| Coagulation is the most commonly used method in tap water treatment nowadays.However,there are some disadvantages in the coagulation process,such as residue in the process of use,poor adaptability to water quality and weak ability to remove natural organic matter,which cause many sanitary and safety problems of drinking water.Therefore,the development of a new coagulant or flocculant with simple preparation process,low cost,strong function of coagulation and sedimentation,and good hygienic safety,will have extensive application prospects.Two kinds of waste paper flocculants(WPF)were prepared from waste paper and used to treat low turbidity water.The preparation method,applying conditions and mechanism of enhanced coagulation and sedimentation were studied,in order to change waste into valuables and provide efficient and safe water purifying agent.First,waste paper was used to prepare waste paper fiber flocculant(WPFF)by physical modification,and then combined with aluminum sulfate(AS)to treat low turbidity water.The optimize preparation process,applying conditions,effect and mechanism of enhanced coagulation and sedimentation were all researched to establish foundation of improving the treatment effect of low turbidity water by using WPFF combined with AS.After that,waste paper pulp flocculant(WPPF)was prepared and formulated separately with polyaluminum chloride(PAC)and polyaluminium ferric chloride(PAFC)to obtain the performance as composite coagulant,which could expand the raw material source and use method of WPF.On the basis of clarifying the use effect of the two kinds of WPF,the hygienic safety of using WPF was evaluated.The large-scale production route of WPF was designed combining the paper pulping process,and the use efficiency of WPF was also specified.The main results of these research contents are as follows:(1)The process of preparing WPFF from waste paper by physical modification was studied,and WPFF was used in combination with conventional coagulant to treat low turbidity water,with the preparation process and coagulation conditions being optimized,and improved the treatment effect on low turbidity water.The research results showed that WPFF can be prepared by the process of crushing,sieving,wet stirring and liquid swelling.In this process,waste corrugated paper was the most suitable raw material.The dry crushing time of waste paper should be 240 s.The WPFF prepared by long fiber obtained by sieving had better flocculation performance,while the non-sieving fiber was more cost-effective.The swelled fiber suspension with the concentration of 1.00%was formulated by wet stirring to increase the specific surface area of the waste paper fiber and improve the dispersion property.Using WPFF in combination with conventional coagulant to treat the raw water with its turbidity was 15.5 NTU,when the dosage was 20 mg/L of AS,20 mg/L of WPFF,the effluent turbidity was 2.03 NTU after 20 min of sedimentation,which was increased by 51.20%compared to that use AS alone.The treatment effect was better than the combination of WPFF and FC,as well as WPFF and PAC.Meanwhile,the optimal conditions of coagulation and sedimentation were dosing WPFF before medium-speed stirring,stirring at 200 r/min for 1 min,100 r/min for 5 min,and 50 r/min for 10 min,12 min of sedimentation time.The results of orthogonal experiment showed that the importance order of experimental factors on the coagulation and sedimentation treatment were:dosage of AS>dosage of WPFF>fast stirring speed>dosaging time of WPFF,which indicated that coagulant and flocculant had more significant effect on the treatment effect.In addition,the treatment effect was improved under the water quality conditions of higher turbidity and water temperature,as well as near-neutral acidic.(2)Based on the analysis of enhanced coagulation and sedimentation theory,the enhanced coagulation and sedimentation function and the mechanism of using WPFF and AS in treating low turbidity water was studied through experiments.The results indicated that the combined use of WPFF and AS played a good effect of enhancing the coagulation and sedimentation effect.The removal efficiency of turbidity,CODMn,UV254 and residual aluminum were improved after adding WPFF.The surface micromorphology of fibers was characterized by scanning electron microscopy,which demonstrated that WPFF had the ability of adsorption and net capture of micro flocs.The flocs were larger and denser with the effect of WPFF,when observed by optical microscopy,so the turbidity treatment effect was significantly better than that of AS alone at the same time.It reduced the time required to reach the turbidity standard by 50.00%,and obtained the turbidity removal speed of 4.77 NTU/min at the beginning of sedimentation.The mechanism of enhanced coagulation and sedimentation effect of WPFF combined with AS mainly included:adsorption and net capture of flocs,enhanced condensation,adsorption,net capture and the body structure improvement effect of WPFF,complexation reaction and electric neutralization of Al3+,with NOM,and the synergistic effect of Al3+ and cellulose,the polymerization between the above reaction products,and the synergistic interaction of using AS and WPFF together.In addition,turbidity removal had the greatest contribution to the removal of NOM and Al3+,pH had a great influence on the enhanced coagulation effect.When pH was 6,a good removal effect of turbidity,UV254 and residual aluminum were obtained at the same time,because of the stronger complexation reaction,substitution reaction,and the adsorption of NOM by flocs.(3)To expand the source and use of WPF,WPPF was prepared from waste paper pulp,and the using effect of composite WPPF with inorganic polymer coagulants was investigated.The results showed that corrugated waste pulp was suitable to formulated WPPF.When composited WPPF with PAC and PAFC separately to treat low turbidity water,the treatment effect of composite coagulants was better than that of single use.The optimal conditions for using WPPF and PAC as composite coagulants were:10 mg/L of PAC and 20 mg/L of WPPF,both of them were added before rapid stirring,and 100 r/min of the medium-speed stirring.When the raw water with the turbidity of 21.8 NTU was treated under this condition,the turbidity of effluent was 2.29 NTU,and the turbidity removal rate was 89.50%.The optimal conditions for the combination of WPPF and PAFC were:10 mg/L of PAFC,20 mg/L of WPPF,and both were added before rapid stirring,100 r/min of the medium speed stirring.When the raw water with the turbidity of 21.8 NTU was treated under these conditions,the effluent turbidity was 1.53 NTU,and the turbidity removal rate was 92.98%.Meanwhile,the higher turbidity and weakly alkaline water quality were beneficial to improve the treatment effect of the composite coagulants on low turbidity water.(4)In order to evaluate the production and application prospects of WPF,firstly,the safety of using WPF was researched.Based on the characteristics of the impurities contained in the waste paper,the negative effects of impurities on water quality were eliminated through demonstration.The water quality index related to the impurities and safety involved of the effluent after using WPF were selected and determined.The results showed that all the water quality indicators meet the requirements of the"Sanitary Standard for Drinking Water"(GB5749-2006),which proved the good hygienic safety of using WPF.Then the raw material selection and production process of WPF were analyzed combining with paper pulping process.The process of preparing WPF in paper pulping production line was preliminary designed,laying the foundation for WPF to develop large-scale production by means of papermaking platform.Finally,the advantages of producing WPF were introduced from aspects:environmental protection benefit,economic benefit and social benefit,which demonstrated that the preparation and application of WPF could turn waste into treasure,save energy and reduce emissions,as well as its strong practical significance and practical value. |
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