Tackling knowledge gaps on hospital wastewater systems

In the second in a series of hospital wastewater-related articles running in HEJ this year (the first was published last month), Peter Orendecki, Senior Contracts manager and Water AP at University Hospital Southampton NHS Foundation Trust, highlights the apparent lack of understanding of the risks posed by hazardous bacteria in hospital waste systems among some designers, architects, and even infection control personnel. He asks whether there may here be an opportunity here for the UK to lead in such systems’ design.

The general design of effluent drainage within all buildings broadly relies on gravity to allow waste water from a number of different processes – including, but not limited to, handwashing, dish cleaning, showering, the use of toilets, macerators, bedpan washer-disinfectors, and other clinical uses, to drain away from the point of use into a vertical pipe, known as a stack. An individual stack receives all wastewater sources in its vicinity and all stacks link to the main sewer, effectively linking all drainage within a building. The lack of segregation of wastewater systems is a major factor in allowing microbes to move from one area of a hospital to another via different modes of transport, active growth, movement of air, and aerosols and the wastewater itself.

At the proximal end of the drainage system waste traps of various designs are used to hold water, thereby separating the drainage system air from the air in the local environment. This comes with its own issues. Bacteria dwell in the U-bend and form complex biofilms. Disposing of a carbon source down a sink drain will stimulate the growth of biofilm up the vertical section of the drain at a rate of 1 mm/hour, reaching the sieve at the top of the drain. Water from an outlet directly hitting the sieve can disperse organisms in the biofilm up to 2 m away. (see Figure 1).