Bathgate Sewage Treatment Works Sand Filters

Colloide was appointed by Scottish Water to upgrade the sand filters in its Bathgate Sewage Treatment Works.

The treatment works had previously been operating with one sand filter as a tertiary treatment stage. This filter was regularly overloaded and we were appointed to recommend and integrate an additional sand filter into the treatment process, to increase capacity. We had to recommend a solution that would integrate and operate in parallel with the existing filter.

Colloide designed a complete new filter, manufacturing and installing all mechanical and electrical components, whilst also refurbishing the existing filter with new filter cells and media.



This filter was constantly overloaded and thus, a new sand filter, similar in design to the existing plant was required to increase the capacity of the plant and installed as part of this refurbishment contract to act in parallel with the existing unit.

Flow is split in the splitting chamber immediately upstream of the two filters and flows to each filter in parallel. As the flow passes through the filters (by a small gravitational differential head), solids are removed. The final treated effluent then flows from both filters into the collection manholes through the sampling chamber and then to the outfall.

These solids are removed from the filter by a travelling bridge which moves over each cell in turn and backwashes than cell, discharging the dirty backwash water into trough which in turn is returned to the head of the works.

Each filter consists of 46 ‘cells’ providing approximately 1.5m2 filtration surface area each. These cells are washed individually on a regular basis, the backwash being triggered automatically or manually. The plant remains idle and only moves and is active when backwashing and the flow is passing through the sand filter. Flow is controlled to the plant via a manual penstock and weir arrangement situated at the inlet end of the existing filter.


Why choose Colloide?

Colloide’s sand filter systems are a high performing and reliable solution for water and wastewater treatment.

Each of our filters are engineered to meet the specific performance requirements of individual wastewater treatment plants.


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Scottish Water



  • Municipal Water Treatment
  • Facilities Engineering