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Journal of Environmental Management 124 (2013) 62e71

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Journal of Environmental Management

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Review

Odor control in lagoons

X.L. Zhang a, S. Yan a, R.D. Tyagi a,*, R.Y. Surampalli b

a Institut National de la Recherche Scientifique-Eau, Terre et Environnement, 490, rue de la Couronne, Québec, Québec G1K 9A9, CanadabU.S. Environmental Protection Agency, P.O. Box 17-2141, Kansas City, KS 66117, USA

a r t i c l e i n f o

Article history:Received 29 June 2012Received in revised form1 March 2013Accepted 12 March 2013Available online

Keywords:Lagoon odor controlPhysical coverOxidationBiological cover

* Corresponding author. Tel.: þ1 (418) 654 2617; faE-mail address: rd.tyagi@ete.inrs.ca (R.D. Tyagi).

0301-4797/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.jenvman.2013.03.022

a b s t r a c t

Lagoons are widely used in rural area for wastewater treatment; however, the odor problem hashampered its application. The root of odor emission from lagoons varies from one to another. The key ofcontrolling the odor is to find out the cause and accordingly provide strategies. Various physical,chemical, and biological methods have been reported and applied for odor control. Physical technologiessuch as masking, capturing and sorption are often employed to mitigate the pressure from compliantwhile not to cut off the problem. Chemical technologies which act rapidly and efficiently in odor control,utilize chemicals to damage the odorant production root or convert odorant to odorless substances.Biological methods such as aeration, biocover and biofiltration control the odor by enhancing aerobiccondition or developing methanogens in lagoon, and biologically decomposing the odorants. Comparingto physical and chemical methods, biological methods are more feasible.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Lagoons are one of the oldest means of wastewater treatmentand still extensively used due to the fact that they are easy tooperate, facile to maintain, cheap to build, and less sludge pro-duction (Muga andMihelcic, 2008; Türker et al., 2009). Lagoons arepond-like water bodies designed based on the specific site andneed, such as the local climate, available amount of land area, thetype of wastewater to treat, and the regulation to meet. There arethree major types (aerobic, facultative, and anaerobic) of lagoonaccording to the biological process taking place in the treatmentprocess (Hunt et al., 2009; Moura et al., 2009; Chandra et al., 2011).Aerobic lagoons use aerobic bacteria and/or algae to treat waste-water in oxygen-adequate condition which is accomplished byeither constructing the lagoons shallow so that air and sunlight cantransfer into the system or relying on proper aeration. Facultativeones are between aerobic and anaerobic lagoons and the treatmentoccurs with the aid of facultative microorganisms. Anaerobic la-goons are oxygen free system in which anaerobic microorganismsplay significant role in the treatment process. In fact, apart frommicroorganism function, settling, filtration, and chemical reactioncould simultaneously exist in lagoon wastewater treatment (Finchand Smith, 1986; Bonnet et al., 1999). Generally, lagoons can pro-vide expected stabilized effluent without offensive odor emission;

x: þ1 (418) 654 2600.

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however, when the system is upset due to certain changes, forexample large quantity wastewater abruptly enters the lagoons,consequently nuisance odor emission will occur (Report, 2008;MacLeod and Wong, 2010).

Odor emission is one of the most common problems in lagoonsand has grabbed increasing attention due to the concern of seriouscomplaints from the neighborhood citizens. Spray perfumes tocover up the odor is the simplest and rapidest method of handlingthe complaints. Addition of chemicals to the wastewater treatmentcan also eliminate odor. Horseradish peroxidase (HRP) as a ferri-protoporphyrin group of peroxidases had been used to reduce para-cresol which is a persistent odor contributor, and the studyrevealed that nearly 50% of para-cresol was reduced within an hour(Eniola et al., 2006). It indicates that HRP can be used to controlodor emission of lagoons in which para-cresol is the main cause.Siemens Water Technologies (2009a, b) have reported thathydrogen peroxide 50% and chlorine dioxide could efficientlycontrol odor emission resulted by the existence of sulfide. That toproviding sufficient oxygen to create anaerobic condition in lagoonis also an efficient way of odor control. Research has exhibited thataeration could mitigate or even eliminate odor production (Zhangand Zhu, 2005; Zhu et al., 2005).

The combination of strategies, which first collecting the odorousgases by covering lagoons with flexible materials and then coop-erating with chemical treatment, such as oxidation and precipita-tion, or biological treatment such as biofiltration, can efficientlyaccomplish the odor control (Florencio et al., 2001; Otten et al.,2004; Xie et al., 2009).

X.L. Zhang et al. / Journal of Environmental Management 124 (2013) 62e71 63

This paper provides information on technologies for odor con-trol in lagoons. The odor control principles of the technologies arealso discussed. In addition, suggestion has beenmade to predict thefeasibility of various technologies.

2. Odor control principles

Odor emission in lagoons is due to the production of odorouscompounds, their emission to the atmosphere, and their trans-portation to the receptors. The keys of odor control of lagoons areprevention of the production, the emission, and/or the trans-portation of the odorous compounds. Odor is considered as a resultof the microbial activities and caused by the production of theodorous volatile compounds such as volatile fatty acids, phenols,ammonia, volatile amines, hydrogen sulfide (the major one), andvolatile sulfur-containing compounds, which are intermediate orend products in organic matter degradation during anaerobicprocesses (Cook et al., 2010; Purdy et al., 2010).

Under anaerobic condition, the microbes have no dissolvedoxygen available for respiration which allows microbes known as‘sulfate-reducing bacteria’ to thrive. This type of microbes wouldtake the sulfate ion (SO4

2�) that is naturally abundant in most wa-ters as an oxygen source for respiration, and lead to the productionof hydrogen sulfide (H2S) which has a low solubility in the waste-water and a strong, offensive, rotten-egg odor. In addition, odorouscompounds are generated from fermentative degradation oforganic matters. In a normal anaerobic process, organic contami-nants are converted into biogas through hydrolysis, acidogenesis,and methanogenesis, and acidogenesis is the step that odoroussubstances are generated, while methanogenesis is the step toconsume the odorous substances to finally formmethane. If there isan imbalance between acidogenesis and methanogenesis, theodors will be generated. Ammonia production during biosoliddigestion is another contributor to the odor problem. As anaerobiccondition is the major cause of odor problem, thus enhancingaerobic process would reduce or eliminate odor emission. Adequatedissolved oxygen supply through aeration or the addition ofchemicals which can provide chemically bound oxygen in aquasolution is necessary for remaining aerobic condition. When theproduction of the odorous compounds is not controlled, cutting offthe compound emission to the environment should be performed.Surface modification with microorganisms which can efficientlycatch and decompose the odorous compounds would be a method.When odorous compounds have been produced and emitted intoair, the odorous compounds transportation to the receptors shouldbe eliminated/reduced. Collection of the odorous compounds fol-lowed by passing them through adsorption column to adsorb orconvert the odorous compounds into odorless substances would bean option. Moreover, covering or masking the odor with pleasantsmell can mitigate the odor effect on the receptors.

3. The technologies in odor control

3.1. Physical technologies

The lagoon site is an important factor in odor control. As dis-cussed above, the transportation of the odorous compounds toreceptor is responsible for the odor problem in lagoons. Wind is themain drive of the compound transportation; therefore, to build thelagoons on the downwind direction would somewhat control theodor problem in lagoons. Generally, most regions experience windfrom various directions over the year, however, the data of thepercentage of wind direction are available. Therefore, locating thelagoon in the downwind site of the largest percentage of the winddirection would inhibit the odor problem to some extent.

Proper designed and operated lagoons normally are stable andhave no odor emissions (http://www.aces.edu/pubs/docs/A/ANR-1090/); therefore, to design the lagoon according to the waste-water characteristics such as organic and suspended solids con-centration would also mitigate the odor emission. For instance,pretreatment or multi-stage treatment should be performed if thewastewater has high organic and suspended solids concentration,while the retention tank should be added when the organic con-centration of the wastewater frequently fluctuates (Module, 1997;Gyger et al., 2007). In addition, it could also reduce odor productionby separating solid from waste stream before it enters lagoonbecause of the reduction on organic loading (Garcia et al., 2009;Rico et al., 2012).

One of the easiest and fastest ways to solve the odor problem isto use perfumed products which are biodegradable, nontoxic,safe, and inexpensive, on the odor source. The principle of thismethod is to cover or mask the odor with pleasant smell, and thusprevent complaints on the odor from the surrounding area. Atpresent, various sprays, powders, and jells are available inthe market, and have been used in practice to mitigate odoroffence to the public (http://www.alibaba.com/showroom/odor-neutralization.html). However, it is not a preferred solutionbecause of the fact that the use of the perfumed products justcovers or masks but not eliminates the odor, which implies thatthe possibility of toxic odor from lagoons to attack the neighbor-hood still exists. Apart from these products, since 1990’s com-mercial odor abatement products such as CB-PA, ESP Enzyme(López Torres and Espinosa Lloréns, 2008) and a Link 2000 wereavailable to be used to lower the odor (Ecochem, 1998). Recently, acommercial odor control spray, called Odoreze�, has also beenreported to control the odor in lagoons (http://www.imtek.biz/page/N/CTGY/od_lag_spr). These products don’t merely maskthe odors, while eliminates and prevents the production ofodorous compounds. There are three mechanisms, and normallythey work together for odor control. For case of Odoreze� appli-cation, firstly, when Odoreze� is applied to lagoons, it immedi-ately attacks and destroys the odorous compounds such ashydrogen sulfide and ammonia. Secondly, it can inactivate theenzyme urease which converts nitrogen and urea to noxious andunpleasant smelling gases such as ammonia. Thirdly, it candestroy odor producing anaerobic bacteria and promotes thegrowth of friendly aerobic odor destroying bacteria.

Collecting odorous compounds from lagoons with flexiblecovers, also called floating covers, to prevent their escape to at-mosphere can be a solution of odor problem. Different types offlexible lagoon covers are commercially available. GeomembraneTechnologies Inc., Lemna Technologies, Inc., and EPURAE are majorcompanies supplying lagoon covers. The covers made of sheets offlexible synthetic materials were themost often utilized type due tothe low cost; however, they were difficult to maintain because ofthe wind and fluctuations in the wastewater levels during the year.Polyethylene and polypropylenemembrane cover is a favorable oneas it is easy to maintain and construct. They can be installed in bothconcrete and earthen lagoons (Bicudo et al., 2003; Funk et al., 2004;Hudson et al., 2008). It was found that the polyethylene and poly-propylene cover could reduce the emission by up to 76% (Hudsonet al., 2008). Normally, flexible cover method requires additionaltreatments such as adsorption and conversion to consume thecollected odorous compounds. Zeolite themselves (Cai et al., 2007)and activated carbon (Calgon, 2010) are typical odor eliminatorsthat are used to adsorb odor gases without chemical change in theeliminators.

In anaerobic lagoons, sludge which is a mixture of degradableand non-degradable solids accumulates in the bottom as time goesby, which would lead to high odor emission. Therefore, periodically

X.L. Zhang et al. / Journal of Environmental Management 124 (2013) 62e7164

sludge removal from lagoons should be performed in order tocontrol odor.

Physical technologies normally cannot thoroughly control theodor. The methods are not to cut off the production of the odorsubstances or to convert them to odorlessmaterials. Therefore, theycan be only temporary strategies to mitigate the odor problemswhen complaints on nuisance odor from public break out.

3.2. Chemical technologies

Wastewater characteristic is significantly important in chemicalmethods of odor control. For instance, wastewater rich in sulfatecould result in high hydrogen sulfide while wastewater rich in ni-trate would cause high ammonia gas emission due to anaerobiccondition.

3.2.1. Odor control by pH adjustmentThe pH has significant effect on the form change of sulfide and

ammonia in aqua solution. In aqueous solution, sulfide (S2�),hydrogen sulfide ion (HS-) and hydrogen sulfide (H2S) are threeforms of sulfides. Equations (1) and (2) describe the disassociationof H2S to HS- and S2-, respectively. The pK values of Equation (1)(pK1) and 2 (pK2) determine the presence of H2S, S2� and/or HS�.H2S is the major specie presenting in the solutionwhen pH is lowerthan 6 (pK1 > pH) (Sharma et al., 1997). The concentration of H2Sand HS- is equal at pH 7 (pK1 ¼ pH). HS� are the main specie at pHgreater than 7. From pH 12, S2� starts to present, while at only pHgreater than 13.8, it becomes the dominant with some HS�.Ammonium (NH4

þ) can transferred to ammonia (NH3) when OH�

presents in the solution (Equation (3)). The pK value of the reactionis 9.25 (Sharma et al., 1998); therefore, there is almost no NH3existing at pH under 6. While as pH goes up, fraction of NH3 in-creases, and NH3 is around 10% at pH 8 and 50% at pH 9.25 (¼pK).Therefore, sulfide and ammonia present in the gas form (H2S andNH3) at pH below 6 and above 8, respectively.

H2S4HS�þHþðpK1 ¼ 7Þ (1)

HS� þ OH�4S2 þ H2OðpK2 ¼ 13:8Þ (2)

NHþ4 þ OH�4NH3 þ H2O

�pK ¼ 9:25

�(3)

The optimal growth pH of methanogenic bacteria is from 6 to 7.5(Steinhaus et al., 2007; Jigar et al., 2011), hence adjusting ormaintaining pH between 6 and 7.5 would highly inhibit the for-mation of hydrogen sulfide and ammonia gas without upsetting

Table 1The comparison of oxidation technologies in hydrogen sulfide odor control.

Oxidants Oxidationpotential(volts)

pHdependence

Half-life inwastewater

Reactiontime (min)

Decomposiproducts

Ozone 2.1 �8 1e30 min <2 O2

H2O2 1.8 �7 30 min <5 H2O, O2

Potassiumpermanganate

1.7 �7 0.9e7 h < 5 MnO2

Chlorine 1.4 �7 1.3e5 h <7 Chlorinatedspecies

Sodium hypochlorite 1.6 6e8 >220 d <10 Chlorinatedspecies

Chlorine dioxide 1.5 5e9 20e180 min <10 Chlorinatedspecies

Ferrate (VI) 2.2 �13 0.01 se15 min <1 Fe3þ, H2O

methanogenic bacteria. Sodium hydroxide and magnesium hy-droxide are two most applied chemicals for pH adjustment tosuppress the hydrogen sulfide and ammonia gas production(Jefferson et al., 2002; Semerjian and Ayoub, 2003; Radhakrishnan,2011). Compared to magnesium hydroxide, sodium hydroxide gavebetter and faster odor control performance due to its high solubility(Jefferson et al., 2002). When the method is applied for odor con-trol, the cause of odor problem should be first found out, whichmeans the type of produced odorous compounds should bedetected. For example, if the odor is resulted by the production ofhydrogen sulfide, the pH should be maintained above 6 butattention should be paid to prevent the inhibition on methano-genesis and ammonia production.

3.2.2. Odor control by oxidationChlorine, chlorine oxygen compound, hydrogen peroxide,

ozone, potassium permanganate, and ferrate, are considered asstrong oxidants. Chlorine and chlorine oxygen compound candissociate to form hypochlorite ion (ClO�) in water. Hypochloritehas very low stability due to the disproportionation and can oxidizemany organic and inorganic substances. The oxidation property ofpotassium permanganate is from MnO4

� in which manganese is inthe highest oxidation state (7þ) resulting in its highly reactivecharacter; while its oxidation capacity is depended on pH. It is astrong oxidant at pH lower than 7, but mild in alkaline solution.Hydrogen peroxide is one of the most powerful oxidants due to therelease of hydroxyl radical, and the oxidation potential is higherthan chlorine, chlorine oxygen compounds, and potassium per-manganate (Table 1). Ozone consists of three oxygen atoms and isan allotropewhich leads to its unstable property. Ozone can rapidlydecompose to hydroxyl and hydrogen peroxyl radicals under highpH condition. The free radicals have unpaired electrons and tend toform a stable structurewhich results in the great oxidizing capacity.Ferrate is the ion in the 6 þ oxidation stage which leads to its highreactivity. In aqueous solution, ferratewill rapidly decomposed intooxygen which plays the important role in oxidation, while theconversion typically occurs at low pH in order to maintain ironsolubility. The addition of the oxidants can convert sulfide ion intoodorless forms including sulfate and element sulfide (Equations (4)and (5)), is more often used to control hydrogen sulfide emissioncompared to pH adjustment (Jefferson et al., 2002; Siemens WaterTechnologies, 2009b, a; California Water Technologies, 2011). Ingeneral, the employment of oxidants does not interfere with othertreatment processes or plant conditions. However, some reportspresented that the oxidants would inactivate microorganisms suchas bacteria, fungi, viruses, and algae due to direct oxidation of cellmaterial or specific enzyme destruction (Dietrich et al., 2007;

tion Dosage ofremoving1 mg/L H2S

H2S removalefficiency (%)

Products References

4.0 mg/L 100 S0 and SO42� (Vogelphohl and Kim, 2004)

4.0 mg/L 100 S0 at pH 7 andSO4

2� at pH > 7(US Peroxide, 2012;Charron et al., 2006)

6.2 mg/L 100 S0 and SO42� (Regenesis, 2007)

8.3 mg/L 100 S0 (EPA, 1999;Zhang et al.,2008)

5 mg/L 100 S0 (White, 1999;Zhang et al.,2008)

2.5 mg/L 100 SO42� (Agency for Toxic Substances

and Disease Registry, 2004)2 mol/L 100 Sulfite, thiosulfate,

and sulfate(Tiwari et al., 2005;He et al., 2009)

X.L. Zhang et al. / Journal of Environmental Management 124 (2013) 62e71 65

Vandekinderen et al., 2009; Cho et al., 2010); while generally theinactivity only occurs when the dosage of oxidants was highenough (such as the addition of potassium permanganate> 20 mg/L), while the dosage is low (such as the addition of potassiumpermanganate is around 10 mg/L) when used for odor control.

In fact, the oxidants can completely remove hydrogen sulfidein less than 10 min, yet the removal depends on the pH of thesystem. Chlorine and its oxygen compounds normally have thelowest efficiency in odor control due to their reaction with othersubstances (organic matters) in the wastewater (Pandit et al.,2006; Zhang et al., 2008). Moreover, the harmful impact on hu-man health has suggested that the use of chlorines should becarefully evaluated. Ozone can rapidly attack the odorants andconvert them to odorless substances, and in addition it can reducebromate in the water. The pH of the solution determines theinitiation of ozone decomposition to free radicals which reduceH2S to S0 or further SO4

2� (von Gunten, 2003). For high removal ofH2S, pH greater than 8 is required. Ozone decomposes fast and itsproduction needs a costly investment in equipment (Fiessingeret al., 1981; Clayton et al., 2006). Potassium permanganate hascommonly been used in industry for odor and taste control;however, its use inwastewater odor control is not favorable due tothe high cost and the low solubility (Arunraj et al., 2008; Zhanget al., 2008). Currently, modified potassium permanganate suchas HS-600 consisted of silica and potassium permanganate whichis cheap has emerged (Filter Innovations INC., 2010); usingmodified potassium permanganate instead of pure potassiumpermanganate would be an alternative. Hydrogen peroxide canrapidly reduce sulfide concentration and provide oxygen to thesystem to inhibit the growth of anaerobes which are the producerof odorous compounds in the wastewater (Krischan et al., 2012).Hydrogen peroxide 50% and 27% are commercially available oxi-dizers for pond or lagoon odor control (Siemens WaterTechnologies, 2009a). Using hydrogen peroxide generally re-quires special consideration in H2O2 addition due to its shortlifespan (around one and a half hours); therefore, multi-pointaddition should be performed (Charron et al., 2006). The H2Soxidation with H2O2 occurs only at neutral and alkaline conditionand the final products are S0 at pH 7 and SO4

2� at pH 9.2. At slightacidic and Ferrate is found to oxidize organic and inorganiccompounds in acidic and alkaline condition (He et al., 2009;Sharma, 2011), The rate of oxidation of H2S with Fe(VI) deceases aspH increases from 7 to 12 (Sharma et al., 1997; Sharma, 2010). Theproducts of the oxidation are thiosulfate at pH 7 and sulfite,thiosulfate, and sulfate at pH 12.

Half-life of the oxidants inwastewater is significantly importantin odor control since it decides the cost, the addition frequency, andthe additionmethod. The half-life depends onmany aspects such asthe pH, initial concentration, and contaminants in the wastewaterand the general values are summarized in Table 1 (EPA, 1999;White, 1999; Agency for Toxic Substances and Disease Registry,2004; Vogelphohl and Kim, 2004; Regenesis, 2007; US Peroxide,2012). Odor control with oxidants alone mainly works onhydrogen sulfide induced odor problem. Recently, researchersobserved that catalytic oxidation could efficiently control the odorproblem contributed by organic compounds (Eniola et al., 2006; Luet al., 2012). Eniola et al. (2006) reported that horseradish peroxi-dase assisted hydrogen peroxide oxidation could efficiently reducethe concentration of para-cresol (odorant).

Nitrate is another type of oxidant using for odor control becausenitrate can provide chemically bound oxygen which can be used tooxidize odorous compounds. Studies have revealed that nitrate(sodium nitrate or calcium nitrate) gave even better performance inhydrogen sulfide emission control than hydrogen peroxide due tonitrate insufficient oxidation potential which enhances oxidation

(Poduska and Anderson, 1981; Jefferson et al., 2002). In fact, twomechanisms have been predicted in odor control by nitrate addi-tion, one is that nitrate oxygen is more readily used by sulfatereducing bacteria than sulfate oxygen hence reduced sulfide pro-duction, while the other is the addition of nitrate develops deni-trification process where nitrate is reduced by oxidizing theproduced sulfide (Zhang et al., 2006; Bories et al., 2007; Jiang et al.,2011). Addition of carefully controlled amounts of nitrate is neededin order not to cause additional treatment of excess nitrate. Thecomparison of oxidation technologies for odor control is shown inTable 1.

3.2.3. Odor control by precipitationMany metal sulfide such as ferrous sulfide, copper sulfide, and

zinc sulfide are insoluble; therefore, using metal ion (iron, copper,and zinc) to precipitate sulfide provides a way to control odorproblems. Compared to other metals, iron is more effective incontrolling the sulfide concentration in wastewater (Jameel, 1989;Hvitved-Jacobsen et al., 2002; Altas and Büyükgüngör, 2008;Mokone et al., 2012), which leads to its wide use in hydrogen sul-fide emission prevention. Three iron salts including ferrous chlo-ride, ferrous sulfate, and ferric chloride aremostly used in hydrogensulfide emission control (Bielefeldt et al., 2002; Firer et al., 2008;Gutierrez et al., 2010). The conversion of sulfide into odorlesscompounds is shown in Equations (1) and (2). It was reported thatferric salt was more efficient in sulfide removal than ferrous salt(Tomar and Abdullah, 1994; Firer et al., 2008). This is due to thateachmolar of Fe3þ removes 2 M sulfide (one molar becomes sulfideelement, and one molar becomes ferrous sulfide precipitant afterFe3þ is reduced to Fe2þ) while each molar of Fe2þ removes onemolar sulfide (ferrous sulfide). The mixture of ferric and ferroussalts has the highest efficiency in sulfide concentration control(Padival et al., 1995; Firer et al., 2008). It is possibly owing to thatFe2þ used by sulfide (Equation (1)) can be continuously compen-sated through Fe3þ reduction (Equation (2)) and hence enhancesferrous sulfide production.

Fe2þ þ S2�/FeSY (4)

Fe3þ þ S2�/Fe2þ þ S0 (5)

3.2.4. Odor control by combustionCombustion is a common method in controlling air pollution

contributed by organic compounds, and could be used for controlodor problem in lagoons. It would require the cooperation withphysical lagoon which can collect the odorants, and the sufficientodorant concentration which is to support appreciable heat ofcombustion. Three methods direct flame, catalytic, and open flarecombustion could be used.

Burning the collected odorous gases in fuel-fired combustionchamber at high temperature is called direct flame combustion. Theodorants are oxidized into odorless substances after being injectedinto the chamber and well mixed with air. Generally, temperaturerange of 650e750 �C is needed for completing odor elimination(Hein, 1964) and the products of combustion should be cooledbefore discharging for safety reasons.

Catalytic combustion is a flameless oxidation of odorant in thepresence of catalyst, and its temperature is more than 200 �C lowerthan that for direct combustion (Hein, 1964; Guan et al., 2007).Platinum alloys are generally applied catalyst as they provided highand stable combustion efficiency (Karagiannidis et al., 2007; Jianget al., 2010; Smyth and Kyritsis, 2012). In order to accomplish thegreatest contact between odorants and catalyst, well arrangedsupports of the catalyst should be employed. It was reported that

X.L. Zhang et al. / Journal of Environmental Management 124 (2013) 62e7166

microreactors with channel height in microscale (0.3e1.0 mm)were stable and efficient (Karagiannidis et al., 2007, 2011).

Open flare combustion can be considerable only when theodorant concentration of the gas effluent from lagoon cover is ableto support combustion. Open flare combustion would be thesimplest one for the omission of the complex construction ofcombustion chamber.

Normally the odorant concentration of gas effluent of lagoons isnot sufficient to support the combustion. Hence, direct flame andcatalytic combustion could be more practical for odor control. Toour best knowledge, no application of combustion for odor controlhas been reported; therefore, work is required to evaluate the use ofcombustion in odor control in reality.

3.2.5. Odor control by odor neutralizationOdor neutralization is a mature technology in lagoon odor

control (Bio Triad, 2009). The neutralization system normally con-sists of a neutralizer storage tank, a vapor producer, a spreader, anda control unit. The odor is eliminated through the following steps:1) converting the stored neutralizer to vapor by heating; 2) sendingthe vapor to the distribution line which is located along the lagoonexterior wall; 3) spreading vapor from the openings facing out thelagoons to neutralize the odorants. The vapor cover distance issignificant factor of odor control efficiency because the short onewill result in the skip of odor emissionwhile the long onewill allowthewaste of the neutralizer. Therefore, the cover distance should bearound the perimeter of the lagoon tank.

3.3. Biological technologies

Physical and chemical methods for odor control are expensiveand energy consuming, and additionally, the odor problem willreappear once the treatment stops (Hein, 1964; Zhang et al., 2008).Biological method is the way to control odor by inhibiting theodorant production which is the root cause of odor problem orodorant emission. To adjust the type of microbes in the system isthe main principle of biological odor control.

3.3.1. Odor control by enhancing aerobic condition in the lagoonAnaerobes are responsible for the odorant production. Sulfate

reducing bacteria (SRB) such as Desulfovibrio sp., Desulfobacter sp.,Desulfobulbus sp., Desulfomonas sp. Desulfomicrobium sp., andDesulfotomaculum sp. thrives in sulfate rich and oxygen deficientenvironment (Gibson et al., 1993; Tebo and Obraztsova, 1998;Azabou et al., 2007; Achá et al., 2011; Shao et al., 2012). SRB convertsulfate into sulfide and then leads to hydrogen sulfide production.Acidogenic anaerobes such as Acetobacterium woodii, Bacillus hal-odurans, Centipede periodontii, Clostridium hastiforme, Desulfobulbuselongatus, Gracilibacter thermotolerans, Lactobacillus rhamnosus,Lactobacillus casei, Lactococcus plantarum, and Thermomonas hae-molytica are important in biogas production as they decomposecomplex carbon into volatile fatty acids which will be further usedby acetogenic bacteria and methanogens to produce methane (Leeet al., 2004; Kim et al., 2010). Therefore, controlling the growth ofthe anaerobes and developing aerobes which degrade organicmaterials into stable inorganic products would be efficient way forodor control (Zhu et al., 2005; Ndegwa et al., 2007).

Aeration is one of the most efficient methods for increasingoxygen concentration to maintain aerobic condition in wastewatertreatment. Odor can be efficiently prevented when oxygen supplywas up to 50% of chemical oxygen demand (Zhang et al., 2006).Zhang et al. (2006) studied the odorant compounds elimination oftwo lagoons Waseca and New Richland, which had odor emissionproblems. Two reactors with 91.6 cm in height and 15.3 cm in in-ternal diameter were built to simulate the real lagoon construction

and operated under ambient temperature ranged from 15 to 32 �Cfor 90 days. Solids concentrations were fixed at 0.5, 1, 2, and 4%w/v.The aeration was accomplished by air pumping through reactorsfrom the bottom using an air pump at a flow rate of 1.2 L/s/m3 withaeration length of 0.5, 4, and 16 days (counted from the first day ofoperation), respectively. The results showed that aeration had greatimpact on pH, total volatile solids (TVS), BOD5, volatile fatty acids(VFA), and total Kjeldahl nitrogen (TKN). The aeration had increasedpH from 7.5 to 8w11 and high pH could inhibit the growth of odor-causing bacteria (Zhu et al., 2001). TVS was reduced only after theaeration length up to 16 days and the reduction rate decreased withthe increase of the initial solids concentration (for example, 22%reduction for 4% solids concentration, 45% reduction for 0.5% solidsconcentration) and the performance maintained for the rest of theperiod (90 days of aeration length). VFA takes the major re-sponsibility of odor problem of lagoons. The results showed thatlonger aeration length and lower solids concentration were, thehigher VFA reduction occurred. The highest VFA reduction (>90%)was observed at 16 days aeration length for 0.5% solids concen-tration reactor. The volatile fatty acids are the intermediate prod-ucts generated during the microbial decomposition of wastematerial (Zhang et al., 1997). The key to preventing odorant com-pound generation is to keep the equilibrium of the production ofacids by the indigenous bacteria and the consumption of acids bythe methanogens to produce methane and carbon dioxide (Zhu,2000). Normally, substrates are abundant in lagoon wastewater,and thus the equilibrium is difficult to be maintained, which wouldresult in less biodegradation of VFA than the VFA generation, andhence created odor problem. TKN removal was found varying as theaeration length change, and the long aeration time led to high TKNremoval (Zhang et al., 2006). The reductionwas due to the emissionof nitrogen containing gases including ammonia, nitrous oxide, andnitrogen gas, and among all, ammonia counted the largest part ofthe emission (above 70%). Ammonia is considered as one of theodor contributors; when TKN concentration is high in the originalwastewater, aeration should be used for odor control, or pH shouldbe controlled (pH < 8) to reduce ammonia emission.

Due to the high energy requirement of thorough aeration forodor control, surface aeration which can form a dissolved oxygenrich blanket on the liquid surface and hence leads to the develop-ment of aerobes in the top layer, has been reported for odor control(Zhang et al., 1997; Zhu et al., 2005). When the odorants generatedby anaerobes try to escape from the surface of the liquid they willbe captured and decomposed into odorless compounds, and resultsin the odor emission reduction. To achieve effective odor control,the thickness of aeration layer should be at least 6 inches, and insome cases it is required up to 24 inches (Bundy et al., 1998; Zhuet al., 2005). The dissolved oxygen concentration (0.3e2.5 mg/L)is significant factor in controlling the top layer aerobic condition(Zhang et al., 1997; Zhu et al., 2005). However, it is reported thathigh rate aerationwould result in high ammonia gas emission, thusthe surface aeration should be carefully performed in practice ac-cording to the lagoon condition.

Apart from aeration, there are other approaches to enhance theaerobic condition in lagoons. One of the methods is the addition ofaerobic microbe bio-activator which contains essential microbialgrowth-promoting factors and can motivate the existing aerobicmicrobial community to greater metabolic capacity and efficiency,and hence control the odor production. The bio-activator is nor-mally scientifically formulated organic acid complex that canaccelerate the natural oxidation of organic matter. It contains aro-matic acids (hydroxyl groups bound to benzene rings, sub-fractionsof humic acid, and bio-catalysts), secondary metabolites which arebiological extracts (amino acids, enzymes, hormone, and poly-saccharides), and some nutrients (macronutrients, micronutrients,

X.L. Zhang et al. / Journal of Environmental Management 124 (2013) 62e71 67

traceminerals, vitamin complexes). It is reported that a commercialbio-activator, BIO ENERGIZER, has successfully solved the odorproblem of a 570 acres lagoon located in US (Probiotic Solutions,2008).

3.3.2. Odor control by controlling anaerobic condition in the lagoonIn anaerobic biodegradation, most of the odorants are generated

in the acidogenesis step which follows hydrolysis step. Themethanogens thriving lagoons have no odor problem because theodorants can be completely degraded into methane and carbondioxide. It implies that the development of methanogens in lagoonsis critical for odor control in anaerobic degradation. Therefore,providing suitable environment for methanogens growth willefficiently prevent the odor production. Methanogens, strictlyanaerobic bacteria, grow well in either mesophilic (20e45 �C) orthermophilic (40e75 �C) temperature ranges at pH from 6.5 to 8.8depending upon genera (Franzmann et al., 1992, 1997; Asakawaet al., 1993; Ferrari et al., 1994; Leadbetter and Breznak, 1996;Kotelnikova et al., 1998; Leadbetter et al., 1998; Lomans et al., 1999;Lin, 2002; Shlimon et al., 2004; Krivushin et al., 2010; Leahy et al.,2010; Mori and Harayama, 2011). The optimal growth condition ofsome methanogens is summarized in Table 2. Strict anaerobiccondition, suitable temperature, proper pH should be provided inorder to enhance methanogenesis. However, the ideal condition isdifficult to accomplish for outdoor lagoons, and up to date, there isno practical case has been reported.

The concentration of salt and ammonia which are toxic to theanaerobes might buildup as the retention time proceeds; therefore,researcher suggested that fresh water dilution should be conductedwhen the risk was detected (Module, 1997).

Table 2The optimal growth temperature and pH of methanogens.

Methanogens Temperature(�C)

pH References

Methanobacteriumaarhusense

45 7.5e8 (Shlimon et al., 2004)

Methanobacteriumsubterraneum

20e40 7.8e8.8 (Kotelnikova et al., 1998)

Methanobacteriumveterum

28 7.0e7.2 (Krivushin et al., 2010)

Methanococcoidesburtonii

23.4 7.2 (Franzmann et al., 1992)

Methanogeniumfrigidum

15 7.0 (Franzmann et al., 1997)

Methanomethylovoranshollandica

34e37 6.5e7.0 (Lomans et al., 1999)

Methanobacteriumpetrolearium

35 6.5 (Mori and Harayama, 2011)

Methanobacteriumferruginis

40 6.0e7.5 (Mori and Harayama, 2011)

Methanobrevibactergottschalkii

37 7 (Lin, 2002)

Methanobrevibacterthaueri

37 7 (Lin, 2002)

Methanobrevibacterwoesei

37 7 (Lin, 2002)

Methanobrevibacterwolinii

37 7 (Lin, 2002)

Methanobrevibacterruminantium

38 7.2 (Leahy et al., 2010)

Methanobrevibacterarboriphilicus

30e37 7.5e7.8 (Asakawa et al., 1993)

Methanobrevibactercurvatus

30 7.2 (Leadbetter and Breznak, 1996)

Methanobrevibactercuticularis

37 7.7 (Leadbetter and Breznak, 1996)

Methanobrevibacterfiliformis

30 7.2 (Leadbetter and Breznak, 1996)

Methanobrevibacteroralis

37 6.9e7.4 (Ferrari et al., 1994)

3.3.3. Odor control by the biological coverUnlike physical covers, biological cover uses microorganism

attachable materials floating on the surface of wastewater to pre-vent the emission of the odor. The principle of the odor controlincludes: 1) the biological cover provides a barrier for odorantaccessing to environment and for oxygen accessing to the waste-water and hence provide a strict anaerobic condition for metha-nogens growth; 2) odorants are captured and oxidized by aerobicmicroorganisms attached to the cover materials when they passthrough the cover. For instance, enteric bacteria including Escher-ichia coli, Campylobacter jejuni, and Shigella are found capable ofconverting ammonia nitrogen to nitrate (Cole, 1996), which sug-gests that enteric bacteria inhabiting biocover can effectively con-trol the odor problem resulted by ammonia emission. Phototrophicand chemotrophic bacteria such as Beggiato sp., Chlorobium limi-cola, Chlorobium thiosulfatophilum, Thiobacillus thiooxidans, Thio-bacillus ferrooxidans, Thiobacillus denitrificans, Thiobacillus novellus,Thiothrix nivea, Thermothrix azorensis, Thioalkalispira micro-aerophila, Pseudomonas acidovorans, and Pseudomonas putida, arecapable of biooxidizing hydrogen sulfide to S0 or SO4

2� (Kim andChang, 1991; Odintsova et al., 1996; Oyarzún et al., 2003; Syedand Henshaw, 2003). It indicates that the biocover mainly in-habits these bacteria would have high efficiency for hydrogen sul-fide odor control.

Peat bed covered lagoon could reduce the hydrogen sulfideemission rate up to around 85% (Picot et al., 2001). The study alsoexpressed that the modification on the peat bed with the additionof iron salt (FeCl3) and plant (Zhang et al., 2008) could furtherdecrease the H2S emission rate to more than 95%. It was predictedthat the oxidation and precipitation of sulfide by ferric ions hadtaken place. Geotextile fabric and recycled polyethylene foamcovers exhibited efficient control on odor caused by hydrogensulfide, ammonia, and hydrocarbon emissions (Regmi et al., 2007).Straw covers are popular as they are cheap and efficient(Agriculture and Rural Development of Alberta, 1993). The strawcover thickness was critical on odor control (Clanton, 1997; Horniget al., 1999). The odor reduction (47%, 69%, and 76%) increased withthe straw cover thickness (10 cm, 20 cm, and 30 cm, respectively)increased (Clanton, 1997). Another study revealed that a strawcover varying in thickness between 5 and 15 cm reduced odoremissions by about 84%, and especially efficient on ammoniaemission control which would be reduced by 80% (Hornig et al.,1999). However, biological covers also have problems in theapplication. First, the cover is applied to the lagoon by blowers; it isdifficult to control the thickness. Moreover, the odor controleffectiveness of the covers reduces with time because of the satu-ration and sinking of the straw, which leads to their short longevity(usually last two to six months, depending on the amount applied(depth), evenness of application, basin size, and climatic conditionsof the area) (Bicudo et al., 2003). In addition, due to the problem ofcover material sinking, it would increase the organic matter con-centration in the lagoon, which would results in more serious odoremission problem; therefore, periodical cleaning is required. Toprevent lagoon influent and effluent point blocking, chopperpumps should be used in the wastewater pumping (influent andeffluent) instead of normal pumps.

3.3.4. Odor control by biofiltrationBiofiltration is one of the most popular technologies for odor

control in industry (Nicolai and Janni, 2000; Sheridan et al., 2003;Xie et al., 2009). Generally, it has to be associated with physicalcover technology. The odorants are collected by physical covers andsequentially injected into a biotrickling filter or biofilter filled withbiocarriers such as wood chips or polymers. The odorants could beeliminated by interacting with the biocarriers or being adsorbed by

X.L. Zhang et al. / Journal of Environmental Management 124 (2013) 62e7168

the biocarriers or being converted into odor free compounds bymicroorganisms growing in/on the biocarriers. Physical sorptionand biological decomposition are the reasons of odor control bybiofiltration. However, the available sites in the carriers for inter-action and sorption are limited, thus biological decomposition ofthe odorants bymicroorganisms is majorly responsible for the odorcontrol. Therefore, microorganism is the key of biofiltration forodor control. Bacillus sp., and Thiobacillus sp. are twomajor bacteriaused in biofiltration to remove hydrogen sulfide (Kim et al., 2002;Oyarzún et al., 2003; Park et al., 2009; Ramírez-Sáenz et al., 2009;Xie et al., 2009). Paracoccus sp. and Enterobacter were reported toefficiently remove volatile organic compounds (Shim et al., 2005;Tsang et al., 2007; Xie et al., 2009). Pseudomonas sp. could simul-taneously eliminate H2S, NH3, and volatile organic compounds (Xieet al., 2009; Lebrero et al., 2011). Biofiltration can be a self-inoculated (packed with compost or wastewater sludge) or anintroducing-inoculated system (Table 3). The former system ischeap but responds slow (Otten et al., 2004; Pagans et al., 2006;Taghipour et al., 2008; Liu et al., 2009; Hort et al., 2012). It is due tothe time required for microbial community shifting from originalmicrobes in compost or sludge to odor removal microbes. Thesystem introducing microbes with odor removal ability is stableand can be pertinent.

Several parameters including gas residence time, moisture,packing porosity, temperature and pH, are important in bio-filtration operation. The proper control on these parameters ismainly due to the consideration on the maintenance of microor-ganism growth in the biofilter. Among all, residence time, alsocalled empty bed time, and moisture are two most significant fac-tors.When the gas residence time determines is short, the odorantsin the gas stream will escape from the biofiltration before they canbe captured. Residence time required in odorous compoundsremoval is normally less than 1 min (Table 3). The minimummoisture required tomaintain thewell performance of microbes on

Table 3The removal of odorants by biofiltration.

Biofiltration material Microbes Retention tim

Granular activated carbon Thiobacillus thioparus 20e60Peat Thiobacillus thioparus 16.67Wood chip Enterobacter sp.

Moraxella sp.Pseudomonas sp.

32

Compost e 13.14Compost e 60Compost, sludge and

pieces of hard plasticse 60

Compost e 32.5e65Cork Nitrosomonas; Nitrobacter;

Thiobacillus thioparus;Pseudomonas aeruginosa;Pseudomonas putida;Pseudomonas putida

40

Glass ringsLava rock vermiculite

Thiobacillus sp.;Rhodococcus sp.

31

Waste straw and cortex Bacillus sp.;Pseudomonas sp.

120

Granular activated carbon Alcaligenes faecalis 29Compost and perlite Pseudomonas fluorescens 32Peat Moraxellaceae sp.;

Acinetobacter sp.;Pseudomonas sp.

60

Polyurethane Fusarium solani 60

Compost with yard waste e 59Mature compost with sewage

sludge and yard wastee 59

a VOC representing volatile organic compounds.

odorant reduction is 40% (Oyarzún et al., 2003; Pagans et al., 2006;Taghipour et al., 2008).

Biological technologies generally require longer response timeto cure the odor emission problem of lagoons; however, they aremore cost- and energy-efficient compared to physical or chemicaltechnologies. Among all the biological technologies, biologicalcover is the promising technology due to its easy operation andhigh efficiency.

4. Case studies

The addition of commercial odor eliminating products is themost commonly used method of odor control in lagoon. Vegetableprocessor wastewater lagoons in Southern Ontario had beencomplained by the surrounding community. The odor was due tothe large organic loading to the lagoon. BCP60 and STIMULUSproduced by Bionetix International (2011) were utilized to controlthe odor. After two days operation, the odor was eliminated. Theaddition of BCP60 and STIMULUS rapidly decomposed the organiccompounds such as protein, fat, and carbohydrates, and hencereduced the organic load, which altered the disordered lagoon to ahealthy condition. Wastewater lagoons of a food processing in-dustry in California, USA had great odor emission and resulted inextensive complaints from the local residence. Custom OE pro-duced by Custom Biologicals US was introduced to the lagoons.After two weeks treatment the odor was reduced and no com-plaints were received since after (Custom Biologicals, 2012). Com-mercial product application is suitable for the lagoon of small sizeand that urgently needing solution for odor control as they workfast but costly.

In practice, utilization of covers on the surface of lagoons is themost common method in odor control (Zhao et al., 2008). Air-filledclay balls using as cover has also showed encouraging performanceof 56e90% odor reduction (Livestock and Poultry Environmental

e (s) Removal efficiency (%) References

H2S NH3 VOCa

99.9 92 e (Kim et al., 2002)100 e e (Oyarzún et al., 2003)e e 100 (Sheridan et al., 2003)

e e 100 (Otten et al., 2004)e e 97 (Pagans et al., 2006)e 97.9 e (Taghipour et al., 2008)

e e 95 (Liu et al., 2009)100 100 90 (Park et al., 2009)

99 e 99 (Ramírez-Sáenz et al.,2009)

98 91 90 (Xie et al., 2009)

100 e e (Rattanapan et al., 2010)96e100 e 99 (Lebrero et al., 2011)90e99 e e (Omri et al., 2011)

e e 100 (Gutiérrez-Acostaet al., 2012)

95e100 e e (Hort et al., 2012)70 e e (Hort et al., 2012)

X.L. Zhang et al. / Journal of Environmental Management 124 (2013) 62e71 69

Stewardship (LPES), 2011). Odor emission from manure storagelagoons in Wisconsin, US, has been observed over two years mea-surement (Wisconsin Department of Agriculture Trade andConsumer Protection and Resources, 2009). The lagoons werereceiving 400e2500 head of cattle manure. In odor to control theemission, four types of treatment including anaerobic digestion,impermeable cover, permeable cover, and solid separation andaerationwere conducted. The operation started in August 2005 andended in June 2009. Hydrogen sulfide and ammonia gas are thecause of the odor emission. The impermeable cover made ofpolyethylene was air tightly sealed around the perimeter of thelagoon which was collecting the manure of 875 milking and drycow. The result showed that the odor reductionwas 100%. The totalcost of the treatment over the operation period was around300 000 US $. Anaerobic digestion provided only 15% reduction ofthe odor emission of the lagoon which was obtaining 1850 cow’swaste. The total cost was 9 350 US $. Permeable geotextile mem-brane cover installed in the lagoon which was received 2000milking cow’s waste and the odor reduction was up to 70%. Thetotal cost was 200 000 US $. Solid separation and aeration treat-ment did reduce odor emission while increased it due to that theaeration aspirated the hydrogen sulfide getting out from the lagoonsurface. The total cost was 141000 US $. Impermeable polyethylenecover is the most efficient and has the longest life-span (more than10 years) while it is also the most costly technology. Anaerobicdigestion is the cheapest one due to the avoidance of the cost oncontrol technology but the odor reduction was low. Permeablecover would be a suitable option of manure storage lagoon odorcontrol as it is cost- and reduction- efficient approach.

5. Conclusion

Lagoon odor control grabs growing attention due to the pressurefrom its surrounding public. Many technologies and commercialproducts are available to be used for odor control; however, theirapplications should be built upon the investigation of practicelagoon. When complaints break out, commercial products utiliza-tion should be first considered; meanwhile permeable cover shouldbe built up as it is practical, affordable, and efficient.

Acknowledgements

Sincere thanks are due to the Natural Sciences and EngineeringResearch Council of Canada (Grant A 4984, Canada Research Chair)for their financial support. The views and opinions expressed in thispaper are those of the authors.

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