Managing the cost of phosphorous removal in AMP7

Chemical use lies at the forefront of cost-saving plans as the water industry in England and Wales enters the new regulatory asset management period.

Bruce Quilter, sector specialist – industrial & environmental at WMFTG explains how optimisation of chemical dosing will drive efficiencies across wastewater treatment operations.

The water industry in England and Wales entered a new regulatory asset management period (AMP7) on 1 April 2020 and utilities face challenges on many fronts – reducing customers’ bills, eliminating pollution incidents and achieving zero carbon by 2030.

AMP7 runs from 2020-25 and some £5.3 billion is expected to go on improving the environment and of this, £4.5 billion is related to wastewater treatment obligations, with £2.2 billion earmarked for phosphate removal. 

Around 1,000 new final effluent phosphorus (P) consents will come into force before 2025 as part of the Environment Agency’s Water Industry National Environment Programme (WINEP).

All 20 water companies operating in England are expected to complete the programme in order to contribute towards meeting their environmental obligations, which include protection and improvement of at least 6,000km of rivers, 24 bathing waters and 10 shellfish sites.

Regulatory drivers

The P-removal programme is driven by European legislation and utilities will require a mix of solutions to meet tighter consents, including higher chemical usage. Chemicals can be added at any stage of the treatment process, but to achieve consent limits of 1mg/l or less, multi-point dosing will almost certainly be required.

Given that the quantity of chemicals required will rise, chemical usage necessarily lies at the forefront of utilities’ cost-saving plans. Optimisation of chemical dosing will drive ongoing efficiencies across plant operations.

Chemicals also carry a heavy embedded carbon footprint due to the scale of production and transportation they represent. The water industry is the first sector in the UK to commit to net zero carbon emissions by 2030 and reducing emissions caused by wastewater treatment processes is one of many options that will need to be implemented.

Dosing precision

All wastewater effluent returned to the environment is subject to stringent standards. Ensuring the appropriate treatment chemicals are used in the correct quantities, and at the right time, is the cornerstone of successful plant operation and staying within regulatory law.

Underdosing and overdosing can reduce the efficiency of treatment processes, risking repeated breaches of environmental license conditions, regulatory fines and reputational damage. Discharge consents include strict levels on both phosphorus and iron, so it is necessary for utilities to maintain a tight balance when treating phosphorus with an iron-based fluid.

Underdosing means the process may not achieve the necessary pH adjustment and could fail to remove enough phosphorus.

Where an excess of metal salts is added to wastewater, P-removal might be sufficient, but a reaction that could remove the alkalinity required for ammonia treatment may occur. If the alkalinity concentration is too low, the final effluent may fail its consent.

Overdosing can also lead to high levels of iron in the sewer outflow, potentially killing aquatic life. It also leads to unnecessarily high chemical requirements which, as well as extra cost, compound higher embedded carbon emissions from chemical production and transportation.

Precision dosing will become more important than ever as utilities move to scale up phosphorus removal. Reviewing the performance of dosing pumps at each site is one way of identifying potential cost savings and efficiency opportunities. 

Pump evaluation

Questions when evaluating pump types include: 

• Can the dosing pumps handle pressure changes from variable flows?
• Are the pump valves getting blocked?
• What are my energy costs?
• What are my maintenance costs?

Several UK utilities have installed peristaltic dosing pumps as an effective way of achieving the higher levels of accuracy and repeatability needed to pump ferric sulphate for reducing phosphorus levels.

Watson-Marlow’s Qdos range has a ±1% accuracy range providing significant savings in chemical overdosing.

Blockage prevention

Maintenance is another area offering significant savings. The higher demand on ferric suppliers due to the tightening regulations means chemical quality is decreasing.

Larger iron particles are appearing in supplies and these are prone to cause more frequent blockages in diaphragm pumps. The reduction in ancillary equipment required with peristaltic pumping systems means they are much less likely to clog, block or leak.

In addition, Qdos pumps provide a reduced maintenance with single, no-tools, ReNu pumphead replacement. This significantly reduces downtime, which is even more important at works where no standby pump exists. 

Data sharing

Another opportunity for water companies to drive efficiency would be willingness to share more data. Were suppliers to have sight of key data on chemical costs, for example, this might make better savings possible through recommendation of particular pumps.

The water industry faces extraordinary challenges on cost and environmental performance over the next five years and beyond. By reviewing total expenditure on chemical dosing with a view to upgrading systems, there are savings and major efficiencies to be had.