Economic feasibility of microalgal bacterial floc production for wastewater treatment and biomass valorization_ A detailed up-to-date analysis of up-scaled pilot results

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Bioresource Technology 224 (2017) 118–129
Contents lists available at ScienceDirect
Bioresource Technology
journal homepage: www.elsevier .com/locate /bior tech
Economic feasibility of microalgal bacterial floc production for
wastewater treatment and biomass valorization: A detailed up-to-date
analysis of up-scaled pilot results
http://dx.doi.org/10.1016/j.biortech.2016.11.090
0960-8524/� 2016 Elsevier Ltd. All rights reserved.
Abbreviations: ACWW, aquaculture wastewater from a pikeperch production facility; AD, anaerobic digestion; CAS, conventional activated sludge; CAPEX
expenditures; CASEF, CAS effluent, i.e. effluent from a CAS plant from a food production company; CHP, combined heat and power; DM, dry matter; EAC, equivalen
cost; EAW, equivalent annual worth; EPDM, ethylene propylene diene monomer rubber; HDPE, high-density polyethylene; HRT, hydraulic retention time; M
microalgal bacterial floc; RAS, recirculation aquaculture system; SBR, sequencing batch reactor; OPEX, operational expenditures; TSS, total suspended solids; VSS
suspended solids; WWT, wastewater treatment.
⇑ Corresponding author.
E-mail addresses: Elien.Vulsteke@ugent.be, Elien.Vulsteke@gmail.com (E. Vulsteke), sofie_vdhende@yahoo.com, shende@espol.edu.ec (S. Van Den
info@bebouwenenbewaren.be (L. Bourez), info@catael.be (H. Capoen), Diederik.Rousseau@ugent.be (D.P.L. Rousseau), Johan.Albrecht@ugent.be (J. Albrecht).
URLs: http://www.ceem.ugent.be (E. Vulsteke), http://www.ibw.ugent.be, http://www.cenaim.espol.edu.ec, http://www.espol.edu.ec (S. Van Den Hende), http
catael.be (H. Capoen).
Elien Vulsteke a,⇑, Sofie Van Den Hende b,c, Lode Bourez d, Henk Capoen e, Diederik P.L. Rousseau b,
Johan Albrecht a
aCentre for Environmental Economics and Management (CEEM), Department of General Economics, Ghent University, Tweekerkenstraat 2, B-9000 Ghent, Belgium
b Laboratory of Industrial Water and Ecotechnology (LIWET), Department of Industrial Biological Sciences, Ghent University, Graaf Karel de Goedelaan 5, B-8500 Kortrijk, Belgium
cCentro Nacional de Acuicultura e Investigaciones Marinas, CENAIM, Facultad de Ciencias de la Vida, Escuela Superior Politécnica del Litoral, ESPOL, Campus Gustavo Galindo, Km
30.5 Vía Perimetral, P.O. Box 09-01-5863, Guayaquil, Ecuador
dBebouwen en Bewaren – Water Sanitation and Ponds, Beukendreef 22, B-8020 Hertsberge, Belgium
eCatael – Automation, Doornikserijksweg 149, B-8510 Bellegem, Kortrijk, Belgium
h i g h l i g h t s
� MaB-floc system costs are comparable to other wastewater treatment systems.
� Capital costs and mixing costs represent the largest expenses.
� Substantial revenues are generated with shrimp feed commercialization.
� Conversion of MaB-flocs to biogas generates little value.
� High-purity phycocyanin production from food-industry MaB-flocs is most lucrative.
a r t i c l e i n f o
Article history:
Received 31 August 2016
Received in revised form 21 November 2016
Accepted 22 November 2016
Available online 24 November 2016
Keywords:
Algae
MaB-floc
Valorization
Scale-up
Economic analysis
a b s t r a c t
The economic potential of outdoor microalgal bacterial floc (MaB-floc) raceway ponds as wastewater
treatment technology and bioresource of biomass for fertilizer, shrimp feed, phycobiliproteins and biogas
in Northwest Europe is assessed. This assessment is based on cost data provided by industry experts, on
experimental data obtained from pilot-scale outdoor MaB-floc ponds treating aquaculture and food-
industry effluents, and from different biomass valorization tests. MaB-floc ponds exhibit a cost-
performance of EUR 0.25–0.50 m�3 wastewater which is similar to conventional wastewater treatment
technologies. The production cost of MaB-flocs in aquaculture and food industry effluent is EUR 5.29
and 8.07 kg�1 TSS, respectively. Capital costs and pond mixing costs are the major expenses.
Commercializing MaB-flocs as aquaculture feed generates substantial revenues, but the largest profit
potential lies in production of high-purity phycobiliproteins from MaB-flocs. These results highlight
the large economic potential of MaB-floc technology, and justify its further development.
� 2016 Elsevier Ltd. All rights reserved.
, capital
t annual
aB-floc,
, volatile
Hende),
://www.
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mailto:Elien.Vulsteke@ugent.be
mailto:Elien.Vulsteke@gmail.com
mailto:sofie_vdhende@yahoo.com
mailto:shende@espol.edu.ec
mailto:info@bebouwenenbewaren.be
mailto:info@catael.be
mailto:Diederik.Rousseau@ugent.be
mailto:Johan.Albrecht@ugent.be
http://www.ceem.ugent.be
http://www.ibw.ugent.be
http://www.cenaim.espol.edu.ec
http://www.espol.edu.ec
http://www.catael.be
http://www.catael.be
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E. Vulsteke et al. / Bioresource Technology 224 (2017) 118–129 119
1. Introduction
Shallow raceway ponds with microalgae is a technology that
serves the dual purpose of wastewater treatment and biomass pro-
duction. To address the high cost of microalgae harvesting, the
microalgal bacterial floc (MaB-floc) technology was developed
(Gutzeit et al., 2005; Van Den Hende et al., 2014a). In MaB-floc
ponds, microalgae and bacteria aggregate into fast-settling MaB-
flocs. During nighttime, these flocs settle by gravity in the pond.
Hereafter, the MaB-floc-free effluent, i.e. the upper supernatant,
is discharged. In the morning, the pond is filled with untreated
wastewater, and this wastewater is treated during daytime, until
flocs settle again during nighttime. Therefore, this technology is
called MaB-floc sequencing batch reactor raceway pond (MaB-
floc SBR raceway pond, or short, MaB-floc pond). Pilot-scale exper-
iments with a 10–12 m3 MaB-floc pond in Belgium have demon-
strated relatively high biomass productivities and an efficient
biomass dewatering (Van Den Hende et al., 2014a, 2016b). Addi-
tionally, the technical potential of different applications of the
resulting biomasses from aquaculture and food-industry wastewa-
ters have been successfully demonstrated, i.e. shrimp feed (Van
Den Hende et al., 2014b), fertilizer (Coppens et al., 2016), pigment
production (Van Den Hende et al., 2016a) and biogas production
(Van Den Hende et al., 2015, 2016a).
To assess the economic potential of MaB-floc pond technology
at industrial scale, an economic analysis is needed. As the microal-
gae species present in MaB-flocs differ significantly between
wastewaters (Van Den Hende et al., 2014b; Wieczorek et al.,
2015), comprehensive process analysis is required if a complete
and realistic assessment of the economic viability of MaB-floc
ponds in Northwest Europe is to be made. This study evaluates
for the first time the cost-benefit profile of a MaB-floc pond system
for treating aquaculture and food-industry wastewater in North-
west Europe. Next to the wastewater treatment, the economic via-
bility of four MaB-floc valorization pathways was assessed. This
study relies on data of biomass productivities in outdoor pilot
experiments in Belgium, on data of biomass valorization in lab-
scale and pilot-scale experiments, and on updated cost data pro-
vided by industry experts.
2. Materials and methods
2.1. Wastewaters and scale-up of MaB-floc ponds
The results of a pilot-scale outdoor MaB-floc pond treating two
wastewater types in Belgium are scaled-up from pilot to industrial
scale. These types include (1) drum filter effluent from a recirculat-
ing aquaculture system (RAS) for pikeperch culture at Inagro in
Beitem (termed aquaculture wastewater, abbreviated to ‘‘ACWW”)
(Van Den Hende et al., 2014a) and (2) effluent from the conven-
tional activated sludge (CAS) treatment plant at food company
Alpro in Wevelgem (termed CAS effluent, abbreviated to ‘‘CASEF”)
(Van Den Hende et al., 2016b) (Fig. 1a–b). Details on the wastewa-
ter composition and pretreatment steps are givenby Van Den
Hende et al. (2014a) and Van Den Hende et al. (2016b).
In case of ACWW treatment, the hydraulic retention time (HRT)
in the up-scaled MaB-floc ponds in this study is 4 days, and the
pond depth is 0.40 m, as in the pilot-scale operation (Van Den
Hende et al., 2014a). The volumetric loading of wastewater is the-
oretically scaled-up to 1000 m3 d�1, which is representative for a
large-scale RAS pikeperch farm of a 400 ton annual production
(Sfez et al., 2015). The total water volume of 4000 m3 is divided
over 7 ponds (10 m wide and 135 m long, with rounded ends) of
1,429 m2 pond surface each. Total pond surface is 10,000 m2 and
total plant area, taking into account walking trails, is 15,075 m2
(Fig. 1c–d).
In case of CASEF treatment, the HRT is 2 days, the pond depth is
0.40 m and the actual daily wastewater volume treated of the stud-
ied food company is 1000 m3 d�1 (Van Den Hende et al., 2016b).
The total water volume of 2000 m3 is divided over 3 ponds (10 m
wide and 159 m long, with rounded ends) of 1,667 m2 pond surface
each. The CASEF plant has a total water surface of 5,000 m2 and
total plant area is 7,535 m2.
2.2. Pond construction
The costs of three methods of pond construction are compared,
i.e. (1) dug-out earthen ponds covered by EPDM-liners (i.e. ethy-
lene propylene diene monomer rubber), (2) concrete brick ponds
covered by EPDM-liners, and (3) novel self-assembly ponds. In
the first case of dug-out ponds, the earthen ponds are 0.80 m deep.
The bottom of the earthen pond is located 0.30 m below the sur-
face, and the dug-out soil is used to construct earthen embank-
ments of an additional 0.50 m height. As such the upper layer of
arable land is not mixed with less fertile deeper soil layers. In this
way, the agricultural value of the land is preserved. The second
case considers the aboveground construction with large hollow
concrete blocks reinforced with steel cables, as this type of large
bricks (0.60 m � 0.20 m) allows fast construction. In this case, the
walls are of 0.60 m height. The EPDM liner has a lifetime of 20 to
30 years. Therefore, a lifetime of 30 years is assumed to be the life-
time of the entire algae pond system. The third case assesses self-
assembly ponds, which are shallow ponds (0.40–0.60 m) of rein-
forced geomembrane supported by metal brackets. Self-assembly
ponds are currently on the market as spill containment ponds,
but according to a manufacturer they can be manufactured with
radial pond ends and a baffle in the middle.
All ponds are operated as SBR. This means that after a MaB-floc
settling phase during the night, MaB-floc-free effluent needs to be
withdrawn from the ponds. To ensure a non-turbulent flow when
this effluent leaves the pond by gravity flow, 5 drains are installed
on each side of the pond, spread over 100 m length (Fig. 1d). These
additional, flanged drains should ensure that the settled MaB-flocs
are not re-suspended when effluent (flow of 1000 m3 over 5 hours
during the night) leaves the pond. These tubes also convey influent
to the ponds, propelled by a 15 kW centrifugal pump (Fig. 1c–d).
To assess the influence of individual pond sizing on the cost of
pond construction, the construction costs for dug-out earthen
ponds of 250 m2, 750 m2 and 1500 m2 water surface were assessed
in a sensitivity analysis.
2.3. Pond mixing
In MaB-floc reactors a sufficient pond mixing is crucial, as MaB-
flocs settle much faster than suspended microalgae by their very
nature (Van Den Hende et al., 2014a). In general, MaB-flocs settle
within 15 min as soon as the mixing pumps are switched off
(Van Den Hende et al., 2014a). It was long assumed that paddle-
wheel mixers are the most efficient way to mix microalgae ponds.
However, recent work suggests that propeller mixers are more
energy-efficient (Chiaramonti et al., 2013). The pilot-scale MaB-
floc pond facility of 12 m3 (Van Den Hende et al., 2014a) was stir-
red by two propeller pumps of 0.75 kW, one after each raceway
bend. This pilot-scale stirring setup is oversized and therefore
should not be simply extrapolated to the up-scaled raceway ponds.
The hydraulics of raceway ponds are not yet well-studied, and
mixing energy requirements are calculated using assumptions
about friction losses in the pond bends. These assumptions are
yet to be verified on a large scale (Chiaramonti et al., 2013). Using
the extrapolation series of Passell et al. (2013) based on the
(a)
(b)
(c) (d)
(e)
Propellor
mixers
Flue gas
diffusors
In- and effluent
tubing
Slurry
pump
Influent
pump
150 m 7 m
100 m
Sedimentation
basin
Belt filter press
0 
5 
10 
15 
20 
25 
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 
B
io
m
as
s p
ro
du
ct
iv
ity
 (g
 m
-2
 d
-1
) 
Month 
Scenario 1 TSS Scenario 1 VSS 
Scenario 2 TSS Scenario 2 VSS 
Scenario 3 TSS Scenario 3 VSS 
0 
5 
10 
15 
20 
25 
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 
B
io
m
as
s p
ro
du
ct
iv
ity
 (g
 m
-2
 d
-1
) 
Month 
Scenario 1 TSS Scenario 1 VSS 
Scenario 2 TSS Scenario 2 VSS 
Scenario 3 TSS Scenario 3 VSS 
 Settling Dewatering 
0.05-0.06 % TSS 
CASEF pigment extraction + biogas 
 7 % TSS 45 % TSS 
MaB-floc
growth 
 Settling MaB-flocgrowth 
shrimp feed Drying and 
grinding 
 7 % TSS 45 % TSS 
fertilizer 
ACWW 
0.05-0.06 % TSS 
Dewatering 
(f)
Fig. 1. MaB-floc production diagram and valorization pathways for ACWW (a) and CASEF (b), overview of the 15,000 m2 MaB-floc plant for the treatment of 1000 m3 ACWW
per day (c), detail of the MaB-floc pond configuration (d), and MaB-floc biomass productivity scenarios for ACWW (e) and CASEF (f).
120 E. Vulsteke et al. / Bioresource Technology 224 (2017) 118–129
up-scaling of small commercial ponds with a paddlewheel, a
capacity requirement of 2.1 Wm�2 would be obtained for a pond
of 1,500 m2. Chiaramonti et al. (2013) estimated a demand of
1.1 Wm�2 for a 0.20 m deep paddlewheel raceway pond of
500 m2, stirring at a speed of 0.20 m s�1. In the up-scaled pond of
this MaB-floc study a conservative approach is taken, and 2 times
3 propeller pumps of 0.5 kW are installed along the 5 m width of
the pond channel, which amounts to 3 Wm�2 (Fig. 1d).
E. Vulsteke et al. / Bioresource Technology 224 (2017) 118–129 121
2.4. Influent and supernatant pumping
As in Belgium the day length varies considerably between sea-
sons, the mixing time is adjusted between 8 and 14 hours per day.
At night as the mixing stops, the flocs settle within an hour into a
sludge layer with a thickness between 0.04 and 0.10 m. A volume
of 1000 m3 clear supernatant flows by gravity out of each pond
during the next 5 hours, and is discharged. For the next 5 hours
1000 m3 of wastewater is pumped into the ponds by means of a
15 kW centrifugal pump. During the last hour of influent pumping,
the mixing propellers in the pond are switched on again.
Periodically, a fraction of the pond volume is led to the
sedimentation basin to remove MaB-flocs in order to keep the
MaB-floc density in the raceway pond constant. After settling,
the supernatant in the sedimentation basin is pumped back to
the ponds (see ‘2.10 Harvesting and dewatering’).
2.5. pH control
When the pH in the MaB-floc pond rose above the effluent dis-
charge standard of 9.5 during the pilot experiments, synthetic flue
gas with 89 ± 2 g CO2 Nm�3 was sparged just below the propeller
mixers for both wastewater types (Van Den Hende et al., 2014a,
2016b). In the pilot-scale pond, the flue gas flow rate ranged from
3 to 5 L min�1 for ACWW and from 5 to 8 L min�1 for CASEF. For
ACWW, sparging duration was between 5 h and 14 hours per day.
The flue gas used during the pilot operations was sourced exter-
nally. It would be interesting to produce CO2 on-site with a CHP
unit, as the price of bottled liquid CO2 gas is at least EUR 100 ton�1
(European Commission, 2010). If 5 L min�1 is sparged during 8
hours in the pilot pond, this means for the industrial-scale ACWW
plant a flue gas demand of 800 Nm3 d�1 or 71.2 kg pure CO2 d�1(89.0 g CO2 Nm�3 and CO2 density of 1.977 kg.m�3).
2.6. Combined heat and power production
By using a micro-CHP fueled by natural gas, the required elec-
tricity for the up-scaled plant is produced on-site at a smaller cost
than electricity purchased from the electricity net. For the ACWW
plant, the maximum electricity demand of 560 kWhel d�1 could be
produced by a micro CHP of 29 kWel. The electricity demand of the
plant fluctuates during the day. The required electrical capacity
varies during the day between 18.5 and 28 kWel. Assuming a 38%
electrical efficiency and a 42% thermal efficiency (IEA, 2010), the
CHP has a thermal capacity of 32 kWth and a total capacity of
76.3 kWtot. Details on the CASEF CHP unit are presented in Table 1.
Micro CHP technology is rapidly evolving, and manufacturers
are continuously developing products with higher electrical effi-
ciencies. Micro CHP’s with a capacity around 30 to 50 kWel display
today an electrical efficiency of 25–34% (deWit and Näslund, 2011;
EPA, 2015). IEA foresees that the efficiency for this technology can
still increase with a few percent (IEA, 2010). As such we assume
that electrical efficiencies of 38% will be achieved for a 29 kWel
CHP in the near future. Thermal efficiency is assumed to be 42%.
Capital costs (i.e. equipment plus installation cost) of a CHP with
a capacity around 30 kWel were estimated at EUR 3,280 kWel�1 y�1
(Cogeneration Observatory and Dissemination Europe, 2014). A
maintenance cost of EUR 0,011 kWhel�1 is used (Cogeneration
Observatory and Dissemination Europe, 2014). Operational costs
associated with the CHP are based on a natural gas price of EUR
0.05 kWhtot�1 (European Commission, 2016b). With an electrical effi-
ciency of 38% the CHP generates electricity at EUR 0.13 kWhel�1,
which is cheaper than electricity bought from the net at EUR
0.19 kWhel�1 (European Commission, 2016a). In the up-scaled plant
CO2/flue gas is sparged with 10 disc air diffusers per pond and one
air compressor (0.5 kW) for the total ACWW plant.
2.7. Pond heating
In the pilot-scale MaB-floc facility, the water temperature in the
pond was kept at minimum 12 �C by means of copper tubing incor-
porated under the steel pond (Van Den Hende et al., 2014a). The
heat demand to the water boiler on natural gas was equal to
0.19 MJ d�1 when the pilot reactor ran on ACWW in 2013 (Sfez
et al., 2015). As to the best of the authors’ knowledge, there are
no temperature models of shallow algal ponds available yet for
Northwest Europe, the heat demand of the pilot plant was linearly
up-scaled to the industrial-scale plant, obtaining a heat demand of
16,511 kWhth y�1 for the ACWW plant. On colder winter days the
total heat demand of the up-scaled ACWW plant is estimated at
97.7 kWhth d�1, based on a natural gas consumption of 30 L d�1
in the ACWW pilot plant as described by Sfez et al. (2015). At
industrial scale, the copper tubing heating system of the pilot-
scale MaB-floc pond should be replaced by another, cheaper heat
transfer mechanism. In recent years, plastic polymer heat exchang-
ers (in HDPE, i.e. high-density polyethylene) were developed with
adequate heat transfer properties, and have been used in geother-
mal applications, in the chemical industry and in aquaculture. The
materials for these heat exchangers are 25 to 250 times cheaper
than stainless steel (Ramm-Schmidt, 2006). In the up-scaled
ACWW plant, a heat recovery boiler of 32 kWth total capacity
(installed cost estimated at EUR 1000 kWth�1) (Cogeneration
Observatory and Dissemination Europe, 2014) with circulator
pump (3 kW) provides warm water to HDPE heat exchangers
(EUR 618 kWth�1) (GSHPA, 2007).
2.8. Automation
In each pond the water level and water temperature are contin-
uously monitored, as well as the water flow in the pond drains. It is
assumed that the water treatment performance is comparable over
all the ponds at one point in time, and as such automatic water
quality analysis (i.e. monitoring of pH, NH4+, NO3� and dissolved
oxygen concentration) is done in one pond only. For the ACWW
(CASEF) plant, three (one) small control panels control the pond
propellers and sensors (one panel between each two ponds), and
an additional fourth (second) small control panel steers the pro-
pellers, sensors and water quality probes of the pond in which
the water quality is monitored. A large control panel commands
the pumps, valves, CHP, effluent pH probe, filter press and other
processing equipment; and is connected to the small control pan-
els. The large control panel is placed in a transport container,
which also accommodates the filter press, the dryer, and the mill.
2.9. Biomass productivities
The effect of the MaB-floc biomass productivity is examined by
comparing three different scenarios. Scenario 1 uses an average
year-round MaB-floc productivity which is the average of the pro-
ductivities achieved during operation of the pilot-scale outdoor
MaB-floc pond on ACWW and CASEF (Van Den Hende et al.,
2014a, 2016b), i.e. 9.2 g TSS m�2 pond area d�1 (or 33 ton ha�1 y�1)
for ACWW and 6.8 g TSS m�2 pond area d�1 (or 25 ton ha�1 -
pond area y�1) for CASEF (Fig. 1e–f). Scenario 2 reflects the
monthly variability in biomass productivities as experienced dur-
ing the pilot tests. Furthermore, in this scenario, low productivities
experienced during the pilot operations’ start-up period and during
the periods with a negative biomass productivity, most probably
due to grazers, were left out, leading to annual average productiv-
ities of 10.9 g TSS m�2 pond area d�1 (ACWW) and 6.3 g TSS m�2 -
pond area d�1 (CASEF) (Fig. 1e–f). By means of Scenario 2 the
effect of seasonal variation in the productivity on the MaB-floc pro-
duction cost is assessed. Scenario 3 assumes that technologies are
Table 1
Capital cost items of MaB-floc ponds (CAPEX), equivalent annual capital cost (EAC) (using a 10% discount rate) and annual operational expenditures (OPEX) for Scenario 2.
CAPEX Unit cost
(EUR)
Life-time
(y)
ACWW (total plant surface 1.5 ha) CASEF (total plant surface 0.75 ha)
Number of
units
Total cost (EUR) EAC (EUR y�1) Number of
units
Total cost
(EUR)
AEC
(EUR y�1)
Land cost 50,000 30 1.51 ha 75,375 7,996 0.75 ha 37,675 3,997
Algae production
Pond wall (concrete blocks) 19,850 30 7 138,950 14,740 3 59,550 6,317
Pond surface (stabilized sand) 9,000 30 7 63,000 6,683 3 27,000 2,864
Pond lining 16,545 30 7 115,815 12,286 3 49,635 5,265
Pond effluent tubes with 10
flanges
2,400 30 7 16,800 1,782 3 7,200 764
Propeller H-profiles 1,790 30 14 25,060 2,658 6 10,740 1,139
Propeller mixers 3,520 10 42 147,823 24,058 18 63,353 10,310
Influent pump 7,594 15 1 7,594 998 1 7,594 998
Electrical ball check valve 1,692 10 2 3,384 551 2 3,384 551
CHP 3,280 15 29 kWel 95,120 12,506 17 kWel 55,760 7,331
Heat recovery boiler 1,000 20 32 kWth 32,000 3,759 19 kWth 19,000 2,232
Warm water circulator pump 4,200 10 1 4,200 684 0.5 2,100 342
Pond loop heat exchangers 618 15 4 kWth 2,471 325 2 kWth 1,236 162
Flue gas spargers (discus-shaped) 30 15 70 2,100 276 30 900 118
Sparger connection blocks 120 15 14 1,680 221 6 720 95
CO2 distribution network 6 15 1,170 m 6,435 846 520 m 2,860 376
Flue gas compressor 2,600 15 1 2,600 342 1 2,600 342
Container 3,700 30 1 3,700 392 1 3,700 392
Small control panel ponds 1,660 20 4 6,640 780 2 3,320 390
Meters and probes 31,662 6,669 17,966 4,339
Large control panel container 3,900 20 1 3,900 458 1 3,900 458
Automation engineering 8,800 20 1 8,800 1,034 1 8,800 1,034
General electrical equipment and
installation
10,434 20 1 10,434 1,226 1 10,434 1,226
Sedimentation
Sedimentation tank 9,040 30 1 9,040 959 1 9,040 959
Slurry pump 2,767 15 1 2,767 364 1 2,767 364
Supernatans pump 2,940 15 1 2,940 387 1 2,940 387
Dewatering
Belt filter press 38,220 20 1 38,220 4,489 1 38,220 4,489
Further processing Pathway 1 and 2
Total cost EAC
Fluidized bed dryer 49,400 15 1 49,400 6,495 Pathway 3 Pathway 4
Biomass mill 5,850 15 1 5,850 769 Total cost EAC Total cost EAC
Digestor 4,505 20 29,009 1,058 2 9,009 1,058
Pigment extractiona 10 1 30,798 5,012
Installed equipment cost subtotal + land cost 912,760 114,730 867,519 108,524 492,201 63,311
Installed equipment cost subtotal 838,385 792,144 454,526
Yard piping (5%b) 41,919 4,447 39,607 4,202 21,186 2,247
Plumbing (15% of building cost) 555 59 555 59 555 59
Maintenance of plant operations
(5%b)
41,919 4,447 39,607 4,202 21,186 2,247
Mobilization, bonds and
insurance (5%b)
41,919 4,447 39,607 4,202 21,186 2,247
Contingencies (10%b) 83,839 8,894 79,214 8,403 55,631 5,901
Construction cost subtotal 1,048,536 990,735 556,315
Contractor overhead and profit
(15%c)
157,280 16,684 148,610 15,764 83,447 8,852
Total CAPEX 1,281,192 153,707 1,139,346 145,355 695,393 84,866
OPEX EUR y�1 EUR y�1 EUR y�1
Mixing 10,754 10,754 4,609
Influent pumping 3,602 3,602 3,602
Heat circulation 3,458 3,458 1,482
CO2-sparging 192 192 82
CHP maintenance 1,594 1,594 863
Harvest and dewatering 3,190 3,190 1,140
Drying and milling 266 0 0
Biogas digestion 0 450 0
Pigment extraction 0 0 24,053
Automation equipment
maintenance
1,000 1000 750
Other equipment maintenance (1%b) 3,222 3,222 1,694
Additional labor cost (1% of total OPEX cost) 273 275 383
Total OPEX 27,552 27,738 38,658
a Pigment costs are the average of costs reported in Reis et al. (1998) and Ramanan (2000) for food-grade C-PC.
b % of installed equipment cost subtotal.
c % of construction cost subtotal.
122 E. Vulsteke et al. / Bioresource Technology 224 (2017) 118–129
E. Vulsteke et al. / Bioresource Technology 224 (2017) 118–129 123
applied which eliminate grazing by predators (see e.g.
Montemezzani et al. (2015)), and multiplies the TSS productivities
of Scenario 2 by a factor 1.25 for ACWW (to 13.6 g m�2 d�1) and 1.7
for CASEF (10.8 g m�2 d�1) (Fig. 1e–f). For ACWW this is the maxi-
mum productivity obtained over the different testing periods. In
comparison to the ACWW pilot runs, which ran from winter till
autumn (i.e. 231 days), the experiments with CASEF did not run
as long, i.e. from summer till autumn (i.e. 122 days). As such it is
assumed that the MaB-floc raceway pond in these CASEF runs
did not reach its maximum productivity yet, and that the produc-
tivity could have increased with 50% if the pilot-scale experiments
could have been performed for a longer time period. This potential
productivity increase is incorporated in Scenario 3, together with
potential productivity increases from the implementation of mea-
sures against grazers (similar to the ACWW case). In total, the pro-
ductivities of CASEF Scenario 2 are multiplied by a factor 1.7 to
obtain Scenario 3, accounting for potential productivity increases
from both more stabilized pond operations (i.e. 50% increase) and
measures against grazers (i.e. 20% increase).
2.10. Harvesting and dewatering
MaB-flocs are harvested by sedimentation in a sedimentation
basin, after which the MaB-floc sludge is dewatered with a filter
press (Van Den Hende et al., 2014a, 2016b). The MaB-floc concen-
tration is kept at 500 mg TSS L�1 in the ponds, so depending on the
growth rate a smaller or larger pond volume needs to be pumped
to the sedimentation basin. This basin is designed to handle the
maximum productivity of 60 mg TSS L�1 d�1 (i.e. the maximum
productivity in Scenario 3 for ACWW), based on productivity max-
ima for ACWW in Van Den Hende et al. (2014a). When at the up-
scaled plant the MaB-floc productivity is as high as 60 mg TSS L�1 -
d�1, a MaB-floc liquor volume of 429 m3 needs to settle every day.
This volume is treated in cycles. The sedimentation velocity is sig-
nificantly higher in the case of MaB-flocs compared to suspended
microalgae. Van Den Hende et al. (2014a) obtained adequate sedi-
mentation after one hour of settling time. Because MaB-flocs need
to be shielded from shear stress as much as possible to avoid floc
disintegration, a simple sedimentation tank is used to harvest the
MaB-flocs. Based on pilot-scale results, it is assumed that at the
up-scaled plant (1) the volume of MaB-floc liquor can be led by
gravity to the sedimentation unit in 30 min, (2) the MaB-floc slurry
can be removed in 20 min from the tank bottom and (3) the sedi-
mentation supernatant can be pumped back to the ponds in
15 min. In this way, 7 sedimentation cycles over 14 hours can be
run per day on the most productive days.
The MaB-floc liquor contains 500 to 1000 mg TSS L�1 and settles
in one hour to a MaB-floc sludge layer of 7% TSS. In this study, an
on-site constructed shallow, square sedimentation basin with con-
ical bottom (concrete, below surface, 1.50 m deep, 6.50 m long) is
used with a submerged sludge pump at the bottom.
Both in the case of above-ground concrete ponds and dug-out
earthen ponds (bottom 0.17 m below ground level), MaB-floc
liquor flows by gravity from the ponds to the sedimentation unit
taking advantage of the height difference between the water sur-
face of the ponds and the sedimentation basin (drop of 0.25 m
and 0.13 m respectively). MaB-floc slurry is removed from the sed-
imentation basin bottom with a lobe pump (1.5 kW) in 20 min. The
clear supernatant is pumped out of the sedimentation basin back
to the ponds with a small supernatant pump (3 kW).
Settled MaB-floc sludge is dewatered in two steps, first by grav-
ity filtration and subsequently by filter pressing. At productivities
of 45 mg TSS L�1 d�1 and 60 mg TSS L�1 d�1 (i.e. maximum for
ACWW in Scenario 2 and Scenario 3), per day 186 kg TSS and
232 kg TSS of MaB-flocs are produced. When MaB-flocs in the reac-
tor liquor are fully settled, a sludge density of 70.3 g TSS L�1 is
obtained. Per day a volume of maximum 3.6 m3 (i.e. 0.26 m3 h�1)
(Scenario 3) MaB-floc slurry needs to be processed. In Van Den
Hende et al. (2014a) and Van Den Hende et al. (2016b) plate and
frame filter pressing powered by water pressure (4 bar) was used,
but the pressure during this pilot-scale filtering process was too
high as there was evidence that cells passed through the filter
cloth. The latter authors suggest that at industrial scale an
electric-powered belt filter press with a lower pressure should be
used. In this study a mini belt filter press (0.37 kW) is used. It is
assumed that the electricity consumption of the belt filter press
is equal to the electricity consumption of a plate filter press, i.e.
0.55 kWh kg�1 TSS (Udom et al., 2013).
2.11. Biomass valorization pathways and revenues
For each wastewater case study, different biomass valorization
pathways are assessed. MaB-flocs grown on ACWW are processed
to either shrimp feed (Pathway 1) or fertilizer (Pathway 2); or are
digested in their entirety to biogas (Pathway 3) (Fig. 1a). For CASEF
the simultaneous extraction of C-phycocyanin (C-PC) and C-
phycoerythrin (C-PE) and anaerobic digestion of the residual bio-
mass to biogas is analyzed (Pathway 4) (Fig. 1b). The economic
evaluation of these pathways is based on pilot-scale and lab-
scale test results of Van Den Hende et al. (2014a) Van Den Hende
et al. 2014b; Van Den Hende et al. (2015); Van Den Hende et al.
(2016a) and Van Den Hende et al. (2016b).
2.11.1. Wastewater treatment cost and avoided levies
In Belgium a wastewater levy is imposed per pollution unit pre-
sent in discharged wastewater to cover the cost of sewage treat-
ment. Through the wastewater treatment functionality of the
MaB-floc ponds the pollutant load in the wastewater is reduced,
leading to a lower wastewater levy. The avoided levy per water
volume (OECD, 2010) is compared to the wastewater treatment
cost of the MaB-floc system.
2.11.2. Dried MaB-flocs for shrimp feed and fertilizer
In Pathway 1 and Pathway 2 dewatered MaB-floc biomass
grown on ACWW is dried and milled, and subsequently used as
shrimp feed or fertilizer. Drying of the dewatered MaB-floc con-
sumes 0.29 kWh kg�1 TSS (Van Den Hende et al, 2014b) and
milling with a mill of 3.75 kW processing 114–122 kg h�1 con-
sumes 0.032 kWh kg�1 TSS. As in this case the fluidized bed dryer
uses waste heat from the CHP, it is assumedthat the actual energy
consumption for drying is only 10% of the aforementioned con-
sumption, i.e. 0.029 kWh kg�1 TSS.
Van Den Hende et al. (2014b) showed that MaB-flocs incorpo-
rated at 8% in shrimp feed enhance shrimp pigmentation. Other
authors have shown that microalgae incorporated in shrimp feeds
are powerful immunostimulants and feed attractants (Yaakob
et al., 2014). Additionally, MaB-flocs could be used as an alterna-
tive to yeast extracts, which is a single-cell protein source cur-
rently used in shrimp feeds (FAO, 2015). Yeast extracts are often
used as feed attractant and immunostimulant, and are incorpo-
rated at 2% to 4% in feeds. They contain nutritionally interesting
peptides, free amino acids, vitamins B and nucleotides. They are
also used as single-cell protein as replacement to fishmeal and
soy meal. The quality of different yeast products can be inconsis-
tent and depends greatly on the source of supply (Tacon, 2012).
Yeast extracts for feed are sold at EUR 0.8–2.9 kg�1 DM (Kollaras
et al., 2012), with prices of astaxanthin-containing phaffia yeast
at the high end of this range (Martin, 2012). Because of the low
control on MaB-floc composition, but having nonetheless sufficient
shrimp coloring properties, a market value of EUR 1.5 kg�1 TSS for
MaB-flocs as shrimp feed supplement was assumed.
124 E. Vulsteke et al. / Bioresource Technology 224 (2017) 118–129
The value of MaB-flocs as fertilizer is assumed at EUR 0.60 kg�1
TSS, based on comparable fertilizer performance of organic fertiliz-
ers (Coppens et al., 2016), and their additional ability to enhance
the red pigmentation and sugar content of tomatoes (Coppens
et al., 2016), adding to the market value of MaB-flocs. The effect
of different market values for dried MaB-flocs on the profitability
of MaB-floc ponds for wastewater treatment is assessed in a sensi-
tivity analysis.
2.11.3. Biogas production
Two biogas valorisation pathways are compared. In Pathway 3,
dewatered ACWW-fed MaB-flocs in their entirety are digested
anaerobically to methane; whereas in Pathway 4 the biomass that
is left over after C-PC and C-PE extraction from CASEF-fed MaB-
flocs is digested anaerobically to methane. MaB-flocs grown on
ACWW, harvested throughout the year and undergoing mesophilic
anaerobic digestion show a biochemical methane yield (BMY)
ranging from 0.133–0.235 Nm3 CH4 kg�1 VSS with an average of
0.152 Nm3 CH4 kg�1 VSS, representing an anaerobic digestion effi-
ciency ranging from 25.0 to 36.2% (Van Den Hende et al., 2015).
For ACWW, a sensitivity analysis is done assessing the increase
of MaB-floc digestibility from 0.152 Nm3 CH4 kg�1 VSS to
0.300 Nm3 CH4 kg�1 VSS (i.e. increasing anaerobic digestion effi-
ciencies from 30% to 60%). MaB-flocs grown in CASEF undergoing
extraction of water-soluble phycopigments and mesophilic anaer-
obic digestion show a biochemical methane yield (BMY) of
0.272 Nm3 CH4 kg�1 VSS, representing an anaerobic digestion effi-
ciency of 41.5% (Van Den Hende et al., 2016a). However, in case of
CASEF, 22.1% of the initial VS is lost during the pigment extraction
process, and is therefore not available for digestion. The cells of the
MaB-floc biomass after pigment extraction have been ruptured in
this extraction process, facilitating the anaerobic digestion process.
The parasitic energy consumption of the mesophilic digestion
process is assumed to be 0.14 kWhel Nm�3 biogas and 4.9 MJth -
Nm�3 biogas (ecoinvent v.22; cited in Sfez et al., 2015). Electricity
production from biogas is below 42 kWhel d�1 in Scenario 2 for
both ACWW (digestion efficiency of 30%) and CASEF, so an anaer-
obic digestion reactor with a biogas production capacity of 2 kWel
is sufficient. For Scenario 3 the required digester capacity is 3 kWel.
The capital cost of the digester is taken as EUR 4,505 kWel�1 (incl.
biogas treatment equipment), with an annual operational cost of
5% of the initial capital investment per year (IRENA, 2012). The
resulting biogas is used by the central CHP unit. In Belgium, elec-
tricity generation through biogas production with CHP conversion
receives a subsidy of EUR 0.093 kWhel�1 (European Commission,
2016d) and EUR 0.031 kWhth�1 (European Commission, 2016c).
2.11.4. Phycocyanin and phycoerythrin extraction
In Pathway 4 the potential of phycobiliprotein commercializa-
tion from CASEF-fed MaB-flocs is assessed. Pilot runs with the
CASEF-fed MaB-flocs contained a relatively high amount of phyco-
biliproteins, more specifically C-PC and C-PE. Indeed, these MaB-
flocs contained in total 91.4 g C-PC kg�1 VSS and 23.3 g C-
PE kg�1 VSS (Van Den Hende et al., 2016a). The purity of the phy-
cobiliprotein extract, indicated by the A620/A280 value, is the deter-
mining factor of the market value. A low-grade C-PC extract (i.e.
A620/A280 of 0.75–0.50) for human food applications is today avail-
able on the market at a price1 of EUR 192 kg�1 to EUR 269 kg�1.
However, the phycobiliproteins extracted from MaB-flocs cannot
be marketed as food-additives, as the MaB-flocs are produced on
wastewater. They could be marketed as dyes for non-food purposes
such as paint pigment, if an adequate light stability can be obtained.
1 Prices for large orders, based on quotes from companies and prices mentioned on
the company website of Soley Biotechnology Institute (India) (Soley Biotechnology
Institute, 2015) in August 2015. The ranges are based on minimum market prices.
In the case of a non-food purpose, the market price of this C-PC
would likely be lower than the price of food additive C-PC. Very pure
extracts (A620/A280 > 4.0) can be brought to the market as fluorescent
imaging tag for biomedical research, diagnostics and therapeutics
(Gupta et al., 2013). Although this purity could not be reached in
the first purification experiments of MaB-floc phycobiliproteins
(Van Den Hende et al., 2016a), there is opportunity to improve the
purification method. Further research efforts on C-PE and C-PC
recovery and purification of aqueous extracts of the underresearched
cyanobacterial species present in the CASEF-fed MaB-flocs will most
likely increase the total purity above the currently achieved value of
1.32. The total recovery in the additional purification steps was
59.1 mg C-PC g�1 VSSinitial and 12.2 mg C-PE g�1 VSSinitial (with
VSSinitial defined as the VSS of the MaB-floc biomass before pigment
extraction) or 64.6% and 26.7% of the total amount present in MaB-
flocs.
To make an estimate of the profitability of C-PC and C-PE pro-
duction, reported processing costs of phycobiliproteins by Reis
et al. (1998) and Ramanan (2000) were used, complemented with
an average (‘‘Intermediate”) processing cost. In the case of
Ramanan (2000), labor costs amount to 44% of total processing
costs. Only 10% of these labor costs are taken into account as it is
assumed that the extraction process could be automated to a
higher extent. As such an extraction cost of EUR 186.2 kg�1 is
obtained from Ramanan (2000), EUR 4.7 kg�1 from Reis et al.
(1998) and an intermediate value of EUR 95.5 kg�1. In the prof-
itability analysis, these processing costs were compared to the
average market value for food-grade C-PC of EUR 230.5 kg�1. C-
PE is currently only sold as high purity extracts, so the business
case for food-grade phycobiliproteins only concerns C-PC. The
additional purification step to obtain reactive grade extracts
(A620/A280 > 3.5) of C-PC and C-PE adds respectively EUR 39.1 or
199.0 g�1 to the processing cost according to Reis et al. (1998)
and Ramanan (2000), averaged to an intermediate processing cost
of EUR 119.1 g�1. The additional loss of C-PC and C-PE in further
purification steps is assumed to be 50% of C-PC and C-PE when
food-grade protein is further purified to high-purity C-PC or C-PE.
The market price of intermediate and reactive grade phycobilipro-
teins seems to vary substantially, depending on supplier and
requested quantity. In this analysis, the processing costs are placed
against a market revenue for reactive grade PC and PEthat is the
minimum market price for reactive grade C-PC obtained from a
market research2, i.e. EUR 0.450 mg�1, as a conservative revenue
estimate (market prices for reactive grade PE are higher). A sensitiv-
ity analysis was done to assess the effect of productivity increases
from Scenario 2 to Scenario 3 and the effect of increasing C-PC con-
centrations from 5.91% to 10% of MaB-floc TSS on the profitability of
food-grade C-PC commercialization. Additionally, the minimum
required market price for C-PC/C-PE was determined to run break-
even, to account for potential market price decreases as the supply
of C-PC and C-PE to the market increases.
2.12. Economic analysis
The cost of MaB-floc production is compared to the revenues
that could potentially be generated. Costs are composed of capital
expenses (CAPEX) and annual operational costs (OPEX). Operational
costs consist of energy costs, maintenance costs and labor costs.
Capital costs are composed of the initial capital investments in year
0 and capital equipment replacement costs incurred over the life-
time of the project. It is assumed that annual operational costs are
2 Prices for large orders, based on quotes and prices mentioned on the company
ebsites of Soley Biotechnology Institute (India) (Soley Biotechnology Institute,
015), Prozyme (US), Pragmatech (UK), Chromaprobe (US) and Santa Cruz Biotech
S) in August 2015. The ranges are based on minimum market prices.
w
2
(U
E. Vulsteke et al. / Bioresource Technology 224 (2017) 118–129 125
constant over the project lifetime. The capital costs (i.e. initial cap-
ital cost and periodical capital equipment replacement costs) are
converted to a constant equivalent annual cost (EAC) by multiply-
ing each capital cost item by its capital recovery factor (Eq. (1))
(Park, 2004):
EACCAPEX ¼
X
all components
CapitalCost:
ið1þ iÞL
ð1þ iÞL � 1
" #
ð1Þ
where i is the discount rate, CapitalCost is the capital cost of a capital
equipment component and L is the service lifespan of the capital
equipment component. In this analysis, a discount rate of 10% is
used. The discount rate reflects the profits that could be made by
investing money in another project or fund, and the additional risk
an investor faces by investing in the MaB-floc project. The higher
the investor’s risk, the larger the discount rate needs to be, to com-
pensate for this risk. An indicative estimate of the long-term return
of common stocks is about 6.5% (Otuteye and Siddiquee, 2015). The
discount rate of 10% used in this study is thus a conservative mea-
sure, taking into account the novelty of the business case and uncer-
tainties in expected revenues and costs. A sensitivity analysis is
done with a discount rate of 5% in the determination of the WWT
cost associated with the use of MaB-floc ponds.
The total equivalent annual cost of the MaB-floc plant is the
sum of the annual operational cost and the EAC of the capital costs
(Eq. (2)) (Park, 2004).
EACtotal ¼ OPEX þ EACCAPEX ð2Þ
The EAC per kg MaB-flocs produced or per m3 water treated is
obtained by dividing the EACtotal by the number of units produced
or treated per year (Park, 2004). The equivalent annual worth
(EAW) of the project is obtained by subtracting the EACtotal from
the annual revenues (assuming that annual revenues are constant
over the project lifetime). If the annual revenues are larger than the
EACtotal (i.e. EAW > 0), the project should be accepted (Park, 2004).
In this analysis, taxes and the cost of financing are not taken into
account. Taxes are calculated on the total of the profits or losses
of all the company’s projects and including taxes on this one pro-
ject would not reflect the actual revenue generating potential of
this wastewater treatment project. Interest rates are dependent
on the mood of the financial market, and as such including the
potential costs of financing would again give a distorted picture
of the actual EAW. Prices were adjusted for inflation using an
annual inflation rate of 2%. The project lifetime is 30 years, and
the biomass valorization strategy remains the same for 30 years.
3. Results and discussion
3.1. Plant infrastructure and operational costs
The plant infrastructure costs and operational costs of the up-
scaled MaB-floc pond system were assessed. CAPEX and OPEX for
the up-scaled MaB-floc ponds treating ACWW and CASEF are given
in Table 1.
Firstly, the infrastructure costs of three different pond types are
compared, i.e. (1) dug-out earthen ponds covered with an EPDM-
liner, (2) a concrete brick pond also covered by an EPDM-liner,
and (3) novel self-assembly ponds. The construction cost for 7
ponds of 1500 m2 is estimated at EUR 42,464 for the dug-out
earthen ponds; EUR 45,395 for the concrete brick pond; and EUR
123,834 for the self-assembly ponds. Despite the low cost of exca-
vation for the dug-out earthen ponds, the total cost of earthen
lined ponds is comparable to the cost of the concrete brick ponds.
This is because of the complexity of applying a liner to the banks of
the excavated ponds. Furthermore, it is deemed that the risk asso-
ciated with potential sliding of the banks in case of water overflow
from the ponds (strong winds, etc.) makes this option unfavorable.
The option of novel self-assembly ponds was assessed because of
the apparent advantage of their easy construction and removal,
allowing flexible use of the terrain, which is interesting in view
of potential unforeseen company activities as a company may be
required to restructure its terrain. The flexibility of this production
infrastructure reduces the investment risk of microalgae produc-
tion. However, the cost of these ponds is 3 times as high as building
concrete ponds. Therefore the pond construction method of choice
in this study is aboveground concrete ponds.
Secondly, a sensitivity analysis of the pond size was performed.
The economies of scale gained by constructing large ponds instead
of small ones is illustrated by a cost example for excavated earthen
ponds. The excavation cost of 7 ponds of 1500 m2 is estimated EUR
76,048 (i.e. EUR 10,864 pond�1), whereas the total cost to construct
40 ponds of 250 m2 amounts to EUR 182,101 (i.e. EUR
4,553 pond�1). For 14 ponds of 750 m2, total excavation costs
amount to EUR 119,504 (i.e. EUR 8,536 pond�1). According to
Richmond (1992), the size of commercial algae ponds varies from
1000 to 5000 m2. Not only are large ponds cheaper to construct,
they are also cheaper in energy consumption and maintenance,
as pumps with a larger capacity are usually more energy efficient.
Thirdly, the operational costs are studied. An electricity, heat
and CO2 balance of the ACWW plant for the production of dewa-
tered MaB-flocs in Scenario 2 for winter, summer and average con-
ditions showed that under average circumstances the CO2 demand
(87 kg CO2 d�1) for sparging and the thermal energy requirements
for pond heating (61.9 kWhth d�1) are met by the CO2 and heat pro-
duction of the CHP (305 kg CO2 d�1 and 488 kWhth d�1), respec-
tively. Furthermore, thermal requirements for pond heating are
met in winter (97.7 kWhth d�1) and CO2 demand in summer is ful-
filled by the CHP for both Scenario 2 and 3 (Fig. 2a). The heat
demand for MaB-floc drying during maximum productivities in
summer (i.e. at most 61 kWhth d�1) is also covered by CHP heat
production. The excess of available heat (produced by the CHP
unit) will likely bring the water temperature above 12 �C and thus
increase the pond productivity. The cost advantage of using an on-
site CHP producing 1162 kWhtot d�1 (i.e. associated with year-
average electricity production at the ACWW plant under Scenario
2) with natural gas at EUR 0.05 kWh�1 assuming an electrical effi-
ciency of 38%, compared to buying 442 kWhel d�1 at EUR
0.19 kWhel�1 from the net, is EUR 25.8 d�1 or EUR 9,419 y�1. Taking
into account the value of the CO2 produced annually on-site (i.e.
EUR 2,598 y�1), the cost advantage of a CHP rises to EUR
12,009 y�1.
3.2. MaB-floc production cost and biomassvalorization revenues
3.2.1. Aquaculture wastewater
Three scenarios with different biomass productivities were
compared. In Scenario 1, with an average productivity of
9.2 g TSS m�2 pond area d�1, MaB-flocs are produced at EUR
5.29 kg�1 TSS. The variability of MaB-floc production costs over
the course of a year is assessed in Scenario 2 and 3. For Scenario
2 this results in MaB-floc production costs ranging from EUR 2.69
to 8.45 kg�1 TSS. Increasing the MaB-floc productivity with 25%
(from Scenario 2 to Scenario 3) decreases the MaB-floc production
cost range to EUR 2.17–6.78 kg�1 TSS in Scenario 3 (Fig. 3a–b). It
must be noted that MaB-flocs consisted for about 65% of ash (ash
is defined as the difference between the mass of TSS and VSS). Tak-
ing this into account, a VSS production cost of EUR 15.05 kg�1 VSS
is achieved in Scenario 1. CAPEX costs comprise the bulk of the pro-
duction cost, followed by mixing costs (Fig. 3a–b). If wastewater
treatment would be the only function of the MaB-floc ponds, the
wastewater treatment cost is EUR 0.50 m�3 (Fig. 2b). The revenues
from biomass valorisation as shrimp feed are about EUR 0.14 m�3
(a) (b)
(c) (d)
(e) (f)
Fig. 2. Electricity, heat and CO2 balance of the ACWW plant and contribution of biogas energy production to the ACWW plant energy consumption (a), comparison of
wastewater treatment costs of the ACWW-fed MaB-floc pond and revenues from MaB-floc sales (i.e. sales revenues minus cost of drying and milling of MaB-flocs) in function
of biomass productivities (total pond surface of 1 ha) and MaB-floc selling prices (b), remaining wastewater treatment cost when dried MaB-flocs are sold at various selling
prices under the different biomass productivity scenarios using a discount rate of 10% and 5% for the ACWW plant (c) and the CASEF plant (d), food-grade C-PC revenues and
biomass production cost per kg MaB-floc VSS in function of biomass productivity, C-PC concentration and C-PC net revenue estimate (i.e. sale revenue minus extraction cost)
method (e), EAW of food-grade C-PC commercialization in function of C-PC processing costs, C-PC extraction level and biomass productivity (f).
126 E. Vulsteke et al. / Bioresource Technology 224 (2017) 118–129
(a) (b)
(c) (d)
Fig. 3. Production cost of MaB-floc biomass using a discount rate of 10% (i = 10%) and 5% (i = 5%) in ACWW Scenario 2 (i.e. variable monthly productivities) (a), ACWW
Scenario 3 (i.e. 25% productivity increase) (b), CASEF scenario 2 (i.e. variable monthly productivities) (c) and CASEF scenario 3 (i.e. 70% productivity increase) (d).
E. Vulsteke et al. / Bioresource Technology 224 (2017) 118–129 127
at the average productivity of 92 kg MaB-floc TSS d�1 (Scenario 1)
as obtained during pilot operations (with a MaB-floc selling price
of EUR 1.5 kg�1 TSS) (Fig. 2b). When MaB-flocs are sold at EUR
1.5 kg�1 TSS (Pathway 1), remaining WWT costs are EUR 0.37–
0.31 m�3 when a discount rate of 10% is used, and EUR 0.23–
0.17 m�3 using a 5% discount rate (Fig. 2c). Selling MaB-flocs as fer-
tilizer (Pathway 2) at EUR 0.6 kg�1 TSS results in a WWT cost of
EUR 0.45–0.43 m�3 (EUR 0.32–0.31 m�3) at a discount rate of
10% (5%) (Fig. 2c). This wastewater treatment cost is comparable
to the cost of other wastewater treatment systems. Although nutri-
ent removal rates are lower in the MaB-floc ponds, this is paired
with the fact that in MaB-floc ponds nitrogen is upcycled to high
value proteins in the MaB-floc biomass. A necessary condition to
use MaB-floc wastewater treatment technology is the availability
of sufficient land nearby the wastewater source at a cheap enough
price (i.e. agricultural land as opposed to land designated for indus-
trial purposes, which is significantly more expensive). The avoided
levy from reducing the pollution load in the wastewater by apply-
ing the MaB-floc technology is EUR 1.36 m�3, based on the removal
efficiencies of COD, BOD, TN and TP in the pilot experiments (Van
Den Hende et al., 2014a; OECD, 2010).
When feed-in tariffs, the value of the produced electricity and
heat, and the capital and operational costs to generate biogas
(Pathway 3) are taken into account, the net biogas revenues range
from EUR 0.005 m�3 (EUR 0.05 kg�1 TSS) in Scenario 1 with a
digestion efficiency of 30% to EUR 0.015 m�3 (EUR 0.11 kg�1 TSS)
in Scenario 3 with a digestion efficiency of 60%. Under the condi-
tions of Scenario 1 this means that revenues from biogas produc-
tion are more than 30 times smaller than the revenues of MaB-
floc sales at EUR 1.5 kg�1 TSS. Without subsidies these net rev-
enues decrease to EUR 0.002 m�3 or EUR 0.03 kg�1 TSS (Scenario
1, digestion efficiency of 30%) and EUR 0.007 m�3 or EUR
0.05 kg�1 TSS (Scenario 3, digestion efficiency of 60%). Although
these revenues are small, anaerobic digestion avoids sludge dis-
posal costs, which are in the range of EUR 18–156 ton�1 sludge
(European Commission, 2012), or EUR 0.04–0.36 kg�1 MaB-floc
TSS.
The contribution of energy generation from MaB-floc anaerobic
digestion to the total energy consumption of the plant is 4.8%
(Fig. 2a), when the MaB-floc productivity is at the minimum of
56 kg TSS d�1 (i.e. winter productivity in Scenario 2), and only rises
to 7.5% when biomass productivity increases to 240 kg TSS d�1 (i.e.
maximum productivity in Scenario 3), as the VSS content of the
MaB-flocs decreased as MaB-floc TSS productivities increased
(Van Den Hende et al., 2014a). So, from an energy perspective
the digestion of MaB-floc biomass does not contribute significantly
to the energy demand of wastewater treatment by MaB-floc ponds.
3.2.2. CAS effluent
Due to low MaB-floc productivities, MaB-flocs from CASEF are
almost twice as expensive to produce as MaB-flocs from the
ACWW. Scenario 1 produces MaB-flocs at EUR 8.07 kg�1 TSS, based
on constant year-round productivity of 6.8 g TSS m�2 pond area
d�1. In Scenario 2 production costs range from EUR 15.25 kg�1 in
winter months to EUR 4.59 kg�1 in summer. As productivities
increase with 70% in Scenario 3, these costs drop to EUR
128 E. Vulsteke et al. / Bioresource Technology 224 (2017) 118–129
9.01 kg�1 and EUR 2.74 kg�1 (Fig. 3c–d). CASEF-fed MaB-flocs con-
tain around 40% ash (ash defined as the difference between the
mass of TSS and VSS). Taking this into account, a production cost
of EUR 11.73 kg�1 VSS is obtained in Scenario 1. This VSS produc-
tion cost is lower than the VSS production cost obtained from
ACWW because in the case of CASEF a higher VSS productivity is
obtained compared to ACWW (4.19 g VSS m�2 pond area d�1 ver-
sus 3.2 g VSS m�2 pond area d�1). Again CAPEX costs are the largest
contributor to the total production cost (Fig. 3c–d). The wastewa-
ter treatment costs for CASEF are EUR 0.248 m�3 (EUR
0.197 m�3) for Scenario 1 and EUR 0.253 m�3 (EUR 0.199 m�3)
for Scenario 3 respectively using a discount rate of 10% (5%)
(Fig. 2d). The avoided wastewater discharge levy resulting from
the wastewater treatment functionality of the MaB-floc ponds is
EUR 3.82 m�3, based on the removal efficiencies of COD, BOD, TN
and TP in the pilot experiments (Van Den Hende et al., 2016b;
OECD, 2010).
A potential revenue is extraction of phycobiliproteins, as these
pigments are found in high concentrations in the CASEF-fed
MaB-flocs (Pathway 4). To profitably sell food-grade C-PC at a mar-
ket price of EUR 230 kg�1, C-PC extraction costs need to be in the
range as proposed by Reis et al. (1998), i.e. EUR 4.7 kg�1 food-
grade C-PC and extraction efficiencies need to increase to 100 mg
C-PC g�1 VS or biomass productivities need to increase to those
of Scenario 3 (Fig. 2e-f). However, it must be noted that market
revenues of EUR 230 kg�1 will most likely not be obtained because
MaB-floc C-PC is produced in (food industry) wastewater. In the
case of processing costs in the range of Reis et al. (1998), market
prices for food-grade C-PC are allowed to drop to EUR 188–
112 kg�1 to bring the profitable cases of Fig. 2f to just break-even.
Further purifying C-PC to a purity gradeA620/A280 of 3.5 returns
a very high positive equivalent annual worth (EAW) even with the
actual C-PC extraction efficiencies and lower biomass productivi-
ties. In the case of Scenario 2 productivities, high processing costs
(Ramanan, 2000) and an extraction level of 6%, the EAW is EUR
44 Mio y�1, equivalent to a profit of EUR 8,916 kg�1 TSS. However,
it is important to realize that this revenue is sensitive to the market
price that can be received for reactive grade C-PC that is produced
on (food industry) wastewater. Market prices for reactive grade C-
PC/C-PE are allowed to drop to respectively EUR 200, 119 and
39 g�1 C-PC before reactive grade MaB-floc production becomes
unprofitable, in the case of Ramanan (2000), Intermediate and
Reis et al. (1998) processing costs respectively. The additional
purification to reactive grade C-PC and C-PE is thus a potentially
more profitable business case than the commercialization of
food-grade C-PC.
Anaerobic digestion of the residual biomass contributes at the
most EUR 0.005 m�3 or EUR 0.16 kg�1 TSS when feed-in tariffs,
the value of the produced electricity and heat and the capital and
operational costs to generate biogas are taken into account. With-
out subsidies these revenues decrease to EUR 0.002 m�3 or EUR
0.07 kg�1 TSS. As in the case of ACWW these revenues are small,
but anaerobic digestion avoids sludge disposal costs, which are in
the range of EUR 18–156 ton�1 sludge (European Commission,
2012), or EUR 0.04–0.36 kg�1 MaB-floc TSS.
4. Conclusion
MaB-floc raceway ponds exhibit a cost performance similar to
conventional wastewater treatment technologies, i.e. EUR 0.25–
0.50 m�3. Capital costs are the largest expense. MaB-flocs are pro-
duced at EUR 5.26–8.07 kg�1 TSS. Selling ACWW-fed MaB-flocs as
shrimp feed supplement reduces the wastewater treatment costs
considerably. In contrast, biogas revenues are negligible. Extraction
of phycobiliproteins from CASEF-fed MaB-flocs generates substan-
tial revenues if MaB-floc productivities increase and market prices
stay sufficiently high. This study shows that optimization of MaB-
floc ponds and valorization pathways sufficiently improve the eco-
nomic outlook of MaB-floc ponds for wastewater treatment and
biomass production.
Acknowledgements
This research is part of the EnAlgae-project, which is funded by
the INTERREG IVB Northwest Europe programme, the Flemish
Government, Province East-Flanders and Province West-Flanders.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.biortech.2016.11.
090.
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	Economic feasibility of microalgal bacterial floc production for wastewater treatment and biomass valorization: A detailed up-to-date analysis of up-scaled pilot results
	1 Introduction
	2 Materials and methods
	2.1 Wastewaters and scale-up of MaB-floc ponds
	2.2 Pond construction
	2.3 Pond mixing
	2.4 Influent and supernatant pumping
	2.5 pH control
	2.6 Combined heat and power production
	2.7 Pond heating
	2.8 Automation
	2.9 Biomass productivities
	2.10 Harvesting and dewatering
	2.11 Biomass valorization pathways and revenues
	2.11.1 Wastewater treatment cost and avoided levies
	2.11.2 Dried MaB-flocs for shrimp feed and fertilizer
	2.11.3 Biogas production
	2.11.4 Phycocyanin and phycoerythrin extraction
	2.12 Economic analysis
	3 Results and discussion
	3.1 Plant infrastructure and operational costs
	3.2 MaB-floc production cost and biomass valorization revenues
	3.2.1 Aquaculture wastewater
	3.2.2 CAS effluent
	4 Conclusion
	Acknowledgements
	Appendix A Supplementary data
	References