Study On The Decomposation Of Waste Activated Sludge And Phosphorus Pesticides By Persulfate Advanced Oxidation Process

Persulfate-based oxidation has attracted much attention in recent years for the relatively wider adaptability range of pH compared with classical Fenton reaction,and compared to traditional remediation mathods,persulfate salts?PS?catalyzed through heat,light and interim metal activation process have a higher reduction potential?2.6 V?,which have been proved could almost completely decompose refractory hazardous organic species existed in reaction system.In this study,persulfate salts activated with various methods adopted as replacement of the classical Fenton-like reagent for the release of nutrients from excess waste activated sludge?WAS?.The results indicated that this tecnology can efficiently disintegrate WAS zoogloea,improve dewatering performance and filterability,and the mechanism of WAS decomposition and nutruits recovery by PS process was elucidated.Finally,the degradation proccess of trichlorfon?one kind of organophosphorus pesticides widely used to control a variety of arthropod pests in the agricultural production process?in the aquatic environment through thermally activated persulfate has also been investigated.In order to reveal the mechanism of phosphate release by chemically enhanced process and recovery from waste activated sludge respectively,potassium persulfate?K₂S₂O₈?was adopted as a replacement of the classical Fenton-like reagent for the release of nutrients from excess sludge.The results indicated that the increases in the temperature and PS dosage could significantly improve the release of phosphate from sludge by PS process.When the PS process the aid of ultraviolet radiation was performed at 65^oC and PS:WAS mass ratio 1.5:1 for 6 h,the phosphate and ammonia nitrogen concentrations in the supernatant reached 204 mg/L and 216 mg/L,respectively,accompanying with sludge reduction by 64%.In the phosphate recovery process,98.9%of the phosphate and 34.8%of the ammonia nitrogen can be recovered from the supernatant by struvite precipitation at pH 11.5 and Mg/P molar ratio 2.Hybrid alkali-persulfate disintegration of waste activated sludge in low dosage could not efficaciously destroy the structure of cell membrane of zoogloea,while EPS mainly composed of macromolecular microbial secretions and products of cellular lysis or macromolecule hydrolysis will be drastically destroyed,the proteins and polysaccharides therein were further decomposed by SO₄^·–and·OH radicals.And the organic phosphorus and organic nitrogen contained in these substances are converted into inorganic states,resulting in an increase of PO₄-P,NH₄-N and COD concentrations in the supernatant.During the dynamic characteristics research of organophosphorus pesticide degeneration process,the experiment data obviously indicated that the release of phosphate in the degradation process of trichlorfon using persulfate oxidant could be enhanced in higher temperature,which removal efficiency of trichlorfon in synergistic degeneration system with ultraviolet irradiation?UV,80^oC,PS/Trichlorfon=7?could reach 95.63%.And 93.4%of the phosphate could be recovered from the supernatant by struvite precipitation at pH 9.5 and Mg/P molar ratio 1.3 in the phosphate recovery process.We have found that the addition of ascorbic acid could improve the effectiveness of waste activated sludge decomposition and dewatering process when the WAS was treated with different disposal methods.And the experiment results shows that the high dosage ascorbic acid addition at the early stage of persulfate WAS oxidation process will substantially improve the dewaterability and filterability of sludge with shorter response time,conversely,which almost has no influence on variation tendency of capillary suction time?CST?of waste activated sludge in the alkali pre-treatments process.Finally,it is noteworthy that the improvement of WAS dewaterability and filterability in alkali-persulfate disintegration may attribute to decomposation of EPS which rich in proteinaceous organic matters such as protein,humic acid and DNA,because there is a coincidence phenomenon of the TN concentration change in supernatant and the variation characteristic of capillary suction time?CST?of WAS.