Many rural areas of Latin America and the Caribbean (LAC) region are economically depressed. Rural sewage treatment in most areas of LAC is deficient or non-existent. Consequently, the possibility of generating economic revenue from treated sewage is an attractive option for deprived areas of developing countries. Given its peculiar characteristics, rural sewage may be coupled with biological systems such as algae for nutrient cycling. Acceptable algae growth and nutrient elimination were obtained from rural sewage whose treatment may have fallen short of current disposal standards. In this study, aerobic systems working on an 8-month cycle at three different volumetric loading rates (Bv) were assessed in relation to the lifetime growth of three algae strains native to Ecuador. Results indicate Chlorella sp. M2 as the optimal algal strain, with the highest growth rate at Bv of 1 g COD L−1 d1 and a removal of organic-N (30%), PO43–-P (87%) and NH4+-N (95%). Concomitantly, the kinetic constants of the sewage resulted in a low biomass yield coefficient, making the proposed system highly suitable for developing countries. Finally, the proposed partial recovery stream method, combining nutrient recovery with economic resource generation, appears to contain great potential.

Rural areas of the Latin America and the Caribbean (LAC) region have limited capacities in sewage treatment systems and suffer from a lack of opportunities to expand their economy (Sparkman & Sturzenegger 2016). In developing countries, up to 90% of sewage is discharged without proper treatment, affecting mainly the poor. Water is a very important concern as it is interwoven with sustainable development issues. Therefore, any possibility of obtaining economic revenue from treated sewage of emergent nations is worth investigating.

Sewage treatment has been widely studied, both from the perspective of the chemical and biological processes involved and with reference to the source; that is, urban, synthetic, separated and mixed pipelines, contaminated with agricultural runoff or industrial water, among others (Aiyuk & Verstraete 2004; Aiyuk et al. 2004). Nevertheless, only a few studies touch upon the behaviour of the aerobic microbial population growing in rural domestic sewage of developing countries. The organic fraction of the solid waste stream in these countries is considerably higher (from 40% to 80% of the total) compared to those from developed nations (Hoornweg & Bhada-Tata 2012; Ozcan et al. 2016). This strongly suggests an organic sewage composition derived mainly from kitchen food residues and preparation. The widespread use of non-processed organics, mainly fruits and vegetables, in developing countries results in sewage with less oxidized organic matter, higher biochemical and chemical oxygen demand (BOD/COD) ratio, peculiar micronutrients and vitamin concentrations (folic acid being of special interest) (Selimoğlu et al. 2015). This may eventually affect kinetics, and particularly, the biomass yield (Velho et al. 2016).

Algae have become a potential raw material in the production of locally valuable resources (animal feed, starch, pigments). There is, consequently, some economic potential in coupling traditional biological wastewater treatments with native algae cultivation. From Abdel-Raouf et al. (2012), micro-algae culture offers a promising tertiary bio-treatment step, involving the production of potentially valuable biomass. Still, optimising volumetric organic loading rates (Bv) in sewage treatment to favour algae growth is currently an underresearched area (Zamalloa et al. 2012). The present study aims to identify a particular Bv that promotes optimal algae growth via coupling of partially biologically treated rural sewage. Importantly, the algae used should be resistant to the local solar energy radiation, as well as to the presence of competitors.

Wastewater characteristics and collection

The sewage used in the present study comes from a countryside community (27 °C mean temperature and 140 m.a.s.l) located 100 km east of Guayaquil, Ecuador. Due to cyclic variations in its organic load, samples were taken from the community collector during a 1.5-hour daily interval representative of the highest COD load (352 ± 32 mg COD L1). Thus, in case of extrapolation of this study to a pilot or industrial scale bio-refinery facility, bulk water with lower organic load (80 ± 50 mg L1) could be treated with any other less energy-demanding technique.

The physical-chemical characteristics of rural sewage (Table 1) were determined according to Standard Methods for the Examination of Water and WastewaterAPHA/AWWA/WEF (2012): 5220 B for COD; 5210 B for BOD; 2320 B for alkalinity; 2540 B for total solids (TS); 2540 D for total suspended solids (TSS) and total dissolved solids (TDS); 2540 E for total fixed solids (TFS), fixed suspended solids (FSS), fixed dissolved solids (FDS), total volatile solids (TVS), volatile suspended solids (VSS) and volatile dissolved solids (VDS); 4500-P D for phosphorus; 4500-NO3 E and 4500-NO2 B for nitrate and nitrite, respectively; 4500-NH3 C for ammonia; 4500-Norg B and direct colorimetric nesslerization for organic nitrogen. pH values were measured using a 510 series Oakton benchtop meter.

Table 1

Physical-chemical characteristics of the rural sewage samples under study (n = 32)

ParameterUnitValue
pH – 7.3 ± 0.3 
COD mg L1 352 ± 32 
BOD mg L1 330 ± 21 
sCODa mg L1 196 ± 34 
Alkalinity mg L1 310 ± 19 
TANb mg L1 32 ± 3.7 
Nitrate mg L1 0.4 ± 0.2 
Nitrite mg L1 <0.01c 
TKNd mg L1 51 ± 4 
TS mg L1 438 ± 23 
TDS mg L1 355 ± 35 
VSS mg L1 39.3 ± 8 
PO43-P mg L1 8.21 ± 2 
ParameterUnitValue
pH – 7.3 ± 0.3 
COD mg L1 352 ± 32 
BOD mg L1 330 ± 21 
sCODa mg L1 196 ± 34 
Alkalinity mg L1 310 ± 19 
TANb mg L1 32 ± 3.7 
Nitrate mg L1 0.4 ± 0.2 
Nitrite mg L1 <0.01c 
TKNd mg L1 51 ± 4 
TS mg L1 438 ± 23 
TDS mg L1 355 ± 35 
VSS mg L1 39.3 ± 8 
PO43-P mg L1 8.21 ± 2 

aSoluble COD.

bTotal ammonia nitrogen (NH4+-N + NH3-N).

cThe lowest detection limit.

dTotal Kjeldahl nitrogen (organic, NH3 and NH4+ nitrogen).

COD, TS, TDS, and TSS were compared with those values of urban sewage.

Treatment of rural sewage with the highest COD

The experimental design for the treatment of rural sewage is shown in Figure 1.

Figure 1

Schematic setup of the integrated treatments used in the present study. (a) Storage tank, (b) influent, (c) homogenization compartment, (d) aerobic compartment, (e) secondary clarifier, (f) effluent, (g) multilayer filter, (h) UV-light chamber, (i) photobioreactors.

Figure 1

Schematic setup of the integrated treatments used in the present study. (a) Storage tank, (b) influent, (c) homogenization compartment, (d) aerobic compartment, (e) secondary clarifier, (f) effluent, (g) multilayer filter, (h) UV-light chamber, (i) photobioreactors.

Close modal

Aerobic systems setup

Three aerobic systems were constructed (S1, S2 and S3). For each system (Figure 1, from c to f), the homogenisation compartment was equipped with overflow and the secondary clarifier with a siphon for the discharge of treated water. The 10 L aerobic compartment (34.5 cm (L) × 20.5 cm (W) × 14 cm (H)), was equipped with three air diffusers located at the bottom and arranged in parallel to keep the oxygen level above 2 mg O2 L1. Additionally, the diffusers were covered with a perforated plate to ensure a uniform distribution of bubbles.

Aerobic systems operation

S1, S2 and S3 operated simultaneously at 25 ± 2 °C for about 8 months in continuous-flow mode involving extended aeration. In order to select the range at which COD removal rates took place, a wide range of Bv were tested in advance. Finally, the chosen values were 0.7, 1.0 and 1.4 g COD L1d1; the mixed liquor volatile suspended solids (MLVSS) were 1,390, 1,360 and 1,290 mg VSS L1, for S1, S2 and S3, respectively. The pH in the aeration tanks was adjusted to 7.6 ± 0.1.

The kinetics of sewage were computed based on the usual imposed and measured parameters.

Sludge characteristics and excess biomass (ΔX)

In the initial stages, S2 and S3 showed negligible biomass growth, while S1 showed an appreciable growth (from 39 to 7,600 mg VSS L1). After 3 weeks, the activated sludge appeared fluffy, sticky and highly settleable in all systems. In order to have similar MLVSS concentrations, the sludge from S1 was equitably distributed in S2 and S3.

Due to non-homogeneity and physical irregularities of the sludge flocs, the excess biomass (ΔX) was determined by measuring the entire biomass present in each system (own method). For that, the total biomass was poured into Imhoff cones, decanted over 20 minutes, and the surplus sludge taken away, thus achieving the required MLVSS. The sludge density (1.12, 1.1 and 1.0 g cm3, for S1, S2 and S3, respectively) was previously determined and correlated with the VSS levels.

Use of partially treated wastewater as a medium for growth of native algae

A multilayer filter (Figure 1) composed of quartz, activated carbon, white, red and medical sandstone was used to remove debris from the aerobic effluents. Afterwards, UV-light was used to eliminate ciliates. Effluents S1, S2 and S3, free from debris and ciliates, were used as a medium to grow three algal strains native from Ecuador, viz. Chlorella sp. M2, Chlorella sp. M6 and Scenedesmus sp. R3 (NCBI accession number: MF677855, MF677856 and MF677857, respectively). Previously, they were isolated and propagated as described in Aray-Andrade et al. (2019).

The algae were cultivated in triplicate for 7 days, outdoors, with an initial concentration of 630 algal cells ml1, using 3-liter glass-made cylindrical (115 cm in height and 7 cm in diameter) photo-bioreactors. Growth rate was determined by microscopic counting and expressed as cell ml1. Agitation was provided by air bubbling, using a 1 L min1 flow. Algae biomass was harvested by filtration using glass microfiber filters PALL 61631 Type A/E and a Whatman GF/D (pore size 1 and 27 μm, respectively), according to cell size.

The mean temperature registered for the site was 37 °C; however, the greenhouse effect raised it inside the photobioreactor to about 46 °C. Conversely, in summer, the temperature decreased to about 18 °C.

Evaluating the potential of coupling biological systems for conversion of rural sewage to resources

This cleaner production approach differs from the typical linear sequence of sewage treatment (i.e. collection, low energy demand biological treatment, clarification and disposal) in that it includes the cycling of sewage nutrients for algae production, as shown in Figure 2. In view of this, stage 6 must work at the selected Bv optimal for algal growth and consequently, to a high organic load. The spent media in process 9 must be adequate to fulfil the above-mentioned parameters in order to be recycled to stage 6 or sent to either stage 4 or stage 5 directly. Finally, stages 8 and 9 would depend on the location, on further processes applied to the cultivated algae, and on the characteristics of the spent media, which were not part of the present study.

Figure 2

Proposed stages in the partial stream recovery concept for rural sewage in developing countries.

Figure 2

Proposed stages in the partial stream recovery concept for rural sewage in developing countries.

Close modal

Solid analysis of rural sewage

From the TS mean value (438.3 ± 43 mg L1, Table 1), 123.3 ± 9 mg L1 (28.2%) corresponded to TFS and 315 mg L1 (71.8%) to TVS. TSS was 83.3 mg L1 (19%) and TDS, 355 mg L1 (81%). Roughly, 53% of TSS was VSS (44 mg L1). TDS resulted in 56.85 and 43.1% for VDS and FDS, respectively; indicating that most of the solids were soluble and organic. In addition, the distribution of organic and inorganic matter in TSS was roughly 50%. Rural TS values scored lower than urban sewage values (652 ± 34 mg TS L1), which approximated to those reported by Van Haandel & Lettinga (1994), studying sewage in Latin American cities. In the present study, urban sewage TS were 48.5% TVS, which means a lower content in organics, compared to rural sewage. Moreover, the percentage of urban TDS was higher than TSS, but much less than rural sewage. These differences are attributable to the presence of more stabilized organic matter as sewage stays longer in the main collectors.

COD, Bv and nutrients in the systems

From Table 1, COD values of rural sewage (high COD load in the present study) were much lower than those found for urban sewage (620 ± 53 mg L1); urban sewerage systems could be exposed to other kinds of organic matter.

An inverse correlation was observed between both the influent Bv (in a range from 0.7 to 1.4 g COD L1 d1) and organic loading rate (Bx, from 0.5 to 1.1 g COD g1 DW d1), with the effluent COD values, attributable to the effect of higher biomass-substrate contact.

From Table 2, the mean NH4+-N removal levels of 76%, 62% and 46% obtained for S1, S2 and S3 respectively, are a balance between aerobic transformation of organic-N to ammonium, and the remaining ammonium levels initially present. Ammonium levels were not greatly reduced, contrary to what might be expected in extended aeration, perhaps owing to the high ambient temperature typical of tropical countries. On the other hand, S1, S2 and S3 showed significant organic-N removal rates.

Table 2

Influent and effluent COD and nutrients levels of the sewage entering the systems of study

ParameterSystem 1
System 2
System 3
Level mg L−1Removal (%)Level mg L−1Removal (%)Level mg L−1Removal (%)
CODi 352 ± 38.2 89 352 ± 38.2 72 352 ± 38.2 43 
CODe 39 ± 2.2 98.5 ± 6.2 151 ± 8.3 
NH4+-Ni 32.2 ± 3.7 76 32.2 ± 3.7 62 32.2 ± 3.7 46 
NH4+-Ne 7.7 ± 0.7 12.2 ± 1.3 17 ± 3.4 
Org-Ni 12.2 ± 2.1 98 12.2 ± 2.1 96 12.2 ± 2.4 93.7 
Org-Ne 0.28 ± 0.02 0.45 ± 0.1 0,76 ± 0.1 
PO43-Pi 8.21 ± 1.2 99 8.21 ± 1.2 98.2 8.21 ± 1.2 97.3 
PO43-Pe 0.1 ± 0.03 0.15 ± 0.02 0.22 ± 0.01 
ParameterSystem 1
System 2
System 3
Level mg L−1Removal (%)Level mg L−1Removal (%)Level mg L−1Removal (%)
CODi 352 ± 38.2 89 352 ± 38.2 72 352 ± 38.2 43 
CODe 39 ± 2.2 98.5 ± 6.2 151 ± 8.3 
NH4+-Ni 32.2 ± 3.7 76 32.2 ± 3.7 62 32.2 ± 3.7 46 
NH4+-Ne 7.7 ± 0.7 12.2 ± 1.3 17 ± 3.4 
Org-Ni 12.2 ± 2.1 98 12.2 ± 2.1 96 12.2 ± 2.4 93.7 
Org-Ne 0.28 ± 0.02 0.45 ± 0.1 0,76 ± 0.1 
PO43-Pi 8.21 ± 1.2 99 8.21 ± 1.2 98.2 8.21 ± 1.2 97.3 
PO43-Pe 0.1 ± 0.03 0.15 ± 0.02 0.22 ± 0.01 

i: influent. e: effluent.

The lowest COD and NH4+-N removal rates were observed for S3 at the highest Bv of the study. Thus, this system reflected the low solids retention time applied and consequently a poor bacteria-substrate contact. As with COD and NH4+-N, a high removal of P was also observed for all the systems, with S3 the least effective in this respect (from 8.21 ± 1.2 mg to 0.2 mg PO43–-P L1).

Kinetic constants

The organic loading rate (Өx) applied to the systems ranged from 0.51 to 1.1 g COD g DW1d1, resembling an extended aeration mode. However, atypically for this mode, good sludge settleability was observed in the secondary clarifier. The maximum substrate utilization rate (qmax), half-saturation constant (Ks) and decay coefficient (kd) of rural sewage were 0.69 d1, 0.021 g L1 and 0.136 d1, respectively. The growth yield coefficient, 0.32, was lower than the usual values from urban sewage (0.4–0.6) commonly reported (El-Seddik 2017). Velho et al. (2016) obtained low Y values for sewage rich in vitamins and minerals, especially after folic acid addition. Senorer & Barlas (2004) found higher efficiency in treatments after progressive folic acid dosage to sewage. Moreover, from Fujii et al. (2010), algae harvesting effluents contain amino acids, vitamins and folates, among others, that would magnify bacterial metabolic activity with consequent improved COD removal.

Algal growth

From Table 3, NH4+-N removal was the highest (97.7%) when Scenedesmus sp. R3 grew on the S2 effluent. On the other hand, organic-N showed the highest removal rate, 70.45%, when Chlorella sp. M6 was fed on the S3 effluent; also, PO43–-P removal rate was the highest when Chlorella sp. M2 was fed on the S2 effluent. Scenedesmus sp., growing on wastewater, reported 96% P removal and 97% NH4+-N removal (Acevedo et al. 2017). Praveen & Loh (2016) reported a NH4+-N removal efficiency of 93% by Chlorella vulgaris using wastewater as growth medium at 6.16 mg NH4+-N L1. This initial value appears close to that found in S1. Similarly, Chan et al. (2014) using Chlorella sp. reported higher ammonia removal in secondary sewage at initial concentrations of 12 mg L1, comparable to S2 and a PO43–-P removal rate of 50% at initial levels nearly to 0.2 mg L1, similar to S1. P levels in effluents are very low. Interestingly, Bowman et al. (2007) showed that low P-values in the range of 0.1–5.6 μg L1 did not interfere in the attainment of good algae growth.

Table 3

Influents and effluents nutrient values for microalgae cultures using cylinder type photo-bioreactors at 32 ± 2 °C

 NH4+-N (mg L−1)
Organic-N (mg L−1)
PO43–-P (mg L−1)
I(1)E(2)
IE
IE
Chlorella sp. M2Chlorella sp. M6Scenedesmus sp. R3Chlorella sp. M2Chlorella sp. M6Scenedesmus sp. R3Chlorella sp. M2Chlorella sp. M6Scenedesmus sp. R3
S1 7.7 ± 0.3 0.52 (93.2)(3) 0.54 (93.0) 0.60 (92.2) 0.30 <0.05(4) <0.05 <0.05 0.1 0.03 (70) 0.03 (70) 0.05 (50) 
S2 12.2 ± 3 0.67 (94.5) 0.67 (94.5) 0.28 (97.7) 0.4 0.28 (30) 0.3 (25) 1.5 0.15 0.02 (86.6) 0.03 (80) 0.16 (8.8) 
S3 17.2 ± 3 4.65 (72.9) 5.60 (67.4) 0.8 (95.3) 0.76 0.65 (14.5) 0.224 (70.5) 1.2 0.22 0.08 (63.7) 0.22 0.1 (54.5) 
 NH4+-N (mg L−1)
Organic-N (mg L−1)
PO43–-P (mg L−1)
I(1)E(2)
IE
IE
Chlorella sp. M2Chlorella sp. M6Scenedesmus sp. R3Chlorella sp. M2Chlorella sp. M6Scenedesmus sp. R3Chlorella sp. M2Chlorella sp. M6Scenedesmus sp. R3
S1 7.7 ± 0.3 0.52 (93.2)(3) 0.54 (93.0) 0.60 (92.2) 0.30 <0.05(4) <0.05 <0.05 0.1 0.03 (70) 0.03 (70) 0.05 (50) 
S2 12.2 ± 3 0.67 (94.5) 0.67 (94.5) 0.28 (97.7) 0.4 0.28 (30) 0.3 (25) 1.5 0.15 0.02 (86.6) 0.03 (80) 0.16 (8.8) 
S3 17.2 ± 3 4.65 (72.9) 5.60 (67.4) 0.8 (95.3) 0.76 0.65 (14.5) 0.224 (70.5) 1.2 0.22 0.08 (63.7) 0.22 0.1 (54.5) 

(1) Influent (2) Effluent (3) Percentage of removal (4) The lowest detection limit.

Table 3 also shows the lowest removal rates for NH4+-N when effluent S3 (highest Bv) was used as growth media. Probably, this was due to bacterial mediated algal cellular lysis (Bolch et al. 2017) or excretion of small organic molecules, which may affect nutrient removal rates (Wang et al. 2009). Contrarily, the removal rate of organic-N does not follow a pattern and varies depending on the algal specie and the effluent used. The growth rate of the three algal species used was consistent among species (Figure 3). The growth rate of Chlorella sp. M2 (μ = 0.56 ± 0.02 day1) was comparable to Chlorella sp. (0.53 day1, 26 ± 1 °C) (Min et al. 2011). Chlorella sp. M6 (μ = 0.45 ± 0.04 day1) growth rate was comparable to C. Zofingiensis (μ = 0.49 day1) when using piggery wastewater with an initial COD of 400 mg L1 as media (Zhu et al. 2013). Finally, the growth rate of Scenedesmus sp. R3 (μ = 0.50 ± 0.01 day1) was similar to the findings of Latiffi et al. (2017) in Scenedesmus sp. (μ = 0.44 day1). Thus, the suitability of the collected, isolated, propagated and cultivated native species is remarkable; growth rates of native algae on the selected medium with a range of temperatures between 18 and 46 °C were very similar to those of closely related species, growing at a controlled temperature.

Figure 3

Growth curve of Chlorella sp. M2, Chlorella sp. M6 and Scenedesmus sp. R3.

Figure 3

Growth curve of Chlorella sp. M2, Chlorella sp. M6 and Scenedesmus sp. R3.

Close modal

Of the three algal strains tested, Chlorella sp. M2, cultured in cylindrical-type photo-bioreactors, showed the highest growth rate. For this, the optimal Bv was 1 g COD L1 d1 attaining a removal of 72% COD, 30% organic-N (30%), 87% PO43–-P, and 95% NH4+-N. Interestingly, the proposed system resulted in a low biomass yield coefficient of 0.3, possibly due to the peculiar characteristics of the substrate.

The partial stream recovery concept proposed in this study presents itself as a promising strategy for nutrient capture and reduction of organic load peaks. The method allows for extraction of the highest organic portion of daily sewage (advantageously present in low volume) for algae growth while leaving the lower bulk contamination for less energy demanding treatments. To maintain suitable parameters for algal growth, the spent media could be either re-circulated or sent straight to a low energy final treatment.

The authors would like to thank the local authorities of the Marcelino Maridueña rural municipality for making their facilities available for this study.

Abdel-Raouf
N.
,
Al-Homaidan
A. A.
,
Ibraheem
I. B. M.
2012
Microalgae and wastewater treatment
.
Saudi Journal of Biological Sciences
19
(
3
),
257
275
.
Acevedo
S.
,
Peñuela
G. A.
,
Pino
N.
2017
Biomass production of Scenedesmus sp. and removal of nitrogen and phosphorus in domestic wastewater
.
Ingeniería Y Competitividad
19
(
1
),
185
193
.
Aiyuk
S.
,
Amoako
J.
,
Raskin
L.
,
Van Haandel
A.
,
Verstraete
W.
2004
Removal of carbon and nutrients from domestic wastewater using a low investment integrated treatment concept
.
Water Research
38
(
13
),
3031
3042
.
APHA/AWWA/WEF
2012
Standard Methods for the Examination of Water and Wastewater
, 22nd edn.
American Public Health Association/American Water Works Association/Water Environment Federation
,
Washington, DC
,
USA
.
Aray-Andrade
M.
,
Moreira
C.
,
Santander
V.
,
Mendoza
L.
,
Bermúdez
R.
2019
Characterization of three algal strains used as tertiary treatment for rural wastewater of Ecuadorian Littoral
. In:
European Biomass Conference and Exhibition Proceedings
,
Lisbon, Portugal
, pp.
241
248
.
Bowman
M. F.
,
Chambers
P. A.
,
Schindler
D. W.
2007
Constraints on benthic algal response to nutrient addition in oligotrophic mountain rivers
.
River Research and Applications
23
(
8
),
858
876
.
Chan
A.
,
Salsali
H.
,
McBean
E.
2014
Nutrient removal (nitrogen and phosphorous) in secondary effluent from a wastewater treatment plant by microalgae
.
Canadian Journal of Civil Engineering
41
(
2
),
118
124
.
El-Seddik
M. M.
2017
Fractional-order activated sludge model (MFASM) for aerobic microbial growth in wastewater
.
Inorganic Chemistry-An Indian Journal
12
(
2
),
117
.
Fujii
K.
,
Nakashima
H.
,
Hashidzume
Y.
2010
Isolation of folate-producing microalgae, from oligotrophic ponds in Yamaguchi, Japan
.
Journal of Applied Microbiology
108
(
4
),
1421
1429
.
Hoornweg
D.
,
Bhada-Tata
P.
2012
What A Waste: A Global Review of Solid Waste Management
.
Urban development series; knowledge papers no. 15. World Bank, Washington, DC
.
Min
M.
,
Wang
L.
,
Li
Y.
,
Mohr
M. J.
,
Hu
B.
,
Zhou
W.
,
Chen
P.
,
Ruan
R.
2011
Cultivating Chlorella sp. in a pilot-scale photobioreactor using centrate wastewater for microalgae biomass production and wastewater nutrient removal
.
Applied Biochemistry and Biotechnology
165
(
1
),
123
137
.
Ozcan
H.
,
Guvenc
S.
,
Demir
G.
2016
Municipal solid waste characterization according to different income levels: a case study
.
Sustainability
8
(
1044
),
1
11
.
Selimoğlu
F.
,
Öbek
E.
,
Karataş
F.
,
Arslan
E. I.
,
Tatar
S. Y.
2015
Determination of amounts of some vitamin B groups in domestic wastewater treatment plants
.
Turkish Journal of Science and Technology
10
(
2
),
1
5
.
Senorer
E.
,
Barlas
H.
2004
Effects of folic acid on the efficiency of biological wastewater treatment
.
Fresenius Environmental Bulletin
13
(
10
),
1036
1039
.
Sparkman
D.
,
Sturzenegger
G.
2016
Fostering Water and Sanitation Markets in Latin America and The Caribbean
.
The Inter-American Development Bank
,
Washington, DC, USA
.
Van Haandel
A. C.
,
Lettinga
G.
1994
Anaerobic Sewage Treatment: A Practical Guide for Regions with A hot Climate
.
John Wiley & Sons
,
Chichester
.
Velho
V. F.
,
Daudt
G. C.
,
Martins
C. L.
,
Belli Filho
P.
,
Costa
R. H. R.
2016
Reduction of excess sludge production in an activated sludge system based on lysis-cryptic growth, uncoupling metabolism and folic acid addition
.
Brazilian Journal of Chemical Engineering
33
(
1
),
47
57
.
Wang
L.
,
Min
M.
,
Li
Y.
,
Chen
P.
,
Chen
Y.
,
Liu
Y.
,
Wang
Y.
,
Ruan
R.
2009
Cultivation of green algae Chlorella sp. in different wastewaters from municipal wastewater treatment plant
.
Applied Biochemistry and Biotechnology
162
(
4
),
1174
1186
.
Zhu
L.
,
Wang
Z.
,
Shu
Q.
,
Takala
J.
,
Hiltunen
E.
,
Feng
P.
,
Yuan
Z.
2013
Nutrient removal and biodiesel production by integration of freshwater algae cultivation with piggery wastewater treatment
.
Water Research
47
(
13
),
4294
4302
.