Sustainable Treatment and Reuse of Municipal WastewaterFor Decision Makers and Practicing Engineers

Menahem Libhaber and Álvaro Orozco-Jaramillo

In many countries, especially in developing countries, many people are lacking access to water and sanitation services and this inadequate service is the main cause of diseases in these countries. Application of appropriate wastewater treatment technologies, which are effective, low cost (in investment and especially in Operation and Maintenance), simple to operate, proven technologies, is a key component in any strategy aimed at increasing the coverage of wastewater treatment.

Sustainable Treatment and Reuse of Municipal Wastewater presents the concepts of appropriate technology for wastewater treatment and the issues of strategy and policy for increasing wastewater treatment coverage. The book focuses on the resolution of wastewater treatment and disposal problems in developing countries, however the concepts presented are valid and applicable anywhere and plants based on combined unit processes of appropriate technology can also be used in developed countries and provide to them the benefits described.

Sustainable Treatment and Reuse of Municipal Wastewater presents the basic engineering design procedures to obtain high quality effluents by treatment plants based on simple, low cost and easy to operate processes. The main message of the book is the idea of the ability to combine unit processes to create a treatment plant based on a series of appropriate technology processes which jointly can generate any required effluent quality. A plant based on a combination of appropriate technology unit processes is still easy to operate and is usually of lower costs than conventional processes in terms of investment and certainly in operation and maintenance.

www.iwapublishing.comISBN 13: 9781780400167

Sustainable Treatment and Reuse of M

unicipal Wastew

aterM

enahem Libhaber and

Álvaro O

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Sustainable Treatment and Reuse of Municipal Wastewater_final.indd 1 24/05/2012 10:16

Sustainable Treatment and Reuseof Municipal Wastewater

Sustainable Treatment and Reuseof Municipal WastewaterFor Decision Makers and Practicing Engineers

Menahem Libhaber and Álvaro Orozco-Jaramillo

Published by IWA PublishingAlliance House12 Caxton StreetLondon SW1H 0QS, UKTelephone: +44 (0)20 7654 5500Fax: +44 (0)20 7654 5555Email: publications@iwap.co.ukWeb: www.iwapublishing.com

First published 2012© 2012 IWA Publishing

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11.2 COMBINATION 1: ROTATING MICRO SCREENS FOLLOWED BYUASB FOLLOWED BY FACULTATIVE LAGOONS11.2.1 IntroductionIn this combined processes the effluent of a UASB plant is polished by facultative lagoons. This is a verylogical scheme and an exemplary appropriate technology process. Preliminary treatment is achieved byrotating screens and, if needed, a vortex grit chamber, which is the best available preliminary treatmentscheme. The screen opening should not be less than of 6 mm in order to avoid removing organic matterwhich is necessary for the proper functioning of the UASB reactor. The removal of the main portion oforganic matter is achieved in this combination by the USAB process, which is one of the main unitprocesses of appropriate technology and is discussed in detail in Chapter 6. It is a simple, effective lowcost process. The facultative or maturation lagoons system used for polishing the UASB effluent is asimple reliable system discussed in Chapter 5. Removal of pathogenic organisms can be achieved in thisprocess naturally (without disinfection), if sufficient detention time is provided in the lagoons system.The emphasis of the design of the lagoon must be on the removal of pathogens, since the bulk of organicmatter is removed in the UASB Reactor. In several plants visited the lagoon are designed with a veryshort detention time, practically operating as clarifier where settled sludge is decomposed in the bottom.Such an approach should be avoided and the lagoons need to be designed for the removal of pathogens.The design basis for disinfection in lagoons is discussed by Arthur (1983).

This combined process generates solid waste material in the rotating screen and excess sludge in theUASB reactor. This process includes therefore the disposal of the screened material, usually in a sanitarylandfill, and the handling of the UASB excess sludge, mainly by drying beds, without mechanicalequipment. The main disadvantage of this combined process is that the lagoons occupy large extensionsof land. If area is scarce, deeper lagoons with mixers can be used. An ultrasound device can be used todecrease algae content in the final effluent. Because of the use of lagoons as part of this process, it issuitable for small and medium size cities, but not for large cities (Libhaber, 2007). The biogas generatedin the UASB reactor can be collected and put to use, if economically feasible. As a whole this is a goodand recommended process. A schematic flow diagram of this process is presented in Figure 11.1.

This process is being applied in several plants in Brazil and in Colombia, using conventional preliminarytreatment, not RMS. The largest plant of this type in Colombia is the Rio Frio plant in Bucaramanga. A photoof the plant is presented in Figure 11.2. This plant, commissioned in 1991, is one of the oldest in the worldlarge scale UASB-based facilities treating municipal wastewater. The plant’s original design flow was740 l/s serving a population of 240.000. The UASB reactors are located at the bottom of Figure 1.2 andnext to them are the sludge drying beds (not seen in the figure). The UASB reactors are equipped withaluminium covers and the collected biogas is flared. Pretreatment for the UASB reactors is provided by6 mm screens followed by grit chambers. The reactors are followed by two facultative lagoons. Removalefficiency of BOD is about 80% in the USAB plant and 33% in the facultative lagoons, achieving a totalBOD removal in the range of 85–90%.

Paragraph 1.19 of Chapter 1 present Table 1.11 with all the programs used in the book, including theCombinations, and a short explanation of how to use them. Note that that combination 2 is calculatedwith program CHAP 6-ANAEROBIC-UASB-AF.xls, and each of the other combinations has its ownprogram working analogous to the process programs. Also note that in combination programs theeffluent of a preceding unit is the influent to the following unit. For all other details the programs workexactly as presented in each process program, of course with the specific influent for each case.

Combinations of unit processes of appropriate technology 467

The plant has been able to achieve essentially secondary treatment levels compatible with that ofconventional processes at a very low capital and O&M costs, thereby demonstrating the potential ofapplication of this process in developing countries. The Rio Frio plant has two problems: (i) thedetention time in the facultative lagoons is way too low (about 2 days) and this limits their performance;and (ii) the potable water in Bucaramanga has elevated sulphate levels, and most of the sulphates presentin the raw wastewater are effectively reduced to H2S in the anaerobic reactors, generating odour aroundthe plant and promoting corrosion of plant equipment. Addition of aluminium covers and the collectionand flaring of the biogas has helped to reduce the intensity of the odours and the corrosion of the equipment.

With time the population served by the Rio Frio plant increased and its capacity needed to be augmented.The plant is now being upgraded and its flow diagram is being modified. The UASB reactors section isbeing expanded but the facultative lagoons have been eliminated since there was no area available toincrease them. The lagoons are being replaced by an activate sludge unit. As previously mentioned, thistransforms the entire plant to a conventional treatment plant, and it ceases to be an appropriatetechnology treatment plant. However, the UASB unit performed well during a period of 20 years and hasnot been eliminated, so it will continue to function in the foreseeable future, and the configuration ofUASB followed by lagoons proved to be a successful configuration which performed well and providedduring 20 years a high quality effluent, comparable to that of conventional treatment, at a fraction of the cost.

Figure 11.2 A photo of the Rio Frio Plant, Bucaramanga, Colombia

Figure 11.1 A schematic flow diagram of the combined process of preliminary treatment followed by UASBfollowed by facultative lagoons

Sustainable Treatment and Reuse of Municipal Wastewater468

Several plants of UASB followed by lagoons are in operation in Brazil. SANEPAR, the water utility ofthe state of Parana in Brazil operates several plants of this type. Figure 1.62 shows a photo of a UASB plantfollowed by a facultative lagoon in Ronda, a small town, part of the city of Ponta Grossa in the state ofParana. Another plant in Parana based on this process is the Padilha Sul Plant located in the city ofCuritiba, the capital of Parana. A photo of this plant is presented in Figure 1.63. The first stage of thisplant was designed for an average wastewater flow of 440 l/s and is serving an equivalent population of318,000. It will be expanded to handle an average flow of 600 l/s. The UASB reactors occupy the smallarea at the left hand side of the bottom of the figure. As can be seen, the UASB reactors unit occupiesonly a small portion of the total plant area. Also seen in the photo is that the UASB reactors are locatedat a close vicinity to residential areas. That means that the UASB units do not present an environmentalnuisance to the nearby residential areas.

11.2.2 PerformanceThe advantages of combined process of UASB followed by lagoons are: (i) low capital and operation cost,(ii) easy maintenance, it does not use mechanical equipment, (iii) small quantities of sludge, and (iv) goodeffluent quality. The main disadvantage of this process is that the lagoons occupy a large land area. Theapproach of deeper lagoons equipped with mixer can reduce the area of the lagoons).

The plant of Rio Frio, Colombia, obtained BOD removal of about 80% in the UASB reactor and 33% inthe maturation ponds, for a total removal of BOD of 85–90%. In general, this process achieves 80–90%BOD removal and 70–80% SST removal. The removal of FC depends on the design of the lagoons. If ashort detention time is provided, the FC removal is low. However, properly designed lagoons canachieve a high FC removal.

Construction costs for the existing facilities of the Rio Frio treatment plant in Bucaramanga wereapproximately 15 US$/Capita. Operating costs are 0.79 US$/Yr/Capita or 0.015 US$/m3 treated(Osorio, 1996). However, this plant was constructed in the early 1990s. It is estimated that today Theinvestment cost in a UASB reactor followed by a lagoons system is in the range 30–50 US$/Capita,depending on the design of the lagoons, and the O&M cost is in the range 1.0–1.5 US$/Yr/Capita.

11.2.3 Design(The model program for this Example is available online at http://www.iwawaterwiki.org/xwiki/bin/view/Articles/Software+Developed+for+Sustainable+Treatment+and+Reuse+of+Municipal+Wastewater)

The design procedures and a detailed example of the design of a UASB reactor and a lagoons systemwhich make up this combination are presented in Chapter 6 and 5 respectively. The reader is referred tothe design examples in these chapters. The results of application in series of a UASB reactor and alagoons system for the example of 20,000 people, with an influent Fecal Coliform of 5 × 106 MPN/100ml are presented below. The Excel program COMB 1-USAB-MATURATION LAGOON-01.xls is theprogram used to calculate example of this combined process.

Variables selected by the designerThe quality parameters of the raw wastewater are the same of all other examples and presented inTable 11A. The specifics of each process design are explained in the corresponding chapter (in this case,Chapters 5 and 6). Please note that the following Tables identified by alphabetic order contain computercalculated results.

Combinations of unit processes of appropriate technology 469

UASB

The designer variables selected for the UASB are presented in Table 11B. For design details see Chapter 6,Section 6.3, Paragraph 4. See also the important note in the Box in Section 11.1.

Table 11A

WW quality

Variable Value Unit Value Unit

BOD5 277.8 mg/L 0.28 kg/m3

COD 596.1 mg/L 0.60 kg/m3

COD/BOD5 2.1

TKN 40.0 mg/L 0.04 kg/m3

N-Nitrate 2.0 mg/L 0.00 kg/m3

Total Phosphorus 5.8 mg/L 0.01 kg/m3

pH 7.1 UN

Alkalinity 100.0 mg/L 0.10 kg/m3

TSS 202.6 mg/L 0.20 kg/m3

VSS 173.6 mg/L 0.17 kg/m3

O&G 100.0 mg/L 0.10 kg/m3

Fecal Coli 5000000.0 MPN/100mL 50000000000.00 MPN/m3

Table 11B

Designer variables

Variable Value Unit Value Unit Observation

UASB standard

Settling basin width, ws 4.0 m Figure 6.10: UASB-SM

GSLS heigth, HG 2.5 m Figure 6.10: UASB-SM

Baffle width, wb 0.15 m Figure 6.10: Baffle width

Reactor velocity, vr 0.75 m/h ,1.00 m/h; vr , vs;Table 6.3

Gas velocity, vg 1.0 m3/h · m2 .1.00 m/h; Tabla 6.3

Yield coefficient, Y 0.08 Table 3.2: 0.08

Fraction of CH4, η 0.65 Typical

Maximum Efficiency, Emax 90.00 % 80 to 90%

Volumetric load, Lv at 15°C 2.0 kg/m3 · d 2.0–4.0 kg/m3 · d at 15°C,applied to liquid volume

Efficiency, E 89.31 % DBO5 orsCOD

Equation 6.3

Actual volumetric load, Lv (T) 5.44 kg/m3 · d Equation 6.4

(Continued )

Sustainable Treatment and Reuse of Municipal Wastewater470

Maturation lagoonThe designer variables selected for the maturation lagoons are presented in Table 11C. For design details seeChapter 5, Section 5.3, Paragraph 6.

Table 11C

Designer variables

Variable Value Unit Value Unit Observation

Maturation lagoon

Depth, HM 1.5 m 2–5 m

Tmin air 18.0 °C Coldest month

Ti water 25.0

# Lagoons M, nM 2 Parallel

L/w (ratio length towidth)

2 Between 1 and 3

Pipe velocity, v 1 m/s 0.6–2.0 m/s

LS= 350 (1.107−0.002T)(T–25) or 400

216.5 kg BOD5/ha · d Equation 5.14 or 400

(Continued )

Table 11B (Continued ).

Designer variables

Variable Value Unit Value Unit Observation

Water temperature 25.00 °C Coldest month of year

sCODe or BOD5, S 29.69 mg/L 0.03 kg/m3 Equation 6.5

Methane production, VCH4124.34 m3/d Equation 6.6

Biogas production, Vbiogas 191.29 m3/d 7.97 m3/h Ecuación 6.7

Inlet structures

Branch manifold flow 0.020 m3/s QD/2

Manifold velocity, v 0.03 m/s Goal seek: see notein cell N38

orifices per m2, ε0 2.00 1 a 2 per m2

# orfices, preliminary, n0 114.00 Equation 6.27

# distribuitors, nd 11.00 Equation 6.27a

# orifices per distributor, nod 5.00 Equation 6.28

Outlet structures

Module flow, QM =QD/nM 0.01 m3/s

Channel widthl b 0.30 m Select

Draying bed

Applying rate, qx 150 kg/m2 · yr Between 120–150

Combinations of unit processes of appropriate technology 471

DesignUASB

The results of the design calculations of the UASB unit are presented in Table 11D. See Chapter 1, Section1.19 for explanation of how the programs work, and Chapter 5 for design details. Note that the UASB mainobjective is to remove BOD (to about 30 mg/L BOD5) and the maturation lagoons objectives are to removeFecal Coliforms and helminths so as to be close to the targets of FC, 20,000 MPN/100 mL and helminthsof no more than 1 Ova/L.

Table 11D

Design

Parameter Value Unit Value Unit Observation

UASB standard

Reactor area, Ar 192.4 m2 Equation 6.8

Net height, HN 0.9 m Equation 6.9

Effective liquid height, HL 2.5 m Equation 6.10 (minimo 2 · 5 m)

UASB heigth, HT 5.0 m Equation 6.11

Detention time, td 6.7 h Equation 6.12

UASB total volume, VUASB 962.2 m3 Equation 6.13

Sludge blanket volume, VL 481.1 m3 Equation 6.14

Total gas extraction area, Ag 8.0 m2 Equation 6.15

Design UASB length, LUASB 17.0 m Equation 6.16

Net UASB width, WUASB 11.3 m Equation 6.17

Total gas width, Wg= nMP · wg 0.47 m Equation 6.18

(Continued )

Table 11C (Continued ).

Designer variables

Variable Value Unit Value Unit Observation

KL (20°C) 0.35 d−1 Tipical

θ (BOD5) 1.06 1.04–1.09

Influent BOD5i, S0M=SF 29.7 mg/L UASB Effluent

KB (20°C) 2.7 d−1 Tipical FC

θ (CF) 1.19 Tipical FC

Influent FC: B0M 5000000 MPN/100mL UASB does notremove

Influent helminthes 10 Ova/L Between 300–800

Target FC 20000 MPN/100mL Between 1000 and20000

Target helminthes eggs 1 Ova/L ,1 Ova/L

Sustainable Treatment and Reuse of Municipal Wastewater472

Maturation lagoonsThe results of the design calculations of the lagoons system are presented in Table 11E. For details seeChapter 5. Note that the effluent contains 20,000MPN/100 mL of Fecal Coliforms and 0.2 Ova/L ofhelminths, meeting the proposed targets.

Table 11D (Continued ).

Design

Parameter Value Unit Value Unit Observation

# preliminar modules, nMP 2.52 Equation 6.19

# modules, nM 3.00 Integer rounded up

Gas throat width, wg 0.16 m Equation 6.20

Design UASB total width,WUASBD

13.4 m Equation 6.21

Settling basisn total area, As 204.0 m2 Equation 6.22

Design SOR or vsD=QD/As 0.71 m/h ,1,00 and.vrD. If otherwisechange change vr or/and vg

Design UASB area,ArD=WUASBD × LUASB

227.27 m2 For nM modules: Equation 6.22a

Design vr, vrD=Qb/ArD 0.64 m/h Equation 6.23

Design UASB volume,VUASBD=ArD · HT

1136.35 m3 6.24a

Design detention time,tdD=VUASB/QD

7.87 h

Sludge production

Qx=VUASBD Y(S0−S)/tdD 68.76 kg/d Equation 6.25

Biogas production

Volume per day, Vg 191.3 m3/d Equations 6.6 and 6.7

Inlet structure

Manifold area am 0.696 m2 Equation 6.26, con QD/2

Manifold diameter,φ= (4 am/π)∧(1/2)

0.942 m 37.0 pulg

Distribuitor area, ad= 0.4 am/nD 0.025 m2 From Equations 6.29 and 6.27a

Distributor diameter,= (4 ad/π)∧(1/2)

0.180 m 7.0 pulg

Orifice area, ao= 0.4 ad/no 0.002 m2 From Equations 6.30 and 6.28

Orifice diameter,φ0= (4 ao/π)∧(1/2)

0.051 m 2.00 pulg Goal seek: set cell L38to 2 by changing C14

Outlet structures

Channel water depth, h 0.102 m Equation 6.31

Total channel depth, hc 0.202 m h+ 0.10

Drying bed

Abed=Qx/qx 167.3 m2 Equation 6.33

Combinations of unit processes of appropriate technology 473

Table 11E

Parameter Value Unit Value Unit Observation

Maturation Lagoon

LS 216.5 kg BOD5/ha · d Selected in input

td 38.6 d Equation 5.11; tdmin= 3 d

Volume, V′F=Q · td 133868.6 m3 Equation 5.21

Final Volume, VF 133868.6 m3 Greater of td and tdmin= 3 d

Area, As=VF/h 89245.7 m2 Equation 5.20

Lagoon area, as= (As/nF) 44622.9 m2

Lagoon width, w= [as/(L/w)]0,5 149.4 m

Lagoon length, L= (L/w) w 298.7

TL= (AsfTa+QTi)/(Asf+Q) 18.5 °C Equation 5.8

KL= KL(20°C) θ(T-20) 0.32 d−1 Equation 5.7

Effluent BOD5 SM=S0/(1+ KL · td) 2.22 mg/L Equation 5.4, parallel

Effluent BOD5 SM=S0/(1+ KL · td/n)n 0.57 mg/L Equation 5.5, series

vF= 0,00091VF(S0−S)/(1+ 0.05td) 1141.39 kg/yr 1141.39 m3/yr Equation 5.24

Filling years= 0.5 VF/vF 58.6 years 1/2 volume

Maturation lagoon: fecal coliform and helminthes removal and efficiencies

KB=KB(20°C) θ(T-20) 6.4 d−1 Equation 5.26

Effluent FC: B=B0/(1+KB · td) 20000.0 MPN/100mL Equation 5.25; Goal seekTarget effluent FC

Effluent Helminthes 0.2 Ova/L

Efficiency FC= 100 · (B0−B)/B0 99.6 % From Equation 5.25

Efficiency Helminthes= 100 [1− 0.41exp (−0.49 td+ 0.0085td

2)]98.2 % Equation 5.15

Efficiency BOD5 removal maturation 92.5 %

Total efficiency BOD5 99.2 % Combination system

Total efficiency fecal coliform 99.6 % Combination system

Total efficiency helminthes 98.2 % Combination system

Inlet and outlet structures

Total diameter, φ=(4 · PI · v · QD/1000)0,5 0.226 m 9.00 In With QD

Lagoon diameter, φL=φ=[4 · PI · v · (QD/4)/1000]0.5 0.160 m 6.00 in With QD/4

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A drawing of a typical plant based on the combined process of UASB followed by lagoons is presented inFigure 11.3.

11.3 COMBINATION 2: ROTATING MICRO SCREENS FOLLOWEDBY UASB FOLLOWED BYANAEROBIC FILTER11.3.1 IntroductionIn addition to the use of anaerobic filters as the main treatment unit, they can be used as polishing units forimprovement of the quality of the effluent of a preceding unit. They are in fact more suitable to perform aspolishing units since when fed with treated effluent of a preceding unit they are less bound to be clogged byinorganic suspended solids.

A combined process composed of Rotating Micro Screens as preliminary treatment, followed by UASBas the unit for removal of the main portion of organic matter, then followed by an anaerobic filter forpolishing of the UASB effluent, and finally, if necessary, followed by a disinfection unit (chlorination orUV disinfection) for removal of pathogens. is a reasonable schemes and an effective appropriatetechnology process. The screen opening in the preliminary treatment unit should not be less than of6 mm in order to avoid removing organic matter which is necessary for the proper functioning of theUASB reactor. This combined process is similar to the process described in the previous section and isbasically the replacement of the lagoons by an anaerobic filter followed by a disinfection unit. Theadvantages of this process are that it yields a high quality effluent and is compact, i.e. does not occupy alarge land area. This process can be applied in cases where area for locating a treatment plant is scarceand insufficient for installation of lagoons. The process includes also the disposal of the screened

Figure 11.3 Plan and typical cross section of the combined process of preliminary treatment followed byUASB followed by facultative lagoons

Combinations of unit processes of appropriate technology 475