Recovery And Versatile Reuse Of Organic Carbon From Municipal Wastewater

With the urgent demand of social sustainable development,the function and orientation of today's municipal wastewater treatment plants(MWTPs)have turned from pollutant removal to energy and resource recovery.Shifting from aerobic to anaerobic treatment offers exciting opportunities to achieve the above purposes.However,the energy performance of anaerobic process would vary greatly upon the wastewater strength and operation conditions.In addition,due to the national diversities in economic development level and environmental conditions,how anaerobic technologies should be selected to suit the local conditions for maximizing treatment sustainability is unclear yet.In addition to the energy recovery,the value-added reuse mode of MW organic matters could be versatile.It is possible to synthesize functionalized carbon material using organics and their transformed products and then apply it for wastewater remediation.So far,the relevant studies are scarce.Therefore,the aim of this dissertation is to systematically explore and develop the possible organic recovery methods to achieve energy production and resource recovery from MW.With a focus on carbon separation,recovery and value-added reuse process,this work is valuable for MWTPs to have a better sustainable practice.The main contents and results of this dissertation are as follows:1.Evaluation of the effectiveness and efficiency of organic recovery from MW by anaerobic technologies in China.By using the acquired 3604 MWTPs influent data,the energy consumption for MW decarburization in China was estimated and the energy recovery potential via implementation of CAS + sludge anaerobic digestion(CAS+SAD),high rate activated sludge + SAD(HRAS+SAD),and anaerobic membrane reaction(AnMBR)was evaluated.Results indicate that the energy requirement for MW decarburization has increased by 10.3 times from 2001-2015.The high energy-consuming provinces include Guangdong,Shandong,Jiangsu,and Zhejiang.The HRAS+SAD process outperforms CAS+SAD in net energy production,while AnMBR is preferable only in the regions where COD is higher than 335 mg/L.If an optimal MW treatment paradigm with tailored AD technologies is applied,the annual energy production from China's MW sector would reach 4.165 billion kWh.2.Evaluation of the sustainability of organic recovery system for MW.The national-specific sustainability of different anaerobic technologies by application in selected developed and developing countries was evaluated.A multi-criteria assessment criterion based on economical,energetic,technical,social and environmental aspects was adopted to conduct such an evaluation.We also explored the sustainability of AD-coupled de-carbonization processes in the future scenario.At present,the HRAS+SAD was identified as the most sustainable technology to be applied in China,United States,and United Kingdom,while the UASB+AS was the best for India.By 2025,HRAS+SAD will be the best technology for all these countries.Furthermore,for the developed countries it is more economically feasible to explore and implement the overall energy and nutrient recovery technologies,while developing countries would still lay a high priority on the economics and environmental impacts than on resource recovery in the near future.3.Exploration of the effectiveness of coagulation-microfiltration-based process for organic separation from MW and its membrane fouling characteristics.Although direct membrane filtration of MW was effective in organic carbon separation from MW but severe membrane fouling also occurred due to the cake layer formation on the membrane surface.Multivariate curve resolution-alternating least squares analysis was integrated with infrared attenuated total reflection mapping and chemical quantitative analysis to explore the process.Biopolymer clusters with a size of 1-8?m in MW were found to be the main foulants responsible for severe membrane fouling,and the protein-induced fouling on the membrane surface was more severe than that of humic substances and polysaccharides.Coagulation pretreatment was effective in removing foulants and greatly improved the membrane filtration performance but the mechanism of different coagulants on mitigating membrane fouling were different.In the light of practical application,the anti-fouling performance of inorganic coagulant would be superior to that of organic polymers.4.Reusing of organic embodied chemical sludge to synthesize cathode catalyst of electro-Fenton system.By using the formed chemical sludge as precursor,the metal-carbon composite catalyst with a high H2O2-producting capacity(432 mg/h/g)by one-step pyrolysis strategy was successfully synthesized.By applying the prepared material as a cathode catalyst in an electro-Fenton system,a green waste pollution control strategy for urban cities' sustainable development is proposed.Further experiment result indicated that phenol(40 mg/L),a model pollutant in industrial wastewaters,was completely degraded in catalyst fabricated electro-Fenton system within 40 min at a potential of 0.15-0.35 V(vs.RHE).Meanwhile,approximately 60%of total organic carbon was efficiently removed by the electro-Fenton system within 4 h at 0.25 V,and the hydroxyl radicals were found to be the main oxidation agent for the phenol degradation.5.Reusing of organic embodied bio-sludge to synthesize carbon-based persulfate catalyst.By using bio-sludge as raw material,biochar was synthesized and used for catalyzing peroxymonosulfate(PMS)to degrade bisphenol-A(BPA).An average removal rate of 3.21 mol BPA/mol PMS/h could be achieved in a wide pH rang of 4.0-10.0 at a biochar dosage of 0.2 g/L.Singlet oxygen,which was catalytically produced by ketone structure inside the biochar,was revealed as the main reactive species responsible for pollutant degradation.More importantly,metals in the sludge precursor were found to play an important role in improving catalytic activity of biochar during sludge pyrolysis process.6.Exploration of calcium-assisted pyrolysis of organic matters to synthesize and immobilize metal-free PMS activator.With the calcium-assisted pyrolysis strategy,the metal-free catalyst by using proteins,polysaccharides,and fibers,which are the main organic matters in MW,as precursors for PMS decomposition was prepared.With 0.1 g/L catalyst and 0.2 g/L PMS dosage,0.1 mM BPA could be totally removed within 30-min.Further material characterization and structure analysis results revealed that the calcium played an important role in pore development and active site formation.The main reactive specie responsible for BPA removal in the system was singlet oxygen,rather than 'OH or SO42-.In addition,catalysts were immobilized by using Ca2+ and alginate mediated hydrogel and such immobilized granules were packed into an expanded bed reactor to investigate the performance of persulfate-based process for wastewater treatment.At 2 h of hydraulic retention time,30%of packing volume and[PMS]/[BPA]=2.0/1 dosage,the average COD removal efficiency of the reactor exceeded 80%.