facultative pond advantages and disadvantages facultative pond advantages and disadvantages

However, large surface areas and expert design are required. <>stream %%EOF FPs can result in the removal of 80 to 95% of the BOD5 (SPERLING 2007), which means an overall removal of 95% over the two ponds (AP and FP). n:'6(l]HJ{6| YaLZ]W[;|D't?zU3%0;?7t&j={'E: n.=\ll|YFn*L}H3. <>/Metadata 2123 0 R/ViewerPreferences 2124 0 R>> It also considers aspects such as management and safety. Besides the poor economic situation and little political support, it is also the lack of training and research that contributes to this situation. The aerobic and anaerobic organisms work together to achieve BOD reductions of up to 75%. There are three types of ponds, (1) anaerobic, (2) facultative and (3) aerobic (maturation), each with different treatment and design characteristics. Virus and microorganisms get also removed. Ft#sqD|)qr vDu International Water Association (IWA Publishing), Notes in the Design and Operation of Waste Stabilization Ponds in Warm Climates of Developing Countries, Compendium of Sanitation Systems and Technologies. In cold climates, the HRT and loading may be adjusted. Waste Stabilization Ponds and Constructed Wetlands Manual. facultative pond advantages and disadvantages. They are designed for BOD removal and can treat water in the BOD range of 100 to 400 kg/ha/day corresponding to 10 to 40 g/m2/day at temperatures above 20C (MARA and PEARSON, 1998). In the case of high salt content, the use of the water for irrigation is not recommended. W&+I4@aI\'@ fish ponds). CHrc!xGEc3"Xes.pS`yqGR9)G2 A study on management and institutional aspects regarding the challenges and possible improvements in managing faecal sludge. Oxygen is unable to be maintained at the lower layers if the pond is too deep, and the colour too dark to allow light to penetrate fully or if the BOD and COD in the lower layer is higher than the supply. the article or any translations thereof. (= Integrated Environmental Technology Series endobj HWr x}tliU@$f/G9EPrT\i the wastewater-fed fishponds in Calcutta in India. Index of dept/chem-eng/Biotech-Environ/FUNDAMENT. If the design or operation management is not in place, it will cause secondary pollution . HP@)54]n8>X Effluent from some types of lagoons Contains algae and often requires additional treatment or polishing to meet discharge standards. 2008). These systems are composed of a series of ponds: (1) anaerobic ponds, (2) facultative ponds, and (3) maturation ponds. <> 11 0 obj Comparison of the treatment performance of different waste stabilisation ponds. -Mx-BGT""D4h0D BOToBr M v:]O%W!dR5!Cd6h"0 ;(S#[email protected]="ps<2xCDT9]h2 f!@eu8\&eq!C@2G,r9#e5P'+@6pdqC4:5aGO\OOY|:A` =~uA.OONaS='t> *>o{ ":QwONp'KO~OmOo X\"di0'x? The report suggests that emerging trends in low-cost, decentralised naturally-based infrastructure and urban wastewater management which promote the recovery and reuse of wastewater resources are increasingly relevant. Before the exit of the stabilization pond, a scum baffle should be installed, but before the advanced treatment pond, no baffle should be installed to avoid trapping algae . High self-help compatibility concerning maintenance. They are simple to operate and maintain and generally require only part-time stuff. The stable pond can not only effectively treat high-concentration organic water, but also low-concentration sewage . However, when mean temperatures fall below 12 C during several month of the years, WSPs seem not to be appropriate (ARTUHR 1983). Pond Treatment Technology. Experts are tested by Chegg as specialists in their subject area. The purpose of this guide is to assist local contracting authorities and their partners in identifying those sanitation technologies best suited to the different contexts that exist within their town. The straight-line distance between the inlet and the outlet should be as large as possible . facultative pond advantages and disadvantagesjewelry district nycjewelry district nyc Construction can take place by semi- or unskilled labourers. Require little energy, with systems designed to operate with gravity flow. Ests aqu: research opportunities for high school students fall 2021; lakeside high school football; ADVANTAGES AND DISADVANTAGES Some advantages and disadvantages of facultative lagoons are listed below: Advantages Moderately effective in removing settleable solids, BOD, pathogens, fecal coliform, and ammonia. 18 0 obj As a result of the photosynthetic activities of the pond algae, there is a diurnal variation in the concentration of dissolved oxygen. Required fields are marked *. m}~pPeh'/H+:Z~PO{izUG[4@'a5uIUWI{r AwOU[XkotJ^JDB]$% pP2A=-__T[5O :-fS0'[t!(!AD#AySAuJv;$YL1d|iqvl p.E~0W Technologies for these sanitation options are presented. <> The oxygenation of the aeration pond is the same as other aerobic processes . Depending on the requirement for the final effluent in terms of pathogen reduction, only anaerobic and facultative ponds are necessary in some instances. Settleable solids accumulate and are digested on the bottom of the pond. 3 0 obj It has the characteristics of low energy consumption, convenient operation and maintenance, and low cost . Waste or Wastewater Stabilization Ponds (WSPs) are large, man-made water bodies in which blackwater, greywater or faecal sludge are treated by natural occurring processes and the influence of solar light, wind, microorganisms and algae . They use less energy than most waste water treatment methods. % N;Pplo+goGW;3cOl#D4VBk`AdU[bL}gg-8~hBI{$()P^-3y(GdS?>c'c%: 13 0 obj Wastewater Use in Agriculture, Compendium of Sanitation Systems and Technologies (Arabic), Epuration des eaux uses par Lagunage a Microphytes et a Macrophytes en Afrique de l'Ouest et du Centre- Etat des lieux, performances puratoires et critres de dimensionnement, How to Select Appropriate Technical Solutions for Sanitation, Environmentally sound technologies in wastewater treatment for the implementation of the UNEP/GPA "Guidelines on Municipal Wastewater Management", Lagunas de Estabilizacion para Descarga de Liquidos de Camiones Atmosfericos, Ecological Sanitation and Reuse of Wastewater. 51 0 obj <> endobj Some of AIWPS applications are given, emphasizing removal efficiencies in every unit. MILLS, S.W. 7 0 obj Waste Stabilization Ponds and Constructed Wetlands Design Manual. [11 0 R 12 0 R] endobj The 55 chapters are divided into 7 parts over two volumes: Volume One: (1) Introduction to wastewater characteristics, treatment and disposal; (2) Basic principles of wastewater treatment; (3) Stabilisation ponds; (4) Anaerobic reactors; Volume Two (also available in the SSWM library): (5) Activated sludge; (6) Aerobic biofilm reactors; (7) Sludge treatment and disposal. 0000007026 00000 n These ponds do not require primary treatment and the added depth is needed to handle the substantial increase in solids loadings. Ponds have many advantages and disadvantages compared to treatment in plants. Lagoon Technology International Ltd, MARA, D.D. Provides information on the limitations, advantages and disadvantages, applicability, performance, design criteria, operation and maintenance, and costs of such lagoons. <> Solids and BOD removal occurs by sedimentation and through subsequent anaerobic digestion inside the accumulated sludge (see also anaerobic digestion general). If used in combination with algae and/or fish harvesting (see Fish Pond), this type of pond is effective at removing the majority of nitrogen and phosphorus from the effluent. Biological Wastewater Treatment in Warm Climate Regions gives a state-of-the-art presentation of the science and technology of biological wastewater treatment, particularly domestic sewage. In a series of WSPs, the effluent from the anaerobic pond is transferred to the facultative pond, where further BOD is removed. The first part of the guide contains a planning process and a set of criteria to be completed; these assist you in characterizing each area of intervention so that you are then in a position to identify the most appropriate technical solutions. The stabilization pond is located in the natural environment, and the climate has a great effect on it . A plant, in contrast, must install an aerator to add oxygen to the water. 7 0 obj However, this depends on the availability of land and its price. This makes them particularly suitable for developing countries where many conventional wastewater treatment plants have failed because water and sewer utilities did not generate sufficient revenue to pay the electricity bill for the plant (IRC 2004) (see also -financing projects). The principal objective of the study was to asses if existing treatment ponds could be used in the future as thickening ponds for the sludge. In addition, it is one of the few low-cost natural processes, which provides good treatment of pathogens. The construction structure is simple, and most of them are earth-rock structures. CHrc!xGEc3"Xes.pS`yqGR9)G2 2008). WSPs are among the most common and efficient methods of wastewater treatment around the world. 8 0 obj 'b* [V;.Kih+'^\j_.OUzwt^ tah;,zGb'hLOY k_!uJUu^zX{h @cxxZIup y,"hA}[ 0000006544 00000 n c. If a multi-stage stabilization pond system is adopted, the overtaking setting should be considered between the stabilization ponds at all levels . Design Manual for Waste Stabilization Ponds in Mediterranean Countries. <>/Font<>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 720 540] /Contents 12 0 R/Group<>/Tabs/S/StructParents 1>> At peak sun radiation, the pond will be mostly aerobic due to algal activity, while at sunrise the pond will be predominantly anaerobic (ERTAS et al. endobj They are very effective at removing disease-causing organisms (pathogens) from wastewater. It covers both technical and non-technical (socio-cultural, economic, political etc.) It should be fully compacted and as flat as possible, and the completed height difference of the pond bottom shall not exceed 0. Based on operational simplicity, low cost and high removal efficiencies (99% BOD5, suspended solids and coliform bacteria removal), AIWPS is highly recommended for up to 1000 mg/L BOD5 concentration. WSPs are low-cost for O&M and BOD and pathogenremoval is high. What are the advantages and disadvantages of these three Waste Stablization Ponds listed below: a) Anaerobic Pond, b) Facultative Pond, and c) Aerobic Pond This problem has been solved! 8.1.1.4 The advantages and disadvantages of the stabilization pond treatment process. What are lagoon systems?, Advantages and Disadvantages of Lagoon Systems, Two, Three or Four Lagoons are Better than One, Facultative Lagoons Treat Wastewater Naturally, Lagoons Use Simple Design, Lagoons Need Proper Operation, Maintenance, . Odor can become a nuisance during algal blooms or with anaerobic lagoons and lagoons that are inadequately maintained. 0000000729 00000 n The annexe contains a practical collection of factsheets on selected sanitation system options. Facultative waste stabilization ponds, sometimes referred to as lagoons or ponds, are frequently used to treat municipal and industrial wastewater in the . If you have any concerns or complaints relating to the article, please send an email, providing a detailed Facultative ponds and open digesting tanks are the most commonly used anaerobic processes for the treatment of POME (Yacob et al., 2005). 5 0 obj The book has been divided in two parts. This website makes no representation or warranty of any kind, either expressed or implied, as to the accuracy, completeness ownership or reliability of Dar es Salaam/Copenhagen: www.waterworld.com is using a security service for protection against online attacks. It can beautify the environment and form an ecological landscape . Various case studies on the reuse of pond and lagoon treated water in urban agriculture. endobj endobj 8) What is the most common type of pond in use today? Rensselaer Polytechnic Institute (RPI), SHILTON, A. <> to, Advantages and disadvantages of stabilization pond treatment process, Fluid, Electrolyte, and Acid-base Balance, Longmen Town, Lintao County, Gansu Province, launched a large-scale investigation and major renovation of the starch processing industry, The Market Supervision Office of Longmen Town, Lintao County, Gansu Province, carried out a special inspection of food safety before the "Double Festival", Benxi biological hepatitis B and AIDS test box have been registered. 90% BOD and TSS; high pathogen reduction and relatively high removal of ammonia and phosphorus; Total HRT: 20 to 60 days, Low capital costs where land prices are low; very low operation costs. endobj Facultative Treatment Ponds are the simplest of all WSPs and consist of an aerobic zone close to the surface and a deeper, anaerobic zone. substantially reduces the land area required for facultative ponds. The ponds can be used individually, or linked in a series for improved treatment. <> <>/Font<>>>/MediaBox[0 0 612 792]/Rotate 0>> Stabilisation ponds also have the advantage of very low operating costs since they use no energy compared to other wastewater treatment technologies and only low-tech infrastructure (see also operation and maintenanceand ensuring sustainability). Waste Stabilisation Ponds is the third volume in the series Biological Wastewater Treatment. The effluent from lagoon systems can be suitable for irrigation (where appropriate), because of its high-nutrient and low pathogen content. xref <> <> As the wastewater flows over the . Emery, R. KAYOMBO, S. MBWETTE, T. S. A. KATIMA, J. H. Y. LADEGAARD, N. JORGENSEN, S. E. The most serious disadvantages are a long retention time, the release . 0000188309 00000 n PEARSON, H.W. The major variants of pond systems are fully covered, namely: facultative ponds, anaerobic ponds, aerated lagoons, maturation ponds. <> You'll get a detailed solution from a subject matter expert that helps you learn core concepts. The construction land has the advantages of short construction period, easy construction and low capital construction costs. <> The Clinton Water District provides a secondary level of wastewater treatment by using a facultative lagoon system. `# ~a8ivHjy2_diw"sfGDl2lG] <> 47 0 obj <>stream ). H} 0C' 6 (2006): This Sanitation Sourcebook distils some of the core concepts of sanitation in a user-friendly format so that the book can serve as a practical reference to sanitation professionals and investment decision-makers, particularly the local governments. London: The process (as in septic tanks) relies on the sedimentation of settable solids and subsequent anaerobic digestion in the resulting sludge layer. According to the International Water and Sanitation Centre (IRC), stabilisation ponds are the most cost-effective (semi-)centralised wastewater treatment technology for the removal of pathogenic microorganisms. stream This training manual emphasizes basics of biogas technology as well as design principles and technical considerations. <> It is the shallowest of the ponds, ensuring that sunlight penetrates the full depth for photosynthesis to occur. !J=WIt@XY>APw~4 r89>g)#l0|#@d{&9 endobj rate of 0.6 m 3 of facultative pond effluent per m of RF volume per day was about 9 mg BOD, about 7 mg SS, about 3 mg ammonia-N per liter and 10 to 1,000 fecal coliforms per 100 mL. a. The last ponds serves for the retention of stabilised solids and the inactivation of pathogenic microorganisms via heating rise of pH and solar disinfection. They are simple to operate and maintain and generally require only part-time stuff. For the restricted and unrestricted reuse of the effluent in agri- and aquaculture, please refer to the WHO (2006) guidelines. The liner can be clay, asphalt, compacted earth, or another impervious material. aspects and provides practical information on design, financing and planning of faecal sludge treatment plants. which doesn't represent ECHEMI's opinion. Please enable cookies on your browser and try again. Almost all wastewaters (including heavily loaded industrial wastewater) can be treated, but as higher the organic load, as higher the required surface. T w"F:ddH^0% /@ 0[#a%KI E@' _{a~d Q/d"8+ .U p9 GG^tS~0-o_Oa/Vxi>5IJvo}=~4iKuz};p/^x],;^{?-{m*:Vt7u@@7*@ y;tv DG3H.>k+>'//_^V^vzK_^|.^a{uw]+uOZ{uu_Q`dIvP$#&fGF#R0=_ppV f=]%&z\/_uvz/.}=ko_an_]I&^z}-o]_s! Stabilization Ponds . Volume II. Because photosynthesis is driven by sunlight, the dissolved oxygen levels are highest during the day and drop off at night. endobj Basins with surface areas many times larger than conventional biological reactors, that utilize relatively low . If the water is reused for irrigation, the salinity of the effluent should be controlled regularly in order to prevent negative impact on the soil structure. Pre-treatment (see Pre Treatment Technologies) is essential to prevent scum formation and to hinder excess solids and garbage from entering the ponds. <> An aerobic pond is commonly referred to as a maturation, polishing, or finishing pond because it is usually the last step in a series of ponds and provides the final level of treatment. Two products can be put into production this month, The difference between PU and NC wood paint Seven differences to look at carefully. Wind energy is one of the important auxiliary energy sources of the stabilization pond. Various case studies are mentioned, e.g. 8 0 obj Waste Stabilization Pond Systems are summarized and Advanced Integrated Wastewater Pond Systems (AIWPS) are investigated. Hence, this paper can be useful as a technical manual. A Thinkpiece on ecological sanitation, Sewage Fed Aquaculture Systems of Kolkata. Leeds: (2) Disadvantages It covers a large area . The stabilization pond is located in the natural environment, and the climate has a great effect on it . endstream (2004): 2 0 obj Require much less land than facultative ponds, depending on the design conditions. This process is automatic. endobj endobj Bekldve: 2022. mjus 29. vasrnap Szerz: . Facultative ponds treat BOD, typically within a range of 100-400 kg BOD/ha/day, by removing BOD by 95 %. For facultative ponds sludge removal is even rarer and maturation ponds hardly ever need desludging. The pond body directly below the surface aerator of the aeration pond must be reinforced with concrete . The concept of managing urban wastewater flows at a decentralised or "intermediate" level, based on micro watersheds, is explored. BOD removal in both types of facultative pond is in the range 60-80%. 71 0 obj<>stream facultative pond advantages and disadvantages facultative pond advantages and disadvantages. The Compendium gives a systematic overview on different sanitation systems and technologies and describes a wide range of available low-cost sanitation technologies. The relative advantages and disadvantages of ponds are compared to other small community treatment systems, such as rotary biological contactors, biological filters and reed-bed systems,. b. Some advantages and disadvantages of facultative lagoons are listed below: Advantages Moderately effective in removing settleable solids, BOD, pathogens, fecal coliform, and ammonia. W&+I4@aI\'@ b. 1 0 obj The effluent still contains nutrients (e.g. The WHO (WHO 2005 in MOREL & DINER 2006) does not promote pond systems if appropriate mosquito control measures are not guaranteed. Fact sheet that discusses facultative stabilization ponds or lagoons used in the treatment of municipal and industrial wastewater, as well as common modifications to the lagoons. y"wmlVUvC 2nd Revised Edition, Biological Wastewater Treatment in Warm Climate Regions Volume 1, Training Material on Anaerobic Wastewater Treatment, Greywater Management in Low and Middle-Income Countries, Review of Different Treatment Systems for Households or Neighbourhoods, Guidance Manual on Water Supply and Sanitation Programmes, Advanced Integrated Wastewater Pond Systems, Waste Stabilization Ponds and Constructed Wetlands Design Manual, Design Manual for Waste Stabilization Ponds in Mediterranean Countries. c) Aerobic Pond, Water stabilization ponds are the large man-made basins in which greywater, blackwater or faecal sludge can be treated to an effluent of relatively high quality and apt for the reuse in agriculture (e.g. It is usually arranged diagonally . If there is a certain height difference between the inlet water elevation of the aeration pond and the pond water surface elevation, then this height difference can be considered for oxygenation by falling water . As a complete process, the anaerobic pond serves to: BOD removal in anaerobic ponds is governed by the same mechanisms that occur in all other anaerobic reactors (MARA et al. 0000003487 00000 n In particular, the appendix and annex provide a working example and a simple methodology to help the designer in preparing adequately detailed designs. 1992) and anaerobic ponds do not or only rarely contain algae. Facultative ponds mean large, but shallow basins meant for the treatment of the sewage through the application of both anaerobic and aerobic processes (Bougrier et al. Anaerobic ponds are built to a depth of 2 to 5 m and have a relatively short detention time of 1 to 7 days. Anaerobic and facultative ponds are designed for BOD removal, while aerobic ponds are designed for pathogen removal (see also pathogens and contaminants). The design of the pond body should consider impact resistance and damage resistance . This report compiles international experience in greywater management on household and neighbourhood level in low and middle-income countries. o2Ctdd5[I,L 3p,cL0uWEL%#N*dv 22 0 obj <>/Type/XObject/Subtype/Image/ColorSpace/DeviceGray/Name/im1/Width 1926/BitsPerComponent 1/Length 2956/Height 2190/Filter/CCITTFaxDecode>>stream WSPs generally produce good-quality effluent in terms of organic matter and pathogen removal, but their application has disadvantages. Due to the algal activity, pH rises leading to inactivation of some pathogens and volatilisation of ammonia. <>stream N-^WJCQoU8lgL^laYXk lq5!JWDlpDS|WqxHlwaB#5nJy>y8b5:ypcluxqu6/*W!9?G! %PDF-1.7 Easy to operate. In contrast of waste stabilisation ponds where the oxygen required for stabilising the organic matter is furnished by algae, the oxygenation is provided in Aerated . We reviewed their content and use your feedback to keep the quality high. To protect the pond from runoff and erosion, a protective berm should be constructed around the pond using the excavated material. Unless they are property maintained, lagoons can provide a breeding area for mosquitoes and other insects. The recovered biogas can be used for heating, cooking or, if sufficient amounts can be collected for energy production (biogas combustionand biogas electricity small-scale). Learn more about troubleshooting WordPress. T$1MoG##}vQP"$=q^(XknABEo2$ w6+,i~}v_4S22$p_h+r"\v+xU~56Uu_AtW`:1ci0whs1VSJpANM9qAn@WM>u.E YD O=Sl %2zFPztVOZT?pI!>?>}{ZOE/ The purified sewage is introduced into the artificial lake and used as a water source for landscape and sightseeing . In a first pond (anaerobic pond), solids and settleable organics settles to the bottom forming a sludge, which is, digested anaerobic by microorganism. facultative pond advantages and disadvantages. 9 0 obj <> A berm can protect from erosion or the invasion by vegetation and a fence can protect the lagoons from people and animals and prevent that garbage is thrown in. What is cereal alcohol? c. Anti-seepage measures must be taken . endobj INTRODUCTION An aerated lagoon or aerated basin is a holding and/or treatment pond provided with artificial aeration to promote the biological oxidation of wastewaters. 1. 1. <> endobj 2003-2023 Chegg Inc. All rights reserved. irrigation) or aquaculture (e.g. Th~yp.5"j%=D2Bj#=pIq )t$dILVHkTn}$2YXZgla)hI,?>h6s[,7oJD8nx?W?m/ Lagoon Technology International, RPI startxref typically up to 500 mm). Part A provides a comprehensive summary concerning the various aspects of constructing, operating and maintaining pond systems. Common Lagoon Problems, Two Montana Towns Use Lagoons, For More Information. 19 0 obj endobj You'll get a detailed solution from a subject matter expert that helps you learn core concepts. 1. <> <>/Font<>>>/MediaBox[0 0 612 792]>> Source: WSP (2007). Perspectives are like filters: they compile and structure the information that relate to a given focus theme, region or context. For the most effective treatment, WSPs should be linked in a series of three or more with effluent being transferred from the anaerobic pond to the facultative pond and, finally, to the aerobic pond. 8. %PDF-1.6 % endobj 17 0 obj 2 0 obj Advantages and Disadvantages of WSP The advantages of WSP include: The direction from import to export should avoid the prevailing local wind direction throughout the year to prevent odor pollution . During anaerobic digestion, biogas is produced which could be collected by covering the anaerobic pond with a floating plastic membrane (PENA VARON 2004;WAFLER 2008). For strong wastes (common in developing countries, as water consumption is low), the facultative pond is usually the biggest of all. This document provides information and instructions on waste stabilisation ponds. The two lagoons are operated in series and cover approximately 26 acres. 0000001862 00000 n 3m away from the pond surface . The wind has an important effect on the behavior of facultative ponds, as it induces vertical mixing of the pond liquid. endobj ALABASTER, G.P. ^ZJw\xw@y9/#}m]Y"}. Further, the ponds can be combined with aquaculture to locally produce animal feed (e.g. hQk0=n/&DP|C1&p6jo$b=t/~) n2\^?t Waste Stabilization Ponds (WSPs) are commonly used for sewage treatment. Ideally, several aerobic ponds can be built in series to provide a high level of pathogen removal. Some further information on the physical design is given in ARTHUR (1983) and the international Water and Sanitation Centre(2004). endobj 12 0 obj 6 0 obj stream Case Study on the fishponds in sewage-fed lagoons in Kolkata. The anaerobic pond must be de-sludged approximately once every 2 to 5 years, when the accumulated solids reach one third of the pond volume. x[:4iMH8y'8`"mPIB?/=}~#2,X0@1M?#_73?|qwfTf?i$"1l}8 p\@TeK,O#yFd(rg?dbi'p?,>,Pz|= ? Both have to deal with aeration of the water being treated, but in ponds, oxygen is transferred directly into the water across the surface area without the need for any equipment. A Century-old Innovation of Farmers. endobj 10 0 obj Wastewater stabilization ponds: Principles of planning and practice. Advantages Disadvantages 5) A pond with DO distributed throughout is a _____ pond. EMERY, R. WSP are also recommended for the treatment in order to reuse the effluent in agriculture and aquaculture, because of its effectiveness in removing nematodes (worms) and helminth eggs (WHO 2006, Volume II), while preserving some nutrients. ADVANTAGES AND DISADVANTAGES Some advantages and disadvantages of TFs are listed below. Perspectives are different frameworks from which to explore the knowledge around sustainable sanitation and water management. endobj 0000001643 00000 n A sample design exercise and some technical drawings and sketches are also given.