Operational Performance of an AnaerobicAnoxic-Aerobic Treatment System

Abstract

An anaerobic (UASB)-hybrid aerobic (suspended and attached growth activated sludge) wastewater treatment system was evaluated on the removal of organic matter, solids and nitrogen following its pre-operational phase. Analysis were made weekly based on composite samples, prepared by grab samples taken every four hours, during 24-hour cycle, weighted by flow rate, on each monitoring point (raw sewage, UASB, anoxic chamber, aerobic reactors, return sludge from secondary decanters and final effluent). The plant presented an average flow rate of 908 m3/h with peaks from 10 to 14 h. BOD was removed by 86% (310 to 41 mg/L) being the highest parcel accounted by UASB reactors (70%) and removal of total suspended solids reached 63% (190 to 94 mg/L). Mean removals of TKN (71%) and Ammonium (77%) were above the value predicted by design and, probably the nitrification-denitrification process was not the dominant route.

Full text

Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
247
Operational Performance of an Anaerobic-
Anoxic-Aerobic Treatment System
Andre Luis Calado Araujo
1
Danillo Luiz de Magalhães Ferraz
2
Paulo Eduardo Vieira Cunha
3
Cícero Fernandes Neto
4
Fernando José Araújo da Silva
5
ABSTRACT:
An anaerobic (UASB) – hybrid aerobic (suspended and attached growth activated sludge) wastewater
treatment system was evaluated on the removal of organic matter, solids and nitrogen following its pre-
operational phase. Analysis were made weekly based on composite samples, prepared by grab samples
taken every four hours, during 24-hour cycle, weighted by flow rate, on each monitoring point (raw
sewage, UASB, anoxic chamber, aerobic reactors, return sludge from secondary decanters and final
effluent). The plant presented an average flow rate of 908 m3/h with peaks from 10 to 14 h. BOD was
removed by 86% (310 to 41 mg/L) being the highest parcel accounted by UASB reactors (70%) and
removal of total suspended solids reached 63% (190 to 94 mg/L). Mean removals of TKN (71%) and
Ammonium (77%) were above the value predicted by design and, probably the nitrification-
denitrification process was not the dominant route.
Keywords: Pollution Control; Organic Matter Removal; UASB Reactor; Wastewater Treatment.
1
Ph.D. in Civil Engineering at the University of Leeds, LEEDS, England. Lecturer at the Instituto Federal de Educação,
Ciência e Tecnologia do Rio Grande do Norte, IFRN; and at the Universidade Federal do Rio Grande do Norte, UFRN,
Brazil. acalado@ifrn.edu.br
2
Master in Sanitary Engineering at the Universidade Federal do Rio Grande do Norte, UFRN, Brazil.
guardian_ferraz@yahoo.com.br
3
Ph.D. in Hydraulic and Sanitation at the Escola de Engenharia de São Carlos/USP, EESC/USP, Brazil. Environmental
analyst at the Companhia de Águas e Esgotos do Rio Grande do Norte, CAERN, Brazil. pauloeduardovc@gmail.com
4
University Graduate in Civil Engineering at the Universidade Federal da Paraíba. University Graduate in Sanitary
Engineering at the Faculdade de Saúde Pública da Universidade de São Paulo, Brazil. Civil and Sanitary Engineer at
Companhia de Águas e Esgotos do Rio Grande do Norte (CAERN), Brazil. neto.cicero@uol.com.br
5
Ph.D. in Civil Engineering at the Universidade Federal do Ceará, UFC, Brazil. Lecturer at the Universidade Federal do
Ceará, UFC, Brazil. fjas@cariri.ufc.br

Operational Performance of an Anaerobic-Anoxic-Aerobic Treatment System
Andre Luis Calado Araujo; Danillo Luiz de Magalhães Ferraz; Paulo Eduardo Vieira Cunha
Cícero Fernandes Neto; Fernando José Araújo da Silva
Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
248
hile infrastructure of human settlements, the environmental sanitation is a subject
highlighted in social, economic, political, and environmental areas. Such attention occurs
from the fact that coverage ratios per collective systems of water and sewage, as well as
the quality of service are important indicators of life quality. This infrastructure comprises four systems:
water supply, sewerage, drainage and management of rainwater, and solid waste.
In Brazil, the Law 14445/07, The National Sanitation Policy, and the increments of
environmental laws has stimulated advances in the sector. In this regard, it is highlighted the protection
scope of water resources on effluents discharge in water bodies. The country has CONAMA
resolutions 357/2005 and 430/2011, where in the first, the classification criteria and surface water
bodies framework are established, while in the second, discharge standards are established. For
environmental protection, sewage treatment is the most effective measure in pollution preventing and
disruption of disease dissemination cycles. This helps to explain the recent scenario, in which, over the
past decade, occurred an increase in number of wastewater treatment plant (WTP) in the country,
including projects, implementing and operation.
As for technological profile used in design of many of these equipments, it emphasizes the
integration of anaerobic and aerobic reactors. The sum of different treatment techniques means,
potentially, to achieve treatment stations configurations including greater balance between efficiency
and cost, as much operating as capital. This aspect is significant against fast growing of urban centers.
The increasing availability of intellectual capital to maintain and operate such stations (i.e., engineers,
technologists and technicians), is another motivator to more complex treatment systems development.
As for WTP conception, until the beginning of this century, it was common understanding to
evaluate distinctly the anaerobic and aerobic digestion technology, often treating them as separate
alternatives. Low utilization of power supply and easy operation in tropical climates are the main
characteristics of anaerobic systems, since high temperatures favor the organic matter digestion process
(Foresti 2001, Mara 2004, Lettinga 2011). As for aerobic systems, it is highlighted mainly for its high
power of organic matter reduction, however, with high sludge generation (von Sperling 2005, Jordão
and Pessoa 2009). There is also, at less extent, the use of reactors operating under anoxic conditions.
In a mature and more recent understanding, the biological treatment system configurations
have become hybrid. This occurs not only on the combination of biochemical mechanisms prevalent in
pollutants degradation, but also in biomass sustaining, and on its action in the treatment itself. Figure 1
W

Operational Performance of an Anaerobic-Anoxic-Aerobic Treatment System
Andre Luis Calado Araujo; Danillo Luiz de Magalhães Ferraz; Paulo Eduardo Vieira Cunha
Cícero Fernandes Neto; Fernando José Araújo da Silva
Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
249
presents a general structure on biomass in reactors of biological treatment system of wastewater, and
helps showing the complex of potential arrangements.
It is also highlighted that, other technologies may be added to biological reactors settings,
those not involving microbial biomass, such as coagulation-flocculation, sedimentation, flotation,
ozonization, and ultrasound, as Gogate and Pandit review (2004a; 2004b). Thus, it is assumed a more
innovative character for wastewater treatment.
The fact is that WTP are intricate systems of unit operations and processes operating on
physical, chemical, and biological base. Therefore, at first, it is difficult to describe and evaluate, in
detail, all processes involved (Potier and Pons 2006).
The advantages of the anaerobic treatment, like the up-flow anaerobic sludge blanket reactor,
UASB, are well known (Lettinga et al. 1992, van Haandel and Lettinga 1994, Conceição et al. 2013,
Singh et al. 20013, Hernandes and Rodrigues 2013). The association of UASB with activated sludge
systems has been extensively researched for the treatment of domestic and industrial wastewaters (von
Sperling et al. 2001, Huang et al. 2005, Huang et al. 2007, Tawfik et al. 2008, Saliba and von Sperling
2017). Combining these two reactors can be energy cost effective with lower sludge production and
high effluent quality. In Natal, capital of the state of Rio Grande do Norte, a major program of
expansion of the sanitary sewage collection network is under development and WTP design is based on
Figure 1. Systematic representation of biomass biological treatment systems.
Source: adapted from Jianlong et al. (2000).

Operational Performance of an Anaerobic-Anoxic-Aerobic Treatment System
Andre Luis Calado Araujo; Danillo Luiz de Magalhães Ferraz; Paulo Eduardo Vieira Cunha
Cícero Fernandes Neto; Fernando José Araújo da Silva
Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
250
the association of UASB-activated sludge reactors. The Central WTP (675 L/s), object of this paper, is
under operation and two new WTP (1000 L/s and 1250 L/s) are under construction.
In addition, while a dynamic system, the wastewater treatment plant requires operational
optimization. This study is based on this premise and tries to better understand the operation of a
biological treatment system, in order to contribute to a better technical culture. The research purpose
was The Central WTP, which was not evaluated with duly minuteness as for performance. The study
presents the results of monitoring and initial assessment of this treatment system.
MATERIALS AND METHOD
THE STUDY TREATMENT STATION
The Central Wastewater Treatment Plant (Central WTP) is located in Natal (5 º47 ’23.7 ”
south – 35 º 12 ’ 42.7 ” west, 31 m above sea level) in Rio Grande do Norte State, northeast of Brazil.
The WTP was designed to receive an average flow of 675 L/s, at the final plan (in 2024) and is
subdivided into three modules (lines) with a capacity of 225 L/s, each.
The modules have a common mechanical pretreatment system, consisting of grids (coarse [e =
20 mm]; fine [e = 3 mm]) and sandpit. After preliminary treatment stage, each module comprises a
biological treatment line in itself. Two module (lines) have already been implemented, and are the focus
of this work. Figure 2 shows a schematic representation of the WTP and a flow chart, while Table 1
shows the volumes and hydraulic retention time of processing phases.
The total effluent flow (2Q) from preliminary treatment stage (Figure 2b) is divided into equal
portions (Q). Each one goes to a biological treatment line (Line 1 and Line 2 – Figure 2b) consisting of
a set of four UASB reactors (Anaerobic Reactor of Sludge Blanket) arranged in parallel, followed by an
anoxic chamber (CANX), an hybrid aerobic reactor (RAEH), and a secondary clarifier (DS).
At the end of treatment, effluents form Line 1 and Line 2 are collected and sent to the same
disinfection unit by ultraviolet radiation, for further disposal on the environment. The WTP has all
equipment for the solid phase treatment, which was not the purpose of this study.
Table 1. Physical and operational characteristics of the reactors.
* Based on the mean flow rate (908 m3/hour)
REACTOR
VOLUME
UNIT (M3)
QUANTITY
VOLUME
TOTAL (M3)
HRT* (H)
UASB
1420
8
11424
15.0
CANX
1298
2
2596
2.9
RAEH
1482
2
2964
3.2
Source: The Authors.

Operational Performance of an Anaerobic-Anoxic-Aerobic Treatment System
Andre Luis Calado Araujo; Danillo Luiz de Magalhães Ferraz; Paulo Eduardo Vieira Cunha
Cícero Fernandes Neto; Fernando José Araújo da Silva
Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
251
Considering each line, on liquid phase, the UASB reactors received around 75% of total line
flow (Q), and a sludge recirculation flow of the secondary clarifier (LREC). The remaining 25% is sent
Figure 2. Schematic representation of Central WTP (a) and flow chart of liquid phase (b).
(a)
(b)
Source: The Authors

Operational Performance of an Anaerobic-Anoxic-Aerobic Treatment System
Andre Luis Calado Araujo; Danillo Luiz de Magalhães Ferraz; Paulo Eduardo Vieira Cunha
Cícero Fernandes Neto; Fernando José Araújo da Silva
Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
252
directly to the anoxic chamber (CANX) as the supplementary source of carbon (C) to assist in
denitrification. A distribution box containing different weirs located at the end of the preliminary unit
was used for flow division. Besides, the anoxic chamber is fed with the effluent flow of UASB, and
receives a recirculation flow of the secondary clarifier (LREC) and an internal recirculation flow of the
hybrid aerobic reactor (RAEH), as a source of nitrate. CANX was equipped as two submersible mixers for
homogenization and to avoid dead spots and short circuit.
The CANX effluent goes to the hybrid aerobic reactor composed of aerated tank with biodiscs
(surface area of 10,400 m2, for biofilm formation), using corrugated conduit as support media. Blowers
composed the aeration system, to introduce fine and coarse bubbles for aeration and biodiscs
movement, respectively.
The plant was commissioned in June 2011 and no inoculum was used to during the startup
period.
SAMPLING AND ANALYTICAL PROCEDURES
The study lasted five months (from June to October 2012), based on weekly collection of
composite samples, considering the inflow, every four hours, during 24-hour cycle. Ten samples were
collected per week, comprising the effluent of the primary treatment unit, after sandpit (RS); UASB
reactor effluent set, through collected and homogenized samples (UASB1 and UASB2); effluent from
anoxic chamber (CANX-1 and CANX-2); effluent from aerobic hybrid reactors (RAEH-1 and RAEH-
2); return sludge from secondary decanters (LREC-1 and LREC-2) and; final treaty effluent (FE),
before disinfection unit.
In the field, temperature parameters, pH and dissolved oxygen (DO) were determined at
collections time, where DO was measured only in hybrid aerobic reactors and treated effluent samples,
before disinfection. The following parameters were determined in laboratory: biochemical oxygen
demand (BOD), total suspended solids (TSS), and volatile suspended solids (VSS), total alkalinity,
ammonia nitrogen, organic nitrogen, and nitrate. Analytical procedures followed methods described in
APHA et al. (2005). Flow measurement was performed through electromagnetic flowmeter installed in
pumping pipeline of raw sewage lifting station.

Operational Performance of an Anaerobic-Anoxic-Aerobic Treatment System
Andre Luis Calado Araujo; Danillo Luiz de Magalhães Ferraz; Paulo Eduardo Vieira Cunha
Cícero Fernandes Neto; Fernando José Araújo da Silva
Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
253
RESULTS AND DISCUSSION
FLOW RATE AND PHYSICAL-CHEMICAL CHARACTERISTICS OF RAW SEWAGE
Inflows in the first two months, in general, were lower than those recorded in subsequent
months, since the station was still in testing phase, therefore, not receiving the entire sewage flow
generated in sewage basins, which composes the system. Considering the entire period, the average
affluent flow was 908 m3/h (Figure 3), around 56% of design total capacity (1620 m3/h), considering
both built modules. It is highlighted that, around June 20, the Collector General 1 was interconnected
(CG1) to WTP. With inflow increasing, there was a cleaning system crash in one of the sandpit, fact
that forced the drastic decrease in inflow for about three weeks (Figure 3).
Figure 4 summarizes the hourly average flow rates over the weekdays. The higher flow was
verified between Mondays and Fridays, and the smallers, over the weekend. However, variance analysis
of 0.05 confidence level showed no significant differences between average hourly over weekdays (p =
0.10741).
Hourly flow variation over 24 hours, every day of the week, was normal as mentioned in
literature, with the lowest values occurring in the early hours (from 0 to 4 h), increasing rapidly
throughout the morning, up to the maximum peak around 10 to 12 h, to then decrease gradually until
midnight (Figure 5).
Figure 3. Inflow variation of average hourly.
Source: The Authors

Operational Performance of an Anaerobic-Anoxic-Aerobic Treatment System
Andre Luis Calado Araujo; Danillo Luiz de Magalhães Ferraz; Paulo Eduardo Vieira Cunha
Cícero Fernandes Neto; Fernando José Araújo da Silva
Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
254
The physical-chemical characteristics of raw sewage are depicted on Table 2.
Figure 4. Comparison between average hourly of flows over weekdays.
Source: The Authors
Figure 5. Variations in average hourly flows over the day.
Source: The Authors
Table 2. Physical-chemical characterization of raw sewage.
PARAMETERS
N
MEAN
STANDARD
DEVIATION
MINIMUM
MAXIMUM
Temperature (oC)
20
28.3
0.7
27,0
30,0
pH
20
7.14
0.22
6.87
7.73
BOD (mg/L)
20
310
29
270
360
TSS (mg/L)
20
190
65
66
318
VSS (mg/L)
20
138
76
10
300
Organic N (mg/L)
20
3.6
3.3
0.6
14.1
NH3 (mg/L)
20
29.8
5.3
20.3
37.1
NO3 (mg/L)
20
0.7
0.8
0.0
2.7
Alcalinity (mg/L)
20
181
14
163
200
Source: The Authors
700
750
800
850
900
950
1000
1050
1100
Sunday Monday Tuesday Wednesday Thrusday Friday Saturday
Flow rate (m3/h)

Operational Performance of an Anaerobic-Anoxic-Aerobic Treatment System
Andre Luis Calado Araujo; Danillo Luiz de Magalhães Ferraz; Paulo Eduardo Vieira Cunha
Cícero Fernandes Neto; Fernando José Araújo da Silva
Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
255
TEMPERATURE, PH AND DO
Reactors effluents show generally, average temperatures between 28 oC and 30 oC, following
external environment changes.
Raw sewage average pH was close to neutral (7.10) and decreased slightly in anaerobic reactors
effluent for 6.80 (UASB1) and 6.90 (UASB2), remaining constant in anoxic chambers, and decreasing
slightly again in aerated tanks, where values of 6.70 were observed in both lines. The final effluent from
WTP showed average pH of 7.00.
In the first months of monitoring, hydrated lime was added in UASB reactors effluents, due to
low pH values in the sludge blanket.
Aerated tanks had dissolved oxygen (DO) variations between 1.4 and 2.5 mg/L, 3.2 and 3.4
mg/L, respectively for RAEH-1 and RAEH-2, in two checkpoints. Problems in line 1 aeration system
(RAEH-1) caused different concentrations ranges between aerated tanks. Thereafter, during an
operational procedure and routine maintenance, it was figured out that some diffuser lines were
clogged. Treated sewage showed an averaged of 5.9 mg/L. This high concentration average can be
explained by the high turbulence caused in effluent fall, through secondary decanters channels, and in
disinfection system entry.
ORGANIC AND SOLID MATTER
The affluent BOD ranged between 270 and 360 mg/L, with an average of 310 mg/L. After
the entire treatment process, the final effluent showed an average of 41 mg/L ranging between 17 to 70
mg/L. It is important to highlight that the WTP was designed based on an effluent BOD of 250 mg/L,
fact that may cause organic overload in reactors when the plant start receiving all designed flow. BOD
removal of total efficiency ranged between 78% and 95%, with a general average of 86%, a value
slightly lower than those estimated in the project (90%). A decreasing trend in BOD removal efficiency
was observed throughout monitoring period, probably related to inflow increase tendency.
The total suspended solids concentrations varied in ranges from 66 to 318 mg/L and 24 to
288 mg/L, respectively, in raw sewage and final effluent. The average in both points were respectively,
190 mg/L and 94 mg/L, representing an average removal efficiency of 63%. As for BOD, the smaller
solids removal efficiencies were observed at the end of monitoring period and are associated to floating
sludge release in secondary decanters, probably due to denitrification.

Operational Performance of an Anaerobic-Anoxic-Aerobic Treatment System
Andre Luis Calado Araujo; Danillo Luiz de Magalhães Ferraz; Paulo Eduardo Vieira Cunha
Cícero Fernandes Neto; Fernando José Araújo da Silva
Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
256
Salles (2001) evaluated existing data on Miranda WTP operation, in Mato Grosso do Sul State,
West-Central of Brazil, with design similar to Central WTP project, using biodiscs system in its aerated
reactor, and found out removal efficiencies of 95% of BOD, and 99% of total suspended solids. BOD
concentrations in final effluent are within the range observed by Oliveira and von Sperling (2005), in
treatment stations located in Minas Gerais and São Paulo states, southeast of Brazil, as well as within
the range (13 to 63 mg/L) mentioned for WTP composed of UASB reactors with post-treatment.
However, in the same study, the authors observed total suspended solids concentrations ranging from
17 and 85 mg/L, while in this study the variation range was much higher (24 to 288 mg/L). It is worth
to point that through the experimental period the sludge was continuously recirculated and besides no
sludge excess was removed from UASB. This may have caused a solids overload in secondary decanters
and a higher variation on solids concentrations. In combined UASB-activated sludge system Tawfik et
al. (2008) found overall removal of BOD above 95%, and a similar removal (94%) was observed by
Saliba and von Sperling (2017) on Betim Central WTP (514 L/s) in southeast of Brazil.
Assessing the behavior of each treatment line, UASB reactors presented a similar performance
in BOD removal. UASB1 and UASB2 effluent showed and average of 101 mg/L and 97 mg/L,
respectively, with no statistical difference at the significance level of 5% (p > 0.05). BOD removals
average was close to 70%, as predicted in project. The worst results were observed in October/2012,
probably due sludge recirculation rate of secondary decanters for UASB reactors to control solids
release in decanters due denitrification process. This increased the upflow speed, probably causing a
greater release of solid. During the study period average, the UASB reactors operated with a volumetric
organic load (VOL) of 2.2 kgDBO/m3.day, a volumetric hydraulic load of 1.6 m3/m3.day, an upflow
speed of 0.42 m/hour and a HRT of 15 hours.
Rizvi et al. (2015) studied the influence of temperature (17 oC to 38 oC) and sludge ages (60 to
180 days) on UASB performances. They found DBO removals values from 61% to 85% and related
the higher performances with higher temperatures and sludge ages. Tawfik et al. (2008) operated UASB
reactors at 20 oC to treat a combined domestic and dairy wastewater with HRT of 24 h and organic
loadings from 1.9 to 4.4 kgCOD/m3.day and they found performances of BOD removal from 69% to
79%.
TSS concentrations in anaerobic reactors effluent showed a wide range of variation (20 to 204
mg/L), with mean average of 89 mg/L (UASB1) and 81 mg/L (UASB2), not differing statistically (p >
0.05), corresponding to an average removal around 58%. TSS values were not different from the
research performed by Silva et al. (2012), who analyzing TSS concentrations in UASB reactor, reached

Operational Performance of an Anaerobic-Anoxic-Aerobic Treatment System
Andre Luis Calado Araujo; Danillo Luiz de Magalhães Ferraz; Paulo Eduardo Vieira Cunha
Cícero Fernandes Neto; Fernando José Araújo da Silva
Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
257
an average of 88 mg/L. Florencio et al. (2001) monitored UASB reactors of Mangueira WTP, located in
the metropolitan region of Recife-PE, and observed an average concentration of 80 mg/L. Oliveira and
von Sperling (2005), assessing 166 WTP data, found that UASB reactors showed concentration
variation range between 49 and 137 mg/L. In this same study, the UASB reactors showed BOD
concentrations between 67 and 129 mg/L. Rizvi et al. (2015) observed, in UASB reactors, TSS
removals from 41% to 73% while Tawfik et al. (2008) reported efficiency of around 70%.
As samples were composed proportionally of inflows, it was noticeable at collection time, that
the largest TSS contributions occurred during periods of high flow, as well as Carvalho et al. (2008)
showed in his study, by applying cyclical sinusoidal variations of flow, observing greater dragging of
solids in periods of upflow speed increase. However, the sewage upflow speed in reactors was very low,
an average of 0.4 m/h, because the average inflow is still far from those designed in the project. Thus,
the variation may be related with sludge recirculation routines from secondary decanters to UASB
reactors, as well as the disposal for sludge treatment line. Solid treatment line (sludge) was not operating
yet, and there was impasses in its sludge destination, i.e., excess sludge discard was not performed,
causing a high concentration of solids in UASB reactors.
Anoxic chambers showed TSS concentrations ranging from 2130 to 5000 mg/L (CANX-1), and
from 1780 to 5125 mg/L (CANX-2), with average of 3633 mg/L and 3441 mg/L, respectively, while VSS
concentrations presented averages of 2932 mgL (CANX-1) and 2712 mg/L (CANX-1). TSS concentrations
in RAEH-1 (3605 mg/L) and RAEH-2 (3032 mg/L) were lower than the project (4000 mg/L), and the
averages of volatile fractions were 2843 mg/L and 2348 mg/L, respectively. The increase of suspended
solids in these compartments is due to microbial growth, being inherent to the technology type in
question, and it is required to promote an efficient degradation of organic matter in the effluent. Figure
6 highlights the average concentrations of solids obtained in units composing the WTP, and variance
analysis at 5% level, showed that both treatment lines showed similar behavior in relation to
concentrations of TSS and VSS (p > 0.05).
The average of VSS/TSS relations indicated the predominance of volatile solids (biomass)
compared to fix (inert), at all treatment stages. UASB1 and UASB2 show relations of 0.63 and 0.59
respectively, showing a large stabilization of sludge if compared with other stages. In this case, it is
important to point that UASB reactors also work as sludge digester from secondary decanters. Anoxic
chambers and aerated tanks showed similar results, with relations ranging from 0.76 and 0.81, and the
highest percentage was found in sludge recirculation lines (0.84 and 0.90).

Operational Performance of an Anaerobic-Anoxic-Aerobic Treatment System
Andre Luis Calado Araujo; Danillo Luiz de Magalhães Ferraz; Paulo Eduardo Vieira Cunha
Cícero Fernandes Neto; Fernando José Araújo da Silva
Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
258
NITROGEN
Figure 7 shows nitrogen behavior during the treatment process. As verified for solids, the
variance analysis at a 5 % level, indicated that both treatment lines showed similar behavior in relation
to nitrogen concentrations (p > 0.05).
Average concentrations of ammonia nitrogen increased between raw sewage (29.8 mg/L) and
anaerobic reactors (36.0 mg/L) due to ammonification process of organic nitrogen present in raw
sewage, and in sludge recirculation lines of secondary decanters for anaerobic reactors. In anoxic
chambers, ammonia nitrogen concentrations were reduced to 14.8 mg/L (CANX-1) and 14.2 mg/L (CANX-
2) and, later, to 6.7 mg/L and 6.5 mg/L, respectively, in aerated reactors RAEH-1 and RAEH-2, which may
be associated with assimilation and nitrification processes.
Organic nitrogen concentrations increased around 3.0 mg/L, in effluent of anaerobic reactors,
for values ranging from 16.2 mg/L to 18.1 mg/L in CANX and RAEH, probably due to high concentration
of biomass in these reactors. After secondary decantation, treated sewage showed a low concentration
of organic nitrogen (3.5 mg/L), being practically similar to those observed in raw sewage and effluents
of anaerobic reactors. On the other hand, in sludge recirculation lines, higher concentrations were
observed reaching averages of 21.4 mg/L and 22.5 mg/L in LREC-1 and LREC-2, respectively, attesting the
large amount of nitrogen assimilated by biomass. At the end of the treatment process, average removals
of 71 % of NTK and 77 % of N-NH4 were found far above 50 % of predicted removal by ETE
project.
Nitrate levels were quite similar in CANX and RAEH (Figure 7), and the final effluent showed a
concentration of 2.5 mg/L.
Figure 6. TSS and VSS average at monitoring points.
Source: The Authors

Operational Performance of an Anaerobic-Anoxic-Aerobic Treatment System
Andre Luis Calado Araujo; Danillo Luiz de Magalhães Ferraz; Paulo Eduardo Vieira Cunha
Cícero Fernandes Neto; Fernando José Araújo da Silva
Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
259
The alkalinity in reactors is directly related to nitrification and denitrification processes. Figure
8 shows alkalinity increases of raw sewage (175 mg/L) for UASB effluents (247 mg/L), probably due to
addition of hydrated lime. Subsequently, continuous alkalinity decreases were observed in effluent of
CANX (147 mg/L) and RAEH (104 mg/L), reaching in the final treated effluent, a concentration of 97
mg/L. It is possible to observe lower alkalinity in RAEH regarding CANX, probably due to its
consumption during the nitrification process.
FINAL CONSIDERATIONS
The mean influent BOD was 310 mg/L while the plant was designed by using 250 mg/L.
Therefore, it is extremely important, if possible, to make surveys to assess the real characteristics of raw
sewage, in the WTP planning and projects design phase. In addition, regarding new WTP projects, it
Figure 7. Average of nitrogen at monitoring points.
Source: The Authors
Figure 8. Alkalinity average at monitoring points.
Source: The Authors

Operational Performance of an Anaerobic-Anoxic-Aerobic Treatment System
Andre Luis Calado Araujo; Danillo Luiz de Magalhães Ferraz; Paulo Eduardo Vieira Cunha
Cícero Fernandes Neto; Fernando José Araújo da Silva
Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
260
was observed that for pre-denitrification systems, operational flexibility is important due to required
recirculation rates.
Nitrogen biological removal, in systems with pre-denitrification, is affected by diverse
operating factors, especially internal recirculation ratios of nitrified sewage, sludge recirculation of
decanters for anoxic chambers, and the availability of carbon source in anoxic zone. Von Sperling
(1997) shows that for pre-denitrification systems, the internal recirculation ratio varies between 100 %
and 400 %. Therefore, it is very important that WTP be similarly configured to the present study, in
order to achieve satisfactory removal of nitrogen, and present great operational flexibility.
During monitoring period, the aerated hybrid reactor operated with a constant internal
recirculation ratio to the anoxic chamber of 936 m3/h. Between June and July, when occurred the
smaller inflows; internal recirculation flow was about 128 % above the inflow. In subsequent months,
the inflow increased by interconnections of collectors of sewerage system, so that, the internal
recirculation ratio decreased for values close to 90 %. Observing the end of WTP plan, this may
present a maximum internal recirculation ratio of 100 %.
Globally, the WTP showed an average efficiency of BOD removal, which is below of those
estimated in the project, even operating with flow below that designed for final plan. High removal of
ammonia nitrogen was achieved, as well as pH ranges and appropriate temperature, meeting the
Brazilian Discharge Guidelines. However, it is important to observe that, during monitoring time, the
plant average inflow was still 56 % lower of the value presented for final plan.
UASB reactors showed average removal efficiencies of BOD slightly lower than the 70 %
expected in the project, which were mainly affected by TSS concentrations in effluents, even operating
with high hydraulic retention times, and low ascension speeds. There is a tendency that these results are
related to recycling procedures and disposal of excess sludge of secondary decanters, for digestion in
UASB reactors, mainly by the fact that, during monitoring, the disposal operation and sludge
dehydration had not started, yet. Thus, sludge disposal in excess was impaired forcing then, excessive
recirculation, for both anoxic chambers and UASB reactors.
Regarding nitrogen removal, the results showed good efficiencies, however, with a downward
trend during monitoring, probably due to increased flow and consequently decrease of internal
recirculation ratio of aeration tanks for anoxic chambers. In addition, the removal did not occur
through nitrification and denitrification processes probably, since too low concentrations of nitrate in
effluent of aeration tanks were found. Nitrogen removal should be studied further, in order to

Operational Performance of an Anaerobic-Anoxic-Aerobic Treatment System
Andre Luis Calado Araujo; Danillo Luiz de Magalhães Ferraz; Paulo Eduardo Vieira Cunha
Cícero Fernandes Neto; Fernando José Araújo da Silva
Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
261
determine the best setting of recirculation flow and sludge disposal, as well as bypass ratio for anoxic
zone.
It is recommended to evaluate and improve the sludge disposal routine, digested in UASB
reactors, as well as excess of sludge receiving from secondary decanters, in order to obtain
improvements in solids removal efficiency.
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Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
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Operational Performance of an Anaerobic-Anoxic-Aerobic Treatment System
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Cícero Fernandes Neto; Fernando José Araújo da Silva
Fronteiras: Journal of Social, Technological and Environmental Science • http://revistas.unievangelica.edu.br/index.php/fronteiras/
v.6, n.3, set.-dez. 2017 • p. 247-263. • DOI http://dx.doi.org/10.21664/2238-8869.2017v6i3.p247-263 • ISSN 2238-8869
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Avaliação Operacional de uma Estação de Tratamento de Esgotos
Anaeróbia-Anóxica-Aeróbia
RESUMO:
Um sistema anaeróbio (UASB) - híbrido aeróbio (lodo ativado com biomassa suspensa e
aderidaligado) foi avaliado na remoção de matéria orgânica, sólidos e nitrogênio após sua fase pré-
operacional. As análises foram feitas semanalmente com base em amostras compostas, preparadas por
amostras individuais coletadas a cada quatro horas, durante o ciclo de 24 horas, ponderadas pela vazão,
em cada ponto de monitoramento (esgoto bruto, UASB, câmara anóxica, reatores aeróbios, linha de
recirculação de lodo decantadores secundários e efluente final). A ETE apresentou uma vazão média de
908 m3/h com picos entre 10 e 14 h. A DBO foi removida em 86% (310 para 41 mg/L), sendo a maior
parcela nos reatores UASB (70%) e a remoção de sólidos suspensos totais atingiu 63% (190 a 94
mg/L). A remoção média de TKN (71%) e Amônia (77%) foi superior ao valor predito pelo projeto e,
provavelmente, o processo de nitrificação-desnitrificação não foi a rota dominante.
Palavras-Chave: Controle de Poluição; Reatores UASB; Remoção de Matéria Orgânica; Tratamento
de Águas Residuais.
Submissão: 06/02/2017
Aceite: 19/12/2017