IMPLEMENTING SOLUTIONS FOR REDUCTION OF NITRATE LEVELS IN POTABLE WATER SUPPLIES
Robert Harris and Irene Banham.
Grontmij Ltd
(free)
The causes of increasing nitrate levels in groundwater are well documented. This paper addresses the engineering options available to treat nitrates in drinking water. We shall not dwell for long on the processes which remove nitrates although these are briefly explained. Instead the paper covers the engineering difficulties of trying to fit the nitrate treatment process into an existing water treatment works.
There are several stages of treatment in changing from raw water to finished potable water, even if the water starts off as a good quality ground water source. The nitrate treatment stage must fit in and interact with these other stages to form a cohesive whole.
In order to illustrate the point a single, relatively straightforward, water treatment works is used as an example, Stoke on Tern borehole site in Shropshire. Historically the plant worked well and nitrates were reduced in the final water by blending the water with another source. However as nitrate levels continued to rise the blending option became unsustainable, therefore treatment became necessary. A nitrate treatment plant has now been installed on this site and is operational, however considerable difficulties had to be overcome.
Firstly, design and construction related issues such as; fitting the nitrate treatment process in with existing site processes, finding sufficient space on an existing site both for provision of adequate permanent access and for construction access, ensuring a high level of operational/contractor cooperation during construction and programming constraints for other works which impact upon the nitrate treatment plant.
Secondly, commissioning related issues such as; disposal of large quantities of waste water, producing sufficient cycles of test activities for the nitrate plant within a restricted commissioning period, ensuring compliance with expected waste constituents during commissioning and determining the dividing line between commissioning and plant optimisation.
There have been many and varied lessons learnt to date from this plant. Amongst the most important is that a standard, reliable technological solution to nitrate treatment can be made very complex by the constraints on the site around it.
KEY WORDS ion exchange, nitrate treatment, water treatment
