| Kitchen waste is perishable and rich in organic matter and nutrient elements,which shows immense potential in biological treatment.Aerobic composting embodies several characteristics like high temperature,fast fermentation,low operating cost,which make it possible for the resource regeneration of kitchen waste.Nevertheless,when processed with aerobic composting,kitchen waste which is of high moisture content and poor pore structure commonly requires a certain amount of additives.Matured compost obtained by aerobic fermentation is of low moisture content,developed pores and rich microbial communities.All these advantages make it become a common-used compost additive.In this paper,fermentation parameters of kitchen waste composting were optimized by orthogonal experiments.Subsequently,effects of adding different proportions of matured compost on the physico-chemical properties and humus acid of compost were studied under the optimized parameters.Finally,a drum composting reactor utilizing matured compost as additive was designed and then optimized by simulation.All efforts mentioned above were made to provide a certain theoretical basis for practical application of matured compost additive.The main findings are listed as follows:（1）Orthogonal test results showed that all experimental groups remains above 50℃for more than 10 days.All meet the hygienic requirements for composting temperature.After 40-day aerobic composting,all groups realized obvious reduction effect and were decomposed.Turning frequency have most significant effect on accumulated temperature,and it was followed by ventilation and moisture content;When it comes to factors influencing the degradation rate of organic matter,ventilation was the highest,followed by turning frequency,then moisture content.The results revealed that the optimal levels of factor for the aerobic composting were 0.10 m3·（min）-1 for ventilation,60%for moisture content and the 8 d for turnover frequency.（2）Compared with the control group added with sawdust,adding matured compost extended the duration of high temperature above 55℃by 1-3 d in experimental groups,and it was conducive to non-hazardous treatment of kitchen waste.Its adding improved the initial p H value in compost,which reduced the influence of acidification to metabolism of microorganisms.Adding matured compost significantly increased the electrical conductivity and the content of organic nitrogen,ammonium nitrogen and nitrate nitrogen,reduced the organic carbon content,and maintained the C/N ratio within an appropriate range.It actually facilitated the conversion of ammonium nitrogen to nitrate nitrogen and the control of nitrogen loss.Therefore,its addition was beneficial to improve the nutrient content in compost product,but restrained the degradation of the organic carbon slightly in the meantime.Results indicated that the optimal mixing ratio of matured compost and kitchen waste was 0.8:1～1.6:1.When this ratio was 0.8:1,compost maturity reached the best.（3）Each component of humic acid showed downward trend as the composting proceeded.At the end of experiment,the content of humic acid increased with the rising proportion of matured compost,while the loss rate of humic acid decreased gradually.Its addition improved the E4/E6 ratio by 20.0%on average,and the HA/FA ratio decreased by 5.3%on average at the same time.When the content of reducing sugars and amino acids gradually decreased during composting,the content of polyphenols increased first and then decreased.The activities of dehydrogenase,catalase and polyphenol oxidase showed a rising trend.Matured compost additive inhibited the decomposition of humic acid,which can improve the concentration of humic acid and compost fertility effectively.Adding matured compost significantly increased the content of reducing sugars,amino acids and polyphenols,as well as the activities of dehydrogenase and polyphenol oxidase during composting,while catalase activity showed a slightly drop.Its addition was conducive to the formation and accumulation of humic acid.In the meantime,it suppressed the growth of polymerization and aromatization degree of humus acid to a certain extent.Therefore,the mixing ratio be lower than 1.6:1.（4）Filling rate had the most significant influence on the reflux effect of matured compost in the newly designed drum composting reactor.The optimized rotate speed was1 r/min,filling rate was 40%,and number of plates was 3 sets.When ran under the above conditions for only 51 minutes,the reflux ratio of reactor reached 80%,which means that after optimized,the designed reactor is capable of mixing fresh material with matured compost efficiently.Gasflow simulation results showed that with the increase of the pores spacing in ventilation pipe in the reactor,the gas flow rate and dynamic pressure in pipe increased gradually,and the airflow could cover a larger area and distribute more evenly.In consequence,the pores spacing in ventilation pipe should be set to 70 mm. |
