None of us really gives much thought to where the water we use (wastewater) goes. We know that it runs into the sewer and eventually makes its way to rivers or oceans.
Typically located in remote or large industrial areas, wastewater treatment plants can be identified by their large tanks, open-air reservoirs and network of pipes.
A population of just 500,000 can generate over 400 million litres of wastewater yearly, making the treatment of water critical to the sustainability of our planet. These plants use multi-stage treatment systems (including filtration, aeration and aerobic digestion) to ensure impurities are safely removed from water.
Rich in nitrogen and phosphorous, biosolids can be used in many ways such as agriculture, environmental rehabilitation and mining. Considering where biosolids come from, they are a remarkable feat of recycling ingenuity. The extraction of these biosolids takes place primarily in digester tanks – enormous tanks where extracted solids are broken down by bacteria, removing pathogens and odours.
This is a delicate process: the contents of the tanks produce lots of methane, an extremely flammable gas. The tanks need to be purged to make them a safe working environment: in general nitrogen is used, as it is non-explosive.
Typically, wastewater treatment plants have relied on bottled nitrogen for digester tank inerting. The nitrogen is fed into the digester tank until purging is completed. For decades, this has been the only solution.
Plant operators have a keen interest in cost effectiveness and process efficiency; looking at the benefits of portable nitrogen generators is often all that is required to make the switch.
Trailer-mounted generators are easy to tow into position and started immediately. In comparison, bottled nitrogen cages require a forklift to move – a time consuming and costly process. Bottled nitrogen also needs to be placed in a safe area, where sudden release of the gas will not cause asphyxiation.
These numbers are critical to an efficient project. Bottled nitrogen usually comes at 99.99% purity. However, purities between 95% and 99.95% are often all that is required to safely inert the tanks.
With pressurised bottles, depending on how long the nitrogen has been stored for, this wastage can be up to 20% of the initial volume. Plus, you have the freedom to extract exactly as much nitrogen as you need to complete the project, no more no less, so you’re only paying for what you use.
These are just some of the benefits of on-site nitrogen generation.