Hello,

I am researching for a proposal to do a pilot project to use treated municipal wastewater to irrigate high water content crops such as tomatoes, cucumber and strawberries.
I am looking for information on low cost alternatives for wastewater treated with chlorine. The only alternative I have come across is Ultraviolet rays which is a costly method.

Thanks in advance for any help

Also expensive, but a membrane bioreactor treatment plant would be an very efficient option too.

Alternatively... well if you can strictly avoid contact with the vegetables, it is not that necessary to desinfect the waste-water. Obviously this is difficult to do though; underground drip irrigation would probably work, but you would need to filter the wastewater to avoid clogging of the small pipes and drippers.

An low tech alternative that I think might be interesting to use with wastewater also (not sure if it has been done before) is buried clay pot irrigation. Just do a search on google for it. Basically you take an unglazed and thus slowly water permeable clay pot and bury it close to the roots of the plants. Then you fill it up with (waste) water and put a lid on it. The water then slowly percolated into the soil.
This method has been used in north Africa I think for a long time... however it has it's share of problems too, and you would still need to find a way to safely fill the pots with your wastewater and remove the accumulating sludge.

Dear Mr. Lillian,

I would advise you that, you must have a proper wastewater treatment plant. I would prefer aerated lagoons wastewater treatment plant (grit removal, primary sedimentation, aeration unit with cage rotors, final sedimentation tank, and sludge drying beds). If it is well-designed and you have adequate liquid retention times in all units, especially the aeration unit, you would be able to get a reasonably good quality treated effluent (BOD < 40 mg/l; SS < 50 mg/l - typically).

Now, if you want to chlorinate it, then, the best way to do it, is to add a slow sand filtration unit at the end of the plant, with a low filtration rate [(e/g, 2 liters/square meter per minute (0.05 gallons/minute/square foot)]. The effluent that you get will be, almost, (depending on the design and operation of the plant) equal to, as if you have chlorinated it. Do it and you will thank me for that - a low-cost alternative.

F H Mughal (Mr.)
Karachi, Pakistan
PS: I'm attaching a useful publication - Enjoy!

Thank you for your replies.

Mr Mughal,
We do have a proper wastewater treatment plant, very similar to the one you described. It has been running since 2000.
I am interested to know more about the sand filtration system. What kind of (quality)sand does it need to be and do you have any designs for such systems that I could take a look at?
Also it seems that the publication was not attached.

Regards,

Lillian

Hi,
the most effective low-cost treatment for reducing microbial contamination of municipal wastewater is by waste stabilisation ponds (lagoons). If you already have a pond treatment system, adding maturation ponds would further improve the hygienic quality of effluent. Maturation ponds are shallow ponds that allow good penetration of sunlight (UV) and that add more retention time to the whole pond system.
Disadvantages are high land requirement and water loss by evaporation, which may be an issue in your dry climate.

However also these ponds don't achieve absolute disinfection. So if you absolutely want to irrigate high-risk crops (strawberries and cucumber are crops that will be eaten raw and that are likley to come in direct contact with irrigation water) pond treatment may not be enough. Disinfection by chlorine or UV, preceeded by filtration or other treatments may be the only way then. This may not be economic any more.

A better option may be to consider different crops (not to be eaten raw, or not coming into direct contact with irrigation water).

Best, Florian

Dear Ivolat

Using of cholrine is the most cost effetive option has been known for water and waste water disinfection ,but I like draw your attention for [u]trihalomethanes [/u]hazard by products which produce when cholrine affects on orgaing matter presence in water
They carcenogen and with high retention in soil.
In 2008 thanks to BGR( Hannover) ,I visited brunshwich waste water treatment ,it was prefect water water tretament without using any disinfectant.
screening,floattion, sedmenation ,aeration aremethod they use in thier recycling and reusing perfect and success waste water treatment system I have seen.
About using UV it is not cost effective not perfect becuase need high budget and experinces shows biofilms formed on quartz UV lamp tube preventing reach UV radtion to waste water and turbidity and polloution rate are negative factors effect waste water disinfection.

Ozone othe option but it also has its problem including high expenses, maintance and othe issue may not be cost effetive and practical.

I am attaching a file about trihalomethanes byproducts.

Thank you and with best regards;

Mohammad Mojtabaei

www.fpp.ir
Telfax:00985117629569
P.O Box:91865-358
Mashhad,Iran