Keeping the UK’s water clean is a tricky job. A number of water firms have faced public anger and government criticism for not protecting supplies. Keeping track of water quality – and the extent to which wastewater treatment plants are up to the task – is an engineering challenge.
But a new engineering solution could provide a lightweight and remote way to ensure plants are doing their jobs: tiny tracking chips added to the sand that filters liquid.
Hydro International has launched a new UK tertiary wastewater treatment partnership with Netherlands company Brightwork, whose moving bed filter technology is designed to remove suspended solids, nitrogen and phosphorus from wastewater. The goal, says Hans Wouters, managing director at Brightwork, is to make the process of filtration monitoring easier to install and monitor, and more reliable at a time when water companies are under pressure to meet tighter discharge permits.
Water operators need to know not only what is coming out of a plant, but also what is happening inside the process. Sand is used as the filtering material, but part of that sand is also constantly being cleaned and recirculated. As Wouters explains, that means “we do not have to stop the filter to backwash the filter, to remove the solids and the biology… we are doing that simultaneously”.
The sand’s continuous movement is what makes the process useful – and simultaneously tricky to track. Brightwork’s Sand-Cycle system places small RFID tags into the filter bed, which move with the sand. As they are lifted through the system, an antenna records each tag’s identity and timestamp. That data can then be turned into a live picture of what is happening inside the filter.
The tags move through the filter bed, get sucked into the airlift, pumped to the top, washed, then brought back again, giving a new stream of process data to operators. “We are actually collecting a database of timestamps and unique tech numbers, and with this database we can convert these data into process-related data,” Wouters says.
The ability to track the sand’s movement helps counter uneven filtration and poor removal of pollutants – raising awareness of the need for maintenance earlier than it might otherwise be noticed. If tags are moving differently, operators know the sand is not moving homogeneously. Lost RFID tags can indicate possible sand washout, while the number of tags passing through the airlift can act as a proxy for wear and tear.
Ross Brace from partner Hydro International welcomed the new technology. “With ammonia, phosphorus and nitrogen limits expected to become more stringent in sensitive catchments, water companies are under increasing pressure to deploy tertiary treatment that can be delivered quickly, efficiently and with long-term operational resilience,” he said.
For Wouters, that regulatory pressure is the reason this kind of monitoring matters. “In order to meet these very stringent criteria, say 0.25mg per litre of total phosphorus, you need to have a filter that is capable of acting as a good barrier for phosphorus flocs [clumps of phosphorous] and for solids,” he says. That can only happen, he adds, “if you know that the filter is functioning, from an operating point of view, in the best possible way”.
The engineering challenges are plentiful – for one thing, RFID tags aren’t usually meant to be submerged in water and churned through an abrasive bed of moving sand. “When we started with this idea it sounded perfect, but we had to overcome some issues when we first tried this at the full-scale plant,” says Wouters.
The first pilot took place in the Netherlands nearly a decade ago, after Brightwork approached a nearby sewage works with the idea.
What began as a monitoring tool is also now becoming a control system. Instead of only checking whether the filter is circulating properly, Brightwork says the data can be used to actively adjust the process. Before the monitoring system, the filter was “just a black box”, Wouters explains.
The next step could be to use the same idea for more than nutrient removal. For the UK, the immediate question is whether smart monitoring can help water companies meet their existing wastewater obligations faster and more reliably. But the broader implication is that the future of water treatment may not just be more filtration, but filters that can tell engineers what is happening inside them.
Wouters believes the same idea may eventually be used for a tougher class of contaminants, including medicine residues and other micropollutants. In the Netherlands, he says, Brightwork is already testing systems designed “not only [to] remove phosphorous but also remove micropollutants, which are becoming more and more critical in wastewater treatment”.
Extracted from IMechE website, read more here