Typical FDE Systems

In Northland, heavy soils, hilly terrain and prolonged wet weather often makes effective land disposal difficult. "Environmentally friendly" systems are generally those with high volume storage or treatment ponds combined with land application when soil conditions are suitable.

Land Application

Effluent can be irrigated to land directly from the dairy shed or from a storage pond. Irrigating directly from the dairy shed does not meet the contingency requirement of the permitted activity rule. Daily land application is a high maintenance option and without contingency storage often has a high risk of discharging untreated effluent to water. Irrigation from a storage pond offers much greater flexibility in the timing of effluent application.

Pond Systems

The purpose of oxidation ponds is to change the physical and chemical nature of the effluent. To achieve this the effluent should remain in the treatment system for at least 90 days, which enables the settling out of solids and the breakdown of organic material by microbes.

Typically, two ponds are used. The first pond (anaerobic pond) is where solids settle out and are digested by bacteria that thrive in the absence of oxygen. An effective anaerobic pond will result in a 75% reduction in the organic load in the effluent. These ponds should be at least 3 metres deep. The second pond (aerobic pond) is shallower, enabling the penetration of sunlight, which kills bacteria and encourages algae growth and aeration by wind to maintain higher oxygen levels

Constructed Wetlands

Often used as a tertiary treatment following a pond system. Constructed wetlands can be effective at stripping nutrients and producing an overall better treated discharge. However this is dependant on the effectiveness of the pond system and the design and maintenance of the wetland.

Ditch systems

Barrier ditches are essentially elongated ponds. As with pond systems they must be designed to ensure that the effluent is retained in the system for 90 days or more. For successful operation the ditch must be divided into at least two sections by an earthen or timber baffle. The first section operates like an anaerobic pond by retaining the majority of the solids.

Newer Technology

Some newer technologies being used to manage FDE include mechanical solids separators and "Geo-tubes" (essentially big perforated bags which retain the solids), Advanced Pond designs incorporating barriers and aeration are also operating on some larger farms.

Feed Pads and Standoff Pads

The proliferation of feed pads and standoff pads combined with increased stocking rates and supplementary feed is of concern where adequate treatment is not provided. Investigations indicate that huge organic loads discharge from feed pads.

Performance targets for farm dairy effluent

To monitor compliance with farm dairy effluent discharge standards, by:

· Inspecting all farm dairy effluent treatment and discharge systems that are non-consented, record inspection details and report these to the farmers responsible and to the Council.

· Testing effluent and receiving water quality for systems with resource consents.

· Follow up on all systems with poor grades or non-complying, requiring maintenance or upgrades when needed.