mechanically or manually removed for disposal or further treatment and reuse. andreuse. treatment mechanically ormanually removed for disposal orfurther beds of drying where these it remains until desired moisturethe content is achieved. It is subsequently A FS treatment plant consists beds (FSTP) of in drying several one location. Sludge is deposited on each TREATMENT PRINCIPLE 7.2 andodourpotential. footprint relatively large the and low against cost beconsidered needsto on the intended enduse option. When or considering the installation of a drying bed, manually the ease of operation bed the from removeddepending required be may reduction pathogen is and stabilisation for processing sludge mechanically.Further the dryness, desired the reaching (Tilley After discharge 2014). to prior al., et treated and collected be to needs which leachate), (or liquid a volume as sludge off the drains of 50-80% approximately of fraction variable a characteristics, (FS) sludge faecal the on Depending designed. properly are bed the onto sludge the depositing for points inlet the and selected well is rate loading sludge the provided straightforward, fairly is bed drying the of operation the as well as design The air. the to sludge the of surface the from water of evaporation and bed, the of bottom to the sand and gravel the of bed liquidis based through on processdrainage in a drying drying 7.1).The (Figure dewatering for surface the onto discharged is Sludge leachate. collect to bottom at the under-drain an with gravel and fisand fishallow with lters are lled beds drying sludge Unplanted 7.1 INTRODUCTION Le • Be able to design an unplanted drying bed to achieve the desired treatment objectives. treatment desired the achieve bedto designanunplanted Beableto drying • the for necessary monitoring maintenance and operational of level appropriate the Know • characteristics their beds, drying unplanted of components main the of overview an Have • bedfor dewatering. sludge ofanunplanted drying Have anunderstanding • arning Objectives operation of unplanted drying beds. ofunplanted drying operation beds. ofthe performance onthe effect and their Unplanted Drying Beds Unplanted Drying Pierre-Henri Dodane andMariska RonteltapPierre-Henri Chapter 7 141

Technology Technology • Rainfall: in locations where rainfall is frequent and occurs for long periods of time intense, a drying drying a intense, time of for periods long occurs frequentand is rainfall where locations in Rainfall: high • and humidity low relatively with combination in also temperatures, higher Temperature: • process; drying the to ofevaporation contribution the highhumidityreduces Humidity: • following: bedsincludethe ofunplanted drying operation the affecting factors Climate Climate factors 7.3.1 following sections. discussedinthe aspectsare these All surface. bed total the layer,and sludge the of into thickness the drying rate, loading sludge sludge the include process the taken on impact an have be that parameters key to Other treated. be need to sludge of type that the and factors influencing several factors climate under grouped be can are and location, to location from vary there aspects These consideration. bed, drying a designing When SLUDGE DRYING UNPLANTED BEDDESIGNPARAMETERS 7.3 inChapter 8. is explained which loss, sludge water to thickened contributes also preliminary evapotranspiration beds with drying sludge 2011). planted (Badji, study In a in observed was leachate no example, more For has water. that sludge bound with percolation less and evaporation more is there but water, signifi free a of with cant amount sludge for typical is range This FS. with beds drying in evaporation to due 50% to Heinss weeks. to days of period a over place takes typically process this and fraction water bound water the removes evaporation, free of volumes large contains that sludge (Section 3.2), and is relatively signifi with fast, ranging from hours to days (Heinss is cant process This gravel. and sand The fiprocess is based on two The principles. drying through leachate is percolation of the principle rst Schematic overview ofanunplanted bed(Tilley sludge drying 7.1 Figure 142 which depends on the phaseofdrying. dependsonthe which of intensity the sludge, the rewet may will Rainfall roof. a with them covering by or period, that in beds the using not by for accommodated be can seasons rainy Pronounced feasible. be not may bed removed viaevaporation; amountofwater total wind, willenhancethe 80 cm drainage layer but isanessential 7.5). element (Section . (1998) reported removal of 50 to 80% by volume due to drainage, and 20 and drainage, to due volume by 80% to 50 of removal (1998)reported al. et drainage water outlet et al. et et al., et 1998). The second process, , 2014).Asplash plate isnotvisible , totreatment iue72 Freshly dewatered loadedandpartially sludge bedsat Niayes faecal onunplanted drying sludge faecal Figure 7.2 ., 2007; Cofi al.,2007; et al ., 2006). e et of type this (Koné dewaterability mix the enhance to sludge) tank septic to (e.g. sludge stabilised older,more is with sludge alternative An sludge. toilet public fresh with obtain diffi to liquid is solid cult properseparation a Generally sludge. stable more to comparable some – results drying in variation Pescod (1971) out fresh with experiments pit carried sludge latrine on beds drying and a obtained wide beds. for drying may not beappropriate specifi sludge higher c a has it Because will be less removed,time water maya longer sludge be drying required, or it for dewatering resistance 2). Chapter also (see settled not have particles digested: not a typically is at toilets public from Sludge or rate. loading sludge higher layera at or sludge rate loading solids total higher thicker a in applied be can therefore It dewatering. for resistance specifi sludge c lower a contain to considered is it words, other In FS. fresh than dewatered readily more hence is and sludge has less bound water beds . Septic tank when using drying sludge is important of the The origin Type7.3.2 sludge offaecal surface area of 25 m 25 of area surface aum rcs ihn h ct o Kms ad rnpre t te rjc st. f h 50 ³d of m³/d 500 the Of site. m 1.5 project produced, the FS to transported and Kumasi of city the within trucks by vacuum public-toilets) unsewered and latrines pit tanks, (septic systems sanitation onsite from is FS collected November. early to mid-September from one minor a and July early to February late from one major a seasons, rainy two with wet sub-equatorially is climate The Ghana. Kumasi, for designed was bed drying sludge small a 5.1) Study (Case plant pilot co-composting a for sludge pre-dry to order In from(Adapted Cofie andKoné, 2009). Case Study bedinKumasi, Ghana 7.1:Designing asludge drying characteristics that were taken into account for the design are listed inTable listed designare 7.1. accountfor into the were taken that characteristics and details technical The sizes. particle and fi thickness gravel-sand different a of of layers material lter treatment plant, Dakar, (photo: Senegal Linda Strande). 3 2 /day is treated in the pilot plant. Two unplanted drying beds were built with a with built were beds drying unplanted Two plant. pilot the in treated is /day each (to hold 15 m³ excreta with a depth of 30 cm). They consisted of different different of consisted They cm). 30 of depth a with 15excreta hold m³ (to each 143

Technology Technology 144 al . Technical recommended andcharacteristics details for sludge faecal dewatering beds indrying Table 7.1 co-composting 5.1). (CaseStudy the into beds once 10it can be removed by to spade (after drying FS is removed days) fromand stored prior the discharged and tank storage leachate a in before fi BuobaiFSTP pondofthe stabilisation facultative anearby into stream. Thedried collected nal discharge is beds drying the from leachate The was beds drying the for design determined: following the 7.1 Table in presented details technical the on Based 1:2 Ratio ofpublictoiletsludgetoseptage= month =1.5m³/d Volume ofFS treated:15m³/cycle=45m³/ 3 dewateringcycles/month 3 FS truckloads/cycle(1carries~5m³) the gravel base Sand thoroughly washedpriortoapplicationonto Sand easilyavailable locally donotcrumble Sand particles Sludge with≤30%shareofpublictoiletsludge public toilet) stabilised(septageormixtureofseptage and Partly 100-200 kg TS/m 25 –30cmsludgelayer onbeds 0.08 m solids) Untreated sludgecharacteristics: 2 /cap Sand characteristics: Sizing ofthebeds: 2 /year (TS standsfortotal month Dried sludgeproduced: 1.5m³/cycle=4.5m³/ 90% FS through volume dewateringassumed: reduction beds:50m² ofsludgedrying Surface beds:30cm/cycle Hydraulic loadondrying oxygen demand), 100%HE(helminth eggs) 97% SS(suspendedsolids),90%COD (chemical Leachate treatment toohighforirrigation Salinity fairlycomparabletotropical wastewater Quality biosolids priortouseinagricultureas Hygienisation necessary 0.1 m³perfreshFS channel, andsplashplates Reduce pressurefl chamber,ow viasplitting inlet Drying bedremoval effiDrying ciency: Production offiProduction lter layers: Dried sludgeproduction: Leachate: which typically vary between 100 and 200 kg TS/m kg 200 and 100 between vary typically which rates loading sludge of range a indicate to possible is it However, greatly. vary conditions local the as estimate, an be only can depth loading and area surface bed rate, loading sludge a to dried be to sludge TS/m CofiTS/m kg 300 rate. to up of e rate loading a at loading sludge applied example sludge higher even an achieve to cases conditions some in Optimal possible be It FS. may sludge. stabilised fresh and precipitation, of of amount low proportion a temperature, large high humidity, low a a comprise and/or rainfall, of periods low humidity, long high entail temperature, conditions Poor 1990). (Duchêne, Europe in climates temperate in used one m one layer to allow for the increased volumelayer increased ofliquid. allow to for the sludge of cm 30 to 20 planned the than higher be to need walls the tanks, settling to opposed as truck a from discharged sludge receive beds the If cm. 20 than greater much be will drained-off is water the different accommodate to loadings. enough For example, high if a layer are of 20 beds cm is applied drying with a water content of the 90%, the initial of height before sidewalls the that important also is It the prolonged cm 10 only of layer timeby 100%. 50to drying sludge necessary the in increase an that found (1971) Pescod conditions, weather same the under dried sludge particular any For year. per used be can bed the times of number the in reduction a and time, drying increased an in result will however,this bed; one to applied be can depth, in cm 30 to sludge more as layer sludge 20 thicker a apply to of option better a seem maylayer It cm. 20 for a preference a with in applied typically is sludge that shows literature the of review A ofthesludgeThickness layer 7.3.4 pilot-scale experiments. through bedetermined conditionsneedto Optimal localoperating m TS/ kg in expressed is (SLR) rate loading sludge The Sludge loading rate 7.3.3 iue73 Proposed lay-out for sludge afaecal treatment plantwith unplantedThebedsare beds. sludge drying Figure 7.3 300 kg TS/m kg 300 odtos n 20 o otml odtos wie prxmtl 5 k SS/m kg 50 approximately while conditions, optimal for 200 and conditions 2 2 /year was estimated to be an effective rate for a FS with 5 g in TS/L the same climatic conditions. of bed in one year. Pescod (1971) states that any general number linking the total amount of amount total the linking number general any that states (1971) Pescod year. one in bed of wetlands (HPCIDBC, 2011). laid outinacircular design with oneinlet. Theleachate isto betreated inhorizontal flow constructed 2 /year to be effective for dewatering thickened FS with 60 g TS/L, while about 150 kg 150kg about while TS/L, g 60 with FS thickened dewatering for effective be to /year 1 3 2 4 4 Horizontalflowconstructedwetland 3 Sludgedryingbeds 2 Rampfortruck 1 Existingcommercial wastewater treatmentsystem 2 2 /year in tropical climates, with 100 for poorer poorer for 100 with climates, tropical in /year /year. It represents the mass of solids dried on dried solids of mass the /year.represents It 2 /year. Badji (2011)/year.Badji of SLR a found also 2 ya i commonly is /year . (2006) for (2006) al. et 145

Technology Technology example calculations are givenexample calculations are inSection7.7. including one day for loading and two days for one removal, bed can be filled 26 times per year. Further period, drying week two a indicate tests drying these from results the example for If removed. readily be can that sludge a obtain to least at or sludge, the of content solids total desired a obtain to order in fi The daysrequired conditions. of number the determine to be will tests drying conducting in stage rst local under tests drying preliminary from or experience from either knowledge local obtain to needs interdependency of In factors. the order to provide a bed drying suitable design, designing the engineer applicable to all cases. However, they do provide as examples of taken acceptable ranges, and an be indication cannot of the therefore and climate and type sludge on based context local the for research local through determined were section this fiin and provided calculations gures the that noted be must It ofdesign parameters Summary 7.3.6 7.3). as43m one inlet per two calculated bedis beds(Figure with drying sludge ofthe Thearea circles, two in arranged beds, the of line-up circular a (2011)designed HPCIDBC valley, Kathmandu m 25 of beds two adequate for factor safety treatment the FS, with variable or poor operation, increases but also increases capital costs.beds Cofiof e number increased An rain. of frequency or removal, sludge of frequency example for conditions, operating actual the on based beds of number the adapt to important also is It thickness. layer sludge optimal the considering decreased or increased be then can beds of number The required. is 10beds of minimum a week, per days 5 arriving FS and duration drying of weeks two for instance, For rate. loading sludge allowable the and layerthickness sludge the time, of unit per plant the at arriving sludge of amount the on depends required beds of number The Number ofbeds 7.3.5 Loading ofthebedsat Niayes sludge faecal treatment plant, Dakar, (photo: Senegal Linda Strande). Figure 7.4 146 total of 28 beds and a loading rate of 250 kg TS/m of250kg of28bedsandaloading rate total 2 , with a loading rate of 7.5of m rate loading a with , 3 of sludge per bed at a loading depth of 30 cm. For the the For cm. 30 of depth loading a at bed per sludge of 2 /year . et al. et (2006) utilised 2 with a with 7.4.1 Gravel andsand 7.4.1 qualityto the required for reclamation or for receiving bodies water (see Chapter 10 details). for further it needs to be before and treated environment,it nutrients, can be to the discharged according material, can leachate the that is leachate treatment. high As in the suspended point discharging solids, or organic further to the drain such installed is is system drainage the where towards downwards the slopes of bottom bed 7.1, the Figure in shown was As bottom. sealed a with soil, the from excavated shape rectangular a typically is bed drying The drying. after sludge the of disposal or important use proper is for allow This to bed. the entering from sludge the in present trash and rubble keep to essential are fi sand layer very wouldthe plate, the be destroyed during inlet Bar at screens the loading operation. rst layer and to allow even of distribution sludge the (Tilley sand the of erosion prevent to used be must plate splash A beds. drying the into pumped being before sludge. Alternatively, a holding or settling can tank be into installed which sludge the is fi rst discharged (Cofibeds the between sludge e the divide to splitter a with beds, two for inlet one creating confias such various exist case, gurations this In beds. the onto trucks from directly loaded be can Sludge tanks. settling-thickening potentially and sludge, the of drying continued and storage for beds the of outside area designated a system, drainage bed A treatment drying consistsfacility of beds an the with inlet and an outlet, a leachate collection and SLUDGE CONSTRUCTION DRYING OFANUNPLANTED BED 7.4 of 8 dewatering cycles over 10 months due to clogging in a pilot scale implementation. For a full scale full a For implementation. scale pilot a in clogging to due 10overmonths cycles dewatering 8 of Coficlog. to likely more e is sand diameter larger fibed a particles, larger with sand on with lled faster up builds matter organic As sand. the on build-up to starts bed the and matter organic Kuffour clog. of build-up a is there when replaced be to needs also sand The sequences (Badji,2008). 25drying 5cmislost after inDakar FSTP Cambérène the Duchène replaced (1990) a reported loss of a few be centimetres of sand for each 5-10 sequences, to drying whereas at removed be need therefore will will and sand sludge the the when the sludge is to removed. It is bound that therefore recommended that the sand is that is chosen is note sand easily obtained. the to of amount important certain is a as occasionally, it bed, the for sand selecting When al.,2009). et 0.5 mm)isused(Kuffour organic of accumulation of matter, clogging, is risk increasing This thereby the reduced risk if sand a with smaller fast diameter (0.1- relatively the in result can mm) (1.0-1.5 diameter larger a with sand as crucial is sand the of diameter The gravel. the of spaces pore clogging, the in lodging prevents from sludge and the keeps it as drainage enhances layer sand The gravel. the of top on placed is layer sand A canalsobeusedaccordingwhatislocallyfor to example available, 2-6mm. small gravel mm of layer third 10a layers, a gravel the into layer sand with the from particles of gravel migration of Tothe diameter.avoid cm 10 underneath layer supporting cm 15 a in applied mm 19 of diameter Cofiexample, For e design. infl the an on have uence also will materials available Locally 5-15mm. example forlayer, sand upper the and gravel coarse the between fi diameter layercontains a with intermediate the gravel and ner mm 20-40 around of diameter a with gravel coarser contains usually layer lower The drain. the into avoiding washing on particles based small is from clogging layers the in size diameter of distribution 7.1).The (Figure gravel of different diameters two with layers three or two typically are there sand. and support of a additions as function layers supplemental gravel further The for and construction, initial the for both important is This fifrom bed the of clogging prevent to particles. order ne in gravel and sand washed use to essential is it beds, drying constructing When system. drainage the of top on applied are sand and gravel of Layers (2009) observed a link between the rate of clogging and the rate of organic matter matter organic of rate the and clogging of rate the between link a observed (2009) al. et ., 2006), by designing the bed with a ramp for the inlet of the the of inlet the for ramp a with bed the designing by 2006), al., et (2006) had to replace the sand twice in a series series a in twice sand the replace to had (2006) al. et et al., et 2008). This is as crucial, a without splash . (2006) made use of gravel with a with gravel of use made (2006) al. et 147

Technology Technology Nepali conditions). in the sludge, rain water can pass straight through the sludge and drains through the drying bed. drying the through anddrains sludge the through canpassstraight water rain sludge, in the is period prolonged. When the sludge is drying already enough dry to expose the the sand layerand through the cracks again increases sludge the of content moisture the case, this In drained. completely is sludge the of water free the before occurs rainfall if problematic considered is sludge the of Rewetting year, isemployedtreatment endproducts. inorderproduceandconsistent reliable to one to up of periods for controlled more heaps a that however, recommended is It inoccur. can reduction pathogen time stored which during frequently is sludge dried The bed. drying the removed is from it after evaporation by achieved be can this required, is sludge drier a If bed. the access to equipment other or barrows wheel allow to provided be must ramp a sludge, the remove to order In 7.5). (Figure most commonmanualmethod being the a to prolonged drainage leads time. Sludge which is removed rate mechanically or drainage manually, the with shovels lower and wheel the barrows resistance, dewatering sludge the higher The resistance. dewatering sludge the is which of one factors, of number a on specifidepends a type of sludge time c lagoons beds, and and content of drying found at a sludge leastTS with 25% fit for The removal. drying including technologies, treatment and sludge of types different with experiments out carried (1971) In order for the sludge to be removed properly, it needs to be enough dry that it can be shovelled. Pescod Sludge removal 7.4.2 TS/m kg 250 of rate loading sludge a at years three of period exchange (2011)sand HPCIDBC a application, estimated 148 Removing sludge from bedsat Cambérène treatment unplanted drying plant, Dakar, (photo: Senegal Figure 7.5 Linda Strande). 2 /year, a sludge fi lling height of 20 cm and a one week drying period (applicable to to (applicable period drying week one a and cm 20 fiof sludge height a lling /year, and either remain in the sludge or are present in the leachate. leachate. inthe present orare sludge inthe remain and either mind, in not FS are removedremoval may in the present occur. anyTherefore, pollutants some biodegradation although pathogen or stabilisation with designed not therefore are beds Drying solids. and liquid between separation physical a i.e. dewatering; achieve to is bed drying a of purpose main The SLUDGE OFDRIED ANDLEACHATE QUALITY 7.5 340 kg TS/m kg 340 beds and later collected by collected publicworks companiesbeds andlater for soilenrichment. As presented in Case Study 6.2, the Cambérène FSTP is a combination of settling/thickening tanks tanks and unplantedbeds. beds The drying were drying settling/thickening designed based on a 200 kg TS/m of combination a is FSTP Cambérène the 6.2, Study Case in presented As Case Study sludge treatment 7.2:Cambérène faecal plant(continuedfrom Case Study 6.2) deep dried sludge layer from a 130 m 130 a from layer sludge dried deep The COD/L). mg removingfor daystwo worker about One shovel.needs by manually removed 7 cmthe is 3,600 sludge dried SS/L, mg 1,900 TS/L, mg (2,500 concentrated highly still is leachate The beds, sludge Unplanted removal drying andaccumulation at Cambérène treatment plant, Figure 7.6 FSTP produces about 600 m 600 about produces FSTP removal, each of the 10 beds of 130 m 130 of beds 10 the of each removal, sludge dried the organising for more week one takes operator the As sludge. the layerof deeper the in dry The season. rainy matter content reaches the about 50%, which is an during average, with a layerdrier even on top and drying, 20-30% matter dry days 30-35 to corresponds this Dakar, of conditions climatic the In anymore. layer sand the to sticking not is sludge the when i.e. spade, a with removed easily be can it suffiwhen sludge dried the ciently considers operator The layer. sludge deep cm 20 a 2 Dakar, (photos: Senegal Pierre-Henri Dodane). .year. As a consequence, the operator usually uses only 6-7 beds instead of the 10 usually usesonly ofthe 6-7bedsinstead operator beds. .year. Asaconsequence, the 3 /year of dried sludge. The dried sludge is fi rst stored behind the drying drying fithe is behind sludge stored rst dried The sludge. dried of /year 2 bed. The dried sludge density is about 300 kg/m 300 about is density sludge dried The bed. 2 takes 40 day cycles. This leads to an effective loading rate of rate loading effective an to leads This cycles. day 40 takes 2 /year loading and 3 . Cambérène Cambérène . 149

Technology Technology inactivate all helminth eggs, all and helminth count inactivate a of total up to 38 beds notalone was suffi drying on the at least was content 20%. Dewatering TS until the to dry cient to storage time or other treatment options for increased pathogen reduction. reduction. options treatment for pathogen increased timeorother storage (Koné viable were 25–50% which of dewatering, al . Prevalence andTrichuris public toilet eggsinKumasi’s sludge ofAscaris andfaecal (Koné Table7.3 /m between196 321rate and loading TS a at beds kg drying unplanted sludge to ratios different in applied was 7.3. Sludge Table in presented are sludge tank septic and sludge toilet public Koné inChapter 10. enduseasdescribed 2002),orrecovered for anappropriate Strauss, and Montangero - 5 Chapter (see ponds in example for stream, waste liquid concentrated a as treated and collected be should leachate the bodies, water fi receiving far for the to standards according or use nal still Hence, was mg/L. 870 of leachate concentration BOD the a example day,for with last disposal for safe the environmentally from on lower were concentrations measured the (Table Although parameters 7.2).of variety a fifor of day ltration last the fiand the rst on leachate the analysed and Koné Analyses ofleachate from bedsinKumasi, Ghana(from sludge drying Koné et al.,2007) Table 7.2 150 b a Numberofeggs/g TS Percentage (%)ofviableeggs inparentheses pH Sample 1 Public toiletsludge EC (µS/cm) TKN (mg/L) Sample 2 SS (mg/L) NO Sample 3 Septic tanksludge COD (mg/L) Sample 4 BOD (mg/L) Sample 5 NH 3 3 -N (mg/L) - 20) lo nlsd S rm rig es o Acrs n Tihrs gs Te eut of results The eggs. Trichuris and Ascaris for beds druing from FS analysed also (2007) al. et (2007) carried out experiments with mixtures of septic tank and public toilet sludge, sludge, toilet public and tank septic of mixtures with experiments out carried (2007) al. et -N (mg/L) Ascaris 13 94 29 3 a (38%) (23%) (53%) (37%) First day 21,900 5,600 1,350 b 520 590 600 8.2 50 , 2007). This illustrates the need for additional for need the illustrates This 2007). al., et Trichuris and Ascaris 24 15 2 9 2 (13%) (52%) (0%) (58%) (25%) 11,400 Last day 3,600 eggs recovered was after Trichuris 170 260 370 290 870 7.9 118 16 44 Total 9 5 2 /year, and left /year,left and (34%) (52%) (13%) (54%) (32%) Difference et al. et -10,500 -2,000 -260 -220 -310 -480 , 2007) -0.3 120 Equation 7.2: M=30 comesto: situation,this described per year. the For Since the plant will be built in a region with desirable climate conditions (Section 7.4.1), a sludge sludge a 7.4.1), (Section conditions climate desirable with loading rate of region 200 kg TS/m a in built be will plant the Since a sludge loading height of 0.20 m and a loading rate of 50 m 50 of rate loading a and m 0.20 of height loading sludge a required to treat 1,950 treat to required m in sludge quantityin sludge andquality. changes anticipated and potential investment the on depends added be can that beds extra of number FS; the but is also essential to enable maintenance to necessary plant, the such as sand replacement. The extra beds is not only recommended for increased fl exibility in case of changes in quality and quantity of few a Adding sludge. incoming the treat and receive to plant 10this forof minimum required a is beds fibe fi considerations, the twoweeks, these on Based After again. twoweeks. used in be lled can bed rst plant at a load of 50 m the at arriving TS/L g 30 of concentration a with sludge for designed being is plant a example, this In sludge undergoodExample climate 2:Design conditions for settled 7.6.2 TS/m kg 50 of density day,a per at solids total of kg calculations made in Section 7.4An example of the section. A plant is is providedreceive to 500 in this perbedataloading depthof20cm) weeks time (two Example 1:Known drying 7.6.1 This sectionprovides beds. two for examples ondesignrequirements unplanted drying DESIGNEXAMPLE 7.6 the use of wedge wire, mixing and coagulants. These are discussed in the following sections. discussedinthe useofwedgemixingandcoagulants.Theseare wire, the loss. sand reduce and rates greenhouses, in drying drying systems, piping of installation the include increase investigated been have that Aspects to order modifi in be ed potentially could beds Drying INNOVATIONS ANDADAPTATIONS INSLUDGE DRYING BEDS 7.7 Equation 7.1: M=c from equation receivedThe annualmassofsludge canbecalculated 7.1: definition of climate conditions). The plant receives sludge only on weekdays, for 52 year.of weeks the be available. Assuming that one bed can accommodate 250 m 250 accommodate can bed one that Assuming available. be In which M is the sludge load in kg TS per year, c sludge load TS in kg In which M is the a drying bed with an area of 390,000 (kg TS/year) / 200 kg (TS/m kg 200 / TS/year) (kg 390,000 of area an with bed drying a 2,500 m 2,500 is duration twodrying the weeks. Hence, 10 beds are will be needed. thus beds The surface total drying sludge. To robust,easier and more and maintenance it that could be recommended operation make the these beds, With duration the drying will be one week, with one day left for the operator to remove the at plant the in arriving g Q TS/L, day, one bed of 67 m drying cycle and can therefore be used 26 times per year. At a loading rate of 500 kg TS/day or 10or m TS/day kg 500 of rate year.loading per a times At 26 used be therefore can cycleand drying full a for weeks two needs sludge of fitype for this receiving bed one excavation, for daystwo and lling day fione desired Including content. the solid reach 11 to total daystakes nal sludge of type this of cm consecutive beds with a20cmlayer.consecutive bedswith 2 , and the effective sludge loading rate is 160 kg TS / m / 160TS is kg rate loading sludge effective the and , 2 is filled each day.only on arrive week Assuming trucks days,the that 10 beds will 3 /day in a setting with good climate conditions (see section 7.3.1 for a divison and i

2 . Q . . 50 2 i /year can be applied. Therefore, taking the yearly sludge load into account,

. t . 5 i is flthe ow in m . 52 = 390,000 kg TS/year. 52=390,000kg i i 3 is the average total solids concentration in the sludge in the solids concentration total average is the per day,delivery and t is number the of days delivery 3 . Based on preliminary tests it was found that 15 that found was it tests preliminary on Based . 3 /day, a capacity of 250 m 250 of capacity /day,a 2 /day, a minimum of 8 drying beds are are beds drying 8 of minimum /day,a 2 /year. Sludge is applied once a day to to day a once applied is /year. Sludge 2 /year) = 1,950= m /year) 2 is required. For For required. is 2 /day needs to to needs /day 151 3 /

Technology Technology not yet beenreported. has drying FS for effectiveness its sludge wastewater of drying the for effective is this Whilst 2002). (Tchobanoglous removal upon sludge the with partitions that sand of amount the reduce to or and drainage, to enhance option sludge drying steel wedge is wire to as use a stainless surface A further Wedge7.7.3 wire 7.6). project (www.sandec.ch/fame;FaME Figure 2013). Various researchers are currently working on adapting lower cost options for FS, for example the often US, the in sludge combined an with wastewater active mixing device and blowers to forprocessenhance drying the (Huber Technology,applied actively technology a also is greenhouses in bed. Drying the from away air saturated water the of transport the facilitate to order in passively, or actively either ventilated, well be to needs beds the of involvingcovering system any that note to important is It reported. was 25-35% of time drying the in reduction A industry. pharmaceutical the from sludge Bux 7.7.2 Greenhouses al.,2012) heat(Dieneret waste ofindustrial recovery with also beachieved modifi interesting could an This bed. offer does it drying but expensive, more standard be the of cation most be would modifisuffiis system would there system where of and This type space This light. limited sun ed cient with areas moisture.for suitable 8% achieve to dried further was sludge the period 18day an After drying. of 10days only after achieved be could result same the 70°C, to heated water modifi this on using dried bed when 18ed but of days, period a over moisture 33% to 96% from dried bed standard a on treated sludge wastewater that found was It process. drying the enhance to order in bed drying bed drying sludge the sludge through it circulating to prior wastewater water up heat to a used was heating solar whereby of modification the investigated (2011) Al-Zboon and Radaidah Piping systems 7.7.1 152 Pilotresearch scale at Cambérène treatment facility plant, Dakar, Senegal. Evaluating rates of Figure 7.6 (2002) experimented with covering beds with glass panels in order to enhance the drying of drying the enhance to order in panels glass with beds covering with experimented (2002) al. et dewatering with passive andactive ventilation with greenhouses (photo: Linda Strande). et al., et Pescod, M. B. (1971). Sludge handling and disposal in tropical developing countries. Journal of Water Pollution and Pollution Water of Journal countries. developing tropical in disposal and handling (1971). Sludge B. M. Pescod, SANDEC/EAWAG Management, Sludge M.(2002).Faecal Strauss, A., Montangero, Notes. Lecture CofiD., Koné,Awuah, M., R., Anyemedu,Strauss, E., F.O.K., A. Kuffour, particle different using of Effect (2009). E. e, inactivation eggs Helminth (2007). M. Cofi D., Koné, Strauss, S., Drescher, D., Moser, K., Gallizzi, C., Zurbrügg, O., e, Huber Technology (2013). Huber Solar Active SRT Dryer (PDF). Website www.huber-technology.com, accessed May M. Strauss, (1998). Heinss S.A., U., Larmie Solids and Separation Pond Systems for Treatment of the PoweredFaecal Sludges in High Valley, Kathmandu the in Management Sludge Faecal for Strategy and Status (2011). HPCIDBC collectivités. petites des d’épuration stations des boues des traitement de systèmes Les (1990). P. Duchène, Diener, S., Reiser, J.C., Murray, Mbéguéré, M., A., Strande, L. (2012). Recovery of industrial waste heat for faecal sludge organic & sludge faecal of Co-composting projects: sanitation sustainable of study Case (2009). CofiD. Koné, O., e, using sludge faecal of liquidseparation Solid- (2006). CofiA. Montangero, H., Esseku, M., Strauss, S., Agbottah, O., e, Bux, M., Baumann, R., Quadt, S., Pinnekamp, J., Mühlbauer, W. (2002). Volume reduction and biological stabilization la affectant éléments : vidange de boues des Traitement (2011), D., Kone M., Mbéguéré, P.H., Dodane K., Badji Badji, K., 2008. des Traitement boues de vidange : éléments la des affectant performance lits de séchage non plantés en 7.9 REFERENCES overcoming problems. and understanding in assist to and operation, and design their on guidelines clear provide to order in required is research detailed more exists, treatment FS for beds knowledge drying sludge some unplanted of use while the on that concluded be can it chapter, this in provided information the on Based 7.8 CONCLUSIONS project. FaME ofthe aspart isalsobeingconducted treatment FS for coagulants on Research season. dry the during sludge the significonditioning in advantage cant no was there as season, wet the during out carried be only should alum with conditioning that found alum where Thailand Bangkok, in Luong This study of drying. rate FS in order added to increase the to the byaluminium was sulphate) (potassium conducted study a to reference makes (1971) Pescod Additives to7.7.4 thesludge to drying enhance Control Federation 43(4),p.555-570. Control Federation sizes ofsandasfi Desalination248, sludge. faecal p.308-314. mediafor dewatering lter p. 41(19), Research Water4397-4402. climates. tropical in co-composting and dewatering sludge faecal effi by ciency 21, 2013. No.5/98 SecondEdition,EAWAG/SANDEC, Report SANDEC Tropics. the Switzerland. Duebendorf Nepal. BagmatiCivilization,Kathmandu, Developmentofthe for Integrated Committee from www.fndae.fr/archive/PDF/fndae09-a.pdf. 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Technology Technology ily E, üh, . Mrl A, ubüg C, cetneb R (04. opnim f aiain ytm and Systems Sanitation of Compendium (2014). R. Schertenleib, C., Zurbrügg, A., Morel, C., Lüthi, E., Tilley, / edition 4th Reuse, and Treatment Engineering: Wastewater (2002). H.D. Stensel, F.L., Burton, Tchobanoglous,G., Strauss, M., Montangero, A. (2002). FS Management – Review of Practices, Problems and Initiatives. DFID Engineering intensive using by beds drying effisand conventionalthe (2011).of Increase K. ciency K. Al-Zboon, A., J. Radaidah, 154 4. Describe what types of treatment objectives can be met with unplanted drying beds. unplanted drying objectives whattypesoftreatment canbemet with Describe 4. unplanted designing when consideration into taken be to need that factors critical four List 3. Name two keyof sludge unplanted mechanisms beds with for uPDBs. drying dewatering the 2. of fundamentals basic the and beds, drying unplanted of components main the Describe 1. End ofChapter Study Questions drying beds. drying operation. their Switzerland. edition.Available 2ndrevised from www. sandec.ch. Technologyand Science Aquatic of Institute Technologies.(EAWAG) Federal Swiss Dübendorf, WSSCC. and andComputer ScienceBooks. Engineering McGraw-Hill revised. Kingdom,73p. United GHK,the to report Knowledge Project andResearch -R8056.Consultancy science andtechnology. IPCBEEvol. 6,IACSIT Singapore. Press, environmental on 2011 conference the at International 2nd Presented Jordan. from study case a energy: solar