Dr Richard Coulton explores the key effluent treatment technologies and how they are being used
The focus of UK manufacturing is typically, and understandably, on driving up plant throughput. Although this is a valid and sensible objective, it can put a big strain on the effluent treatment plants of many companies. These plants play a critical part in the production process, dealing with the wastewater produced as a natural by-product of day-to-day operations. Yet they are often situated at the back of factories – overlooked and under invested in. Effluent treatment problems have considerable effects on compliance and the latest technologies can be used to improve the situation.
Through its role of providing effluent treatment equipment to the UK’s process manufacturing community, Siltbuster Process Solutions has gained a good sense of how wastewater treatment plants are managed. Although they are frequently out of sight, the company firmly believes that they should be anything but out of mind. Its team therefore wanted to better understand how and why companies prioritise, invest in and manage their effluent treatment plants. To achieve this, it commissioned an independent study among the production directors and engineers responsible for over 156 manufacturing sites in the UK and the findings were very revealing.
Why investment in effluent treatment needs to be a priority
According to the study, 30% of companies had experienced a significant effluent treatment problem in the previous year that put their compliance at risk, with effluent treatment plant failure or breakdown the most common cause (31%).
A third of the companies questioned said investing in waste treatment plant is a priority, but 28% of production heads reported that their treatment plan is under-invested in. 41% of the companies last invested in the plant more than five years ago and 23% more than 10 years ago. 15% believe this is because the Board is only interested in investing in new production lines; a further 13% say that effluent treatment is viewed as a peripheral area that senior management doesn’t want to think about.
However, if carefully planned, waste treatment can, in fact, be an enabler – a well thought through effluent treatment strategy can help companies reduce their energy and water costs as well as cutting maintenance costs and plant downtime. The good news is that the technology to achieve this is available.
The latest effluent treatment technologies
One technology that should be high on the list for consideration is dissolved air flotation (DAF), which is being used in many interesting ways.
DAF units are commonly used for the removal of fats, oils and greases, suspended solids and associated biochemical oxygen demand (BOD), which would typically 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 to be treated by a compact unit. For instance, at one typical customer’s site, Siltbuster’s 2.4m wide x 6m long unit was used to treat a peak flow rate of 144m3/h and DAF solutions are available whether the flow rate is 1m3 or 150m3/h.
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. This flexibility means DAFs can be used in a variety of creative ways to aid problem solving.
For example, producers of seasonal products can experience significant production spikes that create big waste treatment issues and serious cost implications. To manage this, Siltbuster is increasingly seeing manufacturers using temporary DAF equipment to add extra effluent treatment capacity during busy periods.
Well-planned effluent treatment can also deliver broader commercial benefits to a business. For example, Siltbuster helped Dartmouth Foods solve a wastewater problem and, at the same time, reduce its energy costs. The fats, oils and greases (FOG) produced at its meat processing plant in South Devon were putting such a large strain on the local sewerage infrastructure that it was asked by the region’s water company to install a system for FOG removal.
Siltbuster installed a combination of a mix tank and a packaged lamella DAF unit, designed specifically to remove suspended solids. The system can treat 1.5m3/h, neutralising the effluent before removing the FOG, TSS and associated COD. The removed fat is then pumped to the mix tank where it is combined with other sludges from the site before being pumped into its anaerobic digestion facility where it is used as feedstock. As a result, Dartmouth Foods has the reassurance of knowing it is maintaining its consent compliance at the same time as improving its environmental credentials. Importantly, using the waste from its processing plant to generate energy has improved the overall cost efficiency of the site.
Over 30% of the companies involved in Siltbuster’s study had experienced an emergency effluent treatment problem that put their compliance at risk and, again, DAFs are ideal in this scenario. They can be installed very quickly and easily and, if necessary, can be fully operational within just hours of arrival.
DAF technology is also an easy way to boost permanent treatment capacity, keeping companies compliant by managing effluent treatment as production increases.
Bringing MBBR technology to the UK
Moving bed biofilm reactors, or MBBRs, are another technology that the company has been focused on developing to support the market for the better management of effluent. While it’s true that MBBR is not a new technology –having been in successful operation in Scandinavia since the late 1980s – its use has yet to become established in the UK. This is surprising, when in comparison with a popular technology such as submerged aerated filter systems, the MBBR process offers greater treatment capacity per unit volume and so, on a like for like basis is considerably less expensive.
Siltbuster has been able to successfully apply MBBR technology to a number of temporary and permanent applications, including BOD removal from municipal sewage, nitrification and the treatment of various industrial effluents ranging from whiskey distilleries to carrot juice. In doing so the company has learnt an awful lot about the technology and the high removal rates it can sustain. As a result, it is more convinced than ever that MBBR has a significant role to play in industrial wastewater treatment. MBBR technology has been extensively embraced by the rest of the world, and the firm’s successful trials have demonstrated that it can work equally well in the UK, in a multitude