FEATURE WATER & WASTE TREATMENT
There is currently a strong focus on phosphorus removal from wastewater, with growing concerns about the capacity of the chemical dosing manufacturing base to meet the demand for equipment during AMP7. Here, Graham Ward of WES, suggests a way forward
I
n AMP7, the UK water industry’s Asset Management Period for 2020 to 2025,
there is a strong focus on phosphorus. Excessive levels cause eutrophication, an over-enrichment of nutrients which generates algal blooms in lakes, rivers and other surface waters. Limits are becoming stricter and, crucially, chemical dosing to remove phosphorus is becoming necessary on many smaller sites which previously had no such requirement. Industry regulator, Ofwat, has also challenged companies to deliver solutions more cost-effectively and efficiently, with better customer service and value for money. To reduce dosing system manufacturing
lead times and costs, water companies will need to move away from large, expensive and often over-engineered systems to smaller, more standardised systems. These can be built quickly and in greater quantities, with economies of scale.
COLLABORATIVE EFFORT As well as using smaller, standardised units, coordinated efforts to manage phosphorus could go much further, beginning with measures to reduce the amount reaching water treatment works in the first place. For example, detergent and food manufacturers could be encouraged to reduce the amount of phosphates in their products, while greater use could be made of composting and aerobic digestion in removing phosphorus from waste food. To help water companies remove
phosphorus more effectively and at a lower cost, the Environment Agency is exploring options such as ‘catchment permitting’. By granting a single permit to cover discharges across a number of sites, this more flexible approach spreads a company’s compliance risk over an extended area and enables it to achieve optimum benefit from its existing assets. Although chemical dosing is a crucial
34 JUNE 2020 | PROCESS & CONTROL
Packaged systems like the DS1500 from WES can be bought or hired, and are suitable for indoor and outdoor applications that require small to medium capacity units
SIMPLIFICATION & STANDARDISATION OF CHEMICAL DOSING
As well as using smaller, standardised chemical dosing units, coordinated efforts to manage phosphorus (and so reduce the extent of algal blooms) could go much further, beginning with measures to reduce the amount reaching water treatment works in the first place
element in phosphorus removal, its improvements must be integrated with those in other treatment methods which precede and follow it. Filtration technology, for example, continues to advance. There are even techniques for extraction of phosphorus as a revenue- earning resource. These and other innovations can reduce the amount of chemical needed in the dosing process. Dosing levels can also be reduced by
designing and equipping treatment plants for optimum mixing and flocculation: rapid mixing of an initial dose, at the front end, maximises the chemical’s effect and slow mixing of a second dose, at the back end, promotes flocculation which enhances phosphorus removal through sedimentation. Compact systems have an immediate
flexibility advantage over their large predecessors as they will fit easily into the smaller sites which now require dosing. Inbuilt weather protection also expands their applicability to both outdoor and indoor locations. While ferric sulphate and ferric chloride
are commonly used as dosing chemicals, the system should be adaptable to alternatives. If increased industry
demand reduces the availability and increases the cost of an operation’s first- choice chemical, a switch can then easily be made. The materials used in the pumps, valves, pipes and other components also need to be specified to suit this potential chemical range. Chemical storage tank capacity is another important consideration, to allow for convenient and cost-effective deliveries to prevent runouts.
VARIABLE DOSING DEMANDS Reliable control of dosing levels is also essential, and the system must permit different methods of setting and varying rates as appropriate to the size and circumstances of each site. For example, on some very small sites with less stringent limits on chemical levels, a suitable fixed dose rate might be acceptable, whereas a larger site might require dosing to be programmed to follow a predicted diurnal profile. Packaged systems like the DS1500 from
WES can be bought or hired to slot into the industry’s current thinking process around simplification and standardisation of chemical dosing units. Ideal for indoor and outdoor applications that require small to medium capacity units, this compact and tough product is fully enclosed within a weatherproof, rotationally moulded structure. With the introduction of AMP7, water
companies, contractors and their supply chains have the opportunity to work in partnership with manufacturers in the development and use of simpler and more standardised systems. This is the key to producing more equipment, faster, and at a cost that keeps water businesses profitable.
WES
www.wes.ltd.uk
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