Recent industry research by Siltbuster, performed across a mix of industries including food and drink manufacturers showed that effluent treatment is a significant area of investment for over a third of companies. Whether it’s being used temporarily - to solve a short-term problem or in case of emergency - or as a permanent solution, one technology which is increasingly being looked at by food producers is Dissolved Air Flotation (DAF).
How DAFs Work
Compact, nimble, modular, easy to operate and with a big treatment capacity for their size, DAF units can help companies boost their treatment capacity at peak times, reduce energy costs and stay compliant when a production problem strikes. But before we look at some first-hand examples of DAFs being used in these ways, it is worth understanding more about how they work.
DAF units are commonly used for the removal of fats, oils and greases (FOGs), suspended solids and associated Biochemical Oxygen Demand (BOD), where typically the solids have poor settling characteristics. DAF units create ‘white-water’ by dissolving air under pressure into recirculated water - as the pressure is released when the water is returned back into the DAF unit, micro-fine air bubbles are formed, which attach themselves onto the solids, and rise to the surface. Here, the accumulating solids thicken and dewater before being removed by means of a mechanical scraper. The addition of lamella plates to a DAF allows a relatively high flow rate of wastewater to be treated by a compact unit. For instance, at one typical customer’s site, our 2.4m wide x 6m long DAF unit was used to treat a peak flow rate of up to 144m3/h. DAF solutions are available whether the flow rate is 1m3 or 150 m3 per hour, making them ideally suited to the food and beverage sector.
In building-block fashion, modular DAF units can be easily combined with other equipment to create tailored solutions, where ancillary mixed reaction tanks, containerised dosing and pumping equipment can be deployed with the DAF to provide additional treatment capacity when it is needed.
How They’re Being Used
Whilst the technology behind a DAF is interesting, what is more instructive is the way in which they are being used. With both hire and purchase options available, DAFs are increasingly becoming an effective and efficient option within a plant’s effluent treatment process.
Seasonal Demand
According to our research, more than one fifth (21%) of food producers have no additional treatment capacity. Yet in the food and drink industry, particularly for producers of seasonal products, there can be significant production spikes. These can create big waste treatment issues – and therefore, cost implications. The intuitive answer might appear to be simply install a plant with enough ‘headroom’ to accommodate seasonal variations. This is not necessarily the answer, as it may mean that during the rest of the year the plant is oversized and may not operate efficiently. In response, many such as Heineken’s Universal Beverages Ledbury (UBL) are using temporary DAF equipment to flex up their water treatment capacity during these busy periods.
UBL’s plant in Herefordshire, which was the UK’s first large-scale beverage production facility, and is now a dedicated fruit and vegetable milling operation, is capable of processing over 15,000 tonnes per day. The apple milling period, which typically extends from late August to late November, pushes production to its peak, resulting in significantly higher levels of waste water with additional suspended solids and COD loading onto the site’s own large effluent treatment plant. The addition of DAF technology has allowed the beverage specialist to treat peak effluent flows during this period and discharge the water no matter the flow rate is.
Ideal for Emergencies
Over 30% of the companies in our study have had an emergency effluent treatment problem in the past year which put their compliance at risk. It is easy to understand why, as there are many factors which can impact on effluent, such as spillages, changes in product formulation, out of specification product dumps and new hygiene regimes. It is not just what comes down the pipe which can cause havoc. Changes in personnel, shortage of critical spares or chemicals, mechanical failure have all been known to cause effluent treatment problems.
Many food producers recognise that DAF units are ideal in such scenarios, not least because they are compact and can be very quickly and easily installed on site. If necessary, they can be delivered by lorry mounted crane and be fully operational within just hours of arrival. This is a major benefit for a system with such considerable treatment capacity.
Reducing Plant Stress
There is huge pressure on food production companies to increase their plant through-put. However, if the treatment plant does not increase its capabilities, a treatment problem will arise. In response, some companies deploy DAFs as a permanent supplement to the effluent treatment plant
Part of an Energy Strategy
The proliferation of Anaerobic Digestion (AD) facilities in the UK has created a demand for feedstock. In the right circumstances DAF sludge can be such a feedstock, adding to the appeal of this technology. Ballyrashane Creamery (part of LacPatrick) is a prime example where this route is being used. Whilst the treatment plant was primarily designed to ensure discharge compliance, the high concentration of fat in the effluent means that there is a secondary benefit of using the DAF. It is generating feedstock for AD facilities. At Ballyrashane, the recovered, highly calorific fat from the DAF is mixed with other sludges and feedstock to feed the company’s own AD plant.
Reducing Mogden Charges in a Small Footprint
With space on-site often being limited, having a solution that is not only effective, but able to fit within the very tight working constraints, is a key consideration. DAFs can come as small as 1.7m long x 0.9m wide, with such a small unit able to treat 8m3/hr. It was space efficiency which was one of the drivers behind Quattro Foods’ use of a DAF. The company wanted to remove FOGs from its wastewater prior to discharge to drain, so that it could expand production at its current site, but also reduce its Mogden charges. With space a premium, an iD5 DAF, featuring integrated mixed reaction tanks, was installed. The recovered solids and FOG matter were, as with Ballyrashane, ultimately used as feedstock for an Anaerobic Digestion facility.
Reduce Strain on Sewerage Infrastructure
Some companies are mindful of the pressure they are putting on sewerage infrastructure. In these situations, DAFs are sometimes being used within companies with FOGs to deal with. One such company is Dartmouth Foods, who has two factories surrounded by some of the UK’s most beautiful scenery. These sites are responsible for producing predominately shredded duck and chicken. The FOGs produced by this activity were putting such a large strain on the sewerage infrastructure that South West Water asked it to install a system for FOG removal.
Dartmouth Foods, who prides itself on its environmental credentials responded quickly, installing a grease interceptor. However, it soon became clear that it was not up to the task. The grease trap filled up quickly, and it just could not keep up with the pace of its production. It then introduced a Mix Tank, plus a packaged lamella DAF unit from Siltbuster, which treated 1.5m3/hr, neutralising the effluent before the FOG, TSS and associated COD were removed. The removed fat was pumped to the mixing tank with other sludges from the site before being pumped into an anaerobic digestion facility. Given the DAFs performance, Dartmouth Foods bought the system after just two months of use.
Growth Planning
Lastly, for companies like Euro Quality Lambs, sensitive to the connection between their business growth and their ability to manage their effluent, using DAF technology has been an easy way to boost permanent treatment capacity, keeping them compliant and ahead of the growth curve.
Conclusion
With DAFs being straightforward to install and operate, and the fact they are so simple to get on site fast, it is easy to see why they are becoming an increasingly important solution for the food and beverage manufacturing industries. This proven, widely used technology has a low running cost, is easily maintained with minimal moving parts and can work alongside chemical dosing within a small footprint. As food producers and key decision makers start to realise the benefits of expanding their production capabilities, DAFs are becoming increasingly popular.
Clwyd Jones, Business Unit Manager at Siltbuster Process Solutions
Website: www.siltbuster.com
Telephone: 01600 772256
Email: enquire@siltbuster.com
