Mainly cattails (Scirpus) and bulrushes (Typha), with a plant density of approximately 4 plants per m2, are used. The root development of these reeds is very effective and roots, together with gravel, serve as substrate for micro-organisms while the roots of the reeds also supply the bacteria with oxygen. The roots of reeds can also secrete sugars which sustain bacteria. These plant species also offer resistance to diseases and plagues. More than one plant species are used in the wetland to retain the ability to offer resistance. The reeds are established once the wetland has been filled with fresh water. Once the plants have reached maturity (approximately 3 to 12 months), wastewater is allowed into the wetland at a very slow tempo (approximately 10 days retention time in the system) and flowing at a 0,5 % slant through the wetland. Micro-organisms, such as algae and bacteria, function in a mutually symbiotic relationship and purify the wastewater especially by breaking down organic pollution elements. These disintegration processes occur more rapidly in the daytime and in open areas than in the dark or shadow.
Two kinds of artificial wetlands are used in water purification. In a free-water wetland the water is above the gravel of the wetland, while the water in a sub-surface wetland is below the first layer of gravel and therefore not visible.
It is important to note that artificial wetlands serve as a secondary process and that solid particles first have to be separated from the wastewater to allow the system to function efficiently. Cellar wastewater normally contains high levels of COD, salts (Na in particular) and a low pH. It also contains organic acids, alcohols, proteins and sugars. Natural bacteria present in the wastewater may hasten the breaking down process. However, cellar wastewater contains 10 to 100 times more organic substances compared to municipal wastewater. It is therefore necessary that aeration plays an important role in water purification, otherwise the plants’ growth may be impaired or they may even die. Where possible, mechanical aeration should therefore precede the wetlands process. A constant inflow of the same quality wastewater is also important for efficient water purification. Variation in composition of wastewater must therefore be prevented where possible. The quality of the outflow should comply with the irrigation requirements that are applicable to any crop.
Artificial wetlands systems in Adelaide, Australia
During a visit to artificial wetlands systems in Adelaide, Australia, various cellars were visited with Mr Anthony Radford of the South African Environmental Protection Agency (EPA) to investigate wastewater treatment methods. In the Barossa valley artificial wetlands are successfully used in the purification of cellar wastewater by Miranda wine cellar, as well as in the McLaren Vale area at Boarsrock wine cellar. Although no statistical information was available, it was clear that this technique can be successfully applied in water purification and that it is probably the cheapest water treatment method for cellar wastewater.
Miranda wine cellar presses 6 000 tons of grapes annually. Wastewater is not separated from rainwater or solid particles and a total of 7 megalitres of wastewater is generated per annum. This water is pumped into a sealed dam, away from the cellar premises. Sewerage water is also pumped into the dam. The wetland is 3 m wide, 82 m long and 1 m deep and sealed with 1 mm black plastick. The 82 m length (L-shape) is composed of “cells” consisting of 1 m coarse gravel (50 mm diameter) for turbulence and the accompanying oxygen enrichment, 5 m fine gravel (20 mm diameter) in which reeds have been planted, for pH adjustment, and 4 metres coarse gravel without plant growth, the so-called “clean” area. Cells are varied by the establishment of reeds (Phragmites australis) in water or gravel. Water migration occurs when water is allowed to flow in through two 200 mm openings, at a flow tempo of approximately 9 litres per minute. Once the water has moved through the wetlands, it is collected in an irrigation dam, used for the irrigation of Cabernet Sauvignon for the past 3 years. Although no data was available, the water quality complied with national legislation for irrigation, said Mr Radford. The colour of the water changed noticeably from the inlet to the outlet from reddish brown to clear, while the characteristic anaerobic smell of cellar wastewater was entirely absent at the outlet.
Boarsrock wine cellar also presses 6 000 tons of grapes annually, but solid particles are separated from the wastewater by using basket sieves. Water is then pumped into two gravitation tanks. As soon as it flows over, the wastewater enters the wetland. The wetland is approximately 300 m long and forms 3 large serpentines so that a total area of 1,5 ha is covered. The same principles for cell size, type of gravel and type of vegetation apply as for Miranda wine cellar, but the wetland is sealed with a clay layer instead of plastic. Inflow moves through the 300 metres of wetland between 12 and 20 days, ending in an irrigation dam. The water quality in the system is monitored on a monthly basis in the various cells and indicates that the system is extremely successful. Data indicates that this system may increase pH values from 3,8 to 7,4 and reduce biological oxygen demand (BOD) values from 11 600 mg/l to just 8 mg/l in the peak harvest period.
Artificial wetland systems in California, USA
During a trip to the USA artificial wetland systems were visited at three wine cellars in the Napa and Sonoma areas, in the company of Dr Heather Shepherd, an expert and reasercher in this field. The wine cellars were Imagery, Benziger and Fetzer. All three wetland systems are sub-surface systems and wastewater is separated from solid particles before being exposed to the wetland to ensure efficiency of the systems.
Imagery wine cellar presses 2 000 tons of grapes annually. At this cellar the artificial wetland system was newly constructed (2001) and some plants were not yet established. Before exposing the wastewater to the wetland, the solid material is separated from the wastewater by means of a drum filter. The wastewater is then pumped into an aeration dam, whereafter it is pumped into the wetland at a 2 % slope. The wetland then serves as the next polishing process. The purpose of the 2 % slope is to allow water flow when the plant roots are growing densely in the wetland. Bullrushes and cattails were already planted, while other species such as calla lilies (arum), kannas (canna), irises (iris) and arrowheads (sagitaria) were to be planted to evaluate their effectiveness. Although the wetland was still in the construction phase, no water quality data have been generated. The intention was to purify 600 000 litres of wastewater per wetland hectare at a retention time of 10 days. The total wetland splits into two sections, each with a width of 7,5 m and length of 19 m. Pea bud size doleritic gravel (5 mm diameter) with 35-40 % porosity is used to fill the depth of 1 m. Although this wetland was not in use during the visit, it was already clear that the 2 % slope would probably be too steep to establish plants.
Benziger wine cellar presses 1 200 tons of grapes per annum. A subsurface of artificial wetland, 40 metres long, 7,5 metres wide and 1 metre deep, with a slope of 1 %, is constructed and 470 000 L wastewater can be treated per wetland hectare on a daily basis, after being separated by a drum filter and exposed to an aeration dam. Retention time is 4 days, mainly because it involves a polishing action only. COD-values of the cellar wastewater were reduced from 8000 mg/L to below 5 mg/L by the artificial wetland, through the establishment of mainly cattails and bulrushes, with fewer calla lilies and cannas. The wastewater flows into the wetland by means of a perforated pipe every 14 metres at a right angle to the direction of the stream. The 5 mm diameter doleritic gravel that is used, has a porosity of 30-40 % after a root mat has been formed.
At Fetzer wine cellar a wetland was constructed in 1998 with a 0,5 % slope in a previously unsealed sedimentation dam (90 m x 51 m x 1 m) and filled with unsorted local boron containing gravel (20-50 mm diameter). Cattails and bulrushes were established mainly in the wetland. A retention time of 10 days is used. Thirty five thousand tons of grapes are pressed at this cellar annually and the intention is to purify 360 000 L wastewater per wetland hectare on a daily basis. In the previous season (2000) the wetland was overburdened with organic material, however, since the solid particles had not been separated from the wastewater, the wetland was being rehabilitated during the visit. Another problem was the high boron content of the local gravel used, which caused the boron content of the water to increase to such an extent that it could not be used for irrigation.
Artificial wetlands in the South African wine industry
Although the purification of cellar wastewater by artificial wetland systems is being successfully applied in Australia and the USA, it cannot be simply accepted that all elements in successful wetland systems will be the same in various regions and countries. Existing information must therefore be adjusted before being applied to South African conditions. Current research results indicate that wastewater from wine cellars and distilleries in South Africa does not comply with the minimum legal requirements for application to natural water resources or to soil. However, values do not fall outside the general limitations for treatment by artificial wetlands and expectations are that artificial wetlands also lend themselves to being used with great success in the South African wine industry to purify cellar and distillery wastewater. The most important issues in the design, planning and implementation of these systems under South African conditions are currently being investigated by ARC Infruitec-Nietvoorbij and includes especially the type of construction material, layout, type of vegetation, seasonal availability of wastewater, amount and composition of wastewater generated, as well as the size of wetlands for specific volumes of wastewater. This project forms part of a bigger programme consisting of 8 projects in a consortium with ARC-Engineering and the University of Stellenbosch (Department of Chemical Engineering), and is partially funded by Winetech. The purpose of the bigger programme (Winetech Environmental Programme) is to develop an integrated management programme for the handling, treatment and purification of effluent from the wine, spirits and grape juice industries, but also to prevent research by these organisations from overlapping.
Three small-scale experimental wetlands (6 m x 2,4 m x 1 m) have been constructed at Spier wine cellar in line with Dr Heather Shepherd’s specifications and another three at Goudini distillery (Olof Bergh Brandy), while two large-scale wetlands (45 m x 4 m x 1 m) were constructed at Goudini. The small wetlands have each been dug 6 m long, 2,4 m wide and 1 m deep and lined with 1 mm plastic. Dolomitic gravel (19 mm diameter) was used as a substrate for roots, algae and bacteria. The two large-scale wetlands are used for a large-scale comparison of substrates of dolomitic gravel and local soil. Local plant species, namely Typha and Phragmitis australis, with a plant density of 10 plants per m2, have been established. Normally the plant density is lower, but since some of the plants had to be removed during the trial period, more plants were planted. The vegetation is established in cells of 1 m x 2 m, with 0,5 m gravel separations. Fresh water was first used so that the reeds could grow efficiently and wastewater will be applied in the coming pressing season.
International workshop presented in 2002
In April 2002 ARC Infruitec-Nietvoorbij and the University of Stellenbosch, in conjunction with SASEV, offer an international workshop and seminar about the responsible management of cellar and distilling wastewater. The workshop and seminar are funded by Winetech and the South African Wine Industry Trust (SAWIT). On this occasion 4 international speakers, i.a. Dr Shepherd and Mr Radford, will appear as guest speakers.
For further particulars about the use of artificial wetlands in the purification of cellar and distilling wastewater and the international workshop and seminar, contact the author.
About the Author:
Lourens van Schoor, Environmental Manager, ARC Infruitec-Nietvoorbij, Tel. 021-809 3158 , Fax: 021-809 3002, e-mail: email@example.com