Effectively managing salt levels in winery effluent is a significant issue for wine production. The use of sodium in particular through caustic soda has significant environmental impact which can lead to the build up of sodic soils.
To produce the perfect drop there is a lot of water, unspent grapes, juice, alcohol, sugar and a raft of other chemicals that will eventually end up flushed into the waste water stream. Leading industry bodies all argue that taking action early and limiting the amount of contaminants that get into your waste water not only is commercially savvy but will do your waste water a world of good too.
In wineries, wastewater mostly comes from cleaning operations and is “…primarily made up of wine, grape juice suspended solids (during vintage) and cleaning agents (eg NaOH, KOH)” (Mosse et al, 2011).
The inputs that are washed into the waste water stream can have a significant environmental impact and Mosse argues that it is essential that wine producers know the composition of their waste water in order for improvements to be made. The “… minimisation of both quantity and content of solutes and solids is desirable on both economic and environmental fronts” (Mosse et al, 2011).
In wineries salts form as a result of a reaction between strong alkali cleaning agents and wine. This has a significant environmental impact on soil and water quality, especially if high pH cleaning agents (eg caustic) are used.
The issue with too much sodium in the environment is that it reduces the availability of water to plants (Rengasamy et al,1994) and creates a saline environment. Mosse argues that a highly saline environment combined with high levels of organic matter (another by-product of wine production) exacerbate the clogging of soil pores and in turn further limit plant growth (Mosse et al, 2011). This has the potential to also lead onto sodic soils.
The Australian Wine Industry Public Environment Report (2003) indicated a value of 0.812 kg caustic/tonne of grapes (Kumar et al, 2009). For a winery that crushes 500 tonnes this means that over 400kg of caustic cleaning agent will typically be washed into their waste water stream annually.
What this all equates to is a significant amount of salt being produced and then flushed out into your winery soil. Once the salt has been flushed into the waste water stream there are not many feasible means for wineries to remove it. Highlighting the argument for preventing too much salt from entering the waste water stream.
Salt removal processes such as reverse osmosis are often expensive and require specialised equipment/infrastructure. A further problem with salt removal technologies is that a highly concentrated brine is often produced, which requires specialised disposal (Metcalf and Eddy 2004)(Mosse et al, 2011).
To counter issues associated with sodium, many winemakers are looking to potassium based cleaning agents. While there are associated benefits to soil fertility with potassium, Mosse (2011) states that long term application may still lead to changes in the physiochemical properties of the soil structure. The GWRDC makes it very clear that:
“Salts and many chemicals cannot be cheaply removed in treatment. Keeping them out of effluents to begin with, by reducing their use or early segregation, can be very effective.” (Day et al, 2011).
There is no doubt that by using less chemical there will be less salt washed into the waste water stream. However when looking at reducing salts in waste water, another key concept to take into account is the pH of cleaning products. Higher pH cleaning agents tend to have a faster rate of reaction, which in the modern winery is a valuable commodity. However, the downside is that they create more salt as a by-product, which ultimately ends up in the waste water stream. This is because a greater concentration of OH- ions are required to be neutralised from higher pH solutions. However, we know from basic chemistry that the rate of reaction can also be increased by using hot water (40-60 ºC). So rather than increasing the concentration of your cleaning products to increase pH, hot water can be used as an effective means to increase cleaning efficiency and reduce salt by-product output.
Every winemaker will tell you, the most tenacious soil to remove from a tank is tartrate. The reality is that tartrates can be removed with a non-dangerous, zero salt producing cleaning weapon. Warm water. The fact is, that if you are using chemicals to clean your tartrates, you need to ensure there is sufficient water to enable the tartrates to be dissolved in solution and thus removed from your tank walls. Chemicals only assist the water in doing it’s job, they don’t replace it.
AIRD alkaline cleaning products have a lower pH, to minimise salt production, and have additional surfactants to keep organic solids in solution meaning you can wash everything from your tanks. Give them a go - you’ll be glad you did!
Further Reading:
References
Day et al, 2011, Winery Waste Water Management and Recycling Operational Guidelines, Grape and Wine Research and Development Corporation
Kumar A, Frost P, Correll R, Oemcke D (2009) Winery wastewater generation, treatment and disposal: A survey of Australian practice. CSIRO. Adelaide SA.
Mosse et al, 2011, Review: Winery Waste Water Quality and Treatment Options in Australia, Australian Society for Viticulture and Oenology Inc, Australian Journal of Grape and Wine Research 17 p111-122.
Rengasamy et al, 1994, Introduction to Soil Sodicity, Co-Operative Research Centre for Soil and Land Management, University of Adelaide in conjunction with the CSIRO