Man made Surface water drainage settling lagoon - Literature review Example

?MAN-MADE LAGOONS FOR SETTLING SURFACE WATER DRAINAGE Introduction Surface water is the “precipitation falling on land areas and moving on the land surface as sheet flows or as stream flow” (Gupta, 2010 p.20). It is also the accumulation of water in low lying areas such as swamps and lakes. Surface water is naturally replenished by precipitation, and released by evaporation and subsurface flow to groundwater. A coastal lagoon is “an area of salt or brackish water separated from the adjacent sea by a low-lying sand or shingle barrier” (Barnes, 1980 p.1); or it is a body of water similar to a lake enclosed in a coral atoll. On the other hand, artificial, sustainable drainage systems (SUDS) for the collection and temporary storage of surface runoff, are constructed for the purpose of attenuation or reduction of released water flow volume as well as water purification. These include Basins, Ponds and alternative forms of attenuation. Thus, Basins are of two types: detention basins and extended detention basins. Ponds are of five types: lagoons, balancing or attenuating ponds, flood storage reservoirs, retention ponds and wetlands. Alternative Forms of Attenuation include the use of over-sized pipes as in rainwater harvesting, tanks, and green roofs. Combined infiltration/ attenuation systems consist of swales and filter strips (SUDS, 2011). Thesis Statement: The purpose of this paper is to investigate the different types of lagoons. The naturally formed coastal lagoons will be examined, followed by a study of the artificial surface water drainage settling lagoon, and the various types of surface run-off storage water bodies, legislation, their management, purpose and concept. Coastal Lagoons are Natural Formations Coastal lagoons are found on all continents, particularly in the low latitudinal zone. They occupy 13 percent of the world’s coastline. These lagoons “occupy shallow coastal depressions and are separated from the ocean by a barrier” (Kjerfve, 1986 p.63). They are at risk of being completely infilled by sediments, or separated from the sea by littoral drift. In the British Isles there are comparatively few examples of this type of habitat. The coastal lagoon’s physical characteristics and differences are predominantly based on the nature of the channel connecting the lagoon to the adjacent coastal ocean; they are classified as choked, restricted, and leaky systems. Choked lagoons have a single entrance channel which is proportionately smaller in cross-sectional area as compared to the surface area of the lagoon; they are commonly found in coastlines with medium to high wave energy. On the other hand, leaky lagoons have several entrance channels, and have a naturally large ratio of entrance channel cross-sectional area in relation to the surface area of the lagoon. They are strongly influenced by the ocean’s salinity and tidal variability, and have an occasional significant wave energy. Restricted lagoons form the middle of the spectrum, between the choked and leaky extremes (Kjerfve, 1986). Coastal lagoons are similar to and also different from Manmade surface runoff water collection and storage systems such as ponds, basins and lagoons. Coastal lagoons are characterised by their salt water, and by being impacted by features such as the sea’s tides, the extent of build up of the reefs separating the lagoon from the adjacent sea, and other factors relating to oceanic conditions. These conditions do not affect manmade lagoons. However, natural coastal lagoons as well as manmade lagoons are similarly influenced by rainfall. At the same time, they differ in the surface runoff water that drains into them. Coastal lagoons are mostly polluted by the soil and other natural debris. On the other hand, the surface runoff that enters ponds, lagoons and basins frequently contains waste materials and sewage from industry, agriculture or other human activities besides soil impurities and natural deposits. Artificial Surface Runoff and Waste Water Drainage Settling Lagoons Ponds constructed for waste water stabilisation are artificial man-made lagoons which treat blackwater, greywater or faecal sludge by means of naturally occurring processes, as well as “the influence of solar light, wind, microorganisms and algae” (SSWM, 2012). The ponds or lagoons are used either individually or in a series of anaerobic, facultative, and aerobic maturation pond. Wastewater stabilisation ponds have the advantage of costing less for Operation and Maintenance (O & M) as well as for Biological Oxygen Demand (BOD). Moreover, pathogen removal is of a high efficiency. The disadvantages are that large surface areas are required, along with expert design for maximum sustainability. The effluent continues to retain its nutrients such as nitrogen and phosphorus; therefore it is suitable for reuse in agricultural irrigation, building constructions, industry and in aquaculture in fish or macrophyte ponds, but is not appropriate for direct recharge in surface waters. Surface run-off water drains into lagoons which permit suspended solid particles to settle, before releasing the water. The artificial water bodies or ponds are used for treating waste water through preliminary, primary, secondary, and tertiary treatment levels. The goal of preliminary treatment is the elimination of coarse solids, while primary treatment removes solids that may settle, as well as part of the organic matter (von Sperling, 2005). This is reiterated by Salvato, Nemerow and Agardy (2003 p.663) who add that “primary treatment with a grit chamber, comminutor and rack, and ponds or cells arranged for series operation are recommended”. Physical pollutant removal mechanisms play a significant part in both initial levels. The purpose of secondary treatment is to eliminate organic matter and nutrients such as nitrogen and phosphor by mainly biological techniques. “The objective of tertiary treatment is the removal of specific pollutants, usually toxic or non-biodegradable compounds” (von Sperling, 2005 p.166), or the additional removal of pollutants inadequately removed in the secondary treatment. Tertiary treatment is rare in developing countries. Lagoon systems typically comprise of a series of ponds: anaerobic/ facultative, aerobic/ maturation to achieve reduction in biological oxygen demand (BOD), nutrient reduction, and lowering of pathogen levels before transfer to the environment for re-use in irrigation, industry or other purposes. Loading determines the appropriate treatment series. Additionally, it is possible to overcome shortcomings of ponds oxidation capacity by installation of mechanical aeration which helps in dissolving oxygen as well as mixing ability, and the prevention of shortcircuiting (Laginestra and vanOorschot, 2007 p.3). Table 1. below compares the treatment performance of anaerobic ponds, facultative ponds, and maturation ponds. The removal of pathogens is found to be highest by the maturation pond, which is also the most efficient in eliminating biological oxygen demand (BOD) from waste water. Table. 1. Comparison of the Treatment Performance of Different Waste Stabilisation Ponds Pond BOD Removal Pathogen Removal HRT Anaerobic Pond 50 to 85%   1 to 5 days Facultative Pond 80 to 95%   5 to 30 days Maturation Pond 60 to 80% 90% 15 to 20 days (SSWM, 2012) Man-made or artificial lagoons are developed for the purpose of settling the effluents in surface water that drains into them. These artificial lagoons are also in the form of waste stablisation ponds. “With increasing urbanisation and industrialisation, the volume of domestic sewage, industrial effluents, agricultural wastes, and urban run-offs is steadily growing” states the WHO (1971 p.11). This is reiterated by Woodard (2001) who further states that industrial wastes differ according to the manufactured products; hence different combinations of techniques may be required for waste water treatment. The Settling Lagoon in Fig.1 below shows well-maintained primary lagoons. In the foreground is a floating pump taking clean water for dust suppression by water browsers. In Fig.2 is seen the T-piece joining two lagoons in a manner permitting the free flow of water below the surface from one lagoon to the other, while not allowing the transfer of surface scum or oil (Sustainable Aggregates, 2011). Fig.1. Settling Lagoon (Sustainable Aggregates, 2011) Fig.2. Settling Lagoon with Outflow Taking Water Below Surface Level (Sustainable Aggregates, 2011) Fig.3 Polishing Lagoons Surrounded by Storm Overflow Drain (Sustainable Aggregates, 2011) Fig.4. Polishing Lagoons with Central Water Inlet (Sustainable Aggregates, 2011) Figs. 3 and 4 reveal the final stage of treatment by specially developed polishing lagoons. Those in Fig.3 are surrounded by a storm overflow drain, which prevent overflow from spreading in the surrounding areas during phases of considerable rainfall, when the lagoons may be unable to cope with the vast volumes of water. These polishing lagoons are “rectangular, broad-crest weir type, where the water rises through the centre and flows out over the complete perimeter” (Sustainable Aggregates, 2011). This promotes exceedingly slow flow rates, which supports further settling of sediment. Adhering to safety rules, the picture shows that security fencing and lifebuoys are positioned around the lagoons; and several warning signs are posted. Fig.5 depicts a channel leading from the lagoons to the location from where it will be dispersed for use. Fig.5. Channel Leading to Discharge Point (Sustainable Aggregates, 2011) All the waste waters are required to be assimilated into the environment without adversely affecting the health and well-being of man. Hence, it is frequently necessary to facilitate the natural processes of purification with the help of biological waste treatment plants. The type of facility required is based on the assimilative capacity of the environment, and on the purpose for which the receiving water or the treated waste water will be used (WHO, 1971). Rainfall, snow or other events of water precipitation can cause surface water runoff. In an industrial, agricultural, or other site, surface water runoff has high levels of solid contents and waste materials. A surface water runoff lagoon is a type of pond, which uses the Sustainable Drainage Systems (SUDS) technique of attenuation to “reduce the rate and volume of surface water discharges from sites to the receiving environment” (SUDS, 2011 p.H.1) which may be the natural watercourse, public sewer, etc. Additionally, water pollution is reduced, and the water that is released from the lagoon is of a higher quality. Ponds are “designed to control discharge rates by storing the collected runoff and releasing it slowly once the risk of flooding has passed” (SUDS, 2011 p.H.6). Lagoons are similar to balancing/ attenuating ponds, besides being also designed for the settlement of suspended soils. Most lagoons are long and narrow in shape to ensure the longest retention time, towards achieving an efficient elimination of suspended solids. At the same time, lagoons are generally devoid of vegetation, hence they do not biologically treat the water. Wastewater treatment through lagoon based systems to undertake reduction of biological oxygen demand (BOD) and other contaminants derives its techique from natural systems, though in a controlled manner. Although its ecological footprint is considerably larger thatn mechanical or constructed bioreactor systems, lagoons “have specific uses, are considered sustainable, provide reasonable treatment and are generally prevalent in rural applications” (Laginestra and vanOorschot, 2007 p.1). Lagoons are useful in the treatment of intensive agricultural industry wastewater, and also in the treatment of municipal sewage. The performance of lagoon based waste water treatment varies, being related to a range of factors. These incude the type of pond: whether anaerobic, facultative, aerobic, aerated or maturation); loading and wastewater characteristics; the climate; and the arrangement. Additionally, on the basis of loading and general performance, odours from the lagoon may be an important issue, and a challenge for operators of pond systems to resolve. This is particularly necessary due to the “encroachment of residential and semirural communities into previously industrial or nonpermanent inhabited areas” (Laginestra and vanOorschot, 2007 p.1). Thus, man-made waste water or run-off water settling lagoons similar to waste stabilisation ponds are a vital means of waste water treatment and disposal for increasing numbers of communities which lack both trained personnel as well as funds. In these water bodies, beneficial organisms “stabilise the waste water into a liquid that can be released to the environment without endangering man directly” (WHO, 1971 p.11). Further, the treated water does not have detrimental effects on the environment, or adversely impact a downstream user. Waste water treatment lagoon systems are classified into different types depending on their depth and the biological reactions that take place in the lagoon. “Using this classification, the four primary types of lagoons are aerobic, facultative, aerated and anaerobic” (Vesilind, 2003 p.9-2). The main advantage of lagoon systems is their simplicity to develop and operate; however their non-mechanical characteristic necessitates greater volume, and subsequently larger area and footprint in treating wastewater as compared to conventional treatment systems. The lagoons’ ability “to achieve significant reductions of contaminants is attributed to their diverse biology and incorporation of aspects of conventional treatment including biochemical reactions, settlement of solids, and disinfection” (Laginestra and vanOorschot, 2007 p.1). Different types of ponds serve different purposes, and the range of operating parameters determines the type and performance. Ponds are differentiated mainly by the dissolved oxygen of the layers within the ponds, which in turn is based on the loading of the pond system. The different pond types are distinctive in their characteristics. Anaerobic lagoons are planned for coping with high organic loading, usually lack dissolved oxygen, and contain do not contain significant levels of algal population. They involve long durations of detention, and are deeper than other ponds because of the requirement to exclude oxygen. Facultative lagoons (Fig.6) employ two different operating techniques including aerobic at the surface, and with the settlement of the sludge, anaerobic at the base of the pond. These water bodies are typically shallower than anaerobic lagoons (Laginestra and vanOorschot, 2007). Fig.6. A Facultative Waste Stabilisation Lagoon (WHO, 1971 p.59) Aerated lagoons (Figs. 7, 8, 9 and 10) are mechanically incorporated with air, and are generally deeper than naturally aerobic ponds because the aeration reaches the lower layers (Laginestra and vanOorschot, 2007. Fig. 7. Aerated Lagoon (Water Treatment, 2012) Fig.8. Fixed Type Aerators (Water Treatment, 2012) Fig.9. Floating Aerators (Water Treatment, 2012) Fig.10. Two Different Types of Aerated Waste Stabilisation Lagoons (WHO, 1971 p.85) Aerobic lagoons are shallow to permit algal development and to receive lower solids or Biological Oxygen Loading (BOD). Maturation or oxidation lagoons are mainly used for polishing of effluent, “and are shallow to allow for ultraviolet light penetration and subsequent disinfection” (Laginestra and vanOorschot, 2007 p.2). Evaporation ponds are also used where it may be difficult to dispose of effluent, as in cases of high salinity. These are usually very shallow, less than 1.5 metres, with volumetric requirements associated with environmental factors such as temperature, humidity and rainfall levels. The chief disadvantage of lagoon and pond systems is that they are unable to significantly remove nutrients. However, reduction takes place to some extent, caused by “volatilisation of ammonia, algal assimilation in biomass, and possibly biological nitrification/ denitrification” (Laginestra and van Oorschot, 2007 p.2). Legislation Pertaining to Settlement Lagoons According to Environment Agency (2007), settlement lagoons or tanks should retain contaminated water for a sufficient duration of time allowing for silt to settle out. The length of time will vary according to the type of silt, with finer clay solids taking longer durations to settle. If planning to use flocculants this option has to be first discussed with the Environment Agency because flocculants can themselves cause pollution and water toxicity, and hence require careful use and monitoring to be effective. The following guidelines on surface water drainage lagoons pertain to the volume of lagoon needed for a three-hour settlement at a defined rate of inlet discharge. The checklist includes specific requirements: the maintenance of a constant pumped inlet rate; minimisation of the inlet flow to the lowest rate possible by using energy dissipators or rip rap; the positioning of inlet pipe work vertically to dissipate energy; providing lined inlet chamber to reduce velocity of flow; lining of inlet chamber and outlet weir with materials like geotextiles, brickwork, polythene or timber; having a long outlet weir to minimise disturbance; increasing silt retention through developing two or three lagoons in series; regular cleaning of inlet chamber; and frequent monitoring of discharge quality (Environment Agency, 2007 p.7). Filtration: When space for lagoons is not available, and the water is contaminated with coarse silt, tanks filled with filter material may be used. “Single sized aggregates 5-10 mm, geotextiles or straw bales can be used as filter” (Environment Agency, 2007, p.7). The inlet pump rate and discharge quality have to be monitored carefully. Pump to grassland: Permission from the Environment Agency and the landowner is required before planning to pump the treated water to grassland. It is essential that the discharge rate should match the rate of infiltration into the soil which will differ according to the type of soil, amount of vegetation cover, and the gradient. Discharge to sewer: If this method of diverting waste water is possible, permission of the local sewerage provider will be required. This should be obtained at an early stage of the construction or other project. They may issue a consent or authorisation limiting the volume and content of the discharge. Tanker off site: In the absence of other disposal routes, contaminated water can be collected and disposed off site by tanker. This may be a costly alternative, and has to be discussed with the Environment Agency at the initial planning stage of the project (Environment Agency, 2007 p.8). Management of Lagoon Systems With the help of lagoons, ponds and other attenuating water bodies such as basins, sustainable drainage of surface water runoff can be achieved. Sustainable drainage involves controlling surface water runoff “as close to its origin as possible by slowing flows, allowing adequate settlement and biological action to take place” (Environment Agency, 2007 p.6) before water is allowed to stream out to a water course or to the ground. Sustainable drainage practices emulate natural drainage instead of traditional piped drainage solutions. These methods are employed both in the design and development of the project. After the cells or lagoons are constructed, it is vital that periodic maintenance is conducted to ensure their optimal functioning. According to Saskatchewan Environment (2004), management and maintenance of the lagoon dykes includes rodent control or regular checks for burrowing animals. Trapping or shooting have to be undertaken to control rodents, and the damaged dyke has to be repaired. Seepage control of the ground at the base of the dyke, erosion control on both inner and outer slopes with the help of rip-rap material. Proper grading has to be undertaken to eliminate surface runoff around the perimeter of the lagoon to prevent exterior dyke erosion. Similarly sludge mounds around the inlet have to be removed periodically, more frequently in the winter. Maintenance of overflow is necessary between the primary and secondary cells, because overtopping the dyke due to overflow block can lead to breaching and failure of the dyke.Further, fence and gate repairs are required for preventing trespassing by unauthorised personnel and livestock. Vegetation control by cutting or burning is essential to prevent the breeding of mosquitoes. Growth including weeds and bulrushes in the cells have to be regularly cut. Additionally, “a properly designed receiving area, pad or chutes should be employed and maintained” (Seskatchewan, 2004 p.5). Conclusion This paper has highlighted man-made lagoons, after first examining natural coastal lagoons. The four primary types of settling lagoons for surface water runoff include: aerobic, facultative, aerated and anaerobic. They are vital in reducing water pollution through minimizing the levels of contaminants in water containing wastes from industry, agriculture, building construction, and activities related to human life. The treated water is then reused for most of the above purposes, other than for human consumption Further, legislation pertaining to surface water drainage lagoons, as well as the management of the lagoon systems were discussed. Besides control of water pollution, and water recycling, it is evident that the purpose of adopting sustainable drainage through lagoons and ponds is to reduce diffuse pollution from surface water runoff, eliminate the risk of pollution to groundwater, flood risk from development within a river catchment, minimise environmental deterioration such as bank erosion and damage to habitats, maintain or restore the natural flow of the receiving watercourse, and maintain recharge to ground water. Environment Agency (2007) support the usefulness of man-made lagoon systems, and add that sustainable drainage also ensures “environmental enhancements, improvement to wildlife habitats, amenity and landscape quality” (Environmental Agency, 2007 p.6). Bibliography Barnes, R.S., 1980. Coastal lagoons: The natural history of a neglected habitat. Cambridge: Cambridge University Press. Environment Agency, 2007. Pollution prevention guidelines: Works and maintenance in or near water: PPG5. 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EPB 310. http://www.saskh2o.ca/DWBinder/EPB310TwoCellLagoonOperation_and_MaintenanceGuide.pdf [Accessed 14 February 2012]. SSWM (Sustainable Sanitation and Water Management). Waste stabilisation ponds. http://www.sswm.info/category/implementation-tools/wastewater-treatment/hardware/semi-centralised-wastewater-treatments/w [Accessed 14 February 2012]. SUDS (Sustainable Drainage Systems), 2011. SUDS Information: Alternative SUDS Techniques. Strategic Flood Risk Assessments (SFRA) Appendix H. http://www.north-herts.gov.uk/sfra_appendix_h_alternative_suds_techniques.pdf [Accessed 14 February 2012]. Sustainable Aggregates, 2011. Water: Operational Phase. Environmental Management. http://www.sustainableaggregates.com/sourcesofaggregates/landbased/water/water_opsstage_page6.htm [Accessed 14 February 2012]. Vesilind, P.A., 2003. Wastewater treatment plant design. Great Britain: International Water Association (IWA) Publishing. Von Sperling, M., 2005. Biological wastewater treatment in warm climate regions, Volume 1. London: International Water Association (IWA) Publishing. Water Treatment, 2012. Aerated lagoon. The Water Treatments: Sewage Treatment. http://www.thewatertreatments.com/wastewater-sewage-treatment/aerated-lagoon/ [Accessed 14 February 2012]. WHO (World Health Organisation), 1971. Waste stabilisation ponds. World Health Organisation Monograph Series No.60. http://whqlibdoc.who.int/monograph/WHO_MONO_60_(part1).pdf [Accessed 14 February 2012]. Woodard, F., 2001. Industrial waste treatment handbook. New York: Butterworth- Heinemann. Read More