Getting some air into the pond combined with chemical dosing with some lime is the best first step to rectify the problem if you detect the hydrogen sulphide smell. It’s necessary to get the odour under control before you continue with irrigating.
Stirring alone is unlikely to solve this issue, you do need some chemical intervention as well! If your pond does not have a stirrer then you might want to contact a spreading contractor as most will have tractor driven stirrers to help stirring the ponds before the contents are spread.
Odour problems can arise when the pH drops below 6.5. This condition can be temporarily corrected by applying lime to increase the pH.
We recommend adding 16 kg per day of agricultural lime per 1000 m3 of pond volume until the pH has stabilised at an appropriate level. This should be added by sprinkling in and mixing well.
How does lime work?
An anaerobic pond will have a pH range of 7 to 8 (slightly basic). Odour problems can arise when the pH drops below 6.5. This condition can be temporarily corrected by applying lime which increases the pH.
As shown in the graph below hydrogen sulphide reduces when the pH is increased. However, it is preferable not to go too alkaline as there is the potential to generate ammonia, another odorous gas.
What about other chemicals?
There are a number of other chemicals that may also help reduce the odour although they tend to be more expensive than lime and some care is needed to store and handle them.
Sodium or calcium nitrate is also worth considering and can be purchased from a chemical store. Adding a nitrate source is a proven technology for hydrogen sulphide control.
To determine the dosage rate it is best to collect an effluent sample from the pond and send it to a lab so they can measure the BOD content. BOD is essentially a procedure involving the measuring of oxygen consumed by living organisms in the sample. Click here for more detailed information.