Green Water Recycling
Recycling Green Water from dairy effluent to flood wash the yard, feedpad or barn is an excellent way to reduce farm water use, effluent volume (pond size) and time/power costs associated with pumping hours per day/year, shifting irrigators and servicing of equipment.
The removal of solids from the effluent simplifies land application systems, and enables the remaining liquid (green water) to be used for wash down. It is important that any Green Water Washing System complies with the New Zealand Food Safety Authority Code of Practices for the Design and Operation of Farm and Dairies (NZCPI). By removing the bulk of the organic matter (solids), the level of troublesome anaerobic activity is significantly less, reducing odour, pathogens and nitrogen loss.
Solids separation is best achieved with fit for purpose screening systems (solids separators) or drying beds with weeping walls – see the solids separation section.
Flood Wash Systems
A successful green water flood wash system is dependent upon
- The discharge volume and valve system to ensure a quick and sustained flow of green water.
- Concrete pad slopes to ensure sufficient velocity of the green water down the concrete pad for cleaning.
- Discharge system pipework size to ensure uniform distribution of green water across the concrete pad.
- Wastewater collection system drain shape, size and slope to ensure flushing of all solids and that there is no risk of point of discharge overflow.
Cow Yard Gate Wash Systems
Green water gate wash systems can be used on the backing gate along with a scraper to provide a more comprehensive clean. Green water can be used to drive backing gate drive systems alternatively an electric drive can be used.
A successful green water gate wash system is dependent upon:
- Adequately sized and distributed jet nozzles
- Pumping system automation for on demand ease of use
- Robust but simple backflow prevention design to prevent potable water supply contamination.
- Adequate solids separation
Other Important Considerations
- Green water recycling results in less fresh water therefore higher nutrient concentration (with and without solids separation), especially in summer when there is less rain water. It is important to monitor this and adjust system management to suit e.g. lower application depths, less irrigator passes over the same area and the ability to fresh water wash when necessary (connect fresh water to the flood wash and gate wash systems as well).
- Solids separation is not always necessary if you have a low solids loading e.g. dairy shed only effluent or high rainfall area with a very large pond and only pumping off the top of pond when recycling. The solid and nutrient concentration is much less in systems like this which makes them easier to manage – Flood wash systems must be used as gate wash systems will block.
- If the infrastructure is set up correctly, you can re-use the effluent from the mornings dairy shed fresh water wash down for flood washing a feed pad. However, this does come with caution as your pond liquid viscosity, solids loading and nutrient concentration will increase and if the solids are not removed then the effluent application system will be at high risk of blockage and nutrient application monitoring is much more difficult.
- Good design is essential. Setting up the infrastructure incorrectly with little understanding of required management will result in high compliance risk, increased labour/stress, poor nutrient utilisation (return on investment) and a system that will not meet current and future regulatory requirements.