Reliable and accurate dosing of alkali was critical to the treatment of many surface waters. Historically, lime (calcium hydroxide) had been the alkali of choice on cost, but the dosing systems are notorious for mechanical failure. Blockage and scaling of dosing lines at many sites leads to poor process pH control and high maintenance costs. Recent alternatives to dry lime include: on-site hydration of "high quality" calcium oxide (cheaper than lime for large works), stable lime suspension (expensive, but allows simpler dosing system design).
There was a need to examine the technological developments over the last 10 years and compare the major alternatives by cost and reliability. The work identified good design practice for all technologies.
- Reduced risk of "trival exceedances" of water quality standards through more reliable equipment design.
- Reduced maintenance costs for existing lime systems.
- Reduced whole life costs for new lime systems.