Characteristics Of Natural Organic Conditioners Promoting Deep Dewatering Of Cyanobacteria And Carbon Emission Reduction Property

Eutrophication of the lake leads to the production of large quantities of salvaged cyanobacteria every year,which still have a water content of over 95%after pre-dewatering treatment.However,various methods of resource disposal of cyanobacteria require a low water content and therefore require deep dewatering.Due to the unique cellular properties of cyanobacteria,traditional inorganic coagulants and organic synthetic polymer flocculants applied for deep dewatering of sludge will not only increase the difficulty of subsequent treatment of cyanobacteria,but also greatly affect the efficiency of resource utilization,and therefore are not suitable for deep dewatering of cyanobacteria.Natural organic flocculants are diverse and widely available,and more importantly,as a biomass material,the application of natural organic flocculants in deep dewatering will not affect the subsequent resourceful application of cyanobacteria.At the same time,in the context of"carbon peaking and carbon neutrality",the treatment and disposal of cyanobacteria as part of the urban water treatment system,its carbon emission reduction accounting cannot be ignored.In this paper,based on the property of cyanobacterial cells,synergistically dewatering by mixing cyanobacteria with sludge in a certain ratio to eliminate the adverse effect of cyanobacterial cells was carried out.At the same time,the feasibility of its practical application is demonstrated by combining the improvements in filtrate water quality,dewatering cost,and resource efficiency.On this basis,inorganic coagulation agents and natural organic flocculants were selected to replace the traditional conditioning agents in order to eliminate the constraints of traditional conditioning agents on the final resource-based disposal efficiency of cyanobacteria,and to study their effects on the improvement of dewatering performance and explore their mechanisms of action.To carry out carbon emission accounting for the whole process of cyanobacterial treatment and disposal and analyze its carbon emission reduction characteristics,so as to provide a theoretical basis and practical reference for the practical engineering of cyanobacterial deep dewatering and resource-based disposal.The following findings were obtained:（1）Cyanobacteria and sludge were mixed in the ratio of 2:1 by weight of dry matter,and combined with ferric chloride and quicklime for conditioning,and the feasibility of deep dewatering of sludge in cooperation with cyanobacteria was explored by measuring the characterization performance and filtrate water quality.The results showed that the dewatering performance of cyanobacteria was significantly improved after conditioning,but the deterioration of filtrate water quality was serious,indicating that cell lysis occurred during the conditioning process.The extraction of extracellular polymeric substances（EPS）from the cyanobacteria and the determination of their protein and polysaccharide contents revealed that the higher concentration of protein substances in the SMP-EPS and LB-EPS layers of the cyanobacteria,as well as the protein and polysaccharide substances in the TB-EPS layer,combined to limit the deep dewatering effect of the cyanobacteria.Meanwhile,cyanobacteria have a high heating value due to their high organic matter content,which helps to reduce the overall cost of deep dewatering.（2）Five combinations of inorganic conditioning agents were selected for the treatment of cyanobacteria.The combination of Fe Cl₃+PAC agents was found to show good improvement in dewatering performance,filtrate water quality,comprehensive cost of dewatering,resource recovery efficiency and carbon emission intensity of sludge-containing cyanobacteria,and has the potential to replace traditional inorganic conditioning agents.At the same time,the results of carbon emission accounting for the whole process of the three treatment and disposal routes of cyanobacteria using Fe Cl₃+PAC showed that the"Deep dewatering-Drying-Incineration-Landfill"route had the highest carbon emission intensity,while the"Anaerobic digestion-Deep dewatering-Drying-Incineration-Landfill"and"Deep dewatering-Aerobic Composting-Landfill"routes had lower carbon emission intensity due to the existence of carbon sink.Electricity consumption and chemical consumption are the most significant sources of carbon intensity in the treatment and disposal of sludge-containing cyanobacteria.（3）Five groups of agricultural wastes were selected as natural organic flocculants for the conditioning of cyanobacteria.It was found that Fe Cl₃+tea meal powder conditioning could not only significantly improve the dewatering performance of cyanobacteria,but also notably improve the deterioration of filtrate water quality.In addition,this group has the lowest integrated cost of deep dewatering and the highest heating value.The results of carbon emission intensity calculation for the whole process of treatment and disposal of cyanobacteria when Fe Cl₃+tea meal powder is used show that the"Deep dewatering-Aerobic composting-Landfill"route still has the lowest carbon emission intensity among the three treatment and disposal routes.The use of natural organic flocculants resulted in a significant reduction in total carbon emission intensity compared to the groups of inorganic agents.The main reason is that natural organic flocculation has a lower carbon emission factor and the dosage is lower than that of inorganic coagulants,resulting in less indirect carbon emissions due to chemical digestion.Therefore,each group of natural organic flocculants is an excellent performance,low-carbon and environmentally friendly conditioning agent with great potential to replace traditional inorganic coagulants and is feasible in practical applications.