Research Article Nitrogen Removal in a Full-Scale Domestic Wastewater...

Hindawi Publishing CorporationJournal of Environmental and Public HealthVolume 2013, Article ID 504705, 6 pageshttp://dx.doi.org/10.1155/2013/504705

Research ArticleNitrogen Removal in a Full-Scale Domestic WastewaterTreatment Plant with Activated Sludge and Trickling Filter

Davood Nourmohammadi,1 Mir-Bager Esmaeeli,1

Hossein Akbarian,1 and Mohammad Ghasemian2

1 Tehran Sewerage Company, Tehran 15688, Iran2 Environment Research Center, School of Health, Isfahan University of Medical Sciences,Isfahan 8613846191, Iran

Correspondence should be addressed to Mohammad Ghasemian; [email protected]

Received 13 November 2012; Revised 27 February 2013; Accepted 13 March 2013

Academic Editor: Mohammad Mehdi Amin

Copyright © 2013 Davood Nourmohammadi et al. This is an open access article distributed under the Creative CommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

During the last decade, more stringent effluent requirements concerning the nutrients effluent values have been imposed bylegislation and social concern. In this study, efficiency of total nitrogen removal in activated sludge and trickling filter processes(AS/TF) was investigated in Tehran North wastewater treatment plant. Biological system in this site was included, anoxic selectortank, aeration tank, final sedimentation, and trickling filter. A part of treated wastewater before chlorination was mixed withsupernatant of dewatered sludge and fed to the trickling filter. Supernatant of dewatered sludge with high concentration of NH

4-N

was diluted by treated wastewater to provide complete nitrification in trickling filter Produced nitrate in trickling filter was arrivedto the anoxic tank and converted to nitrogen gas by denitrification. According to the study result, low concentration of organiccarbone and high concentration of NH

4-N led to nitrification in TF, then nitrate denitrification to nitrogen gas occurred in selector

area. NH4-N concentration decreased from 26.8mg/L to 0.29mg/L in TF, and NO

3-N concentration increased from 8.8mg/L to

27mg/L in TF. Consequently, the total nitrogen decreased approximately to 50% in biological process. This efficiency has beenobserved in returned flow around 24% from final sedimentation into TF. It was concluded that, in comparison with biologicalnutrient removal processes, this process is very efficient and simple.

1. Introduction

Many industrial effluents, agricultural wastes, or otherhuman activities generate high strength ammonium wastew-ater [1]. Water pollution represents one of the most seriousenvironmental problems due to the discharge of nutrientsinto receiving waters. Hence, stricter standards for the oper-ation of wastewater treatment plants (WWTPs) have beenimposed by authorities. In order to meet these standards,improved control of WWTPs is needed. WWTPs shouldbe controlled in such a way that plant operating costs areminimized, while effluent standards are still maintained.Different control algorithms for WWTPs have been intro-duced over the years [2]. Approximately 25% of all waterbody impairments are due to nutrient-related causes (e.g.,

nutrients, oxygen depletion, algal growth, ammonia, harm-ful algal blooms, biological integrity, and turbidity). Totaleffluent nitrogen comprises ammonia, nitrate, particulateorganic nitrogen, and soluble organic nitrogen.Thebiologicalprocesses that primarily remove nitrogen are nitrificationand denitrification [3]. Advances in secondary wastewatertreatment processes and increased implementation of reg-ulations on discharged effluents over the last few decadeshave led to variations in wastewater treatment ranging fromsimple organic carbon oxidation to the removal of nitrogen(N) and phosphorus (P) [4]. Nitrogen removal is normallyrealized by sequentially alternating between oxic and anoxicconditions or by the creation of separated zones with suitableconditions for nitrification and denitrification, respectively.Alternatively, high rates of simultaneous nitrification and

2 Journal of Environmental and Public Health

denitrification (SND) can be achieved, in activated sludgeand biofilm type systems alike, at operational conditionswhere both oxic and anoxic microenvironments are present.Nitrification can occur at the liquid/biomass interface, whiledenitrification of nitrate (or nitrite) may be found in deepersubsurface biomass zones [5].

Organic matter and nutrient removal from wastewaterimproves the environmental conditions as well as provideshealth and well-being to the citizens [6]. Activated sludgeprocess is one of the most widely used biological treatmentsof wastewaters containing carbon and nitrogen pollutants [7].Conventional nitrogen removal fromwastewater by activatedsludge is most often achieved by sequential aerobic andanoxic processes.There is a tremendous need to develop reli-able technologies for the treatment of domestic wastewaterin developing countries. Such treatment systems must fulfillmany requirements, such as simple design, use of nonso-phisticated equipment, high treatment efficiency, and lowoperating and capital costs. In addition, consonant withpopulation growth and increase in urbanization, the costand availability of land are becoming a limiting factor, and“footprint size” is increasingly becoming important in thechoice of a treatment system [8]. There are a number ofBNR process configurations available. Some BNR systemsare designed to remove only TN or TP, while others removeboth. For BNR systems to result in low TN and TP effluentconcentrations, proper operation and control of the systemsare essential. Operators should be trained to understand howtemperature, dissolved oxygen (DO) levels, pH, filamentousgrowth, and recycle loads affect system performance. BNRcosts differ for new plants and retrofits. New plant BNRcosts are based on estimated influent quality, target effluentquality, and available funding [9]. One of the key designparameters for any biological nutrient removal system is theinfluent C, N, and P ratios [1]. The COD/N ratio influencesthe population of microorganisms. Since an increase in thisparameter results in a decrease in nitrification efficiencyand an improvement of denitrification efficiency [10]. Thecontrol of DO concentration is also crucial as it determinesthe dominant processes in the reactor. A high DO inhibitsdenitrification, whereas a low DO causes a limitation ofammonia oxidation [11]. DO is easily controlled by manip-ulating the air supply, and it strongly influences the costof wastewater treatment resulting from aeration. A lowCOD/N ratio and a lowDOpromote partial nitrification, andthis diminishes the oxygen demand by 25% and the CODrequirement for denitrification by 40% [12].Themost impor-tant factors affecting SND are organic carbon, DO concen-tration, and floc size [13]. Simultaneous growth of nitrifiers(autotrophs) and heterotrophs in a single reactor with ahigh COD/N ratio causes low nitrification efficiency due tocompetition between these two bacterial groups [14]. Theoptimal DO concentration for effective nitrogen removal viaSND equals 0.5mg O

2/L [15]. The aim of this study is survey

of efficiency of total nitrogen removal in activated sludge andtrickling filter processes (AS/TF) in TehranNorth wastewatertreatment plant.

2. Materials and Methods

2.1. Description of TWWTP. Tehran wastewater treatmentplant (TWWTP) will consist of 4 modules, designed for2,100,000 person and an average daily inflow of 5.2m3/s.This plant is located within the latitude and longitude of35.569098 and 51.439877. The two wastewater streams arecombined down flow of separate flow measurements andtreated together bymechanical and biological treatment stepssupplemented with sludge treatment units.

Aeration tanks are employed for biological removal ofpollutants using the activated sludge process. Each of thefour aeration tanks consists of a selector cascade and twoadditional cascades. The basins are designed as plug flowreactors of rectangular shape. The outlet of the tricklingfilters will also be transferred into the inlet channels of theaeration tanks. During normal operation, each of the fourtrickling filters, will discharge its outlet in one inlet channelof the aeration tanks. Thus, equal distribution of nitrate tothe four lines is provided. However, in case of maintenancework in either an aeration tank or a trickling filter it willalso be possible to combine the trickling filter outlets in acombined collection/distribution structure and to distributethe flow to all lines (which are in operation) by gravity flow.The aeration tanks represent the very location in which thebiological treatment of wastewater takes place by adoptingthe medium-loaded activated sludge process. Due to thetreatment target and the system chosen, mainly degradationof BOD

5(organic pollutants) will be performed.The required

denitrification will mainly be achieved in the anoxic selectorcascade and by simultaneous denitrification in anoxic zonesof the aerated part of the tank and within the sludge flocks.During periods with low wastewater temperature the pre-denitrification and simultaneous denitrification will providea nitrate-free effluent. During periods with high wastewatertemperature, somenitratemight remain in the effluent, whichis not affecting the effluent quality as long as severe deni-trification in the final sedimentation tanks is prevented. Toprevent this “wild” denitrification, it will be possible to reducethe sludge retention time in the final sedimentation tanks tobelow 1 hour by control of the return sludge flow. A selectoris employed to prevent and to control filamentous bacteriagrowth. Air or mechanical mixers can be used for sufficientmixing within the selector compartment. In this case, theselector will mainly provide anoxic conditions due to the inletof nitrate from trickling filter effluent. Some air supply is fore-seen for mixing purposes only. With regard to denitrificationcapacity, the introduced air is considered in the design asshownbelow.Generally, the air supplywill only have a limitedeffect on denitrification due to the high respiration rate in thisinitial compartment of the aeration tank (up to 4 times higherthan average respiration rate). Effluent transfers the treatedwater to agricultural network, in case of noncompliance of thetreated water quality with the stipulated treatment standard.

2.2. WWTP Measurements

2.2.1. Full-Scale Experiments. A year monitoring campaignwas set up in one of the beds (March, 2011, and March, 2012),

Journal of Environmental and Public Health 3

Screening

Grit chamber Primary sedimentationAerationSelector

Final sedimentation

Gravity thickener

Belt thickener Digester

Belt filter press

Trickling filter

Sludge cake

measurements measurements

measurements

measurements

NO3-N, NH4-N, TN, BOD, COD,𝑄 NO3-N, NH4-N, TN, BOD, COD,𝑄

NO3-N, NH4-N

NO3-N, NH4-N, TN,𝑄

Figure 1: The TWWTP schematic and sampling points.

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Figure 2: BOD5in influent and effluent.

including the measurement of flow rate (in flow and out flowof the plant, tricking filter inflow) and the collection of weeklysamples (one single sample by week, during 57 weeks) in fourpoints: influent and effluent and two samples in inlet andoutlet of trickling filter to determine the total nitrogen (TN),ammonia nitrogen (NH

4-N), and nitrate nitrogen (NO

3-N).

For determination of COD/N in this study, COD samplein influent was taken. Figure 1 shows the WWTP processesschematic and location of sampling.

TheCODwas determined with cuvette tests LCK 314 (15–150mgCOD/L) and LCK 514 (100–2,000mgCOD/L), fol-lowing DIN 38049-4, and a CADAS 50 spectrometer (HachLange, Germany). Total nitrogen, ammonia nitrogen, andnitrate nitrogen were obtained using the cuvette tests LCK238 (5–40mgN/L), LCK 303 (2–47mgNH

4-N/L), LCK 342

(0.6–6mgNO2-N L21), and LCK 339(0.23–13.50mgNO

3-

N/L), following standards DIN38406-E 5-1 and DIN 38402-A51 and the same spectrometer. BOD was determinedaccording to the standard methods for the examinationof water and wastewater [16]. The experimental apparatusconsisted of three parallel module with electrodes for acontinuous monitoring of pH, temperature and dissolvedoxygen (DO), and computer control system to maintain DOconcentration and temperature around set points.

3. Result and Discussion

Sewer system which transfers sewerage to Tehran Northwastewater treatment plant is too long and reaches to morethan 30 kilometers in some branch.Height deference betweenthe highest and lowest levels in abovemention system ismorethan 700meters. This matter causes the BOD

5concentrating

in sewer to decrease by reaeration. Average concentrations ofBOD5in influent and effluent of the plant were, respectively,

255mg/L and 8.2mg/L per studied duration. In such condi-tion, ammonification also happens (see Figure 2). BetweenNH4-N, NO

3-N, and TN in raw wastewater is shown in

Figure 3.Due to the importance of COD/TN, this factor and its

trend was calculated. In NH4-N was analyzed in inlet andoutlet of trickling filter, and that removal efficiency was


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Total N

Con

cent

ratio

n (m

g/L)

ASTF

NO3-N NH4-N

Figure 3: NO3-N, NH

4-N, and total nitrogen in AS and TF.

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Figure 4: COD/TN and TN removal efficiency in influent.

98%. Between TN removal efficiency and COD/TN showsthat these parameters are not related directly, and this trendimplies the effective parameters on the total nitrogen removalefficiency. The proof which approves the above result is thestable removal of BOD

5and unstable removal efficiency of

total nitrogen as shown in Figure 4.Concentration of NH

4-N before trickling filter and

after aeration tank has shown that nitrification was welldone. NH

4-N concentration decreased from 26.8mg/L to

0.29mg/L in TF (see Figure 5), and NO3-N concentration

increased from 8.8mg/L to 27mg/L in TF.Since, the main inflow of trickling filter is supplied by

effluent, absorbed oxygen in this unit is used for convertingNH4-N to NO

3-N, and there is no requirement to consume

oxygen for organic carbon oxidation. Base on Figure 7,average ratio for TF inflow to total plant flow was 24% anddata approves that this ratio is desirable for 50% of TNremoval.

Average concentration of total nitrogen of Tehranwastewater treatment plantwas analyzed andwas shown to be

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out

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NH4-N inNH4-N out

Figure 5: NH4-N in before and after TF.

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(mg/

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Figure 6: NO3-N in before and after TF.

55mg/L of which 35mg/L is related to NH4-N and 0.8mg/L

for NO3-N as in Figure 6.

Relation between tricking filter flow to total plant flowratio and total nitrogen removal efficiency has been demon-strated in Figure 7, in which the average of 𝑄TF/𝑄in reachesto 24%.This figure shows that nitrification and denitrificationhave been done well, and dissolve oxygen has been availableand enough for nitrification in trickling filter. In order toevaluate TN removal efficiency, this parameter ismeasured inbefore and after biological units Based on the plant design, atleast 50% of TN must be removed. Therefore, trickling filterwas used, and the same time, the power consumption alsodecreased. Reduction of energy consumption was related tolower dissolve oxygen in aeration tanks; the concentration ofdissolve oxygen in aeration tank is set to 0.9mg/L, and underthis condition, BOD

5and TN diminished to the defined

Journal of Environmental and Public Health 5

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𝑄TF/𝑄inTN

rem

oval

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of N

O3-N

TN out

Figure 7: Removal efficiency of TN, 𝑄TF/𝑄in, and TN out.

limit. Also trickling filters are employed for the nitrificationof ammonia contained in the highly concentrated filtratefrom sludge dewatering Figure 8 illustrates BOD and TNremoval efficiency. Additionally, a part of the effluent of theactivated sludge stage is returned via the trickling filtersfor nitrification. Due to subsequent denitrification of theproduced nitrate in the activated sludge stage, the effluentrequirement of Ntotal ≤ 30mg/L will be achieved. Beside thetransfer of ammonia to the trickling filters, the recirculationof final clarifier effluent also serves for dilution of the sludgedewatering filtrate in order to provide sufficient alkalinity inthe trickling filters. Differing from the original design, it isnow foreseen to transfer only filtrate from sludge dewateringto the trickling filters. All other sludgewaters andwashwaterswill be transferred to the primary sedimentation or to theactivated sludge stage. Due to this process adaptation, theBOD5load and suspended solids (SSs) load to the trickling

filters will be very low.Albuquerque et al. reported that ammonia removal rates

reached higher values (from 172 gN/m3 d to 564 gN/m3 d)for C/N = 2 and lower values (from 13.6 gN/m3 d to34.6 gN/m3 d) for C/N = 20. Between 50% and 70% of theammonia was removed in the upper section of the filter [17].

In Ryu et al. study, NH4-N removal performance was

stable with the removal efficiency of 95-96% on average,regardless of HRT applied. At the TCOD- to TKN-ratio of3 : 6 of four-stage biological aerated filter system, the effluentNO3-N concentration of denitrification columnwas 2.7mg/L

which was excellent in nitrogen removal performance byemploying four columns functioning as sorption, nitrifica-tion, denitrification, and purification, respectively [18].

Based on Timothy et al. study, in various operating con-dition, the TFs removed an average of 2.4× 10−4 kgN/(dm2),and the NTFs removed an average of 1.5× 10−5 kgN/(dm2)because of low loading [19].

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Figure 8: BOD5and TN removal efficiency.

In the full-scale bioreactor for treating an average leachateflow of 304m3 d−1 with a SRT range of 12 and 18 d, the averageCOD, NH

4

+-N, and NO3

−-N concentrations at the upstreamend of the bioreactor, that is, influent, were 554, 634, and3mg L−1, respectively, whereas no NO

2

−-N was detected inthe influent [20].

The resulting independence of the trickling filter frompossible fluctuations of the quality of other process streamsis a further advantage. Due to the low BOD

5and SS load,

it is evident that the main target of this treatment stepis the oxidation of ammonia only. Some degradation oforganic pollutants can be seen as side-effect, and it should bestressed that with the low organic load figures TF cloggingis definitely prevented. The biologically active biomass willadhere to the filter material and will create a biologicallawn mainly consisting of nitrifying bacteria (Nitrosomonasand Nitrobacter), which will accomplish the oxidation ofammonia to nitrate and further to nitrate. After passing thefilter material, the nitrified water is collected and transferredto the inlet of the aeration tank by gravity.

During normal operation, each trickling filter will bedirectly connected with the inlet channel of one aerationtank. For redundancy reasons, it will also be possible tocombine all trickling filter outlet flows before distribution tothe aeration tanks.The recycle of the trickling filter effluent tothe activated sludge stage contributes to an overall low energydemand of the biological treatment stage.

4. Conclusion

In AS/TF system, low concentration of organic carboneand high concentration of NH

4-N led to nitrification in TF

part, then nitrate denitrification to nitrogen gas occurredin selector area. So, these advantages in TF part causes abetter performance than for TN removal in TF and AS


separately. NH4-N concentration decreased from 26.8mg/L

to 0.29mg/L in TF, and NO3-N concentration increased

from 8.8mg/L to 27mg/L in TF. Consequently, total nitrogendecreased approximately to 50% in biological process. Thisefficiency has been observed in returned flow around 24%from final sedimentation into TF. It was concluded that, incomparison with biological nutrient removal processes, thisprocess is very efficient and simple.

References

[1] M. Islam, N. George, J. Zhu, and N. Chowdhury, “Impactof carbon to nitrogen ratio on nutrient removal in a liquid-solid circulating fluidized bed bioreactor (LSCFB),” ProcessBiochemistry, vol. 44, no. 5, pp. 578–583, 2009.

[2] A. Stare, D. Vrecko, N. Hvala, and S. Strmcnik, “Comparisonof control strategies for nitrogen removal in an activated sludgeprocess in terms of operating costs: a simulation study,” WaterResearch, vol. 41, no. 9, pp. 2004–2014, 2007.

[3] S. Jeyanayagam, “True confessions of the biological nutrientremoval process,” Florida Water Resources Journal, pp. 37–46,2005.

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[10] Z. Magdalena, B. Katarzyna, and C. Agnieszka, “Nitrogenremoval from wastewater and bacterial diversity in activatedsludge at different COD/N ratios and dissolved oxygen concen-trations,” Environmental Biotechnology, pp. 10–70, 2011.

[11] G. Tchobanoglous and F. Burton, Wastewater Engineering:Treatment and Reuse. Metcalf and Eddy, McGraw-Hill, NewYork, NY, USA, 4th edition, 2003.

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[14] E. Gorgun, N. Artan, D. Orhon, and S. Sozen, “Evaluation ofnitrogen removal by step feeding in large treatment plants,”Water Science andTechnology, vol. 34, no. 1-2, pp. 253–260, 1996.

[15] S. Schlegel, “Operational results of waste water treatmentplants with biological N and P elimination,” Water Science andTechnology, vol. 25, no. 4-5, pp. 241–247, 1992.

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[19] E. A. Evans, G. Timothy, M. Ellis, H. Gullicks, and J. Ringe-lestein, “Trickling filter nitrification performance characteris-tics and potential of a full-scalemunicipal wastewater treatmentfacility,” Journal of Environmental Engineering, vol. 130, no. 11,pp. 1280–1288, 2004.

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