By way of introduction can I please point out from the off-set that I am fairly new to the distilling industry and my only real interest prior to 2009, was in collecting single malts, a hobby that I still invest in, much to the despair of my partner who cannot understand why I want to just collect bottles of malt whisky and not drink them!
I should also point out that this paper concentrates solely on our work undertaken on Scottish Malt Whisky Distilleries, although I would like to point out that the team at Penderyn Distillery in Wales have also helped in preparing this paper, however all their effluent is tankered away from site at present. Similarly at St Georges in England their effluent is tested and sent for land-spreading. However I would like to apologise to our Celtic Cousins from Ireland who might be here, having felt the wrath of your own Environment Agency (EA) in other industries, I am sure that this paper will have some relevance to you as well as our friends in Scotland, should your own Environment Agency start to move the goal posts on effluent discharges.
Copper within whisky is traditional associated with coming from the distillation processCopper pot stills are used even on the newest malt whisky distilleries for their efficient heat transferring process, the Copper playing a very important role in the spirit quality, as the spirit vapour comes into contact with the Copper still, it generally reduces the less desirable sulphur compounds, such as Dimethyl Trisulphide (DMTS). The greater reactions being between the Copper and the spirit vapour than the copper and spirit still in its liquid form. Although our forefathers could not have known the full benefits of using Copper in the manufacturing of pot stills, there is little doubt that overall the use of copper in the distilling process has a positive benefit to the process
However Copper picked up at this stage of the distilling process is in a soluble form, and although some will be picked up in the final malt whisky, tests showing these levels in Scottish Malt Whiskies to be in the range of 385ng/l – 480ng/l. Some will pass through the whole of the process and find its way into the final discharge effluent.It is also picked up when various parts of the system are cleaned. Normal cleaning programmes introduce high alkaline detergents (caustic), which pick up the Copper as a Hydroxide and carry it through into the discharge water.Typically levels of above 10ppm (mg/l) are found in the effluent at this stage
The traditional way of extracting the Copper would have been by allowing balancing of the effluent discharge. This means typically having a large enough tank system to be able to hold at least a full day’s worth of effluent from the distillery. This then balances out (hopefully) the extremes of pH variation throughout a days’ discharge. A lot of sites then have biological processes, to hopefully take out the high levels of copper. This would be okay if the biological plant was good enough to cope with the normal standard discharges. However discharges with high pH from the cleaning process, followed by low balancing capacity, usually resulted in traditional effluent treatment systems not always taking out copper. Say a balance tank that can only hold 50cum3 and the site is discharging 200cum3/per day, then the holding capacity could be as low as 6 hours. If this ties in with a major cleaning programme then the effluent plant would not be capable of balancing out the effluent, including dealing with the Copper.
Discharges from distilleries can go to a variety of water courses, e.g. town sewage, river, lake or tidal. Both the Scottish Water (SW) and Scottish Environment Protection Agency (SEPA), driven by European Legislation such as the Priority Substance Directive, have been forced to put pressure on distilleries to clean up their effluent and have amongst these changes have requested tighter and tighter discharge consent limits for Copper.The amount of Copper allowed in discharges varies tremendously throughout Scotland, for those sites discharging to Scottish Water, the discharge consent for Copper varies from a high of 40ppm down to a low of 2ppm. This range tends to be in place as some discharges then go for further treatment at Scottish Water run facilities. The norm for SEPA which covers the majority of distilleries, particularly in the high concentration area of the Speyside where typically the permitted level for Copper discharge is 0.5ppm (mg/l)
Although personally not involved historically I understand that previously sites did not have issues in general with obtaining discharge limits in the range of 2 – 5mg/l. Indeed I understand that it is only since 2001, that there have been discharge limits for Copper. Since then however there have been further reductions in Copper to levels, some discharges being of the order of 0.5mg/l and this has proved a challenge to most distillers.
Several methods of removing the Copper have previously been proposed by a number of companies, systems such as Reverse Osmosis and Electro – Coagulation, which although good at taking out metals, are not very good at coping with the organic fouling and tend to blind quite easily. In addition the cost and maintenance of the plates used in this type of system was found to be extremely expensive.
For the purpose of our work once the disadvantages of the aforementioned systems had been looked at more traditional systems of effluent treatment were accessed, in many industries the normal way of treating effluent is pH correction, followed by a variety of chemical combinations to take out the Suspended Solids and normally some of the Chemical Oxygen Demand (COD).
It is known that the maximum solubility of Copper is in the range of pH 8 – 8.5, therefore using samples obtained from within the one of the Scottish Distilling companies, initially tests were undertaken to see how much Copper could be removed using this pH range as a guide.
A range of, metal precipitants, coagulants and polymers were also tried to bind up the Copper and other solids, once the critical solubility had been obtained. It was found that some coagulants do not work well within this alkaline pH range, similarly with the metal precipitants, one of which would only work at an acidic pH, thus putting more cost onto the treatment process, by having to adjust the pH. Likewise there was a variety of success with polymers. However eventually it was found that Aluminium based coagulants, were effective however it was found that the polymer used would need to be site specific.
In addition it was found that although the reduction was good, typically above 90% in terms of Copper reduction this process on its own would not be good enough to take out all the Copper, especially for those sites with discharge consents of less than 0.2mg/l. And therefore the effluent would still need to go to a further treatment as most of the initial sites we worked with had biological processing, the suggested combination of this additional treatment in conjunction with the existing biological treatments was thought to be more than adequate to take out the remaining Copper, certainly when discharge is to river
The next stage was to find a physical technology that would assist the chemical process and remove the solids from the effluent water. To this end it was found that Dissolved Air Floatation (DAF) units were effective in this area, and support was obtained from a company to further prove the technology would work.
Based on the work undertaken above and working with people within the one of the distillery groups, it was found that the best place to fit in this process would be at the front end of a site’s effluent treatment and a test site was given to set up the first set of trials.
The trials proved very successful with regular levels of 1ppm or less being obtained off the DAF/Chemical process for the effluent going onto the old biological process. On average the initial effluent had Copper levels of 4ppm; therefore reductions of over 70% in Copper were obtained. In addition as other solids were removed this assisted the biological process by taking off some of the heavier loading from the bio-towers, which follow this new stage.
This is because the chemical/physical treatment is only capable of taking out the un-dissolvable Chemical Oxygen Demand (COD); the remaining soluble COD such as the sugars have to be taken out by biological treatment. However the ‘solids’ removed is the part of the effluent likely to cause blinding on biological treatments; therefore their removal would be an added bonus to any treatment processes
As a result of this success, further units were installed in 2 other distilleries within this distillery group. In addition the chemistry part of the process on its own was further applied to a system at another distillery. In this application the treatment was undertaken post biological to take out the solids, as there was a good Balancing system up front of the Bio-Tower, and the initial driver on this site was to ensure that the site met its discharge consent from Scottish Water of pH within 5 – 11 and Chemical Oxygen Demand (COD) lower than 4,000mg/l. Interesting the Copper level for this site is unusual in that it is required by Scottish Water as ‘Soluble Copper’ one of only 2 distilleries in Scotland working to this particular discharge requirement with Scottish Water Needless to say all 4 of the systems above are still in operation and working successfully.Based on this work, an enquiry was obtained from another company with a distillery that discharges to a Scottish Water treatment works and other than a Balancing Tank had no effluent treatment, as a result site were coming under pressure from Scottish Water to undertake further treatment. Amongst the factors to take into consideration on site was the limited space available to install any treatment system, as the Balance Tank is situated near to a service road and part of the distillery tour route.
Initial tests were undertaken and showed that there was no problem with repeating the successful chemistry employed elsewhere. However it soon became apparent that the effluent on site could vary, and normally pre-treatment could be in the order of pH 11 – 12. The discharge from site being a very generous 5 – 11pH from Scottish Water.Tests were therefore undertaken on the sites effluent, using these high pH’s to see if there was still sufficient reduction in Copper using the proposed chemical programme to take the site to under their discharge limit of 10ppm (10mg/l) Total Copper
As can be seen the level of Copper beforehand, on the day of testing were not unduly high being in the region of 12mg/l through the day. (Red line) The pH alteration being achieved by site pumping finished Cleaning in Place (CiP) cleaning solution over to the almost empty Balance Tank and thereby raising the pH, (blue line) the main alkaline detergent used on site is Caustic 32%. If required fine-tuning of the pH was undertaken in the site laboratory.Overall the results obtained during this experiment showed as anticipated, but somewhat satisfying trend, in that as the pH raised the level of Copper remaining, increased, (wavy purple line) although on this particular site, this was still within consent limits. No other aspect of the chemical treatment, in terms of Coagulant and Polymer were adjusted during this experiment.
A sample from the day was also tested independently back at the group’s main laboratory and found to be 3.57mg/l summary for the work undertake at this particular site it was found that the chemical programme on its own had several positive contributionsIt was able to take the Copper to within sites discharge limits for Total CopperThe pH was typically reduced by 1pH so even at a high pH of 12; the chemical treatment on its own was good enough to take the pH to within discharge consent.There was a reduction in Chemical Oxygen Demand (COD), although a generous allowance of 5,000mg/l, a general reduction of the order of 20% means that as the site is under Scottish Water Mogden Formula charging then there is an additional cost saving by reducing the CODThe same applies to the Suspended Solids (SS) allowance, again a generous consent of 2,000mg/l, but again as the SS reduction is substantial (65%) then this contributes again to a reduction in the effluent charging to site
Overall so far, sites own figures have found that the reduction in Copper has been in the order of 30%, this is mainly due to working at the high pHsIt was found that in future should site be required to reduce their discharge consent for say Copper from 10mg/l down to 5mg/l then by refining the pH to within 8 – 9.0 pH was adequate to strip out more of the Copper.
To demonstrate this samples were taken at various pH’s these were then treated at their current pH range, as previous and then as part of the initial treatment, Hydrochloric Acid (24%) was used to take the pH lower and then the already suggested chemical treatment programme was introduced. The results were extremely encouraging and show that maybe when the goal-posts are narrowed by Scottish Water in the future, then this treatment programme can assist this particular site in achieving it next anticipated discharge consent.
Hydrochloric Acid was used as there are no issues with chloride consent in the site’s discharge and 24% is still classed as irritant rather than corrosive as Hydrochloric Acid is at higher strengths.With regard to the future using this technology, there is already interest from several other distilling companies to install this system mostly alongside technologies, predominately biological, and usually as an initial treatment stage to take off some of the loading to the biological programme on sites
That said there are still several sites with currently no effluent treatment, where with the Scottish Water discharge consent being between 5 – 10mg/l, there is no reason why this technology on its own would not be able to assist these sites meet their discharge consents.
Longer term it is felt, that whilst this technology has a place, it is not good enough to entirely strip out the whole of the Copper, and certainly in terms of COD reduction 60 – 70% is the maximum ever likely to be achieved. Therefore should discharge licences be reduced even further in the future, it is suggested that technologies such as micro-filtration, or electro-coagulation might be possible solutions if the effluent is treated by physical/chemical processing first to keep the loading off such systems.
The process outlined is in itself also not reducing the Copper it is merely transferring the Copper (and other parts of the effluent) from one area to another, and still has to be disposed of in a sludge form. Although currently the majority of the sludge goes for land spreading there is nothing to say that long term this route may change and as a result the process, whether chemical or physical might have to change also.
Alternatively processes such as anaerobic digestion, working alongside this technology should be adequate. Indeed anaerobic systems are already in use within some distilleries, although sadly the claims made by the companies selling such systems have not lived up to the expected return on investment, certainly in terms of energy return, leading to some scepticism on some part as to the value of this treatment However for now we will have to wait and see what the full implication will be of European Legislation such as the Priority Substance Directive, and to see how Scottish Water and SEPA interpret this legislation.
In conclusion I would like to thank FaridTuran of Wehlre Environmental who was instrumental in starting this project and to the staff at the various distilleries where this technology is being used for having the confidence to stick by us.