Carolyn went to New Zealand to participate in a technical tour focussing on the management and re-use of treated winery wastewater, with particular reference to wine grape irrigation. This article focuses on the visits to industries other than wineries to see how they manage their wastewater. She reports …
The Western Cape is experiencing one of its worst droughts to date. Urban users are currently limited to 105 L of water per person per day, so water is a precious, scarce resource. Approximately three years of good rainfall is needed to recover from the drought. This implies that despite the winter rainfall of 2018, the region will still feel the negative consequences for some time thereafter. Therefore, alternative sources of irrigation water for vineyards, e.g. using treated wastewaters, will become more important under the above-mentioned conditions or if climate change reduces long-term winter rainfall.
The geography and climate of Palmerston North
Palmerston North is a city on the North Island of New Zealand. It is located on the eastern Manawatu Plains. Palmerston North is the country’s seventh largest city. The climate of Palmerston North is temperate with maximum daytime temperatures averaging 22°C in summer. Average daily temperature is highest in February and lowest in July. Annual rainfall is approximately 918 mm, with rainfall occurring throughout the year.
Massey University dairy farm near Palmerston North
Cows come to the milking shed twice per day. Whilst they are waiting to be milked, they wait on the concrete pad (Picture 1). The concrete gets dirty from urine and dung, and has to be washed regularly. The washing process generates approximately 70 L of effluent water per cow per day. It should be noted that the amount of dairy effluent water generated is highly variable and in New Zealand there are no government guidelines as to how much water can be used per cow per day. However, the wastewater produced from the milking cows is of a high quality. The wastewater is collected in deep, large effluent dams. In New Zealand, cows are generally not kept indoors, because it is not cold enough. Though, when conditions become very wet, the cows have to be housed indoors. In the cow houses where they are housed (Picture 2), they eat a lot and generate substantial amounts of dung and urine. The waste is collected and stored in a wastewater dam (Picture 3), which is clearly marked with a danger sign. Cow house shelters yield wastewater with poor water quality, and high nitrogen (N), phosphorus (P) and potassium (K) levels. There are guidelines in New Zealand for the wastewater dams and storage. Sludge is removed from the wastewater dams every three years. The size of the storage dam that is required to store the dairy wastewater can be calculated using an effluent dairy storage calculation. Inputs include parameters such as climate, soil, solids, catchments and irrigations. The storage dam should also have a lining. The wastewater is used to irrigate farmland. There are guidelines about the amount of N that can be applied to an area. This amount is variable. In the Palmerston North region, the amount of N that can be applied via the wastewater is 150 kg N per ha per year. In addition, the application of irrigation should not cause drainage or run-off. No soil sampling or monitoring of the effluent water quality is required.
PICTURE 1. The cow pad at Massey University dairy farm near Palmerston North.
PICTURE 2. The cows had to be housed indoors due to wet conditions outside.
PICTURE 3. The wastewater dam with its warning sign at Massey University dairy farm near Palmerston North.
Affco meat processing plant near Palmerston North
The wastewater from the Affco meat processing plant near Palmerston North does not contain a lot of blood, because there is an excellent recovery of blood in the facility. Thus, the wastewater contains less N than in the past. The P content in the wastewater has to be managed. The P comes from the stomach contents. The P also doesn’t break down or change form. The solids from the processing plant are collected in a solid pond. The solid pond contains green waste with floatables in it. The solids could be used for composting. The associated compost results in a lot of weeds, because the animals have living weed seeds on their bodies. Therefore, composting is not a high priority. Water is drained off from the solid pond. For the liquids (Picture 4), there is an anaerobic pond that drains into an aerobic pond. The water is used to irrigate pastures. Up to 400 kg per ha per year of N can be applied via the irrigation water. Nutrients in the wastewater promote the growth of the pastures. However, elevated P in the soil can be a concern. Approximately 660 mm of water is applied to the pastures per year.
PICTURE 4. Liquid storage pond at Affco meat processing plant near Palmerston North.
Municipal wastewater treatment plants near Palmerston North
The sewage goes to the treatment plant. Historically, the resource consent was to the river, but now it will be to land as well. At the treatment plant, there is a digestion tank. The wastewater dam has submerged aeration (Picture 5). Thus, in the dam bubbles are continuously been blown up through the water. The sludge is composted (Picture 6). Currently, research is being done to see what combination of materials will yield the best compost. For composting, the material must be contained on a concrete pad. It is also important to turn the compost heaps properly. The compost can be used by garden centres or the council. In New Zealand, a cut and carry process (Picture 7) is used to make straw. The advantage of this is that animals are kept off the land.
PICTURE 5. The municipal wastewater treatment dam at Feilding near Palmerston North.
PICTURE 6. Composting of sludge at Feilding municipal wastewater treatment plant.
PICTURE 7. Cut and carry process used at Feilding municipal wastewater treatment plant.
In this area, there is an abundance of land and the terrain is very flat. The water table is very shallow. It can become very dry over summer. The municipal treatment system at Himatangi Beach is a basic, simple system which does not require much management (Picture 8A – C). The municipal wastewater is collected in a dam, which has a floating wetland. The water is irrigated to grazed pastures with a number of different irrigation systems. One hundred and fifty kilograms of N can be applied per ha per year. Note the unwanted ponding of municipal wastewater which was observed at the site (Picture 8D).
PICTURE 8. Irrigation of municipal wastewater to grazed pasture (A, B and C) at Himatangi Beach near Palmerston North. Notice the ponding in Figure 8D.
The municipal wastewater dam at Shannon has a sophisticated control system that can turn irrigation on and off. The system will also stop irrigating when the permitted amount of N per year has been applied to a particular area.
In South Africa and New Zealand, there is some level of legislation regarding irrigation with wastewater. Information pertaining to dairy effluent is readily available online for the New Zealand dairy industry. In New Zealand, beneficial irrigation with dairy and municipal wastewater is strived for. The element of concern in dairy and municipal wastewaters is N. Limits for elements in wastewater are not given in absolute values, but in amount of element applied per ha.
The South African Society for Enology and Viticulture (SASEV) for awarding the prize for the best article in 2014. Winetech for funding of the prize for best article in the SAJEV journal. Funding for the technical tour was also provided by the Local IWA Organising Committee. The ARC Infruitec-Nietvoorbij for the opportunity to undertake the technical tour. All my hosts in New Zealand who showed exceptional hospitality and showed such an interest in the South African wine industry.
– For more information, contact Carolyn Howell at firstname.lastname@example.org.