Purification Efficiency Of Conventional Biochemical Treatment On Anaerobically Digested Food-waste Slurry And A Novel Process Of Bio-coagulation Dewatering Followed By Bio-oxidation

In recent years,with the acceleration of urbanization and the improvement of life quality,various catering enterprises have developed rapidly,and the amount of restaurant food waste（RFW）has also increased dramatically.Normally,RFW mainly includes rice,noodle food residues,vegetables,fats and vegetable oils,meat and bones,etc.With the high organic matter content of RFW is very perishable and deteriorates,emits foul odor,spreads diseases that contaminate the environment.Anaerobic fermentation technology of RFW has been used more widely（such as medium and high temperature wet anaerobic fermentation and dry anaerobic fermentation）compared to the traditional treatment technology（including sanitary landfill,incineration,production of feed,etc.）.The reduction and harmlessization of RFW can be achieved by anaerobic fermentation technology,but also producing biogas to maximize energy recovery and economic benefits.However,the anaerobically digested effluent（abbreviated as "anaerobically digested food-waste slurry"）produced by the anaerobic fermentation of RFW is an organic wastewater with high concentration of salinity,ammonia nitrogen,and COD（chemical oxygen demand）.Because there are no better methods to carry out nowadays,therefore,properly treatment has become the most critical part of RFW recycling.Based on "three principles" and the biochemical effectiveness of anaerobically digested food-waste slurry had been analyzed:（1）Relying on a large-scale RFW Treatment Plant in Hebei Province as the research platform,the analysis of the effectiveness of anaerobically digested food-waste slurry treatment process and the existed problems and solutions through irregular sampling of each unit in the on-site process were proposed.The results showed that anaerobically digested food-waste slurry was organic wastewater with high SS（26400 mg·L-1）,COD（29440 mg·L-1）,ammonia nitrogen（3512 mg·L-1）,phosphorus（433 mg·L-1）and salinity（14100 mg·L-1）.Due to highly pollution load caused by unsatisfactory removal of SS and ammonia nitrogen that mainly led to poor biochemical effectiveness which also followed by imbalanced carbon nitrogen ratio and the pond volume size.Therefore,in order to improve the purification effectivness of the current process,especially the biochemical unit,we recommended to remove SS and NH4+-N concentration of the influent thoroughly before the biochemical system,and appropriately expand the biochemical pool volume,improve biodegradability of anaerobically digested food-waste slurry,and restore the density and activity of microorganisms.（2）The original anaerobically digested food-waste slurry and its centrifuge liquid,filtrate and the filtrate after denitrification for biochemical effectiveness under different conditions by the simulation of SBR were investigated.The results（removal effectiveness of COD,ammonia nitrogen and TN,etc.）showed that the denitrificated filtrate>filtrate>centrifugal liquid>anaerobically digested food-waste slurry,and the highly removal of SS and ammonia nitrogen was more conducive to improve the biochemical effectiveness.Secondly,the biochemical effectiveness of denitrificated filtrate was better than filtrate with the same conditions,such as carbon source adding,carbon-nitrogen ratio（C/N=6）and the RFW seriflux could be used to microorganisms by the simulation of SBR.Finally,adding different carbon sources（glucose and RFW seriflux）and domesticating activated sludge gradually by increasing the influent load to the biochemical system for average removal rates of COD,ammonia nitrogen and TN were 81%and 61.7%,61.6%and 53.1%,58.9%and 56.1%,respectively.At the end of the operation,the system of adding glucose and RFW seriflux of final effluent COD,ammonia nitrogen,and TN were 373,109,173 mg·L-1 and 648,269,401 mg·L1,respectively.Moreover,during the domestication of activated sludge,adding glucose as a carbon source to biochemical effectiveness was better,but both of them were unable to operate steadily for long-term.（3）Relying on the RFW Disposal Center in Tongliao City as the object,different parameters（dosing carbon source,C/N,HRT,A/O time ratio,etc.）and the domestication of activated sludge to the biochemical effectiveness of denitrificated filtrate were systematically investigated by the simulation of SBR.The results showed that the biochemical effectiveness of operational mode with A/O（injection for 0.5 h anaerobic for 17.5 h+aerobic for 6 h）was the best and most stable during different stages.Secondly,the hydrolyzed acidified liquid of RFW could be used as an additional carbon source for the biochemical system and the operational effectiveness was best with conditions of C/N=6 and operational mode.All indicators could reach the standard steadily.Furthermore,the biochemical system with adding glucose as additional carbon source could run stably,but the COD of the effluent and ammonia nitrogen and TN of the biochemical system with C/N=4 and C/N=8 all couldn’t reach the standard stably.In addition,the maximum load treatment capacity of the denitrificated filtrate by simulated SBR with C/N=6,hydrolyzed acidification liquid as the carbon source could increase to 8%and the hydraulic retention time（HRT）could be shortened to 12.5 days.The biochemical effectiveness of SBR system by adding hydrolyze the acidified liquid（C/N=6）was best and all indicators could reach the standard steadily after changing the operational mode to A/O.The final effluent COD,ammonia nitrogen,TN,and SS concentrations were 155,20,53,and 210 mg·L-1,respectively,which could reach the designed effluent water quality standards.（4）The "biological coagulation dewatering combined with conventional biochemical method（inverted A2/O）" process was directly put into engineering production and degradated filtrate after nitrogen fixation which was produced by dewatering of anaerobically digested food-waste slurry through activated sludge culturing and domesticating activated sludge gradually.For more than 4 months continuously operation with the conditions of adding hydrolyzed acidification liquid（C/N=6）,reasonably adjusting the alkalinity of the biochemical pool（pH maintained between 7.5～8.5）,properly discharging excess sludge and domesticating the activated sludge by orderly accelerating the influent load that showed the average removal rates and effluent concentrations of COD,ammonia nitrogen,TN,TP were 69.5%,87.5%,79.7%,93.4%and 166.4,13.7,32 and 1.78 mg·L-1,respectively.The average removal rates of COD,ammonia nitrogen,TN in the primary and secondary A/O system were 59.1%,64.9%,59.9%and 17.1%,59.7%,26%,respectively.Most of the pollutants had been degraded in the first stage.The final effluent concentration of COD,ammonia nitrogen,TN,TP,and SS were 176,11,27,2,and 136 mg·L-1,respectively,which could reach the effluent standard stably.The "biological coagulation dewatering combined with convetional biochemical method（inverted A2/O）" process with high strength impact resistance to pollution loads during operation,which can stably reach the standards for processing anaerobically digested food-waste slurry,but also provides better technical support for continuously operating of RFW anaerobic fermentation.