ARTICLES

Back

Effluent Ponds

The effluent pond system is a cost-effective method which has been traditionally used in New Zealand to treat dairy, pig, meat factory and other agricultural waste. The system comprises either a single pond for effluent storage or two (or more) ponds in series which converts the waste into a less environmentally offensive form by reducing the volume of nitrogen, ammonia, phosphorus, etc which can enter waterways causing pollution. The other main benefit is killing disease carrying bugs. An effluent pond system can be built to meet the demands of the RMA (Resource Management Act 1991) which highlights important issues for dairy farmers including water right renewals and pollution of water ways.

Effluent enters the first pond (Anaerobic) which is generally steep (2:1) to encourage anaerobic (nil oxygen) bacterial action.  Pond dimensions are based on herd size, and in general length is not greater than two to three times the width and a surface area of 350 m2 / 100 head of dairy cows.

The second (Aerobic) is shallower, generally 1m to 1.5m, to enable the penetration of sunlight to maintain higher oxygen levels. An aerobic pond relies less on temperature for breakdown. Length can be as required, maximising surface area for efficiency.

Permathene Ltd is a 50 year old Geosynthetic company based in New Zealand and has specialised in pond lining design and installations for most of that time. Permathene offers several liner types for effluent control. These include HDPE (High Density Polyethylene), Permaliner FPP (flexible polypropylene), and Epidem (polyester reinforced Evaloy). All three geomembranes offer excellent resistance to UV, resistance to chemical and have superior mechanical strength.

The selection of material is determined by several factors including ground stabilisation, access, and economics. HDPE must be installed by an installation crew which can take from one day to several weeks depending upon size, weather, etc. Permaliner FPP and Epidem Evaloy can both be manufactured in our factory and delivered to site in large panels. These panels can be installed by our crews or by the owner following our installation guide. In large ponds HDPE is the most economical choice.

Permaliner FPP also meets the criteria for UV (beyond 20 years) and chemical resistance. The main advantage of selecting this material option for effluent ponds is a lighter lining (polypropylene) which can be factory manufactured to required size and delivered to site to be installed by the owner.  FPP is suitable for ponds up to 4500 m2.

A new material Permathene offers is Epidem (reinforced Elvaloy). This product is recognised for excellent UV, mechanical strength and very high chemical resistance. It is a flexible material and easily conforms to uneven ground surfaces.

Permathene recommends the use of a cushioning geotextile for protection of any geomembrane, including heavy HDPE. The company offers various grades of (Syntex) environmental nonwoven geotextile for this application. It is easily rolled out and overlapped prior to geomembrane installation. This can be done by our installation crews or by the owner following our installation guide.

The photographs that are part of this article are of a wastewater treatment pond project (commissioned in April 2007) for a meat processing plant. Permathene supplied and installed the geomembranes as part of the upgrade of the effluent treatment system which was necessary in order to bring the plant in line with current and future legislative criteria governing the discharge of effluent.

The two new ponds, anaerobic and aerobic unit were designed to reduce discharge of pollutants as well as odour. Situated side by side, each of the new ponds is 90m x 30m with a depth of 7m. The excavations were lined with 1.5mm High Density Polyethylene (HDPE) geomembrane, the new primary anaerobic pond also having a floating cover supplied and installed by Permathene.

The secondary aerobic pond was installed with aerators in order to increase oxygen levels and has an inspection pier cast in concrete. Permathene supplied HDPE profiles which were cast into the concrete in order for the liner to be attached by extrusion welding at the time of installation.

As part of QA/QC extrusion welds (pipe joints, etc) were spark tested to ensure integrity, fusion welded seams were pressure peel and shear tested. All testing and reporting was in accordance with the GRI (Geosynthetic Research Institute). Permathene installation crews are independently certified by the IAGI (International Association of Geomembrane Installers).

effluent pond installation

effluent ponds