Articles & Case Studies

Peristaltic technology aids in prevention of ‘feminised’ male fish

Posted: Thursday 25th June 2009

Chemically-disrupted water streams are causing a substantial increase of ‘intersex’ fish - and peristaltic technology is addressing the problem of water pollution through more effective treatment techniques.

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 fifteen years has revealed that the underlying cause of this ‘intersex’ fish phenomenon lies in our improved water quality allowing fish to colonise rivers which were previously fishless. This has meant that 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 the wastewater effluent are causing the intersex effect in male fish such as 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 that the processes traditionally used to treat contaminants found in waste water are insufficient for completely removing EDCs. For example, trickling filters are likely to remove less 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 different 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 different advanced treatments for removal. In addition they are carrying out some 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 useable the tap water in the sample tanks, the chlorine in the water must be neutralised. For this purpose, Severn Trent specified use off 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 either by weight or volume, allowing for 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 are that the suction lift is good so that 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 that 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 like sodium thiosulphate during treatment processes.

One of the central challenges of the EDC research programme is how to maximize 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.

Philip Bolton, Water Industry Specialist at Watson-Marlow, comments: “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 our surface water system. With growing technological expertise, the UK is well prepared to reduce the impact of EDCs on our river-dwelling wildlife.

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