It’s the story that has become a national curiosity: male fish swimming in our rivers have begun spontaneously developing female characteristics. Research dating back more than 15 years has revealed the underlying cause of this phenomenon lies in our improved water quality, allowing fish to colonise rivers that were previously fishless.
This has meant fish are surviving in the upper reaches of urban river systems and are more exposed to treated sewage effluent. It is believed that endocrine disrupting chemicals (EDCs) such as natural and synthetic hormones in wastewater effluent are causing the intersex effect in male fish through the appearance of oocytes (egg cells) in the testes of male fish.
EDCs are typically found in waste water at concentrations of less than one part per ten billion, and are a minute fraction of all the organic material present. This means the processes traditionally used to treat contaminants found in waste water are insufficient for completely removing EDCs. Trickling filters, for example, are likely to remove fewer EDCs than a nitrifying activated sludge plant, and processes such as ozone and granular activated carbon treatment are likely to remove even more.
Further research is therefore imperative. The Environment Agency, in collaboration with the UK Government and the water industry, has coordinated a £40 million national programme to examine EDCs and assess the effectiveness, costs and benefits of their removal in existing or enhanced sewage treatment. The programme is gathering data from 13 types of sewage treatment works across England and Wales, including a notable project at Ilkeston STW in Derbyshire.
Undertaken by Severn Trent Water, the Ilkeston project requires the company to carry out a side-by-side evaluation of three advanced treatments for removal. In addition, it involves carrying out fish tests using native roach to determine the effects of different waters on the fish. The experiments include the comparison of river water, treated sewage effluent and dilutions of treated sewage effluent in tap water.
In order to make tap water in the sample tanks useable, chlorine in the water must be neutralised. For this purpose, Severn Trent specified the use of Watson-Marlow’s 520SN/R2 peristaltic pumps for dosing of sodium thiosulphate, which dechlorinates the water. The 520 series of peristaltic pumps can be calibrated by weight or volume, allowing the precise dosing and metering that is necessary in the Ilkeston trial.
Severn Trent is also using SPX25 hose pumps, which feed the river water and treated effluent to the tanks. The benefits of the hose pump for the river water include the fact that the suction lift is good, meaning the pump can be situated safely inside the works perimeter fence with only the suction hose suspended in the river. The ability to handle solids also meant only a simple weed screen was necessary to prevent blockages with weeds etc.
Because peristaltic pumps retain the chemical completely within the tube and have no valves that can leak or corrode, they can be used for the closely-controlled metering of problematic chemicals such as sodium thiosulphate during treatment processes.
One of the central challenges of the EDC research programme is how to maximise removal efficiency by modifying current treatment technologies, while also remaining cost-effective. Advanced water treatment technologies are often more expensive than conventional treatment. This is another way in which the increased use of peristaltic technology is aiding EDC removal, by improving cost-effectiveness.
Mr Bolton, of Watson-Marlow, said: “The previous engineering solution for this kind of trial used gear pumps to achieve the flow rate and pressure required, but this involved a high level of maintenance, as well as a complicated pressure regulation system utilising bypass valves. By contrast, peristaltic pumps are simpler and more reliable. Decreased maintenance requirements of peristaltic pumps mean that not only are costs lower, but engineers’ time is freed up to be spent elsewhere.”
The Ilkeston trial, which finishes in the coming months, should provide us with increased knowledge of EDCs and the best methods to keep them out of the surface water system. With growing technological expertise, the UK is well prepared to reduce the impact of EDCs on river-dwelling wildlife.