Unplanted Sludge Drying Beds

  Drying Beds

  Publ i shed on SSWM ( ht t p: / / www.sswm.i nfo )

  Co m p ile d b y : D o r o t h e e Sp u h le r ( s e e c o n in t e r n a t io n a l g m b h )

Dry in g bed s a re eith er p la n ted or u n p la n ted sea led sh a llow p on d s filled w ith sev era l d ra in a g e la y ers

a n d d esig n ed for th e sepa ra tion of th e solid from th e liq u id fra ction of (fa eca l) slu d g e from la trin es,

sep tic ta n k s, biog a s rea ctors, trick lin g filters, etc. Slu d g e is d ried n a tu ra lly by a com bin a tion of

p ercola tion a n d ev a p ora tion . W h en p la n ts a re p resen t, ev a p ora tion is en h a n ced by tra n sp ira tion

(ev a p otra n sp ira tion ). Th e p ercola te still con ta in s p a th og en s a n d n eed s to be collected for trea tm en t or

con trolled reu se. After trea tm en t in p la n ted d ry in g bed s (h u m ifica tion bed s), th e d ried slu d g e, a

n u trien t-rich soil am en d m en t, ca n be d irectly u sed in a g ricu ltu re. If u n p la n ted slu d ge d ry in g bed s are

u sed , a d d ition a l trea tm en t by com p ostin g m a y be foreseen . Un p la n ted d ry in g bed s n eed to be

d eslu d g ed before fresh slu d g e is a p p lied , w h ile h u m ifica tion bed s ca n be filled u p in term itten tly

req u irin g d eslu d g in g on ly on ce ev er 5 to 10 y ea rs. Dry in g bed s a re rela tiv ely ea sy to con stru ct a n d

sim p le to m a in ta in , a lth ou g h la rg e su rfa ce a rea s a n d m a n - or m ech a n ica l p ow er is req u ired for

reg u la r d eslu d g in g .

  In Out

  Faecal Compost (for furt her off-si t e compost i ng), Soi l , Tr eat ed Wat er, Fer t i gat i on Wat er or Wat er Sl udge r equi er i ng fur t her t r eat ment

  Al l or gani c degradat i on pr ocesses produce sl udge (SASSE & BORDA 1998). Sl udges fr om wast ewat er col l ect i on or t reat ment uni t s are of var i abl e consi st ency (f rom sept i c t anks , smal l and l ar ge scal e anaer obi c di gest er s ,

  

anaerobi c di gest er s for organi c wast e , anaerobi c baffl ed r eact ors , wast ewat er st abi l i sat i on pond syst ems , et c.).

  General l y, t hey do not have a hi gher sol i ds cont ent t han 2 t o 10 % and can t her efore not be t ransport ed easi l y wi t h si mpl e equi pment . Apar t fr om t hi s, sl udge i s cont ami nat ed and occupi es l ar ge vol umes f or st or age (SASSE & BORDA 1998). Ther ef or e i t i s bet t er t o dr y or dewat er sl udge before fur t her use or dumpi ng. Sl udge dr yi ng beds ar e one of t he si mpl est and ol dest t echni ques for sl udge dewat er i ng (SANIMAS 2005). They ar e a si mpl e means t o reduce t he vol ume of t he sl udge and pr epar e r euse as fer t i l i ser. Sl udge dryi ng beds ar e basi cal l y i mpermeabl e beds fi l l ed wi t h di ff er ent l ayers of gr avel and sand. Dr ai nage pi pes ar e i ncor por at ed i n t he bot t om of t he beds.

  Indi scr i mi nat e di sposal of f aecal sl udge, Ouagadougou. Sour ce: EAWAG/ SANDEC (2008)

  

Let t uce f ar m f er t i l i sed wi t h saf e compost made out of f aecal sl udge t r eat ed i n dr yi ng beds at Gyenyasi f ar mer s associ at i on i n Kumasi .

Sour ce: ERIKSEN-HAMEL & DANSO (2008)

  Sl udge i s appl i ed i n l ayers on t op of t he gr avel beds and i s nat ur al l y dr i ed. The bed can be ei t her pl ant ed or unpl ant ed. Aft er t reat ment i n pl ant ed dr yi ng beds (humi fi cat i on beds), t he dr i ed sl udge, a nut r i ent -r i ch soi l amendment (or bi osol i d), can be di rect l y used i n agr i cul t ur e. If unpl ant ed sl udge dr yi ng beds ar e used, addi t i onal t r eat ment by compost i ng may be for eseen. Thi s al l ows t o st abi l i se t he sl udge and t o ret ur n nut ri ent s and or gani c mat t er i nt o t he soi l for agr i cul t ur e. The per col at e cont ai ns pat hogens and i s col l ect ed i n t he drai nage pi pes. It can be r eused, but t hen r equi res t r eat ment .

  Unpl ant ed and pl ant ed dr yi ng bed. Sour ce: TILLEY et al . (2008)

  A t r adi t i onal sl udge dr yi ng bed can be used for dewat eri ng and dr yi ng of faecal sl udge and anaerobi c di gest er r esi due. Anaer obi c sani t at i on syst ems (e. g. l at r i nes, sept i c t anks, aqua pr i vi es, anaerobi c baff l ed react or s, bi ogas react or s) pr oduce l ess sl udge t han aer obi c t r eat ment s (e.g. f rom t r i ckl i ng fi l t er s, act i vat ed sl udge) and anaerobi c sl udge al so dr i es bet t er and r esul t s i n fewer odours as i t i s more st abi l i sed. Sl udge i s dewat er ed by per col at i on, whi l e t he sol i d f ract i on r emai ns on t he fi l t er sur face and i s dr i ed by nat ur al evaporat i on. In pl ant ed dryi ng beds, t he pl ant s enhance evaporat i on by t ranspi r at i on. Thi s process i s cal l ed evapot r anspi rat i on.

  In pr i nci pl e t he const r uct i on of unpl ant ed and pl ant ed sl udge dr yi ng beds i s si mi l ar t o gr avel / sand fi l t er s, st ar t i ng wi t h an i mper meabl e shal l ow pond, dr ai nage pi pes i n t he bot t om (perf or at ed PVC pi pes or hol l ow bl ocks), and di ffer ent drai nage l ayer s. The bed f rame i s usual l y made f rom concr et e or a pl ast i c l i ner wi t h t he bot t om sur faces sl i ght l y sl oped i n or der t o faci l i t at e per col at i on and dr ai nage. The l owest l ayer of t he bed consi st s of a dr ai nage st r at um made of coar se gravel . Upper l ayers consi st of di ffer ent sand and gr avel wi t h fi ner grai n si ze at t he t op. For t he sl udge appl i cat i on, a spl ash spat e may be used t o avoi d sput t er i ng.

  U n p la n te d S lu d ge D ryin g Be d s

  Cr osscut of an unpl ant ed dr yi ng bed. Sour ce: STRAUSS & MONTANGERO (2002) Unpl ant ed sl udge dr yi ng beds ar e si mpl e sand and gr avel fi l t ers on whi ch bat ch l oads of sl udge are dewat ered.

  Indi cat i on about t he di amet er of t he medi um and t he hei ght of t he di f ferent gr avel and sand l ayer s var y dependi ng on t he sour ce (SASSE & BORDA 1998; STRAUSS & MONTANGERO 2004). General l y, t he coar se gr avel l ayer (grai n di amet er : 15 t o 50 mm) i s wi t hi n 20 t o 30 cm of hei ght . A gr avel l ayer (di amet er of 7 t o 15 mm) of 10 t o 15 cm fol l ows t hi s l ayer. Thi s l ayer can be fol l owed of a si mi l ar one of sl i ght l y l ower di amet er (see pi ct ure bel ow, STRAUSS & MONTANGERO 2002), but t hi s i s not compul sor y (SASSE 1998). There shoul d be a fi nal sand l ayer of 25 t o 30 cm. As some sand wi l l be l ost each t i me t he sl udge i s manual l y removed, i t may be hi gher (STRAUSS & MONTANGERO 2004; TILLEY et al . 2008).

  

Unpl ant ed dr yi ng beds i n Ghana (l ef t ) and r ai n pr ot ect ed unpl ant ed dr yi ng bed at t he Ar cat a wast ewat er t r eat ment pl ant , USA (r i ght ).

Sour ce: EAWAG/ SANDEC (2008); HUMBOLDT EDU (2008) The sl udge i s appl i ed i n a bat ch mode about once per week i nt er val s i n l ayers of no more t han 20 t o 30 cm.

  About 50 t o 80 % of t he i ni t i al vol ume i s removed by percol at i on (STRAUSS & MONTANGERO 2002), r esul t i ng i n t ot al sol i d (TS) cont ent of 20 t o 70 % (STRAUSS & MONTANGERO 2004) dependi ng on t he l ocal weat her condi t i ons and cl i mat e. In r egi ons wi t h f requent rai nfal l , cont our bounds can pr event surf ace runof f t o ent er t he ponds and cover i ng t he dryi ng beds wi t h a r oof may be consi der ed.

  Dr yi ng i nduces par t i al pat hogen r emoval . However, t he dr i ed sl udge st i l l may cont ai n pat hogens, par t i cul ar l y Hel mi nt h eggs, and shoul d t her efore be handl ed car ef ul l y and r ecei ve fur t her t r eat ment such as compost i ng or prol onged st or age befor e use i n agr i cul t ur e. The percol at e fr om dewat er i ng cont ai ns al so pat hogens, mai nl y bact er i a and vi ruses and has t o be furt her t r eat ed as wel l (STRAUSS et al . 1997). In t he case of fr equent appl i cat i on of sl udge and t o enhance r et ent i on t i mes, t wo or mor e dr yi ng beds can be const r uct ed i n par al l el and used al t ernat el y.

2 On an annual basi s, about 100 t o 200 kg TS/ m can be appl i ed on a dr yi ng bed. Dryi ng t akes 10 t o 20 days. Land

  2

  r equi rement s ar e 0.05 m per capi t a for a 10 days cycl e (STRAUSS & MONTANGERO 2002). Bef or e fr esh sl udge i s appl i ed, dr i ed sl udge needs t o be desl udged and br ought t o a compost i ng si t e, what makes i t a rat her l abor i ous t reat ment opt i on.

  Pla n te d S lu d ge D ryin g Be d ( H u m ifica tio n Be d )

  Cr osscut of a pl ant ed dr yi ng bed. Sour ce: STRAUSS & MONTANGERO (2004) Pi l ot beds of t he VFCW devel oped f or f aecal sl udge dewat er i ng st udy i n sub-Sahar an count r i es. Sour ce: KONE & KENGE (2008)

Pl ant ed sl udge dr yi ng beds, al so desi gnat ed as r eed beds or const r uct ed wet l ands, coul d mi ni mi se t he need f or f r equent r emoval of dr i ed

sl udge as t hey can be oper at ed f or sever al year s bef or e sl udge r emoval becomes necessar y. Sour ce: EAWAG/ SANDEC (2008)

  As for unpl ant ed beds, pl ant ed beds consi st of an i mper meabl e shal l ow pi t f i l l ed wi t h di ffer ent l ayer s of coar se t o f i ne sand. General l y, t her e ar e t hr ee l ayers, st ar t i ng wi t h a l ar ge gr avel l ayer (di amet er of 20mm) of 25 cm hei ght , fol l owed by a fi ne gr avel l ayer wi t h gr anul es of 5 mm i n di amet er (al so 25 cm hei ght ) and fi nal l y cover ed wi t h a sand l ayer of some 10 cm (EAWAG/ SANDEC 2008). Unl i ke unpl ant ed beds, pl ant ed beds do not need desl udgi ng befor e each new appl i cat i on as t he r oot syst em of t he pl ant s mai nt ai ns t he permeabi l i t y. The sl udge i s added i nt er mi t t ent l y once a week and onl y r emoved ever y 5 t o 10 year s (STRAUSS et al . 1997; STRAUSS & MONTANGERO 2002). Once t he sl udge i s r emoved i t i s wel l mi ner al i sed and has a soi l -l i ke st ruct ure wi t h a TS cont ent of 40 t o 70 % (STRAUSS & MONTANGERO 2002). Ther efore, pl ant ed sl udge dr yi ng beds ar e al so cal l ed humi fi cat i on beds. It i s best t o st op appl yi ng sl udge one or t wo year s befor e removi ng i t (whi l e a par al l el bed r ecei ves t he sl udge). In such a way, t he humi fi ed sl udge i s near l y pat hogen fr ee and can be reused di r ect l y as bi osol i d i n agr i cul t ur e. Per col at e qual i t y al so consi der abl y i mproves by t he pr esence of pl ant s but may st i l l r equi r e a pol i shi ng t reat ment (STRAUSS et al . 1997).

2 Pl ant ed beds can r ecei ve about 250 kg TS/ m per year (STRAUSS & MONTANGERO 2002).

  Co s ts Co n s id e ra tio n s

  The i nvest ment cost s of sl udge dryi ng beds are moder at e wher e l and pr i ces ar e l ow and f i l t er mat eri al (gravel / sand) i s l ocal l y avai l abl e (SANIMAS 2005). However, t he pond may needs t o be made i mper meabl e and exper t ski l l s are r equi r ed f or desi gn. Oper at i on cost s ar e l ow as no ener gy or compl i cat ed equi pment i s r equi red. However, desl udgi ng, part i cul ar f or unpl ant ed beds i s l abori ous.

  Costs Moder at e i nvest ment cost s and l ow oper at i on cost s Self-help Compat ibility

  A p p lic a b ilit y

  Requi r es space; odour can occur; (and fr equent desl udgi ng i n t he case of unpl ant ed beds).

  Main weakness

  Reliability Hi gh, i f t he area i s kept dr y (rai n, r unoff). Main strength Low-t ech and no r equi rement of energy.

  Appl i cat i on of sl udge, desl udgi ng, cont r ol of dr ai nage syst em and of t he secondar y t reat ment for percol at e or dr i ed sl udge. Desl udgi ng for unpl ant ed beds ever y one t o several weeks and ever y 5 t o 10 year s for pl ant ed dr yi ng beds.

  O&M

  Can be pr oduced wi t h l ocal l y avai l abl e mat er i al , but r equi res expert desi gn. Operat i on i s si mpl e but st af f/ communi t y shoul d be t r ai ned.

  Depends st r ongl y on t he l ocal cl i mat e (rai n, runof f); TS cont ent of 20 t o 70 % can be achi eved. Some of NH4 i s l ost t o ai r. Pat hogen r emoval i s moderat e f or unpl ant ed beds wi t h shor t ret ent i on t i me, but hi gh for pl ant ed dr yi ng beds wi t h l ong r et ent i on t i mes.

  Op e ra tio n a n d M a in te n a n ce

  Performance

  Requi r es l arge l and-surf aces and can cause odour ; t her ef or e gener al l y i nst al l ed i n r ural areas.

  Capacity/ Adequacy

  Dr yi ng beds are si mpl e seal ed shal l ow ponds fi l l ed wi t h sever al dr ai nage l ayers. Sl udge i s appl i ed on t he t op and dr i ed by per col at i on and evapor at i on. In pl ant ed dryi ng beds, t he pl ant s mai nt ai n t he por osi t y of t he soi l and enhance t he evapor at i on by t ranspi r at i on (evapor at i on). Dr i ed sl udge can be used as bi osol i d i n agr i cul t ur e.

  At a Gla n ce Working Principle

  Fresh sl udge i s gener al l y hi ghl y pat hogeni c and shoul d be handl ed wi t h car e. Al so a cer t ai n di st ance t o t he i nst al l ed beds (especi al l y when sl udge has been recent l y appl i ed) shoul d be r espect ed. Per col at es f rom sl udge dryi ng beds cont ai n al so pat hogens and need t o be fur t her t r eat ed. Sl udge fr om unpl ant ed beds shoul d be compost ed before r euse t o enhance pat hogen r emoval . Dr i ed sl udge fr om pl ant ed dr yi ng beds (i f t her e was no f resh appl i cat i on of sl udge dur i ng t he past 1 t o 2 year s) i s gener al l y fr ee f rom pat hogens and can be used di rect l y (STRAUSS et al . 1997).

  H e a lth As p e cts

  Operat i on and mai nt enance i ncl udes appl i cat i on of sl udge, desl udgi ng, cont r ol of dr ai nage syst em and t he cont r ol of t he secondar y t r eat ment s f or percol at e or dr i ed sl udge. Even t hough expert s are not compul sor y f or t he oper at i on and mai nt enance, a wel l -organi sed communi t y group, whi ch has exper i ence i n or gani c fert i l i ser use and prepar at i on i s r equi r ed (SANIMAS 2005).

  Sl udge dryi ng beds ar e a secondar y t r eat ment for al l ki nds of sl udge, i ncl udi ng faecal sl udge fr om on-si t e sani t at i on syst ems, anaerobi c di gest er s at communi t y or l ar ge-scal e l evel . But l ar ge surf ace areas are r equi r ed and odour i s fr equent . Therefor e, t hey shoul d be const ruct ed f ar away fr om housi ngs. The met hod i s si mpl e but requi r es pr of essi onal desi gn and i nf or med manpower for t he oper at i on. Dr yi ng beds ar e not adapt ed for regi ons wi t h heavy rai nfal l s and fr equent fl oodi ng or where t he wat er t abl e i s hi gh. In any case, t he ponds shoul d be seal ed t o pr event i nfi l t rat i on of t he pat hogen cont ai ni ng per col at e and a count er bound can pr event r un-off t o fl ow i n.

  A d v a n t a g e s

  Dr i ed sl udge can be used as fert i l i ser (ei t her di r ect l y i n t he case of pl ant ed beds or af t er compost i ng i n t he case of unpl ant ed beds) Easy t o oper at e (no expert s, but t rai ned communi t y requi r ed) Hi gh reduct i on of sl udge vol ume Can achi eve pat hogen r emoval Can be bui l t wi t h l ocal l y avai l abl e mat er i al s

  D i s a d v a n t a g e s

  Requi res l ar ge l and area Requi res t r eat ment of per col at e Onl y appl i cabl e dur i ng dry seasons or needs a roof and cont our bund Manual l abour or speci al i sed equi pment i s requi r ed t o remove dr i ed sl udge f rom beds Can cause odour probl ems

  R e fe r e n c e s

EAWAG (Edi t or); SANDEC (Edi t or) (2008): Fecal Sludge Management . Present at i on. Duebendorf : Sw i ss Federal Inst i t ut e of Aquat i c Sci ence

(EAWAG), Depart ment of Wat er and Sani t at i on i n Dev elopi ng Count ri es (SANDEC). URL [ Accessed: 18. 02. 2011] .

  

EAWAG/ SANDEC (Edi t or) (2008): Household Wat er Treat ment and Saf e St orage (HWTS). Lect ure Not es. Duebendorf : Sw i ss Federal Inst i t ut e of

Aquat i c Sci ence (EAWAG), Depart ment of Wat er and Sani t at i on i n Dev elopi ng Count ri es (SANDEC). URL [ Accessed: 08. 04. 2010] . PDF

Lect ure not es on t he t echni cal and non-t echni cal aspect s of sani t at i on household-lev el dri nki ng w at er t reat ment and saf e st orage (HWTS) i n

dev elopi ng count ri es.

  

ERIKSEN-HAMEL, N. S. ; DANSO, G. (2008): Urban Compost : A Soci o-economi c and Agronomi c Ev aluat i on i n Kumasi , Ghana. In: REDWOOD, M.

(Edi t or) (2008): Agri cult ure i n Urban Planni ng: Generat i ng Li v eli hoods and Food Securi t y. . URL [ Accessed: 23. 06. 2010] .

  

HEINSS, U. ; LARMIE, S. A. ; STRAUSS, M. (1998): Soli ds Separat i on and Pond Syst ems f or t he Treat ment of Faecal Sludges i n t he Tropi cs . Lessons

Learnt and Recommendat i ons f or Preli mi nary Desi gn. . Duebendorf : Sw i ss Federal Inst i t ut e of Aquat i c Sci ence (EAWAG), Depart ment of Wat er

and Sani t at i on i n Dev elopi ng Count ri es (SANDEC). URL [ Accessed: 12. 04. 2010] . PDF

The report set s out t o prov i de gui deli nes f or t he preli mi nary desi gn of f aecal sludge t reat ment schemes compri si ng soli ds-li qui d separat i on

and st abi li sat i on ponds. The document i s based on t he result s of collaborat i v e f i eld research conduct ed by t he Ghana Wat er Research Inst i t ut e

and SANDEC on f ull and pi lot -scale f aecal sludge (FS) t reat ment plant s locat ed i n Accra, Ghana.

  

KONE, D. ; KENGE, I. (2008): Technology Transf er – Forage Plant s Used i n Faecal Sludge Dew at eri ng Beds i n Sub-Saharan Af ri ca. In: Sandec

New s 9. PDF

In collaborat i on w i t h t he Asi an Inst i t ut e of Technology (AIT), Bangkok, Eaw ag has prev i ously demonst rat ed t hat const ruct ed w et lands,

especi ally i n Thai land, of f er a v i able solut i on f or t he t reat ment of f aecal sludge. How ev er, si nce t he charact eri st i cs of sludge v ary w i dely

f rom one regi on t o anot her, appropri at e i ndi genous plant s had t o be i dent i f i ed so as t o ensure successf ul operat i on of t hese f aci li t i es. SANIMAS (Edi t or) (2005): Inf ormed Choi ce Cat alogue. pdf present at i on. BORDA and USAID. PDF

Thi s i nf ormed choi ce cat alogue f or communi t y based w ast ew at er t reat ment t echnologi es helps t o i dent i f y sui t able sani t at i on opt i ons and

f aci li t at es t he assessment of di f f erent sani t at i on syst em component s w i t h regard t o st akeholder pref erences. A pow erf ul t ool f or t echni cal

bot t om-up planni ng gi v i ng ov erall i nf ormat i on about t echni cal opt i ons at a "glance".

  

SASSE, L. ; BORDA (Edi t or) (1998): DEWATS . Decent rali sed Wast ew at er Treat ment i n Dev elopi ng Count ri es. Bremen: Bremen Ov erseas

Research and Dev elopment Associ at i on (BORDA). PDF

Exhaust i v e report on t echnologi cal, operat i onal and economi c aspect s of decent rali sed w ast e w at er t reat ment syst ems. Spreadsheet examples

support t he reader i n desi gni ng and planni ng w ast e w at er t reat ment syst ems component s.

  

STRAUSS, M. ; LARMIE, S. A. ; HEINSS, U. (1997): Treat ment of sludges f rom on-si t e sani t at i on — Low -cost opt i ons. In: Wat er Sci ence and

Technology 6, 129-136. URL [ Accessed: 23. 06. 2010] . PDF

Publi shed i n 1997, t hi s art i cle gi v es an ov erv i ew on current li t erat ure-based know ledge regardi ng f aecal sludge t reat ment along w i t h result s

and conclusi ons f rom f i eld research.

  

STRAUSS, M. ; MONTANGERO, A. (2002): FS Management – Rev i ew of Pract i ces, Problems and Ini t i at i v es. London and Duebendorf : DFID Proj ect

R8056, Capaci t y Bui ldi ng f or Ef f ect i v e Decent rali sed Wast ew at er Management , Sw i ss Federal Inst i t ut e of Aquat i c Sci ence (EAWAG),

Depart ment of Wat er and Sani t at i on i n Dev elopi ng Count ri es (SANDEC). URL [ Accessed: 24. 05. 2012] . PDF A st udy on management and i nst i t ut i onal aspect s regardi ng t he challenges and possi ble i mprov ement s i n managi ng f aecal sludge.

  

MONTANGERO, A. ; STRAUSS, M. (2004): Faecal Sludge Treat ment . Duebendorf : Sw i ss Federal Inst i t ut e of Aquat i c Sci ence (EAWAG), Depart ment

of Wat er and Sani t at i on i n Dev elopi ng Count ri es (SANDEC). URL [ Accessed: 10. 06. 2010] . PDF Thi s document rev i ew s current pract i ces of f aecal sludge management and t reat ment .

TILLEY, E. ; LUETHI, C. ; MOREL, A. ; ZURBRUEGG, C. ; SCHERTENLEIB, R. (2008): Compendi um of Sani t at i on Syst ems and Technologi es.

Duebendorf and Genev a: Sw i ss Federal Inst i t ut e of Aquat i c Sci ence and Technology (EAWAG). URL [ Accessed: 15. 02. 2010] . PDF

Thi s compendi um gi v es a syst emat i c ov erv i ew on di f f erent sani t at i on syst ems and t echnologi es and descri bes a w i de range of av ai lable

low -cost sani t at i on t echnologi es.

HUMBOLDT EDU (Edi t or) (2008): Arcat a's Wast ew at er Treat ment Plant & The Arcat a Marsh and Wi ldli f e Sanct uary. Arcat a: Env i ronment al

Resources Engi neeri ng, Humboldt St at e Uni v ersi t y. URL [ Accessed: 22. 05. 2012] .

  

For furt her readings, case studies, awareness raising mat erial, t raining mat erial, import ant weblinks or

t he relat ed powerpoint present ation, see www.sswm. info/ cat egory/ implementat ion-tools/ wast ewat er-

t reat ment/ hardware/ sludge-t reat ment/ drying-beds