Planned Confined Space Entry to “unblock” aeration nozzles and improve Process Performance.

Huddersfield Waste Water Treatment Works accepts industrial chemical waste effluent via a private sewer from a local Herbicide/Pesticide Manufacturer (Syngenta).

This waste is treated in a High Rate Activated Sludge Plant comprising two large aeration tanks and two circular clarifiers. Each aeration tank is equipped with 75 jet aerators (nozzles) through which Process Air enters the tanks.

This Process Air is critical to the performance of the process and any reduction in aeration capacity and efficiency will seriously compromise Final Effluent Quality at Huddersfield.

Due to operational issues and a worsening of plant performance PMP were requested to remove, inspect and clean all 150 nozzles. The waste that is treated is highly toxic and contains a number of potentially carcenogenic organic compounds hence any work around this plant is extremely hazardous and all necessary precautions have to be taken.

Following the production of very detailed Risk Assessment and Method Statement (RAMS), which were reviewed and approved by the Resional Safety Officer, PMP were allowed access to one tank at a time. Due to the confined space and hazardous nature of the work a seven man team was used such that rescue could be achieved with immediate effect. We also had to “vent” the tanks and entry was by use of full Breathing Apparatus restricting individual time in the tank to a 20 minute period.

Due to our expertise in working in hostile and confined environments we successfully removed, cleaned and re-installed 150 nozzles without incident. This resulted in an immediate improvement in plant performance and a reduction in operating and maintenance cost due to improved dissolved oxygen control.