The Effects And Mechanisms Study Of Malemine And Cyanuric Acid In Biological Nitrogen And Phosphorus Removal And Activated Sludge Anaerobic Digestion Process

Triazine,a compound containing a heterocyclic ring,is a significant raw material for industry and home furnishings,and an intermediate for pharmacy because of the extensive biological activity.Triazine has a mount of derivatives,among them melamine and cyanuric acid are two common triazines with basic heterocyclic ring structure.They are both significant raw materials for commercial chemicals such as coatings,adhesives,resin,flame retardant,and have been widely used in construction,textile,rubber,plastic,paper making,and a chemical intermediate for pharmaceutical manufacturing.Melamine had been illegally adulterated in food?especially the pet food and infant formula?to give the illusion of an increase of the apparent protein content because of the high nitrogen content?66.7%by mass?,which led to the acute kidney failure and even death of dogs,cats and infants.Cyanuric acid is not only used as the raw material for the production of hydroxyzine,but also widely added to outdoor pools,recreation waters and scenic water to stabilize chlorine in case the decomposition of the chlorine disinfectant by ultraviolet light.As the final defense line prior to entering into the aquatic environment,wastewater treatment plant?WWTP?with activated sludge has been reported to remove many pollutants via aggregation,precipitation,biosorption,degradation,or other processes.But,the presence of contaminants may a potential negative impact on the wastewater treatment process.Previous studies have shown that there were trace amount of melamine and cyanuric acid in water,but the behavior of these two pollutants in biological wastewater treatment and sludge anaerobic digestion were rarely reported.The aim of this thesis was to evaluate the mass balance of melamine and cyanuric acid in wastewater biological nitrogen and phosphorus removal and activated sludge anaerobic digestion derived short chain fatty acids?SCFAs?production,and to investigate the potential effect and functional mechanisms of melamine or cyanuric acid on biological nutrient removal and activated sludge anaerobic digestion derived SCFAs production.Firstly,the effect of melamine on wastewater biological nutrient removal was investigated in a long-term exposure period in an anaerobic/aerobic/anoxic sequencing batch reactor?SBR?.Experiments showed that MA was removed during biological wastewater treatment process,and the removal was mainly achieved by activated sludge adsorption instead of biodegradation.Low level of MA(0.10 mg·L^-1)in wastewater had negligible influence on the performance of activated sludge,but the impacts form high levels could not be ignored.It found that the surfaces of cells were damaged by MA exposure at the high concentrations(1.00 and 5.00 mg·L^-1)investigated because of the increasingly blurred cellular outline.1.00 and 5.00 mg·L^-1 of MA deteriorated biological nitrogen and phosphorus removal.The presence of MA(1.00 and 5.00 mg·L^-1)decreased total nitrogen removal efficiency from 94.15%to 79.47%and 68.04%,respectively.The corresponding concentration of effluent phosphorus increased from 0.11 mg·L^-1 to 1.45 and 2.06 mg·L^-1,respectively.It was also observed that MA changed the microbial diversity,inhibited the enzyme activities of nitrite oxidoreductase?NOR?,nitrate reductase?NR?,nitrite reductase?NIR?and exopolyphosphatase?PPX?,which were closely relevant to nitrogen and phosphorus removal.Further investigation showed that the presence of high MA concentrations promoted the consumption and synthesis of glycogen,thereby providing the advantage for the growth of glycogen accumulating organisms?GAOs?.The study of melamine in waste sludge anaerobic digestion showed that the impact of melamine on hydrolysis process?especially the hydrolysis of protein?and SCFAs production from the anaerobic digestion was dose-dependent.It is found that melamine caused the inhabitation of hydrolysis and acidogenesis processes,especially the hydrolysis process of protein.The presence of melamine at 0.10,1.00 and 5.00 mg·g-VSS^-1 inhibited SCFAs production by 4.69?15.68 and 22.03%,respectively,comparing with the control test(366.14mg-COD·g-VSS^-1).The presence of melamine also decreased the microbial diversity,especially the abundance of functional microbes.During the sludge anaerobic digestion,melamine was absorbed by the activated sludge and mainly stored in loosely-bound extracellular polymeric substance?LB-EPS?.0.10,1.00 mg·g-VSS^-1 of melamine could be completely absorbed,but the initial melamine with 5.00 mg·g-VSS^-1 was still remained in the digestion liquid at 12^th days of the sludge anaerobic digestion process.Furthermore,desorption of melamine from waste sludge occurred under the constant alkaline condition?pH=10.0?.Subsequently,the work investigated the fate of cyanuric acid at different levels of 0,0.01,0.10 and 1.00 mg·L^-1 in biological wastewater treatment system and its impact on biological nutrient removal.Experimental results showed that cyanuric acid(0.01 and 0.10 mg·L^-1)was removed in biological wastewater treatment process,which was mainly achieved by biodegradation of particular species?Acidovorax and Pseudomonas?in the anaerobic condition.However,1.00 mg·L^-1 cyanuric acid was reluctant to be degraded in biological wastewater treatment system.The presence of cyanuric acid promoted both the synthesis and decomposition metabolisms of poly-hydroxyalkanoates and glycogen,thereby providing the advantage for phosphorus removal.Cyanuric acid could inhibit nitrification process because of inhibition to nitrite oxidizing bacteria.With the cyanuric acid level increase from 0 to 1.00mg·L^-1,total nitrogen removal efficiency decreased from 97.23 to 74.72%.Moreover,the microbial community of activated sludge was changed by the exposure of cyanuric acid.PAOs,such as Bacteroidetes,Chloroflexi and Saccharibacteria increased,but the abundance of Nitrospirae was decreased.The research of cyanuric acid in waste sludge anaerobic digestion with different alkaline condition controlled exhibited the different results on SCFAs production.With the constant alkaline condition?pH=10.0?,the SCFAs production with the level of cyanuric acid at 0,0.01,0.10 and 1.00 mg·g-VSS^-1 was 380.36,392.08,408.29 and 377.60 mg-COD·g-VSS^-1,respectively.Cyanuric acid with 0.01 and 0.10 mg·g-VSS^-1 benefited both the hydrolysis and acidogenesis processes,especially the digestion of polysaccharides,and increased the proportion of acetate in SCFAs.Whereas,1.00 mg·g-VSS^-1 cyanuric acid could not enhance the anaerobic digestion process but inhibited the hydrolysis process of polysaccharides.Further investigations with microbial community analysis revealed that the pertinent presence of cyanuric acid(1.00 mg·g-VSS^-1)decreased the abundance of functional microbes.Trace of cyanuric acid(0.01 and 0.10 mg·g-VSS^-1)could be biodegraded completely during the sludge anaerobic digestion and SCFAs production.The degradation efficiency of cyanuric acid was52.04%at the 12^th day of the anaerobic digestion process.With the condition of initial pH=10.0,the presence of cyanuric acid benefit the SCFAs production and increase the proportions of acetate and propionate in SCFAs.1.00 mg·g-VSS^-1 cyanuric acid enhanced the sludge solubilization,the hydrolysis and acidogenesis processes.This study investigated the absorbability of melamine or the biodegradability of cyanuric acid,clarified the potential effects and the function mechanisms on wastewater biological nutrient removal and waste sludge anaerobic digestion and SCFAs production of two substances.Furthermore,the results of this study could provide a theoretical reference for stringent regulation on melamine,cyanuric acid and even other triazine production,marketing,application and ultimate disposal,and could give a reminder and scientific basis for water environment security management in the future.