Effect of Temperature on Algal Removal by Alum Coagulation

123 Pages·2016·7.22 MB·English

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Reports Utah Water Research Laboratory
1-1-1974
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Muhammad Anis H. Al-Layla
E. Joe Middlebrooks
Donald B. Porcella
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Al-Layla, Muhammad Anis H.; Middlebrooks, E. Joe; and Porcella, Donald B., "Effect of Temperature on
Algal Removal by Alum Coagulation" (1974). Reports. Paper 650.
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EFFECT OF TEMPERATURE ON ALGAL
REMOVAL BY ALUM COAGULATION
by
Muhammad Anis H. Al-Layla
E. Joe Middlebrooks
Donald B. Porcella
Utah Water Research Laboratory
College of Engineering
Utah State University
Logan, Utah 84322
July 1974 PRWG139-!

ABSTRACT
Questions about the effect of temperature on algal cell coagulation and the relationships
between algae removal and temperature, alum dosage, paddle speed, flocculation time, and settling
time are answered. The investigations consisted of two series of tests: Studies on algae cultured
under laboratory control, and algae in wastewater stabilization ponds. The jar-test technique was
used for the coagulation of algal suspensions by alum.
Coagulation of algae is caused mainly by the insoluble floes of aluminum hydroxide. Other
aluminum species also have coagulative properties but are far less effective. The destabilization of
algal colloids results from enmeshment within the hydroxide precipitates, or by adsorption of
coagulant species. Neutralization of the pH-dependent charges of algal cells is not necessary for
coagulation, but does aid coagulation.
Analyses of variance of the variables and their interactions showed significantly the effect of
all variables and most of their interactions. Step-wise multiple regression technique was used for
the development of mathematical models for the estimation of algal removal.
Increased temperatures adversely affected the percentage removal of algal cells by alum
coagulation. The effect of temperature on the removal of algae grown in the wastewater
stabilization pond effluent was more pronounced than that found for the algae cultured in the
laboratory. Alum was effective in removing algae from Logan wastewater stabilization ponds.
However, high alum dosages are required which may not be justified economically.
It also was found that at low concentrations of algal cells the straight line portion of the
Langmuir isotherm describes the removal of algae with alum.
iii
ACKNOWLEDGMENTS
The principal author is indebted to the Iraqi Government for awarding him the scholarship
which made this research project possible. Thanks are also extended to Mosul University for
nominating him for the Iraqi Government Scholarship. Appreciation is expressed to the Utah
Water Research Laboratory for providing the funds for assistance, laboratory facilities, and
equipment.
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TABLE OF CONTENTS
Page
INTRODUCTION
Nature of the problem
Natural waters .
Oxidation ponds
Benefits from algae 1
Waste stabilization ponds 3
Concentration, dewatering, and drying algal suspensions 3
Variables in chemical coagulation. 4
Study rationale and objectives . . . 4
LITERATURE REVIEW AND THEORY . 5
Historical background of coagulation 5
Terminology . . . . . . . . . 6
Studies related to algal coagulation 6
Theory of colloidal stabilization 9
General ....... . 9
Source of charges 9
Diffuse double layer (DDL) 9
Zeta potential . . . . . . 10
Hydrophilic and hydrophobic characteristics 12
Theory of coagulation and flocculation 12
General ....... . 12
Perikinetic coagulation 12
Orthokinetic flocculation 13
Mechanisms of coagulation 14
Destabilization . . . 14
Effect of pH on coagulation 16
Effect of alkalinity on coagulation 16
Effect of ions on coagulation . . . 16
Adsorption mechanisms in coagulation . 17
EXPERIMENTAL DESIGN-ALGAE 19
Materials and methods . . . . 19
Complete factorial design 19
Algal cultures . . . . . 19
Relationship between algal suspensions as volatile suspended solids
and relative fluorescence . . . . . 20
Apparatus and experimental procedure 22
Determination of coagulant dosages . . 23
Determination of the effect of algal concentration 23
v
TABLE OF CONTENTS (Continued)
Page
Results and discussion . . . . . 24
Mechanisms of algal removal 24
Effect of temperature and alum dosage on algal removal 25
Effects of temperatures on settability of algal floes . . . 27
Effect of temperature and paddle speed on algal removal 28
Effect of temperature and flocculation time on algal removal 29
Analysis of variance . . . . . . . . . . . . 30
Step-wise multiple regression analysis . . . . . 31
Effect of algal concentration on algal removal . . 32
Adsorption phenomena of algal cells to alum floes 35
CHEMICAL COAGULATION OF ALGAE IN LOGAN WASTEWATER
STABILIZATION POND EFFLUENT 39
Materials and method 39
Statistical design 39
Wastewater stabilization ponds 39
Experimental procedure . 39
Algal identification . . . 40
Wastewater characteristics 40
Jar test procedure 40
Determination of relative fluorescences and turbidity . 41
Determination of total organic carbon . 41
Determination of total phosphate (asP) 41
Results and discussions-Algae removal . 41
Determination of coagulant dosages 41
Analyses of variance . . . . . . 42
Effect of temperature and alum dosage on algal removal in Logan
wastewater stabilization ponds . . . . . . . . . . . . . 42
Effects of temperature and settling time on algal removal from Logan
wastewater stabilization pond effluents . . 44
0 • • • • • • 0 •
Effect of temperature and paddle speed on algal removal from Logan
wastewater stabilization pond effluent . . . . . . . . . . 45
Effect of temperature and flocculation time on algal removal from
Logan wastewater stabilization pond effluent . 46
Step-wise multiple regression analysis . . . . . . . . . . 47
Results and discussion-Algae, turbidity, total organic carbon, and
total phosphorus removals . . . . . . . . . 49
Experimental design and analysis of variance 49
Removal of algae, turbidity, total organic carbon (TOC), and total
phosphorus . . . . . . . . . . . . . . . . . . . . . . 49
Effects of temperature on the removal of algae, turbidity, and total
phosphorus . . . . . . . . . . . . . . . . . . . . . . . 51
Step-wise multiple regression analysis for algae, turbidity, TOC, and
total phosphorus . . . . . . . . . . . . . . . . . . . . 52
Correlation between the removal of algae and turbidity, TOC, and
total phosphorus . . . . . . . . . . . . . . . . . . . . 53
vi
TABLE OF CONTENTS (Continued)
Page
Economic studies . 54
Capital costs . 54
Operating costs. 55
Total treatment costs 55
SUMMARY AND CONCLUSIONS 57
Summary 57
Conclusions 57
Coagulation of algae mechanisms 57
Coagulation of algae in practice . 57
Experimental design for algae cultured in NAAM medium . 58
Mathematical models . . . . . . . . . . . . . . . 58
Effect of temperature on algal removal . . . . . . . . 58
Effect of temperature and alum dosage on algal removal 58
Effect of temperature on the settleability of algal floes . 58
Effect of temperature and paddle speed on algal removal 58
Effect of temperature and flocculation time on percentage removal of algae 58
Algal concentration . . . . . . . . . . . . . . . . . . . . . 59
Algae of Logan wastewater stabilization lagoon . . . . . . . . . 59
Algae, turbidity, total organic carbon, and total phosphorus removal
from Logan wastewater stabilization pond effluent 60
Area for further study 60
liTERATURE CITED 61
APPENDICES . . 65
Appendix A Composition of new algal assay (NAAM) 67
Appendix B Results of experimental design-Algae . 69
Appendix C Results of algae coagulation from Logan wastewater
stabilization ponds . . . . . . . . . . . . . 83
Appendix D Results of the removal of algae, turbidity, total organic carbon,
and total phosphorus . . . . . . . . . . . . . . . . . 87
Appendix E Statistical analysis of variance and step-wise multiple regression 91
vii

LIST OF FIGURES
Figure Page
Variables affecting chemical coagulation . . . . . . . . . . . 4
2 Ion concentration in the diffuse double layer of a negatively charged particle
with constant surface potential (after Van Olphen, 1962) 10
3 Diagram of the double diffuse layer . . . . . . . . . 11
4 Variation of potential with distance from negatively charged particle surface 11
5 Potential energy at negatively charged particle surface 12
6 Solubility equilibria of amorphous Al(OHh (s) at 25°C (Weber, 1972) 15
7 Diagram of the complete factorial design (levels and variables) 20
8 Algal culture equipment . . . . . . . . . . . . . . . . 21
9 Correlation of algal concentrations as VSS (mg/1) with relative
fluorescence units . . . . . . . . . . . . . . . . 21
10 Phipps and Bird, Inc. Richmond, Virginia, multiple stirrer 22
11 Jar test apparatus, water bath, and refrigeration unit 23
12 Factorial design for algal concentration experiment . 24
13 The relationships between pH and alum dosage in mg/1 (experimental design) . 25
14 Effect of alum dosages on algal removal at different temperatures
(experimental design) . . . . . . . . . . . . . . . . . . 25
15 Effect of temperature on algal removal at different alum dosages
(experimental design) . . . . . . . . . . . . . . . . . . 26
16 Effect of settling time on algal removal at different temperatures
(experimental design) . . . . . . . . . . . . . . . . . . 27
17 Effect of temperature on algal removal at different settling time
(experimental design) . . . . . . . . . . . . . . . . . . . 28
18 Effect of paddle speed on algal removal at different temperatures
(experimental design) . . . . . . . . . . . . . . . . . . . 28
19 Effect of temperature on algal removal at different paddle speeds
(experimental design) . . . . . . . . . . . . . . . . . . . 29
20 Effect of flocculation time on algal removal at different temperatures
(experimental design) . . . . . . . . . . . . . . . . . . . . 29
21 Effect of temperature on algal removal at different flocculation time
(experimental design) . . . . . . . . . . . . . . . . . . . . 30
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