Since October 2011, Water and Sewerage companies (WaSC’s) have taken responsibility for private sewers and lateral drains that extend beyond a private premises or combine flows from two residences. WaSC’s respond to around 200,000 sewer blockages per annum, with more occurring in private drains. In 2010, estimates were that up to 75% of blockages are caused by Fats Oils and Grease (FOG), hardening within the sewer network creating restrictions to flow. Much of the remainder is caused by flushable products resulting in the flooding of some 3,000 homes per year. On combined sewer networks, FOG and accumulated flushable rags may cause flow restrictions resulting in early discharge to the environment through CSO’s.
Data and information is sparse and FOG formation points in sewer networks are not fully understood. Anywhere where cooking or processing of foodstuffs occur provides a potential source of FOG for instance maintenance records from Dublin indicate that FOG problems occur where there are hot spots of Food Service Establishments. In Dublin, FOG producers are now required to be licenced under trade effluent legislation and in the UK, the Water Industry Act (1991) makes discharge of any material prejudicial to sewer function illegal although WaSC’s do not carry the same licensing powers. Domestic producers make up a significant load of FOG disposed to sewer but this varies with seasons, geographic location and customer information programmes.
FOGs are often associated with waste food and are rich in potential energy materials with calorific values in the region of 39MJ/kg. Changes in energy generation tariffs especially combined with increasing landfill costs have created a resource market from the waste product with FOG being used in: combustion direct for energy, co digestion with other substrates in Anaerobic Digestion and conversion through to Biodiesel. Source separation and independent collection of FOGs from FSE’s has become widespread with the potential to increase to domestic scale collections although mechanisms and benefits have yet to develop fully.
More information can be found on the AquaEnviro website.