The use of coagulation-flocculation as a treatment for starch factory effluent
Bench-scale jar test experiments using chemical coagulation followed by sedimentation were conducted with effluent generated from a starch and gluten manufacturing factory. The objectives of these trials were to achieve maximum removal of the colloidal suspended solids fraction of the effluent by optimising physical and chemical parameters of the jar test and the various coagulating agents. Aluminium sulphate (alum) and ferric sulphate were the two metal salts assessed for their ability to
... e the suspended solids. A range of cationic (Zetag) and anionic (Magnafloc) synthetic polyelectrolytes were also assessed as was the cationic polymer chitosan (a derivative of the naturally occurring chitin). All coagulants were tested over a broad concentration and pH range. The effects on suspended solids removal were also investigated by combining the metal salts with various polyelectrolytes. The results demonstrated that coagulation was most effective in the pH range of 7-10. Ferric sulphate was consistently more effective than alum, removing up to 63% suspended solids from the effluent at pH 8 compared to 53% removed by alum at pH 8. The optimum concentration for both these metal salts was 75 mg/L. When Zetag 92 at 7.5 mg/L was used with ferric sulphate (75 mg/L) suspended solids were reduced by about 69%. Chitosan proved to be the most effective of all the polyelectrolytes evaluated, removing about 69% of the suspended solids at 10 mg/L, pH 7. The addition of 5 mg/L alum reduced the suspended solids in the effluent by 78%. CONTENTS CHAPTER 1 INTRODUCTION CHAPTER 2 LITERATURE REVIEW 2.1 Introduction 2.2 Characteristics of colloids and suspended partricles 2.3 Colloidal and particle stability 2.3.1 lsomorphous replacement or substitution 2.3.2 Adsorption of ions 2.3.3 Ionisation or chemical reactions of surfaces sites 2.4 The electrical double layer 2.4.1 The DL VO Theory 2.4.2 The Zeta Potential 2.5 Coagulants 2.5.1 Inorganic or metal coagulants 2.5.2 Aluminium and ferric salts 2.5.3 Aluminium sulphate (alum) 2.5.4 Polyaluminium chloride (PAC) 2.5.5 Ferric salts 2.6 Mechanisms of destabilisation using metal salts 2. 7 Polyelectrolytes 2. 7. 1 General characteristcs of polyelectrolytes 2. 7 .2 Preparation and use of polyelectrolytes 2.8 Chitosan 2.8.1 General chitosan chemistry 20 21 24 24 27 29 30 2.9 Mechanisms of destabilisation using polyelectrolytes 2.9.1 The bridging mechanism 2.9.2 The electrostatic patch mechanism 2. 1 O Other uses of polyelectrolytes 2.11 Sludge 2.12 Rapid mixing and flocculation 2.12.1 Rapid mixing 2.12.2 Flocculation 2.13 The Jar Test 2. 13. 1 Floes 2.14 Applications of coagulation and flocculation 2.14.1 Coagulation-flocculation of food wastes 2.15 The treatment of starch manufacturing effluents 188.8.131.52 Magnafloc 336 and Ferric sulphate 4.7 Chitosan CHAPTER 5 DISCUSSION 5.