|
A Technical Guide for Wine Producers
|
|
RECENT ARTICLES | WYNBOER HOME
Cost Of A Constructed Wetland At Goudini Distillery
A.R.Mulidzi
ARC Infruitec-Nietvoorbij, Stellenbosch
INTRODUCTION
The wine industry produces wastewater during the washing, racking and filtration processes, as well as during pressing and the first fermentation phases of wine processing. Such wastewaters have the potential to cause considerable environmental damage (Van Schoor, 2002). To offset this possibility, international requirements as well as national legislation exert pressure on wine producers to manage their wastewater responsibly. In fact, wastewater management has been part of winery management for many years. Constructed wetlands nevertheless offer a relatively new approach to the treatment of winery wastewater, an approach that has been extensively tested over the past decade (Mulidzi, 2005).
The rationale for using constructed wetlands as winery wastewater treatment facilities is that wetlands are most biologically active natural ecosystems on earth (Shepherd & Grismer, 1997). Several types of constructed wetlands have been developed for use in wastewater treatment. Of these, free water surface wetlands, in which the water surface is exposed, and subsurface flow wetlands, where the water table lies below the top of the material filling the wetland, are the most common (Shepherd, 2002). In constructed wetlands, vegetation growing on a thick bed of coarse gravel provides a substrate (roots, stems and leaves) upon which micro organisms can proliferate (Figure 1). Treatment occurs when the wastewater passes over the prolific root structures to which the bacteria are attached.
Apart from environmental friendliness and effectiveness, the main advantages of constructed wetlands are low construction and operating costs. As an example, this article provides a breakdown of the estimated costs of the construction of a wetland for the treatment of wastewater at Distell’s Goudini distillery (Figure 1).
CONSTRUCTION AND MATERIALS
The wetland is 45 meters long, 4 meters wide and 1.2 meters deep. It is filled to a depth of 0.9 meters with dolomitic gravel having a particle size range of 20 to 30mm). The porosity of the gravel bed was 35%, giving a total wetland volume of 162 cubic metres, and a pore volume (accessible to roots and wastewater) of 56.7 cubic metres.
The materials to be considered include the bed liner (floor and sides of the constructed wetland must be lined with an impermeable membrane to prevent leakage into the ground water), rooting substrate (sand or gravel), piping, pumps (varies with situation) and vegetation. Construction considerations include excavation of the bed and the structures needed to apply the wastewater and collect the processed outflow.
SELECTION OF PLANTS FOR CONSTRUCTED WETLAND
Plants in the wetland must be able to survive in a saturated medium. Plants which produce hard tissues are better than those having soft tissue, mainly because their root structures tend to remain more porous. High substrate porosity facilitates the inflow of oxygen, which is an essential requirement for odour-free operation, and which is also associated with reduced plant maintenance. Ideally, only native plants species should be used. Wherever possible, these should, in addition, be endemic to the locality in which the wetland is located. Avoid plants that could spread into the surrounding area as weeds. When selecting plants for constructed wetlands, the main factors to be considered are their pH and temperature tolerances. Worldwide, the most commonly used wetland plants are cattails (Scirpus spp.), bulrush (Typha spp.) and reeds (Phragmites spp.).
Plants suitable for use in constructed wetlands must possess certain characteristics. These include an ability to adapt to the local climate and to variations in that climate, tolerance to high concentrations of nutrients and pollutants and resistance to pests and diseases. The plants should also have deeply penetration root systems. Wherever possible the system should be flushed with clean water before planting. The aim of this process is to remove fine material from between the gravel fragments, thereby maximising pore volume and hydraulic conductivity. Planting density should be six to 10 plants per square meter. During the immediate post planting period, continuing until the plants are established only clean water should be applied.
HOW MUCH DID THE WETLAND SYSTEM COST?
Approximate costs associated with the construction of a 56.7 cubic metre pore volume wetland at Goudini distillery are tabulated below:
MATERIALS COSTS Dolomitic
gravel
540
tons @108.21 per ton= R 26 295
Dam
liner (6.8m x 50m),
1000µm
R
26.50 per m2
= R9 010 Excavation
and construction R
8 000 Sand
(transport costs) R
1 000 Drainage
pipes R
2 000 Other
fittings R
1 000 Water
pump R
3 000 Plants R1
000 (using local plants, where possible) TOTAL R
51 305 (excluding Vat)
The cost of R51 305 is considerably lower than that of alternative treatment systems, such as aerators. Constructed wetlands also have considerably greater aesthetic appeal than other forms of wastewater processing facility.
CAPACITY
Since the Goudini wetland has a liquid capacity of 56.7 cubic metres, it is able to process 4.05 cubic metres of wastewater per day at a retention time of 14 days. Where the quality of the wastewater is not heavily polluted, with a fairly low chemical oxygen demand, it may be possible to decrease the retention time to seven days, with a corresponding processing rate of 8.1 cubic metres per day.
CONCLUSIONS
The costs of constructed wetlands are low in comparison to those of other types of treatment system for winery and distillery wastewaters. Because wetlands do not require extensive maintenance, other than occasional cleaning and maintenance, their running costs are extremely low.
Information concerning the performance of constructed wetland will be published in a subsequent article.
For further information about the costs and use of constructed wetland for winery and distillery wastewater, contact Reckson Mulidzi on (021) 809 3070 or at mulidzir@arc. agric.za.
REFERENCES
Mulidzi, A.R. 2005. Monitoring performance of constructed wetlands in California. Wineland, May, 85-87.
Shepherd, H.L., 2002. Use of constructed wetlands in treating winery process wastewater: Design issues and field investigations. International Workshop and Seminar on Effects and treatment of cellar and distillery effluent, Stellenbosch, South Africa, 23-24 April.
Shepherd, H.L & Grismer, M.E. 1997. Constructed Wetlands: An alternative for treating winery wastewater. Vineyard & Winery Management. September/October, 65-68.
Van Schoor, L.H. 2002. The use of artificial wetlands in the purification of winery wastewater. Wineland. March, 33-35.
|
|
Wynboer is incorporated in WineLand, magazine of the SA wine producers.
Visit our sister sites:
|
| UP |
COPYRIGHT (C) 2000 WineLand |