| Municipal and industrial wastewater treatment plants（WWTPs）produce"clean water"that meets discharge standards,but also grow large amounts of sludge containing organic and inorganic components.Owing to the strengthening of national awareness of the community with shared future for mankind and individual awareness of health,the agricultural utilization and landfill of sludge is increasingly restricted,and the extensive promotion of anaerobic digestion and incineration process has been put on the agenda.Different forms of energy recovery from sludge is one of the most competitive strategies for sludge disposal problem.Sludge pretreatment by Fenton oxidation is not only beneficial to improving the sludge dewaterability and can effectively improve the biodegradability during anaerobic digestion process and the sludge heating value during the incineration process,making it possible for a simultaneous realization of sludge dehydration,reduction and energy recovery.Up to now,there are no in-depth studies on environmental impact assessment based on Fenton-treated sludge management strategy at home and abroad.Life cycle assessment system coupled with the domestic sludge disposal process for the sludge pretreated by the Fenton pretreatment was firstly proposed in this research,aiming to obtain the information of environmental impact load in the process.The life cycle assessment of sludge treatment and disposal system with different feedstock organic matter content（60%,70%,80%）under the action of Fenton process and enhanced coupled Fenton process（electro-Fenton（EF）,ultrasound-Fenton（US+F）,ultraviolet-Fenton（UV+F））was implemented on the platform of Open LCA software.To compare with the control group scenarios without Fenton pretreatment,this research was advanced in an orderly series of steps:establish a total environmental impact calculation model,identify evaluation objectives,boundary range,inventory analysis,influencing factors,and summarize life cycle explanations.The results indicated that the conventional landfill scenario for Fenton-pretreated sludge（F-L）was higher in 15 midpoint impact categories than that of the control scenario（Landfill）,and the total impact potential was 2.3 times that of the control scenario.The anaerobic digestion scenario for Fenton-pretreated sludge（F-AD）scenario engendered 125%,48%and 35%reduction of environmental benefits for the three kinds of organic matter content sludge,respectively.At Incineration routes,the total potential impact of the F-I scenario was 47%to 48%lower than at Incineration control scenario.This can be attributed to the long-term impact caused by the direct discharge of heavy metals and other pollutants into the natural environment during the production process of hydrogen peroxide by anthraquinone method.Therefore,the future direction for the improvement of Fenton method is to explore the optimization technology to minimize the contribution of H2O2,or to develop substitution agentia for H2O2（such as Ca O2）.The total environmental impact potential of enhanced coupled Fenton processes combined with anaerobic digestion route is ranked as EF-AD>US+F-AD>UV+F-AD.UV+F-AD scenario accomplished contribution of environmental benefit at 70%and 80%organic matter content,but it is still not superior to F-AD scenario under the same sludge condition in each impact index.Further reducing the dosage of agents and improving the effective radiation of ultraviolet light and the energy recovery efficiency of sludge biogas are the core development orientations for improving the environmental benefits of UV-Fenton coupling technology.In conclusion,the comprehensive ranking of environmental impact potential of each scenario was:Incineration>F-I>F-L>Indigenous>EF-AD>US+F-AD>UV+F-AD>F-AD>AD.In terms of energy balance,economic cost and environmental cost,comparison and analysis of the advantages and disadvantages of Fenton process in the whole sludge reduction and disposal routes were conducted in this study.Furthermore,the results improved and supplemented the database and calculation model of life cycle cost inventory of sludge reclamation and reuse.The sequence of energy balance coefficient of each scenario was:F-AD>AD>UV+F-AD>US+F-AD>EF-AD>F-I>Incineration;and the sequence of total life cycle cost of the scenarios was:Incineration>F-I>Landfill>AD>EF-AD>US+F-AD>UV+F-AD>F-AD>F-L.In summary,the Fenton technology combined with anaerobic digestion route is the optimal route when taking the environmental impact,energy balance and life cycle cost into account.The knotty point is that the contribution ratio of H2O2 is too high,which is also the bottleneck why F-AD scenario is inferior to the AD scenario in environmental impact,so it is imperative to further optimize the Fenton process. |
