The Study On Humification Characteristics And Process Enhancement Of Sludge Composting In Middle-high Altitude Areas

With the expanding of the treatment capacity of sewage plants,the production of excess sludge has increased significantly,and the treatment and disposal of sludge has become an environmental issue in China.Aerobic composting is an effective way to realize the resource utilization of excess sludge.However,there are still some problems,such as slow temperature rise,long humification process and low quality of compost products.This paper based on the unique conditions in the middle and high altitude areas,the internal relationship between temperature,water removal and substrate metabolism during the composting process of wet organic wastes was analyzed.Combined with the migration and transformation of organic substrates,the variations of enzyme activity and microbial population during the composting process were investigated,the effects of metal mineral types and their addition dosage on the humus formation were discussed,and the process and characteristics of humification intensification for sludge-metal oxide composts were clarified.The main conclusions were as follows:（1）The addition of metal minerals during sludge composting extended the high temperature period of composting.At the end of composting,the pH was stable at8.8～9.0,EC was less than 4.0 m S/cm,E4/E6 was maintained at 1.5～1.9,and GI was greater than 50%,which met the requirements of composting maturity.When electrolytic manganese slag was added to sludge compost,organic matter and humus precursors were completely degraded,and polyphenol oxidase activity was as high as 780 nmol·（h·g）^-1.When the ratio of sewage sludge and electrolytic manganese slag was 100:1（w/w,wet weight）,the compost maturity was the highest,HA/FA increased to 49.1%,organic matter degradation rate was 19.2%,high temperature period maintained for 4 d,pH and EC were within the recommended range of compost maturity.（2）The effects of characteristics of medium and high altitude areas on sludge composting were as follows:low pressure was beneficial to accelerate water removal during composting;however,the large temperature difference between day and night would adversely affect the temperature rise of the compost pile,which would affect the maturity of the compost pile.Compared with the humification of sludge composting in Kunming,the time of sludge composting in Lhasa to reach the high temperature period was delayed by 1 d,the water removal rate was increased by 11%～14%,and the water-soluble organic carbon content was increased by 216～487 mg/L.（3）After adding metal oxides to the sludge compost,the total nutrients in the compost products increased by 5.6%～9.2%;the GI value was 95%～117%,which had no inhibitory effect on seed growth.The heavy metal content met the’Agricultural Sludge Pollutant Control Standard’（GB 4284-2018）Class B standard.（4）When metal minerals or metal oxides were added during the sludge composting process,the microbial population diversity was improved and the species abundance changed significantly.The main microorganisms at the genus level were Bacillus,Tepidimicrobium,Sphingobacterium and Dechloromonas.Temperature,Moisture content（MC）,Dissolved organic carbon（DOC）,and pH had important effects on bacterial community succession.Bacillus and Tepidimicrobium were positively correlated with temperature and were the dominant bacteria in the high temperature period,accounting for 20%～31%and 9%～14%,respectively.Bacillus was a beneficial bacterium for composting,which was negatively correlated with organic matter（OM）and positively correlated with soluble sugar,soluble protein and dissolved organic carbon.It could participate in the degradation of organic matter and the formation of humus precursors.（5）The addition of Fe（Ⅲ）and Mn（Ⅳ）oxides could promote the polycondensation reaction of sludge composts and convert small molecular organic matter into humic acid substances with diverse components and complex structures.The composting effect of MnO₂ and Fe₂O₃ was the most obvious.The polyphenol oxidase activity and alkaline protease activity were as high as 949 nmol·（h·g）^-1 and 309μg·（h·g）^-1,the organic matter was degraded by 17.4%,the Hu Fu ratio（HA/FA）was increased by 29.6%,and the small molecule FA was transformed into the macromolecule HA.In this study,the humification characteristics of sludge composting in middle and high altitude areas were analyzed in depth,and innovative technologies for adding metal oxides to strengthen the humification process of sludge were developed.The production and metabolism of organic matter such as protein and sugar in different composting stages were explored.Combined with microbial population succession and enzyme activity test,the mechanism of strengthening the humification process of sludge composting was preliminarily explored.The compost product can be used as a modifier for landscaping and degraded soil.The research results provide technical support for sludge treatment,disposal and resource utilization in middle and high altitude areas.