Southern Water Sewage Treatment Plant


Southern Water


Budds Farm Sewage Treatment Plant

Customer Requirement

Combined heat and power (CHP) biogas power station


Feasibility studies, design, equipment supply, ancillary equipment, project management, installation, commissioning, ongoing operation, maintenance, genuine parts supply 

Power Need

Finning were required to deliver a modular combined heat and power (CHP) system owered by biogas that halved the installation and engineering time spent at Southern Water’s Budds Farm sewage treatment plant. Before installing the system, the site was using biogas from the digesters as fuel to run a sludge dryer.   



Finning suggested that this biogas should be used as fuel to power a Cat G3520C generator set to produce 2MW of electrical power. This makes sound economic sense for Southern Water since not only can the site produce its own electrical power, but it can also sell green electricity back to the grid as renewable obligation certificates (ROCs).

The heat recovered from this system and the dryer warms up the digesters to the optimum temperature for biogas production. Biogas is not a perfect fuel source with the level of contaminants varying from site to site.  For Budds Farm the main contaminants were siloxanes and hydrogen sulphide (H2S). Finning’s system is designed to remove such contaminants so that the generator set can use the biogas as a fuel.  The solution was delivered in four modules. The first module was a fully packaged generator set that included synchronised switchgear and the company’s LIMA control system.  This connects to and monitors the site’s HV switchgear. The second module was a fully packaged heat recovery system designed to capture heat from both the jacket water and exhaust of the high efficiency G3520C generator. Module three was a gas collection and compression station that filters and also removes some of the solids and vapour from the biogas. Finally the fourth module is a gas clean up skid that removes other contaminants.  It uses new technology to remove siloxanes, which if left would coat the engine cylinder head with a glass hard surface that would damage the cylinder heads and valves.  The filters use a regenerative media instead of activated carbon filters.  The charges in these last up to five years and eliminate the problem of waste carbon disposal.


 Finning has agreed a commercially guaranteed ten year operation and maintenance contract with Southern Water to optimise the generator’s output and heat recovery from the available fuel.

Martin Ross, Carbon Policy Manager at Southern Water commented, “Southern Water is using CHP technology from Finning across several of its sites.  The solution delivered by Finning has proved extremely reliable.”