Project 002-073 Clay Precipitation from Water
Project Name: Clay Precipitation from Water
Project Details
Reference Sponsoring Entity Commenced Status Budget
22-23 23-24 24-25 25-26
002-073 KIRRAutility (Ku) 28-10-2023 Complete $ - $ 20 $ 100 Unallocated
Project Overview
With water scarcity, every drop counts. This is particularly the case for water when it comes to gardens and animals. There is great potential to catch rain water from the ground and other hard surfaces that can be used for washing, garden watering and animals. There is however the issue of clay suspension in the water, which makes it "dirty" and whilst this won't harm animals or plants, it could be easily cleaned up.
Removing the clay suspension, which is caused by a charge on the clay keeps the clay suspended by preventing it from "clumping" as like charges repel and the clay particles are all charged alike. This is easily remedied by forcing the clay suspension to precipitate (more accurately "Coagulate") then either removing the clarified water from the top, or removing the precipitate from the bottom of the container that is used.
Using chemicals like Alum (Aluminium Sulfate) also is a viable choice, this like Gypsum causes coagulation. Many refer to this process as flocculation, but it is in fact, coagulation. In this experiment, we don't use Alum. If you use Alum, you will need to follow the direction on the packaging.
IMPORTANT: This process does not purify the water, it clarifies it. If you are planning on consuming this water, you should pass it though a 6 stage filter system to remove all contaminants. The final stage of the 6 stages, is exposure to UV light to kill pathogens.
Aim
Improve the quality of the rain water that is captured from the ground which ends up in ponds, dams, streams and lakes on the property.
Method
STEP 1: Move a known quantity of water from the dirty water to a container so the volume of water is known. This could be a 1,000 litre IBC tote, or a 20 litre bucket. In this experiment we use a 1,000 litre IBC tote.
STEP 2: In a separate container of about 10 litres, mix about 1 Kg of Gypsum (calcium sulfate dihydrate CaSO 4·2H2O) with hot water and stir vigorously for 60 seconds. Although this will dissolve an amount of the Gypsum, but become saturated very quickly and not all the gypsum will dissolve.
STEP 3: Add the Gypsum slurry to the IBC tote, which contains the clay suspended water. Make sure that you only add the dissolved gypsum, reserving the solids at the bottom of the container. These can be reused or you can perform STEP 2 again, with another 10 litres of hot water, using the remaining gypsum in the container.
The more of the gypsum that you can get into the clay suspension the greater the clarity of the final water will be and the quicker it will react.
STEP 4: Leave the 1,000 litre IBC tote for a period of 2 - 3 days. Over this time you will notice the clay start to precipitate at the bottom of the IBC tote.
STEP 5: Once the water have achieved the clarity desired, you can either open the valve on the IBC tote to expel the heavy clay precipitate or use a sump pump to remove the clarified water.
(Images) Gypsum added to a 20 litre bucket showing clarity and precipitate at the bottom of the bucket.
(Images) The precipitate falling out of a clay suspension in a 1,000 litre IBC tote. The precipitate is visible just below the 200 litre marking on the tote.
Conclusion
This project allows the clarification of as much water as is required within the amount of water available.
Gypsum doesn't alter the pH of the water, so the resulting clarified water can be used for sensitive projects like hydroponics or aquaponics.
The clarity of the water will improve over time, so the longer it is left the greater the clarity achieved.
Cost-Benefit Analysis
Gypsum in a gardening grade is more than suitable for this purpose. It is available from Bunnings (at the time of writing) for $11.19 per 15 Kg, this should be sufficient to clarify more than 20,000 litres of clay suspended water for washing, animals and gardens.
