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Ana erobic sewage treatment: state of theart , constraints and challenges

ARTICLE in REVIEWS IN ENVIRONMENTAL SCIENCE AND BIO/TECHNOLOGY · SEPTEMBER 2015Impact Factor : 3.33 · DOI: 10.1007/s11157-015-9377-3

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Jules van Lier

Delft University of Technology

395 PUBLICATIONS 6,204 CITATIONS

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Adalberto Noyola

Universidad Nacional Autónoma de M…

85 PUBLICATIONS 887 CITATIONS

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Thiago Ribeiro

Federal University of Minas Gerais

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Available from: Jules van LierRetrieved on: 10 April 2016

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REVIEW PAPER

Anaerobic sewage treatment: state of the art, constraints

and challengesC. A. L. Chernicharo . J. B. van Lier . A. Noyola .T. Bressani Ribeiro

Springer Science+Business Media Dordrecht 2015

Abstract The interest in high-rate anaerobic (pre-)treatment of sewage using UASB reactors is steadilygrowing since its introduction in the mid-1980s.Today there are hundreds of full-scale plants inoperation in various parts of the tropical world,notably in Latin America and India. The mainadvantage of UASB technology is the very low oreven zero energy demand, leading to an up to tenfolddrop in operational costs compared to activatedsludge. This paper presents a literature reviewfocussing on current design criteria and post-treatmentoptions, alongside discussing the centralized anddecentralized approach. The current limitations and

constraints regarding temperature, nutrients, pathogenremoval, odour nuisance, operational constrictionsand methane emissions are also presented and dis-cussed. Further, recent challenges in relation to energyrecovery from biogas, sludge and scum are discussed,alongside with advances related to recovery of dissolved methane and sludge management. Finally,the paper provides some outlooks for upcomingdevelopments.

Keywords Anaerobic digestion Domesticwastewater Anaerobic sewage treatment Biogas Full-scale reactors UASB reactor

1 Introduction

With the emergence of the upow anaerobic sludgeblanket (UASB) technology in the 1980s (Lettingaet al. 1980), several countries, especially those in LatinAmerica and India, began to adopt anaerobic sewagetreatment technology to the owsheets of sewagetreatment plants (STP). Anaerobic sewage treatment,in various cases followed by units of aerobic post-treatment systems, was regarded an alternative to thetraditional wastewater treatment systems used histor-ically, such as the mechanized activated sludge and theland-based pond systems. The favourable climateconditions and the large investments in research anddevelopment, made Latin America, notably Brazil,

C. A. L. Chernicharo ( & ) T. Bressani RibeiroDepartment of Sanitary and Environmental Engineering,Federal University of Minas Gerais, Av. Anto ˆnio Carlos,6.627, Pampulha, Belo Horizonte, MG 31270-901, Brazile-mail: [email protected]

J. B. van Lier

Section Sanitary Engineering, Department of WaterManagement, Faculty of Civil Engineering andGeosciences, Delft University of Technology,PO Box 5048, 2600 GA Delft, The Netherlands

J. B. van LierUnesco - IHE, PO Box 3015, 2601 DA Delft,The Netherlands

A. NoyolaInstituto de Ingenierı´a, Universidad Nacional Auto´nomade México, Circuito Escolar, Ciudad Universitaria,04510 Coyoacá n, Mexico, D.F., Mexico

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Rev Environ Sci BiotechnolDOI 10.1007/s11157-015-9377-3

http://crossmark.crossref.org/dialog/?doi=10.1007/s11157-015-9377-3&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1007/s11157-015-9377-3&domain=pdf


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Colombia and Mexico, to become the present fron-trunner in the proper use of UASB reactor systems forthe treatment of municipal wastewater.

In Brazil, the use of UASB reactors for wastewatertreatment was introduced in the early 80s, whenresearch by several groups of academics and engineers

in the area of wastewater treatment started. During itsintroduction, the inappropriate use of UASB reactorsdamaged the credibility of this technology within statewater companies and environmental protection agen-cies. However, this has been restored in recent decadesasa resultof theintensicationof studiesand research inthe area, and also due to the experience gained in theoperation of full-scale plants. Undoubtedly, a greatcontribution to the consolidation and dissemination of the anaerobic technology for the treatment of domesticsewage in Brazil came from the National ResearchProgramme on Basic Sanitation—PROSAB,which wascarried from 1997 to 2007 (Chernicharo et al. 2001).

Likewise, the Indian government launched animportant programme to improve the water qualityof the Yamuna River basin in 1990, called YamunaAction Plan—YAP, which was based on the previousexperience with the Ganga Action Plan. Under thisYAP, the government decided to implement 16 full-scale UASB reactors with a total capacity of 598,000 m 3 day - 1 , recognizing the technology as astandard method for sewage treatment in India (Ue-mura and Harada 2010).

A recent survey in the Latin American region(Noyola et al. 2012) identied three major technologiesfor municipal wastewater treatment: stabilizationponds, activated sludge (extended aeration and conven-tional processes) and UASB reactors. A survey of 2734treatment facilitieswas carried out in sixcountries in theregion (Brazil, Colombia, Chile, Dominican Republic,Guatemala and Mexico). The distribution by number of these three technologies were 38, 26 and 17 %,corresponding altogether to 81 % of the surveyedfacilities (Fig. 1a). It is worth noticing that the UASBsystem, although a newcomer in the eld of municipalsewage treatment with no more than 25 years of application within this specic market, took the thirdplace, behind more than a century old processes.However, this picture changes when the technologiesin Latin America are ordered by treatment capacity(design ow). In such case, both versions of activatedsludge turn out to be the most important, followed bystabilization ponds, enhanced primary treatment and

UASB in the fourth place, i.e. 58, 15, 9 and 7 % of thetotal design ow in the sample (Fig. 1b). It is clear thatstabilization ponds, and even UASB, arewidely appliedin the region, but in small facilities. In fact, the surveyalso found that 67 % of the STPs in Latin America aresmall, with designowsof less than 25 L s - 1 , and 34 %

are very small, less than 5 L s - 1 .UASB reactors used for the treatment of domestic

wastewater are now considered a consolidated tech-nology in Latin America, where several large full-scale plants, treating a population equivalent up to onemillion inhabitants (Onça STP, Belo Horizonte,Brazil), have been in operation for more than 10 years.The costs of a treatment plant with UASB reactorfollowed by aerobic biological treatment usually allowcapital expenditures (CAPEX) savings in the range of 20–50 % and operational expenditures (OPEX) sav-ings above 50 %, in comparison with a conventionalactivated sludge plant (von Sperling and Chernicharo2005; Chernicharo 2006). This is considered one of thereasons for the increase in wastewater treatmentcoverage in Latin America. The cost-effectiveness of UASB technology was demonstrated, not only at theexpense of activated sludge processes but also incomparison to pond systems (Oomen and Schellinkh-out 1993). In fact, land based treatment systems areconsidered very expensive near urban areas whereland prices are high. For that reason, large-scale pondsystems are hardly applied near the urban areas inIndia. Similarly, the Dutch consultant DHV performedan economic assessment for the best possible treat-ment solution for the urbanised centres in the irrigatedagricultural sites of the Fayoum, 80 km south of Cairo,Egypt. In this study, pond systems were rapidlydiscarded because of a too high demand of valuableagricultural land. Comparing conventional activatedsludge with a UASB system followed by a stone-lledtrickling lter showed 40 % less CAPEX and about90 % less OPEX, mainly related to avoidance of fossilenergy use for sewage treatment.

Table 1 summarizes the recent literature reports onthe performance of full-scale municipal anaerobicsewage treatment plants, notably employing UASBreactors.

In the last 10 years, several review papers havebeen published discussing the anaerobic sewagetreatment feasibility (Aiyuk et al. 2006; Foresti et al.2006 ; Gomec 2010; Chong et al. 2012). This reviewarticle focuses on practical aspects of the most

Rev Environ Sci Biotechnol

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https://www.researchgate.net/publication/279295857_Typology_of_Municipal_Wastewater_Treatment_Technologies_in_Latin_America?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/279295857_Typology_of_Municipal_Wastewater_Treatment_Technologies_in_Latin_America?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/279295857_Typology_of_Municipal_Wastewater_Treatment_Technologies_in_Latin_America?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/225245842_Anaerobic_Processes_as_the_Core_Technology_for_Sustainable_Domestic_Wastewater_Treatment_Consolidated_Applications_New_TrendsPerspectives_and_Challenges?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/225245842_Anaerobic_Processes_as_the_Core_Technology_for_Sustainable_Domestic_Wastewater_Treatment_Consolidated_Applications_New_TrendsPerspectives_and_Challenges?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/225245842_Anaerobic_Processes_as_the_Core_Technology_for_Sustainable_Domestic_Wastewater_Treatment_Consolidated_Applications_New_TrendsPerspectives_and_Challenges?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/225245842_Anaerobic_Processes_as_the_Core_Technology_for_Sustainable_Domestic_Wastewater_Treatment_Consolidated_Applications_New_TrendsPerspectives_and_Challenges?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/225245842_Anaerobic_Processes_as_the_Core_Technology_for_Sustainable_Domestic_Wastewater_Treatment_Consolidated_Applications_New_TrendsPerspectives_and_Challenges?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/225245842_Anaerobic_Processes_as_the_Core_Technology_for_Sustainable_Domestic_Wastewater_Treatment_Consolidated_Applications_New_TrendsPerspectives_and_Challenges?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/225245842_Anaerobic_Processes_as_the_Core_Technology_for_Sustainable_Domestic_Wastewater_Treatment_Consolidated_Applications_New_TrendsPerspectives_and_Challenges?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/225245842_Anaerobic_Processes_as_the_Core_Technology_for_Sustainable_Domestic_Wastewater_Treatment_Consolidated_Applications_New_TrendsPerspectives_and_Challenges?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/225245842_Anaerobic_Processes_as_the_Core_Technology_for_Sustainable_Domestic_Wastewater_Treatment_Consolidated_Applications_New_TrendsPerspectives_and_Challenges?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/279295857_Typology_of_Municipal_Wastewater_Treatment_Technologies_in_Latin_America?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/225245842_Anaerobic_Processes_as_the_Core_Technology_for_Sustainable_Domestic_Wastewater_Treatment_Consolidated_Applications_New_TrendsPerspectives_and_Challenges?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/225245842_Anaerobic_Processes_as_the_Core_Technology_for_Sustainable_Domestic_Wastewater_Treatment_Consolidated_Applications_New_TrendsPerspectives_and_Challenges?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/7691222_Anaerobic_and_complementary_treatment_of_domestic_sewage_in_regions_with_hot_climates_-_a_review_Bioresour_Technol?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/7691222_Anaerobic_and_complementary_treatment_of_domestic_sewage_in_regions_with_hot_climates_-_a_review_Bioresour_Technol?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==


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employed anaerobic system treating domestic wastew-ater, i.e. the UASB reactor, bringing together com-piled information regarding design criteria and currentlimitations and constraints, notably in full-scaleapplications. The paper also evaluates matters regard-ing odour and methane emissions reported in theliterature, as well as operational constraints, chal-lenges and perspectives regarding treatment andrecovery of nutrients.

2 State of the art of anaerobic sewage treatment

2.1 Current design criteria

Given the increasing importance of the UASB reactorfor sewage treatment, several measures should betaken in relation to the adequate design and operationof the system. One of the most important aspects of theanaerobic process applying UASB reactors is its

Fig. 1 Major technologiesfor municipal wastewatertreatment in Latin Americanregion. a Distribution of treatment technologiesaccording to their type,b accumulated ow treatedper each type of technology.Source : Noyola et al. (2012)


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https://www.researchgate.net/publication/279295857_Typology_of_Municipal_Wastewater_Treatment_Technologies_in_Latin_America?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/279295857_Typology_of_Municipal_Wastewater_Treatment_Technologies_in_Latin_America?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/279295857_Typology_of_Municipal_Wastewater_Treatment_Technologies_in_Latin_America?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/279295857_Typology_of_Municipal_Wastewater_Treatment_Technologies_in_Latin_America?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==


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ability to develop and maintain sludge with excellentsettling characteristics. From the foregoing, thescheme of a UASB sewage treatment plant (STP) asdepicted in Fig. 2 can be considered as a standardisedconcept. Notwithstanding, some factors such as localpractice, contractor’s experience, available funds,efuent requirements, etc. determined the exact con-gurations and dimensions of the functional units atspecic sites (van Lier et al. 2010).

Therefore, when designing a UASB system anumber of parameters need to be evaluated. The mostcritical design aspects are well explained by vanHaandel and Lettinga ( 1994) and von Sperling andChernicharo ( 2005). In order to cope with this, theBrazilian Association of Technical Standards hasrecently published a technical standard ‘‘Hydraulicand sanitary engineering design for wastewater treat-ment plants’’, under the code ABNT NBR

Table 1 Performance of the more recently installed full-scale anaerobic sewage treatment plants treating municipal sewage indifferent parts of the world

Location STP Efuent concentration Removal efciency Population equivalent(inhabitants)

References

COD(mg l - 1 )

BOD(mg l - 1)

TSS(mg l - 1 )

COD(%)

BOD(%)

TSS(%)

India UASB 202 60 150 63 67 70 93,500 Pandey and Dubey(2014)

India UASB 139–567 57–159 72–452 29–75 45–79 40–70 – Khan et al. ( 2014)Brazil ST ? AnF 473 – 190 39 – 36 2,141 Silva et al. ( 2013)Brazil UASB 283 – 132 58 – 49 3,047 Silva et al. ( 2013)Brazil UASB 114 38 132 79 84 59 70,000 Rosa et al. ( 2012)

Brazil UASB 251 98 85 65 74 71 24,000 Oliveira and vonSperling ( 2011 )

India UASB 515 115 113 41 50 47 – Mungray and Patel(2011 )

India UASB 405 153 167 44 40 36 – Mungray and Patel(2011 )

India UASB 145–250 55–75 160–240 45 60 34 – Walia et al. ( 2011 )

Colombia UASB – 60 – – 77 – 320,000 WERF ( 2010)Brazil UASB 170 66 75 58 68 56 544,000 Franco ( 2010)Brazil UASB 247 97 112 62 67 54 – van Lier et al. ( 2010)India UASB 285 121 357 46 41 49 – van Lier et al. ( 2010)Brazil UASB 190 70 60 60 65 61 1,000,000 Chernicharo et al.

(2009)

Colombia UASB 144 – 81 58 – 65 – Penã et al. (2006)Brazil UASB 181 75 127 64 74 51 24,719 Bare á and Alem

Sobrinho ( 2006)

Brazil UASB 106 69 – 72 72 – 150,000 Carraro ( 2006)

Brazil UASB 161 66 – 77 78 – – Tachini et al. ( 2006)India UASB 403 130 380 47 50 7 55,000–570,000 Sato et al. ( 2006)Middle

EastUASB 221 83 63 71 70 85 – Nada et al. ( 2006)

India UASB – – – 61 61 66 – Khalil et al. (2006)

Jordan UASB 632 – 180 58 – 62 – Halalseh et al. (2005)Brazil UASB 237 64 127 60 69 52 3,808 Busato ( 2004)Brazil UASB 202 – 80 67 – 61 18,000 Florencio et al.

(2001)Colombia UASB 177 69 72 66 78 69 9,000 Penã et al. (2000)Mexico UASB – – – 70–80 – – – Monroy et al. (2000)


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https://www.researchgate.net/publication/43129607_Biodegradation_and_Adsorption_of_Antibiotics_in_the_Activated_Sludge_Process?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/43129607_Biodegradation_and_Adsorption_of_Antibiotics_in_the_Activated_Sludge_Process?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/43129607_Biodegradation_and_Adsorption_of_Antibiotics_in_the_Activated_Sludge_Process?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/223739252_Anaerobic_digestion_for_wastewater_treatment_in_Mexico_State_of_the_technology?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/223739252_Anaerobic_digestion_for_wastewater_treatment_in_Mexico_State_of_the_technology?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/223739252_Anaerobic_digestion_for_wastewater_treatment_in_Mexico_State_of_the_technology?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/223739252_Anaerobic_digestion_for_wastewater_treatment_in_Mexico_State_of_the_technology?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/43129607_Biodegradation_and_Adsorption_of_Antibiotics_in_the_Activated_Sludge_Process?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==


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12209: 2011 . This standard was updated and for therst time included hydraulic and process engineeringdesign criteria for UASB reactors, among othertechnologies. Specically in the case of UASBreactors, the main design criteria can be summarizedas shown in Table 2.

In the case of typical domestic sewage, theconcentration of organic matter is low, usually below1000 mgCOD l - 1 , and therefore the resulting appliedvolumetric organic load is also very low, most of the

times ranging from 2.0 to 3.5 kgCOD m - 3 day - 1 .Since the use of higher volumetric organic loadingrates would result in excessive hydraulic loads and,consequently, in high upow velocities, the reactor isalways designed based on the volumetric hydraulicload and not on the organic load (von Sperling andChernicharo 2005). Meanwhile, in many arid climatecountries with limited water supply, sewage concen-trations can be much higher, up to 2500 mgCOD l - 1

(Halalsheh et al. 2005a). Resulting implications arebelow discussed in the topic Temperature Constraints.

Regarding the excess sludge withdrawal, theaforementioned standard recommends at least onedischarge point per 100 m 2 bottom area. In addition,there should be discharge pipes with a minimumdiameter of 100 mm at two different heights, close tothe bottom and between 0.8 and 1.3 m above thebottom. With respect to the management of biogas, itis recommended that STPs with average ow capacityabove 250 l s - 1 , without gas utilization, must have atleast two ares, one as backup. The biogas pipeline

must be designed with a maximum velocity of 5 m s - 1

from the average gas ow, and a minimum diameter of 50 mm.

Regarding the Indian experience, Table 3 summa-rizes the design criteria and basic assumptions used inthe Indian UASB reactor designs. As reported by vanLier et al. (2010), in addition to the UASB tank itself,pre-treatment functional units, such as grit removalsystems and screens, as well as post-treatment unitsare of crucial importance for the overall performance

of the STP.

2.2 Current post-treatment facilities

Considering the intrinsic limitations associated with theanaerobic systems and the stringent discharge stan-dards, it is imperative to include a post-treatment stagefor the efuentsfromanaerobic reactors. In addition, theneed to develop technologies that are more appropriateto the reality of developing countries is still a concern.Therefore, the polishing stage has the purpose toimprove the microbiological quality of the efuents,in view of the public health risks and limitationsimposed on the use of treated efuents in agriculture. Inan environmental approach, the post-treatment need toguarantee the efuent quality in terms of organic matterand nutrients, in view of the environmental damagescaused by the discharge of these remaining pollutantsinto the receiving surface water.

Post-treatment options for anaerobically pre-trea-ted sewage is well discussed in the literature, with the

Fig. 2 General process conguration of a UASB based STP. Source : van Lier et al. (2010)


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various papers addressing the available technologiesand discussing important experimental results, reveal-ing the advantages and disadvantages of each alterna-tive (Chernicharo 2006; Foresti 2006; Chan et al.2009 ; Kassab et al. 2010; Khan et al. 2011; Chonget al. 2012). It is worth mentioning the most frequentlyapplied ow sheets of the so-called combined systems(anaerobic/aerobic), such as: UASB ? PolishingPonds; UASB ? Overland Flow System;UASB ? Wetlands; UASB ? Trickling Filter (TF);

UASB ? Activated Sludge (AS); andUASB ? Flotation Unit (von Sperling and Cher-nicharo 2005). These alternatives allow the achieve-ment of the necessary efciencies to comply with thedischarge standards in most of developing countries.

Table 4 summarizes the main results regardingdemo and full-scale systems and lists the qualitativeranges of efuent concentration and typical removalefciencies considering systems properly designedand operated (Chernicharo 2006).

Table 2 Main design criteria adopted in Brazilian UASB reactors, according to national standard ABNT NBR 12209: 2011

Parameter Unit Value Comment

Hydraulic retention time (HRT) h 6–10 a,b 6 h for sewage temperature [ 25 C7 h for sewage temperature 22–25 C8 h for sewage temperature 18–21 C

10 h for sewage temperature 15–17 CUpow velocity at average ow m h - 1 B 0.7 Less than 1.2 m h - 1 for the maximum peak owUseful depth m 4–6 The minimum useful depths of digestion and settling

compartments are 2.5 and 1.5 m, respectivelyFeed inlet density m 2 per feed point 2.0–3.0 The minimum inlet pipe internal diameter shall be 75 mmAngle of gas collector Degrees C 50 The UASB reactors must have scum removal device

Based on above design criteria and typical characteristics of Brazilian sewage, the UASB per capita costs usually vary between 15and 25 US$/inhabitant for the construction costs and 1.3–1.9 US$/inhabitant.year for the operation and maintenance costs (basis: US$1.00 = R$ 3,13; July 2015) (adapted from von Sperling and Chernicharo 2005)a Values in terms of average owb This range means a recommended VHL (volumetric hydraulic load) between 2.4 and 4 m 3 m- 3 day - 1

Table 3 Design criteria adopted in most of the Indian UASB reactors

Parameter Unit Value Comment

Hydraulic retention time h 8–12 HRT at average ow4 HRT at peak ow

Upow velocity m h - 1 0.5–0.6 Values at average owMaximum velocity through the apertures to the

settlerm h- 1 5

Feed inlet density m 2 per feed

point

4 Maximum feed inlet density

Angle of gas collector Degrees 50Centre-to-centre distance between gas domes m 4.0 The clear distance between gas domes shall be

3.0 mGas hood width m 0.44Overlap of gas collector over deector beam m 0.15Settling zone surface % 75 Percentage of total surface

Adapted from van Lier et al. ( 2010)


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https://www.researchgate.net/publication/41039297_Sequential_Anaerobic-Aerobic_Treatment_for_Domestic_Wastewater_-_a_Review?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/41039297_Sequential_Anaerobic-Aerobic_Treatment_for_Domestic_Wastewater_-_a_Review?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/41039297_Sequential_Anaerobic-Aerobic_Treatment_for_Domestic_Wastewater_-_a_Review?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/41039297_Sequential_Anaerobic-Aerobic_Treatment_for_Domestic_Wastewater_-_a_Review?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/41039297_Sequential_Anaerobic-Aerobic_Treatment_for_Domestic_Wastewater_-_a_Review?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/41039297_Sequential_Anaerobic-Aerobic_Treatment_for_Domestic_Wastewater_-_a_Review?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/41039297_Sequential_Anaerobic-Aerobic_Treatment_for_Domestic_Wastewater_-_a_Review?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/41039297_Sequential_Anaerobic-Aerobic_Treatment_for_Domestic_Wastewater_-_a_Review?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/41039297_Sequential_Anaerobic-Aerobic_Treatment_for_Domestic_Wastewater_-_a_Review?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/41039297_Sequential_Anaerobic-Aerobic_Treatment_for_Domestic_Wastewater_-_a_Review?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/41039297_Sequential_Anaerobic-Aerobic_Treatment_for_Domestic_Wastewater_-_a_Review?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/41039297_Sequential_Anaerobic-Aerobic_Treatment_for_Domestic_Wastewater_-_a_Review?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/41039297_Sequential_Anaerobic-Aerobic_Treatment_for_Domestic_Wastewater_-_a_Review?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/41039297_Sequential_Anaerobic-Aerobic_Treatment_for_Domestic_Wastewater_-_a_Review?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/41039297_Sequential_Anaerobic-Aerobic_Treatment_for_Domestic_Wastewater_-_a_Review?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/225245842_Anaerobic_Processes_as_the_Core_Technology_for_Sustainable_Domestic_Wastewater_Treatment_Consolidated_Applications_New_TrendsPerspectives_and_Challenges?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/225245842_Anaerobic_Processes_as_the_Core_Technology_for_Sustainable_Domestic_Wastewater_Treatment_Consolidated_Applications_New_TrendsPerspectives_and_Challenges?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/225245842_Anaerobic_Processes_as_the_Core_Technology_for_Sustainable_Domestic_Wastewater_Treatment_Consolidated_Applications_New_TrendsPerspectives_and_Challenges?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/223265058_A_Review_on_Anaerobic-Aerobic_Treatment_of_Industrial_and_Municipal_Wastewater?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/223265058_A_Review_on_Anaerobic-Aerobic_Treatment_of_Industrial_and_Municipal_Wastewater?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==https://www.researchgate.net/publication/223265058_A_Review_on_Anaerobic-Aerobic_Treatment_of_Industrial_and_Municipal_Wastewater?el=1_x_8&enrichId=rgreq-11087990-fa38-42a2-aff1-6d30e0238c64&enrichSource=Y292ZXJQYWdlOzI4Mzk4MDE3MDtBUzoyOTk2MDM4NDE4MzA5MTRAMTQ0ODQ0MjUzMDUyMA==


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T a

b l e 4

M a i n r e s u l t s a d d r e s s e d i n

r e v i e w p a p e r s r e g a r d i n g t h e m o s t f r e q u e n t l y a p p l i e d p o s t - t r e a t m e n t o w s h e e t s

U A S B

A S

E f u e n t c o n c e n t r a t i o n

[ A v e r a g e r e m o v a l e f c i e n c y ( % ) ]

R e f e r e n c e s

S i z e

( m 3 )

H R T

( h )

O L R

( k g C O D m

- 3

d a y -

1 )

C O D

( m g l -

1 )

S i z e

( m 3 )

H

R T

( h )

C O D

( m g l -

1 )

B O D

( m g l -

1 )

T S S ( m g l -

1 )

N H

4 – N

( m g l -

1 )

F C ( o r g / 1 0 0 m l )

H e l m .

e g g s

I n f .

E f f

.

U A S B — A c t i v a t e d s l u d g e s y s t e m s ( A S )

3 5 . 1

1 3

8 . 5

2 . 1

8 0 3

4 5 5

5 3 4 4

6 . 3

1 2 7 [ 8 4 ]

1 6 [ 9 4 ]

8 9 [ 6 2 ]

–

3 9

1 0 5

[ 5 . 8

]

–

M u n g r a y

a n d P a t e l

( 2 0 1 1 )

–

–

–

–

1 8 0 – 2 7 0

–

–

6 0 – 1

5 0

[ 7 5 – 8 8 ]

2 0 – 5

0 [ 8 3 – 9 3 ]

2 0 – 4

0 [ 8 7 – 9 3 ]

5 – 1 5 [ 5

0 – 8 5 ]

1 0 6

– 1 0 7

[ 1 – 2

]

[ 1

C h e r n i c h a r o

( 2 0 0 6 )

U A S B

P o l i s h i n g p o n d s



R e f e r e n c e s

S i z e

( m 3 )

H R T

( h )

O L R

( k g C O D m

- 3

d a y -

1 )

C O D

( m g l -

1 )

S i z e

( m 3 )

H R T

( d a y )

C O D

( m g l -

1 )

B O D

( m g l -

1 )

T S S

( m g l -

1 )

N H

4 – N

( m g l -

1 )

F C ( o r g / 1 0 0 m l )

H e l m .

e g g s

I n f .

E f f

.

U A S B — P o l i s h i n g p o n d s

1 3 . 6 – 4

4 7 7

9 . 1 – 9 . 8

–

3 1 8 – 1 1 9 4

1 4 9 – 5 1 0

1 7 5 – 4 9 3 3 3

1 . 1 – 1 2

. 4

1 8 4 [ 5 9 ] a

5 4 [ 6 7 ] a

1 3 6 [ 6 0 ] a

–

–

v o n S p e r l i n g

a n d d e

A n d r a d a

( 2 0 0 6 ) ;

S a t o e t a l .

( 2 0 0 6 ) ;

W a l i a e t a l .

( 2 0 1 1 )

–

–

–

–

1 8 0 – 2 7 0

–

–

1 0 0 – 1 8 0

[ 7 0 – 8 3 ]

4 0 – 7

0 [ 7 7 – 8 7 ]

5 0 - 8

0 [ 7 3 – 8 3 ]

1 0 - 1

5 [ 5 0 – 6 5 ]

1 0 2

– 1 0 4

[ 3 – 5

]

\ 1


( 2 0 0 6 )


1 3


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T a

b l e 4

c o n t i n u e d

U A S B

S A B



R e f e r e n c e s

S i z e

( m 3 )

H R T

( h )

O L R

( k g C O D m

- 3

d a y -

1 )

C O D

( m g l -

1 )

S i z e

( m 3 )

H R T

( h )

C O D

( m g l -

1 )

B O D

( m g l -

1 )

T S S

( m g l -

1 )

N H

4 – N

( m g l -

1 )

F C ( o r g / 1 0 0 m l )

H e l m .

e g g s

I n f .

E f f

.

U A S B — S u b m e r g e d a e r a t e d b i o l m s ( S A B )

3 5

9

1 . 6

5 2 3

1 8 6

1 2

0 . 3 4 6

8 0 [ 8 5 ]

–

2 6 [ 8 8 ]

–

–

–

G o n ç a l v e s e t a l .

( 2 0 0 2 )

–

–

–

–

1 8 0 - 2 7 0

–

–

6 0 – 1

5 0

[ 7 5 – 8 8 ]

2 0 – 5

0 [ 8 3 – 9 3 ]

2 0 – 4

0 [ 8 7 – 9 3 ]

5 – 1 5 [ 5

0 – 8 5 ]

1 0 6

– 1 0 7 [ 1 – 2

]

[ 1


( 2 0 0 6 )

U A S B

T F



R e f e r e n c e s

S i z e

( m 3 )

H R T

( h )

O L R

( k g C O D m

- 3

d a y -

1 )

C O D

( m g l -

1 )

S i z e

( m 3 )

H R T

( h )

C O D

( m g l -

1 )

B O D

( m g l -

1 )

T S S

( m g l -

1 )

N H

4 – N

( m g l -

1 )

F C ( o r g / 1 0 0 m l )

H e l m .

e g g s

I n f .

E f f

.

U A S B — T r i c k l i n g l t e r ( T F )

1 7 -

2 2

7 . 7 – 8 . 5

0 . 4 6

b – 1 . 4

3 0 3 – 5 3 2

1 0 7 – 1 7 4

3 . 8 7 – 1

8 . 7 5

2 . 5 – 3 . 6

6 3 [ 7 9 ] a

2 3 [ 8 4 ] a

1 4 [ 9 0 ] a

1 9 [ 2 7 ] a

–

–

A l m e i d a e t a l .

( 2 0 0 9 ) ; P o n t e s a n d


( 2 0 1 1 )

8 . 4

–

–

2 5 0

9 4

1 3 . 8

7

–

6 8 [ 7 6 ]

8 [ 9 1 ]

4 5 [ 7 4 ]

–

–

–

T a k a h a s h i e t a l .

( 2 0 1 1 ) c

1 6 . 8

9

1 . 2

4 5 0

1 8 0

1 . 8 5

2

5 0 [ 8 8 ]

1 0 [ 9 7 ]

2 0 [ 9 1 ]

2 [ 9 5 ]

–

–

A l m e i d a e t a l .

( 2 0 1 3 ) c

–

–

–

–

1 8 0 – 2 7 0

–

–

7 0 – 1

8 0

[ 7 3 – 8 8 ]

2 0 – 6

0 [ 8 0 – 9 3 ]

2 0 – 4

0 [ 8 7 – 9 3 ]

[ 1 5 [ \

5 0 ]

1 0 6

– 1 0 7

[ 1 – 2

]

[ 1


( 2 0 0 6 )

U A S B

C W



R e f e r e n c e s

S i z e

( m 3 )

H R T

( h )

O L R

( k g C O D m

- 3

d a y -

1 )

C O D

( m g l -

1 )

S i z e

( m 3 )

H R T

( h )

C O D

( m g l -

1 )

B O D

( m g l -

1 )

T S S

( m g l -

1 )

N H

4 – N

( m g l -

1 )

F C ( o r g / 1 0 0 m l )

H e l m .

e g g s

I n f .

E f f

.

U A S B — C o n s t r u c t e d w e t l a n d s ( C W )

7 – 2 5

. 5

6 – 1 1

0 . 7 2 – 2 . 2

3 1 5 – 1 0 5 0

1 4 5 – 5 2 5

4 3 . 4 – 7

8

1 . 2 – 4 . 9

5

7 3 [ 6 7 ] a

1 6 [ 8 5 ] a

9 [ 8 4 ] a

2 5 [ 2 2 ] a

4 . 7 9

1 0 5

a

–

G r e e n e t a l . (

2 0 0 6 ) , R u i z

e t a l . (

2 0 0 8 ) , D o r n e l a s

e t a l . (

2 0 0 9 )

a

A v e r a g e v a l u e s

b

O r g a n i c l o a d i n g r a t e i n k g B O D m

- 3

d a y -

1

c

T r i c k l i n g l t e r e m p l o y i n g p o l y u r e t h a n e s p o n g e m e d i a


1 3


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Additionally, in terms of efuent quality improve-ment, it is worth mentioning the treatment potentialsof anaerobic membrane bioreactors (AnMBRs).AnMBRs can provide an alternative strategy fordomestic wastewater treatment, especially at lowtemperatures, where hydrolysis of particulate matter

is the rate-limiting step (Lettinga et al. 2001b). Basedon various review papers focusing different aspects of AnMBRs (Liao et al. 2006; Smith et al. 2012;Skouteris et al. 2012; Lin et al. 2013; Ozgun et al.2013), some points can be highlighted, comprisingadvantages and critical obstacles to full-scaleimplementation:

2.2.1 Advantages

• There are broad integration possibilities of mem-branes with different types of anaerobic reactors

systems, both completely mixed and sludge reten-tion systems. Recent research shows promisingpotentials of integration with UASB reactors sincethey provide an SS reduction by entrapment andbiodegradation in the sludge bed. This reduced SSload to the membrane minimizes fouling due tocake layer formation and cake compression.

• In addition to reaching a high efuent quality, interms of COD, SS and pathogen counts, the

permeate of AnMBRs should be of interest foragricultural use, since macronutrients are notremoved by anaerobic bioprocess.

• The improved SRT may reduce the start-up periodin comparison to other anaerobic systems.

2.2.2 Critical obstacles

• There is a lack of long term reliability andoperability evaluations of AnMBRs in municipal

wastewater treatment, as well as fundamentalinformation on cost and energy issues. Besides,most of the research reported is restricted to bench-scale experiments.

• The main drawbacks such as low ux, membranefouling, high capital and operational costs are stilllimiting the economic feasibility of AnMBRs.Novel developments using lter cloths instead of real membranes may importantly reduce thecapital costs (Ersahin et al. 2014).

• The lower limits of HRT and temperature, as wellas the relationships among HRT, SRT and mem-brane fouling, have yet to be established for anadequate treatment performance.

3 Centralised versus decentralised approach

Historically, sewerage systems were constructed toconvey sanitary ows and urban spills away frompopulated areas. In the many expanding cities of the19th and 20th century this indeed improved thehygienic conditions considerably, leading to a drasticdrop in waterborne diseases. The collected sewage wassubsequently discharged to surface waters, threatening

the environmental health of the receiving water bodies.The latter, however, was not yet part of governmentalregulations. In the industrialized countries of WesternEurope and Northern America, environmental regula-tions were only implemented in the last 3–4 decades of the past century. The large cities, which were alreadyserved with extensive sewerage systems, were alsotargeted to be the rst served by STPs. The hugesewage ows of these cities had a tremendous impacton the environmental health of the recipient waterbodies. In most cities, the rst STPs were located at the

central outfall of the sewerage prior to discharge toopen surface waters. By addressing this large pointsource, the environmental impact could be reduced byimplementing a single STP. As such, centralizedsewage treatment was borne, being a logic conse-quence of historic developments. However, this cen-tralized approach also puts a nancial burden toauthorities for constructing, maintaining, and extend-ing these services to all citizens (Lettinga et al. 2001a ).

In the past decades, the centralized treatmentapproach, with its advantages of economy of scale,

developed as a kind of blue print for sanitary systems,sewerage and treatment. Particularly in hilly areas, thecentralized sewerage systems requirepumping stationsand siphons, as well as large trunk sewers in order tocollect all the sewage from the expanding cities. Withthe full coverage by multi-tap drinking water supply athousehold level and the increase in drinking waterconsumption, the sewage outfalls became huge and soalso the required STPs. The latter became industrialcomplexes consisting of advanced technology,


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requiring highly qualied personnel. The discrepancybetween the served large areas in industrializedcountries and non-served areas in the less prosperouscountries became larger and larger. Up to date thecentralized approach is more than often considered asthe blue print for adequate sanitation and environmen-

tal protection, also in developing countries. This hasresulted in situations where governments pursuecentralized sanitation and high-level treatment but isnot able to implement this owing to huge nancialconstraints (van Lier and Lettinga 1999). Painfulexample can be found in the Middle East wherestringent environmental laws are indeed met at veryfew centralized treatment plants in the large urbanareas of e.g. Cairo, whereas the majority of the countryis not even served by primary treatment.

Recognized constraints of the centralized approachare:• High investments costs for (trunk) sewers, pump-

ing stations and siphons. Regular maintenance isindispensable and renovations are required every60–70 years.

• Limited exibility owing to long planning horizons.Difcult to anticipate on large demographic changes.

• Central outow (even if treated) poses a high loadof pollutants to the environment. As such, moreadvanced treatment is required with a higher

degree of centralization.• Gravity ow sewer systems require minimum owconditions to prevent sewer clogging. In (semi) aridclimate countries, which suffer from limited tapwater supply, minimum ows are not guaranteed.

• Centralized systems generally consist of sewersthat carry both urban sanitation and urban drainageof pluvial waters. This approach results in largeows of contaminated water.

• Extensive combined sewerage networks have lim-ited hydraulic capacity. Exceeding this capacity

results in sewage overows, contaminating theenvironment.• Extensive sewerage systems are vulnerable for

ruptures and cracks, particularly in seismic sensi-tive areas, which may result in severe pollution of water reservoirs and aquifers.

• Urban population sense little ownership of cen-tralized services, possibly resulting in dischargesof hazardous compounds into the sewer byresidents, industries, etc. (‘out of eye, out of

concern’). Toxic discharges will constrain the STPand the possible reuse of treatment by-products.

• Combined centralized sewer systems in relation toa fully paved urban environment results in thepossible exportation of rainwater from the resi-dential areas, leading to decreasing groundwater

levels in the urban area.

3.1 Optimal degree of decentralisationand existing examples

Local conditions fully determine what will be the mostproper sanitation approach taking socio-economic andenvironmental constraints intoaccount.Proper sanitationis a function of mass ow per areaper timeunit, in whichsocio-economic factors determine the pallet of sanitationsolutions (Letema et al. 2014). Sanitation option criteriawill nally determine what solution is most adequate at aspecic location (Malekpour et al. 2013). Generally,economic considerations determine the paceof sewerageinfrastructure investments, meaning that the poorestregions are often refrained from proper sanitation. Adecentralised approach may help in advancing onlocalised proper sanitation, without having the need torstly provide a massive sewerage infrastructure (Mas-soud et al. 2009; Al-Shayah and Mahmoud 2008; vanLier and Lettinga 1999; Lettinga 2006). Furthermore,decentralized systems allow for exibility in manage-ment and a series of processes can be combined toprogressively meet treatment goals and address environ-mental and public health protection requirements (Mas-soud et al. 2009), as depicted in Fig. 3.

With regard to water reuse, decentralisation showsvarious advantages which, so far, are hardly taken intoaccount in sewerage master plans. Decentralisationprevents the mixing of wastewaters coming fromhouseholds and industries, providing better opportuni-ties for agricultural reuse (Huibers and van Lier 2005;

van Lier and Huibers 2004, 2010). Decentralisationalso offers potentials for localised water reclamation,avoiding large sewage collection and treated waterdistribution systems (van Lier and Lettinga 1999). Adecentralised approach also provides the opportunity tokeep wastes concentrated, facilitating the treatmentand recovery of valuable resources from the sewage,such as energy and the nutrients nitrogen and phos-phorus (Zeeman et al. 2008; Kujawa-Roeleveld andZeeman 2006). The latter is currently being researched


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at demonstration and even full-scale in countries like

Germany, Sweden and the Netherlands (Zeeman et al.2008). By separating the black toilet waters from thehousehold grey waters, dilution of the most hazardouspollutants is prevented. In the meantime, the poten-tially valuable resources are kept concentrated, partic-ularly when the black water collection systems isoperated with extreme low water volumes. This can beachieved by using vacuum sewer systems that only use0.7–1.0 l per ush (Zeeman et al. 2008). The optimaldegree and the way that decentralisation is imple-mented depends on a number of site-specic condi-

tions. Interestingly, irrespective these conditions,present research at various locations couples decen-tralisation to resource recovery, instead of purelysolving a sanitary problem. By adding a value chain tothe sanitary ows, the implementation of propersanitation systems might be enhanced, more rapidlyserving a larger share of the population. In the abovedecentralised examples, anaerobic digestion plays acentral role in stabilising the (concentrated) sewageand/or the faecal matter, meanwhile converting theorganic matter into biogas. Particularly for developing

countries, the avoidance of fossil energy for sewageand/or slurry treatment is advantageous for anydecentralised application, lowering the threshold fortechnology implementation.

4 Current limitations and constraints

Although the application of anaerobic technology forsewage treatment has signicantly expanded in the last

two decades (Lettinga and Hulshoff Pol 1991; Foresti

2001a , b; Florencio et al. 2001; Chernicharo andNascimento 2001; Wiegant 2001; Chernicharo et al.2009), some limitations and constraints still need to besolved and have guided the investigations of manyresearch institutions and operators, as discussed in thissection. Especially the design, operational, and man-agerial aspects of UASB reactor systems need improve-ments, since thefurther expansion of thetechnologyandits wider acceptance in the near future can be signi-cantly hindered by sub-optimal functioning UASBs.

Research has been focused on topics aiming at

improving the design and operation of UASB reactors.Particularly research related to scum accumulation,biogas and waste gas management, post treatment andenergy recovery, have received most attention, ashighlighted in Fig. 4.

The main constraints that remain are the potentialodor problems and difculties associated with it, butalso on the increasing demand for nutrient removal inthe treatment scheme, as well as on problems inoperation and maintenance as discussed below. Theoverall advantages and constraints of anaerobic

sewage treatment in comparison to activated sludgeprocesses are listed in Table 5.

4.1 Temperature constraints

Sewage treatment by anaerobic systems in temperateclimates is still considered a challenge since municipalwastewater belongsto the complex wastewater categorydue to the high fraction of particulate organic material(suspended solids), moderate biodegradability and low

Fig. 3 General objectivesof wastewater managementreected on a decentralisedsanitation approach.Adopted from Massoudet al. (2009)


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strength (Lettinga et al. 2001a). The suspended solidsmay constitute 50–65 % of the total COD. Therefore,total CODconversionis largely limited by hydrolysis of particulate matter. Particularly when the sewage tem-perature drops to \ 18 C, the biological conversioncapacitywill determine the overall COD removal ratherthan the prevailing hydrodynamic conditions. In fact,

because of the low temperature and the high TSS/CODratio, the range in which the HRT determines thevolumetric sizing of the UASB reactor, viz.Vr = HRT.Q, is relatively small. When temperaturedrops and non-digested sludge starts to accumulate inthe sludge bed, the hydrolytic and methanogeniccapacity of the sludge will gradually decrease,

Fig. 4 Topics of interest forimprovements in UASBreactors treating domesticwastewater. Source :Chernicharo et al. ( 2013)

Table 5 Advantages and constraints of high-rate anaerobic sewage treatment systems over aerobic processes

Advantages Constraints

Substantial (reaching 90 %) savings in operational costs as noenergy is required for aeration

Potential reductions in investment cost considering that primaryclarication, the bioreactor, secondary clarication and thesludge digester are combined into one tank: the UASB reactor.However, the UASB reactor needs to be extended by a posttreatment step to reach efuent requirements

The produced methane (CH 4) is of interest for energy recovery orelectricity production

The technologies do not make use of high-tech equipment, exceptfor main headwork pumps and ne screens. The treatmentsystem is less dependent on imported technologies

The process is robust and can handle periodic high hydraulic andorganic loading rates

The system is compact with HRTs of 6–9 h, and is, therefore,suitable for applications in urban areas, minimizing conveyancecosts

Small-scale applications allow decentralized treatment, makingsewage treatment less dependent on the extent of sewagenetworks

The sludge production is low, well stabilized and easilydewatered; consequently, it does not require extensive post-treatment

The valuable nutrients (N and P) are conserved which give thetreated wastewater a high potential for crop ferti-irrigation

The extent of organic matter removal is less than the activatedsludge processes, requiring in most cases adequate post-treatment to meet the discharge or reuse criteria

The produced CH 4 is partially dissolved in the efuent(depending on the inuent COD concentration and theapplicable hydraulic ow). So far no measures are applied infull-scale plants to prevent CH 4 escaping to the atmosphere

The collected CH 4 is often not utilized for energy generation andin some cases not even ared (contribution to greenhouse gasemissions)

There is little experience with full-scale application at moderateto low temperatures

Reduced gases, like H 2S, that are dissolved in the efuent mayescape causing odor problems

High inuent sulfate concentrations may limit the applicability of sewage treatment as it results in the conversion of organicBOD/COD to inorganic BOD/COD, meaning that organicmatter gets degraded meanwhile the sulfate gets reduced to theodorous and corrosive sulde

Adapted from van Lier et al. ( 2008)


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deteriorating both particulate and soluble CODremoval, and eventually leading to reactor failure.Apparently, the prime design criterion, even with dilutedomestic sewage, is the reactor solids retention time(SRT), which should be above a minimum value inorder to maintainthemethanogenicconversion capacity

of the sludge. With dilute domestic sewage undertropical conditions, COD \ 1000 mg l - 1 andt [ 20 C, this condition will be always met. Theprevailing SRT depends on various sewage character-istics such as:

• Sewage temperature.• Inuent suspended solids concentration.• Rate of solids digestion in the reactor.• Filtering capacity of the sludge bed, which are

determined by the applied upow velocities and

sludge characteristics.• Growth and decay of new sludge.• Sludge retention in the settler, determined by the

applied liquid velocities.• Withdrawal of excess sludge.

As a rule of thumb, the minimum SRT shouldalways be more than 3 times the doubling time (Td) of the biomass, which is responsible for the rate-limitingstep (van Lier et al. 2008). Since bacterial growth ratesare exponentially correlated to the temperature, therequired SRT will distinctly increase when the sewagetemperature drops. Therefore, the conventional UASBreactor design for municipal wastewater needs recon-sideration when the system will be applied at lowtemperatures and/or when COD concentrations exceed1000 mg l - 1 . In many arid climate countries withlimited water supply, sewage concentrations rangebetween 1000 and 2500 mgCOD l - 1 , e.g. MiddleEast, Northern Africa, Arabic peninsula, etc. Further-more, the temperate climates in the Middle East andNorthern Africa are characterised by cold winters,particularly in mountainous areas.

Experiences in Jordan and Palestine, show munic-ipal sewage COD concentrations reaching2500 mgCOD l - 1 at TSS/COD ratio’s of 0.6 (Halal-sheh et al. 2005a; Mahmoud et al. 2003, 2004;Mahmoud 2008), whereas winter temperatures maydrop to 15 C. Applying the conventional UASBreactor design, the HRT needs to be increasedreaching values of 20–24 h (Halalsheh 2002). This,obviously, will affect the hydrodynamics of the systemrequesting changes in inuent distribution for

preventing short-circuiting. Alternatively, the largesuspended solids load can be addressed in separatereactor units such as a primary clarier or enhancedsolids removal in upow lter systems, coupled to asludge digester (Elmitwalli 2000). A novel approach isto link the UASB reactor to a coupled digester with

sludge exchange (Mahmoud 2002; Mahmoud et al.2004). With the latter system, accumulating solids willbe digested at higher temperatures, whereas themethanogenic activity in the reactor will be increasedby a return digested sludge ow.

Because of climate constraints, the full-scale reac-tor in the Fayoum area, south of Cairo, Egypt, isdesigned for an average HRT of 12 h. Pilot trials inAmman showed the feasibility of the system as anideal pre-treatment method for a low cost reduction inthe COD-load, while generating energy for post-treatment. Table 6 briey resumes the most importantresults of the Jordan Pilot trials (Hallalsheh et al.2005b).

With regard to the required higher SRT at lowtemperatures, AnMBRs have recently emerged as apotential technology. Aside from the current criticalobstacles to full-scale implementation, as previouslydiscussed, the physical biomass retention provided bythe membrane may compensate the decreased specicmethanogenic activity (SMA) and biological removalrate at low temperatures (Ho and Sung 2010;Martinez-Sosa et al. 2011 ). Recently reported researchresults have demonstrated the potentials for achievinghigh quality efuents using AnMBR systems underpsychrophilic conditions: Smith et al. ( 2013) haveobserved 92 ± 5 % COD removal in an anaerobicbench-scale CSTR coupled with membranes at 15 C,while Gouveia et al. ( 2015) obtained similar results(87 ± 1 %) with a pilot UASB with ultraltrationmembranes at 18 C. Additionally, the use of expanded granular sludge bed reactors (EGSB) inAnMBRs was suggested as a potential technology,based on the high COD removal efciencies even atlow temperatures (Chu et al. 2005). Recently, Ozgun(2015) coupled the previously mentioned UASB-Digester system of Mahmoud et al. ( 2004) to anexternal UF membrane for cost-effective water recla-mation under low temperature conditions. Where theUF membrane served as an absolute barrier leading toCOD removal efciencies exceeding 90 %, the addi-tion of a separate digester for non-stabilised sludgedigestion resulted in an improved ltration


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oxidation to nitrogen gas, the so-called anammoxreaction (Sá nchez Guillé n et al. 2014, 2015).

The metabolic routes to remove nitrogen based onpartial nitrication and anammox, like Sharon–Anam-mox and CANON processes (van Dongen et al. 2001;Third et al. 2001) have been mainly applied to treat

concentrated nitrogen containing wastewaters, such assludge digester efuents at STPs (van Loosdrecht2008). The application of the anammox process in themain stream of STPs remains as a challenge for currentand future research. Notwithstanding, with deam-monication processes (removal of nitrogen viaanammox bacteria) it is possible to remove nitrogenon a low energy basis, instead of the conventionalnitrication and denitrication approach. The successof such deammonication process critically dependson stimulation of ammonium oxidizing bacteria(AOB) and suppression of nitrite–oxidizing bacteria(NOB). Possibly, required conditions might beachieved applying an intermittent aeration regime inthe mainstream aeration tanks (Wett et al. 2013).

In this context, a two-step process like UASB-Trickling Filters with polyurethane support media canconstitute a promising alternative to remove nitrogenas a low cost process. The hydrolysis of biomass due tohigher SRT can be an additional source of substrate inthe anoxic zones of the sponge, favouring hetero-trophic denitrication (Tawk et al. 2006; Kubotaet al. 2014; Almeida et al. 2013). These anoxic zoneswould also favour the activity of ammonium tonitrogen gas—oxidizing bacteria.

The application of biological phosphorus removalin combination with UASB technology is virtuallyimpossible for two main reasons: (1) the efuent of theanaerobic reactor doesn’t contain easily biodegradablematter anymore and (2) if one would be able tocultivate phosphorus-rich sludge in a subsequent bio-Pstep by by-passing part of the inuent, then stabilisa-tion of the excess bio-P sludge in the precedinganaerobic reactor makes no sense since all boundphosphorus will be released. At present, phosphorusremoval in treatment plants using anaerobic reactorsseems only be effective if chemical products are usedfor P precipitation (iron or aluminum salts).

By applying source separation in a decentralisedapproach, P could be recovered from the concentratedwaste stream via precipitation or crystallisation tech-niques. The controlled formation of struvite (MgNH 4-PO4 6H2 O) or MAP (magnesium, ammonium,

phosphate) crystallization process has been success-fully reported for different kinds of concentratedwastewaters (Liu et al. 2013). However, struviteformation in an anaerobic STP has not been demon-strated so far. Very likely, the concentrations inmunicipal sewage are simply too low for a cost-

effective precipitation process.

4.3 Restriction for pathogens and microbiologicalindicators

As with most secondary treatment methods, compactanaerobic processes are not efcient in eliminatingpathogenic organisms from the efuents and, as aresult, require a post-treatment stage if pathogenremoval is pursued. For small systems and underproper conditions, polishing ponds can be a veryeffective method for improving the microbiologicalquality of anaerobic efuents (von Sperling et al.2004). If properly designed and implemented, they canachieve very high levels of pathogen removal, withvirtually 100 % helminth eggs and protozoan cystsremoval, and 3–6 log units’ removal for bacteria andviruses (von Sperling and Chernicharo 2005). Inaddition, the ponds also polish the anaerobic efuentin terms of organic matter and oxidize ammonia.Alternatively, the solubilized ammonia can beremoved mainly through algal uptake or volatilizedin the form of ammonium (NH 3) due to the high pH asa result of an intense phototrophic activity (CamargoValero and Mara 2007).

In situations when land availability is limited, acompact disinfection process, such as chlorination, UVradiation and ozonation, should be regarded as an optionfor the post-treatment, as means of improving the overallefciency of pathogen removal, especially bacteria andviruses. However, with regard to chlorination, the risk of the formation of disinfectant by-products is very high,owing to the relatively high concentrations of residualorganic matter in the UASB efuents.

Cost-effective pathogen removal along with exten-sive aeration of residual compounds was obtained inthe so-called Downow Hanging Sponge (DHS)system in combination with a UASB pre-treatment(Uemura and Harada 2010; Tandukar et al. 2005). TheDHS is in fact a biotower trickling lter withreinforced polyurethane as packing material. Owingto the open structure of the DHS, the efuent ispassively fully aerated by improved convective


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airows. The developing aerobic biomass appeared tobe a very successful scavenger of colloidal pathogenicbiomass.

Another alternative that has been addressed in lastyears is the incorporation of membranes to anaerobicmunicipal wastewater treatment, especially due to the

superior efuent quality in terms of pathogen countswhen compared with conventional anaerobic pro-cesses (Liao et al. 2006; Kocadagistan and Topcu2007; An et al. 2009). This would represent animportant upgrade alternative for existing anaerobicSTPs (Ozgun et al. 2013), although drawbacksregarding membrane fouling is still a concern.

4.4 Restrictions for micropollutants

Micropollutants represent a group of several classes of medicine rests (e.g., analgesics, antibiotics, lipid-regulators, anti-inammatories, synthetic hormones,etc.), as well as substances used in cleaning andpersonal care products, compounds used in theproduction of resins and plastics, pesticides, andnatural hormones and their by-products (Froehneret al. 2011; Brandt et al. 2013). They have recentlygained great interest due to their adverse effects on theaquatic life (Kim and Aga 2007). Particularly, STPsare considered as one of the main ‘hotspots’ of potential evolution and spreading of antibiotic resis-tance into the environment (Michael et al. 2013). Thusfar, STPs are not designed to specically removemicropollutants, especially pharmaceuticals and endo-crine disrupting chemicals (EDC). Therefore, anyremoval that may occur is incidental to the wastewatertreatment processes and the characteristics of themicropollutant (USEPA 2009). In this context, moststudies worldwide have assessed the behaviour of micropollutants in activated sludge systems andmembrane bioreactors (Gulkowska et al. 2008; Sipmaet al. 2009; Li and Zhang 2010).

Since some of those compounds are hydrophilicand designed to be biologically resistant, they areexpected to remain in the aqueous phase of thewastewater. Nevertheless, Froehner et al. ( 2011 )showed that the water-soluble compounds such ascaffeine and bisphenol-A are removed almost com-pletely, regardless of the type of treatment chosen(aerobic or anaerobic). However, hydrophobic com-pounds such as hormones are not completely removed,and for the degradation by both aerobic and anaerobic

pathway means the HRT is conserved as a key factor.In this regard, Brandt et al. ( 2013) conrmed that theHRT is an important parameter controlling theremoval of hydrophilic and less biodegradable con-taminants, such as sulfamethoxazole and trimetho-prim. Meanwhile, the authors stated that UASB

reactors were not appropriate for an efcient removalof nonylphenol, bisphenol A, diclofenac, bezabrate,sulfamethoxazole and trimethoprim. In this context,the post-treatment units (polishing ponds, submergedconstructed wetlands and trickling lters) substan-tially increased the removal of most of the targetmicropollutants present in the anaerobic efuent.Therefore, simplied sewage treatment systems,which are comprised of UASB reactors followed bynatural (submerged bed, polishing ponds) or compact(trickling lter packed with sponge-based material)post-treatment units, can remove hydrophilic andhydrophobic pharmaceuticals and EDC as efcientlyas activated sludge systems (Brandt et al. 2013).

5 Odour nuisance

Odorous emissions are a huge concern in anaerobicreactors treating domestic sewage, which certainlymay hamper the diffusion of the technology, espe-cially in urbanised areas. To avoid population’scomplaint, several sewage treatment plants have beenemploying considerable amounts of chemical prod-ucts, with the goal to minimize or mask the hydrogensulde and/or other odorous emission in the vicinity.In most cases, there is no clear identication of theemission’s source, which may be related to the inuentsewage characteristics, reactor performance or theturbulent discharge of the efuent.

Methane and carbon dioxide are the main gaseousproducts of anaerobic digestion; nevertheless,depending on the nature of the incoming precursors,pH and redox potential, different odor-related sub-stances may be biologically formed in anaerobicreactors. Most of the odorous compounds are reducedsulfur and amino compounds, such as suldes,mercaptans, and amino-suldes. Hydrogen sulde,resulting from the de-assimilative reduction of sul-fates or thi

chernicharo et al anaerobic sewage treatment 2015

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