IP&L feature: Stressed assets & their health & safety risks

30 Jul 2020

Industrial Plant & Equipment (IP&L) – ‘Stressed assets & their health & safety risks’

Paul Cree, one of our Technical Sales Engineers, talks to IP&L about the dangers posed by stressed wastewater treatment assets and explains why modular plants are the answer.

Wastewater treatment plants are some of the most potentially hazardous environments to operate in, with workers often required to be at height or in confined spaces and use mechanical and electrical equipment. The biological processes on site, and the chemical usage can present potential exposures to a low oxygen environment or high levels of hydrogen sulphide, methane gas, or ammonia, all of which can cause serious illness or, in the worst cases, fatalities.

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In addition, workers will likely face ‘accident hazards’, such as slips, trips, falls, burns, electrical shocks and be at risk from moving parts, as well as ‘physical hazards’, which include elevated noise levels and coming into contact with chemicals. There are ‘biological hazards’, through exposure to any bacteria and viruses present in the wastewater, and finally the risk of musculoskeletal injuries which often result from handling heavy and awkward loads.

These issues are heightened when operating in older, existing works, where assets are deteriorating, or past their asset life expectancy, and therefore in definite need of replacement or upgrade. With many moving parts, the risks increase, and in some cases are impossible to completely avoid. However, some of the risks can be engineered out if a new treatment works is designed and installed.

System Overload

When treatment units are no longer sized appropriately, due to increases in flow, they become stressed, causing the system to overload or the process to short circuit. This can lead to incomplete wastewater treatment, low dissolved oxygen levels which can result in aeration systems becoming over worked, the build-up of sludge and solids, and the physical short circuiting of units. Over time, the process units themselves can become damaged from the physical stresses, with cracks in tank walls, baffles being distorted, localised ground movement, and internal pipework blockages and damage, all common.

These units that are no longer capable of dealing with changes in flows and loadings, or are not in original working condition, reduce the effectiveness and efficiency of the whole wastewater treatment system. Undersized tanks lack sufficient settlement, undersized pumps struggle to keep up with flows which causes back ups and bypasses. Worn weir plates create hydraulic short circuits, worn pumps can result in insufficient solids removal from tanks and a loss of system capacity, whilst old concrete tank walls can leak exposing the workforce and the surrounding environment to its contents.

In order to repair or replace these stressed assets it is not possible to just switch them off to carry out the work. However, modular wastewater treatment systems can be hired in to treat the wastewater whilst the asset can safely be worked on and repaired in situ. This means the plant can still operate in full treating the wastewater and work can continue in a safe environment.

Not only do old and stressed wastewater treatment assets pose a problem to the function of the treatment works, they can also pose a significant danger to the environment of work too. Corroded handrails and stairways pose a threat especially when people are working at height. Hydraulically overloaded tanks pose a risk of engulfment, whilst the creation of Hydrogen Sulphide can corrode electrical equipment, as well as provide the potential for corrosion of metal and concrete. Exposure to biological hazards increases around old mechanically agitated wastewater systems, and the risk of impingement is high when working with old mechanical screens and rakes that require regular maintenance.

By bringing in pre-tested modular wastewater treatment plants (either for hire or capital sale), sites can still be and remain fully operational before the original asset is ‘switch off’, either for repair or permanently. Equipment can also be hired in to optimise the design of capital plant on a “try before you buy” scenario. Modular systems are also flexible, can easily accommodate changes in the treatment requirements and are space efficient while offering a safe working environment.

Stressed assets create stressed operators, however a simple review of the overall process can greatly improve the performance of the works and also the health and safety of the site and operators.