Description of the polishing process The polishing process is based on a percolating filter bed consisting of an organic medium working in aerobic conditions.

At Birmingham he was responsible for the construction of the first large-scale percolating filter plant, a complete departure from the traditional land treatment in use in the city and elsewhere.

These systems have also been described as roughing filters, intermittent filters, packed media bed filters, alternative septic systems, percolating filters, attached growth processes, and fixed film processes.

The old percolating filters are obsolete and there are plans to empty them and install photovoltaic panels to generate electricity to power the site, with any excess going to the National Grid.

Throughout the last decades, the development of different types of bioreactors to treat atmospheric emissions contaminated with VOS has been observed, such as: the bioscrubber, the percolating filter and the biofilter.

Other changes that he introduced, based on his work in Birmingham, were the separation of sludge digestion, the extraction of methane from sewage for use in power generation and the introduction of flocculation prior to the percolating filter.

Secondary treatment (including both mechanical systems, such as activated sludge methods process or percolating filters, and non-mechanical systems such as lagoons) was provided to 34% of the population, up from 29%, and primary treatment was provided to 22%, up from 20%.