Tuesday, June 13, 2017

Rainwater and river water: collection, treatment and storage

Dear Mr Chen Ko


My name is Thomas, and I am looking to work on a small-scale implementation for a water storage and filtration pipeline. I would like to seek your advice on the following as I deemed them requiring a more informed opinion than just a simple google search. Please excuse me if terminologies used are inaccurate or the context is too generic - I would definitely like to understand more about the practicalities and improve if possible.


This pipeline is a proof of concept to collect rainwater and river water, treating them separately, then mixing it (via manual carry), then storing it in a tank (preferably steel) for later or immediate treatment. The treated water will placed in a separate tank for distribution by tap to pail/smaller storage tanks to be given to the rest of the community or other usages. These will then be boiled on their if used for consumption, otherwise for bathing/watering plants.


1. Natural means to treat water/water tank. The temporary storage tank could hold the aggregated water for a week up to a month - and I think some bacteria could fester, and even if it was already clean, some might stick on to the inner tank surface. I attended some talk which spoke of possibility of using Hydrilla to clear the water, and some other plants/organic (aka cleansing biotopes) material which could dissuade bacteria growth or absorb other harmful things. An use case is cleaning the inner tank itself. This sounded too good to be true from the onset, but I do see some use for the Hydrilla to clear the water before UV treatment. May I know if such methods have been tried before, and whether it would be feasible to focus on this area?


2. Scaling up UV disinfection. I read one of your posts stating the UV Pen (i.e. Steripen: https://www.steripen.com/products/prepare/)  drops in effectiveness if there are still particles above a certain size as bacteria could hide behind them and the light cannot reach them. What about the feasibility of a slightly larger version of the UV pen, to ensure more thorough disinfection? The idea is to shine multiple pens inside the tank, or have a larger UV light do this job. Does the cost increase a lot for such an implementation?


3. Water quality measurement. Taking measurements of water quality (e.g. pool test, turbidity). It seems infeasible to keep sending water samples from this pipeline for testing. And instead of doing a pool test manually each time, what are your thoughts on integrating some sensors to collect this data electronically? 


The assumption is that rain water is cleanest - but mixing with river water introduces some issues, so there is need to check for:

i) E-coli

ii) Heavy metals

iii) Chlorine, Fluoride, Nitrates.


Would you know reliable vendors and quote estimates that can detect these in one? I have done an Internet-of-things module in school, and sensors seemed quite cheap - I might be wrong regarding these specific set of measurements though, thus my question.


Many thanks for reading this, and wishing you a good week ahead!


Warmest regards




Hi Thomas,


Do you have a particular location in mind to implement this project? it sounds like a developing country!


You also did not mention the size of the community you are serving.


1.       Are you collecting rainwater from the roof or from the ground?

2.       If it is from the roof, it is more efficient to have each individual household handle its own collection unless you have a really big community building (e.g. church, hall) to collect it.

3.       You are indeed right to point out that rainwater is clean so I don't see the logic in mixing it with river water.

4.       Even if the location you have in mind does not have adequate rainwater, it is not economical to mix it with river water.

5.       It is easier to have separate treatment trains for rainwater and river water. And perhaps release treated rainwater (treatment should be minimal anyway) for consumption and treated river water for washing/flushing/irrigation.

6.       Phytoremediation has been documented to be effective in cleaning up water. I remembered Hydrilla used too though I can't recall its effectiveness off my head. A few issues to keep in mind though

7.       Most phytoremediation work was to clean up wastewater which means the treated water was not to drinking standard.

8.       Phytoremediation is typically used to remove organic pollutants, nutrients, certain heavy metals. It may reduce the pathogen population in the process but this is usually NOT the reason for phytoremediation. In fact, the process may introduce bacteria of its own into the water. (Admittedly, these introduced bacteria are probably not pathogenic.)

9.       The Steripen (1, 2) is designed for personal UV treatment of water. Instead of using multiple Steripens, you would be better served with the correct sizing of the UV treatment unit. This of course depends on the community size you are serving.

10.   Don't forget the need for electricity (which may not be easily available in your location) if you are installing a large scale UV unit.

11.   And you are right, clarity of water is VERY important for UV to work effectively. Turbidity of less than 1 NTU is ideal.

12.   The technology of Online measurement of water quality parameters has always been progressing in the water industry.

13.   I am not sure what sensors you have seen to be cheap (probably temperature, conductivity, pH) but the rest of the sensors are not cheap and most of the water quality parameters are not available as sensors.

14.   Many WQ parameters require certain sample preparation and chemical reaction, possibly involving heating. These cannot be duplicated by a sensor alone and will require a full suite of automation to accomplish, involving chemical reservoirs, precise sampling, mixing and heating of accurate amounts of chemicals. And you still need a detector which may not be common off-the-shelf kind.

15.   Heavy metals is a big group of very different elements e.g. cadmium, nickel, lead so they cannot be measured together as a single parameter. You have to know exactly which one to measure. And oh, they cannot be measured simply by a sensor alone.

16.   And testing for E. coli typically involves incubation - anyone with 1-2 days to spare?

17.   Having said all the above, yes, I will still recommend that you install the sensors for the cheap tests - temperature, pH, electrical conductivity as they can indicate problems if they are out of specs.

Hope the above are not overwhelming.


Good luck!


Figure: Hydrilla in the wild - Ngee Ann Stream which I have not visited for a long time

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