Synthesis And Application Of The Modified Polymeric Flocculants Based On Polyacrylamide

With the improvement of the urbanization and industrialization, it is extremely urgent toraise the efficiency of wastewater treatment and to protect our water resources. Flocculationwas a method of dewatering sludge by agglomerating solid, which materially improves thedewatering rate and efficiency of many types of sludge, including those used in mining,papermaking, wastewater treatment, and oil-field etc. applications of wastewater treatment.Recently, polymeric flocculants with aggregate properties (chain length, charge density,branching, etc.) were increasingly used for the aggregation of municipal sludge due to theirhigh efficient. The study found that polymeric flocculants were extensively applied intosludge dewatering, the aggregates could be somewhat tailored to give a desired filtration rateor final cake moisture. The structure and property of flocculants play important roles inflocculation.It is known that sludge colloids in water are usually negatively charged. Cationiccopolymers were typically used for sludge flocculation and dewatering in waste watertreatment because of their charge density. The cationic polyacrylamide flocculant (CPAM)was synthesized by inverse emulsion polymerization using potassium persulfate as a freeradical initiator. The effects of reaction variables, such as initiator concentration、the amountof cross-linking agent and emulgator, as well as, oil-water rate on polymerized reaction wereinvestigated by orthogonal experiments. The optimal reaction conditions were confirmed.Chitosan chemically prepared by N-deacetylation of naturally-occurring chitinis wasnontoxic, biodegradable and bicompatible, which was widely applied in water treatment.However, for poor solubility in water under neutral or alkaline conditions and low molecularweight, the applications of natural chitosan were limited. Graft polymerization was aconventional and effective method to improve the performance of chitosan. Herein, the novelchitosan-grafting copolymer (chitosan-g-PAM-AA) as flocculants for sludge dewateringtreatment had been prepared by employing ceric ammonium sulfate (CAS) as a free radicalinitiator under nitrogen atmosphere in aqueous solution. Moreover, the optimum condition forsynthesizing chitosan-grafting copolymers was confirmed by orthogonal experiments. Thecopolymer was modified by introducing a cationic monomer N,N-dimethyl diallyl ammoniumchloride in the same way under the optimized condition.Finally, a complex type flocculant through the chemical bond and electrostaticincorporation was synthesized by employing an inorganic coagulant (Aluminium sulfate) andpolymer flocculant (PAM-AA). The obtained polymers were characterized by FT-IR, XRDand SEM. Flocculation capacity of the above several flocculants to municipal sludge was evaluatedby the moisture content of the filter cake and specific resistance to filtration. The effects ofthe flocculants dosage, temperature, the different pH value, PG and cationic degree (CD)effects on the flocculating properties were investigated under the same other conditions. Theexperiment result indicated that flocculats expressing higher flocculation ability under faintlyacid condition. It was clear that flocculation effect raiseded as temperature of raw sludgeincreased. Hence, in our synthesized polymer, the complex flocculant is the most appropriateflocculants to the municipal sludge dewatering. The water content of sludge decreased from95%to the moisture content of the filter cake62.80%.In sum, four kinds of flocculants were synthesized and achieved good sludge dewateringeffect in municipal sludge. So it is a broad development prospect of research subject.