Study On Simultaneous Degradation Of Algal Sludge Ang Electricity Generation In Bioelectrochemical System

At present, the total emissions of water pollutants has exceeded the waterenvironment load-bearing capacity, which cause serious water pollutions. The mostprominent problem is eutrophication. It directly lead to a bloom of algae and waterplants. How to treat algae-laden water effectively is always a focus in drinking watertreatment plant (DWTP). However, the waste algal sludges produced from the treatmentare rarely paid attention based on waste resource utilization. We can learn from theresources exploitation and utilization experiences of sea algae and the algae ineutrophication water bodies. Algae sludge produced from DWTP should be reasonableuse, and be transformed to energy. The energy can be recovered, thus it brings the profitto DWTP. Bioelectrochemical systems (BESs) is a new biological technology, whichcan oxidize organic matter and simultanous recovery of electricity. This research focuson the degradation and electricity production performance of the algal sludge in BES,changes in components and constructures during the degradation process, and therelationships between organic matters in algal sludge and algal byproducts.Characteristics of algae and their metabolites, including intracellular organic matter(IOM) and extracellular organic matter (EOM) were studied. We also investigated theformation of the algal byproducts, such as disinfection byproducts, microcystin-LR,taste and odor substances. The results demonstrated that concentrations of the organicmatter in EOM were less than that in IOM. Protein and carbohydrate were the majorcomponents for EOM, while only protein was the predominant components for IOM.EOM contained more small molecular weight fractions compared to IOM. There weremore aromatic compounds, protein and amino acid in IOM. The proportion of protein,carbohydrate and lipid in different algal growth phase determined THMs yields. Whenthe initial ratio of Br-/Cl2was constant, the formation and distribution of THMs wasdetermined by the mole ratio of Br-/TOC in the present of bromide. The formation ofMC-LR and2-MIB depended on algae density. The yields were the most at stationaryand dead phases.Degradation of algal sludge using BESs was investigated. Three pretreatments foralgal sludge were compared. Heat-alkali pretreatment was the best, alkali pretreatmentwas better than ultrasonic pretreatment. After alkali pretreatment, concentrations ofSCOD, soluble proteins, soluble carbohydrates were all increased three times. Solubleorganic matter could be effectively removed using BESs, and the removals had an orderas follows: carbohydrate> COD> UV254> protein> TOC. The removals were morecompletely in high load. The concentration from low to high influenced the removal ofalgal sludge. The changes in components and structures of organic matter from influent and effluent algal sludge samples among BESs reactor under open-circuit condition,BESs reactor under closed-circuit condition, and anaerobic reactor were investigatedusing methods, including DOC, SUVA, MW fraction, UV-VIS, EEM, anddetermination of protein and carbohydrate. There are hydrophilic componentscontaining few aromatic rings and double bond both in influent and effluent samplesamong three types of reactors. Organic matter in effluent contained larger proportions oflow MW fractions. The removal rates of protein, carbohydrate and lipid was higest inBESs reactor under closed-circuit condition, and then anaerobic reactor, and the lowestin BESs reactor under open-circuit condition. The contribution of the protein,carbohydrate and lipid, respectively to THMFP were calculated based on purechemicals of bovine serum albumin, glucose and fish oil. Fluorescence parametersthrough three analytic methods (fluorescence intensity, FRI and PARAFAC) wereestablished good relationships with THMFP.On the aspect of electricity generation and recovery, the peak of voltage fromalkali-pretreated algal sludge (A-AS) was better than that in raw algal sludge (R-AS). Itcan bring more profit in A-AS compared to R-AS. The extra profit can offset the costproduced from alkali chemical in DWTP. Power density increased with the increase ofsoluble organic matters, and the highest could reach7.86W/m3. The major componentsvaried with algae in different growth phase and different algae species. Changes of thecomponents during the degradation process could influence the electricity productionperformance. The operating conditions could also influence the electricity productionperformance. Temperature could influence the active growth and metabolism speed ofmicroorganisms, and futher affect the anodic potential and the reactor performance. Thestirring could enhance the mass transfer efficiency, which make a more rapiddegradation speed and reduce about two-thirds of running time. Adding AQDS couldincrease the microbial activity, and thus it can enhance the voltage output and powderdensity. According to the phylogenetic analysis of the16S rRNA gene clone library,degradation of algal sludge mainly depended on syntrophic interaction betweenfermentation bacteria and electrochemically active bacteria. Most of electrochemicallyactive bacteria first oxidized fermentation products to generate electricity. Moreover,the type of electrochemically active bacteria might use endogenous mediators based onpositions of the oxidation-reduction peak. The major component of the mediators wassimilar to the anthraquinones from AQDS.