Published August 2019
A lack of adequate safety and protection measures on many lime storage silos at water treatment plants has resulted in considerable potential risks that the water industry must face up to. Silo over-pressurisation poses a serious threat in terms of pollution and can even put lives at risk.
Water companies are already under pressure to minimise the impact of treatment works on the local environment, especially in terms of odour and pollution, and the potential for lime powder escaping from storage silos is a serious risk. However, this is avoidable with the implementation of proper protection.
Powdered lime is utilised extensively in the treatment of wastewater – for example, it is commonly used to reduce odour in raw, primary sludge, as a cost-effective alternative to using digesters. It is also used in other water treatment processes to help balance pH levels, and as part of composting processes for sludge removed from the bottom of primary tanks after it has been de-watered and compressed. The lime and remaining water in the sludge together creates a heated chemical reaction, accelerating the process.
As with other vessels storing powdered products, lime silos are susceptible to over-pressurisation arising from filtration blockages or excessive input pressures from delivery tankers. This results in serious problems for sites: powder escaping into the environment (particularly problematic with corrosives like lime); damage to equipment and buckling of the silo; and worst of all, potential rupturing or for the filter unit to be blown off the roof by pressure build-up.
At Hycontrol, we regularly see silo-tops covered in a thick layer of powder, often blowing across the site in great clouds during a fill. We see damaged, untested pressure sensors. We see air vent/filter units that are so clogged with powder that they are effectively useless. Companies in the water industry and beyond are worryingly ignorant about the consequences of poorly maintained, poorly monitored silos.
