Characteristics, Process Parameters, and Inner Components of

Review ArticleCharacteristics Process Parameters and Inner Components ofAnaerobic Bioreactors

Awad Abdelgadir12 Xiaoguang Chen1 Jianshe Liu1 Xuehui Xie1 Jian Zhang1

Kai Zhang1 Heng Wang1 and Na Liu1

1 State Environmental Protection Engineering Center for PollutionControl in Textile College of Environmental Science and EngineeringDonghua University Shanghai 201620 China

2 Industrial Research and Consultancy Center (IRCC) Khartoum 13314 Sudan

Correspondence should be addressed to Xiaoguang Chen cxgdhueducn

Received 20 September 2013 Revised 6 November 2013 Accepted 6 November 2013 Published 23 January 2014

Academic Editor Chong-Jian Tang

Copyright copy 2014 Awad Abdelgadir et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

The anaerobic bioreactor applies the principles of biotechnology and microbiology and nowadays it has been used widely in thewastewater treatment plants due to their high efficiency low energy use and green energy generationAdvantages anddisadvantagesof anaerobic process were shown and threemain characteristics of anaerobic bioreactor (AB) namely inhomogeneous system timeinstability and space instability were also discussed in this work For high efficiency of wastewater treatment the process parametersof anaerobic digestion such as temperature pH Hydraulic retention time (HRT) Organic Loading Rate (OLR) and sludgeretention time (SRT)were introduced to take into account the optimumconditions for living growth andmultiplication of bacteriaThe inner components which can improve SRT and even enhance mass transfer were also explained and have been divided intotransverse inner components longitudinal inner components and biofilm-packing material At last the newly developed specialinner components were discussed and found more efficient and productive

1 Introduction

Anaerobic digestion (AD) is an attractive option for wastetreatment practice in which both energy recovery and pol-lution control can be achieved Anaerobic degradation ordigestion involves the breakdown of biomass by a concertedaction of a wide range of microorganisms in the absenceof oxygen The biological processes are essentially used toremove contaminants in wastewater treatment and nowa-daysmany biological treatment options are available and haveshown encouraging results over the treatment of complexorganic matter [1 2] Comparing between anaerobic andaerobic process anaerobic process is especially consideredas a suitable treatment option due to low-energy require-ments and little quantities of sludge production Thereforeanaerobic process has become increasingly demanding inthe treatment of complex industrial wastewater which maycontain toxicmaterials or even low concentrations of domes-tic wastewater [3 4] The ability to attain environmental

protection and resource preservation anaerobic treatmentprocess and anaerobic bioreactors has received great atten-tion [3 5 6]

The anaerobic digestion process is a simple and appliedenergy source A simple digester consists of a digestion cham-ber a dome an inlet an outlet for biogas and an outlet forslurry The biogas trapped by the dome flows under pressurethrough the outlet where it can be used as an energy sourceTheuse of anaerobic reactor began in 1859with the first anaer-obic digester that was built by a leper colony in Bombay India[7] And then in 1895 the technologywas developed in ExeterEngland where a septic tank was used to generate gas for thesewer gas destructor lamp a type of gas lightingThereafter inthe 1930s anaerobic digestion gained academic recognitionthrough scientific research [8]The septic tank represents thefirst generation of anaerobic bioreactor (AB) In the late 1970sthe upflow anaerobic sludge blanket (UASB) process wasdeveloped by Dr Gatze Lettinga and colleagues to representthe second generation of AB [9 10] In the beginning a

Hindawi Publishing CorporationBioMed Research InternationalVolume 2014 Article ID 841573 10 pageshttpdxdoiorg1011552014841573

2 BioMed Research International

Table 1 Advantages and disadvantages of anaerobic process [3 15]

Advantages Disadvantages(i) Reduction of greenhouse gasemissions through methane recovery(ii) High treatment efficiency forbiodegradable sludge(iii) Production of methane gas(potential source of fuel)(iv) A high degree of wastestabilization is possible(v) Simplicity(vi) Flexibility anaerobic treatmentcan easily be applied on either a verylarge or a very small scale(vii) Space saving (higher loading ratesrequire smaller reactor volumesthereby saving on disposal cost)(viii) Less requirement of energy andoxygen(ix) Inoffensive residual sludge may beused as soil conditioner(x) Low nutrients and chemicalsrequirement

(i) Long recovery time itmay take longer time forthe system to return tonormal operatingconditions if shock loadinghappens(ii) Low pathogen andnutrient removal(iii) Long startup(iv) Possible bad odors(v) High sensitivity ofmethanogenic bacteria to alarge number of chemicalcompounds(vi) Small- andmiddle-scale anaerobictechnology for thetreatment of solid waste inmiddle- and low-incomecountries is still relativelynew

UASB reactor was just like an empty tank (thus an extremelysimple and inexpensive design) but an important innercomponent the three-phase separator is added to avoidwashout of granular sludge occurred The third generationof AB such as expanded granular sludge bed (EGSB) andinternal circulation (IC) reactor was developed on thefoundation of the second generation For instance the fasterrate of upward-flow velocity is designed for the wastewaterpassing through the sludge bed The increased flux permitspartial expansion (fluidization) of the granular sludge bedimproving wastewater-sludge contact as well as enhancingsegregation of small inactive suspended particle from thesludge bedThe increased flow velocity is either accomplishedby utilizing tall reactors or by incorporating an effluentrecycle (or both) [3 11ndash13] Some super-high-rate anaerobicbioreactors (SAB) were developed recently by Chen et al[11ndash13] The development of the third generation anaerobicbioreactors and SAB shows that the process parameterssuch as upflow velocity Sludge Retention Time (SRT) andHydraulic Retention Time (HRT) and bioreactor structure(inner components) are the two most important factorsfor microorganismsrsquo cultivation for anaerobic bioreactors[3 11ndash13] Therefore This work will present the advantagesand disadvantages of anaerobic process and explain therepresentative characteristics of anaerobic bioreactor It alsointroduces main process parameters inner components andtheir effects on the performance of wastewater treatment inanaerobic bioreactors

2 Advantages and Disadvantages ofAnaerobic Process

Anaerobic treatment (digestion) is a proven way and efficientmethod to produce biogas (methane) that can be used for

the production of renewable heat and power and a compostlike output The principle of anaerobic treatment is theutilization of anaerobic bacteria (biomass) to convert organicmatter (pollutants) or COD (chemical oxygen demand) intomethane rich biogas in the absence of oxygen

The early stages of the formation of anaerobic granulesfollow the same principles in the formation of biofilm ofbacteria on solid surfaces There is strong evidence thatinert carriers play an important positive role in granulationMany researchers conclude thatMethanosaeta concilii is a keyorganism in granulation [14]

When the system is in balance themethanogenic bacteriause the acid intermediates as rapidly as they appear Howeverif the methane bacteria are not present in suitable numbersor are being slowed down by unfavorable environmentalconditions they will not use the acids as rapidly as theyare produced by the acid formers and the volatile acids willincrease in concentration Thus an increase in acid concen-tration indicates that the methane formers are not in balancewith the acid formers [5] Classification of bacteria dependsupon temperature classes where mesophiles bacteria are likemesophilic temperature while thermophiles bacteria are likethermophilic temperature Advantages and disadvantages ofanaerobic treatment processes are shown in Table 1

3 Characteristics of Anaerobic Bioreactor

31 Inhomogeneous System Anaerobic reactor operatesunder an inhomogeneous system that means that theanaerobic treatment is done through three phases solid(sludge) liquid (wastewater) and gas (methane)

311 Solid Phase Solid phase consists of sludge granuleswhich have a diameter around 05 to 2mm [14] which existin the lower part of the reactor Sludge granules play animportant role for successful operation of UASB and EGSBtechnology a sludge granules are the sum of microorganisms(Bacteria) forming during the treatment of wastewater inan environment with a constant upflow hydraulic regimewithout any support matrix the surrounding and suitableenvironment for bacteria survive is occurring during flowconditions and therefore bacteria able to contact togetherand start growth and proliferate

312 Liquid Phase Liquid (wastewater) flows upwardsthrough a sludge bed located in the lower part of the reactorwhile the upper part contains a three phases (solid liquid andgas) of separation system Three-phase separation device isthe most characteristic feature of UASB reactor It facilitatesthe collection of biogas and also provides internal recyclingof sludge by disengaging adherent biogas bubbles from risingsludge particles

313 Gas Phase Biogas typically refers to a gas producedby bacteria that breakdown organic matter in the absenceof oxygen (organic waste such as dead plant and animalmaterial animal feces and kitchenwaste or industrial organicwaste can be converted into a gaseous fuel called biogas)The

BioMed Research International 3

Influent

EffluentBiogas

Cmnminus1

Fwnminus1

Cmn

ΔVnminus1

ΔVn

Fwn

Φgnminus1

Φmnminus1

Φmn

Figure 1 The granular sludge dynamic behavior

most important thing is that biogas can result in the dynamicbehavior of granular sludge [13]

In Figure 1 120601119892119899minus1 is gas production inΔ119881119899minus1 m3 hminus1 120601119898119899

is downwards transport of sludge from Δ119881119899 to Δ119881119899minus1 kg hminus1

120601119898119899minus1 is sludge transport flux fromΔ119881119899minus1 toΔ119881119899 kg hminus1119862119898119899

is sludge concentration (TSS) inΔ119881119899 kgmminus3119862119898119899minus1 is sludge

concentration (TSS) in Δ119881119899minus1 kgmminus3 119865119908119899minus1 is up-moving

wake stream in Δ119881119899minus1 m3 hminus1 and 119865119908119899 is backmix stream in

Δ119881119899 m3 hminus1

Figure 1 explains the relationships that happen while themovements of sludge up and down due to gas productionand therefore the transport power of sludge resulted fromthe upward fluid flow led by influence and the up-movingwake stream (119865119908119899minus1 m

3 hminus1) led by gas production (120601119892119899minus1)Buijs et al (1982) reported that the sludge transport efficiencyof up-moving biogas can reach up to 202 plusmn 21m3m3(sludgebiogas) in a UASB reactor [16] Figure 1 suggestedthat the downward transport of sludge (120601119898119899 Kg h

minus1) fromΔ119881119899 to Δ119881119899minus1 was caused due to the settling of sludge and bythe back mix stream [13]

32 Time Instability Anaerobic Bioreactor is used for treat-ment of wastewater consisting of complex organic matters Itis become more complicated with the change in productioncycles and quantities Various industrial processes operatingunder different conditions (times temperature and pH) witha different range throughout the four seasons of the year havecreated a challenge on AB Due to the inherent limitationsof anaerobic treatment technologies there is a need to focuson the improvement of these drawbacks thus challenging thedesigners and engineers [6]

Many small sewage treatment plants are operated inde-pendently in local cities due to encouraging processing byanaerobic digestion at a centralized sewage treatment plant(STP) high-solid sewage sludge is helpful because it reducesthe energy and cost required for transporting the sludge fromother STPs Hidaka et al [17] reported that under mesophilic

Complex organic matter

Proteins Carbohydrates Fats

Hydrolysis

Acidogenesis(fermentation)

Intermediates products(butyrate and propionate)

Acetogenesis

Hydrogen and carbon dioxideAcidic acids

Methane and carbon dioxide

Methanogenesis

Fatty acids Amino acids Sugar Soluble organic molecules

Figure 2 The key process stages of anaerobic digestion

condition anaerobic digestion of sewage sludge of totalsolids concentrations (TS) of 10 was successfully treatedwhile under the thermophilic condition sewage sludge of75 TS was not successfully treated when the total ammo-nia concentration was over 2000mgNL But thermophilicanaerobic digestion successfully reduced Salmonella spp andEscherichia coli is below detection limits but not Clostridiumperfringens Spores Thus the final product met Class Abiosolidsrsquo final disposal regulations but further investigationis needed in order to satisfy the future European legislation[18]

33 Space Instability The microbial consortia which achievethe conversion of complex organic matter into biogas areformed of several groups and each performs a specificfunction in the digestion process Together they achieve theconversion of organic matter into biogas through a sequenceof stages The initial stages generate short chain or volatilefatty acids (VFA)The final stage ismethanogenesis (methaneformation) where methanogenic precursors primarily aceticacid and hydrogen are converted to methane and CO2Figure 2 explains the key process stages of anaerobic digestion[19]

The first stage of digestion process is hydrolysis Thisstep is very important for the anaerobic digestion processsince polymers cannot be directly utilized by the fermentativemicroorganisms Therefore the insoluble complex organic


matter such as cellulose converts into soluble moleculessuch as sugars amino acids and fatty acids The complexpolymeric matter is hydrolyzed to monomer for examplecellulose to sugars or alcohols and proteins to peptidesor amino acids by hydrolytic enzymes (lipases proteasescellulases amylases etc) secreted by microbes and makethem available for other bacteria [20 21] Equation (1) showsan example of a hydrolysis reaction where a polysaccharide isbroken down into glucose [20 21]

Hydrolysis reactions is as follows

Lipids 997888rarr Fatty Acids

Polysaccharides 997888rarr Monosaccharides

Protein 997888rarr Amino Acids

C24H40O20 H2O + 3H2O 997888rarr 4C6H12O6

(1)

In the second stage acidogenesis (fermentation) acido-genic bacteria transform the products of the first reaction(such as sugars and amino acids) into carbon dioxide hydro-gen ammonia and organic acids The principal acidogenesisstage products are acetic acid (CH3COOH) propionic acid(CH3CH2COOH) butyric acid (CH3CH2CH2COOH) andethanol (C2H5OH) In an equilibrated system most of theorganic matter is converted into readily available substratesfor methanogenic microbes (acetate hydrogen and carbondioxide) but a significant part (approximately 30) is trans-formed into short chain fatty acids or alcohols [15] Fromthese products the hydrogen carbon dioxide and acetic acidwill skip the third stage (acetogenesis) and be utilized directlyby the methanogenic bacteria in the final stage (methano-genesis) Equations (2) (3) [22] and (4) [15] represent threetypical acidogenesis reactions where glucose is converted toethanol propionate and acetic acid respectively

C6H12O6 997888rarr 2CH3CH2OH + 2CO2 (2)

C6H12O6 + 2H2 997888rarr 2CH3CH2COOH + 2H2O (3)

C6H12O6 + 2H2O 997888rarr 2CH3COOH + 2CO2 + 4H2 (4)

In the third stage acetogenic bacteria convert the organicacids that resulting from the second stage and the rest of theacidogenesis products into acetic acid hydrogen and carbondioxide Equation (5) represents the conversion of propionateto acetate only achievable at low hydrogen pressure Glucose(6) and ethanol (7) among others are also converted toacetate during the third stage of anaerobic digestion process[22] The products formed during acetogenesis are due to anumber of different microbes for example syntrophobacterwolinii a propionate decomposer and sytrophomonos wolfei abutyrate decomposer Other acid formers areClostridium sppPeptococcus anaerobius Lactobacillus and Actinomyces [15]

CH3CH2COOminus+ 3H2O

997888rarr CH3COOminus+H+ +HCO3

minus+ 3H2

(5)


CH3CH2OH + 2H2O 997888rarr CH3COOminus+ 2H2 +H

+ (7)

The fourth and final stage is called methanogenesis Inthis stage methane is produced by bacteria called methano-gens (also known as methane former) in two ways either bymeans of cleavage of acetic acid molecules to generate carbondioxide and methane (8) or by reduction of carbon dioxidewith hydrogen (9)Methane production is higher from reduc-tion of carbon dioxide but limited hydrogen concentrationin digesters results in that the acetate reaction is the primaryproducer ofmethane [21]Themethanogenic bacteria includeMethanobacterium Methanobacillus Methanococcus andMethanosarcina Methanogens can also be divided into twogroups acetate and H2CO2 consumers AlsoMethanosaetais considered to be important in AD as both acetate andH2CO2 consumers [21 23]

CH3COOH 997888rarr CH4 + CO2 (8)

Carbon dioxide reduction is as follows

CO2 + 4H2 997888rarr CH4 + 2H2O (9)

The challenges facing anaerobic digestion such as lowmethane yield and process instability preventing this tech-nology from being widely applied A wide variety of inhi-bitory substances are the primary cause of anaerobic digesterupset or failure since they are present in substantial concen-trations in wastes Considerable research efforts have beenmade to identify themechanism and the controlling factors ofinhibitionThemethane forming bacteria is strictly anaerobicand even small quantities of oxygen are harmful to them [5]Nitrogen is an essential nutrient for anaerobic organisms [24]The ammonia concentration must be maintained in excessof at least 40ndash70mgNLminus1 to prevent reduction of biomassactivity [25] And high ammonia concentrations may lead toinhibition of the anaerobic digestion process [26ndash28]

However improved reactor configuration can reduce thespace instability as soon as possible For example the com-partmentalized anaerobic reactor (CAR) [29] was separatedinto a distribution zone a reaction zone and a separationzone by adding three inners which seem to keep the spacestability As a result the CAR displays a great potential for itsapplication

4 Process Parameters of Anaerobic Bioreactor

Degradation of unwanted componentscontaminants in theanaerobic treatment depends on several parameters Themain parameters are related to reactor operating conditions(temperature pH organic loading rate (OLR) HRT SRTand upflow velocity) and influent characteristics such asparticle size distribution These parameters and their effectsare discussed in the following paragraphs

41 Temperature Temperature an important physical char-acteristic that affects the acceptability of water as well aswater chemistry andwater treatment [30] Anaerobic bacteriaare classified into ldquotemperature classesrdquo on the basis of theoptimum temperature the mesophiles survive in mesophilictemperature around 30∘C to 40∘C while thermophiles are


considered the first microorganism existing at thermophilictemperature around 50∘C to 65∘C [31] Temperature evenaffects all wastewater treatment processes to some degree[30] for example

(i) biological waste treatment cold water reduces theefficiency of high-rate trickling filters by approxi-mately 30 low temperature inhibits nitrification (by75 from 30∘C to 10∘C) more than BOD (biologicaloxygen demand) removal

(ii) digestion the minimum solid retention time variesfrom 2 days at 35∘C to 10 days at 20∘C the heatrequirement of the digester depends on outside tem-perature

(iii) microbial growth temperature affected the richnessand diversity of microbial populations [32]

Temperature affects particle removal through influencingthe wastewater viscosity and conversion of organic matter[33] Because water viscosity is physically coupled to tem-perature changes in temperature can influence the activity ofmicroscopic organisms through both physiological and phys-ical means [34] Increasing the wastewater temperature leadsto enhancing mixing by reducing viscosity more hydraulicturbulence in a reactor enhanceing the sedimentation andbetter entrapment and adsorption due to contact betweensludge and solids and more biogas will be produced [33]A sudden temperature changes can lead to a change in thephysical and chemical properties of the wastewater whichcan considerably affect the design and operation of thetreatment system [35]

411 Low Temperatures Generally temperature has a signifi-cant effect on the intracellular and extracellular environmentof bacteria and it also acts as an accelerator of the conversionprocesses At low temperatures the startup period may takelonger but it can be successfully accomplished by inoculatingthe reactor with digested sludge Anaerobic treatment of rawdomestic sewage (COD = 500ndash700 gmminus3) on different UASBreactors can be accomplished at 12ndash18∘C (HRTs of 7ndash12 h withtotal COD and BOD removal efficiencies of 40ndash60 and 50ndash70 resp) [3] And also the possibility of applying anaerobicdigestion of dilute dairywastewater at 10∘CatOLRs up to 2 kgCODmminus3 dminus1 can gain over 84 of OD removal efficiency[36]

412 High Temperatures The rates of reaction proceedmuchfaster at higher temperatures therefore producing moreefficient operation and smaller tank sizes And also treatmentproceeds much more rapidly at thermophilic temperatures(around 50∘C to 65∘C) and the digestion under high tem-perature conditions offers many advantages such as highermetabolic rates consequently higher specific growth ratesbut frequently also higher death rates as compared to meso-philic bacteria but also the additional heat required to main-tain such temperatures may offset the advantage obtainedThen most treatment systems are designed to operate in themesophilic range or lower [5 37 38]

42 pH pH is an expression of the intensity of the basicor acid condition of a liquid a measure of the acidity of asolution Commonly methanogens in wastewater treatmentsystems are most active in the neutral pH range (70) [39]The concentration range suitable for most organisms is 60ndash90 [30] beyond this range digestion can proceed but withless efficiency The biomass inhibited at pH 9 was able toregain activities after adjusting the pH to neutrality butthat inhibited at pH 5 was not [40] At acidic conditionsproduced can become quite toxic to the methane bacteriaFor this reason it is important that the pH is not allowed todrop below 62 for a significant period of time Because thisparameter is very important thus the system needs to controlthe pH When the methane gas production stabilizes the pHremains between 72 and 82 [19]

McCarty [5] reported that an optimum pH range ofanaerobic treatment is about 70 to 72 but it can proceed quitewell with a pH varying from about 66 to 76

43 Hydraulic Retention Time (HRT) HRT also known ashydraulic residence time is a measure of the average lengthof time that a soluble compound remains in a constructedbioreactor Hydraulic retention time is the volume of theaeration tank divided by the influent flow rate

HRT [d] =Volume of aeration tank [m3]

Influent flow rate [m3d]=119881

119876 (10)

where HRT is hydraulic retention time (d) and usuallyexpressed in hours (or sometimes days) the 119881 is the volumeof aeration tank or reactor volume (m3) and119876 is the influentflow rate (m3d)

Generally HRT is a good operational parameter that iseasy to control and also a macroconceptual time for theorganic material to stay in the reactor In bioreaction engi-neering studies the reverse of HRT is defined as dilution ratefor which if it is bigger than the growth rate of microbial cellsin the reactor the microbe will be washed out and otherwisethe microbe will be accumulated in the reactor Either ofthese situations may result in the breakdown of the biologicalprocess happening in the reactor

44 Organic Loading Rate (OLR) At the industrial scale arange of high-rate anaerobic fluidized-bed (AFB) reactorssuch as upflow anaerobic sludge blanket (UASB) upflow-staged sludge bed (USSB) expanded granular sludge bed(EGSB) internal circulation (IC) and inverse anaerobicfluidized bed (IAFB) reactors can bear very high loadingrates up to 40 kg COD(m3sdotd) [41] The organic loading rate(OLR) and volumetric biogas production (VBP) of the spiralautomatic circulation (SPAC) reactor in our laboratory couldreach up to 306 kg COD(m3sdotd) [41ndash43] Several authorsreported that up to a certain limit the treatment efficiency ofcomplex wastewaters for example potato maize slaughter-house in high rate anaerobic reactors increases with increasein OLR A further increase in OLR will lead to operationalproblems like sludge bed flotation and excessive foamingat the gas-liquid interface in the gas-liquid-solid (GLS)


separator as well as accumulation of undigested ingredientsAs a result the treatment efficiency deteriorates [44 45]Also accumulation of biogas in the sludge bed was noticedforming stable gas pockets that lead to incidental lifting ofparts of the bed and a pulse-like eruption of the gas from thiszone [45 46]TheOLR can be varied by changing the influentconcentration and by changing the flow rate Thus implieschanging the HRT and by changing the flow rate under theseconditions OLR can be expressed in the following form

OLR = (119876 times COD)119881 (11)

where OLR is organic loading rate (kg CODm3sdotd) 119876 is flowrate (m3d) COD is chemical oxygen demand (kg CODm3)and 119881 is reactor volume (m3) By using (10) the OLR can besimplified

OLR = CODHRT (12)

When the solids removal efficiency in upflow reactors isrelated to the OLR it becomes crucial to distinguish betweenthese parameters For this reason OLR is an inadequatedesign parameter to assure good performance of anaerobicreactors

45 Sludge Retention Time (SRT) SRT is known to be thekey parameter affecting biochemical and physical propertiesof sludge [47] The success of UASB reactors is mainlydependent on the sludge retention time (SRT) [48] which isthe key factor determining the ultimate amount of hydrolysisandmethanogenesis in a UASB system at certain temperatureconditions [49] The SRT should be long enough to providesufficient methanogenic activity at the prevailing conditionsThe SRT is determined by the loading rate the fraction ofsuspended solid (SS) in the influent the removal of SS in thesludge bed and the characteristics of the SS (biodegradabilitycomposition etc) [3]

Methanogenesis starts at SRT between 5 and 15 days at25∘C and between 30 and 50 days at 15∘C the maximummethanogenesis found at 25∘C amounted to 51 and 25at 15∘C Maximum hydrolysis occurs at 75 days SRT andamounted to 50 at 25∘C and 24 at 15∘C [47] The SRTand temperature have a significant influence on the hydrolysisof proteins carbohydrates and lipids The most substantialportion of the digestion of proteins carbohydrates and lipidsoccurs within the first 15 and 10 days at process temperaturesof 25∘C and 35∘C respectively [50]

46 Upflow Velocity The upflow velocity is one of the mainfactors affecting the efficiency of upflow reactors An increasein upflow velocity from 16 to 32mh resulted in a relativelysmall loss in SS removal efficiency from 55 to nearly 50which indicates the role of adsorption and entrapment [51]

47 Particle Size Distribution The particle-size distribution(PSD) of a powder granularmaterial or particles dispersed influid is a list of values or a mathematical function that defines

30mm

Φ45mm

Φ150mm

30 mm

60∘

Figure 3 Structural sketch diagram of funnel-shape inner compo-nent

the relative amount typically by mass of particles presentaccording to size The effluent quality from classical filters ishighly related to the specific size of the filtering media Moststudies indicate that smaller media size gives more efficientremoval [52]

5 Inner Components of Anaerobic Bioreactor

The inner components play an important role in enhancingOLR of the reactor help in improving the quality of fluidiza-tion separate the gas bubble from the sludge granules andtherefore enhance the treatment efficiency and so on Theinner components in a biological fluidized bed reactor can bedivided into the transverse inner components longitudinalinner components and biofilm-packing material

51 Transverse Inner Components Themost significant func-tion of transverse inner components is (1) to keep the sludgeinAB effectively and (2) to improve the quality of fluidizationbreak bubbles and enhanced mass transfer significantly Tokeep sludge effectively following a three-phase separatordeveloped in the early 1990s by Lettinga et al [53] manyinvestigators set inner components in the reactor by applyingthe three-phase separation principle Chelliapan et al [54] seta 45∘ angle of the three-phase separator baffle in the outlet ofupflow anaerobic a multistage reactor (UASR) and held thegranular sludge efficientively (5850 gVSSsdotmminus3) In order toreduce the short flow improve the flow pattern and enhancemass transfer many researchers set different inner compo-nents in AB Figure 3 shows that the funnel-shaped diversioncomponents were located in the top of the reactor resulting ina 15 increase in the volumetric oxygen transfer coefficientand liquid mixing time is reduced by 10 to 25 [55]

Karim et al [56] studied the effect of bottom config-uration and a hanging baffle on the mixing inside a gas-lift digester filled with non-Newtonian sludge (Figure 4 andTable 2) Their results showed that to change the configu-ration of the bottom of the reactor (Figures 4(a) and 4(c))


0

010

005

015

Axi

al p

ositi

on (m

)Hanging baffle025

020

0 005 010 0 005 010 0 005 0100 005 010Radial position (m)

A B C D

a a

Figure 4 Comparison of fluidization quality for different conicalbottom digesters with and without hanging inner component

Table 2 Comparison of fluidization quality for different conicalbottom digesters with and without hanging inner component

Bottom configuration The short flow area of the total volume ()No inner components Inner components

Flat-bottomed head 336 214Conical head (120572 = 25∘) 319 158Conical head (120572 = 45∘) 296 117

the figures demonstrate that the conical bottoms resulted inonly slight improvement but Figures 4(b) and 4(d) showadditional suspended inner component to permit fluid flowto the inner wall of the reactor Under the action of aninverted conical head the fluid flows within the draft tubethereby constituting internal circulation and reducing short-stream and the dead zone

The data in Table 2 shows that the change in digesterbottom configuration resulted in about 2ndash4 reduction in thepoorly mixed zone However the introduction of a hangingbaffle reduced the percentage of poorly mixed zones by12 16 and 18 in the case of flat 25∘ and 45∘ bottomdigesters respectivelyTherefore it is clear that a combinationof a hopper bottom and a hanging baffle would significantlyimprove the mixing efficacy inside gas-lift digesters

52 Longitudinal Inner Components Recent research athome and abroad shows that the future development trendof longitudinal inner components is organic integration ofthe components within the multigroup in order to optimizethe flow field and reduce the intermediate product inhibitionVan Lier et al [57] set a number of three-phase separatorsbaffle in the sludge bed of an upflow staged sludge bed (USSB)reactor (Figure 5) Its performance compared to that of anupflow anaerobic sludge bed (UASB) reactor operating at thesame operational conditions and the reaction zone in (USSB)is divided into several compartments and each compartmentcan collect produced gas [58 59]

Guyuan et al and Ji et al [60 61] studied the perfor-mance of the inner components having a certain inclinationmultilayer baffle deflector driven in the spiral upflow reactor(SUFR) by software simulation (Figure 6) Hong-lin et al

Influent

Effluent

Biogas

Three-phase separator

Figure 5 Structural and setup sketch of 3-phase separator baffle inUSSB

[62ndash64] reported that the plurality of sets of helical bladescombined inner longitudinal component used in fluidizedbed reactor to enhance the reactor coagulation granulationand biological degradation

53 Biofilm-Packing Material In 1978 Weber Jr et al [65]placed in a fluidized bed reactor dosing activated carbon part-icles and explored the inner structures of biofilm as the first ofits kindGranular activated carbon dosing has three functionsto provide huge growth of microbial attachment specific sur-face area enhanced biosorption and biodegradation of syn-ergies greatly improve the matrix of the particle surface andoxygen concentration effectively enhance the performanceof microbial oxidation effectively relieve hydraulic shearingaction and maintain a high concentration of microorgan-isms In1980s fixed filler was placed by McCarty and Smith[66] in the bioreactor as the inner component High con-centrations of anaerobic activated sludge was achieved andthus anaerobic filter (AF) was developed [67] Since thenmany researchers added activated carbons [68] sand [69]calcium alginate [70] and porous polymer carrier [71] and soon as inner component in AF and achieved some remarkableefficiency

6 Super-High-Rate AnaerobicBioreactor (SAB)

Under high load conditions the biogas produced in theanaerobic reactor does not escape granular sludge in a timelymanner can reduce the particle density and increase bedslugging In laboratory-scale biological fluidized bed slug-ging cause paralysis of the mechanical operation of the reac-tor In response to this situation Zhengrsquos research group hasdeveloped a new spiral automatic circulation (SPAC) anaero-bic reactor [42] (Figure 7) after more than two years OLRof SPAC can reach up to 300Kg CODsdotmminus3sdotdminus1 much higherthan the performance level of the existing high-rate anaerobicreactor [43] Its main advantages are to effectively eliminatethe slugging phenomenon and ensure the smooth operation


Figure 6 Simulation of flow field in SUFR

Influent

Effluent

Biogas

The spiral baffle within inner component

Figure 7 Structural and setup sketch of spiral baffle

of the reactor bymeans of the reaction force of the spiral platereactor

7 Conclusion

(i) Anaerobic treatment is a proven way and efficient methodto produce biogas (methane) that can be used for the produc-tion of renewable heat and power and a compost like outputInhomogeneous system time instability and space instabilityare three main characteristics of anaerobic bioreactor (AB)

(ii) Anaerobic treatment efficiency has a deep effect byseveral parameters such as temperature pH OLR SRT HRTupflow velocity and size distribution cause of anaerobicreactor operates under inhomogeneous system (Gas-liquid-solid) Therefore anaerobic treatment needs especial kind ofsetting because anaerobic processes successful depends onbacteria living and growth inside the reactor

(iii) The reactor inner components play an importantrole in enhancing the treatment efficiency and the mostsignificant functions of inner components are (1) effectiveto improve the retention sludge reactor capacity and (2)

significantly improve the quality of fluidization broken bub-bles and enhanced mass transfer And they can be dividedinto the transverse inner components longitudinal innercomponents and biofilm-packing material

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors would like to thank the National NaturalScience Foundation of China (Grant no 51208087) theShanghai Natural Science Foundation of China (Grant no12ZR1400800) Doctoral Fund of Ministry of Education ofChina (New Teachers) (Project no 20120075120001) and thecentral university special funds free exploration program

References

[1] G S Mittal ldquoTreatment of wastewater from abattoirs beforeland applicationmdasha reviewrdquo Bioresource Technology vol 97 no9 pp 1119ndash1135 2006

[2] S Wijetunga X-F Li and C Jian ldquoEffect of organic load ondecolourization of textile wastewater containing acid dyes inupflow anaerobic sludge blanket reactorrdquo Journal of HazardousMaterials vol 177 no 1-3 pp 792ndash798 2010

[3] L Seghezzo G Zeeman J B Van Lier H V M Hamelers andG Lettinga ldquoA review the anaerobic treatment of sewage inUASB and EGSB reactorsrdquo Bioresource Technology vol 65 no3 pp 175ndash190 1998

[4] S Aiyuk I Forrez D K Lieven A van Haandel and W Ver-straete ldquoAnaerobic and complementary treatment of domesticsewage in regions with hot climates-A reviewrdquo BioresourceTechnology vol 97 no 17 pp 2225ndash2241 2006

[5] P L McCarty ldquoAnaerobic waste treatment fundamentalsrdquo Pub-lic Works vol 95 no 9 pp 107ndash112 1964

[6] S Chong T K Sen A Kayaalp and H M Ang ldquoThe perform-ance enhancements of upflow anaerobic sludge blanket (UASB)reactors for domestic sludge treatment - A State-of-the-artreviewrdquoWater Research 2012

[7] P-J Meynell Methane Planning a Digester Schocken BooksNew York NY USA 1976

[8] P J Reddy Municipal Solid Waste Management Processing-Energy Recovery-Global Examples CRC Press 2011

[9] G Lettinga et al ldquoUse of the upflow sludge blanket (USB) reac-tor concept for biological wastewater treatment especially foranaerobic treatmentrdquo Biotechnology and Bioengineering vol 22no 4 pp 699ndash734 1980

[10] M T Kato J A Field P Versteeg and G Lettinga ldquoFeasibilityof expanded granular sludge bed reactors for the anaerobictreatment of low-strength soluble wastewatersrdquo Biotechnologyand Bioengineering vol 44 no 4 pp 469ndash479 1994

[11] X-G Chen P Zheng Y-J GuoQMahmood C-J Tang and SDing ldquoFlow patterns of super-high-rate anaerobic bioreactorrdquoBioresource Technology vol 101 no 20 pp 7731ndash7735 2010

[12] X Chen Z Ping S Ding et al ldquoSpecific energy dissipation ratefor super-high-rate anaerobic bioreactorrdquo Journal of ChemicalTechnology and Biotechnology vol 86 no 5 pp 749ndash756 2011


[13] X-G Chen P Zheng M Qaisar and C-J Tang ldquoDynamicbehavior and concentration distribution of granular sludgein a super-high-rate spiral anaerobic bioreactorrdquo BioresourceTechnology vol 111 pp 134ndash140 2012

[14] L W Hulshoff Pol S I De Castro Lopes G Lettinga and P NL Lens ldquoAnaerobic sludge granulationrdquoWater Research vol 38no 6 pp 1376ndash1389 2004

[15] K M Kangle V S Kore and G S Kulkarni ldquoRecent trends inanaerobic codigestion a reviewrdquo Universal Journal of Environ-mental Research and Technology vol 2 no 4 pp 210ndash219 2012

[16] C Buijs P M Heertjes and R R van der Meer ldquoDistributionand behavior of sludge in upflow reactors for anaerobic treat-ment of wastewaterrdquo Biotechnology and Bioengineering vol 24no 9 pp 1975ndash1989 1982

[17] T Hidaka F wang T Togari et al ldquoComparative performanceof mesophilic and thermophilic anaerobic digestion for high-solid sewage sludgerdquo Bioresource Technology vol 149 pp 177ndash183 2013

[18] E Lloret L Pastor P Pradas and J Pascual ldquoSemi full-scalethermophilic anaerobic digestion (TAnD) for advanced treat-ment of sewage sludge stabilization process and pathogenreductionrdquo Chemical Engineering Journal vol 232 pp 42ndash502013

[19] T Abbasi S M Tauseef and S A Abbasi ldquoAnaerobic diges-tion for global warming control and energy generation - Anoverviewrdquo Renewable and Sustainable Energy Reviews vol 16no 5 pp 3228ndash3242 2012

[20] M T Madigan J M Martinko D Stahl and D P ClarkBrock Biology of Microorganisms Benjamin-Cummings Read-ing Mass USA 2008

[21] M Kayhanian ldquoBiodegradability of the organic fraction ofmunicipal solidwaste in a high-solids anaerobic digesterrdquoWasteManagement and Research vol 13 no 2 pp 123ndash136 1995

[22] K OstremGreeningWaste Anaerobic Digestion for Treating theOrganic Fraction of Municipal Solid Wastes Earth EngineeringCenter Columbia University 2004

[23] S Berger C Welte and U Deppenmeier ldquoAcetate activa-tion in methanosaeta thermophila characterization of thekey enzymes pyrophosphatase and acetyl-CoA synthetaserdquoArchaea 2012

[24] RAMahMR Smith andL Baresi ldquoStudies on an acetate-fer-menting strain of Methanosarcinardquo Applied and EnvironmentalMicrobiology vol 35 no 6 pp 1174ndash1184 1978

[25] M Takashima andR E Speece ldquoMineral nutrient requirementsfor high-rate methane fermentation of acetate at low SRTrdquoResearch Journal of the Water Pollution Control Federation vol61 no 11-12 pp 1645ndash1650 1989

[26] K H Hansen I Angelidaki and B K Ahring ldquoAnaerobicdigestion of swine manure inhibition by ammoniardquo WaterResearch vol 32 no 1 pp 5ndash12 1998

[27] M Kayhanian ldquoAmmonia inhibition in high-solids biogasi-fication an overview and practical solutionsrdquo EnvironmentalTechnology vol 20 no 4 pp 355ndash365 1999

[28] S Sung and T Liu ldquoAmmonia inhibition on thermophilic ana-erobic digestionrdquo Chemosphere vol 53 no 1 pp 43ndash52 2003

[29] J Y Ji K Zheng Y J Xing and P Zheng ldquoHydraulic cha-racteristics and their effects on working performance of com-partmentalized anaerobic reactorrdquo Bioresource Technology vol116 pp 47ndash52 2012

[30] N G Adrien ldquoProcessing water wastewater residuals andexcreta for health and environmental protectionrdquo in An Ency-clopedic Dictionary 2008

[31] M T Agler Z Aydinkaya T A Cummings A R Beers and LT Angenent ldquoAnaerobic digestion of brewery primary sludgeto enhance bioenergy generation a comparison between low-and high-rate solids treatment and different temperaturesrdquo Bio-resource Technology vol 101 no 15 pp 5842ndash5851 2010

[32] W J Gao K T LeungW S Qin and B Q Liao ldquoEffects of tem-perature and temperature shock on the performance andmicro-bial community structure of a submerged anaerobic mem-brane bioreactorrdquo Bioresource Technology vol 102 no 19 pp8733ndash8740 2011

[33] N Mahmoud G Zeeman H Gijzen and G Lettinga ldquoSolidsremoval in upflow anaerobic reactors a reviewrdquo BioresourceTechnology vol 90 no 1 pp 1ndash9 2003

[34] M K Winkler J P Bassin R Kleerebezem R G van der Lansand M C van Loosdrecht ldquoTemperature and salt effects onsettling velocity in granular sludge technologyrdquoWater Researchvol 46 no 12 pp 3897ndash3902 2012

[35] G Lettinga S Rebac and G Zeeman ldquoChallenge of psychro-philic anaerobicwastewater treatmentrdquoTrends in Biotechnologyvol 19 no 9 pp 363ndash370 2001

[36] D C Katarzyna Bialek and V OrsquoFlaherty ldquoLow-Temperature(10∘C) anaerobic digestion of dilute dairy wastewater in anEGSB bioreactor microbial community structure populationdynamics and kinetics of methanogenic populationsrdquoArchaea2013

[37] H M El-Mashad G Zeeman W K P Van Loon G P A Botand G Lettinga ldquoEffect of temperature and temperature fluc-tuation on thermophilic anaerobic digestion of cattle manurerdquoBioresource Technology vol 95 no 2 pp 191ndash201 2004

[38] H Ge P D Jensen and D J Batstone ldquoIncreased temperaturein the thermophilic stage in temperature phased anaerobicdigestion (TPAD) improves degradability of waste activatedsludgerdquo Journal ofHazardousMaterials vol 187 no 1-3 pp 355ndash361 2011

[39] L Florencio A Nozhevnikova A Van Langerak A JM StamsJ A Field and G Lettinga ldquoAcidophilic degradation of meth-anol by a methanogenic enrichment culturerdquo FEMS Microbiol-ogy Letters vol 109 no 1 pp 1ndash6 1993

[40] H H P Fang and X-S Jia ldquoSoluble microbial products (SMP)of acetotrophic methanogenesisrdquo Bioresource Technology vol66 no 3 pp 235ndash239 1998

[41] X-G Chen P Zheng J Cai and M Qaisar ldquoBed expansionbehavior and sensitivity analysis for super-high-rate anaerobicbioreactorrdquo Journal of Zhejiang University vol 11 no 2 pp 79ndash86 2010

[42] P Zheng J W Chen and C J Tang ldquoA new type of spiralautomatic circulation anaerobic reactorrdquo ZL20072010618262008 (Chinese)

[43] J Chen C Tang P Zheng and L Zhang ldquoPerformance oflab-scale SPAC anaerobic bioreactor with high loading raterdquoChinese Journal of Biotechnology vol 24 no 8 pp 1413ndash14192008

[44] I RuizM CVeiga P De Santiago andR Blazquez ldquoTreatmentof slaughterhouse wastewater in a UASB reactor and an anaer-obic filterrdquo Bioresource Technology vol 60 no 3 pp 251ndash2581997

[45] S Kalyuzhnyi L Estrada De Los Santos and J R MartinezldquoAnaerobic treatment of raw and preclarified potato-maizewastewaters in a UASB reactorrdquo Bioresource Technology vol 66no 3 pp 195ndash199 1998

[46] T A Elmitwalli M H Zandvoort G Zeeman H Burning andG Lettinga ldquoLow temperature treatment of domestic sewage in


upflow anaerobic sludge blanket and anaerobic hybrid reactorsrdquoWater Science and Technology vol 39 no 5 pp 177ndash185 1999

[47] M Halalsheh J Koppes J Den Elzen G Zeeman M Fayyadand G Lettinga ldquoEffect of SRT and temperature on biologicalconversions and the related scum-forming potentialrdquo WaterResearch vol 39 no 12 pp 2475ndash2482 2005

[48] V H Varel A G Hashimoto and Y R Chen ldquoEffect of tem-perature and retention time on methane production from beefcattle wasterdquo Applied and Environmental Microbiology vol 40no 2 pp 217ndash222 1980

[49] W J Jewell ldquoAnaerobic sewage treatmentrdquo Environmental Sci-ence and Technology vol 21 no 1 pp 14ndash21 1987

[50] N Mahmoud G Zeeman H Gijzen and G Lettinga ldquoAnaer-obic stabilisation and conversion of biopolymers in primarysludge - Effect of temperature and sludge retention timerdquoWaterResearch vol 38 no 4 pp 983ndash991 2004

[51] G Zeeman W T M Sanders K Y Wang and G LettingaldquoAnaerobic treatment of complex wastewater and waste acti-vated sludgemdashapplication of an upflow anaerobic solid removal(UASR) reactor for the removal and pre-hydrolysis of sus-pended CODrdquoWater Science and Technology vol 35 no 10 pp121ndash128 1997

[52] H Landa A Capella and B Jimenez ldquoParticle size distributionin an efluent from an advanced primary treatment and itsremoval during filtrationrdquo Water Science and Technology vol36 no 4 pp 159ndash165 1997

[53] G Lettinga J A Field R Sierra-Alvarez J B Van Lier andJ Rintala ldquoFuture perspectives for the anaerobic treatment offorest industry wastewatersrdquoWater Science and Technology vol24 no 3-4 pp 91ndash102 1991

[54] S Chelliapan T Wilby and P J Sallis ldquoPerformance of anup-flow anaerobic stage reactor (UASR) in the treatment ofpharmaceutical wastewater containing macrolide antibioticsrdquoWater Research vol 40 no 3 pp 507ndash516 2006

[55] C Wei L Li J Wu C Wu and J Wu ldquoInfluence of funnel-shape internals on hydrodynamics andmass transfer in internalloop three-phase fluidized bedrdquo Journal of Chemical Industryand Engineering vol 58 no 3 pp 591ndash595 2007

[56] K Karim G JThoma andM H Al-Dahhan ldquoGas-lift digesterconfiguration effects on mixing effectivenessrdquo Water Researchvol 41 no 14 pp 3051ndash3060 2007

[57] J B Van Lier J L Sanz Martin and G Lettinga ldquoEffect oftemperature on the anaerobic thermophilic conversion of vola-tile fatty acids by dispersed and granular sludgerdquo Water Re-search vol 30 no 1 pp 199ndash207 1996

[58] P N L Lens M C Van Den Bosch L W Hulshoff Pol and GLettinga ldquoEffect of staging on volatile fatty acid degradation ina sulfidogenic granular sludge reactorrdquoWater Research vol 32no 4 pp 1178ndash1192 1998

[59] H Yanling Anaerobic Biological Treatment of WastewaterChina Light Industry Press Beijing China 1998 (Chinese)

[60] L Guyuan D Junfeng J I Fangying and L Ning ldquoStudy on thecharacteristic of spiral Up-flow reactor system and its perform-ance on biological nitrogen and phosphorus removalrdquoActa Sci-entiae Circumstantiae vol 24 no 1 pp 15ndash20 2004 (Chinese)

[61] T Ji G Luo D Wang X Xu and L Zhu ldquoEffect of prolongedsludge age on biological nutrient removal in spiral up-flow reac-tor system and flow pattern interpretationrdquo Journal of Chem-ical Industry andEngineering vol 58 no 10 pp 2613ndash2618 2007

[62] Y Hong-lin L Yong-jun and W Xiao-chang ldquoMicrobial com-munity structure and dynamic changes of fluidized-Pellet-Bee

Bioreactorrdquo Journal of Microbiology vol 27 no 2 pp 1ndash5 2007(Chinese)

[63] Y HonglinW Xiaochang andW Li ldquoComparison ofmicrobialgrowth in a fluidized-pellet-bed bioreactor and an Asim2Oprocessrdquo Acta Scientiae Circumstantiae vol 27 no 6 pp 973ndash978 2007

[64] H L Yuan and Y J Liu ldquoPilot study of a fluidized pelletmdashbedbioreactor for simultaneous biodegradation and solidliquidseparation in municipal wastewater treatment future of urbanwastewater systems decentralization and reuserdquo in Proceedingsof IWA Conference pp 253ndash260 Xian China 2005

[65] W J Weber Jr M Pirbazari and G L Melson ldquoBiologicalgrowth on activated carbon an investigation by scanning ele-ctron microscopyrdquo Environmental Science and Technology vol12 no 7 pp 817ndash819 1978

[66] P L McCarty and D P Smith ldquoAnaerobic wastewater treat-mentrdquo Environmental Science and Technology vol 20 no 12 pp1200ndash1206 1986

[67] F X Zheng PingWaste Biological Treatment Higher EducationPress Beijing China 2006

[68] A Tanyolac and H Beyenal ldquoPrediction of substrate consump-tion rate average biofilm density and active thickness for athin spherical biofilm at pseudo-steady staterdquo Biochemical Engi-neering Journal vol 2 no 3 pp 207ndash216 1998

[69] F K J Rabah and M F Dahab ldquoBiofilm and biomass char-acteristics in high-performance fluidized-bed biofilm reactorsrdquoWater Research vol 38 no 19 pp 4262ndash4270 2004

[70] N F Y Tam and Y S Wong ldquoEffect of immobilized microalgalbead concentrations on wastewater nutrient removalrdquo Environ-mental Pollution vol 107 no 1 pp 145ndash151 2000

[71] X G Chen Y Dayong and H Zhaoji ldquoExperimental study ona three-phase outer circulating fluidized bed by a sequencingbatch reactor of biofilm processrdquo in Seminar on EngineeringEducation CooperationampAcademic Research for Chinese-FrenchUniversities p 367370 2005

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of


Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 2014

Zoology


Molecular Biology International

GenomicsInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


BioinformaticsAdvances in

Marine BiologyJournal of



Signal TransductionJournal of


BioMed Research International

Evolutionary BiologyInternational Journal of



Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Genetics Research International


Advances in

Virolog y

Hindawi Publishing Corporationhttpwwwhindawicom

Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational



Enzyme Research



Microbiology


Table 1 Advantages and disadvantages of anaerobic process [3 15]

Advantages Disadvantages(i) Reduction of greenhouse gasemissions through methane recovery(ii) High treatment efficiency forbiodegradable sludge(iii) Production of methane gas(potential source of fuel)(iv) A high degree of wastestabilization is possible(v) Simplicity(vi) Flexibility anaerobic treatmentcan easily be applied on either a verylarge or a very small scale(vii) Space saving (higher loading ratesrequire smaller reactor volumesthereby saving on disposal cost)(viii) Less requirement of energy andoxygen(ix) Inoffensive residual sludge may beused as soil conditioner(x) Low nutrients and chemicalsrequirement

(i) Long recovery time itmay take longer time forthe system to return tonormal operatingconditions if shock loadinghappens(ii) Low pathogen andnutrient removal(iii) Long startup(iv) Possible bad odors(v) High sensitivity ofmethanogenic bacteria to alarge number of chemicalcompounds(vi) Small- andmiddle-scale anaerobictechnology for thetreatment of solid waste inmiddle- and low-incomecountries is still relativelynew

UASB reactor was just like an empty tank (thus an extremelysimple and inexpensive design) but an important innercomponent the three-phase separator is added to avoidwashout of granular sludge occurred The third generationof AB such as expanded granular sludge bed (EGSB) andinternal circulation (IC) reactor was developed on thefoundation of the second generation For instance the fasterrate of upward-flow velocity is designed for the wastewaterpassing through the sludge bed The increased flux permitspartial expansion (fluidization) of the granular sludge bedimproving wastewater-sludge contact as well as enhancingsegregation of small inactive suspended particle from thesludge bedThe increased flow velocity is either accomplishedby utilizing tall reactors or by incorporating an effluentrecycle (or both) [3 11ndash13] Some super-high-rate anaerobicbioreactors (SAB) were developed recently by Chen et al[11ndash13] The development of the third generation anaerobicbioreactors and SAB shows that the process parameterssuch as upflow velocity Sludge Retention Time (SRT) andHydraulic Retention Time (HRT) and bioreactor structure(inner components) are the two most important factorsfor microorganismsrsquo cultivation for anaerobic bioreactors[3 11ndash13] Therefore This work will present the advantagesand disadvantages of anaerobic process and explain therepresentative characteristics of anaerobic bioreactor It alsointroduces main process parameters inner components andtheir effects on the performance of wastewater treatment inanaerobic bioreactors

2 Advantages and Disadvantages ofAnaerobic Process

Anaerobic treatment (digestion) is a proven way and efficientmethod to produce biogas (methane) that can be used for

the production of renewable heat and power and a compostlike output The principle of anaerobic treatment is theutilization of anaerobic bacteria (biomass) to convert organicmatter (pollutants) or COD (chemical oxygen demand) intomethane rich biogas in the absence of oxygen

The early stages of the formation of anaerobic granulesfollow the same principles in the formation of biofilm ofbacteria on solid surfaces There is strong evidence thatinert carriers play an important positive role in granulationMany researchers conclude thatMethanosaeta concilii is a keyorganism in granulation [14]

When the system is in balance themethanogenic bacteriause the acid intermediates as rapidly as they appear Howeverif the methane bacteria are not present in suitable numbersor are being slowed down by unfavorable environmentalconditions they will not use the acids as rapidly as theyare produced by the acid formers and the volatile acids willincrease in concentration Thus an increase in acid concen-tration indicates that the methane formers are not in balancewith the acid formers [5] Classification of bacteria dependsupon temperature classes where mesophiles bacteria are likemesophilic temperature while thermophiles bacteria are likethermophilic temperature Advantages and disadvantages ofanaerobic treatment processes are shown in Table 1

3 Characteristics of Anaerobic Bioreactor

31 Inhomogeneous System Anaerobic reactor operatesunder an inhomogeneous system that means that theanaerobic treatment is done through three phases solid(sludge) liquid (wastewater) and gas (methane)

311 Solid Phase Solid phase consists of sludge granuleswhich have a diameter around 05 to 2mm [14] which existin the lower part of the reactor Sludge granules play animportant role for successful operation of UASB and EGSBtechnology a sludge granules are the sum of microorganisms(Bacteria) forming during the treatment of wastewater inan environment with a constant upflow hydraulic regimewithout any support matrix the surrounding and suitableenvironment for bacteria survive is occurring during flowconditions and therefore bacteria able to contact togetherand start growth and proliferate

312 Liquid Phase Liquid (wastewater) flows upwardsthrough a sludge bed located in the lower part of the reactorwhile the upper part contains a three phases (solid liquid andgas) of separation system Three-phase separation device isthe most characteristic feature of UASB reactor It facilitatesthe collection of biogas and also provides internal recyclingof sludge by disengaging adherent biogas bubbles from risingsludge particles

313 Gas Phase Biogas typically refers to a gas producedby bacteria that breakdown organic matter in the absenceof oxygen (organic waste such as dead plant and animalmaterial animal feces and kitchenwaste or industrial organicwaste can be converted into a gaseous fuel called biogas)The


Influent

EffluentBiogas

Cmnminus1

Fwnminus1

Cmn

ΔVnminus1

ΔVn

Fwn

Φgnminus1

Φmnminus1

Φmn









Δ119881119899 m3 hminus1








Hydrolysis



Acetogenesis



Methanogenesis












C24H40O20 H2O + 3H2O 997888rarr 4C6H12O6

(1)








minus+ 3H2

(5)



+ (7)




CO2 + 4H2 997888rarr CH4 + 2H2O (9)



















119876 (10)






OLR = (119876 times COD)119881 (11)


OLR = CODHRT (12)






30mm

Φ45mm

Φ150mm

30 mm

60∘








0

010

005

015

Axi

al p

ositi

on (m

)Hanging baffle025

020


A B C D

a a









Influent

Effluent

Biogas









Influent

Effluent

Biogas




7 Conclusion







Acknowledgments


References



















































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


Influent

EffluentBiogas

Cmnminus1

Fwnminus1

Cmn

ΔVnminus1

ΔVn

Fwn

Φgnminus1

Φmnminus1

Φmn









Δ119881119899 m3 hminus1








Hydrolysis



Acetogenesis



Methanogenesis












C24H40O20 H2O + 3H2O 997888rarr 4C6H12O6

(1)








minus+ 3H2

(5)



+ (7)




CO2 + 4H2 997888rarr CH4 + 2H2O (9)



















119876 (10)






OLR = (119876 times COD)119881 (11)


OLR = CODHRT (12)






30mm

Φ45mm

Φ150mm

30 mm

60∘








0

010

005

015

Axi

al p

ositi

on (m

)Hanging baffle025

020


A B C D

a a









Influent

Effluent

Biogas









Influent

Effluent

Biogas




7 Conclusion







Acknowledgments


References



















































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology







C24H40O20 H2O + 3H2O 997888rarr 4C6H12O6

(1)








minus+ 3H2

(5)



+ (7)




CO2 + 4H2 997888rarr CH4 + 2H2O (9)



















119876 (10)






OLR = (119876 times COD)119881 (11)


OLR = CODHRT (12)






30mm

Φ45mm

Φ150mm

30 mm

60∘








0

010

005

015

Axi

al p

ositi

on (m

)Hanging baffle025

020


A B C D

a a









Influent

Effluent

Biogas









Influent

Effluent

Biogas




7 Conclusion







Acknowledgments


References



















































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology














119876 (10)






OLR = (119876 times COD)119881 (11)


OLR = CODHRT (12)






30mm

Φ45mm

Φ150mm

30 mm

60∘








0

010

005

015

Axi

al p

ositi

on (m

)Hanging baffle025

020


A B C D

a a









Influent

Effluent

Biogas









Influent

Effluent

Biogas




7 Conclusion







Acknowledgments


References



















































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology



OLR = (119876 times COD)119881 (11)


OLR = CODHRT (12)






30mm

Φ45mm

Φ150mm

30 mm

60∘








0

010

005

015

Axi

al p

ositi

on (m

)Hanging baffle025

020


A B C D

a a









Influent

Effluent

Biogas









Influent

Effluent

Biogas




7 Conclusion







Acknowledgments


References



















































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


0

010

005

015

Axi

al p

ositi

on (m

)Hanging baffle025

020


A B C D

a a









Influent

Effluent

Biogas









Influent

Effluent

Biogas




7 Conclusion







Acknowledgments


References



















































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology



Influent

Effluent

Biogas




7 Conclusion







Acknowledgments


References



















































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology







































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology




































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology








Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology

Documents

Characteristics, Process Parameters, and Inner Components of