High rate algal pond for greywater treatment in arid and semi-arid areas

88 Pages·2017·1.52 MB·English

Title High rate algal pond for greywater treatment in arid and semi-arid areas
Author(s) DERABE-MAOBE, HINA
Citation 北海道大学. 博士(工学) 甲第11576号
Issue Date 2014-09-25
DOI 10.14943/doctoral.k11576
Doc URL http://hdl.handle.net/2115/57228
Type theses (doctoral)
File Information Derabe_Maobe_Hina.pdf

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Hokkaido University Collection of Scholarly and Academic Papers : HUSCAP
High rate algal pond for greywater
treatment in arid and semi-arid areas

Submitted by
Hina Derabe Maobe

A thesis submitted in partial fulfillment of the requirements for
the degree of Doctor of Philosophy in Engineering

Examination Committee
Supervisor: Prof. Masahiro TAKAHASHI
Member: Prof. Naoyuki FUNAMIZU
Member: Prof. Satoshi OKABE
Member: Assoc. Prof. Hisashi SATOH

Laboratory of Aquatic Environmental Protection Engineering
Division of Environmental Engineering
Graduate School of Engineering, Hokkaido University
September 2014
ACKNOWLEDGEMENTS

I wish to acknowledge the funding given by SATREPS (Science and Technology Research
Partnership for Sustainable Development), JST (Japan Science and Technology Agency) and
JICA (Japan International Cooperation Agency) for the completion of this research.
I would like to express my sincere gratitude to my advisor, Professor Masahiro Takahashi for
the continuous support of my PhD study and research, for his patience, motivation,
enthusiasm, and immense knowledge. His academic guidance and financial support helped
me in all the time of research and writing of this thesis.
Besides my advisor, my sincere thanks go also to Professors Hisashi Satoh and Tatsuya
Fukazawa for their strong scientific support, insightful comments and encouragement
throughout the PhD period. Thanks for your involvement and contribution in both my
research work and personal development.
I would like to thank Professor Naoyuki Funamizu and Professor Satoshi Okabe, members of
my examination committee, for their precious time.
I am also thankful to the Nishihara Foundation and Kubota Foundation for their financial
support. Without this financial support, completion of this thesis would have been extremely
difficult.
I must not forget Dr. Joseph Wethe for his support, motivation to do research, and meaningful
advises.
I thank my dear friends Wasala Bandara, Rathnayaka Lashita and Mohan Amarasiri from Sri-
Lanka, Niti Pitakteeratham from Thailand, Atsushi Takeuchi from Japan, for all the help I
needed, all the funny and spontaneous chats at our free time and also all the fun in the dinners
we shared. Thanks must also go to my fellow lab mates in Aquatic Environmental Protection
Engineering Laboratory for all the fun we have had in the last four years.
Special thanks go to my African fellows from the Hokkaido University African Student
Association. You have been great!
I also would like to thank Aristide Bombo and Mireille Malefou, my old friends for their
encouragement and great support.
Lastly but not the least, I am grateful to: Mirana Diambaye, my mother, Ms Vinaha
Doumgoto, Rila Mandela Moi-Yopaang and Kpanmna Feinam my sisters and brother, for
taking care of my children, for their support and prayers. To my beloved sons Hery and
Tsiory, thank you for your love and patience during my absence while abroad. To all whose
name I could not mention here, thanks!
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ABSTRACT

In recent years, large scale algal production has received lot of consideration due to the
ability of algae to grow extremely rapidly and to accumulate a high quantity of lipid in their
cells for biofuel production. For this purpose, algal photosynthetic growth is required and
finding an economical and reliable method to produce and harvest algae feedstock remains a
challenge. Thereby, apart from closed reactors used for algal production, the use of open
ponds also known as high rate algal ponds which integrate wastewater treatment is nowadays
emerging. For large scale biofuel production, HRAPs treating wastewater are recognized to
be low cost than closed photobioreactors due to the easy operation and cost-effective
construction.
While the concern of algal biofuel production and wastewater treatment is currently
increasing, this thesis focuses on the ability of HRAP to treat greywater and produce
resources for agricultural activities in urban and peri-urban areas of arid and semi-arid
countries. To tackle the increasingly severe issues related to water scarcity and domestic
wastewater treatment in these areas, a greywater treatment system based on high rate algal
pond (HRAP) was developed. As the conventional ponds, this technology is low cost, simple
to build and operate. The HRAP is able to provide efficient wastewater treatment because of
the assimilation of the wastewater nutrients into the algal biomass. Resources like biomass
and energy can be recovered from the wastewater treatment for beneficial use. However,
some negative points regarding the implementation of HRAP concern the large land area
requirements and the washout of algae from ponds which increases the total suspended solids
(TSS) concentration in the effluent. For an efficient wastewater treatment and recovery of
resources usable in agriculture, the main purpose of this work consists to find operating
strategies of HRAP leading to effective production and harvest of high settleable algal
biomass.
At a laboratory scale and under tropical conditions, several reactors simulating HRAP were
set and various operated parameters based on the hydraulic retention time (HRT), solid
retention time (SRT) and algal recycling were applied. In both reactors, the temperature was
kept at 30±2 °C, the mixing of the reactor was performed to avoid algae sedimentation and
LED lamps gave photosynthetic photon density varying from 430-550µmol-2s-1 at the surface
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of the pond. The water qualities of synthetic greywater with their average values ±SD were:
pH (6.76±0.45); T-N (12.41±3 mg/L); T-P (5.26±0.4 mg/L); TOC (22.69 mg/L). Samples
withdrawn from influent tanks, HRAP, SBRs, CFRs and corresponding effluents tanks were
collected once to twice per week and immediately analyzed. Total suspended solids (TSS)
together with settleable solids were determined. Nitrogen and phosphorus species such as
ammonium- nitrogen, nitrite, nitrate, total nitrogen, soluble reactive phosphorus and total
phosphorus (T-P) were measured. As the treated effluent will serve for irrigation purpose,
inactivation of E.coli in the system was also investigated.
Chapter 1
A review of the wastewater and greywater management in urban areas of arid and semi-arid
areas was made and followed by an analysis of greywater treatment options in urban areas of
arid and semi-arid countries. Based on the results of the situation assessment, a treatment
option using high rate algal pond technology and allowing resources recovery for agriculture
was proposed.
Chapter 2
The configuration of the greywater treatment system used in this section consists of a HRAP
which is a photosynthetic reactor followed by an algal settling pond (ASP). In this system, an
HRT of 8 days and various SRT of 10, 15 and 20 days were set. The SRT and the
recirculation of algae had an effect on the self-granulation and settleability of the algae. In
fact, by recirculating the algae, the dominant algal species could be maintained and higher
settleability and removal efficiency of the algae could be achieved. Further, operating long
SRT of 20 days has increased the TSS concentration in HRAP due to the low TSS
concentration caused by the mixture washout during long SRT. For operation under a short
SRT of 10 days, efficient algal removal (86%) together with NH +-N and PO 3--P removal
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(84% and 55% respectively) were achieved. In the ASP, at SRT of 10 days, settleable algae
were dominant and the selection has occurred by simple gravity sedimentation.
Chapter 3
To investigate the selection mechanism of self-flocculated algae, the experiments were
carried out by using 3 replications of sequencing batch reactors (SBR) and 3 other
replications of continuous flow reactors (CFR). The three SBRs which simulated HRAP with
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algae recirculation were operated at a HRT of 10 days and SRT of 20 days. In the three other
CFRs which simulated HRAP without algae recirculation, experiments were carried out using
same HRT and SRT of 20 days. Moreover, the effects of the algae recirculation, HRT and
SRT control were investigated. Despite operation with the same solid retention time (SRT)
and the similarity of the algal growth rate found in both SBRs and CFRs, the algal
productivity was higher in the SBRs owing to the short HRT of 10 days in these reactors.
Further, in contrast to CFR, the operation of HRAP under batch mode has enhanced the
selection of settleable algae through the sedimentation process. It was also found that under
similar operating and physical conditions in the SBRs and CFRs, the control of the algal
productivity and independent control of HRT and SRT were achieved. The comparison of
SBRs and CFRs on their performance to remove the ammonium-nitrogen and T-N has shown
that the SBRs presented greater capacity of removal efficiency during all the experimental
period. In both reactors, more nitrogen than phosphorus was removed and the concentrations
of dissolved phosphorus in the effluents from SBRs were lower. The operation of short HRT
and the effect of sedimentation applied in SBRs resulted in a higher algal concentration and
thus promoted nitrogen and phosphorus removal by assimilation into algal biomass and
sedimentation processes.
Chapter 4
This chapter focuses mainly on the production of resources from the high rate algal pond
(HRAP) to serve the agriculture in arid and semi-arid areas. Furthermore, operating
strategies for the application of HRAP were indicated. Experiments were achieved by using
the systems described in Chapters 2 and 3.
The nitrogen and phosphorus balance were established during the period when the algal
growth in the reactors was not subject to change. Contrary to the CFRs where HRT and SRT
were similar, in the SBRs, the contribution of the excess algae withdrawn from the reactors
has led to the increase of nitrogen exiting the system.
Operating strategies of HRAP to produce settleable algae and treated water for irrigation
were suggested. It was proposed that for urban agricultural irrigation, the selection of
appropriate hydraulic conditions (long HRT and long SRT) can be implemented to meet
different needs. In contrast, the operation of short HRT and short SRT provide effluent with a
lower nutrient concentration which can be discharged into reservoirs. The recovered algal
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biomass from the HRAP could be used either as fertilizer or used as a livestock feed
supplement. Focusing on conventional HRAPs, this method might be applied to achieve
efficient productivity or removal of the algal biomass.
Chapter 5
The reuse of the greywater for irrigation purpose presents many challenges, including the risk
of pathogen infection. In HRAP, algae play an essential role in the process of pathogen
removal by raising the pH and dissolved oxygen concentration which favour inactivation of
bacteria. The main objective in this chapter was to investigate disinfection processes
occurring in HRAP. Therefore under a tropical climate, series of batch experiments were set
up to evaluate the potential of algal sedimentation and other pathways of E. coli and
coliphage (MS2 and Qβ) inactivation.
It was found that the natural decay of bacteria was dominant and UV irradiation was effective.
However the recovery of light-damaged cells at night should be considered. MS2 and Qβ
removal was not effective when pH was neutral. However when pH was increased to 9, the
reduction of 4 log units was observed.
Chapter 6
This chapter discusses the conclusions drawn in this thesis and reports on areas that need
further research.

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TABLE OF CONTENTS

ACKNOWLEDGEMENTS ........................................................................................................ i
ABSTRACT ............................................................................................................................... ii
TABLE OF CONTENTS .......................................................................................................... vi
LIST OF FIGURES .................................................................................................................. ix
LIST OF TABLES ..................................................................................................................... x
Chapter 1 : General introduction and literature review ........................................................ 1
1.1. Background ................................................................................................................. 2
1.1.1. Wastewater and greywater management in urban areas of arid and semi-arid
regions: case of Ouagadougou (Burkina Faso)................................................................... 3
1.1.2. Greywater production and characteristics ............................................................ 4
1.1.3. Wastewater treatment options in urban areas of arid and semi-arid regions of
Africa 5
1.1.4. Reclaimed greywater for irrigation purpose ........................................................ 6
1.1.5. Potentials of microalgae ....................................................................................... 7
1.1.6. The high rate algal pond ...................................................................................... 7
1.2. Problem statement ....................................................................................................... 8
1.3. Objectives of the research ........................................................................................... 8
1.4. Structure and outline of the thesis ............................................................................... 9
Chapter 2 : Impact of simultaneous algae recirculation and solid retention time control
on algal biomass productivity and nutrient removal in a high-rate algal pond ........................ 10
2.1. Introduction ............................................................................................................... 11
2.2. Materials and methods .............................................................................................. 12
2.2.1. Reactor setup and operation ............................................................................... 12
2.2.2. Synthetic greywater composition ....................................................................... 15
2.2.3. Analytical methods ............................................................................................ 15
2.3. Results and discussion ............................................................................................... 17
2.3.1. Algae removal and biomass productivity .......................................................... 17
2.3.2. Nitrogen and phosphorus removal ..................................................................... 20
2.4. Conclusions ............................................................................................................... 24
Chapter 3 Control of algal production in high rate algal pond: investigation through batch
and continuous experiments ..................................................................................................... 25
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3.1. Introduction ............................................................................................................... 26
3.2. Materials and methods .............................................................................................. 26
3.2.1. Reactor setup and operation ............................................................................... 26
3.2.2. Synthetic greywater composition ....................................................................... 28
3.2.3. Analytical methods ............................................................................................ 29
3.3. Results ....................................................................................................................... 32
3.3.1. Algal biomass productivity in SBRs and CFRs ................................................. 32
3.3.2. Nutrient concentrations ...................................................................................... 34
3.4. Discussion ................................................................................................................. 35
3.4.1. Algal biomass productivity in SBRs and CFRs ................................................. 35
3.4.2. Nutrient removal ................................................................................................ 37
3.5. Conclusions ............................................................................................................... 37
Chapter 4 : Operation of a high rate algal pond for greywater treatment and the reuse of
resources 39
4.1. Introduction ............................................................................................................... 40
4.2. Materials and methods .............................................................................................. 40
4.2.1. Operation conditions and analytical methods in HRAP, SBRs and CFRs ........ 40
4.2.2. Total algal biomass productivity in reactors ...................................................... 41
4.2.3. Nitrogen and phosphorus mass balance calculation .......................................... 42
4.3. Results and discussion ............................................................................................... 43
4.3.1. Nitrogen balance ................................................................................................ 43
4.3.2. Phosphorus balance ............................................................................................ 46
4.3.3. Effect of the operating parameters ..................................................................... 48
4.3.1. Options for the reuse of resources and economic considerations ...................... 52
4.4. Conclusion ................................................................................................................. 54
Chapter 5 : Escherichia coli and coliphages MS2 and Qβ removal in a high rate algal
pond treating greywater ........................................................................................................... 55
5.1. Introduction ............................................................................................................... 56
5.2. The health based target of disinfection in HRAP ...................................................... 56
5.3. Material and methods ................................................................................................ 58
5.3.1. Disinfection experiment ..................................................................................... 58
5.3.2. Microorganism culture, sample collection and analysis .................................... 60
5.3.3. Data analysis ...................................................................................................... 61
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5.4. Results and discussion ............................................................................................... 62
5.5. Conclusion ................................................................................................................. 65
Chapter 6 : Conclusions and recommendations ................................................................. 67
References ................................................................................................................................ 70

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