Chemical Dosing

Chemical dosing is the delivery of a chemical substance into foul water, sewage or sludge–like fluid, usually as part of preliminary processing. It is most often used on sewage treatment, as part of the anaerobic digestion process for making energy from waste and for cleaning industrial effluent to be returned to the natural water course. Here Philip Brown, Project Manager for pumping solutions at Verder UK, explains the process.

Industry Sectors

  • Waste Water Treatment
  • Clean Water
  • Anaerobic Digestion
  • Industrial Effluent
  • Power Stations
  • Mining
  • Building services
  • Public Infrastructure

The dosing process

A chemical dosing skid is the most effective way to dispense chemicals, using at least two peristaltic or metering pumps attached to pipe maniflolds encased in a cabinet. One pump acts as a duty standby to ensure the dosing process is uninterrupted should a wearable component need to be serviced.

A chemical dosing system uses pumps to automatically control the dosing process. In the case of wastewater treatment works, there are certain environmental regulations in place from the water regulator, so when sewage enters the works, the effluent has to be filtered, cleaned and processed.

The effluent may contain toxic material which is passed through filter beds, leaving what is, in essence, dirty water that cannot be discharged into the water course; lest it kill of fish and other forms of aquatic life. This is enforced by the UK Environmental Agency, which will impose penalties any water companies doing this.

Therefore, these water companies must dose certain chemicals to achieve a balanced pH level and remove impurities like phosphates, which would otherwise cause algae to grow in a stream, depriving fish of oxygen and affecting livestock drinking water.

pH buffering

Chemicals such as sodium hydroxide or lime are dosed in conjunction with pH measurement - a process known as pH buffering. The amount of buffering will vary according to the time of day; for example in the morning when people use the toilet or bathroom, or in the evening when they finish work. As a result, dosing pumps need to increase the amount delivered at these peak demand times and reduced during the hours of sleep, producing a diurnal, cyclical flow. Water companies will typically work to a standard specification with approved framework suppliers for equipment, tanks, pipework, motors, electrical switchgear, cable and so on.

Verder has framework agreements with several water authorities such as Scottish Water for example, but can also operate outside these agreements where it can show a cost saving, quicker delivery or innovation. For example, Verder uses peristaltic pumps to handle lime which traditionally clogs up other types of pumps.

When a site encounter’s a problem which can’t be resolved by the supplier, Verder steps in to provide a working solution. This could be when a pump has failed or become blocked, or where dosing has been inaccurate.

Verder UK Project Team

Verder supplies complete chemical dosing systems, individual components and service solutions from assessment, design, build and installation – focussed closely on meeting client requirements. The chemical dosing solutions are managed and installed by the Verder Project Team, including a project manager, engineers and support staff who have provided much needed services to water companies in the UK.

By using existing capital equipment on site, Verder can retrofit to and refurbish existing systems in situations where incumbent framework suppliers may only want to offer new systems delivering significant cost reductions.

One of several recent examples involved re-using two existing storage tanks and a kiosk. Following inspection only the pipe work and new dosing pumps were fitted, whereas the rival offer required fitting new tanks and kiosk.

Verder engineers have all the current mechanical and electrical qualifications that are relevant, including the health and safety cards required by every water authority, and overseen by trained site safety supervisors with additional qualifications.

Verder conducts site surveys, produces the risk and method assessments, and performs all the groundwork, modelling everything in 3D computer aided design (CAD) software showing pipework, cabinets and pumps.

Before the system is installed on-site, all these components are first tested at Verder’s Service Centre. For example, one recent application involved building a cabinet at the Verder premises before shipping it to Thames Water in Crawley, West Sussex. There, it was swiftly secured, connected to pipework and had a kiosk dropped over it to house the contents.

Removing Phosphates

Introduction of an iron-based chemical solution like ferrous or ferric sulphate or chloride is needed to remove phosphates.

Alternatively ferrous sulphate can take the form of copperas crystal, a by-product of the pigment industry, which can be mixed in a tank with water in a unique patented process available from Verder in conjunction with Naiad Aquatic Water Services.

Working in conjunction exclusively with Verder UK, Naiad Aquatic Water Services, has developed a range of chemical dosing systems including the Naiad Copperas Saturator. The latter was developed in partnership with Thames Water’s R&D section to provide a cost-effective alternative to liquid dosing.

Naiad chemical dosing systems incorporate feed-back and load profile control options and enable process optimisation for phosphate removal and septicity control. When used to dose chemical to sewage for phosphate removal, phosphate residuals in final effluent consistently meet targets, and odours are minimised.

Verder takes pride in delivering pumping solutions that are designed around the needs of the customer, not off-the-shelf packages which are made-to-fit all.

Customer feedback regularly shows that the quality and robust nature of the end product and how the project team conducted itself on-site and in consultation are viewed as key benefits.

Verder operates an ‘open door’ policy to customers, from the initial contract bid, through to the first phone call for spares or contract maintenance.

In focus: Dosing at Thames Water Crawley STW

Following the successful operation of an initial Verder system, the Verder UK Team provided a replacement dosing system for phosphate removal.

The system uses Verderflex Dura pumps for the delivery of the chemical. Verder UK provided Package Dosing Plant consisting of control panel, dosing rig, pipework, valves, dosing hoses and kiosk assembled and tested at the Verder Service Centre.

The Verder UK Team commissioned the system and gave training to the Thames Water maintenance engineers and supplied a spares and maintenance plan.

Verder is there every step of the way, acting as a one-stop shop but without taking the customer for granted, and rewarding them with highly competitive rates and priority service.

Verder works with engineers in meetings to discuss their requirements, whether the setting is in a boardroom or on-site in boiler suits, presenting a professional attitude combined with courtesy and respect.

Ultimately, Verder aims to save water utilities as much money as possible while providing them with more reliable and robust equipment. The key is avoiding hidden costs having to be added at the end of a project, whilst keeping the customer in the communication loop from start to finish.