Treatment plant
The smell originally came from two sources – the now-emptied trickling filters where the fire occurred and the oxidation ponds.
Oxidation ponds
The fire severely damaged the trickling filters so we lost a critical part of our wastewater treatment process. As a result, poorer quality effluent was discharged into the oxidation ponds, so the ponds began to smell. If you remember Bromley in the 1960s and 70s, that smell would be very familiar.
Churning additional oxygen into the wastewater is key to improving the quality of the water within the oxidation ponds. In May 2023 we completed the installation of the 16 aerators to provide this oxygen.
We've also installed the temporary activated sludge plate that provides the wastewater to the ponds.
Wastewater quality
We installed a series of 16 aerators on Pond 1 to continue churning oxygen and maintaining the health of the wastewater. This work was completed in May.
Now that more, better-quality wastewater is flowing into the ponds, we are only seeing it occasionally struggle over the cooler months.
Air-quality testing
Since April 2022, we’ve taken weekly samples from multiple sites, both at the plant and in the neighbourhood. We also added extra sample locations based on the wind direction.
This work clearly identified reduced sulphur compounds (RSC) as the main cause of the odours. RSC are a complex group of substances that have a strong odour, even in low amounts. The monitoring found extremely odorous compounds, such as methyl mercaptan and hydrogen sulphide, present in varying concentrations, depending on the weather and wind direction.
In the week beginning Monday 30 May, we started using a hydrogen sulphide meter at Bromley School. These meters continuously monitor very low levels of hydrogen sulphide in the air. The trial has been successful and we are leasing two extra meters and will purchase more.
We installed hydrogen sulphide meters for deployment around the Wastewater Treatment Plant site and across the neighbouring residential areas. Now that we have these meters in place we will have a much better understanding of the different types and levels of odours that people are being exposed to over time.
We continue to publish the hydrogen sulphide results weekly on this website.