The use of organic polymers in the chemical purification of peat derived runoff waters
1University of Oulu, Faculty of Technology, Department of Process and Environmental Engineering, Environmental Engineering
|Online Access:||PDF Full Text (PDF, 1.9 MB)|
|Persistent link:|| http://urn.fi/URN:NBN:fi:oulu-201304301210
|Publish Date:|| 2013-04-30
|Thesis type:||Master's thesis (tech)
In our present day wastewater management have a high influence on the quality of our environment, its neglect or poor treatment can lead to very negative effect on our bio-diversity and the environment in general. This study seeks to address the limitations of using inorganic coagulants in the treatment of peat runoff water by evaluating the efficiency of organic polymers as coagulants agents in the chemical purification process. The limitations of inorganic coagulants include; discharge of residual metals into downstream waters, over dependence on pH, high dosage and high sludge production. For our experiments two cationic organic polymers epichlorohydrin/dimethylamine (pAMINE) and polydiallyldimethyl ammonium chloride (pDADMAC) were selected based on their molecular weight and charge density. Polyferric sulfate (PFS) which is the pre-hydrolyzed metal salt coagulant presently being used at several peat extraction treatment sites in Finland was also tested. The optimum dosage requirements of the tested coagulants were determined based on turbidity removal. The dosage requirement of the coagulants were considerably different; optimum dosages of PFS ranged from 190 mg/l to 200 mg/l while that of the organic polymers ranged from 40 mg/l to 60 mg/l for pAMINE and 70 mg/l to 90 mg/l for pDADMAC. Where optimum dosages were applied removal of turbidity ranged from 85 % to 95 %. PFS presented better overall performance in the removal of TOC about 80 % against less than 40 % for both organic coagulants. pAMINE leached nitrogen into the system, the leaching diminished in tests at low temperature. The evaluation of the influence of mixing on the coagulants performance revealed that PFS’s performance is more sensitive to variation in mixing than the organic coagulants. Optimum values for fast mixing intensity were over 100 rpms for all tested coagulants with no improvement or detrimental effects observed for values up to 400 rpm. Optimum observed fast mixing time was 10 s for all coagulants. Best slow mixing speed and time were achieved at above 20 rpm and above 10 minutes for all tested coagulants. Organic polymers and inorganic coagulants alike showed lower dosage requirements with lower pH values, pAMINE achieved purification efficiency at dosages as low as 30 mg/l and pDADMAC was less affected by low pH achieving acceptable turbidity removal at dosages of less than 60 mg/l. PFS dosage requirements dropped by as much as 45 % from 200 mg/l at pH 6.5 to 120 mg/l at pH 4.5.
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