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Constructions and related matters relevant to environmental health
Published in Stephen Battersby, Clay's Handbook of Environmental Health, 2023
John Bryson, Stephen Battersby
A septic tank is again a holding tank into which the sewage from a dwelling drains but the liquid part of the waste is separated and then leaves the tank via a system of land drains while the solids are held within the tank. As the tank holds only the solid waste it can be smaller than a cesspool, and while it will still need to be emptied, this will be required less frequently. Some septic tanks are fitted with grease traps before the inlet, and may have an additional filtration system, for example via volcanic rocks furnace clinker or other filtration medium before the discharge to the system of land drains or “drainage field” – a system of field drainage.
Environmental Engineering
Published in P.K. Jayasree, K Balan, V Rani, Practical Civil Engineering, 2021
P.K. Jayasree, K Balan, V Rani
Although soap, disinfectants, drain solvents, and related materials used individually for household purposes are not harmful to septic tank operation unless used in large quantities, organic solvents and cleaners, pesticides, and compounds containing heavy metals could contaminate the groundwater and well-water supplies and should not be a dump in a septic tank system. Also, sanitary napkins, absorbent pads, and tampons should not be disposed of in septic systems.
Preliminary Design Concepts and Considerations
Published in David Thrasher, DESIGN and USE of PRESSURE SEWER SYSTEMS, 2020
A comprehensive study of septic tanks has been performed by the Department of Health, Education, and Welfare.54,59 Over 600 references were studied to develop information on previous research, and practice and experience were reviewed in 12 countries plus the United States. Over 200 tanks in operation were studied along with many laboratory models. That study shows, for example, that a 900-gallon septic tank serving the average home would have to be pumped every 25 years. However, as the sludge and scum layers build, less detention time is developed so a 25-year pumping interval is longer than recommended. When used in conjunction with drainfields where even the smallest discharge of solids is undesirable, the tanks should be pumped more frequently, but not as frequently as many people believe. Overly frequent pumping is a practice done mostly in hopes of curing failing drainfields.10
The impact of hydraulic retention time on the performance of two configurations of anaerobic pond for municipal sewage treatment
Published in Environmental Technology, 2022
P. H. Cruddas, N. Asproulis, A. Antoniadis, D. Best, G. Collins, E. Porca, B. Jefferson, E. Cartmell, E. J. McAdam
Recently, further understanding of high-rate upflow anaerobic sludge blanket reactors (UASBs) has identified that benefit can be delivered through inclusion of an anaerobic pre-treatment stage, in order to decrease solids loading onto the UASB and provide a more acidified substrate [27,28]. This has led to the development of two-stage high-rate anaerobic reactors, where downstream UASBs have been preceded by septic tanks [29], anaerobic filters [30], and lower-rate UASBs [31,32]. Whilst it has been identified that, especially at low temperatures, two-stage anaerobic designs are essential for both maximising solids retention and degradation in the first stage, and providing preferential substrate to the second stage [21,28], two-stage designs have not been applied to low-rate technologies to date. The context relates to remote/rural; communities that are commonly served by septic tanks and where a short HRT anaerobic pond could offer real advantages in terms of treatment and desuldging frequency. To illustrate, Scottish Water currently operate over 1250 spetic tanks with 100 of these treating population equivalents of over 1000 PE. The septic tanks operate at HRTs of around 0.5–1.0 days and require desludging every 6 months to 2 years which incurs significant costs and disruption to the local community. Two-stage anaerobic ponds have been posited as a future alternative but must be able to operate at short HRTs to be considered economically viable [33].