā£45/25L how much would it cost you? It's unwise right?

Hope this helps.

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#16
In reply to #15

Re: Sewer Disinfection

12/12/2015 11:33 AM

No, it doesn't help.

OP said it is sewage effluent. There are plenty of pathogens in raw sewage, that's why we've evolved to think poo smells bad, so we keep away from it! Pathogens also in sewage final effluent unless it is disinfected. That's why nowadays if discharge is near a bathing beach it is often disinfected. River discharge may be less important, as even if a drinking water plant intake is from the river downstream, the water is always disinfected before going into supply. Nearly always with chlorine for its residual effect in keeping the supply network pathogen free, even if something else eg ozone is used in the water works.

Chlorine for disinfection is added after the aerobic sewage treatment process, so has no effect on it.

The SG of 15% w/w NaOCl is about 1.25, so 1 m3 contains nearly 200kg av chlorine. Putting that in 50m3 water gives a concentration 4000mg/l. That's a crazy dose rate, however much it costs!

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#21
In reply to #16

Re: Sewer Disinfection

12/13/2015 1:18 AM

"The SG of 15% w/w NaOCl is about 1.25, so 1 m3 contains nearly 200kg av chlorine. Putting that in 50m3 water gives a concentration 4000mg/l. That's a crazy dose rate, however much it costs!"

I do not know if you pass college chemistry or just about to make it. Such a sarcasm.

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#22
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Re: Sewer Disinfection

12/13/2015 4:50 AM

I don't know where you're coming from. I wasn't being sarcastic, just stating facts. Don't you agree with the figures? Typical chlorine dose rates for water and effluent treatment are < 10mg/l, 4000 is way out.

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#29
In reply to #14

Re: Sewer Disinfection

12/14/2015 3:24 PM

Killing fish is illegal in many jurisdictions. That is why ultraviolet light is used on tertiary effluent immediately prior to discharge.

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#30
In reply to #10

Re: Sewer Disinfection

09/01/2016 3:50 PM

"(+/- 50m3/hr) its an estimated flow rate of the effluent."

Then the proper terminology would be ~50m3/hr.

~ Indicates approximation

+/- indicates tolerance, as in 24" +/-0.5", which would indicate "No smaller than 23.5", no larger than 24.5"

Using +/- without a leading value insinuates a leading value of zero. +/- 50m3/hr reads as "The flow can be up to 50m3/hr, in either direction."

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#13

Re: Sewer Disinfection

12/12/2015 6:25 AM

Best practice for already treated effluent prior to discharge would include:

Exposed detention, allowing sunlight UV exposure, followed by a filtration process (normally just a sand filter to take outlarger particles but some use membrane filters) and then followed by UV exposure utilising UV source lamps.

Properly treated effluent is suitable for watering of golf courses and even for farming irrigation.

Note that Chlorine will not kill all the pathogens likely to be in the water.

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#17

Re: Sewer Disinfection

12/12/2015 11:59 AM

Forget the Chlorine and the Chlorine solutions which will be heavily regulated by the environmental and sewage authorities. During the late 50's and early 60's the French started to experiment on a full scale with the generation and treatment of sewage with Ozone, O3. It worked so well that many of their facilities switched over to it and still use that process. The USA started experimenting on pilot plant quantities during the mid-60's and began using it in full production in the early 80's.

http://www3.epa.gov/npdes/pubs/ozon.pdf

Set up a temporary ozone generator and experiment with it to determine its effectiveness with your sewage materials. It is much more effective and requires less regulatory "looking over your shoulder" than the chlorine method.

From http://www.water-research.net/index.php/ozonation Ozone has a greater disinfection effectiveness against bacteria and viruses compared to chlorination. In addition, the oxidizing properties can also reduce the concentration of iron, manganese, sulfur and reduce or eliminate taste and odor problems. Ozone oxides the iron, manganese, and sulfur in the water to form insoluble metal oxides or elemental sulfur. These insoluble particles are then removed by post-filtration. Organic particles and chemicals will be eliminated through either coagulation or chemical oxidation. Ozone is unstable, and it will degrade over a time frame ranging from a few seconds to 30 minutes. The rate of degradation is a function of water chemistry, pH and water temperature.

Ozone disinfection is used at large sewage treatment plants and also water treatment plants. One especially nice thing about ozone vs. chlorination is that the ozone does not require extensive capturing of the residual gas such as chlorine does. An over dosage of Ozone is not a problem, it just vents to the atmosphere. Chlorine requires much more extensive control.

Setting up a laboratory scale apparatus is very inexpensive. The major items are a lab condenser with ground glass fittings; some zinc chloride solution; aluminum foil; several feet of non-resistive automobile spark plug wire; a neon sign transformer or an oil burner ignition transformer; and several small inexpensive items.

http://www.water-pollution.org.uk/ozonewastewatertreatment.html

http://www.nesc.wvu.edu/pdf/WW/publications/eti/Ozone_Dis_tech.pdf

If the use of Ozone is not feasible due to its handling, Hydrogen Peroxide can be substituted for it.

Good Luck, Old Salt

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#18
In reply to #17

Re: Sewer Disinfection

12/12/2015 12:41 PM

Ozone has its merits, but a couple of points

it doesn't react with ammonia

it degrades fairly quickly (as you say) but that is a disadvantage in drinking water treatment as it doesn't have a residual effect, so any pathogens entering distribution pipework (which is possible through inward leakage) are not killed. Chlorine has a residual effect all the way through to the customers' taps. It is used on practically all water treatment plants as a final dose before going into supply, both over here and I believe in USA.

Also though ozone is not stored in large quantities but made on site and used immediately, it is as toxic as chlorine and stringent safeguards are needed in the generation area to protect workers. And chlorine can also be made electrolytically on site.

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#19
In reply to #18

Re: Sewer Disinfection

12/12/2015 9:31 PM

Very good!

Ozone also takes care of many micro-pollutants. Those left over of the hormones and drugs we ingurgitate in industrial quantities in the modern world. Most of it goes through us and end-up being feed to the fish and the frogs...

This is why Montreal (Quebec, Canada) is investing $200 Millions in an ozone treatment plant for the effluent of the waste water plant.

http://ville.montreal.qc.ca/portal/page?_pageid=6497,141709696&_dad=portal&_schema=PORTAL

Approximately 30MW of electrical power will be used to produce the oxygen and ozone needed to treat the waste water for a city of about 1 million inhabitant.

They ran pilot tests with chlorine and UV but the fish that were exposed to the treated water were not in good shape at all while the ozone treatment kept them healthy.

If fresh water trouts approve, it is good enough for me.

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#20
In reply to #18

Re: Sewer Disinfection

12/13/2015 12:10 AM

If ozone treatment is not as effective for sewage treatment as chlorine, why are more and more facilities switching from chlorine to ozone? I'm not an ozone expert other than working with it extensively in school but this is the first question that comes to mind. There must be ozone gurus that study this before making the change. There are other treatments in conjunction with the ozone that will treat many of those chemicals present in the effluent in conjunction with ozone.

One disadvantage of chlorine is the "Reporting Quantity" mandated by some laws. One urban sewage plant I am familiar with has changed to ozone due to the expenses and potential fines for having too much chlorine on site. For railcar shipments they had to wait until the car was almost empty before bringing another loaded car in since the RQ was so close to the amount being brought in. Another is the poor public relations cause by any leakage or spillage of chlorine. This same plant had a chlorine leak and the evacuation area was quite large. Lots of bad publicity.

Good Luck, Old Salt

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#23
In reply to #20

Re: Sewer Disinfection

12/13/2015 5:05 AM

I didn't say ozone isn't as good as chlorine for sewage treatment. I agree ozone has a lot going for it. As marcot said in #19, it breaks down micropollutants. Our co did good business in the 80s and 90s (in UK) building ozone/GAC plants for pesticide removal from drinking water.

I still think chlorine is needed for its residual effect in water supply systems. It's added at the end of the process when the water is pure so only a dash is needed to give a (just) positive residual at the taps.

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#24
In reply to #23

Re: Sewer Disinfection

12/13/2015 6:57 AM

There is significant difference between residual Chlorine in drinking water and what the OP seems to be trying with threated effluent.

In drinking water, the residual Chlorine is an INDICATOR that the purified water from the treatment plant has not since been contaminated. Chlorine only kills some particualr pathogens (well really most, but not all). If the Chlorine residual is "consumed", then that is indication that some contaminant is present that was not there when it left the treatment plant. That contaminant may or may not be an active pathogen, just something that Chlorine reacts with.

In treated effluent leaving a Sewer Treatment Plant, to achieve a "Residual" Chlorine level would require sufficient dosage that all possible chlorine reactions had been completed AND there was still some un-consumed Chlorine present. These Chlorine reactions occur not only with live pathogens, but with many other harmless cehmical chains that are there from the combined Aerobic/anaerobic cycles used in treatment.

If the OP really needs a residual, then the dosage would be dependant on the chemistry of the water leaving that process stream and would require dynamic control due to the changing nature of the influent to the plant. It is impossible for us to suggest the dosage that would be needed without a complete understanding of the treatment chain being used.

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#25
In reply to #24

Re: Sewer Disinfection

12/13/2015 11:00 AM

I wouldn't disagree with most of that. Ref chlorine not killing all pathogens - I believe cryptosporidium is one that it doesn't. There was recently a crypto scare in NW England which turned out to be a dead pheasant or duck stuck in a pipe somewhere and it took weeks to find it. Why a dead bird should have crypto in it I'm not sure, but that's how it was reported.

Of course to get a chlorine residual the dose has to be enough for anything with a demand, but after the treatment process this should be low as most of the organics, colloids etc have been removed. Decades ago it was common to pre-chlorinate, which needs a higher dose, as it improved the flocculation and coagulation characteristics. But that stopped due to production of choroform, giving a cancer risk. When I worked on seawater filtration on North Sea platforms (for well injection, 2ndary recovery) a good slug of chlorine at the seawater winning pumps to kill the copepods etc improved filtration no end. Production of nasties obviously isn't a problem there.

OP said he wants a residual 0.2mg/l. My suggested dose was based on the treatment process working well, as I said. Thinking about it again, maybe 5mg/l is on the low side for design, it would be a good idea to do some tests to confirm dose.

Chlorine dosing is usually controlled automatically to maintain a setpoint residual, so that shouldn't be an issue.

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#26
In reply to #25

Re: Sewer Disinfection

12/14/2015 6:27 AM

We are in agreeance.

What is your experience with liquid Hypo deteriorating in storage? We had to downsize our on site storages at the potable water plants due to reduced rate of return over time.

We do have some ambient temperature issues here.

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#27
In reply to #26

Re: Sewer Disinfection

12/14/2015 7:08 AM

Sorry I can't help much on that one, my experience is on the contracting side, not operation. But I'd have thought there'd be guidance on shelf life in the product data/COSHH sheets, or if not a chat with supplier?

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#28

Re: Sewer Disinfection

12/14/2015 3:22 PM

Tertiary final effluent is usually given a dose of ultraviolet light.

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