We have provided some useful information for you to understand the various issues involved in treating sewage. The information provided here is brief. For more detailed technical literature and drawings regarding applications, installation, maintenance or specific options, please contact us. We have both internal and field sales staff who will be pleased to assist. Prior to installation, there is a legal requirement to obtain a Consent to Discharge from the appropriate agency. We offer full assistance in this respect.
Sewage is the wastewater generated from various utilities in our homes and includes kitchen, laundry and bathroom sink, as well as what you flush down the toilet. It is essentially 99.7% water containing solids like food particles, oils, dirt and chemicals like detergents 0.03%. Dirty water from businesses and factories is also discharged into the Sewage Treatment system. This is known as trade waste. Most of the sewage from our homes and businesses flows via large underground sewer pipes to Sewage Treatment Plants, where it is treated to make it safe for release back into the environment.
Sewage generation varies significantly depending on the type of establishment and the number of people involved. Standard residential dwellings generate 150 litres of wastewater per person per day with 45 grams of BOD and 6 grams of ammonia as N. In offices and factories, the presence of a canteen significantly increases wastewater production. Offices without a canteen generate 50 litres, whereas those with a canteen produce 100 litres per person daily. Schools also follow a similar pattern, with non-residential schools generating 50 litres per student, while those with on-site cooking produce 90 litres.
Sewage generation varies significantly depending on the type of establishment and the number of people involved. Standard residential dwellings generate 150 litres of wastewater per person per day with 45 grams of BOD and 6 grams of ammonia as N. In offices and factories, the presence of a canteen significantly increases wastewater production. Offices without a canteen generate 50 litres, whereas those with a canteen produce 100 litres per person daily. Schools also follow a similar pattern, with non-residential schools generating 50 litres per student, while those with on-site cooking produce 90 litres.
Amenity sites like toilet blocks and swimming pools have lower but frequent wastewater generation. A single toilet use results in 10 litres, while a urinal use generates 5 litres. Shower use contributes 40 litres, whereas sports clubs and health centers generate 50 litres per visitor. Golf clubs produce 20 litres per player, while local community sports clubs generate 40 litres. Caravan and tent sites vary, with touring caravan sites producing 100 litres per person, while static fully serviced sites generate 180 litres.
Hospitals and residential care homes require extensive sewage treatment due to their high water usage. Residential nursing homes generate 350 litres per resident, while small hospitals contribute 450 litres per patient. Large hospitals require individual assessment due to their scale. For domestic housing, the treatment system is designed based on the number of bedrooms. A 3-bedroom house requires a 5-person (P) system, a 4-bedroom house needs 6P, and a 6-bedroom house needs 8P.
For groups of houses, the P-value is determined by summing individual household values. A 1-bedroom flat is allocated 3P, while a 2-bedroom flat is 4P. When total P-values exceed 12P, adjustments are made. Groups between 13-25P multiply by 0.9, and those between 26-50P use 0.8. For example, four 4-bedroom houses require a 22P system instead of 24P. Proper sewage treatment planning ensures effective wastewater management and environmental protection.
The first step in setting up an STP involves Consultation & Visual Inspection. This includes assessing whether the land is suitable for septic tank drainage and consulting with the Environmental Regulator for compliance. The drainage field should ideally be located on land that slopes away from the property to prevent flooding issues. Additionally, there must be adequate access for de-sludging vehicles, and nearby water sources such as streams, wells, or springs should be considered when determining the position of the STP. The size of the site, its proximity to boundaries, and the presence of water-loving plant species can indicate poor drainage conditions, making proper assessment critical.
If the initial visual assessment is favorable, the next phase is the Trial Hole stage. Soil characteristics play a vital role in the success of an Effluent Treatment Plant, and well-drained soils typically appear brown, reddish, or yellow, while grey or blue subsoil often indicates heavy clay or poor drainage. Additionally, the water table must not rise to within 1 meter of the Effluent Treatment Plant distribution trench, and at least 0.5 meters of suitable subsoil should be available beneath the trench. If these conditions are met, the site is deemed appropriate to move forward with the next step of the assessment.
The third and final step is Percolation Testing, which determines the soil’s porosity in accordance with BS 6297 and building regulations. This test ensures that the drainage field can handle wastewater efficiently. If percolation is too rapid, it may pose a risk to groundwater resources, while excessively slow percolation can lead to surface waterlogging. The test results dictate the required land area for a sustainable drainage field. A favorable percolation test indicates that the land can support a septic system, while poor results necessitate an alternative disposal solution to prevent environmental hazards.
In conclusion, site assessment is a fundamental process before installing an STP. A suitable site should have a low water table, adequate subsoil, advantageous topography, good accessibility, and sufficient land area. These factors, combined with satisfactory percolation results, suggest that a septic system will function effectively. However, sites with high water tables, shallow subsoil, or heavy clay may fail percolation tests, requiring alternative disposal systems. By following the recommended three-step procedure—visual inspection, trial hole testing, and percolation assessment—homeowners can ensure that their Off-Mains sewage system operates efficiently and sustainably.
Turning Waste into Worth: Sustainable Solutions for a Cleaner Future
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