Comparative Assessment of Performance of Aluminum Sulphate (Alum) and Ferrous Sulphate as Coagulants in Water Treatment
Chapter One
Aim and Objectives of the Study
This study aims to compare the performance of two selected coagulants (alum and ferrous sulphate) in water treatment. Consequently, the following specific objectives are applicable.
- To determine the coagulation efficiency of each coagulant concerning each of the selected water quality parameter sets of parameters.
- To assess the coagulant dosage in relation to optimum coagulation efficiency.
CHAPTER TWO
LITERATURE REVIEW
Coagulation/flocculation processes are of great importance in solid-liquid separation practice16. Findings on various coagulation processes have been reported in literature. Some of these include, studying the effect of dosage and mixing conditions on the flocculation of concentrated suspensions using polymeric coagulants 17,18, coagulation of synthetic water by plant seeds 19 and coagulation of low turbidity water using bentonite 20. Guida et al. (2007) used alum as coagulant to remove Chemical Oxygen Demand (COD) and Total Suspended Solids (TSS) from municipal wastewater samples. The coagulation experiments indicated that alum effectively removed COD (65%) and TSS (>75%) using 150mgL-1 aluminium sulphate at a pH range of 5 – 821.
Coagulation targets the colloid particles of size 10-7 to 10-14cm in diameter. The colloid particles exhibit Brownian movement through the water; their surface is negatively charged so they repel one another, and they form a stable dispersed suspension 22. If colloid particles or ions of positive electric charge are added, it neutralizes the electric negative charge. Flocculation refers to the successful collision that occurs when destabilized particles are driven toward each other by the hydraulic shear force in the rapid mix and flocculation basin. It agglomerates of a few colloids then quickly bridge together to form microflocs which is turned into visible floc masses23, which is shown in figure 1.
The separation of particular matter from the liquid phase is one of the important steps in most wastewater treatment processes. All waters, especially surface waters, contain both dissolved and suspended particles. Coagulation processes are used to separate the suspended solids portion from the water. The suspended particles vary considerably in source, composition charge, particles size, shape, and density. Correct application of coagulation processes and selection of the coagulants depend upon understanding the interaction between these factors. Coagulant chemicals come in two main types, primary coagulants and coagulant aids. Primary coagulants neutralize the electrical charges of particles into the water which causes the particles to clump together 24. Chemically, coagulants are either metallic salts (such as alum) or polymers. Polymers are man – made organic compounds made up of a long chain of smaller molecules. Polymers can be either cationic (positively charged), anionic (negatively charged), or nonionic (neutral charged). Chemical coagulation has been in practice for several decades to precipitate the soluble heavy metals present in the waste water, as hydroxide and facilitate their removal by physical separations through the sedimentation process. The process of coagulation separation consist of four steps, which is shown in figure 2.
CHAPTER THREE
Experimental
Apparatus
- pH – meter
- Magnetic stirrer
- Sedimentation beaker
- Stop watch
- 20 liters white gallon
- 1 liter gallon
- 5 liters gallon
- Conical flask (250ml)
- 50ml beurette
- Heating mantle
- Whaltman filter paper
- Electronic weighing balance
- Spectrophotometer
- Incubator
- Oven and minifurnance
Materials/Reagents
- Buffer solutions of pH 6.8 and distilled water
- Humus soil
- H2S04
- Distilled water
- Clean tap water/Base water
- Aluminum sulphate Al2 (S04)3 18H20 Octadecahydrate (Alum)
- Ferrous sulphate crystalline: FeS04 7H20 Heptadydrate
Coagulant Processing
The two coagulants used for this experiment which are Aluminum sulphate and iron (II) sulphate with chemical formulae Al2(S04)3.18H20 and FeS04.7H20 respectively were purchased from Ogige Main Market Nsukka. The caked coagulants were crushed with ceramics pestle and mortar.
CHAPTER FOUR
RESULTS AND DISCUSSION
Results
The results of various levels of efficiency achieved by different doses of each of the coagulants are shown in tables 3-12. Furthermore, the comparative variations in coagulant performance efficiency have been represented graphically in figure 15-41.
CHAPTER FIVE
CONCLUSION AND RECOMMENDATIONS
Conclusion
The comparative assessment of the performance of Aluminium Sulphate (Alum) and Ferrous Sulphate as Coagulants in water Treatment was carried out on turbid water using sedimentation beaker experiments. The results showed that pH, DO, BOD5, Fluoride, phosphate and COD mean % efficiency were higher for iron (II) sulphate compared to aluminum sulphate at dosage of 10g of coagulant per 3 litres of water. The aluminum sulphate revealed a better performance in TSS, Turbidity and chloride mean % efficiency when compared with iron (II) sulphate at the same coagulant dosage. The overall results of the coagulation studies showed that coagulation efficiency of the coagulant is parameter dependent.
Recommendations
- It is suggested that a combination of lime as a coagulant aid with the used coagulants could improve efficiency in some parameters.
- Application and the use of alternative coagulants like moringa oleifera, prosopis affricana peel powder need to be evaluated at the industrial scale and possibly commercialized in order to guarantee a large range of coagulants available in treatment of all waters in all conditions. This is to ensure safety, efficacy and quality of treated water and protection of our water sources is advocated to minimize the need and intensity of water treatment.
- Finally, the outcome of this work can be an important guide to water treatment operators.
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