Dear Jose,

TMW is a "cleantech" which develops an innovative distillation technology for the production of pure water from saline or polluted waters: MHD technology, multi-stage humidification dehumidification. Simple, economical and ecological, the MHD technology is a response adapted to a major challenge, that of the production of pure water for domestic, industrial or agricultural use. The result of more than 10 years of research and development, it offers numerous applications in desalination and decontamination: salt water desalination, effluent treatment, production of demineralised water and process water, etc. MHD is a unique technology that enables the production of water Soft water from seawater or effluents through the use of 100% renewable energy (solar or geothermal) or waste heat (hot water, steam, gas). Its advantage: a simple operating principle that reproduces the natural cycle of water with evaporation, diffusion of the vapor into the air and condensation of the steam in the form of distilled water.

With my best regards

Prof. Bachir ACHOUR

It’s OK; TMW has developed proprietary technology for seawater desalination and industrial effluent concentration. As rapid global urbanization is making water supply more complex in urban areas, recycling is a must. Moreover, an additional benefit to recycling is that the treatment of waste water also supplies energy and raw materials.

It is not feasible, I believe. Efficiency of evaporation is low and huge energy is needed, and the cost of operational maintenancebut is high.

but theoretically it is doeable.

I agree with Motasem Saiden to some extent but would think that this issue is not a problem  if  you are able to use solar energy to do the evaporation. You are right to worry about transfer  of certain volatiles but cannot visualise a mechanism that would transfer pathogens. 

Thank you very much for your answers, very much appreciated. However none of the questions I'm concerned were answered yet.

I'm interested in designing this low-cost system for poor people with high drinking water scarcity, in a region where the average temperature over the year is one of the highest in the planet (apart from deserts). So solar energy should not be an issue. I am looking for insights on how potable the water might be. I might do some experiments in the lab before building the first prototype, but I am looking for scientific background to support the idea to get the funding...

Thank you all!

Excuse me Mr. Jose , the undesirable microorganisms like bacteria and viruses may be sterilized by high temp., but the suspended and dissolved solids can not be removed. So BOD5 , COD, Nitrogenous compounds and other Heavy metals cannot be removed by simple evaporation. Thank you in advance 

Of course you can purify water by distillation. If it contains volatile organic compounds, it might have off flavours, but it should be safe to drink. But there are good reasons why such methods are not used in water treatment plants. It is far to costly! 

You will need lots of energy to heat (or boil, if you are concerned about bacteria) the waste water. This is only feasible in a desert (or a space station) where you need water for survival. Normal water treatment plants rely on microorganisms, requiring very little energy. The best methods let the sludge water slowly pass through several alternating aerobic and anaerobic conditions, making different kinds of bacteria grow.  In the end, the bacteria form flocs which sink to the bottom and clean water remains. This can be supplemented with chemical treatments to remove any specific chemical contamination if that is a concern.

For small quantities, filtration is normally used. Reverse osmosis can yield potable water very efficiently. A simple sand filter where the water trickles down a bed of fine gravel and sand is another alternative. 

If you want the basis of a solar still for purifying wastewater you should research the survival skills literature issued to Special Forces units. Many of them repo rt  improvisedsolar stills for recycling urine and other wastewaters. You can then think about scaling up.

I suggest to rely on (Stabilization Ponds) for which both Biological Treatment and disinfection by sun  can be accomplished. 

http://www.sswm.info/sites/default/files/reference_attachments/SPERLING%202007%20Waste%20Stabilisation%20Ponds.pdf

Not economical viable for Potable purpose. High level of Pollutants ,TDS and TSS and involvement of gases may create problems during the evaporation and condensation process too.

It Evaporation of wastewater produce condensate that usually contains volatile substances. Analysis of the condensate usually shows COD due to the volatile contaminates. In case the condensate is intended for use, its  additional treatment is needed such as condensate purification unit(s) including RO. 

Jose,

An evaporated and condensated, i.e. distilled water will lack alkalinity and therefore have a very low pH.  I don't think this is safe as I would affect a person's electrolytic balance. I suggest you look at the WHO Drinking Water manual for more information.

The normal practice is to remineralise distilled/desal/RO water.

How much volatile contaminant and water is all about vapour pressure which is related to temperature by the Clausius-Clapeyron equation. Two problems, first the non-volatile solutes in the wastewater will lower the activity of the water and hence its vapour pressure, making it more difficult to evaporate (ultimately elevating the boiling point). Second, you'll need to capture and condense the vapour, and for that you'll need a cold sink, i.e. a constant source of something colder to lower the vapour pressure so as it condenses. So you'll need a refrigeration unit to provide the cold sink. Unfortunately because of the second law of thermodynamics one can't separate the heat from the cold source to drive the evaporation from the waste water without doing work. So for large scale, this could be expensive in terms of water yield for energy input. Good point above about the volatile contaminants, of course you could use fractional distillation to purify to some degree. You certainly won't vaporise pathogens, although you may have to watch aerosol contamination of your pure product.

Dear all, thank you for the discussion, you've gave me very helpful inputs and I can now polish a bit more the concept.

With this project I intend to adapt existing septic tanks and not use the principle for scaling up at industrial levels. The idea is to modify the lid of the tank adding an inclined roof made out of glass or any other low-cost material capable of creating a greenhouse effect inside the tank. An anaerobic environment will be targeted for better COD removal and biogas capture. Water will be then captured via canals on the bottom of the roof after condensed water runs off. This idea came up as a cheaper alternative to implementation of  further DEWATS (yet cheap compared to WWTP) able to produce drinking water in regions with high water scarcity and solar energy availability. So the only energy source will be solar, which is quite abundant all year long (the region is near the equator and quite dry).

Bear in mind that the main wastewater source will be daily wastewater produced in the countryside of northeast Brazil, so I don't expect it to have high levels of chemicals or pollutants. I was even thinking of adding some solid waste and animal manure for higher biogas yield in some cases, as the total solids of this source is generally very low. Is it a good idea? What else must I take in account while working with a mixture of human and animal excreta?

Normally, in these type of community, everyone has a clay container in their homes with ceramic filters, which has been proved to be one of the best methods to bring water to drinking standards, in terms of efficiency and cost. So I expect that the beneficiaries would keep using their filters, especially considering the psychological barrier of "drinking water produced from shit", in slang words.

Paul, thanks for this comment, I've though about that too. Another consideration about the water vapor pressure would be the biogas storage tank, which is normally done under pressure. Therefore a higher pressure in the chamber will build up, varying with the biogas yield and natural temperature variation along the day. I still need to do some calculations to see how feasible this is. The water would be captured through saturation though, which doesn't require any further system apart of the inclined roof. Again, I'm only interested in the cheapest way of producing potable water, so more complex and/or expensive systems must be avoided.

If anyone is particularity interested in the project I would be glad to have a chat.

Best regards,

Jose

Firstly, waste water contains lots of volatile substances or organic substances with low boiling point which will evaporate with water. Secondly, the process is going to be ridiculously costly if the water is to be treated for bulk consumption.

It is not proper way to provide the potable. The reason is that it cost so much and is not usual way of treatment.

For the knowledge of all:

https://www.researchgate.net/publication/273438189_The_application_of_a_solar_still_in_domestic_and_industrial_wastewater_treatment

Article The application of a solar still in domestic and industrial ...

Basically, it looks like everyone is in agreement that the distillate will not be potable (drinkable) without further treatment, and that further treatment could be costly.  As an example, to make portable water from wastewater at a large scale requires RO or thermal desalination, UV-OX or similar for purification to destroy low MW or volatile organics in the permeate or distillate, and re-mineralization. 

You have to overcome many hurdles to reach to your final product (potable water). Low molecular wt. chemical contaminations, aerosol contamination, organic volatile substances and complete lack of minerals in your water are the major challenges. But I wont discourage you that you cannot do or you shouldn't do because inventions are born out of scarcities. Good Luck!

You could make an anaerobic reactor upflow sludge blanket (UASB) according to the number of residences. They are easy to build. The fall of water could be a source of energy and in addition the production of methane would give another source of energy. The water produced can lead to the settling ponds and then filtered with activated carbon or microfiltration membranes adding disinfectant. You must evaluate water quality parameters that are drinkable and safe for human consumption.

There is no drinking water at low cost. Current pollutants are a real challenge to remove from the water and wastewater. Success in your research.

It is possible but expensive, additionally volatile compounds can by carried to the evaporated water. Reverse osmosis with wide pretreatment and remineralization is more cost effective.

Only with cheap energy available and verifying if fractionation of condensate is required.

came across an invention from Sweden(?). They developed a filter based on cellulose with adsorbed cationic surfactants. It was intended for treatment of muddy raw water to remove microbes.

Maybe a combination of anaerobic treatment would be a better approach than solar still.

Dear Dr. Titus Do you have any paper about this cellulose filter.

Regards

I found it on

https://phys.org/news/2017-03-filter-wood-portable-eco-friendly-purification.html