Wastwater, seweage, poo, it has to go somewhere!
96% of the UK’s wastewater is treated at large scale waste water treatment plants; the remaining 4% is treated by use of septic tanks or cesspools on a much smaller scale. These are generally for very remote communities where it is not practical to install a sewage main. All treatment systems work on the following principles:
- Preliminary treatment – this removes grit, gravel and large solids.
- Primary treatment – this is to settle larger suspended, generally organic, matter
- Secondary treatment – to biologically break down and reduce residual organic matter.
- Tertiary treatment – this is used to address different pollutants using different treatment processes.
On large scale treatment plants, covering vast areas, separating these treatments can be straightforward, each getting their own designated area. On a smaller scale a similar process is achieved in septic tanks and cesspools by using a number of chambers to separate the waste and allow it to process.
Regulations for the standard of wastewater treatment are documented in the EC Urban Waste Water Treatment Directive. Within this directive it is set out what level of treatment waste water should receive before it is deemed safe for discharge into the surrounding environment. This is determined by a number of factors including.
- The size of the community – This is measured using an area’s population equivalent.
- The sensitivity to pollutants of the waters receiving the discharge
- Whether the treated waste water is to be discharged to inland, estuarine or coastal waters
Where the waste water originates from whether that’s domestic type properties or food processing plants that will contain food particles and food preparation washings. It could also be rainwater run-off containing organic debris washed from roads and draining to sewers.
There are a number of activities that result in wastewater being created, domestically these could include bathing, washing, using the toilet, and rainwater collection and runoff. Commercially these may be industrial works waste or food products. Depending on where the wastewater originates will determine which level of treatment it is subject to. Wherever it originates from all wastewater can contain a number of containments either from the source or from human intervention, this could include including bacteria, chemicals and other toxins. The risk of water borne disease is present in all wastewater and it is imperative that it is processed accordingly to remove the risk of this.
Sewage networks also need to be designed and constructed to deal with seasonal demands particularly from wet weather; the sewage treatment works must also be able to must also take this into account and be prepared for fluctuating demands. They must both also be designed to cater for seasonal changes for that specific area, for example coastal towns may receive an influx of tourist during the summer months but may be sparsely populated during the winter. Both the network and the sewage treatment plants must take this into account.
- Amitt 800