Optimization Of Advanced Treatment Technology And Water Quality Property Of Tertiary Effluent In Municipal WWTP

Due to the worldwide water scarcity, water reuse has become one of the most efficientsolutions. Municipal secondary effluent is not only stable, but also economical. Therefore, useof municipal secondary effluent as the second water resource has a very bright future.Pathogenic microorganisms, hazardous substances and trace plant nutrients in secondaryeffluent from municipal wastewater treatment plant restricts the recycle of the reclaimedwater. Based on the above issues, the characteristics of organic matter in secondary effluentand after advanced treatment from municipal wastewater treatment plant are studied. Theaims of this study are to understand the change of the physical and chemical characteristicsafter advanced treatment process, to provide a theoretical guidance for optimization of thesewage treatment process, and to probe into the improvement of reclaimed water quality. Thisresearch mainly includes as follows: (A) Optimization of the conventional advanced treatmentprocess. The conventional advanced treatment process of "flocculation - sedimentation -filtration - disinfection" was optimized through the static test, and obtain a suitable advancedtreatment process; (B) Investigations of organic matter and the biological toxicity.Thedissolved organic matter (DOM) in secondary effluent and after advanced treatment frommunicipal wastewater treatment plant are characterized by resin separation technology andultrafiltration membrane. Photobacteria method is used to investigate the changes ofbiological toxicity after advanced treatment in secondary effluent from municipal wastewatertreatment plant. The experimental study of the conventional advanced treatment process'soptimization shows as follows:(1) The best coagulant is PAC, the optimal dosage of PAC is 35×10-5mol/L(Al3+), thebest coagulation time is 20 min, the setting time is 40 min.(2) By the evaluation of conventional indicators and bacterial indicators, the optimaldosage of ClO2 is determined to be 5 mg/L in the course of the trial.Based on the optimization of conventional advanced treatment process, the results of thebiological characteristics of organic compounds and the biological toxicity of water showsthat:(1) In the secondary biological effluent, the acid organic matter and non-acid organicmatter are evently distributed, and the hydrophobic material than hydrophilic material has ahigher proportion. Meanwhile, the absorption of the organic matter in water at UV 254nm isalso mainly from the hydrophobic organic matter. (2) Non-acid hydrophobic (HPO-N) has the highest aromaticity, and the aromaticitydecreases as follows: TPI-A < HPI < HPO-A.The aromaticity has not been changed aftercoagulation treatment and disinfection treatment. While the order of the replacement extent ofaromatic ring by carbonyl, carboxyl, hydroxyl and lipid is: TPI-A < HPO-N < HPI < HPO-A.The replacement extent of aromatic ring has been reduced.(3) DOM in the secondary biological effluent is mainly small molecular organicmatters(MW<3kDa). After treated by coagulation, the compounds of MW between the 5k ¹0kDa and 30k 50kDa have increased, while the organic matter of MW>100kDa reduced.After disinfection treatment, DOM is still mainly MW<3kDa organic matter, the organicmatter of MW>100kDa has been removed.(4) The biological toxicity in secondary effluent from municipal wastewater treatmentplant is large, after coagulation treatment, the biological toxicity is still large. Addition ofClO₂ could reduce the biological toxicity. After disinfection treatment, the biological toxicityis mainly from the ClO₂ residual in the water.